Endocrinology Quiz 5 22-30

Fertilization and early development

t. Fertilization must take place within 24 hours after ovulation and most often occurs in the ampulla of the oviduct. Barriers to sperm entry include the remaining cells of the corona radiata, which have traveled with the oocyte, the zona pellucida, and the cell membrane of the oocyte. When a sperm binds with sperm receptors in the zona pellucida, it triggers a calcium-mediated wave of activity that renders the remaining sperm receptors unable to bind. This is the primary mechanism by which polyspermy is prevented. Next, enzymes of the acrosomal cap erode the remaining structures allowing the sperm's chromosomal material to enter the oocyte. Penetration of the oocyte by a sperm triggers the completion of meiosis II, giving rise first to the mature ovum and a second polar body. In the ovum, male and female chromosomal materials are segregated in two pronuclei. These two pronuclei fuse to create one diploid nucleus, at which point the cell is termed a zygote (fertilized egg). The ovum, properly defined is thus a very short-lived cell. However, note that the term ovum is often used in a more general sense to refer to the female gamete at any stage of development. Following these events, the embryo begins to be formed by successive cellular divisions of the zygote. As the embryo is swept towards the uterus, mitotic divisions occur approximately once per day. The cells produced by these mitotic divisions are known as blastomeres. At the 12-16 cell stage, the mass of blastomeres is known as a morula ("raspberry"), and at this stage these cells begin to follow distinct developmental pathways. Further cell divisions lead to the formation of intercellular cavities. The cells (blastomeres) eventually form a hollow ball called a blastocyst, consisting of a cellular wall, the trophoblast, surrounding a fluid-filled cavity, the blastocoele. At one pole of the blastocyst, a cluster of cells, called the inner cell mass (ICM), adheres to the inner wall of the trophoblast. This group of cells will form the embryo proper.

Chorionic villi.

i. The lacunae filled with maternal blood enlarge and fuse into one large pool of maternal blood. Finger-like, branched extensions of trophoblast begin to project into the lacuna from the chorion. These projections, called chorionic villi, are filled with a core of cytotrophoblast cells covered with syncytiotrophoblast. In the early placenta, immature villi extend from the layer surrounding the fetal tissue. If these villi encounter areas rich in nutrients, they proliferate. Initially, proliferation occurs surrounding the entire conceptus, but as the fetus grows, the villi extending towards the decidua capsularis become less viable and less elaborate than those that extend towards the decidua basalis. The basal region of villous elaboration is termed the chorion frondosum, because of its highly branched appearance, and the adluminal region of villous retraction is termed the chorion laeve. (laeve = left, or unpropitious) As the placenta grows larger, the initially spherical chorion retracts (along with the decidua capsularis) into a more discoid shape, leaving the amnion's connective tissue layer largely exposed in the uterine lumen. In other mammals, the shape of the chorion frondosum is interestingly variable, as it is principally determined by the shape of the uterus and where the invading villi locate a blood supply. Napkin ring (zonary) and punctate (cotelydonary) shapes are common. Human placentas may also adopt non-discoid shapes as an adaptation to pathology or unique uterine anatomies. There are three developmentally successive types of chorionic villi: primary chorionic villi (day 11-13 PF) - solid core of cytotrophoblast cells covered with syncytiotrophoblast. secondary chorionic villi (day 16 PF) - a loose core of mesoderm derived from the chorionic plate extends through the center of the cytotrophoblast layer. tertiary chorionic villi (day 22 PF) - capillaries from the developing embryo grow into the mesoderm core. Tertiary villi also contain fibroblasts, some smooth muscle cells, and macrophages called Hofbauer cells. Chorionic villi continue to grow as cytotrophoblast cells keep dividing and contributing to the syncytiotrophoblast. The villi become progressively more branched as pregnancy progresses. The longest villi reach all the way across the lacunae and make direct contact with tissue of the maternal decidua. These are called anchoring villi. Many villi do not directly contact maternal tissue, but instead terminate in the lacunae. These are called free villi. The system of placental villi and maternal lacunae form a maternal-fetal interface that grows in surface area in direct proportion to the size of the developing fetus, and effectively controls the exchange of materials. There are also important placental components with other functions: The extravillous trophoblast are trophoblastic-derived "scout cells" that migrate away from the villous tree, singly or in small clumps, into the maternal portions of the decidua. Because of their position, these cells are often retained in the uterus after the delivery of the placenta. Many functions have been proposed for these cells, but one obviously important one is the seeking out of maternal spiral arteries. Extravillous trophoblast fuse with the wall of maternal arteries (and veins) and take over the function of smooth muscle, promoting the dilation of these vessels and increasing the blood supply to the placenta, while simultaneously forming the interface between maternal endothelia and the syncytiotrophoblast-lined lacunar space. Despite their compromising position, these cells, like all trophoblast-derived cells, do not normally provoke an immune response. Fibrin (also called fibrin-type fibrinoid, to distinguish it from the clotting protein fibrin, which is its major component) is a primarily fibrous material that is found at sites where the syncytiotrophoblast has been disrupted. It provides an alternate mechanism for the maintenance of a blood-placenta barrier, and is important in achieving mechanical stability of the placenta. It is primarily generated in the area of the villous trees, and is a normal component of mature placentas, although excessive accumulation is a sign of pathology. Fibrinoid (or matrix-type fibrinoid) is a material similar in histological appearance to fibrin, but higher in matrix components and lower in fibrous components. It is primarily generated in areas where trophoblastic migration has occurred, and may also be an important component of trophoblast immune-exclusion.

Case 1 Compare and contrast: Two women, both presenting with amenorrhea, come into the clinic. The first patient is a 30yr. old woman in training for a marathon. She reports losing 15 lbs over 6 months. Her menses ceased after 4 months of training. FSH and LH levels are low. The second patient is a 38-year-old woman who has had amenorrhea for the last 6 months, although her periods were normal before that. She has increasingly experienced mood swings and hot flashes. She is negative for cancer or infections and is of normal weight. Her ovaries are small and barely palpable. LH and, particularly, FSH levels are high.

