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14.4: Age Related Changes to the Reproductive System - Biology

14.4: Age Related Changes to the Reproductive System - Biology



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Female Reproductive System

Female fertility (the ability to conceive) peaks when women are in their twenties, and is slowly reduced until a women reaches 35 years of age. Poor health, including smoking, can lead to earlier loss of fertility and earlier menopause.

As a woman reaches the age of menopause, depletion of the number of viable follicles in the ovaries due to atresia affects the hormonal regulation of the menstrual cycle. During the years leading up to menopause, there is a decrease in the levels of the hormone inhibin, which normally participates in a negative feedback loop to the pituitary to control the production of FSH. The menopausal decrease in inhibin leads to an increase in FSH. The presence of FSH stimulates more follicles to grow and secrete estrogen. Because small, secondary follicles also respond to increases in FSH levels, larger numbers of follicles are stimulated to grow; however, most undergo atresia and die. Eventually, this process leads to the depletion of all follicles in the ovaries, and the production of estrogen falls off dramatically. It is primarily the lack of estrogens that leads to the symptoms of menopause.

The earliest changes occur during the menopausal transition, often referred to as peri-menopause, when a women’s cycle becomes irregular but does not stop entirely. Although the levels of estrogen are still nearly the same as before the transition, the level of progesterone produced by the corpus luteum is reduced. This decline in progesterone can lead to abnormal growth, or hyperplasia, of the endometrium. This condition is a concern because it increases the risk of developing endometrial cancer. Two harmless conditions that can develop during the transition are uterine fibroids, which are benign masses of cells, and irregular bleeding. As estrogen levels change, other symptoms that occur are hot flashes and night sweats, trouble sleeping, vaginal dryness, mood swings, difficulty focusing, and thinning of hair on the head along with the growth of more hair on the face. Depending on the individual, these symptoms can be entirely absent, moderate, or severe.

After menopause, lower amounts of estrogens can lead to other changes. Cardiovascular disease becomes as prevalent in women as in men, possibly because estrogens reduce the amount of cholesterol in the blood vessels. When estrogen is lacking, many women find that they suddenly have problems with high cholesterol and the cardiovascular issues that accompany it. Osteoporosis is another problem because bone density decreases rapidly in the first years after menopause. The reduction in bone density leads to a higher incidence of fractures.

Hormone therapy (HT), which employs medication (synthetic estrogens and progestins) to increase estrogen and progestin levels, can alleviate some of the symptoms of menopause. In 2002, the Women’s Health Initiative began a study to observe women for the long-term outcomes of hormone replacement therapy over 8.5 years. However, the study was prematurely terminated after 5.2 years because of evidence of a higher than normal risk of breast cancer in patients taking estrogen-only HT. The potential positive effects on cardiovascular disease were also not realized in the estrogen-only patients. The results of other hormone replacement studies over the last 50 years, including a 2012 study that followed over 1,000 menopausal women for 10 years, have shown cardiovascular benefits from estrogen and no increased risk for cancer. Some researchers believe that the age group tested in the 2002 trial may have been too old to benefit from the therapy, thus skewing the results. In the meantime, intense debate and study of the benefits and risks of replacement therapy is ongoing. Current guidelines approve HT for the reduction of hot flashes or flushes, but this treatment is generally only considered when women first start showing signs of menopausal changes, is used in the lowest dose possible for the shortest time possible (5 years or less), and it is suggested that women on HT have regular pelvic and breast exams.

Male Reproductive System

As a result of the cumulative changes to the male reproductive system many men experience depression, mood swings, and a general feeling of uneasiness as they approach their 50s or 60s. This time period is referred to as andropause, or male menopause. While the testes continue to function during and after this period men may experience impotence. Regardless, even at advanced ages, some men are able to have sexual relationships and may even remain fertile.

Physiologically the testes decrease in size and firmness with age. This is associated with a gradual age related decline in the secretion of testosterone. Simultaneously there is a decrease in sexual desire. By the age of 60 there is a 30% reduction in sperm count. The prostate gland atrophies between the ages of 50 and 60 years of age, which reduces the secretory capacity. By the age of 70 the prostate gland may enlarge due to masses of potentially cancerous tissue. Additionally the seminal vesicles decrease in weight and storage capacity after age 60 and the penis undergoes some atrophy with age.


14.4: Age Related Changes to the Reproductive System - Biology

The most significant change to the mouth with age is the loss of teeth. This is caused by a combination of bone loss from the jaw, which occurs with age, and gum disease. Both result in a loosening of teeth. While lost teeth can be replaced with dentures these are not equivalent to natural teeth. Dentures can make it difficult to chew comfortably. This can result in a change of eating habits and long term deficits in nutrition.

