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11.8: Glossary- The Appendicular System - Biology

11.8: Glossary- The Appendicular System - Biology


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acetabulum: large, cup-shaped cavity located on the lateral side of the hip bone; formed by the junction of the ilium, pubis, and ischium portions of the hip bone

acromial end of the clavicle: lateral end of the clavicle that articulates with the acromion of the scapula

acromial process: acromion of the scapula

acromioclavicular joint: articulation between the acromion of the scapula and the acromial end of the clavicle

acromion: flattened bony process that extends laterally from the scapular spine to form the bony tip of the shoulder

adductor tubercle: small, bony bump located on the superior aspect of the medial epicondyle of the femur

anatomical neck: line on the humerus located around the outside margin of the humeral head

ankle joint: joint that separates the leg and foot portions of the lower limb; formed by the articulations between the talus bone of the foot inferiorly, and the distal end of the tibia, medial malleolus of the tibia, and lateral malleolus of the fibula superiorly

anterior border of the tibia: narrow, anterior margin of the tibia that extends inferiorly from the tibial tuberosity

anterior inferior iliac spine: small, bony projection located on the anterior margin of the ilium, below the anterior superior iliac spine

anterior sacroiliac ligament: strong ligament between the sacrum and the ilium portions of the hip bone that supports the anterior side of the sacroiliac joint

anterior superior iliac spine: rounded, anterior end of the iliac crest

apical ectodermal ridge: enlarged ridge of ectoderm at the distal end of a limb bud that stimulates growth and elongation of the limb

arcuate line of the ilium: smooth ridge located at the inferior margin of the iliac fossa; forms the lateral portion of the pelvic brim

arm: region of the upper limb located between the shoulder and elbow joints; contains the humerus bone

auricular surface of the ilium: roughened area located on the posterior, medial side of the ilium of the hip bone; articulates with the auricular surface of the sacrum to form the sacroiliac joint

base of the metatarsal bone: expanded, proximal end of each metatarsal bone

bicipital groove: intertubercular groove; narrow groove located between the greater and lesser tubercles of the humerus

calcaneus: heel bone; posterior, inferior tarsal bone that forms the heel of the foot

capitate: from the lateral side, the third of the four distal carpal bones; articulates with the scaphoid and lunate proximally, the trapezoid laterally, the hamate medially, and primarily with the third metacarpal distally

capitulum: knob-like bony structure located anteriorly on the lateral, distal end of the humerus

carpal bone: one of the eight small bones that form the wrist and base of the hand; these are grouped as a proximal row consisting of (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones, and a distal row containing (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones

carpal tunnel: passageway between the anterior forearm and hand formed by the carpal bones and flexor retinaculum

carpometacarpal joint: articulation between one of the carpal bones in the distal row and a metacarpal bone of the hand

clavicle: collarbone; elongated bone that articulates with the manubrium of the sternum medially and the acromion of the scapula laterally

coracoclavicular ligament: strong band of connective tissue that anchors the coracoid process of the scapula to the lateral clavicle; provides important indirect support for the acromioclavicular joint

coracoid process: short, hook-like process that projects anteriorly and laterally from the superior margin of the scapula

coronoid fossa: depression on the anterior surface of the humerus above the trochlea; this space receives the coronoid process of the ulna when the elbow is maximally flexed

coronoid process of the ulna: projecting bony lip located on the anterior, proximal ulna; forms the inferior margin of the trochlear notch

costoclavicular ligament: band of connective tissue that unites the medial clavicle with the first rib

coxal bone: hip bone

cuboid: tarsal bone that articulates posteriorly with the calcaneus bone, medially with the lateral cuneiform bone, and anteriorly with the fourth and fifth metatarsal bones

deltoid tuberosity: roughened, V-shaped region located laterally on the mid-shaft of the humerus

distal radioulnar joint: articulation between the head of the ulna and the ulnar notch of the radius

distal tibiofibular joint: articulation between the distal fibula and the fibular notch of the tibia

elbow joint: joint located between the upper arm and forearm regions of the upper limb; formed by the articulations between the trochlea of the humerus and the trochlear notch of the ulna, and the capitulum of the humerus and the head of the radius

femur: thigh bone; the single bone of the thigh

fibula: thin, non-weight-bearing bone found on the lateral side of the leg

fibular notch: wide groove on the lateral side of the distal tibia for articulation with the fibula at the distal tibiofibular joint

flexor retinaculum: strong band of connective tissue at the anterior wrist that spans the top of the U-shaped grouping of the carpal bones to form the roof of the carpal tunnel

foot: portion of the lower limb located distal to the ankle joint

forearm: region of the upper limb located between the elbow and wrist joints; contains the radius and ulna bones

fossa: (plural = fossae) shallow depression on the surface of a bone

fovea capitis: minor indentation on the head of the femur that serves as the site of attachment for the ligament to the head of the femur

glenohumeral joint: shoulder joint; formed by the articulation between the glenoid cavity of the scapula and the head of the humerus

glenoid cavity: (also, glenoid fossa) shallow depression located on the lateral scapula, between the superior and lateral borders

gluteal tuberosity: roughened area on the posterior side of the proximal femur, extending inferiorly from the base of the greater trochanter

greater pelvis: (also, greater pelvic cavity or false pelvis) broad space above the pelvic brim defined laterally by the fan-like portion of the upper ilium

greater sciatic foramen: pelvic opening formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous ligament

greater sciatic notch: large, U-shaped indentation located on the posterior margin of the ilium, superior to the ischial spine

greater trochanter: large, bony expansion of the femur that projects superiorly from the base of the femoral neck

greater tubercle: enlarged prominence located on the lateral side of the proximal humerus

hallux: big toe; digit 1 of the foot

hamate: from the lateral side, the fourth of the four distal carpal bones; articulates with the lunate and triquetrum proximally, the fourth and fifth metacarpals distally, and the capitate laterally

hand: region of the upper limb distal to the wrist joint

head of the femur: rounded, proximal end of the femur that articulates with the acetabulum of the hip bone to form the hip joint

head of the fibula: small, knob-like, proximal end of the fibula; articulates with the inferior aspect of the lateral condyle of the tibia

head of the humerus: smooth, rounded region on the medial side of the proximal humerus; articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint

head of the metatarsal bone: expanded, distal end of each metatarsal bone

head of the radius: disc-shaped structure that forms the proximal end of the radius; articulates with the capitulum of the humerus as part of the elbow joint, and with the radial notch of the ulna as part of the proximal radioulnar joint

head of the ulna: small, rounded distal end of the ulna; articulates with the ulnar notch of the distal radius, forming the distal radioulnar joint

hip bone: coxal bone; single bone that forms the pelvic girdle; consists of three areas, the ilium, ischium, and pubis

hip joint: joint located at the proximal end of the lower limb; formed by the articulation between the acetabulum of the hip bone and the head of the femur

hook of the hamate bone: bony extension located on the anterior side of the hamate carpal bone

humerus: single bone of the upper arm

iliac crest: curved, superior margin of the ilium

iliac fossa: shallow depression found on the anterior and medial surfaces of the upper ilium

ilium: superior portion of the hip bone

inferior angle of the scapula: inferior corner of the scapula located where the medial and lateral borders meet

inferior pubic ramus: narrow segment of bone that passes inferiorly and laterally from the pubic body; joins with the ischial ramus to form the ischiopubic ramus

infraglenoid tubercle: small bump or roughened area located on the lateral border of the scapula, near the inferior margin of the glenoid cavity

infraspinous fossa: broad depression located on the posterior scapula, inferior to the spine

intercondylar eminence: irregular elevation on the superior end of the tibia, between the articulating surfaces of the medial and lateral condyles

intercondylar fossa: deep depression on the posterior side of the distal femur that separates the medial and lateral condyles

intermediate cuneiform: middle of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the medial cuneiform bone, laterally with the lateral cuneiform bone, and anteriorly with the second metatarsal bone

interosseous border of the fibula: small ridge running down the medial side of the fibular shaft; for attachment of the interosseous membrane between the fibula and tibia

interosseous border of the radius: narrow ridge located on the medial side of the radial shaft; for attachment of the interosseous membrane between the ulna and radius bones