1) For both cases, which other lab tests might you request to help determine the cause of the amenorrhea? Explain your choices. 2) In the first case, what diagnosis do you suspect? What other lab test results would you expect? Would her amenorrhea likely be reversible? Give your reasons for each of your answers. 3) For the second patient, explain how her diagnosis and test results would differ from those of the first patient. Would her amenorrhea likely be reversible? 4) What long-term conditions are these women at elevated risk for? Explain your reasoning Case 1: Primary and secondary hypogonadism in females 1. Though both patients would be expected to have low estradiol levels, this is the only similarity they share. For the first patient, since the LH and FSH levels are low, low estradiol would be consistent and points to a hypothalamic cause for her disease. For the second patient, despite elevated FSH levels, the atrophied gonads suggest that these glands do not have adequate follicular reserve to produce estradiol, pointing to a primary ovarian issue. For both patients, tests could include pregnancy, LH, FSH, estradiol, TSH, and prolactin. LH, FSH, and estradiol are obvious choices given the obvious involvement of the reproductive axis. Prolactin decreases GnRH production, and thus must be considered in amenorrhea cases. Thyroid dysfunction (both hyper- and hypo-) can produce amenorrhea - one possible mechanism might be that if the patient were hypothyroid, high TRH would result through feedback, stimulating prolactin secretion and therefore decreasing GnRH, though the exact mechanism is not elucidated at this time. 2. First Patient: This case is an example of hypothalamic amenorrhea, a form of secondary hypogonadism since the ovaries are capable of normal function. The patient is an athlete, and the combination of rigorous training and rapid weight loss has led to cessation of menstruation. Other situations that might lead to a similar outcome: excessive dieting, malnutrition, systemic illness, emotional trauma, etc. An individual has a different 'set point' at which perceived or actual stress can result in hypothalamic suppression. These factors can suppress GnRH production from the hypothalamus leading to decreased secretion of gonadotropins and sex steroid hormones. This particular set of circumstances is a component of what is referred to as "female athlete triad", i.e. anorexia/amenorrhea/osteoporosis. Lab tests: Pregnancy Test Negative FSH very low LH very low Estradiol low TSH Normal Prolactin Normal What else should be considered? A type of tumor that might correlate to low sex steroid levels, e.g. prolactinoma or another space-filling pituitary tumor inhibiting gonadotrope function, should be ruled out. The time of development of such a tumor in this case would then just coincidentally correspond to the training period. The mechanism of the GnRH suppression in hypothalamic amenorrhea is not clear, although elevated cortisol levels are often noted. Low leptin levels due to weight loss also may be involved. The development of amenorrhea under periods of nutritional or environmental or other extreme stress may perhaps be considered, evolutionarily, as a means of avoiding pregnancy under circumstances where the mother would be unable to cope with the fetal needs. This form of amenorrhea is typically reversible once the stressor has been removed, as long as the hypothalamus and other components of the reproductive endocrine system are functionally competent (as in the present case). 3. Second Patient: The main endocrine finding differentiating this case from the previous case is that LH and especially FSH is high rather than low. Therefore this is a case of spontaneous primary ovarian insufficiency - a type of primary (rather than secondary) hypogonadism. When ovarian failure occurs before the age of 40, it is considered premature ovarian failure (POF; commonly referred to as premature menopause). In its fully developed form, amenorrhea due to POF may be irreversible. However, some patients may have irregular periods and intermittently be able to ovulate and become pregnant, assuming that sufficient viable ova remain. Stated otherwise, there is a 5% lifetime risk of pregnancy in women who have POF. Over the age of 40, complete amenorrhea for at least 1 year with high FSH and low estradiol would be considered menopause. Either POF or menopause is commonly associated with symptoms such as hot flashes and mood swings, which may be due to fluctuating hormone levels. Lab tests: Pregnancy Test Negative FSH very high LH high Estradiol low TSH Normal Prolactin Normal Most women who have POF have had normal puberty and regular menstrual cycles prior to the amenorrhea. As the ovaries begin to lose function, their ability to produce estradiol and inhibin is reduced. LH and FSH levels are both high due to loss of estrogen feedback. However, FSH levels are even higher due to the loss of inhibin, which specifically inhibits FSH production. Therefore high values for FSH in women are a hallmark of primary hypogonadism, including menopause. 4. Both women, as long as the low estradiol levels persist, are at risk for osteoporosis and coronary heart disease due to loss of protective effects of estrogen. Estrogen protects against bone loss by increasing osteoprotegerin levels. In women with chronic hypoestrogenemia, osteoporosis may occur at an earlier age than the normal population, given the earlier onset of the estrogen deficiency. There is conflicting evidence as to whether estrogen has a protective effect in women against atherosclerosis and systemic vascular disease in the post-menopausal period; these effects remain under investigation. However, hormonal supplementation in a woman who has undergone with ovarian dose hormones (estrogen and cyclic progesterone) until the average age of menopause should be strongly considered, especially if remote from the average age of menopause in the United States (51 years).

Case 2 A couple presents for evaluation and treatment of infertility. The wife comments that her husband is "in excellent shape" and works out in the gym several times a week. Her husband claims that in the past he has used anabolic steroids (which are testosterone derivatives) for bodybuilding but has not used them in the past few months. He notes that others have observed increased aggressiveness in him. His sperm count is found to be low, with decreased motility and abnormal morphology. His testes are mildly atrophied. His breasts are unusually well developed (gynecomastia) and he has acne.

1) What lab tests might be appropriate for the patient to determine the cause of his sperm abnormalities? 2) Given his history with anabolic steroids, how could that explain his signs and symptoms? 3) For low sperm count, what differential diagnoses would need to be explored with this patient? 4) For restoring endogenous testosterone production following cessation of anabolic steroid use, hCG is often administered. What is the reasoning behind this approach? Case 2: Hypogonadism secondary to anabolic steroid use 1. Appropriate lab tests: Testosterone: Low Testosterone derivatives: High *some newer formulations of anabolic steroids are not detectable on clinical assays LH and FSH: Low TSH: Normal These lab tests results suggest that either the patient has recently used, or is still using anabolic steroids, causing secondary hypogonadism. The high levels of exogenous testosterone derivatives exert negative feedback on the reproductive axis, resulting in low LH and FSH, and low endogenous testosterone production. In extreme cases due to complete hypothalamic suppression from exogenous T, the gonads are extremely atrophied with no functional spermatogenesis occurring. TSH was tested because abnormal thyroid function can be a cause of infertility. 2. Because of the low levels of LH and FSH, his testes have atrophied. Gonadotropins are required for normal spermatogenesis. Abnormal breast development is due to peripheral conversion of anabolic steroids to estrogens, which stimulate breast tissue and result in growth. Anabolic steroids commonly affect mood, producing aggressiveness. Acne is due to anabolic steroid stimulation of the sebaceous glands. 3. Differential diagnosis: Karyotype analysis was undertaken to rule out genetic conditions such as Klinefelter's syndrome (XXY), which could result in deficient sperm production and breast growth (gynecomastia). Other forms of hypogonadism would need to be ruled out although they would not necessarily be expected to cause gynecomastia. 4. Recovery from anabolic steroid use typically takes three to four months but may take as long as a year. While reproductive function for some men recovers spontaneously within that period of time, in other cases it is advisable to intervene endocrinologically. Although testosterone is required for spermatogenesis, it is not sufficient to restore sperm production, which requires gonadotropinsto stimulate Sertoli (FSH) and Leydig (LH) cell function. For example, T levels within the seminiferous tubule is up to 100x higher than in circulation but must be produced in situ from functional Leydig cells. Administration of FSH and LH may be helpful in recovering gonadal function, since both LH and FSH are required for spermatogenesis. However, FSH appears to be necessary to initiate but not sustain spermatogenesis on an ongoing basis; consequently LH may be sufficient on its own to restore sperm production. In practice, after a male patient has stopped taking anabolic steroids, treatment with hCG, which is functionally indistinguishable from LH, is preferentially administered as a treatment for secondary hypogonadism. Compared with LH, hCG has a much longer half-life and is therefore more suitable for a 3x-weekly injection protocol. hCG stimulates testicular growth, testosterone production and hence spermatogenesis. If hCG alone does not restore function sufficiently, recombinant FSH can be added, either alone or in combination with recombinant LH. Theoretically, pulsatile GnRH may be an option, however, this is an expensive treatment and not available in the U.S. In contrast, hCG is less expensive than the other gonadotropins and is readily available. It is notable that hCG, in association with anabolic steroid use, is on the list of banned substances in many competitive sports. Men who have been taking anabolic steroids for years may never have complete testicular recovery.

Case 4 A 25-year-old woman comes to the clinic complaining of acne, facial hair growth, and irregular periods. She is 4'10" but reports that as a child, she was always one of the tallest in her class. Both of her parents are of normal height. She also notes that she had an early onset of puberty with growth of axillary and pubic hair at about 6 years of age. Examination shows she has moderate to severe hirsutism on her face and chin and mild clitoromegaly. Tests showed high serum androgens and low total cortisol.

