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Physiology (1,062)
Tom Stavraky (262)
Lecture

Reproduction.doc

6 Pages
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Department
Physiology
Course Code
Physiology 3120
Professor
Tom Stavraky

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Description
Reproduction – The Male - 80% of testis mass is the seminiferous tubules. Combined length of tubes is 250 meters. Features of spermatogenesis - Spermatogonia are attached to the basement membrane. These cells undergo mitotic division. Adjacent Sertoli cells create blood-testis barrier via tight junctions. - Spermatogonia possess 2N (are diploid) number of chromosomes. - Speratocytes – cells in the process of becoming sperm - Require temperatures lower than 34 degrees Features of spermiogenesis - Cell acquires a vesicle of enzymes called the acrosome. The nucleus must condense. The cytoplasm is greatly reduced. Cells acquires a flagellum. Mitochondria accumulates in the midpiece. - Fluid is added by the seminal vesicles, prostate gland and Cowper’s gland. Factors which affect spermatogenesis - requires temperatures lower than 34 degrees. High levels of testosterone required. FSH is required for the initial waves of spermatogenesis and when is must be re-initiated. Sertoli cells have FSH receptors, binding initiates the production and secretion of androgen binding protein which functions to maintain high local concentrations of testosterone. - Entire process takes about 64 days - sperm reside in the epididymis for 2 weeks. Testosterone required. While testicular sperm used glucose as an energy substrate and for conversion to a.a’s and lipids, capacity to do this is lost in the epididymis. Surface charge also becomes more negative. - StAR (rate-limiting protein), moves cholesterol into mitochondria - P450scc (sidechain cleavage) turns cholesterol into pregnenolone - 17-B-hydroxy steroid dehydrogenase - cholesterol is the principle precursor for all steroid hormones. Although most is carried in from blood, can also be made from acetate. Androgens can be converted to estrogens by a process called aromatization. - A steroid is terpenoid lipi with a four fused rings in a 6-6-6-5 fashion - LH stimulation by testosterone increases cAMP and results in increased side chain cleavage of cholesterol in mitochondria. - Androgens: (1) Non-reproductive tissues, muscle anabolism, bone proliferation of chondrocytes, skin sebaceous glands becomes active. (2) Secondary Sex Characteristics: body hair distribution, chest and shoulder growth, larynx, behaviour, general body growth spurt in conjunction with GH (3) Required for differentiation of epididymis, vas deferens, prostate/seminal vesicles, penis/scrotum and required for maintenance of epididymis and function of the seminal vesicles and prostate. (4) Required for spermatogenesis - 75% of testosterone is bound to sex hormone binding globulin and 20% to albumin. The unbound form is biologically active - Testosterone is first reduced to dihydrotestosterone by 5a-reductase. Can also be aromatized (occurs in the CNS and adipose tissues). Androgen receptor (AR) is a ligand gated transcription factor. Affect Liver is primary organ involved in biologic inactivation (gets conjugated) and rendered more soluble. - Mechanism of action of GnRH is calcium influx, calmodulin binding and activation of PI pathways. - Relevance to pulsatile secretion of GnRH is because constant exposure would decrease LH secretion and pubertal and seasonal changes that need increase in LH are often reflected in increases in GnRH frequency rather than amplitude. Female - mitotic processes being during fetal life. Oogonia formation stops at 7 months and begin meiotic divisions but become arrested in the prophase of the first meiotic division. - Being with 6x10-6 germ cells in utero, by puberty only 200,000-400,00 follicles will being active reproductive life. - During each cycle, 20-50 primary oocytes will begin to mature but only one will become the dominant follicle (usually the one with the most FSH receptors). - When exposed to a preovulatory surge of LH, the dominant follicle will resume meiosis and extrude the first polar body. Thus, only one will form a secondary oocyte. - The second meiotic division is completed and second polar body excruded prior to the pronuclei of the mother and father joining. Features of steroidogenesis in the ovary - theca interna cells, when stimulated by LH form androgen for aromatization - the primary site of aromatization of testosterone to estrogen is in the granulose cell of the collicle. This is stimulated by FSH. - Transported from granulose cells to theca cells by low-density lipoproteins o Both are cAMP mediated mechanisms. o Eventually the cells make up the corpus luteum Release, Transportation, Mechanism of Action and Inactivation - once made it readily diffuses out. In serum, estradiol binds to steroid hormone binding globulin and albumin. The progesterones are bound primarily to albumin and cortisol binding globulin. - Liver also excretes, but progesterone is not conjugated, the catabolic products are excreted. Ovarian Cycle - early development of primordial follicles is hormone independent. Zona pellucida – seceted by granulose cells, is a glycoprotein material. - theca cell layer is vascularized (unlike granulose cells). - Pre-antral follicle begins showing LH and FSH receptors in layers. - Antral follicle, granulose cells secrete follicular fluid into the antrum - Production of estradiol and progesterone increases toward the end of the follicular phase, this elecits a pre-ovulatory surge of LH. This causes the resumption of meiosis (first polar body). Also changes the granulose cells, from the LH receptors they required in the process of follicular maturation, the LH will now stimulate the granulose cells to make progesterone. - The ovulatory surge of LH is the signal that causes rupture of the follicle. Ovulation – rising estrogen levels act on the endometrium and stimulate LH (progesterone can block this), LH blocks oocyte maturation inhibitor (OMI) which causes the follicle to complete the first meiotic division. Under LH, the now empty follicle develops into a corpus luteum, - Collapsed follicle now forms into a corpus luteum. The granulose cells of the corpus luteum primarily make progesterone. Occurs for about 1 week, then signal occurs for luteolysis and it forms the corpus albicans. Menopause – follicles become less responsive to LH and FSH and thus begin to secrete less estrogen. FSH and LH levels keep rising. Estrogen Effects: - Non sexual tissues: stimulates bone growth and ultimate cessation of bone growth, protects against osteoporosis, protects against atherosclerosis, antagonizes the effects of PTH, promotes blood clottinh - Secondary Sex Characteristics: stimulates female body development, narrow shoulder, broad hips, female body fat distribution. Stimulates breast development, stimulates female body hair pattern. - Secondary Sex Organs: stimulates growth of external genitalia, increase contractions and ciliary activity of fallopian tubes, stimulates proliferation of epithelial linings of reproductive tract, increases layer of vaginal epithelium, prepares uterine endometrium for progesterone’s actions by inducing progesterone receptor synthesis. Progesterone Effects: - Non-sexual characteristics: increases body temp - Secondary Sex characteristics: promotes mammary alveolar development - Reproductive Tract tissues: decreases contractions of fallopian tubes, converts endometrium into glandular structure ready for embryo implantation Pregnancy and Parturition Fimbrium  ampulla  isthmus  uterus - Window of opportunity: ovum viable for 12 hours, sperm viable for 48 hours. - Vaginal sperm 250,000, uterine sperm 100,000, ampullary sperm 50. - Blastocyte implants on day 7 - Sperm may reach egg within 15 minutes Capacitation – metabolic rate of sperm increases, changes in protein components of the sperm
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