Physiology Unit 4 REPRODUCTIVE PHSYIOLOGY Gonads •  Gonads have 2 func7ons –  Gametogenesis •  Spermatogenesis •  Oogenesis –  Secrete steroid hormones •  Testosterone •  Estrogens (3 forms) –  Estradiol, produced by ovaries, placenta •  Progesterone Sex Hormones Males Sex Hormones Female Sex Hormones •  Androgens •  Estrogens –  general masculinizing ac7ons –  Produced by adrenal cortex –  DHEA is an example •  Testosterone –  Produced by testes –  Maintains male reproduc7ve func7on –  Estradiol •  Primary form of estrogen produced •  Produced by ovaries and placenta –  Estrone •  Produced by ovaries and placenta –  Estriol •  Usually only in pregnant women •  Produced by the placenta •  Progesterone –  Produced by ovaries and placenta Male Reproduc7ve Physiology •  Func7on of the testes –  Meiosis •  Forma7on of sperm –  Spermatogenesis •  Matura7on of sperm –  Emission, ejacula7on •  Expulsion of sperm –  Secre7on of male sex hormone •  Testosterone Hormonal Control of the Testes •  Hypothalamus (Brain) –  Pulsa7le secre7ons of GnRH –  Every 90 minutes •  Anterior pituitary –  FSH and LH released by same cell type –  Also show pulsa7lity •  Testes –  Testosterone secre7on by Leydig cells s7mulated by LH Sertoli Cells •  Ac7vated by FSH and testosterone •  Regulate the microenvironment of developing sperm –  Forms the blood-­‐tes7s barrier –  Nourish developing sperm –  Secrete androgen binding protein (ABP) •  Maintains high concentra7on of testosterone in lumen of seminiferous tubules •  Prevents immune system from aTacking developing sperm cells
•  Phagocytosis of defec7ve sperm Spermatogenesis •  Spermatogenesis takes 64 days •  Males produce 30 million sperm/day •  Differen7a7on requires extensive cellular remodeling Puberty in Males •  Reproduc7ve organs mature and reproduc7on becomes possible –  12-­‐16 years of age in males •  First signs of puberty are due to increased secre7ons of adrenal androgens (ACTH controlled) •  All other developments in puberty reflect the increased ac7vity of the hypothalamic-­‐anterior pituitary-­‐gonadal axis Puberty in Males •  Increased GnRH secre7on at puberty –  Increased secre7on of FSH, LH •  Testosterone –  Changes in accessory reproduc7ve organs •  Ducts, glands, penis –  Development of male secondary sexual characteris7cs –  Sex drive Reflex Pathways for Erec7on •  Under res7ng condi7ons sympathe7c input dominant –  NE causes arteriole smooth muscle to contract •  Vasoconstric7on of blood vessels supplying blood to erec7le 7ssue •  During erec7on sympathe7c input is inhibited •  Neurons release NO –  NO causes arteriole smooth muscle relaxa7on •  Vasodila7on of blood vessels supplying blood to erec7le 7ssue Ejacula7on •  Primarily a spinal reflex (spinal nerves S2, S3, S4) •  Divided into 2 stages 1.  Sperm and glandular secre7ons into the urethra (emission) 2.  Semen is expelled from the urethra (ejacula=on) •  Average volume 3 mL •  300,000,000 sperm Seminal Fluid Seminal Glands •  Seminal Glands (Vesicles) –  Produces majority of seminal fluid –  Produces a protein, semenogelen •  Semenogelen encases ejaculated sperm in a protec7ve “gel” to protect it from the acidic environment in the vagina •  Secre7ons contain fructose, nourishes sperm cells Seminal Fluid Prostate Gland •  Prostate Gland –  Produces about 1/3 volume of seminal fluid –  Produces an alkaline fluid –  Produces Prostate Specific An7gen (PSA) •  PSA is a protease that cleaves semenogelen •  PSA is inhibited by high [zinc], present in semen •  Vagina has low [zinc], ac7vates PSA –  PSA cleaves semenogelen allowing the sperm to move freely –  Capacita7on Female Reproduc7ve Physiology •  Func7ons of the ovaries –  Meiosis – Forma7on of ova (eggs) –  Oogenesis – Matura7on of the oocyte –  Ovula7on •  Expulsion of an oocyte –  Secre7on of female sex hormones •  Estrogens •  Progesterone Oogenesis •  Early fetal development •  Oogonia undergo many rounds of mitosis •  7 months gesta7on –  6-­‐7 million oogonia –  Mitosis ceases •  At birth –  2-­‐4 million oocytes remain (atresia: programmed cell death) •  At Puberty –  Ovaries become ac7ve –  2-­‐400,000 oocytes remain (atresia) –  Approximately 400 ova will be ovulated (atresia) Oogenesis •  If the egg is fer7lized, then meiosis II occurs in the fallopian tube –  Ovum retains almost all of the cytoplasm –  2nd polar body released, again much smaller than ovum –  Meiosis II completed ager fer7liza7on Granulosa Cells •  Primary cells of the follicle •  Have receptors for FSH •  Regulate the microenvironment in which the ovum develops –  Secrete estrogen (estradiol) –  Produce one or more factors that act on primary oocytes that maintain them in meio7c arrest •  Follicle grows by mitosis of the granulosa cells •  Secrete fluid that forms and fills the antrum Follicle Development 1.  