Additional changes to the mouth include a decreased level of saliva production, thicker mucus production, and a diminished sense of taste.

Esophagus

Many other people experience difficultly in swallowing. Most often this is a result from incomplete relaxation of the lower esophageal sphincter, but it could be a result of a neurological disorder.

Other issues with esophagus include heartburn caused by stomach acid entering the esophagus through a weakened esophageal sphincter.

Stomach

The mucus membrane of the stomach thins with age resulting in lower levels of mucus, hydrochloric acid, and digestive enzymes. This reduces the digestion of proteins and may result in chronic atrophic gastritis.

Small Intestine

The walls of the small intestines atrophy with age. This alters the shape of the villi and reduces the surface area across which absorption occurs. Along with the atrophy these is a decrease in the production of digestive enzymes. Surprisingly these changes do not result in decreased rate of the absorption of digested food.

Large Intestine

The walls of the large intestines atrophy with age. The thinning of the walls results in outpockets from the wall, a condition known as diverticulosis.

Pancreas

The number of secretory cells in the pancreas decreases with age. This results in a decrease in the level of fat digestion.

Liver

While the liver reduces in size with age it does not show any significant reduction in the ability to perform its various functions in healthy elderly people.


Effect of temperature changes on the reproductive cycle of roach in Lake Geneva from 1983 to 2001

In Lake Geneva, the surface water temperature has increased by 1° C over 20 years probably as a result of climate change. The effects of changes in temperature on the reproductive cycle of the roach Rutilus rutilus were assessed in a 19 year survey. Over time, spawning tended to begin earlier. The consequences of temperature changes were assessed on two different stages of the female reproductive cycle: the development of the ovaries from the beginning of autumn to ovulation, and the onset of the spawning period. The development of the ovaries was studied for 7 consecutive years from October to June. From 1 October to the onset of spawning, it was possible to assess the gonado-somatic index (IG) of females in terms of time expressed as a sum of degree-days. The correlation between IG and the sum of degree-days was +0·97. The onset of the roach spawning period in Lake Geneva was triggered by a thermal threshold (median and range 190 ± 10 degree-days for the 15 previous days). From October to April, climate warming accelerated the development of gonads, then in May, a thermal threshold that triggered the onset of roach spawning occurred earlier.


Results

Animals were, on average, 72 days old at parturition and BMR was measured,on average, 43 days later (Table 1). Of the animals that we measured for BMR (N=304), 87%had successfully given birth and 84% maintained litters to weaning age(Table 1). Our use of proven breeder males makes it unlikely that failure to produce offspring was a consequence of male infertility.

Characteristics of female C57BL/6J mice used in this study

. Birth success . N . Mean ± s.e.m. . Range .
Age at parturition (days) 265 72±0.2 68-85
Body mass at parturition (g) 265 24.1±0.10 19.8-30
Number of pups born 265 6.4±0.10 2-10
Birth litter mass (g) 265 12.4±0.14 4.4-18.2
Birth pup mass (g) 265 2.0±0.03 1.3-4.6
Number of pups weaned 256 6.1±0.12 1-10
Weaned litter mass (g) 256 54.0±0.76 4.9-83.9
Weaned pup mass 256 8.7±0.06 4.9-12.5
Age at BMR measurement (days) 304 115±0.5 100-135
Body mass at BMR measurement (g) No 39 22.2±0.25 19.6-28.0
Yes 265 24.2±0.08 * 17.7-26.0
Total 304 24.0±0.09 17.7-28.0
BMR (W) No 39 0.185±0.0070 0.083-0.303
Yes 265 0.194±0.0020 NS 0.102-0.299
Total 304 0.193±0.0019 0.083-0.303
. Birth success . N . Mean ± s.e.m. . Range .
Age at parturition (days) 265 72±0.2 68-85
Body mass at parturition (g) 265 24.1±0.10 19.8-30
Number of pups born 265 6.4±0.10 2-10
Birth litter mass (g) 265 12.4±0.14 4.4-18.2
Birth pup mass (g) 265 2.0±0.03 1.3-4.6
Number of pups weaned 256 6.1±0.12 1-10
Weaned litter mass (g) 256 54.0±0.76 4.9-83.9
Weaned pup mass 256 8.7±0.06 4.9-12.5
Age at BMR measurement (days) 304 115±0.5 100-135
Body mass at BMR measurement (g) No 39 22.2±0.25 19.6-28.0
Yes 265 24.2±0.08 * 17.7-26.0
Total 304 24.0±0.09 17.7-28.0
BMR (W) No 39 0.185±0.0070 0.083-0.303
Yes 265 0.194±0.0020 NS 0.102-0.299
Total 304 0.193±0.0019 0.083-0.303

Pups were weighed individually at weaning, but at birth the pup mass was calculated from birth litter mass and the number of pups in each litter. Animals were considered successful at birth if they gave birth to live pups. Successful and unsuccessful animals were compared by unpaired t-test. * P<0.001, t=−7.37 NS P=0.237, t=−1.2. BMR=basal metabolic rate.