interosseous border of the tibia: small ridge running down the lateral side of the tibial shaft; for attachment of the interosseous membrane between the tibia and fibula

interosseous border of the ulna: narrow ridge located on the lateral side of the ulnar shaft; for attachment of the interosseous membrane between the ulna and radius

interosseous membrane of the forearm: sheet of dense connective tissue that unites the radius and ulna bones

interosseous membrane of the leg: sheet of dense connective tissue that unites the shafts of the tibia and fibula bones

interphalangeal joint: articulation between adjacent phalanx bones of the hand or foot digits

intertrochanteric crest: short, prominent ridge running between the greater and lesser trochanters on the posterior side of the proximal femur

intertrochanteric line: small ridge running between the greater and lesser trochanters on the anterior side of the proximal femur

intertubercular groove (sulcus): bicipital groove; narrow groove located between the greater and lesser tubercles of the humerus

ischial ramus: bony extension projecting anteriorly and superiorly from the ischial tuberosity; joins with the inferior pubic ramus to form the ischiopubic ramus

ischial spine: pointed, bony projection from the posterior margin of the ischium that separates the greater sciatic notch and lesser sciatic notch

ischial tuberosity: large, roughened protuberance that forms the posteroinferior portion of the hip bone; weight-bearing region of the pelvis when sitting

ischiopubic ramus: narrow extension of bone that connects the ischial tuberosity to the pubic body; formed by the junction of the ischial ramus and inferior pubic ramus

ischium: posteroinferior portion of the hip bone

knee joint: joint that separates the thigh and leg portions of the lower limb; formed by the articulations between the medial and lateral condyles of the femur, and the medial and lateral condyles of the tibia

lateral border of the scapula: diagonally oriented lateral margin of the scapula

lateral condyle of the femur: smooth, articulating surface that forms the distal and posterior sides of the lateral expansion of the distal femur

lateral condyle of the tibia: lateral, expanded region of the proximal tibia that includes the smooth surface that articulates with the lateral condyle of the femur as part of the knee joint

lateral cuneiform: most lateral of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the intermediate cuneiform bone, laterally with the cuboid bone, and anteriorly with the third metatarsal bone

lateral epicondyle of the femur: roughened area of the femur located on the lateral side of the lateral condyle

lateral epicondyle of the humerus: small projection located on the lateral side of the distal humerus

lateral malleolus: expanded distal end of the fibula

lateral supracondylar ridge: narrow, bony ridge located along the lateral side of the distal humerus, superior to the lateral epicondyle

leg: portion of the lower limb located between the knee and ankle joints

lesser pelvis: (also, lesser pelvic cavity or true pelvis) narrow space located within the pelvis, defined superiorly by the pelvic brim (pelvic inlet) and inferiorly by the pelvic outlet

lesser sciatic foramen: pelvic opening formed by the lesser sciatic notch of the hip bone, the sacrospinous ligament, and the sacrotuberous ligament

lesser sciatic notch: shallow indentation along the posterior margin of the ischium, inferior to the ischial spine

lesser trochanter: small, bony projection on the medial side of the proximal femur, at the base of the femoral neck

lesser tubercle: small, bony prominence located on anterior side of the proximal humerus

ligament of the head of the femur: ligament that spans the acetabulum of the hip bone and the fovea capitis of the femoral head

limb bud: small elevation that appears on the lateral side of the embryo during the fourth or fifth week of development, which gives rise to an upper or lower limb

linea aspera: longitudinally running bony ridge located in the middle third of the posterior femur

lunate: from the lateral side, the second of the four proximal carpal bones; articulates with the radius proximally, the capitate and hamate distally, the scaphoid laterally, and the triquetrum medially

medial border of the scapula: elongated, medial margin of the scapula

medial condyle of the femur: smooth, articulating surface that forms the distal and posterior sides of the medial expansion of the distal femur

medial condyle of the tibia: medial, expanded region of the proximal tibia that includes the smooth surface that articulates with the medial condyle of the femur as part of the knee joint

medial cuneiform: most medial of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, laterally with the intermediate cuneiform bone, and anteriorly with the first and second metatarsal bones

medial epicondyle of the femur: roughened area of the distal femur located on the medial side of the medial condyle

medial epicondyle of the humerus: enlarged projection located on the medial side of the distal humerus

medial malleolus: bony expansion located on the medial side of the distal tibia

metacarpal bone: one of the five long bones that form the palm of the hand; numbered 1–5, starting on the lateral (thumb) side of the hand

metacarpophalangeal joint: articulation between the distal end of a metacarpal bone of the hand and a proximal phalanx bone of the thumb or a finger

metatarsal bone: one of the five elongated bones that forms the anterior half of the foot; numbered 1–5, starting on the medial side of the foot

metatarsophalangeal joint: articulation between a metatarsal bone of the foot and the proximal phalanx bone of a toe

midcarpal joint: articulation between the proximal and distal rows of the carpal bones; contributes to movements of the hand at the wrist

navicular: tarsal bone that articulates posteriorly with the talus bone, laterally with the cuboid bone, and anteriorly with the medial, intermediate, and lateral cuneiform bones

neck of the femur: narrowed region located inferior to the head of the femur

neck of the radius: narrowed region immediately distal to the head of the radius

obturator foramen: large opening located in the anterior hip bone, between the pubis and ischium regions

olecranon fossa: large depression located on the posterior side of the distal humerus; this space receives the olecranon process of the ulna when the elbow is fully extended

olecranon process: expanded posterior and superior portions of the proximal ulna; forms the bony tip of the elbow

patella: kneecap; the largest sesamoid bone of the body; articulates with the distal femur

patellar surface: smooth groove located on the anterior side of the distal femur, between the medial and lateral condyles; site of articulation for the patella

pectineal line: narrow ridge located on the superior surface of the superior pubic ramus

pectoral girdle: shoulder girdle; the set of bones, consisting of the scapula and clavicle, which attaches each upper limb to the axial skeleton

pelvic brim: pelvic inlet; the dividing line between the greater and lesser pelvic regions; formed by the superior margin of the pubic symphysis, the pectineal lines of each pubis, the arcuate lines of each ilium, and the sacral promontory

pelvic girdle: hip girdle; consists of a single hip bone, which attaches a lower limb to the sacrum of the axial skeleton

pelvic inlet: pelvic brim

pelvic outlet: inferior opening of the lesser pelvis; formed by the inferior margin of the pubic symphysis, right and left ischiopubic rami and sacrotuberous ligaments, and the tip of the coccyx

pelvis: ring of bone consisting of the right and left hip bones, the sacrum, and the coccyx

phalanx bone of the foot: (plural = phalanges) one of the 14 bones that form the toes; these include the proximal and distal phalanges of the big toe, and the proximal, middle, and distal phalanx bones of toes two through five

phalanx bone of the hand: (plural = phalanges) one of the 14 bones that form the thumb and fingers; these include the proximal and distal phalanges of the thumb, and the proximal, middle, and distal phalanx bones of the fingers two through five

pisiform: from the lateral side, the fourth of the four proximal carpal bones; articulates with the anterior surface of the triquetrum

pollex: (also, thumb) digit 1 of the hand

posterior inferior iliac spine: small, bony projection located at the inferior margin of the auricular surface on the posterior ilium

posterior sacroiliac ligament: strong ligament spanning the sacrum and ilium of the hip bone that supports the posterior side of the sacroiliac joint

posterior superior iliac spine: rounded, posterior end of the iliac crest

proximal radioulnar joint: articulation formed by the radial notch of the ulna and the head of the radius

proximal tibiofibular joint: articulation between the head of the fibula and the inferior aspect of the lateral condyle of the tibia

pubic arch: bony structure formed by the pubic symphysis, and the bodies and inferior pubic rami of the right and left pubic bones

pubic body: enlarged, medial portion of the pubis region of the hip bone

pubic symphysis: joint formed by the articulation between the pubic bodies of the right and left hip bones

pubic tubercle: small bump located on the superior aspect of the pubic body

pubis: anterior portion of the hip bone

radial fossa: small depression located on the anterior humerus above the capitulum; this space receives the head of the radius when the elbow is maximally flexed

