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Reproductive system

Reproductive system. Hormonal Regulation of Reproduction. Hypothalamus : pulse generator Gonadotropin releasing hormone ( GnRH ) Anterior pituitary Luteinizing hormone (LH) Follicle stimulating hormone (FSH) Gonads produce steroid and peptide hormones

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Reproductive system

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  1. Reproductive system

  2. Hormonal Regulation of Reproduction • Hypothalamus: pulse generator • Gonadotropin releasing hormone (GnRH) • Anterior pituitary • Luteinizing hormone (LH) • Follicle stimulating hormone (FSH) • Gonads produce steroid and peptide hormones • Gonads are the main source of sex steroids • Peptide hormones: inhibin and activin

  3. Feedback Loops Control Gonadotropin Release Internal andenvironmentalstimuli CNS GnRH Hypothalamus Short-loop negative feedback KEY Stimulus Anteriorpituitary Integrating center Efferent pathway Effector Long-loop feedbackmay be negativeor positive Tissue response LH FSH Gonads(ovaries or testes) Females only Endocrinecells Gameteproduction Steroid andpeptide hormones

  4. Synthesis Pathways for Steroid Hormones Cholesterol Progesterone Dihydro-testosterone(DHT) Testosterone aromatase Corticosterone Cortisol Estradiol Aldosterone Intermediate steps

  5. Male Reproductive System – overview of structures • The male gonads (testes) produce sperm • Sperms are delivered to the exterior through a system of ducts: • epididymis, • ductus deferens, • ejaculatory duct • urethra • Accessory sex glands: • seminal vesicles, prostate gland, and bulbourethral glands

  6. Protection of the testis • The outermost protection is the scrotum • A sac of skin and superficial fascia that hangs outside the abdominopelvic cavity at the root of the penis • Separated by a midline septum • Its external positioning keeps the testes 3oC lower than core body temperature (needed for sperm production) • Each testis is surrounded by two tunics: • The tunica vaginalis, derived from peritoneum • The tunica albuginea, the fibrous capsule of the testis

  7. Testes protection - Testicular Thermoregulation • Sperms are not produced at core body temperature • In the scrotum, the testes are kept 2-3°C cooler than in the pelvic cavity. This is essential for sperm production. • Cooling mechanisms • The cremaster muscle contains strips of the internal abdominal oblique muscle around the spermatic cord. • It can elevate or lower the testes. • The dartos muscle is a subcutaneous layer of smooth muscle that wrinkles skin reducing surface area of scrotum. Can lifts testis upwards • The pampiniform plexus is an extensive network of veins that surround the testicular artery in the spermatic cord, keeping the testes cooler countercurrent heat exchange that cools arterial blood entering testis

  8. Countercurrent Heat Exchanger

  9. The Testes • Divided to 250-300 lobules by septa • each lobule contains 1-4 seminiferous tubules • Seminiferous tubules: • Produce the sperm

  10. Cells in the testes – 3 types • 2 populations found in the Seminiferous tubule • Germinal epithelium – lines the lumen of the tubules • consisting of several layers of germ cells in the process of becoming sperm • Sustentacular (Sertoli) cells. • Between the seminiferous tubules are clusters of interstitial (Leydig) cells, the source of testosterone (will be discussed later with hormonal control).

  11. The functions of Sertoli cells and BTB • Sertoli cells protect the germ cells and promote their development. Tight junctions between adjacent sustentacular cells form a blood-testis barrier (BTB) • The fluid inside the tubules contains high levels of androgens, potassium and amino acids • The BTB prevents the immune system from attacking the developing spermatozoa (contain specific Ag that are not found on any other cell) • Sertoli cell supply nutrients to the developing sperms • Phagocytize cytoplasm shed by spermatids • Secrete inhibin- negative feedback loop for FSH • Secrete androgen-binding-protein (ABP) – binds testosterone inside tubules to maintain high levels

  12. Meiosis in general andSpermatogenesis – production of sperms

  13. Ovulation with Fertilization Is Followed by Final Step of Meiosis FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm FERTILIZATION 6 One primary oocyteyields 1 egg. One primary spermatocyteyields 4 sperm. 5 Secondpolar bodydisintegrates. Unfertilized eggpasses out of body. Zygote Figure 26-5, steps 1–6

  14. Figure 28-6b Chromosomes in Mitosis and Meiosis Meiosis. The fates of three representative chromosome pairs during the two stages of meiosis Cell Chromosomes Tetrad Chromosomeduplication, synapsis,and tetrad formation Meiosis I Meiosis II 1 4 2 3 2 3 4 1 Gametes Chromosomes of gametes

  15. Spermatogenesis • Cells making up the walls of seminiferous tubules are in various stages of cell division • These spermatogenic cells give rise to sperms in a series of events • Mitosis of spermatogonia, forming spermatocytes • Meiosis forms spermatids from spermatocytes • Spermiogenesis – spermatids to sperm

  16. Spermiogenesis: Spermatids to Sperm • Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming sperm spermiogenesis spermatogenesis http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.htm