Body mass (Mb) of females that successfully gave birth was greater than unsuccessful females at the time when BMR was measured, but BMR was not different (Table 1). The variation in BMR for successful females was large(Table 1), and although the variation in Mb for the same sample was also great, only 6.9% of the variation in BMR could be accounted for by Mb(Fig. 1). Nevertheless, for successful females, the association was significant because of the large sample size (Fig. 1). However,because Mb accounted for so little of the variance, there was a large residual variation in BMR once the effects of Mb had been accounted for. We have presented results concerning BMR as uncorrected BMR as well as residual BMR corrected for Mb effects. There was no association between BMR and Mb for animals that did not successfully give birth(Fig. 1).

Scatter plot of basal metabolic rate (BMR) and body mass(Mb) of female C57BL6/J mice during a 30-day measurement period starting 10 days after weaning. The trend-line(y=0.0054x+0.0639) is for females that successfully gave birth to pups (N=265, r 2 =6.9%, P<0.001). There was no association between BMR and Mb for unsuccessful females (N=39 r 2 =0.3%, P=0.748).

Scatter plot of basal metabolic rate (BMR) and body mass(Mb) of female C57BL6/J mice during a 30-day measurement period starting 10 days after weaning. The trend-line(y=0.0054x+0.0639) is for females that successfully gave birth to pups (N=265, r 2 =6.9%, P<0.001). There was no association between BMR and Mb for unsuccessful females (N=39 r 2 =0.3%, P=0.748).

Histogram showing the number of C57BL/6J mice that gave birth and weaned a given number of pups.

Histogram showing the number of C57BL/6J mice that gave birth and weaned a given number of pups.

Scatter plots showing the relationship between the number of pups born in a litter and (A) litter mass and (B) mean pup mass per litter, which was calculated from litter mass and pup number.

Scatter plots showing the relationship between the number of pups born in a litter and (A) litter mass and (B) mean pup mass per litter, which was calculated from litter mass and pup number.

Litter size for dams that gave birth to live litters varied at birth between two and 10 pups (Fig. 2). The mean litter size was 6.4 pups and the modal litter size was 7 (Fig. 2). Litter mass at birth was positively related to litter size(Fig. 3A) and ranged from 4.4 g for a litter of two pups to 18.2 g for a litter with seven pups. Although four animals gave birth to 10 live pups, the heaviest of these litters at birth was 16.6 g. Because the relationship between litter mass and litter size was not linear (Fig. 3A) the mean pup mass at birth was negatively related to litter size(Fig. 3B). Hence, pups in the smallest litters weighed on average 3.2 g, while those in litters of seven averaged 1.9 g and those in the largest litters weighed on average only 1.6 g.(Fig. 3B).

We ordered the mothers by either their absolute BMR or their residual BMR corrected for Mb and then divided these ordered data into 10 equal-sized groups. Within each group we calculated the proportion of animals that successfully gave birth to live litters (265 out of 304 mated)and those that went on to wean pups (256 out of 265 that gave birth Fig. 4). There was no significant association between the probability of birth success and either BMR (Fig. 4A) or residual BMR corrected for Mb (Fig. 4B). From the 265 animals that gave birth to live litters, only nine failed to maintain them to weaning age. Four of the five (80%) litters with two pups did not reach weaning and four out of the 11 (36%) litters with three pups failed. One of the 57 litters with six pups (1.8%) also failed to reach weaning. Failure to maintain pups to weaning was not related to BMR(Fig. 4C) or residual BMR corrected for Mb (Fig. 4D). However, the females that lost their litters before weaning all gave birth to low numbers of pups. These two factors may have been related and may have resulted from some undiagnosed reproductive problem, so these animals were excluded from further analyses.

Many females lost offspring during the course of lactation but did successfully wean some pups. We used contingency tables to test if there was an association between losses and the number of pups per litter at birth. Excluding the animals that lost their entire litters, we found that the extent of the losses during lactation was not related to large initial litter size(Pearson chi-squared value=5.66, d.f.=8, P=0.686 data not shown).

The percentage of C57BL/6J mice that gave birth to live litters(N=304) and successfully weaned pups (N=265) in each centile of basal metabolic rate (BMR) values or residual BMR corrected for body mass(Mb). There was no significant association between the probability of birth success and either BMR (A binary logistic regression, P=0.129) or BMR corrected for Mb (B P=0.754), or weaning success and BMR (C P=0.954) or BMR corrected for Mb (D P=0.373).

