LECTURE 5: Reproductive System (NYUCD)

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- Sex of the embryo is determined genetically at the time of fertilization (XX vs. XY)
- Primordial germ cells from the yolk sac migrate into the genital ridges @ week 6 [NECESSARY! For development into ovaries/testes]
- However, the gonads do not acquire male or female morphological characteristics until the seventh week of development
Testis- Form in the abdomen and then descend into the SCROTUM - Paired organs that produce spermatozoa and testosterone - Surrounded by a capsule of dense CT called the tunica albugineaTunica albugineacapsule of dense irregular collagenous connective tissue that projects inward into septa separating the seminiferous tubules into lobules.Seminiferous Tubules- convoluted hollow tubes composed of a thick seminiferous epithelium surrounded by a thin layer of connective tissue, the tunica propria. - Each testicular lobe has 1-4 seminiferous tubules - Produce sperm cells - Interstitial cells between tubules are called Leydig Cells (purely endocrine tissue) - Unique and complex stratified seminiferous epithelium --> gives rise to: spermatogenic and sertoli cellsLeydig cells- Interstitial cells - Tunica propia o Thin layer of CT (connective tissue) around the seminiferous tubules o Basal lamina, fibers, fibroblasts, myoid cells (smooth muscle-like cells) - Produce testosterone o In embryo, essential for male gonad development o At puberty, initiate sperm production and development of male secondary sex characteristics o In adulthood, maintain spermatogenesis and secondary male sex characteristicsSpermatogenesis- Process by which spermatogonia are transformed into spermatozoa (sperm cells) - Begins at puberty and continues into old age - Self-renewing, mitotic, spermatogonial stem cell populationOne stem cell makes a lot of sperm- Type A spermatogonia: divide and differentiate - Type B spermatogonia: divide and differentiate into primary spermatocytes - Primary spermatocytes divide (@ Meiosis I) into secondary spermatocytes - Secondary spermatocytes divide (@ Meiosis II) into spermatids - Spermatids mature into spermatozoa (by process of spermiogenesis)Spermatogenesis ProcessSpermatogonia > primary spermatocytes > MEISOSIS I > secondary spermatocytes > MEIOSIS II > spermatids > spermatozoaSpermiogenesisProcess by which haploid spermatids are transformed into spermatozoa (sperm cells) by: - Acrosome formation (head of sperm get stronger) - Condensation of the nucleus - Loss of cytoplasm - Middle piece and tail formationSperm Maturation- Maturation (while being stored in the epididymis) - Activation (when ejaculation occurs) - Capacitation (in the female reproductive tract) - Acrosome reaction (near the oocyte, so genetic material can enter ovum)Sertoli cells are"nurse cells" provide physical and nutritional support for spermatogenic cells (inside lumen)Sertoli Cells- Produces androgen-binding protein (ABP) o Under control of FSH o Promotes spermatogenesis by concentrating testosterone - Produces anti-Mullerian hormone (AMH) o Leads to atrophy of Mullerian duct - Produces inhibin B o Inhibits FSH production - Establishment of blood-testis barrier o Controls microenvironment for spermatogenesis o Tight junctions - Phagocytosis o Excess cytoplasm produced in spermiogenesis is digested o No proteins from sperm normally pass back across the blood-testis membraneHormonal Regulation [Male]@ puberty > gonadotropin releasing hormone levels begin to oscillate (cells of the pituitary are more sensitive to oscillation) > pituitary cells start producing LH and FSH > LH stimulates Leydig Cells to produce more testosterone > More testosterone stimulates sertoli cell = we have sperm maturationRete testisTUBULI RECTI > rete testis > EFFERENT DUCTULES a network of channels lined by cuboidal epithelium formed when spermatozoa from the seminiferous tubules pass from the tubuli recti (terminal part of the seminiferous tubule) into the rete testisIntratesticular genital ductsrete testis (is like the seminiferous tubules and efferent ductules)The rete testes is locatedin the mediastinum testis o CT continuous with the tunica albuginea o In the posterior midline of testisEfferent Ductules/Ductus efferentesRETE TESTES > efferent ductules > EPIDIDYMIS - Short tubules (10-20) that drain spermatozoa from the rete testis, through the tunica albuginea, to conduct the sperm to the epididymis. - Intra-testinal