1) What might explain her condition? 2) Can her growth history be explained by this condition? If so, how? 3) How might you treat this patient? Case 4: Congenital adrenal hyperplasia (CAH) - secondary hyperandrogenism 1. This patient shows signs of virilization and high androgen levels, signs of reproductive dysfunction. However, the low cortisol level raises the likelihood that in this patient, adrenal function is also compromised in some way. This patient has congenital adrenal hyperplasia, an inheritable condition due to 21-hydroxylase deficiency. This enzyme is required to make cortisol and aldosterone, while androgen synthesis is unaffected. Due to feedback, the low cortisol levels cause ACTH levels to be high, thus stimulating the zona reticularis to produce more androgens. The course and manifestations of this disorder vary, depending upon the relative inactivity of 21-hydroxylase. In this patient, presumably the deficiency does not give rise to severe aldosterone deficiency, which would lead to more serious consequences. This patient's early puberty is due to the high androgen levels. Acne, hirsutism, and clitoromegaly are signs of excess androgen production. The disruption of the normal reproductive axis hormonal milieu by the high levels of androgens leads to irregular periods. 2. High androgen levels at an early age bring on not only early puberty but an early growth spurt, so the patient was tall as a child. However, the high androgen levels also induced the epiphyseal plates to close inappropriately early, so that her final height is short compared with parental height expectations. X-rays would show advanced bone age relative to chronological age. 3. Since this patient appears to have sufficient aldosterone activity to maintain reasonably good health, treatment is with corticosteroids such as dexamethasone. Corticosteroids would reduce the ACTH levels through feedback, thereby reducing adrenal androgen production. The treatment regimen would have to be continued through life and may need to be increased during times of stress, e.g. illness or surgery.

Case 3 A 20-year-old male was referred because of failure to enter puberty. Physical exam revealed a 6'2" young man with sparse axillary hair, no beard or pubic hair, and much "baby" fat. His arm span was 6'4". His penis was 1.5cm long and his scrotum was small, non-rugated, and contained about 1 cm soft tissue masses.

1) What tests would you perform to diagnose his condition and why? 2) You also discover that the patient is unable to distinguish the smells of coffee and peppermint, a condition that can be associated with failure of developmental migration of cells to the olfactory placode and other brain locations. Which of your diagnostic tests would be consistent with this observation? 3) Why is the patient's arm span so long? 4) What treatment might be appropriate for this patient? Case 3: Kallmann Syndrome (hypogonadotrophic hypogonadism) 1. Diagnostic tests: LH, FSH: Low Testosterone: very low Karyotype analysis: (46, XY) This case is a form of hypogonadotrophic hypogonadism, i.e. inadequate output of testosterone with low levels of the gonadotrophs (LH and FSH). Pulsatile administration of GnRH produces a normal rise in LH and FSH levels. Therefore, the condition originates in the hypothalamus. Low testosterone levels influence behavior (e.g. less aggressive than normal adolescent males, low libido), puberty and development of secondary sexual characteristics does not occur, and the genitalia are prepubertal in appearance. Females with this condition usually exhibit little breast development or may not menstruate at puberty. 2. This patient has typical features of Kallmann syndrome, a rare genetic disorder resulting in a form of hypogonadotropic hypogonadism with anosmia. Karotype analysis is indicated since a number of genetic conditions give rise to abnormal hormonal patterns. His karyotype is normal. However Kallman syndrome is due to an abnormality in migration of the GnRH neurons in the anterior forebrain during fetal development specifically (which migrate with the olfactory neurons) and as such result in inadequate development of tissues involved in both GnRH-production and olfactory sensory functions. The genetic defect is in cell adhesion proteins which are required for the normal migration of the GNRH secreting cells in the fetus from their site of origin in the olfactory plate. As a result, patients have little or no gonadotropins and therefore very low levels of sex steroids as well as an impaired sense of smell (anosmia). 3. These patients may ultimately be taller than they would be without the hormonal abnormality. During normal adolescence, long bone growth is driven predominantly by GH but receives a boost from rising sex steroids (growth spurt). This growth is ultimately terminated by high sex steroids with closure of the epiphyseal plates. In the absence of rising sex hormones, the pubertal growth spurt does not occur, although long bone growth may continue at a steadier rate (e.g. prepubertal) and for a longer period of time. This results in a so-called "eunichoidal habitus" in which the slow but extended long bone growth results in arms and legs that are disproportionately long compared to the trunk. It is not clear what ultimately limits long bone growth in the absence of the normal pubertal influences, yet unlimited growth in humans clearly does not occur. One potential long term consequence of absence of the sex steroid, as in previous cases, is osteoporosis. 4. Treatment with testosterone may restore secondary sexual characteristics and libido as well as help prevent osteoporosis but cannot by itself restore fertility or change past bone growth patterns. Treatment with pulsatile GnRH or with hCG or gonadotropins is indicated in some reports to promote testicular development and possibly even fertility

2. Contrast these patterns with intermediate clinical outcomes that arise in primary and secondary differences of sex development.

1. Sex chromosome DSD (See Molecules to Cells: Session 11) 45, X (Turner syndrome) 47, XXY (Klinefelter syndrome) 2. 46, XY DSD Disorders of testicular development (gonadal dysgenesis) Disorders of androgen synthesis or response (androgen biosynthesis defect or insensitivity, e.g. androgen insensitivity syndrome) 3. 46, XX DSD Disorders of ovarian development (gonadal dysgenesis, ovotesticular DSD, testicular DSD) Androgen excess (fetal and maternal, e.g. congenital adrenal hyperplasia) Primary DSD refers to the case when the chromosomal and phenotypic sex of the gonad are discordant: in other words, XX individuals with testes and XY individuals with ovaries. Secondary DSD occurs when the chromosomal and external phenotypic sex are discordant even though the chromosomal and gonadal sex are concordant. An example of this is 46, XY DSD, Androgen Insensitivity Syndrome, where the XY patients develop testes internally but exhibit external female development. In many cases of 46, XY DSD and 46, XX DSD, the affected individuals harbor point mutations, deletions, or translocations that affect the sex-determining region Y (SRY) gene. In particular, the SRY locus is especially susceptible to translocation because of its proximity to the pseudoautosomal region. This region of homology between the X and Y chromosomes allows meiotic recombination between the chromosomes when they pair during paternal meiosis. At birth, patients who are SRY - XY (46, XY DSD) appear female, however because two X chromosomes are required for certain loci related to ovarian maintenance and female fertility, they do not develop secondary sexual characteristics at puberty, do not menstruate, and have streak gonads that are incapable of ovulation or estrogen secretion. In contrast, SRY+ XX individuals (46, XX DSD) with an SRY translocation to one of their X chromosomes develop as males, but because they are missing other critical genes from the Y chromosome, they are unable to promote normal sperm development.

F. The decidua.

After implantation, the endometrium becomes called the decidua graviditatis or simply the decidua. The portion of the decidua immediately beneath the site of implantation, which supports the chorion frondosum, is termed decidua basalis. Initially, the conceptus is buried within the mucosal wall of the uterus, but as it grows, the opposite walls of the uterus come in contact, fuse (obliterating the uterine lumen), and the fluid-filled amnionic sac becomes the major space separating opposing uterine walls. The gross arrangement of placenta relative to uterus has medical significance. Placenta previa results when the placenta forms close to or overlying the cervix. Mechanically, such a geometry impedes the normal order of delivery; fetus followed by placenta. Contraction of spiral arteries, a normal occurrence that prevents maternal blood loss after fetal delivery, may in this case deprive the fetus of oxygen prior to delivery. Alternately, hemorrhage of these vessels may endanger the life of the mother. Thus, these babies are prime candidates for delivery by Caesarean section

1. List as many adult reproductive system structures as you can think of that are homologous between male and female pattern development. 2. Where are basement membranes present in the fetal ovary and testis? 3. Describe some common differences in reproductive system development that might be discovered as an incidental finding in an adult.

Also, recall that an anterior migration of the urethral opening occurs as part of male-pattern development. Incomplete migration of the urethra to the penile glans is referred to as hypospadias. Standards for the clinical management of intersex conditions have changed dramatically in recent history. Historically, these have had as much to do with the doctors' (or parents') perceptions of society's norms as with patients' benefit, providing an interesting and important challenge to the traditional Hippocratic oath of "do no harm."