The percentage of C57BL/6J mice that gave birth to live litters(N=304) and successfully weaned pups (N=265) in each centile of basal metabolic rate (BMR) values or residual BMR corrected for body mass(Mb). There was no significant association between the probability of birth success and either BMR (A binary logistic regression, P=0.129) or BMR corrected for Mb (B P=0.754), or weaning success and BMR (C P=0.954) or BMR corrected for Mb (D P=0.373).

There was a positive correlation between litter mass at birth and Mb of females when BMR was measured(Fig. 5A), but there was no relationship between litter mass and BMR(Fig. 5B) or BMR with the effects of Mb removed(Fig. 5C). However, litter size at birth was significantly related to both female Mb(Fig. 6A) and BMR(Fig. 6B). Females that were heavier, or had greater BMR, on average gave birth to larger litters. However,the explained variance in litter size by both Mb and BMR was small (15.3% and 2.1%, respectively) and the gradients of the least-squares fitted regression lines were very shallow. Hence, on average, a female mouse with a BMR of 0.15 W gave birth to a litter of 6.1 pups and a female with a BMR of 0.25 W (67% greater) gave birth to a litter of 6.8 pups(11% greater). Moreover, this effect of BMR on litter size was completely dependent on the shared variation in both traits due to body mass, as there was no significant association between litter size and residual BMR with the effects of mass removed (Fig. 6C).

At weaning, litter mass and litter size both correlated with Mb (Fig. 7Aand Fig. 8A, respectively) and BMR (Fig. 7B and Fig. 8B, respectively) and the relationships were again positive. Heavier females and those with greater BMR weaned heavier and larger litters. However, as with the relationships for litter size at birth (Fig. 6),the gradients of the least-squares fitted regression lines were very shallow. Increases in BMR from 0.15 to 0.25 W (67% greater) were on average associated with increased masses at weaning of 6.4 g (12% of mean litter mass at weaning)and 0.8 extra pups (13% of litter size at weaning). As with the relationships at birth, the significance of the BMR effect was entirely dependent on the shared variation due to Mb as there was no relationship when residual BMR taking mass into account was used (litter mass in Fig. 7C and litter size in Fig. 8C).

The monitoring of body mass every second day enabled us to identify 13 animals that were pregnant but were not successful at birth. Two of these animals gave birth, but only dead pups were found, and the remaining 11 animals experienced Mb gain indicative of pregnancy but later returned to normal Mb, suggesting that foetuses were absorbed or miscarried. We also identified that 25 of the animals that successfully gave birth to live litters had Mb loss or plateau during pregnancy, which indicated that they had lost some pups during gestation. We were unable to quantify what the litter sizes might have been for these animals if they had kept all pups conceived. We ordered these 278(265 successful and 13 pregnant but unsuccessful) animals by either their absolute BMR or residual BMR corrected for BM and then divided these ordered data into 10 equal-sized groups. Within each group, we calculated the proportion of animals that appeared to have absorbed or miscarried foetuses(Fig. 9). We found a significant relationship between the loss of pups during gestation and BMR(Fig. 9A). This indicates that animals with high BMR have an increased probability of losing pups either through miscarriage or the absorption of foetuses. This relationship was independent of the variation found in Mb because the relationship with residual BMR corrected for differences in Mb was still significant(Fig. 9B).

The sex of the pups from 170 litters was recorded at weaning. Two litters contained only male pups and four litters contained only female pups. There was no relationship between the number of female pups weaned and Mb (N=168, r 2 =0.9%, P=0.228), but the number of male pups weaned per litter was related to the Mb of the dam at the time when BMR was measured(N=166, r 2 =12.1%, P<0.001). As pups were not sexed at birth, this could have occurred for two reasons: either dams with high Mb may have given birth to a greater number of male pups or dams with a low Mb may have reduced the number of male pups in litters during lactation. There was no relationship between the number of females or the number of males weaned and BMR(r 2 =1.4%, P=0.122 and r 2 =0.6%, P=0.322, respectively data not shown)or residual BMR corrected for Mb(r 2 =1.0%, P=0.202 and r 2 =0.0%, P=0.854, respectively data not shown). For dams with male and female pups, the ratio of female to male pups was also unrelated to Mb (Fig. 10A) and both BMR (Fig. 10B) and residual BMR corrected for Mb(Fig. 10C).

Scatter plots of litter mass at birth against (A) body mass(Mb) (y=0.414x+2.41), (B) basal metabolic rate (BMR) (y=-0.75x+12.6) and (C) BMR corrected for Mb (y=-4.75x+12.4) for C57BL/6J mice(N=265).