radial notch of the ulna: small, smooth area on the lateral side of the proximal ulna; articulates with the head of the radius as part of the proximal radioulnar joint

radial tuberosity: oval-shaped, roughened protuberance located on the medial side of the proximal radius

radiocarpal joint: wrist joint, located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones

radius: bone located on the lateral side of the forearm

sacroiliac joint: joint formed by the articulation between the auricular surfaces of the sacrum and ilium

sacrospinous ligament: ligament that spans the sacrum to the ischial spine of the hip bone

sacrotuberous ligament: ligament that spans the sacrum to the ischial tuberosity of the hip bone

scaphoid: from the lateral side, the first of the four proximal carpal bones; articulates with the radius proximally, the trapezoid, trapezium, and captitate distally, and the lunate medially

scapula: shoulder blade bone located on the posterior side of the shoulder

shaft of the femur: cylindrically shaped region that forms the central portion of the femur

shaft of the fibula: elongated, slender portion located between the expanded ends of the fibula

shaft of the humerus: narrow, elongated, central region of the humerus

shaft of the radius: narrow, elongated, central region of the radius

shaft of the tibia: triangular-shaped, central portion of the tibia

shaft of the ulna: narrow, elongated, central region of the ulna

soleal line: small, diagonally running ridge located on the posterior side of the proximal tibia

spine of the scapula: prominent ridge passing mediolaterally across the upper portion of the posterior scapular surface

sternal end of the clavicle: medial end of the clavicle that articulates with the manubrium of the sternum

sternoclavicular joint: articulation between the manubrium of the sternum and the sternal end of the clavicle; forms the only bony attachment between the pectoral girdle of the upper limb and the axial skeleton

styloid process of the radius: pointed projection located on the lateral end of the distal radius

styloid process of the ulna: short, bony projection located on the medial end of the distal ulna

subpubic angle: inverted V-shape formed by the convergence of the right and left ischiopubic rami; this angle is greater than 80 degrees in females and less than 70 degrees in males

subscapular fossa: broad depression located on the anterior (deep) surface of the scapula

superior angle of the scapula: corner of the scapula between the superior and medial borders of the scapula

superior border of the scapula: superior margin of the scapula

superior pubic ramus: narrow segment of bone that passes laterally from the pubic body to join the ilium

supraglenoid tubercle: small bump located at the superior margin of the glenoid cavity

suprascapular notch: small notch located along the superior border of the scapula, medial to the coracoid process

supraspinous fossa: narrow depression located on the posterior scapula, superior to the spine

surgical neck: region of the humerus where the expanded, proximal end joins with the narrower shaft

sustentaculum tali: bony ledge extending from the medial side of the calcaneus bone

talus: tarsal bone that articulates superiorly with the tibia and fibula at the ankle joint; also articulates inferiorly with the calcaneus bone and anteriorly with the navicular bone

tarsal bone: one of the seven bones that make up the posterior foot; includes the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform bones

thigh: portion of the lower limb located between the hip and knee joints

tibial tuberosity: elevated area on the anterior surface of the proximal tibia

tibia: shin bone; the large, weight-bearing bone located on the medial side of the leg

trapezium: from the lateral side, the first of the four distal carpal bones; articulates with the scaphoid proximally, the first and second metacarpals distally, and the trapezoid medially

trapezoid: from the lateral side, the second of the four distal carpal bones; articulates with the scaphoid proximally, the second metacarpal distally, the trapezium laterally, and the capitate medially

triquetrum: from the lateral side, the third of the four proximal carpal bones; articulates with the lunate laterally, the hamate distally, and has a facet for the pisiform

trochlear notch: large, C-shaped depression located on the anterior side of the proximal ulna; articulates at the elbow with the trochlea of the humerus

trochlea: pulley-shaped region located medially at the distal end of the humerus; articulates at the elbow with the trochlear notch of the ulna

ulnar notch of the radius: shallow, smooth area located on the medial side of the distal radius; articulates with the head of the ulna at the distal radioulnar joint

ulnar tuberosity: roughened area located on the anterior, proximal ulna inferior to the coronoid process

ulna: bone located on the medial side of the forearm


1. The Bones of the Shoulder Girdle

The pectoral or shoulder girdle consists of the scapulae and clavicles. The shoulder girdle connects the bones of the upper limbs to the axial skeleton. These bones also provide attachment for muscles that move the shoulders and upper limbs.

See the bones of the shoulder girdle in 3D:


Muscles That Move the Eyes

The movement of the eyeball is under the control of the extra ocular (extrinsic) eye muscles, which originate from the bones of the orbit and insert onto the outer surface of the white of the eye. These muscles are located inside the eye socket and cannot be seen on any part of the visible eyeball (Figure 11.4.3 and Table 11.3). If you have ever been to a doctor who held up a finger and asked you to follow it up, down, and to both sides, he or she is checking to make sure your eye muscles are acting in a coordinated pattern.

Figure 11.4.3Muscles of the Eyes: (a) The extraocular eye muscles originate outside of the eye on the skull. (b) Each muscle inserts onto the eyeball.
Muscles of the Eyes (Table 11.3)
Movement Target Target motion direction Prime mover Origin Insertion
Moves eyes up and toward nose rotates eyes from 1 o’clock to 3 o’clock Eyeballs Superior (elevates) medial (adducts) Superior rectus Common tendinous ring (ring attaches to optic foramen) Superior surface of eyeball
Moves eyes down and toward nose rotates eyes from 6 o’clock to 3 o’clock Eyeballs Inferior (depresses) medial (adducts) Inferior rectus Common tendinous ring (ring attaches to optic foramen) Inferior surface of eyeball
Moves eyes away from nose Eyeballs Lateral (abducts) Lateral rectus Common tendinous ring (ring attaches to optic foramen) Lateral surface of eyeball
Moves eyes toward nose Eyeballs Medial (adducts) Medial rectus Common tendinous ring (ring attaches to optic foramen) Medial surface of eyeball
Moves eyes up and away from nose rotates eyeball from 12 o’clock to 9 o’clock Eyeballs Superior (elevates) lateral (abducts) Inferior oblique Floor of orbit (maxilla) Surface of eyeball between inferior rectus and lateral rectus
Moves eyes down and away from nose rotates eyeball from 6 o’clock to 9 o’clock Eyeballs Superior (elevates) lateral (abducts) Superior oblique Sphenoid bone Suface of eyeball between superior rectus and lateral rectus
Opens eyes Upper eyelid Superior (elevates) Levator palpabrae superioris Roof of orbit (sphenoid bone) Skin of upper eyelids
Closes eyelids Eyelid skin Compression along superior–inferior axis Orbicularis oculi Medial bones composing the orbit Circumference of orbit

11.8: Glossary- The Appendicular System - Biology

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Gliding movementsoccur as relatively flat bone surfaces move past each other. Gliding movements produce very little rotation or angular movement of the bones. The joints of the carpal and tarsal bones are examples of joints that produce gliding movements.

Angular movements are produced when the angle between the bones of a joint changes. There are several different types of angular movements, including flexion, extension, hyperextension, abduction, adduction, and circumduction. Flexion, or bending, occurs when the angle between the bones decreases. Moving the forearm upward at the elbow or moving the wrist to move the hand toward the forearm are examples of flexion.Extension is the opposite of flexion in that the angle between the bones of a joint increases. Straightening a limb after flexion is an example of extension. Extension past the regular anatomical position is referred to as hyperextension. This includes moving the neck back to look upward, or bending the wrist so that the hand moves away from the forearm.

Abduction occurs when a bone moves away from the midline of the body. Examples of abduction are moving the arms or legs laterally to lift them straight out to the side. Adductionis the movement of a bone toward the midline of the body. Movement of the limbs inward after abduction is an example of adduction.Circumduction is the movement of a limb in a circular motion, as in moving the arm in a circular motion.


The function of the Axial skeleton

The Axial Skeleton has 2 functions. The first is to support and protect the organs in the dorsal and ventral cavities. The second being that it creates a surface for the attachment of muscles.

The intervertebral disc(which lies between the adjacent vertebrae in the spine) is a classic example of a joint within the Axial skeleton in that it is very strong and will only permit limited movement.