Trace derivatives of mesonephric and paramesonephric duct in male and female.

Although it is considered good practice to shun eponymous names for body structures wherever possible, it is nevertheless still important to recognize the historical names Wolffian duct (for mesonephric duct), and Müllerian duct (for paramesonephric duct). The development of the mesonephric duct was described for renal development. Recall that three regions, pronephros, mesonephros and metanephros represent distinct areas of kidney development, from which only the metanephros is retained. The mesonephric duct, in the region of the mesonephros, because of its location directly beneath the genital ridge, is co-opted in function to become the tubules of the male reproductive system. The cranial end of the mesonephric duct migrates together with the testis to form the rete testis and epididymis, whereas the caudal end retains its connection with the cloaca in the region caudal to the allantois, becoming the future ejaculatory ducts. The pattern of female development, on the other hand, discards the mesonephric duct in favor of a new structure, the paramesonephric duct, formed by tubular invagination from the peritoneal cavity. The degenerate mesonephric duct is occasionally recognized in its adult position within the body of the broad ligament, as structures termed the epoophoron and paraoophoron, which are not clinically relevant unless they should develop into a cyst, or originate a primary cancer (adenoma). The proximal portion of the mesonephric duct remains in the vicinity of the vaginal wall, occasionally presenting as a Gartner's duct cyst. The paramesonephric duct also forms in the male pattern of development, but subsequently degenerates. The degenerate structure migrates with the testis and is sometimes recognized as a structure called the appendix testis, present in the adventitial portion of the testicular wall. Again, this structure may (very rarely) develop pathologies. Normal female-pattern development of the paramesonephric duct sees the cranial end developing into fallopian tubes, and the caudal end developing into the uterus and vaginal fornix. It is important to note that the paramesonephric duct is a paired structure, therefore the uterus also initially forms as a paired structure. Because humans are prone to single, prolonged gestations, the two uteri usually grow together to form one large cavity late in fetal development. If they fail to merge, the resulting anatomy is termed (from least severe to most): arcuate uterus (abnormal shape), septate uterus (retained midline septum), bicornuate uterus (lit. "two horns"), didelphic uterus (including duplication of cervix and/or vagina). Though not uncommon and not otherwise problematic, these variant anatomies require increasing amounts of medical attention during pregnancy and childbirth. The vagina has a dual origin, the distal part resulting from caudal paramesonephric duct, but the proximal part being an expansion of the caudal urogenital sinus. Because the vaginal lumen develops separately and at a later time from either the ureter or uterine lumens, a protective membrane known as the hymen remains to block the connection of the vaginal tract to the outside world during birth and early childhood. It is important to realize that many people today still hold fallacies about the medical or social importance of the hymen. It is rarely of any clinical significance except in the rare case that it remains sufficiently imperforate to block the first menstrual flow at puberty.

Milk production.

Alveolar cells of the active mammary gland have secretory cell characteristics, including abundant RER, Golgi complexes, and secretory vesicles. Fat globules are also seen within the cells. The alveolar cells make most of the proteins, lipids, and carbohydrates found in milk. Other compounds such as vitamins, salts, immunoglobulins, and hormones are obtained from the blood. Immunoglobulins (IgA in particular) are synthesized by plasma cells in the connective tissue surrounding the mammary gland and taken up at the alveolar cells basal surface by receptor-mediated endocytosis. During milk secretion, proteins and carbohydrates are released into the alveolar lumens by merocrine secretion (exocytosis). The major milk fats are secreted by apocrine secretion: as droplets surrounded by a coat of cell membrane. Milk production is under the control of the hormones prolactin and oxytocin. During pregnancy, estrogens and progesterone suppress prolactin. After birth, estrogen and progesterone levels drop and the resulting increase in prolactin stimulates milk production. The act of suckling sends sensory impulses to the hypothalamus that causes the release of prolactin from the adenohypophysis and oxytocin from the neurohypophysis. Oxytocin stimulates the myoepithelial cells at the base of the alveoli to contract and eject the milk. In the absence of suckling, milk secretion ceases and the mammary glands begin to regress. Breastfeeding is known to confer significant protective advantage to the fetus. Some of this advantage can be explained by the stimulation of the infant's immune system caused by secreted antibodies. Other observations are harder to explain. Epidemiological studies suggest that breastfeeding confers protective advantage to the mom against heart disease, ovarian cancers, and several other diseases. Also, exclusive breastfeeding for the first 6 months of life confers more advantage for the infant than does breastfeeding supplemented by other foods. From these facts, one should appreciate that many details of the production and components of colostrum and milk are both important and poorly understood!

Placental hormones

As an endocrine organ, the placenta produces: -steroid hormones - estrogen and progesterone, which help to maintain the pregnancy. By 8 weeks PF the placenta has supplanted the corpus luteum as the major source of these hormones. Interestingly, the estrogen precursors are produced by the fetal adrenal cortex and transported to the syncytiotrophoblast to be converted to estrogen. -peptide hormones - hCG maintains the corpus luteum during early pregnancy. Human chorionic somatomammotropin (hCS) promotes mammary duct proliferation. A variety of growth factors (IGFs, EGF, FGF, etc.) promote placental growth. Relaxin softens ligaments in preparation for parturition. -prostaglandins - involved in the onset of labor. Most of the placental hormones are made by syncytiotrophoblast. Some, such as EGF and IGF, are made by the cytotrophoblast and the decidual cells make some, such as relaxin.

. Trophoblastic lacunae.

As the trophoblast grows and extends into the endometrium, vacuoles (lacunae) form within it. The erosion of the endometrial spiral arteries by the trophoblast causes maternal blood to empty into the trophoblastic lacunar network and establishes a primitive uteroplacental circulation. Eroded uterine glands also empty their contents into the lacunae, thereby providing the embryo with additional nutrients.

1. Recall that an ambipotential embryonic structure precedes establishment of typical reproductive system organization during development.

Human reproductive development begins with an ambipotential embryonic stage, as introduced by Dr. Toth in session 19 of this module. Occasionally, the presence of variants in genes related to reproductive development influences typical sex development in humans. In this session, we will discuss some of these outcomes and their causes. Differences of sex development: see Case Presentation 41 in your text Biological sex in humans can be broken down into the following characteristic components: Genetic or chromosomal sex Gonadal sex Anatomical sex These three elements are linked during typical development. That is, genetic sex promotes development of gonads, and the gonads produce sex hormones that influence further anatomical development. Sex is usually assigned as male or female at birth based on the anatomical presentation of external genitalia. However, sex actually exists on a spectrum, and in cases where the three characteristics above are not all either male or female, differences of sex development (DSD) have occurred. There are numerous causes of DSD. These causes of DSD can be classified as follows, and examples are listed below each category.

List homologous tissues in male and female and explain their differential development Describe the origin of germ cells and differences in their development

In ovarian development, a second wave of epithelial proliferation produces secondary (or cortical) sex cords. Follicular cells originate from the locally derived cells of these cords. Each (primary) oocyte becomes encapsulated together with its follicular cells and a basement membrane. Oocytes are distributed underneath the epithelium of the genital ridge. (This epithelium is the future ovarian epithelium, sometimes termed "germinal epithelium" because of historical confusion surrounding its function.) As the fetal ovary develops, the germinal ridge extends into the peritoneal cavity and adopts the anatomically separated form of the adult ovary. The remaining connection to mesodermal tissue forms into the broad, ovarian and suspensory ligaments. These connections provide the vascular and nervous supply, and vascular and lymphatic drainages of the ovary.