Scatter plots of litter mass at birth against (A) body mass(Mb) (y=0.414x+2.41), (B) basal metabolic rate (BMR) (y=-0.75x+12.6) and (C) BMR corrected for Mb (y=-4.75x+12.4) for C57BL/6J mice(N=265).

Scatter plots of litter size at birth against (A) body mass(Mb) (y=0.48x-5.26), (B) basal metabolic rate (BMR) (y=7.2x+4.96) and (C) BMR corrected for Mb (y=3.11x+6.36) for C57BL/6J mice(N=265).

Scatter plots of litter size at birth against (A) body mass(Mb) (y=0.48x-5.26), (B) basal metabolic rate (BMR) (y=7.2x+4.96) and (C) BMR corrected for Mb (y=3.11x+6.36) for C57BL/6J mice(N=265).


Melatonin and human reproduction

In photoperiodic nonhuman mammals the secretion of melatonin from the pineal gland plays a major role in regulating reproductive physiology in humans these relationships are less clear. The melatonin rhythm changes throughout life with the first substantial change in nocturnal melatonin secretion being reportedly associated with puberty. The transition from Tanner stage 1 to Tanner stage 5 of sexual maturation is associated with a significant reduction in nocturnal melatonin levels, but a cause-effect relationship has not been established. Menstrual cyclicity has been reported to be associated with fluctuations in melatonin production but whether they are related to, eg ovulation or menstruation is not established. At high latitudes the quantity of melatonin produced by the pineal gland varies with season (changes in the light-dark cycle), and there is some evidence that this changes reproductive efficiency accordingly. Menopause is associated with a reduction in melatonin which may relate to the changing gonadotropin levels. In males of the same age melatonin levels also drop with no significant alteration in reproductive physiology. While correlations between melatonin and the status of the reproductive system in humans have been noted, whether they are functionally related remains to be determined.


Anatomy of female puberty: The clinical relevance of developmental changes in the reproductive system

Division of Pediatric Endocrinology, Department of Pediatrics, University of Alabama School of Medicine, 1601 4th Avenue South, CPP II Suite 230, Birmingham, AL 35233, USASearch for more papers by this author

Division of Pediatric Endocrinology, Department of Pediatrics, University of Alabama School of Medicine, Birmingham, Alabama

Division of Pediatric Endocrinology, Department of Pediatrics, University of Alabama School of Medicine, Birmingham, Alabama

Division of Pediatric Endocrinology, Department of Pediatrics, University of Alabama School of Medicine, 1601 4th Avenue South, CPP II Suite 230, Birmingham, AL 35233, USASearch for more papers by this author

Division of Pediatric Endocrinology, Department of Pediatrics, University of Alabama School of Medicine, Birmingham, Alabama

Abstract

Puberty is the period of biologic transition from childhood to adulthood. The changes that occur at this time are related to the increasing concentrations of sex steroid hormones. In females, most pubertal changes are caused by estrogen stimulation that results from the onset of central puberty. Significant development occurs in the organs of the female reproductive system and results in anatomic changes that characterize reproductive maturity. Adrenal and ovarian androgens also increase during puberty, affecting change that includes the promotion of certain secondary sex characteristics. The ability to recognize normal pubertal anatomy and distinguish between estrogen and androgen effects is important in the ability to diagnose and treat disorders of sex development, precocious puberty, pubertal delay, and menstrual irregularities in children and adolescents. An understanding of this developmental process can also help clinicians identify and treat reproductive pathology in adultsand across all female life stages. Clin. Anat. 26:115–129, 2013. © 2012 Wiley Periodicals, Inc.


DISCUSSION

In general, the results of our present study supported our predictions in that feeding and reproductive performance of fleas were better on male than on female hosts. Fleas took relatively more blood, satiated their appetite earlier and produced more eggs when they fed on a male than on a female host,although the difference in feeding performance was manifested mainly during the first feeding event. Because our experiments were carried out in the laboratory and because rodents were not permitted to self-groom, these results suggest that gender difference in the immune defence is the proximate mechanism behind male-biased parasitism.

Proportion (±s.e.m.) of fleas Xenopsylla ramesis that satiated their appetite and left male and female Meriones crassus in less than 60 min on the first, fifth and eighth days of feeding.

Proportion (±s.e.m.) of fleas Xenopsylla ramesis that satiated their appetite and left male and female Meriones crassus in less than 60 min on the first, fifth and eighth days of feeding.

