Block 7 Lecture Notes - Reproductive Systems PDF

outline of the male reproductive tract - the male reproductive system is composed of: 1. the testes which produce male gametes (sperm) 2. a system of ducts for storage and transport of sperm 3. a collection of accessory sex glands 4. several supporting...

outline of the male reproductive tract - the male reproductive system is composed of: 1. the testes which produce male gametes (sperm) 2. a system of ducts for storage and transport of sperm 3. a collection of accessory sex glands 4. several supporting structures including the penis and scrotum organs and supporting structures ducts accessory glands accessory sex gland secretions - seminal vesicles (contribute ~60% semen volume) - viscous seminal fluid: - fructose: fuel for glycolysis for ATP production - prostaglandins: contribute to sperm viability, motility and transport - fibrinogen: aids coagulation of semen in female reproductive tract - prostate (contribute ~ 25% semen volume) - thin seminal fluid: - slightly acid pH: due to citric acid (used for ATP production) - proteolytic enzymes: break down clotting proteins from seminal vesicles - seminalplasmin: seminalplasmin is an antibiotic that destroys bacteria - bulbourethral (Cowper’s) gland: - mucus-like fluid: to minimize damage to sperm during ejaculation - alkaline: protects sperm from acids in urine internal anatomy of a testis histology of a testis – sperm production sertoli cells - “nurse cells” - support sperm-production - support sperm development within densely packed seminiferous tubules leydig cells - testosterone-producing portion of testis - located in connective (interstitial) tissue - between loops of seminiferous tubules - spermatogenesis: the conversion of undifferentiated germ cells (spermatogonia) into specialized, motile sperm (spermatozoa) mitosis - performed by all replicating cells in the human body, including spermatogonia and oogonia - prophase → metaphase → anaphase → telophase → cytokinesis - interphase: decision to divide is made and chromosomes are duplicated in preparation meiosis spermatogenesis - spermatogonia are sperm stem cells, maintaining their number through mitosis - excess spermatogonia enter meiosis: becoming spermatocytes, them spermatids, then (through differentiation), becoming spermatozoa (sperm) - meiosis involves 2 rounds of cell division to yield 4 haploid cells called gametes - in gametes, chromosome number is halves (one copy of each human autosome plus one sex chromosome (X or Y) for a total of 23)  - spermatogenesis (meiosis and spermiogenesis) results in the release of sperm into the lumen of the seminiferous tubules - meiosis I begins as a spermatogonium undergoes differentiation, thereby committing to sperm formation - meiosis II follows immediately after meiosis I, resulting in 4 spermatids - spermatids differentiate into sperm (spermiogenesis) and are released from sertoli cells into the lumen of the seminiferous tubules (spermiation) results of spermiogenesis (differentiation of spermatids into sperm): - resulting morphological changes allow for motility and protection of chromosomes against environmental damage - spermiation: the release of mature spermatozoa from sertoli cells into the lumen of the seminiferous tubule - capacitation: final maturation of the sperm occurs within female reproductive tract (triggered by secretions from the uterus) capacitation - includes hyperactivation of tail - hyperactivation of the sperm tail is required to penetrate the matrix surrounding the oocyte - hyperactivation is triggered by Ca2+ influx, the result of increased progesterone (produced by the woman) acting on the male sperm in the female reproductive tract - men deficient in the progesterone-binding Ca2+ channel (CATSPER 1 null individuals) are infertile hormonal control of male gamete formation - at puberty, increased GnRH triggers increased production of LH and FSH - LH stimulates testosterone production by Leydig cells - testosterone stimulates the final steps of spermatogenesis - testosterone inhibits LH release - FSH acts of sertoli cells to promote spermatogenesis by stimulating ABP production which helps keep local (testosterone) high - sertoli cells also release inhibit which reduces FSH release female reproductive organs and tract female gamete (oocyte) production - ovaries produce female gametes (oocytes) which have the potential to develop into mature ova (eggs) if fertilized by a sperm - for a female, all oocytes are produced prior to her own birth - germ cells migrate to the ovary and become oogonia - oogonia undergo mitosis (divide) most degenerate (atresia) - some develop into primary oocytes and are inactive until puberty - ~200,000 to 2 million oocytes are present at birth - ~40,000 oocytes remain at puberty - ~400 oocytes will mature and be ovulated during a woman’s life - each month, hormone release causes several follicles (each contains one primary