Of the 206 bones in the human body 126 of these make up the appendicular skeleton.


Contents

The concept that individuals might have a "metabolic profile" that could be reflected in the makeup of their biological fluids was introduced by Roger Williams in the late 1940s, [5] who used paper chromatography to suggest characteristic metabolic patterns in urine and saliva were associated with diseases such as schizophrenia. However, it was only through technological advancements in the 1960s and 1970s that it became feasible to quantitatively (as opposed to qualitatively) measure metabolic profiles. [6] The term "metabolic profile" was introduced by Horning, et al. in 1971 after they demonstrated that gas chromatography-mass spectrometry (GC-MS) could be used to measure compounds present in human urine and tissue extracts. [7] [8] The Horning group, along with that of Linus Pauling and Arthur B. Robinson led the development of GC-MS methods to monitor the metabolites present in urine through the 1970s. [9]

Concurrently, NMR spectroscopy, which was discovered in the 1940s, was also undergoing rapid advances. In 1974, Seeley et al. demonstrated the utility of using NMR to detect metabolites in unmodified biological samples. [10] This first study on muscle highlighted the value of NMR in that it was determined that 90% of cellular ATP is complexed with magnesium. As sensitivity has improved with the evolution of higher magnetic field strengths and magic angle spinning, NMR continues to be a leading analytical tool to investigate metabolism. [7] [11] Recent efforts to utilize NMR for metabolomics have been largely driven by the laboratory of Jeremy K. Nicholson at Birkbeck College, University of London and later at Imperial College London. In 1984, Nicholson showed 1 H NMR spectroscopy could potentially be used to diagnose diabetes mellitus, and later pioneered the application of pattern recognition methods to NMR spectroscopic data. [12] [13]

In 1995 liquid chromatography mass spectrometry metabolomics experiments [14] were performed by Gary Siuzdak while working with Richard Lerner (then president of The Scripps Research Institute) and Benjamin Cravatt, to analyze the cerebral spinal fluid from sleep deprived animals. One molecule of particular interest, oleamide, was observed and later shown to have sleep inducing properties. This work is one of the earliest such experiments combining liquid chromatography and mass spectrometry in metabolomics.

In 2005, the first metabolomics tandem mass spectrometry database, METLIN, [15] [16] for characterizing human metabolites was developed in the Siuzdak laboratory at The Scripps Research Institute. METLIN has since grown and as of July 1, 2019, METLIN contains over 450,000 metabolites and other chemical entities, each compound having experimental tandem mass spectrometry data generated from molecular standards at multiple collision energies and in positive and negative ionization modes. METLIN is the largest repository of tandem mass spectrometry data of its kind. 2005 was also the year in which the dedicated academic journal Metabolomics first appeared, founded by its current editor-in-chief Professor Roy Goodacre.


In 2005, the Siuzdak lab was engaged in identifying metabolites associated with sepsis and in an effort to address the issue of statistically identifying the most relevant dysregulated metabolites across hundreds of LC/MS datasets, the first algorithm was developed to allow for the nonlinear alignment of mass spectrometry metabolomics data. Called XCMS, [17] where the "X" constitutes any chromatographic technology, it has since (2012) [18] been developed as an online tool and as of 2019 (with METLIN) has over 30,000 registered users.


On 23 January 2007, the Human Metabolome Project, led by David Wishart of the University of Alberta, Canada, completed the first draft of the human metabolome, consisting of a database of approximately 2500 metabolites, 1200 drugs and 3500 food components. [19] [20] Similar projects have been underway in several plant species, most notably Medicago truncatula [21] and Arabidopsis thaliana [22] for several years.

As late as mid-2010, metabolomics was still considered an "emerging field". [23] Further, it was noted that further progress in the field depended in large part, through addressing otherwise "irresolvable technical challenges", by technical evolution of mass spectrometry instrumentation. [23]

In 2015, real-time metabolome profiling was demonstrated for the first time. [24]

The metabolome refers to the complete set of small-molecule (<1.5 kDa) [19] metabolites (such as metabolic intermediates, hormones and other signaling molecules, and secondary metabolites) to be found within a biological sample, such as a single organism. [25] [26] The word was coined in analogy with transcriptomics and proteomics like the transcriptome and the proteome, the metabolome is dynamic, changing from second to second. Although the metabolome can be defined readily enough, it is not currently possible to analyse the entire range of metabolites by a single analytical method.

The first metabolite database (called METLIN) for searching fragmentation data from tandem mass spectrometry experiments was developed by the Siuzdak lab at The Scripps Research Institute in 2005. [15] [16] METLIN contains over 450,000 metabolites and other chemical entities, each compound having experimental tandem mass spectrometry data. In 2006, [17] the Siuzdak lab also developed the first algorithm to allow for the nonlinear alignment of mass spectrometry metabolomics data. Called XCMS, where the "X" constitutes any chromatographic technology, it has since (2012) [18] been developed as an online tool and as of 2019 (with METLIN) has over 30,000 registered users.

In January 2007, scientists at the University of Alberta and the University of Calgary completed the first draft of the human metabolome. The Human Metabolome Database (HMDB) is perhaps the most extensive public metabolomic spectral database to date. [27] The HMDB stores more than 110,000 different metabolite entries. They catalogued approximately 1200 drugs and 3500 food components that can be found in the human body, as reported in the literature. [19] This information, available at the Human Metabolome Database (www.hmdb.ca) and based on analysis of information available in the current scientific literature, is far from complete. [28] In contrast, much more is known about the metabolomes of other organisms. For example, over 50,000 metabolites have been characterized from the plant kingdom, and many thousands of metabolites have been identified and/or characterized from single plants. [29] [30]

Each type of cell and tissue has a unique metabolic ‘fingerprint’ that can elucidate organ or tissue-specific information. Bio-specimens used for metabolomics analysis include but not limit to plasma, serum, urine, saliva, feces, muscle, sweat, exhaled breath and gastrointestinal fluid. [31] The ease of collection facilitates high temporal resolution, and because they are always at dynamic equilibrium with the body, they can describe the host as a whole. [32] Genome can tell what could happen, transcriptome can tell what appears to be happening, proteome can tell what makes it happen and metabolome can tell what has happened and what is happening. [33]

Metabolites are the substrates, intermediates and products of metabolism. Within the context of metabolomics, a metabolite is usually defined as any molecule less than 1.5 kDa in size. [19] However, there are exceptions to this depending on the sample and detection method. For example, macromolecules such as lipoproteins and albumin are reliably detected in NMR-based metabolomics studies of blood plasma. [34] In plant-based metabolomics, it is common to refer to "primary" and "secondary" metabolites. [3] A primary metabolite is directly involved in the normal growth, development, and reproduction. A secondary metabolite is not directly involved in those processes, but usually has important ecological function. Examples include antibiotics and pigments. [35] By contrast, in human-based metabolomics, it is more common to describe metabolites as being either endogenous (produced by the host organism) or exogenous. [36] [37] Metabolites of foreign substances such as drugs are termed xenometabolites. [38]

The metabolome forms a large network of metabolic reactions, where outputs from one enzymatic chemical reaction are inputs to other chemical reactions. Such systems have been described as hypercycles. [ citation needed ]

Metabonomics is defined as "the quantitative measurement of the dynamic multiparametric metabolic response of living systems to pathophysiological stimuli or genetic modification". The word origin is from the Greek μεταβολή meaning change and nomos meaning a rule set or set of laws. [39] This approach was pioneered by Jeremy Nicholson at Murdoch University and has been used in toxicology, disease diagnosis and a number of other fields. Historically, the metabonomics approach was one of the first methods to apply the scope of systems biology to studies of metabolism. [40] [41] [42]