The immune system is the main tool of defence against parasitism. This system is aimed to discriminate between `self' and `non-self' and to minimize the consequences of contact with foreign molecules introduced into the host by feeding parasites. Immune defence mechanisms of vertebrates include two components: innate and acquired (adaptive) immunities(Janeway et al., 1999). It is acquired immunity that is believed to play a major role in the host developing resistance to parasites (Wakelin,1996). In the case of ectoparasites, this is manifested by a decrease in feeding and in the reproduction of ectoparasites exploiting hosts that have been previously repeatedly attacked by this or closely related parasites (Willadsen, 1980 Fielden et al., 1992 Rechav, 1992) [but see Johnston and Brown and Vaughan et al.(Johnston and Brown, 1985 Vaughan et al., 1989)].

Immunocompetence is the general capacity of an organism to mount an immune response against pathogens and parasites(Schmid-Hempel, 2003). Gender differences in immunocompetence have been reported for a variety of homeotherms, with males being generally less immunocompetent than females(Olsen and Kovacs, 1996 Poulin, 1996) supposedly due to higher levels of androgens that suppress the immune system(Folstad and Karter, 1992). However, the relationship between testosterone and immune function is equivocal (Castro et al., 2001 Rolff, 2002 Schmid-Hempel, 2003 Vainikka et al., 2004). For example, Rolff proposed an alternative hypothesis explaining sexual differences in immunocompetence due to a higher investment of females into immune defence (Rolff, 2002). Nevertheless, testosterone injections reduced the resistance of rodents Myodes glareolus and Apodemus sylvaticus to parasitism of the tick Ixodes ricinus (Hughes and Randolph, 2001). Grieves et al. (Grieves et al., 2006) found that testosterone levels in birds Junco hyemalis were significantly negatively correlated with immune-related variables, suggesting that elevated testosterone levels may compromise immune function.

Our earlier results suggest that male M. crassus are less immunocompetent than conspecific females. Khokhlova et al. found that females of this rodent had higher levels of circulating immune complexes than males(Khokhlova et al., 2004). This indicates a higher synthesis of antibodies and clearance of the antigen through complexation in females. Göuy de Bellocq et al.(Göuy de Bellocq et al.,2006) used the phytohemagglutinin injection assay (PHA test)(Smits et al., 1999) to measure immunocompetence in M. crassus by subcutaneous injection of vegetal lectin, a phytohemagglutinin that induces local T-cell stimulation and proliferation that causes swelling. The PHA response was higher in non-parasitized female than in non-parasitized male M. crassus but this difference disappeared after the rodents were exposed to parasitism by X. ramesis. However, no correlation between the PHA response and egg production and blood consumption of X. ramesis was found in this study. The reason for this could be that the PHA test in this previous study was applied after flea infestation trials and the PHA response appeared to be sensitive to flea infestation. Therefore, the strength of the PHA response did not reflect the overall immunocompetence of individuals(Göuy de Bellocq et al.,2006). Consequently, the relationship between performance of fleas and immunocompetence assessed by the PHA response requires further investigation. Future experiments should involve measuring flea performance after applying the PHA test, which would permit the avoidance of the immuno-suppressing effect of flea infestation. However, Göuy de Bellocq et al. (Göuy de Bellocq et al.,2006) found a correlation between changes in rodent leucocyte concentration after 15 days of flea parasitism and flea fitness (egg production and hatching success) and feeding (blood meal size) variables,implying that the host's immune response affected the reproductive physiology of the fleas.

Apart from the present study, other studies have also suggested that gender differences in immunocompetence can cause gender difference in parasite performance. For example, Haas studied survival and feeding of a flea Xenopsylla vexabilis parasitizing its rodent host, Rattus exulans, and found that the fleas had higher survival and more blood consumption on adult male hosts followed by adult females and juvenile males(Haas, 1965).

The results of our present study strongly advocate that the immediate reason behind male-biased flea parasitism is gender difference in the immune response however, the effect of differential mobility between males and females on their difference in flea infestation in the field cannot be discounted. Indeed, male M. crassus have larger home ranges than females (Daly and Daly, 1975). Consequently, the two mechanisms are not mutually exclusive and both supposedly play a role in gender differences of parasitism pattern. However,during the hot desert summer, when M. crassus do not reproduce(Krasnov et al., 1996) and thus testosterone levels in males are supposedly low, males and females were equally parasitized by fleas (Krasnov et al., 2005). This suggests that gender difference in immunocompetence rather than gender difference in mobility may be a more important mechanism for male-biased parasitism, especially given that male and female M. crassus do not demonstrate seasonal changes in their home range size (G.I. Shenbrot and B.R.K., unpublished data).