1. Illustrate how historical human migration patterns have contributed to genetic variation observed in modern populations. 2. Differentiate between population subgroups defined by racial categories or geographic ancestry in terms of genetic variation. 3. Use the principles of population genetics (e.g. founder effect, HardyWeinberg equilibrium, selection pressure) to evaluate genetic risk and predict frequencies of alleles and genotypes in a given population. 4. Compare and contrast the assisted reproduction approaches available for LGBT patients in terms of clinical outcomes, costs, and legal implications. Assess healthcare barriers that may limit access by LGBT patients. 5. Evaluate the significance of testing for the presence of disease alleles on patients from non-majority ancestral backgrounds and on LGBT couples in a preconception setting. Appraise the potential for false negative results in this context, particularly with respect to donor genetic risk assessment.

In preparation for this discussion, please revisit the background content from Genomic Medicine Session 9. You may choose to return to your pre-class materials from Genomic Medicine in case you took notes on them, and be sure to review in detail as this material is on the open book pre-discussion quiz. In Genomic Medicine, we applied the understanding of population genetics to cases highlighting genetic testing complexities including variants of unknown significance, secondary findings, and duty-to-recontact through the lens of the ancestral background of the patients. In these new Endocrinology / Reproduction cases, we will instead be focusing on how understanding of population genetics informs our analysis of genetic risk when pursuing assisted reproduction, particularly through the lens of family building strategies for LGBT patients. Genome-Wide Testing in the Preconception and Prenatal Settings Preconception and prenatal carrier screening is rapidly moving in the direction of genome-wide testing strategies. Some of these tests are microarray-based, much like the direct-to-consumer testing options we learned about in Emerging Approaches in Genomic Medicine (Genomic Medicine Session 8), and are therefore limited in their ability to detect only the alleles that are represented on the microarray itself. There are also a few approaches that fully sequence a collection of genes thought to be important based primarily on family history and ancestry of the biological parents. In class, we will discuss how these strategies can be used to help same-sex couples grow their families, particularly in cases where the details of a donor's genetic risk profile may not be fully defined.

Relate disorders of fetal genital development to normal tissue development.

In the fetal testes, sex cords elongate into the tubular structures of the seminiferous epithelium. The germ cells (spermatogonia) come to be surrounded by Sertoli cells, formed from the resident epithelial cells in a manner analogous to the encapsulation of the ovarian follicular cells. Many stromal cells differentiate into testosterone-producing Leydig cells, and under their influence, the Sertoli cells produce anti-Mullerian hormone (AMH). Unlike the fetal ovary, the fetal testes remain retroperitoneal structures. A ligament termed the gubernaculum connects each testis with the pelvic floor. At approximately the 26th week of development, the gubernaculum guides the testes through the pelvic floor via the inguinal canal. Peritoneal epithelium is pulled along. As external structures develop, the testes together with their surrounding peritoneal epithelia and connective tissue become encased in the scrotal sac. The surrounding epithelium loses its connection with the peritoneal cavity, thus creating a unique body cavity within the scrotal sac. The now disconnected portion of peritoneal epithelium becomes the visceral and parietal layers of the tunica vaginalis. The cavity between them allows the testes some freedom of movement in the adult. For reasons of differential growth, the maximal freedom of movement for the testicles usually occurs at puberty. The only common "emergency" in andrology is testicular torsion (or tortion), which describes the condition in which the testes rotate 180 degrees or more within the scrotal sac. Such a rotation compromises the vasculature of the spermatic cord, and will result in testicular necrosis if not surgically corrected. (Less commonly, an "extravaginal" torsion of the entire scrotal sac may also occur.) Failure of one or both testes to descend results in cryptorchidism. Typically, surgery is performed to either relocate or remove the retained testis, since a retained testis usually does not produce viable sperm, and leads to an increased risk for adult cancers.

Active mammary gland. During pregnancy, the ducts continue to branch under the influence of estrogen and their terminal part develops a lumen. The alveolar cells increase in size under the influence of progesterone and begin to secrete colostrum, the premilk substance that is higher in protein and antibodies and lower in fat and carbohydrates. Milk production begins several days after parturition.

Inactive mammary gland. In the inactive mammary gland, the chief component is the duct system. It is lined with a single layer of cuboidal (in the smallest ducts) or columnar cells (in the larger ducts), transitioning to a double layer of cuboidal cells in the lactiferous sinus and stratified squamous epithelium in thterminal portion of the lactiferous duct. In the female after puberty the ducts branch and end in spherical groups of cells, the alveoli, which remain small and inactive until pregnancy. The cells of the alveoli resemble those of the ducts until hormonal changes during pregnancy induce secretory differentiation. The processes of a discontinuous layer of myoepithelial cells form a meshwork between the surface epithelial cells and basal lamina of ductal and alveolar areas of the gland.

24./26. Lecture/Discussion: Uterus and Organs of Pregnancy

Lab At the end of the section, the student will be able to... 1.Explain the development of the placenta from extraembryonic and maternal tissues. 2. Describe the changes in the decidua during pregnancy and parturition. 3. Describe the morphology and function of the mammary gland during the stages of development from preadolescence through pregnancy, lactation, and menopause. Lecture At the end of the section, the student will be able to... 1. Describe the sequence of events that occur in the oocyte following fertilization, continuing to implantation of the conceptus. 2. Describe the events that take place in the endometrium and the blastocyst during implantation. 3. Explain the early appearance of the embryo, and identify the embryonic origin of body tissues. 4. Describe the endocrine functions of the placenta and the targets of these hormones (at the level presented in this course). 5. Identify major diseases of obstetrics and gynecology as they relate to tissue morphology (at the level presented in this course).

1. What protects the trophoblast from destruction by maternal natural killer cells? 2. In which fetal organ do B lymphocytes develop early in gestation? 3. Why do RhD blood group differences, but not ABO blood group differences, between the mother and father lead to hemolytic disease of the newborn? 4. What is the hygiene hypothesis?

Qs

3. Connect the basis for differences of sex development and the consequences for affected patients.

Sex determination, in particular male sex determination or testis determination, is very sensitive to gene dosage. For example, some XY individuals who are heterozygous for mutations in the autosomal SOX9, WT1 or SF1 genes develop as females. In these cases, a single dose of the SOX9, WT1 or SF1 gene is insufficient for normal testis development, and these genes are, therefore, said to be haploinsufficient. The key to appropriate care of individuals with DSDs is to create a healthcare environment that is welcoming and accepting, to provide support and resources for the families as they face complex questions, and to delay elective hormonal and surgical interventions until the patient can participate in decisionmaking about their body. It is also important to understand the specific etiology of your patient's DSD, as some forms of DSD do carry increased risk of reproductive cancers or other outcomes that may require screening and/or intervention. Simply put, the principles of patient-centered care are of critical importance always, but especially for individuals born with DSDs.

Blood Circulation in the mature placenta

Since the placenta is derived from two separate organisms, there are two independent blood circulations. First, maternal blood is brought into the lacuna by 80-100 spiral decidual arteries in the basal plate. This maternal blood is pushed into the intervillous spaces with each maternal heartbeat and it is drained passively between heartbeats by decidual veins. Second, by 21 days PF the fetal heart begins to pump oxygenated blood through the fetus and deoxygenated blood into the placenta. Fetal blood enters the placenta through two umbilical arteries that branch to form a capillary network in the tertiary chorionic villi. Fetal blood, freshly oxygenated through diffusion from the maternal blood, passes back to the fetus through a single umbilical vein. The blood supply of the mother and the fetus do not directly contact each other. Exchange of materials takes place across the placental barrier, which is made up of fetal tissues. At its thinnest point, this barrier (in humans) is composed of: -syncytiotrophoblast -cytotrophoblast (if present) -basal lamina of the trophoblast -basal lamina of the endothelial cell -endothelial cell of the villus capillary Exchange of nutrients, gases and waste products takes place across the placental barrier. Carbon dioxide, hormones and waste products pass from fetal blood to maternal blood while oxygen, metabolites, electrolytes, vitamins, hormones and antibodies pass from maternal blood to fetal blood. Gases, fatty acids and electrolytes pass through the placental barrier by diffusion. Larger molecules such as amino acids and antibodies are actively transported. Many potentially dangerous compounds such as alcohol, nicotine, viruses, and heavy metals may cross the placental barrier and therefore should be avoided during pregnancy. These substances are termed teratogenic, meaning they have the capability to induce malformations in the embryo. Although the risk of teratogenesis is always present, for most organ systems it peaks between 3 and 8 weeks PF, corresponding to the time of minimal cell numbers in the embryo, and the loss of pluripotency in those cells. At parturition, several events occur in quick succession. Following expulsion of the newborn, the placental tissue is expelled. Trophoblast cells clamp down on the spiral arteries, reducing blood flow to the lacunar space, and the placental tissue separates grossly at the interface of basal plate and decidua basalis. Interestingly, extravillous trophoblast may be retained.