oocyte) to begin maturing – only one secondary oocyte (out of maturing follicles in both ovaries) completes maturation → released (ovulated) - if the released secondary oocyte is penetrated (fertilized) by a sperm, it becomes a zygote (diploid cell at the 1-cell stage of human development) - if no fertilization occurs, the released oocyte dies  - composed of ovarian follicles which are sac-like structures - each follicle consists of: 1. oocyte: one immature oocyte 2. follicular cells: surround the oocyte ovarian follicles - follicle is basic structural unit in ovary - developing follicle contains single maturing oocyte or “egg” - follicle is also primary endocrine tissue in the ovary during the first half of the ovarian cycle when it synthesizes and secretes estradiol two-cell model of estradiol production - both theca and granulosa cells (as well as LH and FSH) are necessary for estradiol synthesis by mature ovarian follicle the ovarian cycle - total supply of eggs are present at birth - ability to release eggs begins at puberty - reproductive ability ends at menopause - oocytes mature in developing ovarian follicles (primordial → antral → graafian) - 3 phases: 1. follicular phase 2. ovulation 3. luteal phase follicular phase - primordial follicles: primary oocyte - suspended in first meiotic division at birth - cohort of follicles recruited to grow: - proliferation of granulosa cells - theca cells - primary follicle → secondary follicle - tertiary follicle: antrum formation - fluid-filled space - growth stimulated by FSH and LH - graafian follicle: mature follicle - estradiol production requires LH and FSH ovulation - wall of follicle and ovary broken down by proteases, collagenases, and prostaglandins - follicle ruptures - oocyte has just completed first meiotic division - ovum released into abdominal cavity luteal phase - luteinization: follicular wall left behind will transform into corpus luteum under influence of LH - corpus luteum produces progesterone and estrogen histology of the uterus - endometrium - stratum functionalis: shed during menstruation - stratum basalis: replaces stratum functionalis each uterine cycle - myometrium - 3 layers of smooth muscle - perimetrium (not shown) - visceral peritoneum the uterine cycle - 3 phases 1. menses: degeneration and sloughing off of stratum functionalis (also called menstruation or menstrual phase) 2. proliferative phase: regrowth of endometrium 3. secretory phase: endometrial glands secrete special mucous in response to progesterone and estrogen to prepare for potential implantation of a fertilized ovum - regulated by hormone release - in absence of fertilization, corpus luteum will degenerate and the stratum functionalis will be lost with menses - growing human embryo (8 or more days after fertilization) will produce hCG which will halt the cycle by rescuing the corpus luteum from degeneration to support pregnancy (after 3-4 months, placenta takes over hormone production) - typical timing for a 28-day female reproductive cycle - menses lasts ~5 days (by convention, day 1 is defined as the first day of menses) - proliferation phase lasts from day 6 until ovulation by an ovary (day 14 on average) - secretory phase begins after ovulation and continues to day 28 female reproductive cycle - controlled by a monthly cycle of hormones from the hypothalamus, anterior pituitary, and ovary - consists of two coordinated monthly cycles of change in the ovary and uterus 1. ovarian cycle: changes in the ovary during and after maturation of the oocyte 2. uterine cycle: preparation of the uterus to receive fertilized ovum, and if implantation does not occur, the stratum functionalis is shed during menstruation menstrual phase - menstruation lasts for ~5 days - first day is considered beginning of 28 day cycle - in ovary - ~20 follicles that began to develop 6 days before are now beginning to secrete estrogen - fluid is filling the antrum from granulosa cells - in uterus - declining levels of progesterone causes spiral arteries to constrict and glandular tissue degenerates - stratum functionalis layer is sloughed off along with 50 to 150 mL of blood preovulatory phase - lasts from day 6 to 13 (most variable timeline) - in the ovary (follicular phase) - follicular secretion of estrogen and inhibin has slowed the secretion of FSH  - dominant follicle emerges by day 6 - by day 14, graafian follicle has enlarged and bulges at surface - increasing estrogen levels trigger the secretion of LH - in the uterus (proliferative phase) - increasing estrogen levels have repaired and thickened the stratum functionalis to 4-10 mm in thickness - at moderate concentrations, estrogen inhibits release of GnRH - at high concentrations, estrogen stimulates release of GnRH postovulatory phase - most consistent timeline; ~14 days - in the ovary (luteal phase) - if fertilization does not occur, corpus albicans is formed: as hormone levels frop, secretion of