Temporal dynamics of flea responses and host-gender-related differences require some explanation. We found that fleas consumed more blood from a male than from a female host during the first feeding event only. The first feeding event is critically important for fleas as the majority of fleas are able to mate only after feeding. Newly emerged female fleas have underdeveloped ovaries blocked with a follicular plug(Vashchenok, 1966) whereas newly emerged males of many species have a testicular plug that prevents the passage of sperm from the testes to the vas deferens(Dean and Meola, 1997). The first blood meal is a trigger for the development of ovaries in female fleas(Liao and Lin, 1993) and for the dissolution of the testicular plug in males(Kamala Bai and Prasad, 1979). However, after the first blood meal, the relative amount of blood taken from male hosts decreased whereas that taken from female hosts increased. The pattern for male hosts was also supported by the decrease in the proportion of early satiated fleas during the fifth and eighth feeding events as compared with the first feeding event. A possible explanation is that male rodents continued to develop resistance against fleas whereas fleas managed to downregulate the response of female rodents. However, this explanation is highly speculative and requires further investigation.

We also found no host-gender-related differences in the number of eggs produced in the beginning of oviposition. The reason for this may be that first clutches of young fleas are usually small(Vashchenok, 1988 Vashchenok, 1993 Vashchenok, 2001). The rate of egg production then increases, which is followed by a decrease. Vashchenok studied egg production in fleas (Leptopsylla segnis) that were allowed continuous access to a host (laboratory mouse) for 40 days(Vashchenok, 2001). Peak egg production occurred when a flea was 6–10 days old. Unimodality of age-related changes in egg production have also been reported for other flea species, such as Xenopsylla skrjabini, Xenopsylla nuttalli, Xenopsylla gerbilli and Xenopsylla conformis (for a review, see Krasnov, 2008). Larger blood meals are usually associated with higher egg output in blood-feeding arthropods (Lehane, 2005). However, the generally low rate of first egg laying in fleas coupled with the large amount of blood taken during the first feeding event on male hosts is the likely reason behind an apparent contradiction between the trend of oviposition rate to increase over time(Fig. 3, male hosts) and the trend of blood meal size to decrease over time(Fig. 1, male hosts).


Alzheimer’s disease: the impact of age-related changes in reproductive hormones

The relationship between menopause and cognitive decline has been the subject of intense research since a number of studies have shown that hormone replacement therapy could reduce the risk of developing Alzheimer’s disease in women. In contrast, research into andropause has only recently begun. Furthermore, evidence now suggests that steroidogenesis is not restricted to the gonads and adrenals, and that the brain is capable of producing its own steroid hormones, including testosterone and estrogen. Sex hormones have been demonstrated to be of critical importance in the embryonic development of the central nervous system (CNS) however, we are only just beginning to understand the role that these hormones may play in the normal functioning and repair of the adult mammalian CNS. This review will summarize current research into the role of androgens and andropause on cognition and the possible mechanisms of action of androgens, with particular reference to Alzheimer’s disease.

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Babies fed soy-based formula have changes in reproductive system tissues

Infants who consumed soy-based formula as newborns had differences in some reproductive-system cells and tissues, compared to those who used cow-milk formula or were breastfed, according to a new study. The researchers say the differences, measured in the months after birth, were subtle and not a cause for alarm, but reflect a need to further investigate the long-term effects of exposure to estrogen-like compounds found in soy-based formulas.

"Soy formula contains high concentrations of plant-based estrogen-like compounds, and because this formula is the sole food source for many babies in the first six months of life, it's important to understand the effects of exposure to such compounds during a critical period in development," said Virginia A. Stallings, MD, director of the Nutrition Center at Children's Hospital of Philadelphia (CHOP). Stallings is a senior author of a new study published online March 1 in the Journal of Clinical Endocrinology and Metabolism.

The study was funded and led by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health. The first author is Margaret A. Adgent, MSPH, PhD, formerly of NIEHS, now at Vanderbilt University Medical Center. Adgent said, "Modern soy formula has been used safely for decades. However, our observational study found subtle effects in estrogen-responsive tissues in soy-fed infants, and we don't know if these differences are associated with long-term health effects."

Some mothers who don't breastfeed have long used soy formula as an alternative to cow-milk formula, often from concerns about milk allergies, lactose intolerance, or other feeding difficulties. However, soy protein contains high amounts of genistein, an estrogen-like compound. Like other estrogen-mimicking chemicals found in the environment, genistein can alter the body's endocrine system and potentially interfere with normal hormonal development. In laboratory studies genistein causes abnormal reproductive development and function in rodents, but little is known about its effects on infants.

The current study investigated the postnatal development of estrogen-responsive tissues, along with specific hormone levels, according to infant feeding practices. The researchers particularly compared infants fed with soy formula to those fed with cow-milk formula and breastfed infants.

Of 410 infant-mother pairs enrolled, 283 pairs completed the study. Of those, 102 infants exclusively fed on soy formula, 111 on cow-milk formula, and 70 on breast milk. "This was an observational study, not a randomized trial," said Stallings. "All of the mothers had decided on their feeding preferences before we enrolled them in the study."