There has been some disagreement over the exact differences between 'metabolomics' and 'metabonomics'. The difference between the two terms is not related to choice of analytical platform: although metabonomics is more associated with NMR spectroscopy and metabolomics with mass spectrometry-based techniques, this is simply because of usages amongst different groups that have popularized the different terms. While there is still no absolute agreement, there is a growing consensus that 'metabolomics' places a greater emphasis on metabolic profiling at a cellular or organ level and is primarily concerned with normal endogenous metabolism. 'Metabonomics' extends metabolic profiling to include information about perturbations of metabolism caused by environmental factors (including diet and toxins), disease processes, and the involvement of extragenomic influences, such as gut microflora. This is not a trivial difference metabolomic studies should, by definition, exclude metabolic contributions from extragenomic sources, because these are external to the system being studied. However, in practice, within the field of human disease research there is still a large degree of overlap in the way both terms are used, and they are often in effect synonymous. [43]

Exometabolomics, or "metabolic footprinting", is the study of extracellular metabolites. It uses many techniques from other subfields of metabolomics, and has applications in biofuel development, bioprocessing, determining drugs' mechanism of action, and studying intercellular interactions. [44]

The typical workflow of metabolomics studies is shown in the figure. First, samples are collected from tissue, plasma, urine, saliva, cells, etc. Next, metabolites extracted often with the addition of internal standards and derivatization. [45] During sample analysis, metabolites are quantified (liquid chromatography or gas chromatography coupled with MS and/or NMR spectroscopy). The raw output data can be used for metabolite feature extraction and further processed before statistical analysis (such as PCA). Many bioinformatic tools and software are available to identify associations with disease states and outcomes, determine significant correlations, and characterize metabolic signatures with existing biological knowledge. [46]

Separation methods Edit

Initially, analytes in a metabolomic sample comprise a highly complex mixture. This complex mixture can be simplified prior to detection by separating some analytes from others. Separation achieves various goals: analytes which cannot be resolved by the detector may be separated in this step in MS analysis ion suppression is reduced the retention time of the analyte serves as information regarding its identity. This separation step is not mandatory and is often omitted in NMR and "shotgun" based approaches such as shotgun lipidomics.

Gas chromatography (GC), especially when interfaced with mass spectrometry (GC-MS), is a widely used separation technique for metabolomic analysis. [47] GC offers very high chromatographic resolution, and can be used in conjunction with a flame ionization detector (GC/FID) or a mass spectrometer (GC-MS). The method is especially useful for identification and quantification of small and volatile molecules. [48] However, a practical limitation of GC is the requirement of chemical derivatization for many biomolecules as only volatile chemicals can be analysed without derivatization. In cases where greater resolving power is required, two-dimensional chromatography (GCxGC) can be applied.

High performance liquid chromatography (HPLC) has emerged as the most common separation technique for metabolomic analysis. With the advent of electrospray ionization, HPLC was coupled to MS. In contrast with GC, HPLC has lower chromatographic resolution, but requires no derivatization for polar molecules, and separates molecules in the liquid phase. Additionally HPLC has the advantage that a much wider range of analytes can be measured with a higher sensitivity than GC methods. [49]

Capillary electrophoresis (CE) has a higher theoretical separation efficiency than HPLC (although requiring much more time per separation), and is suitable for use with a wider range of metabolite classes than is GC. As for all electrophoretic techniques, it is most appropriate for charged analytes. [50]

Detection methods Edit

Mass spectrometry (MS) is used to identify and quantify metabolites after optional separation by GC, HPLC, or CE. GC-MS was the first hyphenated technique to be developed. Identification leverages the distinct patterns in which analytes fragment which can be thought of as a mass spectral fingerprint libraries exist that allow identification of a metabolite according to this fragmentation pattern [ example needed ] . MS is both sensitive and can be very specific. There are also a number of techniques which use MS as a stand-alone technology: the sample is infused directly into the mass spectrometer with no prior separation, and the MS provides sufficient selectivity to both separate and to detect metabolites.

For analysis by mass spectrometry the analytes must be imparted with a charge and transferred to the gas phase. Electron ionization (EI) is the most common ionization technique applies to GC separations as it is amenable to low pressures. EI also produces fragmentation of the analyte, both providing structural information while increasing the complexity of the data and possibly obscuring the molecular ion. Atmospheric-pressure chemical ionization (APCI) is an atmospheric pressure technique that can be applied to all the above separation techniques. APCI is a gas phase ionization method slightly more aggressive ionization than ESI which is suitable for less polar compounds. Electrospray ionization (ESI) is the most common ionization technique applied in LC/MS. This soft ionization is most successful for polar molecules with ionizable functional groups. Another commonly used soft ionization technique is secondary electrospray ionization (SESI).

Surface-based mass analysis has seen a resurgence in the past decade, with new MS technologies focused on increasing sensitivity, minimizing background, and reducing sample preparation. The ability to analyze metabolites directly from biofluids and tissues continues to challenge current MS technology, largely because of the limits imposed by the complexity of these samples, which contain thousands to tens of thousands of metabolites. Among the technologies being developed to address this challenge is Nanostructure-Initiator MS (NIMS), [51] [52] a desorption/ ionization approach that does not require the application of matrix and thereby facilitates small-molecule (i.e., metabolite) identification. MALDI is also used however, the application of a MALDI matrix can add significant background at <1000 Da that complicates analysis of the low-mass range (i.e., metabolites). In addition, the size of the resulting matrix crystals limits the spatial resolution that can be achieved in tissue imaging. Because of these limitations, several other matrix-free desorption/ionization approaches have been applied to the analysis of biofluids and tissues.

Secondary ion mass spectrometry (SIMS) was one of the first matrix-free desorption/ionization approaches used to analyze metabolites from biological samples. [ citation needed ] SIMS uses a high-energy primary ion beam to desorb and generate secondary ions from a surface. The primary advantage of SIMS is its high spatial resolution (as small as 50 nm), a powerful characteristic for tissue imaging with MS. However, SIMS has yet to be readily applied to the analysis of biofluids and tissues because of its limited sensitivity at >500 Da and analyte fragmentation generated by the high-energy primary ion beam. Desorption electrospray ionization (DESI) is a matrix-free technique for analyzing biological samples that uses a charged solvent spray to desorb ions from a surface. Advantages of DESI are that no special surface is required and the analysis is performed at ambient pressure with full access to the sample during acquisition. A limitation of DESI is spatial resolution because "focusing" the charged solvent spray is difficult. However, a recent development termed laser ablation ESI (LAESI) is a promising approach to circumvent this limitation. [ citation needed ] Most recently, ion trap techniques such as orbitrap mass spectrometry are also applied to metabolomics research. [53]

Nuclear magnetic resonance (NMR) spectroscopy is the only detection technique which does not rely on separation of the analytes, and the sample can thus be recovered for further analyses. All kinds of small molecule metabolites can be measured simultaneously - in this sense, NMR is close to being a universal detector. The main advantages of NMR are high analytical reproducibility and simplicity of sample preparation. Practically, however, it is relatively insensitive compared to mass spectrometry-based techniques. [54] [55] Comparison of most common used metabolomics methods is shown in the table.

Although NMR and MS are the most widely used, modern day techniques other methods of detection that have been used. These include Fourier-transform ion cyclotron resonance, [56] ion-mobility spectrometry, [57] electrochemical detection (coupled to HPLC), Raman spectroscopy and radiolabel (when combined with thin-layer chromatography). [ citation needed ]

The data generated in metabolomics usually consist of measurements performed on subjects under various conditions. These measurements may be digitized spectra, or a list of metabolite features. In its simplest form this generates a matrix with rows corresponding to subjects and columns corresponding with metabolite features (or vice versa). [7] Several statistical programs are currently available for analysis of both NMR and mass spectrometry data. A great number of free software are already available for the analysis of metabolomics data shown in the table. Some statistical tools listed in the table were designed for NMR data analyses were also useful for MS data. [58] For mass spectrometry data, software is available that identifies molecules that vary in subject groups on the basis of mass-over-charge value and sometimes retention time depending on the experimental design. [59]

Once metabolite data matrix is determined, unsupervised data reduction techniques (e.g. PCA) can be used to elucidate patterns and connections. In many studies, including those evaluating drug-toxicity and some disease models, the metabolites of interest are not known a priori. This makes unsupervised methods, those with no prior assumptions of class membership, a popular first choice. The most common of these methods includes principal component analysis (PCA) which can efficiently reduce the dimensions of a dataset to a few which explain the greatest variation. [32] When analyzed in the lower-dimensional PCA space, clustering of samples with similar metabolic fingerprints can be detected. PCA algorithms aim to replace all correlated variables by a much smaller number of uncorrelated variables (referred to as principal components (PCs)) and retain most of the information in the original dataset. [60] This clustering can elucidate patterns and assist in the determination of disease biomarkers - metabolites that correlate most with class membership.