Amnion and Chorion. By day 14 PF, two membranes form around the developing embryo:

The amnion encloses the amniotic cavity, which contains the fetus. Fluid from the amniotic cavity is often sampled around 16 weeks of pregnancy in a process called amniocentesis. Fetal cells in the amniotic fluid are cultured and tested for various genetic defects. The chorion is the outer membrane that faces the decidua and is formed by the trophoblast in conjunction with extra-embryonic mesoderm. The portion of the chorion adjacent to the decidua basalis forms the fetal side of the placenta. Between 10-12 weeks PF the chorion and amnion fuse and form the fetal membranes, also called the chorionic plate.

Mammary Gland

The mammary glands are modified sweat glands that supply the newborn with milk. In the female at puberty and during the menstrual cycle, the breasts undergo development and changes under the influence of estrogens and progesterone. During pregnancy, further development takes place and following pregnancy milk is secreted under the control of other hormones. At menopause, the mammary gland involutes and is replaced with fat and connective tissue. Nipple and areola. The mammary papilla, or nipple, is an elevated area of modified highly pigmented epidermis from which the mammary or lactiferous ducts open. The areola is also modified pigmented epidermis that surrounds the nipple. The areola contains prominent, hairless sebaceous glands and sweat glands. Lobes and lobules. Each breast consists of a single mammary gland embedded in a connective tissue stroma interspersed with adipose tissue. Each mammary gland is made up of fifteen to twenty lobes of branched tubuloalveolar glands. Each lobe is divided into smaller lobules. Lobules consist of a group of alveoli that become most prominent during pregnancy and lactation. Lactiferous ducts connect each lobe of the mammary gland with the nipple. Just beneath the areola, each lactiferous duct is capable of some degree of storage, presumably for keeping milk "at the ready" to aid in conditioning the infant to breastfeed. At their distal end, the lactiferous ducts branch to form the lobes and lobules of the breast. Secretory acini form from the terminal branches within lobules only during pregnancy. Intralobular and interlobular connective tissue also has different organization. Intralobular connective tissue is formed primarily of collagen and reticular fibers, and is highly cellular with many specialized stromal cells present, especially plasma cells, lymphocytes and macrophages. Interlobular connective tissue is mostly fibrous, containing predominantly collagen and elastin. Cells contributing to the glandular epithelium include ductal cells, secretory alveolar cells, and myoepithelial cells. Their relative abundance changes during life, as discussed below.

The placenta is unique in that it is a composite organ that forms from both the maternal endometrium and the fetal trophoblast. It allows communication and exchange of materials between the developing embryo and the mother. These materials include gasses, nutrients, hormones, and antibodies, but not blood

The mature placenta consists of the amnionic sac, which contains amnionic fluid and surrounds the fetus, and a chorion layer, which initially surrounds the embryo, but later is limited to a thick discoid shape contacting only the decidua basalis. Maternal cells from the decidua basalis form the compact layer known as the basal plate and mesh with the chorion. This basal plate is the maternal component of the placenta. The fetal component of the placenta is the chorion frondosum, which is bathed in the maternal blood.

E. External Genitalia The external genitalia develop in both sexes from homologous structures. In the six week fetus, these structures are recognizable as the genital tubercle, anteriorly, and the urogenital sinus, posteriorly. Differentiation to a male or female phenotype begins around the seventh week of development.

Vulva (L., a wrapper or covering) is the term for the external genitalia of the female, including the labia majora, labia minora, clitoris, and vestibule of the vagina. Labia majora (L. the larger lips) are paired outer folds of relatively adipose epidermal tissue. Labia minora (L. the smaller lips) are the hairless, inner epidermal folds. The clitoris is a body of erectile tissue which becomes engorged during sexual stimulation. It consists of an external portion (glans) and larger, paired internal roots (crura (pl.), crus (sing.)). Physicians should be aware that some cultures continue to practice "female genital mutilation," the reduction or excision of one or more of these structures. This procedure which is shunned by health organizations, has no health benefits, and is only rarely performed by professional surgeons, may be a source of lasting physical pain and emotional trauma. See the World Health Organization factsheet on female genital mutilation for a more thorough discussion: The vestibule of the vagina contains numerous minor glands. The volume of glandular tissue varies between individuals, and may sometimes be absent without obvious consequences. Bartholin's glands are paired mucous glands which open to either side of the vaginal orifice and are homologous to the bulbourethral glands of the male in that they secrete during sexual arousal. The paraurethral glands (Skene's glands, "female prostate") form a network of tissue in the space anterior to the vaginal wall, surrounding and opening to the urethra. Though they are not known to serve any function, and indeed are sometimes absent, they have been shown to stain for PSA (prostate specific antigen) which suggests homology with the male prostate. The homologies are important because although full "male" or "female" differentiation is the norm, a pattern of development intermediate along the continuum is also commonly seen - in by some estimates as much as 1/100 births - resulting in the condition known as intersex. The following structures arise from common tissue, and may be present to varying degrees in an intersex individual:

5. Recognize the effects of the microbiome, microbial infections, and breast milk on maturation of the immune system and development of allergies and autoimmune diseases. Maternal-derived passive autoimmunity

[15] Since IgG antibodies can cross the placenta, pathogenic antibodies are sometimes transferred from mother to fetus, leading to disease manifestations in the fetus and newborn. These include autoimmune diseases caused by antibodies, as outlined in the table. In most cases, disease symptoms disappear as the maternal antibodies are catabolized, but plasmapheresis is often used to accelerate the clearance of maternal autoantibodies, to prevent tissue damage. [16] But some autoantibodies can cause severe organ damage and even death, specifically autoantibodies to the Ro and La ribonucleoproteins, which are expressed in cardiac conducting tissue. These autoantibodies cause congenital heart block (CHB, problems in the rate and rhythm of heart pumping) in a high number of cases. CHB can be detected early in pregnant women positive for Ro and/or La autoantibodies by repeated fetal echocardiography. Women carrying affected fetuses are treated with steroids, plasmapheresis, and/or IVIG, leading to improved outcomes in many cases. [17] Another type of pathogenic antibodies that can cross the placenta are antibodies directed to RhD, a blood group protein expressed on erythrocytes and platelets in most people, who are said to be RHD+ (genotypically homozygous or heterozygous). A minority of people who do not express this antigen are RhD-. If a woman is RhD- and carries a first RhD+ fetus (fathered by a homozygous or heterozygous RhD+ man), the woman will be isoimmunized by the RhD antigen during the delivery when fetal erythrocytes enter the maternal vascular system due to bleeding of the placenta. Since the RhD antigen is a protein, it activates B and T lymphocytes bearing complementary antigen-receptors resulting generally in the production of anti-RhD antibodies of the IgG class within 1-2 weeks after delivery. The first RhD+ baby is unaffected by these antibodies. However, in subsequent pregnancies involving an RhD+ fetus, the anti-RhD antibodies cross the placenta and bind to fetal erythrocytes and platelets. This binding initiates type II hypersensitivity reactions, resulting in destruction of fetal erythrocytes and impaired platelet function that leads to internal bleeding (hemorrhaging). [18] This condition is called hemolytic disease of the newborn (HDN). The breakdown products of hemoglobin, especially bilirubin, cause impaired liver function and jaundice, and eventually brain damage. Severe HDN, if untreated, usually leads to death shortly after birth. [19] Hemolytic disease of the newborn is relatively rare in developed countries because of a prophylactic measure taken before delivery of every RhD+ baby (or at the time of miscarriage/abortion of every RhD+ fetus) by an RhD- mother: injection of the mother with anti-RhD antibodies. These passively-administered antibodies bind to the RhD antigens on the fetal erythrocytes that entered the maternal vascular system. This leads to the elimination of the fetal erythrocytes by maternal effector functions before the RhD+ fetal erythrocytes have a chance to interact with and activate anti-RhD maternal B cells.