  17. Mitosis of Spermatogonia • Spermatogonia – outermost cells in contact with the epithelial basal lamina • Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells • Type A cells remain at the basement membrane and maintain the germ line • Type B cells move toward the lumen and become primary spermatocytes

  18. Spermatozoa structure • Sperm have three major regions • Head – contains DNA and has a helmetlike acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the egg • Midpiece – contains mitochondria spiraled around the tail filaments • Tail – a typical flagellum produced by a centriole

  19. Hormonal Regulation of Testicular Function • The hypothalamus releases gonadotropin-releasing hormone (GnRH) • GnRH stimulates the anterior pituitary to secrete FSH and LH • FSH causes sustentacular cells to release androgen-binding protein (ABP) • LH stimulates interstitial cells to release testosterone • ABP binding of testosterone enhances spermatogenesis

  20. 1 GnRH Anterior pituitary Via portal blood 8 7 2 Inhibin 2 LH FSH Interstitial cells 4 3 6 Testosterone Somatic and psychological effects at other body sites Sustentacular cell Spermatogenic cells 5 Seminiferous tubule Stimulates Inhibits Figure 27.9

  21. Testosterone Inhibits the Hypothalamus and Anterior Pituitary GnRH Hypothalamus Anteriorpituitary FSH LH Leydigcells Spermatogonium Inhibin Testosterone (T) Spermatocyte Testes Sertolicell Secondmessenger To bodyfor secondaryeffects Cellproducts Sertolicell Androgen-bindingprotein (ABP) ABP T Figure 26-11 (9 of 9)

  22. Testosterone • The principal androgen (male sex hormone) is testosterone. • This steroid is manufactured by the interstitial (Leydig) cells of the testes. • Secretion of testosterone increases sharply at puberty and is responsible for the development of the secondary sexual characteristics of men. • Testosterone is also essential for the production of sperm.

  23. Effects of Androgens gonads and Secondary Sex Characteristics Table 22.2

  24. Spermatic Ducts • Epididymis (head, body and tail) • 6 m long coiled duct adhering to posterior of testis • site of sperm maturation and storage (fertile for 60 days) • Ductus deferens/vas deferens (peristalsis during orgasm) • muscular tube 45 cm long passing up from scrotum through inguinal canal to posterior surface of bladder • Ejaculatory duct • 2 cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra • Spermatic cord – encloses PNS and SNS nerve fibers, blood vessels, and lymphatics that supply the testes

  25. Epididymis functions • The duct of the epididymis has stereocilia that: • Absorb testicular fluid • Pass nutrients to the sperm • Recycling center for damaged spermatozoa • Storage place for spermatozoa • Facilitate functional maturation preparing them for fertilization: • Plasma membrane changes, alterations in acrosomal membrane

  26. Connection between testis and the body • The structures that connect the testis with the body are enclosed within a connective tissue sheath called the spermatic cord • Blood vessels • Nerve fibers • Vas deferens • Cremaster muscle

  27. Urethra • Conveys both urine and semen • Consists of three regions • Prostatic – portion surrounded by the prostate • Membranous – lies in the urogenital diaphragm • Spongy, or penile – runs through the penis and opens to the outside at the external urethral orifice

  28. Accessory Glands: Seminal Vesicles • secrete 60% of the volume of semen • The composition of the gland secretions include: • High concentration of fructose that is easily metabolized by spermatozoa • Prostaglandins that stimulate smooth muscle contractions in both male and female reproductive tract • Fibrinogen that forms temporary clot within the vagina after ejaculation • When the inactive sperms mix with the seminal fluid they undergo the first step of activation and the flagella start moving (in some book this is done by the help of the prostate) • The secretion of the seminal gland are discharged into the ejaculatory duct under the control of the sympathetic system

  29. Accessory Glands: Prostate Gland • Doughnut-shaped gland that encircles part of the urethra inferior to the bladder • Slightly acidic • Produces 20-30% of the semen volume • Seminalplasmin – prostatic enzyme that kills bacteria • Prostatic enzyme that coagulates semen within minutes after ejaculation (converts fibrinogen to fibrin) • Contains citrate (nutrient source) and enzymes

  30. Accessory Glands: Bulbourethral Glands (Cowper’s Glands) • Pea-sized glands inferior to the prostate • Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra

  31. semen • The combination of spermatozoa and fluids from accessory glands • A typical ejaculation – 2-5 ml • Normal sperm count – 20-100 million/ml • Enzymes in semen: • Protease – help dissolve mucus in vagina • Seminalplasmin– prostatic enzyme that kills bacteria • Prostatic enzyme that coagulates semen within minutes after ejaculation (converts fibrinogen to fibrin) • Fibrinolysin – breaks fibrinogen and allows semen to become liquid again

  32. Accessory Glands Contribute to Semen

  33. The Penis • A copulatory organ designed to deliver sperm into the female reproductive tract • Erectile tissue – spongy network of connective tissue and smooth muscle with vascular spaces • Corpus spongiosum – surrounds the urethra and expands to form the glans and bulb of the penis • Corpora cavernosa – paired dorsal erectile bodies bound by fibrous tunica albuginea • Erection – during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid

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