Approximately half of the babies were girls, and 70 percent of the infants were African American. They were born in eight Philadelphia-area hospitals between 2010 and 2013, and enrolled in the Infant Feeding and Early Development (IFED) Study.

All of the infants were evaluated at CHOP, where researchers repeatedly performed measurements up to age 28 weeks in the boys and age 36 weeks in the girls. The study team assessed three sets of outcomes: a maturational index (MI) based on epithelial cells from the children's urogenital tissue ultrasound measurements of uterine, ovarian and testicular volume, as well as breast-buds and hormone concentrations seen in blood tests.

"The main differences we found related to different feeding preferences were among the girls," said Stallings. Compared to girls fed cow-milk formula, those fed soy formula had developmental trajectories consistent with responses to estrogen exposure. Vaginal cell MI was higher and uterine volume decreased more slowly in soy-fed girls, both of which suggest estrogen-like responses. The study team found similar patterns in differences between soy-fed girls and breastfed girls.

"We don't know whether the effects we found have long-term consequences for health and development, but the question merits further study," said Stallings. In addition to replication studies by other researchers, she added that ideally the children in this cohort should be followed later into childhood and adolescence.

She added, "For new and expectant mothers deciding on how to feed their infants, as always, we strongly support breast-feeding, as recommended by the American Academy of Pediatrics." For mothers who prefer giving formula, the AAP does not recommend soy formula for preterm infants, but states that soy formula is indicated for infants with hereditary disorders that make them unable to properly digest milk, such as galactosemia and the rare condition hereditary lactase deficiency. It also recommends soy formula "in situations in which a vegetarian diet is preferred."


References

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Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

HealthLink BC. (n.d.). Pap test: British Columbia specific information. https://www.healthlinkbc.ca/medical-tests/hw5266

TED-Ed. (2019, July 9). What is HPV and how can you protect yourself from it? – Emma Bryce. YouTube. https://www.youtube.com/watch?v=KOz-bNhEHhQ&feature=youtu.be

TEDx Talks. (2016, April 14). Endometriosis – The mystery disease of women | Cécile Real | TEDxBinnenhof. YouTube. https://www.youtube.com/watch?v=6HeQ4iEqAUk&feature=youtu.be

TEDx Talks. (2015, July 27). The brain and ovarian hormones | Marwa Azab | TEDxMontrealWomen. YouTube. https://www.youtube.com/watch?v=ryNjSP5VVI8&feature=youtu.be

A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.

Cancer of the cervix of the uterus, usually caused by infection with human papillomavirus (HPV).

The neck of the uterus that protrudes down into the vagina and through which a canal connects the vagina and uterus.

The female reproductive organ in which first an embryo and then a fetus grows and develops until birth.

A sexually transmitted virus that may cause genital warts and cervical cancer.

A medical test in which cells are scraped from the cervix and examined under a microscope in order to detect cancer cells, or precancerous cells, if they are present.

A substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease.

The treatment of disease by the use of chemical substances, especially the treatment of cancer by cytotoxic (cell-killing) and other drugs.

An inflammation of the vagina usually caused by an infection with microbes.

External female reproductive structures, including the clitoris, labia, and vaginal and urethral openings.

The physical activity of sex between two people.

An organisms that is so small it is invisible to the human eye.

Infection of the mouth or vagina that is caused by the yeast Candida.

A measure of the acidity or basicity of aqueous or other liquid solutions. The term translates the values of the concentration of the hydrogen ion in a scale ranging from 0 and 14. In pure water, which is neutral (neither acidic nor alkaline), the concentration of the hydrogen ion corresponds to a pH of 7. A solution with a pH less than 7 is considered acidic a solution with a pH greater than 7 is considered basic, or alkaline.

A disease in which endometrial tissue grows outside the uterus, typically causing pain and bleeding.

The process in which the endometrium of the uterus is shed from the body during the first several days of the menstrual cycle also called monthly period or menses.

The response of the innate immune system that establishes a physical barrier against the spread of infection and repairs tissue damage while causing redness, swelling, and warmth.

An alteration in the nucleotide sequence of the genome of an organism.

A sequence of nucleotides in DNA or RNA that codes for a molecule that has a function.

One of two female reproductive organs that carry eggs from an ovary to the uterus and are the site where fertilization usually takes place.

The female reproductive organ that receives sperm during sexual intercourse and provides a passageway for a baby to leave the mother’s body during birth.

A type of disease, such as Type 1 Diabetes, in which the immune system attacks the body’s own cells as though they were pathogens.

Non-steroidal anti-inflammatory drugs ex. ibuprofen.

An operation to remove a woman's uterus.

The failure to achieve a successful pregnancy after at least one year of regular, unprotected sexual intercourse.


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