1. Identify the tolerogenic mechanisms that prevent rejection of the fetus by the maternal immune system The fetus as a tolerated allograft

[2, 3] The fetus is a semiallogeneic graft because one of its haplotypes is derived from the father. [4] However, the fetus is not rejected by the mother due to multiple tolerogenic (tolerance-inducing) mechanisms at the fetomaternal interface: The fetus-derived trophoblast layer of the placenta does not express MHC class II, and expresses only low levels of MHC class I, preventing activation of maternal T cells. The trophoblast expresses HLA-G, a special MHC class I protein of limited polymorphism, which protects the trophoblast cell layer from destruction by maternal natural killer cells. The trophoblast expresses the enzyme indoleamine 2,3-dioxygenase, which breaks down tryptophan, preventing T cell proliferation. Furthermore, the break-down products are immunosuppressive. The trophoblast expresses the cytokines TGF-β and IL-10, which suppress and inhibit development of effector T cells while promoting extrathymic differentiation of CD4+ T cells into so-called induced regulatory T cells (iTregs). These T cells, which are specific for paternal-fetal antigens present in semen, are activated in uterine draining lymph nodes. The iTregs allow implantation of the developing embryo in the uterine wall. High numbers of these anti-fetus Tregs persist throughout pregnancy, maintaining tolerance to fetal antigens until late gestation. Expression of T-cell-attracting chemokines is down-regulated in the maternal decidua lining the uterus, preventing accumulation of maternal effector T cells. [5] PD-L1 and PD-L2 (program death receptor ligands 1 and 2) are expressed on cells of the chorionic villi. Interaction of PD-L1 and PD-L2 with the PD-1 immune checkpoint on maternal T cells prevents activation of the T cells.

Maternally-transmitted microbial infections before, during, and after birth

[20] Maternal infections can be transmitted to the fetus and newborn in-utero by crossing the placenta, during delivery by contact with vaginal secretions, and after birth thru breast milk, as outlined in the table. Maternal and newborn vaccination [21] Vaccination of pregnant women has been traditionally limited because of safety concerns, including unknown effects on the developing fetus. Live vaccines are still currently contraindicated. However three dead vaccines are recommended during pregnancy: - Seasonal influenza vaccine, to prevent the flu during pregnancy, which could have adverse effects on the fetus, as well as the mother. - Tdap (tetanus & diphtheria toxoids and acellular pertussis, adult equivalent of childhood DTaP) vaccine. Whooping cough, caused by Bordetella pertussis, has been increasing in incidence and causes high morbidity and mortality in newborns. Mothers are vaccinated in the second half of each pregnancy to boost the titer of maternal anti-pertussis IgG antibodies. These will be transmitted to the fetus transplacentally for protection during the neonatal period. - Hepatitis A and Hepatitis B vaccines. These are recommended for pregnant women, if indicated by exposure to the respective viruses. [22] The timing of childhood vaccinations reflects a balance between the need to confer immune protection as early in life as possible and two other considerations: the limited ability of neonates to mount effective immune responses; and the presence of maternal IgG antibodies in the blood of neonates, which can interfere with the immunogenicity of the vaccine by eliminating it before it can induce active immunity in the infant. Maternal antibodies interfere most with live vaccines, which contain much lower antigen concentrations than dead vaccines since live vaccines can replicate. The only vaccine given at birth is hepatitis B, with the second dose between 1 and 2 months of age, because of the risk that newborns can acquire the infection during delivery from chronically-infected mothers. The first dose of vaccines for other diseases for which infants are at high risk, including rotavirus, DTaP, Hemophilus influenzae type B, pneumococcal conjugate, and inactivated poliovirus vaccines, is delayed until 2 months of age.

Factors influencing maturation of the immune system & development of allergies and autoimmune diseases

[23] Infants are born with an immature immune system due mainly the immunosuppressive, generally sterile environment during gestation. Much of the maturation occurs in the first year of life and especially in the neonatal period. Several factors are known to influence the maturation of the immune system: - The microbiome, comprised of hundreds of bacterial species, is acquired in part from the mother during vaginal delivery and from the environment shortly after birth. The presence of high relative numbers of Tregs in the neonate allows for development of memory Tregs and establishment of life-long tolerance to components of commensal (beneficial) microbial species and to food antigens. - Microbial infections during infancy contribute to maturation of the immune system by stimulation of innate immune cells through pattern recognition receptors, and provide antigenic stimuli for development of effector and memory T and B cells. - Breast milk, as mentioned above, contains carbohydrates that facilitate the growth of probiotics, which in turn affect antigen exposure and immune maturation. [24] The decrease in microbial infections during infancy in developed countries and, recently, some developing countries correlates with an increase in allergies and autoimmune diseases, which has given rise to the 'hygiene hypothesis,' suggesting a causal relationship. The favored proposed mechanism to account for the hypothesized role of microbial infections in protection against allergies and autoimmune diseases is antigenic competition. Thus, the development of strong immune responses against antigens from infectious agents would inhibit the responses to 'weak' antigens like allergens and autoantigens

3. Discuss the consequences of transplacental transfer of autoantibodies and of infectious agents from mother to fetus. Role of the immune system in repeated miscarriage and initiation of labor

[6] Repeated miscarriage is usually defined as more than three miscarriages before 20 weeks of gestation, and affects 1% of women. 40-50% of repeated miscarriages cannot be explained (are idiopathic) and immune rejection is hypothesized. This is supported by the observation that women who have had repeated miscarriages have increased levels of NK cells, autoantibodies, and inflammatory cytokines compared with women who have not. Therapies used in attempts to alter and down-regulate the immune response, referred to as immunomodulators, include: - Steroid immunosuppressants such as prednisone for general down-regulation of the immune system; and - Intravenous immune globulin (IVIG), which causes suppression of autoantibodies and NK cells, inhibition of complement binding, modification of cytokine production, and expansion of regulatory T cells. These treatments have shown efficacy at reducing repeated miscarriage in some clinical trials but not others, suggesting that better pre-selection of subjects may improve results. [7] Labor is associated with a shift from an anti-inflammatory state, which prevents 'immune abortion,' to a proinflammatory state - leading to delivery of the fetus. During labor, innate immune cells including neutrophils, macrophages, and mast cells are found in the uterus, decidua, cervix and fetal membranes, and the levels of specific chemokines and adhesion molecules are increased in these tissues. Neutrophils are also increased in numbers in women's bloodstream during labor, and mast cells are increased in numbers in the uterus during late gestation. Mediators secreted by mast cells are believed to act on uterine smooth muscle cells to stimulate uterine contractions. Furthermore proinflammatory Th17 cells are preferentially recruited into the rupture zones of the fetal membranes during labor. A premature shift from the anti-inflammatory to a proinflammatory state, with breakdown in feto-maternal tolerance, is thought to induce labor - leading to preterm birth (at less than 37 weeks of gestation). About 10% of all births in the United States are preterm.