genital ducts - Non-ciliated cuboidal and ciliated columnar cells o Cuboidal cells absorb Sertoli cell fluid o Cilia help move the sperm toward the epididymisEpididymisEFFERENT DUCTULES > epididymis > VANS DEFERENS - STORAGE + MATURATION OF SPERMATOZOA - Highly convoluted tubule divided into 3 regions, a head, body, and tail. It is continuous with the ductus deferensEpididymis has:Three parts: - Head - Body - TailEpididymis is lined byPseudo stratified epithelium, contains 2 cell types: - Basal cells: pyramidal cells with round, dark nuclei and clear cytoplasm. They function as stem cells - Principal cells: tall cells with oval lighter nuclei. Non-motile stereociliaPrincipal Function of Epididymis Cells- Re-absorbs luminal fluid - Produce a glycoprotein that inhibits spermatozoa capacitation (capacitation occurs @ female reproductive tract)Ductus (vans) DeferensEPIDIDYMIS > vans (ductus) deferens > EJACULATORY DUCT - CONNECTS EPIDIDYMIS TO EJACULATORY DUCT - thick-walled muscular tube (3 layers) with a small irregular lumen involved in the transport of sperm from the tail of the epididymis to the ejaculatory duct - Is in spermatic cord Pseudo stratifies columnar epithelium with ciliaEjaculatory DuctsWHERE VANS DEFERENS AND SEMINAL VESICLE JOIN - Opens into prostatic urethra - Lined by simple columnar epithelium - Underlying connective tissue folded - No smooth muscle in its wallAccessory Genital GlandsProduce the non-cellular part of the semen (produce seminal fluid but not sperm): - prostate gland - bulbourethral gland - seminal vesiclesProstate Gland- produces a white serous fluid rich in lipids, proteolytic enzymes, acid phosphatase, fibrinolysin, and citric acid. - Consists of 30-50 tubulo-alveolar glands arranged in 3 concentric layers - Lined by simple pseudo stratifies columnar epithelium o Prostatic secretions enter the urethra and help the spermatozoa achieve motilityBulbourethral Glands(also called Cowper's glands) - produce a viscous, lubricating fluid containing galactose and sialic acid o Lubricates the lining of the penile urethra o First secretion upon sexual stimulationSeminal Vesicles70% OF SEMEN VOLUME!! - produce a viscous, yellow fructose-rich fluid (70% of semen volume) - Used by spermatozoa as a source of energyPenis- Functions as an excretory organ for urine and as the male copulatory organ for the deposition of spermatozoa into the female reproductive tract. - Composed of three columns of erectile tissue, known as corpora (singular = corpus) each enclosed in a fibrous connective tissue capsule, the tunica albuginea - 2 corpora cavernosa (singular = corpus cavernosum) - 1 corpus spongiosum, which contains the penile/spongy urethraSperm PathSeminiferous tubules > straight tubules/tubuli recti > rete testis > efferent ductules/ductus efferentes > epididymis > ductus (vans) deferens > ejaculatory duct > urethra@ 4 weeks - Female Reproductive System- Wolffian duct (mesonephric) - Gonadal/genital ridge - Germ cells begin to migrate *same as male*@ 6 weeks - Female Reproductive System- Wolffian and Mullerian ducts - Primitive sex cord and germ cell are in the indifferent gonad *same as male*@ 8 weeks - Female Reproductive System- Wolffian and Mullerian ducts - Medullary cords degenerate - Surface epithelium proliferates@ 16 weeks - Female Reproductive System- Mullerian duct persists (gives rise to oviducts (fallopian tubes), uterine tube, uterus, cervix, and vagina) - Wolffian duct degeneratesFollicular Development(1) Primordial follicle (2) Primary Follicle: (3) Secondary (antral) follicle (4) Graafian follicleOogenesisis the production or development of an ovum - Before birth, oogonia mature into primary oocyte (starts Meiosis I but pauses @ prophase I - diplotene) - After puberty, every month a primary oocyte will finish Meiosis I (just before ovulation) and divides into a secondary oocyte and a polar body (a) - Secondary oocyte begins Meiosis II and pauses @ metaphase II o If fertilization occurs secondary oocyte will complete meiosis II and divide into an ovum and a polar body o Polar body (a) then divides to form another two polar bodies after Meiosis II - Becomes ovum if fertilized - IF not fertilized, corpus lutem degenerates into corpus albicans (in 10-12 days)IF ovum is NOT fertilizedcorpus lutem degenerates into corpus albicans (in 10-12 days)Oogenesis ProcessOogonia > primary oocyte > MEIOSIS I > secondary oocyte > MEIOSIS II > (1) mature oocyte + (3) polar bodies