Linear models are commonly used for metabolomics data, but are affected by multicollinearity. On the other hand, multivariate statistics are thriving methods for high-dimensional correlated metabolomics data, of which the most popular one is Projection to Latent Structures (PLS) regression and its classification version PLS-DA. Other data mining methods, such as random forest, support-vector machines, etc. are received increasing attention for untargeted metabolomics data analysis. [61] In the case of univariate methods, variables are analyzed one by one using classical statistics tools (such as Student's t-test, ANOVA or mixed models) and only these with sufficient small p-values are considered relevant. [31] However, correction strategies should be used to reduce false discoveries when multiple comparisons are conducted. For multivariate analysis, models should always be validated to ensure the results can be generalized.

Machine learning is also a powerful tool that can be used in metabolomics analysis. Recently, the authors of a paper published in Analytical Chemistry, developed a retention time prediction software called Retip. This tool, developed in collaboration with NGALAB, the West Coast Metabolomics Centre and Riken empower all labs to apply artificial intelligence to the retention time prediction of small molecules in complex matrix, as human plasma, plants, food or microbials. Retention time prediction increases the identification rate in liquid chromatography and subsequently leads to an improved biological interpretation of metabolomics data. [62]

A data mining process model that was called (MeKDDaM) have been developed at Aberystwyth University to provide a systematic and formalised framework for guiding and performing metabolomics data analysis in a justifiable, traceable and to promote the achievement of the analytical objectives of metabolomics investigations and to ensure the validity, interpretability and reproducibility of their results. [63] and was then applied to a number of metabolomics datasets to demonstrate and evaluate its applicability to different metabolomics investigations, approaches and data acquisition instruments on one hand, and to different data mining approaches, goals, tasks and techniques on the other. [64]

A strategy for selecting data mining and machine learning techniques in Metabolomics is also available. [65] The strategy defines mechanisms for selecting the right machine learning technique that takes into consideration the goals of data mining techniques on the one hand and the goals of metabolomics investigations and the nature of the data on the other. The strategy aims to ensure the validity and soundness of results and promote the achievement of the investigation goals.

Toxicity assessment/toxicology by metabolic profiling (especially of urine or blood plasma samples) detects the physiological changes caused by toxic insult of a chemical (or mixture of chemicals). In many cases, the observed changes can be related to specific syndromes, e.g. a specific lesion in liver or kidney. This is of particular relevance to pharmaceutical companies wanting to test the toxicity of potential drug candidates: if a compound can be eliminated before it reaches clinical trials on the grounds of adverse toxicity, it saves the enormous expense of the trials. [43]

For functional genomics, metabolomics can be an excellent tool for determining the phenotype caused by a genetic manipulation, such as gene deletion or insertion. Sometimes this can be a sufficient goal in itself—for instance, to detect any phenotypic changes in a genetically modified plant intended for human or animal consumption. More exciting is the prospect of predicting the function of unknown genes by comparison with the metabolic perturbations caused by deletion/insertion of known genes. Such advances are most likely to come from model organisms such as Saccharomyces cerevisiae and Arabidopsis thaliana. The Cravatt laboratory at The Scripps Research Institute has recently applied this technology to mammalian systems, identifying the N-acyltaurines as previously uncharacterized endogenous substrates for the enzyme fatty acid amide hydrolase (FAAH) and the monoalkylglycerol ethers (MAGEs) as endogenous substrates for the uncharacterized hydrolase KIAA1363. [66] [67]

Metabologenomics is a novel approach to integrate metabolomics and genomics data by correlating microbial-exported metabolites with predicted biosynthetic genes. [68] This bioinformatics-based pairing method enables natural product discovery at a larger-scale by refining non-targeted metabolomic analyses to identify small molecules with related biosynthesis and to focus on those that may not have previously well known structures.

Fluxomics is a further development of metabolomics. The disadvantage of metabolomics is that it only provides the user with steady-state level information, while fluxomics determines the reaction rates of metabolic reactions and can trace metabolites in a biological system over time.

Nutrigenomics is a generalised term which links genomics, transcriptomics, proteomics and metabolomics to human nutrition. In general a metabolome in a given body fluid is influenced by endogenous factors such as age, sex, body composition and genetics as well as underlying pathologies. The large bowel microflora are also a very significant potential confounder of metabolic profiles and could be classified as either an endogenous or exogenous factor. The main exogenous factors are diet and drugs. Diet can then be broken down to nutrients and non-nutrients. Metabolomics is one means to determine a biological endpoint, or metabolic fingerprint, which reflects the balance of all these forces on an individual's metabolism. [69]


Human Appendicular Skeleton

The appendicular skeleton is composed of the bones of the upper limbs (which function to grasp and manipulate objects) and the lower limbs (which permit locomotion). It also includes the pectoral girdle, or shoulder girdle, that attaches the upper limbs to the body, and the pelvic girdle that attaches the lower limbs to the body (Figure 19.10).

Figure 19.10. The appendicular skeleton is composed of the bones of the pectoral limbs (arm, forearm, hand), the pelvic limbs (thigh, leg, foot), the pectoral girdle, and the pelvic girdle. (credit: modification of work by Mariana Ruiz Villareal)


11.8: Glossary- The Appendicular System - Biology

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Skeletal system 1: the anatomy and physiology of bones

The skeletal system is formed of bones and cartilage, which are connected by ligaments to form a framework for the remainder of the body tissues. This article, the first in a two-part series on the structure and function of the skeletal system, reviews the anatomy and physiology of bone. Understanding the structure and purpose of the bone allows nurses to understand common pathophysiology and consider the most-appropriate steps to improve musculoskeletal health.

Citation: Walker J (2020) Skeletal system 1: the anatomy and physiology of bones. Nursing Times [online] 116: 2, 38-42.

Author: Jennie Walker is principal lecturer, Nottingham Trent University.

  • This article has been double-blind peer reviewed
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  • Read part 2 of this series here

Introduction

The skeletal system is composed of bones and cartilage connected by ligaments to form a framework for the rest of the body tissues. There are two parts to the skeleton:

  • Axial skeleton – bones along the axis of the body, including the skull, vertebral column and ribcage
  • Appendicular skeleton – appendages, such as the upper and lower limbs, pelvic girdle and shoulder girdle.

Function

As well as contributing to the body’s overall shape, the skeletal system has several key functions, including:

  • Support and movement
  • Protection
  • Mineral homeostasis
  • Blood-cell formation
  • Triglyceride storage.

Support and movement

Bones are a site of attachment for ligaments and tendons, providing a skeletal framework that can produce movement through the coordinated use of levers, muscles, tendons and ligaments. The bones act as levers, while the muscles generate the forces responsible for moving the bones.

Protection

Bones provide protective boundaries for soft organs: the cranium around the brain, the vertebral column surrounding the spinal cord, the ribcage containing the heart and lungs, and the pelvis protecting the urogenital organs.

Mineral homoeostasis

As the main reservoirs for minerals in the body, bones contain approximately 99% of the body’s calcium, 85% of its phosphate and 50% of its magnesium (Bartl and Bartl, 2017). They are essential in maintaining homoeostasis of minerals in the blood with minerals stored in the bone are released in response to the body’s demands, with levels maintained and regulated by hormones, such as parathyroid hormone.

Blood-cell formation (haemopoiesis)

Blood cells are formed from haemopoietic stem cells present in red bone marrow. Babies are born with only red bone marrow over time this is replaced by yellow marrow due to a decrease in erythropoietin, the hormone responsible for stimulating the production of erythrocytes (red blood cells) in the bone marrow. By adulthood, the amount of red marrow has halved, and this reduces further to around 30% in older age (Robson and Syndercombe Court, 2018).