GnRH, FSH and LH rise - if fertilization does occur, developing embryo secretes human chorionic gonadotropin (hCG) which maintains health of corpus luteum and its hormonal secretions - in the uterus (secretory phase) - hormones from corpus luteum promote thickening of endometrium to 12-18 mm - formation of more endometrial glands and vascularization - if no fertilization, menstrual phase will begin hormonal regulation of reproductive cycle - GnRH secreted by the hypothalamus controls the female reproductive cycle - stimulates anterior pituitary to secrete FSH and LH - FSH initiates growth of follicles that secrete estrogen - estrogen maintains reproductive organs - LH stimulates ovulation and promotes formation of the corpus luteum which secretes estrogens, progesterone, relaxin and inhibin - progesterone prepares uterus for implantation and the mammary glands for milk secretion - relaxin facilitates implantation in the relaxed uterus - inhibin inhibits the secretion of FSH changes in hormone concentration during the female reproductive cycle ovarian cycle - follicular phase (days 1-14) - cohort of 8-15 primary follicles - FSH stimulates development of antral follicles - antral follicles secrete estradiol - around day 6 one antral follicle becomes dominant and the rest undergo atresia - estradiol peak precedes LH surge - ovulatory phase (day 14) - LH surge stimulates ovulation of mature follicle within 24-36 hours - luteal phase (days 15-28) - corpus luteum (CL) forms - CL secretes progesterone and estradiol - luteolysis begins ~ day 25 in non-pregnant women uterine cycle - menstrual phase - 1st day of menstruation is day 1 - discharge of endometrial tissue and blood - proliferative phase - estradiol stimulates growth of endometrium - thickening of endometrium - secretory phase - nutrients capable of sustaining embryo - decline of progesterone and estradiol at end of secretory phase permit release of prostaglandins female reproductive hormone level changes throughout life gestation: the period of development from fertilization to birth - gestation (prenatal development) is composed of 3 stages: 1. germinal stage: first two weeks following fertilization 2. embryonic stage: weeks 3 through 8 of gestation 3. fetal stage: weeks 9 through 38+ of gestation - during the germinal stage: - zygote → morula → blastocyst which reaches the uterus - after implantation, the blastocyst is called an embryo - during the embryonic stage: - embryo develops the 3 primary tissue layers and develops rudiments of every organ and organ system - embryo becomes a fetus at the end of the 8th week - the fetal stage of development lasts until birth 1st week of development: implantation 2nd week of development: development of the trophoblast, amnion, and bilaminar embryonic disc 2nd week of development: development of the yolk sac, syncytiotrophoblast, and lacunae 2nd week of development: development of the chrorion and the lacunar network 3rd week of development: development of the connecting stalk and the chrorionic villi 3rd week of development: gastrualtion and development of the three primary germ layers - folding of the ectoderm and migration of some of its cells leads to the development of mesoderm, creating a trilaminar embryonic disc organ and organ system development from the three primary germ layers - ectoderm - all nervous tissue - epidermis of skin - mesoderm - cartilage, bone, and other connective tissues - blood vessels and lymphatic vessels - epithelium of gonads - endoderm - epithelium of digestive tract - epithelium of respiratory system - epithelium of thyroid, liver and pancreas - epithelium of bladder 3rd week of development: development of intervillous spaces and capillaries in chorionic villi 3rd week of development: development of the embryo, amniotic cavity, yolk sac, and vascular supply a view of the fetal period of gestation development of placenta and umbilical cord development of the placenta and the umbilical cord - placenta forms during 3rd month - develops from embryonic chorion as well as uterine tissue - functions of the placenta: 1. site of nutrient, gas, and waste exchange 2. secretes hormones that maintain pregnancy 3. barrier to microorganisms, except some viruses - AIDS, measles, chickenpox, poliomyelitis, encephalitis (its not a barrier to drugs, incl. alcohol (#1 fetal teratogen)) - the umbilical cord, containing two umbilical arteries and one umbilical vein, connects the embryo and the placenta - after delivery, placenta detaches from the uterus (“afterbirth”) endocrine functions of the placenta - human chorionic gonadotropin (hCG) is produced by the chorion of embryo - hCG rescues the corpus luteum from degeneration until the 3rd or 4th month of pregnancy - after 4 months, the placenta takes over the corpus luteum’s production of steroid hormones (estrogens and progesterone) placenta control of hormonal changes during pregnancy term pregnancy and parturition