Throughout infancy and early childhood –  The progression/growth of some primordial follicles occurs 2.  At the beginning of the each menstrual cycle –  10-­‐25 of those follicles begin to develop into larger follicles 3.  About one week into the cycle –  Only one dominant follicle will develop into a Graafian follicle –  Non-­‐dominant follicles enlarge and undergo atresia –  The eggs within the degenera7ng follicles die Follicle Development Ovula7on •  Triggered by LH •  Follicle bulges out from the surface of the ovary as it enlarges (1.5 cm) •  Ovula7on occurs when the thin walls of the follicle and the ovary rupture •  A Graafian follicle ruptures and expels: –  Secondary oocyte –  Zona pellucida (sperm cell binding) –  Corona radiata (2 or 3 layers of granulosa cells) Corpus Luteum •  The follicle collapses ager the discharge the the follicular fluid and the egg •  Granulosa cells enlarge forming the corpus luteum –  Secretes estrogen, progesterone •  If implanta7on does not occur, the corpus luteum reaches is maximum size within 10 days, then degenerates (apoptosis) to form the corpus albicans Hormonal Control of Ovaries •  Hypothalamus –  Pulsa7le secre7ons of GnRH –  Frequency and amplitude of these pulses during a 24 hour period change over the course of the menstrual cycle •  Anterior pituitary –  FSH and LH •  Ovaries –  Estrogen –  Progesterone Ovarian Cycle Ovarian Cycle Puberty in Females •  Average age of onset of puberty is 10-­‐12 •  Increased secre7on of GnRH results in an increasing levels of estrogen –  Development of secondary sexual characteris7cs and the onset of the menstrual cycle •  Increasing levels of lep=n –  Secreted by adipocytes –  S7mulates secre7on of GnRH Menstrual Cycle •  Menstrual Phase –  Day 1 is the first day of menstrual flow •  Endometrium degenerates •  Prolifera7ve Phase –  End of menstrua7on to ovula7on •  Secretory Phase –  Ovula7on to the onset of the next menstrual phase Changes in uterus caused by estrogen and progesterone Pregnancy •  Introduc7on of sperm must occur between 5 days before and 1 day ager ovula7on –  Sperm viable for 4-­‐6 days –  Egg viable for 1-­‐2 days Sperm Capacita7on •  Sperm cells cannot fer7lize the egg un7l they have resided in the female tract for several hours –  Acted on by secre7ons of the female reproduc7ve tract – called capacita=on –  Changes in the paTern of tail movement allow sperm to propel forward in strong surges –  Sperm’s plasma membrane becomes altered so that it may fuse with the plasma membrane of the ovum Fer7liza7on •  Only 100-­‐200 sperm reach the egg •  Many sperm bind to the zona pellucida •  Zona pellucida proteins act as receptors for sperm surface proteins •  Binding triggers the acrosome reac=on –  Vesicles containing diges7ve enzymes released from sperm and digest the zona pellucida Implanta7on and Placenta Forma7on •  Trophoblast cells (fetal cells) produce human chorionic gonadotropin (hCG) –  Maintenance of corpus luteum (prevents menstrua5on) –  Promotes angiogenesis in uterine vasculature –  Blocks immune/macrophage ac7on from mother on foreign, invading placental cells –  Blood 7ters double every day un7l 10th week •  10th week –  Decline in hCG •  Placenta becomes secretory –  5th-­‐6th week –  Secretes progesterone (maintains endometrium) Placental Exchange of Molecules •  No mixing of maternal and fetal blood •  Diffusion –  O2 & CO2 –  Nutrient molecules & waste products •  High metabolic rate in placenta –  U7lizes 1/3 maternal oxygen & glucose –  Rate of protein synthesis exceeds liver Hormonal Changes During Pregnancy