Triglyceride storage

Yellow bone marrow (Fig 1) acts as a potential energy reserve for the body it consists largely of adipose cells, which store triglycerides (a type of lipid that occurs naturally in the blood) (Tortora and Derrickson, 2009).

Bone composition

Bone matrix has three main components:

  • 25% organic matrix (osteoid)
  • 50% inorganic mineral content (mineral salts)
  • 25% water (Robson and Syndercombe Court, 2018).

Organic matrix (osteoid) is made up of approximately 90% type-I collagen fibres and 10% other proteins, such as glycoprotein, osteocalcin, and proteoglycans (Bartl and Bartl, 2017). It forms the framework for bones, which are hardened through the deposit of the calcium and other minerals around the fibres (Robson and Syndercombe Court, 2018).

Mineral salts are first deposited between the gaps in the collagen layers with once these spaces are filled, minerals accumulate around the collagen fibres, crystallising and causing the tissue to harden this process is called ossification (Tortora and Derrickson, 2009). The hardness of the bone depends on the type and quantity of the minerals available for the body to use hydroxyapatite is one of the main minerals present in bones.

While bones need sufficient minerals to strengthen them, they also need to prevent being broken by maintaining sufficient flexibility to withstand the daily forces exerted on them. This flexibility and tensile strength of bone is derived from the collagen fibres. Over-mineralisation of the fibres or impaired collagen production can increase the brittleness of bones – as with the genetic disorder osteogenesis imperfecta – and increase bone fragility (Ralston and McInnes, 2014).

Structure

Bone architecture is made up of two types of bone tissue:

Cortical bone

Also known as compact bone, this dense outer layer provides support and protection for the inner cancellous structure. Cortical bone comprises three elements:

The periosteum is a tough, fibrous outer membrane. It is highly vascular and almost completely covers the bone, except for the surfaces that form joints these are covered by hyaline cartilage. Tendons and ligaments attach to the outer layer of the periosteum, whereas the inner layer contains osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells) responsible for bone remodelling.

The function of the periosteum is to:

  • Protect the bone
  • Help with fracture repair
  • Nourish bone tissue (Robson and Syndercombe Court, 2018).

It also contains Volkmann’s canals, small channels running perpendicular to the diaphysis of the bone (Fig 1) these convey blood vessels, lymph vessels and nerves from the periosteal surface through to the intracortical layer. The periosteum has numerous sensory fibres, so bone injuries (such as fractures or tumours) can be extremely painful (Drake et al, 2019).

The intracortical bone is organised into structural units, referred to as osteons or Haversian systems (Fig 2). These are cylindrical structures, composed of concentric layers of bone called lamellae, whose structure contributes to the strength of the cortical bone. Osteocytes (mature bone cells) sit in the small spaces between the concentric layers of lamellae, which are known as lacunae. Canaliculi are microscopic canals between the lacunae, in which the osteocytes are networked to each other by filamentous extensions. In the centre of each osteon is a central (Haversian) canal through which the blood vessels, lymph vessels and nerves pass. These central canals tend to run parallel to the axis of the bone Volkmann’s canals connect adjacent osteons and the blood vessels of the central canals with the periosteum.

The endosteum consists of a thin layer of connective tissue that lines the inside of the cortical surface (Bartl and Bartl, 2017) (Fig 1).

Cancellous bone

Also known as spongy bone, cancellous bone is found in the outer cortical layer. It is formed of lamellae arranged in an irregular lattice structure of trabeculae, which gives a honeycomb appearance. The large gaps between the trabeculae help make the bones lighter, and so easier to mobilise.

Trabeculae are characteristically oriented along the lines of stress to help resist forces and reduce the risk of fracture (Tortora and Derrickson, 2009). The closer the trabecular structures are spaced, the greater the stability and structure of the bone (Bartl and Bartl, 2017). Red or yellow bone marrow exists in these spaces (Robson and Syndercombe Court, 2018). Red bone marrow in adults is found in the ribs, sternum, vertebrae and ends of long bones (Tortora and Derrickson, 2009) it is haemopoietic tissue, which produces erythrocytes, leucocytes (white blood cells) and platelets.

Blood supply

Bone and marrow are highly vascularised and account for approximately 10-20% of cardiac output (Bartl and Bartl, 2017). Blood vessels in bone are necessary for nearly all skeletal functions, including the delivery of oxygen and nutrients, homoeostasis and repair (Tomlinson and Silva, 2013). The blood supply in long bones is derived from the nutrient artery and the periosteal, epiphyseal and metaphyseal arteries (Iyer, 2019).

Each artery is also accompanied by nerve fibres, which branch into the marrow cavities. Arteries are the main source of blood and nutrients for long bones, entering through the nutrient foramen, then dividing into ascending and descending branches. The ends of long bones are supplied by the metaphyseal and epiphyseal arteries, which arise from the arteries from the associated joint (Bartl and Bartl, 2017).

If the blood supply to bone is disrupted, it can result in the death of bone tissue (osteonecrosis). A common example is following a fracture to the femoral neck, which disrupts the blood supply to the femoral head and causes the bone tissue to become necrotic. The femoral head structure then collapses, causing pain and dysfunction.

Growth

Bones begin to form in utero in the first eight weeks following fertilisation (Moini, 2019). The embryonic skeleton is first formed of mesenchyme (connective tissue) structures this primitive skeleton is referred to as the skeletal template. These structures are then developed into bone, either through intramembranous ossification or endochondral ossification (replacing cartilage with bone).

Bones are classified according to their shape (Box 1). Flat bones develop from membrane (membrane models) and sesamoid bones from tendon (tendon models) (Waugh and Grant, 2018). The term intra-membranous ossification describes the direct conversion of mesenchyme structures to bone, in which the fibrous tissues become ossified as the mesenchymal stem cells differentiate into osteoblasts. The osteoblasts then start to lay down bone matrix, which becomes ossified to form new bone.

Box 1. Types of bones

Long bones – typically longer than they are wide (such as humerus, radius, tibia, femur), they comprise a diaphysis (shaft) and epiphyses at the distal and proximal ends, joining at the metaphysis. In growing bone, this is the site where growth occurs and is known as the epiphyseal growth plate. Most long bones are located in the appendicular skeleton and function as levers to produce movement

Short bones – small and roughly cube-shaped, these contain mainly cancellous bone, with a thin outer layer of cortical bone (such as the bones in the hands and tarsal bones in the feet)

Flat bones – thin and usually slightly curved, typically containing a thin layer of cancellous bone surrounded by cortical bone (examples include the skull, ribs and scapula). Most are located in the axial skeleton and offer protection to underlying structures

Irregular bones – bones that do not fit in other categories because they have a range of different characteristics. They are formed of cancellous bone, with an outer layer of cortical bone (for example, the vertebrae and the pelvis)

Sesamoid bones – round or oval bones (such as the patella), which develop in tendons

Long, short and irregular bones develop from an initial model of hyaline cartilage (cartilage models). Once the cartilage model has been formed, the osteoblasts gradually replace the cartilage with bone matrix through endochondral ossification (Robson and Syndercombe Court, 2018). Mineralisation starts at the centre of the cartilage structure, which is known as the primary ossification centre. Secondary ossification centres also form at the epiphyses (epiphyseal growth plates) (Danning, 2019). The epiphyseal growth plate is composed of hyaline cartilage and has four regions (Fig 3):

Resting or quiescent zone – situated closest to the epiphysis, this is composed of small scattered chondrocytes with a low proliferation rate and anchors the growth plate to the epiphysis

Growth or proliferation zone – this area has larger chondrocytes, arranged like stacks of coins, which divide and are responsible for the longitudinal growth of the bone

Hypertrophic zone – this consists of large maturing chondrocytes, which migrate towards the metaphysis. There is no new growth at this layer

Calcification zone – this final zone of the growth plate is only a few cells thick. Through the process of endochondral ossification, the cells in this zone become ossified and form part of the ‘new diaphysis’ (Tortora and Derrickson, 2009).

Bones are not fully developed at birth, and continue to form until skeletal maturity is reached. By the end of adolescence around 90% of adult bone is formed and skeletal maturity occurs at around 20-25 years, although this can vary depending on geographical location and socio-economic conditions for example, malnutrition may delay bone maturity (Drake et al, 2019 Bartl and Bartl, 2017). In rare cases, a genetic mutation can disrupt cartilage development, and therefore the development of bone. This can result in reduced growth and short stature and is known as achondroplasia.