2. Describe the pre- and post-natal development of the immune system and the role of maternal antibodies in protecting the fetus and newborn

[8] Hematopoietic stem cells (HSCs) are generated in the embryonic yolk sac and migrate to the fetal liver. B lymphocytes develop in the fetal liver and are found in the fetal blood and spleen by 12 weeks of gestation. T lymphocytes develop in the fetal thymus, from precursors that migrate from the fetal liver, and are found in the fetal blood by 14 weeks of gestation. Subsequently, B cells and both CD4+ and CD8+ T cells are found in the fetal spleen. Late in gestation HSCs migrate to the bone marrow, where hematopoiesis occurs to generate B cells and innate immune cells, and from where precursors migrate to the fetal thymus for T cell development. A large proportion of lymphocytes in the fetal spleen and lymph nodes are CD4+ Tregs, and cord blood contains high levels of anti-inflammatory cytokines (IL-4, IL-10, IL-13, TGF-β), which help maintain tolerance to fetal-maternal antigens. Peripheral lymphoid organs are underdeveloped, reflecting the relatively sterile fetal environment, except for a few pathogens that succeed in crossing the placenta (see below). [9] Children are considered infants from birth till 1 year of age and newborn infants (newborns for short or neonataes) from birth till 3 months of age. The immune system of newborns differs from that of older children and adults in both the innate and adaptive arms. The innate immune cells of newborns are comparatively deficient in both numbers and functions, displaying lesser competence at antigen presentation, cytokine production, phagocytosis, and killing functions. Upon exposure to immune stimuli, newborns show a Th2 and Th17 cell polarization and a reduced pro-inflammatory Th1 cell polarization. For this reason, newborns are especially susceptible to infections with intracellular pathogens. They also show limited germinal center B cell responses and limited differentiation to plasma cells, and produce fewer effector and memory T cells. Furthermore, the BCRs and TCRs of newborns have no or short N-regions in their variable regions due to no or low expression of the enzyme terminal deoxynucleotidyl transferase (TdT) during lymphocyte maturation. This results in reduced variability of the neonatal adaptive immune response. [10] Production of endogenous (self) IgM, as reflected in serum concentration, begins halfway through fetal life and increases rapidly after birth, reaching close to adult levels by 1 year of age. IgG and IgA production begins at birth. Serum IgA concentration reaches only 20% of adult level by 1 year of age, but increases steadily through childhood. The serum concentration of IgG in infants reflects contributions from both endogenous IgG and maternal IgG that has been transferred transplacentally during fetal life (see below). At birth, the serum IgG concentration in the newborn is the same as that of the mother. However, the level of maternal IgG drops as it is being catabolized (the half-life of serum IgG is 23 days) to about 1/10th of adult concentration by 3 months after birth. It is not until 6 months that the total serum IgG concentration begins to rise due to endogenous production, leaving a 3-month window of low total IgG levels in infants. This is referred to as physiologic hypoglobulinemia of infancy (since it is not associated with disease).

4. Explain the considerations for maternal and newborn vaccination Maternal-derived passive protective immunity

] IgG is the only Ig class that crosses the placenta and is delivered from maternal to fetal blood. The IgG antibodies are trascytosed by binding to the neonatal Fc receptor (FcRn) in acidified endosomes in the syncytiotrophoblast layer, and are transported through the vesicular system and released into the fetal circulation, which is under physiological pH. The transplacental transfer of IgG begins halfway through gestation, and confers systemic protection to the fetus and, subsequently, the newborn against pathogens that the mother has encountered and to which she has mounted an antibody response. Passive immunity is also transferred from maternal colostrum and milk to the newborn gastrointestinal tract through breastfeeding. IgA is the main Ig class in maternal colostrum and milk, having been transcytosed across the alveolar cells of the mother's mammary glands by the poly-Ig receptor. IgM is also transcytosed into colostrum and milk by the poly-Ig receptor, and small amounts of IgG diffuse between the alveolar cells. These antibodies confer protection to newborns against ingested pathogens. [13] In addition to antibodies, maternal milk contains several anti-microbial components: - Lactoferrin, which binds iron necessary for microbial survival Lysozyme, which degrades bacterial cell walls. - Lipids, which are hydrolyzed to free fatty acids that have a detergentlike activity leading to disruption of microbial membranes. - Carbohydrates, which contain oligosaccharides that mimic bacterial receptors for epithelial cells, thereby inhibiting the attachment and retention of some bacterial species and facilitating the growth of Bifido and Lactobacillus bacterial species, beneficial microbes referred to as probiotics. - Leukocytes, mainly neutrophils and macrophages, which phagocytose and kill microbes. [14] Preterm infants are more susceptible to infection than infants born at term, both because their immune system is less developed and because the maternal IgG level at birth is lower due to insufficient time for transplacental transfer.

Implantation

n Two to three days after entering the uterus (around 6 days PF), the blastocyst makes contact with the endometrium and begins to implant into the uterine wall. Implantation must occur during the implantation window, days 21-25 of the menstrual cycle. The trophoblast cells that lie over the ICM make first contact with the endometrium. Upon contact, the trophoblast cells rapidly invade the endometrium and differentiate into two layers: cytotrophoblast, the mitotically active inner cell layer, and syncytiotrophoblast, the mitotically inactive, multinucleate syncytium that is formed by the fusion of cytotrophoblast cells. The syncytiotrophoblast secretes hormones, including estrogens, progesterone, human chorionic gonadotropin (hCG), and lactogens, and displays characteristics of cells that secrete steroids and peptide hormones The trophoblast grows rapidly as cytotrophoblast cells divide and fuse with the overlying syncytiotrophoblast. As it grows, the syncytiotrophoblast extends columns, or villi, into the endometrium. Enzymes secreted by the syncytiotrophoblast erode endometrial tissue, breaking down spiral arteries and uterine glands. By day 11 PF, the blastocyst has become completely embedded in the endometrial stroma. After implantation, the endometrium changes its name to the decidua graviditatis. The stromal cells of the endometrium have enlarged greatly, becoming hormone-producing decidual cells.

Clinical correlation: breast cancer

nical correlation: breast cancer Breast cancer is one of the most significant diseases in women, affecting 1 in 8 women. Its incidence greatly increases with age. Since it is often possible to detect breast cancer in its earliest stages, morbidity is low compared to other forms of cancer. Cancer arises much more commonly in ductal cells rather than lobular cells. The first step in metastatic cancer occurs when affected cells enter the connective tissue compartment. There, their mobility is increased because of access to the lymphatic circulation. The first sites of metastases are usually the axillary (armpit) lymph nodes, as they receive the most afferent lymphatic capillaries from the breast. Many of the earliest successful pharmacological therapies for breast cancer (such as tamoxifen and raloxifene) are anti-estrogen compounds. Classification schemes for breast cancer are used to predict the types of treatments that may be effective. Currently, breast cancers are described as either ER+, those that express estrogen receptors, PR+, those that express progesterone receptors, HER2/neu, those expressing human epidermal growth factor, and triple-negative, meaning those that do not express either of the above three molecules. (Cancers originating in basal (stem) cells may fall into this category.) ER+ and PR+ types are easiest to treat with simple pharmacological approaches. Cancers expressing HER2/neu are often treated using monoclonal antibodies. Triple negative cancers represent a special challenge, and there is currently intense interest in the role of personalized medicine in treating these patients. "Personalized medicine" refers to the use of the patient's unique genome in creating or evaluating specific drugs for treatment.

Name several common variants of reproductive anatomy.

penile corpora cavernosa - clitoris (crura) glans penis - glans clitoris penile foreskin - clitoral hood scrotum (integument) - labia majora penis (integument) - labia minora