The human growth hormone (somatotropin) is the main stimulus for growth at the epiphyseal growth plates. During puberty, levels of sex hormones (oestrogen and testosterone) increase, which stops cell division within the growth plate. As the chondrocytes in the proliferation zone stop dividing, the growth plate thins and eventually calcifies, and longitudinal bone growth stops (Ralston and McInnes, 2014). Males are on average taller than females because male puberty tends to occur later, so male bones have more time to grow (Waugh and Grant, 2018). Over-secretion of human growth hormone during childhood can produce gigantism, whereby the person is taller and heavier than usually expected, while over-secretion in adults results in a condition called acromegaly.

If there is a fracture in the epiphyseal growth plate while bones are still growing, this can subsequently inhibit bone growth, resulting in reduced bone formation and the bone being shorter. It may also cause misalignment of the joint surfaces and cause a predisposition to developing secondary arthritis later in life. A discrepancy in leg length can lead to pelvic obliquity, with subsequent scoliosis caused by trying to compensate for the difference.

Remodelling

Once bone has formed and matured, it undergoes constant remodelling by osteoclasts and osteoblasts, whereby old bone tissue is replaced by new bone tissue (Fig 4). Bone remodelling has several functions, including mobilisation of calcium and other minerals from the skeletal tissue to maintain serum homoeostasis, replacing old tissue and repairing damaged bone, as well as helping the body adapt to different forces, loads and stress applied to the skeleton.

Calcium plays a significant role in the body and is required for muscle contraction, nerve conduction, cell division and blood coagulation. As only 1% of the body’s calcium is in the blood, the skeleton acts as storage facility, releasing calcium in response to the body’s demands. Serum calcium levels are tightly regulated by two hormones, which work antagonistically to maintain homoeostasis. Calcitonin facilitates the deposition of calcium to bone, lowering the serum levels, whereas the parathyroid hormone stimulates the release of calcium from bone, raising the serum calcium levels.

Osteoclasts are large multinucleated cells typically found at sites where there is active bone growth, repair or remodelling, such as around the periosteum, within the endosteum and in the removal of calluses formed during fracture healing (Waugh and Grant, 2018). The osteoclast cell membrane has numerous folds that face the surface of the bone and osteoclasts break down bone tissue by secreting lysosomal enzymes and acids into the space between the ruffled membrane (Robson and Syndercombe Court, 2018). These enzymes dissolve the minerals and some of the bone matrix. The minerals are released from the bone matrix into the extracellular space and the rest of the matrix is phagocytosed and metabolised in the cytoplasm of the osteoclasts (Bartl and Bartl, 2017). Once the area of bone has been resorbed, the osteoclasts move on, while the osteoblasts move in to rebuild the bone matrix.

Osteoblasts synthesise collagen fibres and other organic components that make up the bone matrix. They also secrete alkaline phosphatase, which initiates calcification through the deposit of calcium and other minerals around the matrix (Robson and Syndercombe Court, 2018). As the osteoblasts deposit new bone tissue around themselves, they become trapped in pockets of bone called lacunae. Once this happens, the cells differentiate into osteocytes, which are mature bone cells that no longer secrete bone matrix.

The remodelling process is achieved through the balanced activity of osteoclasts and osteoblasts. If bone is built without the appropriate balance of osteocytes, it results in abnormally thick bone or bony spurs. Conversely, too much tissue loss or calcium depletion can lead to fragile bone that is more susceptible to fracture. The larger surface area of cancellous bones is associated with a higher remodelling rate than cortical bone (Bartl and Bartl, 2017), which means osteoporosis is more evident in bones with a high proportion of cancellous bone, such as the head/neck of femur or vertebral bones (Robson and Syndercombe Court, 2018). Changes in the remodelling balance may also occur due to pathological conditions, such as Paget’s disease of bone, a condition characterised by focal areas of increased and disorganised bone remodelling affecting one or more bones. Typical features on X-ray include focal patches of lysis or sclerosis, cortical thickening, disorganised trabeculae and trabecular thickening.

As the body ages, bone may lose some of its strength and elasticity, making it more susceptible to fracture. This is due to the loss of mineral in the matrix and a reduction in the flexibility of the collagen.

Diet and lifestyle factors

Adequate intake of vitamins and minerals is essential for optimum bone formation and ongoing bone health. Two of the most important are calcium and vitamin D, but many others are needed to keep bones strong and healthy (Box 2).

Box 2. Vitamins and minerals needed for bone health

Key nutritional requirements for bone health include minerals such as calcium and phosphorus, as well as smaller qualities of fluoride, manganese, and iron (Robson and Syndercombe Court, 2018). Calcium, phosphorus and vitamin D are essential for effective bone mineralisation. Vitamin D promotes calcium absorption in the intestines, and deficiency in calcium or vitamin D can predispose an individual to ineffective mineralisation and increased risk of developing conditions such as osteoporosis and osteomalacia.

Other key vitamins for healthy bones include vitamin A for osteoblast function and vitamin C for collagen synthesis (Waugh and Grant, 2018).

Physical exercise, in particular weight-bearing exercise, is important in maintaining or increasing bone mineral density and the overall quality and strength of the bone. This is because osteoblasts are stimulated by load-bearing exercise and so bones subjected to mechanical stresses undergo a higher rate of bone remodelling. Reduced skeletal loading is associated with an increased risk of developing osteoporosis (Robson and Syndercombe Court, 2018).

Conclusion

Bones are an important part of the musculoskeletal system and serve many core functions, as well as supporting the body’s structure and facilitating movement. Bone is a dynamic structure, which is continually remodelled in response to stresses placed on the body. Changes to this remodelling process, or inadequate intake of nutrients, can result in changes to bone structure that may predispose the body to increased risk of fracture. Part 2 of this series will review the structure and function of the skeletal system.

Key points

  • Bones are key to providing the body with structural support and enabling movement
  • Most of the body’s minerals are stored in the bones
  • Diet and lifestyle can affect the quality of bone formation
  • After bones have formed they undergo constant remodelling
  • Changes in the remodelling process can result in pathology such as Paget’s disease of bone or osteoporosis

Bartl R, Bartl C (2017) Structure and architecture of bone. In: Bone Disorder: Biology, Diagnosis, Prevention, Therapy.

Danning CL (2019) Structure and function of the musculoskeletal system. In: Banasik JL, Copstead L-EC (eds) Pathophysiology. St Louis, MO: Elsevier.

Drake RL et al (eds) (2019) Gray’s Anatomy for Students. London: Elsevier.

Iyer KM (2019) Anatomy of bone, fracture, and fracture healing. In: Iyer KM, Khan WS (eds) General Principles of Orthopedics and Trauma. London: Springer.

Moini J (2019) Bone tissues and the skeletal system. In: Anatomy and Physiology for Health Professionals. Burlington, MA: Jones and Bartlett.

Ralston SH, McInnes IB (2014) Rheumatology and bone disease. In: Walker BR et al (eds) Davidson’s Principles and Practice of Medicine. Edinburgh: Churchill Livingstone.

Robson L, Syndercombe Court D (2018) Bone, muscle, skin and connective tissue. In: Naish J, Syndercombe Court D (eds) Medical Sciences. London: Elsevier

Tomlinson RE, Silva MJ (2013) Skeletal blood flow in bone repair and maintenance. Bone Research 1: 4, 311-322.

Tortora GJ, Derrickson B (2009) The skeletal system: bone tissue. In: Principles of Anatomy and Physiology. Chichester: John Wiley & Sons.

Waugh A, Grant A (2018) The musculoskeletal system. In: Ross & Wilson Anatomy and Physiology in Health and Illness. London: Elsevier.


Watch the video: Appendicular Skeleton. Class 12th biology in pashto. Home Of Biology (July 2022).


Comments:

  1. Holdin

    Something they didn't send private messages, error ....

  2. Kein

    It should be said - rough mistake.

  3. Shaktizuru

    Magnificent sentence and on time



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