Spermatogensis

1. Spermatogenesis (Spermatocytogenesis, Spermiogenesis, Spermiation, Shape and function of cells inside the Testis, Semen and sperm structure, Sperm journey after synthesis to outside)

1. Male Reproductive Physiology Dr . Yasmin Magdi Abd-Elkreem

2. Male Reproductive SYSTEM Testis ( Sperm and hormones) System of ducts ( receive and transport sperm) (Epididymis, Vas deferens, ejaculatory ducts, and urethra ) Accessory sex glands ( secrete fluids into ducts) ( Seminal Vesicles, Prostate, and Bulbourethral Glands) Supporting structures (Scrotum and penis)

3. The Male Reproductive System in Anterior View The Male Reproductive System in Midsagital View

4. Testis Definition :- Is the male gonad in the human -Paired organ Function: 1. Produce male gametes (Spermatogenesis) in seniniferous tubules. 2. Produce steroid hormones ( Steroidogensis ) in interstitium . 3. Nourish the produced sperm. Location : - Lowered in Lower abdomen in external pouch called scortum . (-2/3 ͦ C) - descended from abdomen into scrotum around week 28 of pregnancy. Testicular Anatomy and Physiology: 1. External appearance : Each testis weighs about 25 grams (0.875 ounce) and is 4–5 cm (1.6–2.0 inches) long and 2–3 cm (0.8–1.2 inches) in diameter. The testis descends from a retroperitoneal position through the inguinal canal to take its place in the scrotum.

5. Testis Scrotum : - consists of skin and subcutaneous tissue A vertical septum, of subcutaneous tissue in the center divides it into two parts, each containing one testis. A] Smooth muscle fibers, called the dartos muscle , in the subcutaneous tissue contract to give the scrotum its wrinkled appearance. When these fibers are relaxed, the scrotum is smooth. B] the cremaster muscle , consists of skeletal muscle fibers and controls the position of the scrotum and testes. When it is cold or a man is sexually aroused, this muscle contracts to pull the testes closer to the body for warmth.

6. Testis 2. Internal Structure : Each testis is an oval structure Covered by: tunica albuginea There are about 250 lobules in each testis. Each contains 1 to 4 - seminiferous tubules that converge to form a single straight tubule. Seminiferous tubules - comprise 95% of testicular volume, and are devoted to the production of spermatozoa. Small, coiled tubes, each tubule is 30-70 cm long and 200-300 um in diameter. There are approximately 500 tubules per testis. The tubules are divided by fibrous septae , and surrounded by the tough tunica albuginea .

7. Testis [ O rganization of the cells of the Seminiferous Epithelium :] ( 1 ) SERTOLI CELLS : Nonreplicating physical support cells Function : - Remove excess cytoplasm from developing spermatid - tubulobulbar processes - Move spermatids toward the lumen of the seminiferous tubules - ectoplasmic specializations - Nurture and mediate maturation of spermatids - Segregate groups of developing gametes - Secrete fluid to transport sperm in reproductive tract - Secrete hormones and other factors a.Embryonic - anti- mullarian hormone b.Adult - inhibin -estrogen - Other factor (not a hormone) - androgen binding protein (helps transport androgens from interstitial fluid into seminiferous tubule -promotes spermatogenesis)

8. Testis (2) MESENCHYMAL CELLS : - Each seminiferous tubule is surrounded by mesenchymal cells, which comprise the peritubular myoid cells whose contractile elements generate peristaltic waves along the tubules, but do not present a tight diffusion barrier. (3) INTERSTITIAL TISSUE - located between the seminiferous tubules - comprised of connective tissue, blood vessels, lymphatics , and Leydig cells cells which produce testosterone.

9. Testis (4) SPERMATOGENIC CELLS : - Stem cells which regularly replicate and differentiate into mature sperm as they migrate toward the lumen Function: spermatogenesis continue the spermatocytes progressively move from basement membrane to the luminal side of seminiferous tubule

10. Spermatogenesis Site of Sperm Formation : -Occur in the seminiferous tubules in the testis The Sperm formulation involves three steps: Spermatocytogenesis : spermtogenic cells form rounded cells called spermatids 2. Spermiogenesis : spermatids which in the second step differentiate into specialized cells known as sperms. 3. Spermiation

11. 1. Spermatocytogenesis: .Steps of Spermatocytogenesis : 1.The primitive sex cells appear earliest in 4 th week of intra uterine life in the wall of yolk sac as primordial germ cells They migrate to the developing testes and lie dormant among the cells lining the seminiferous tubules. 2. At puberty the germ cells awaken and start the actual process of spermato genesis 3.. Spermatogonia are the Germ-Line cells. They are diploid (2n). They undergo mitosis to reproduce themselves.(Increase in No.) 4. One of these spermatogonia undergoes meiosis, and it is called a primary spermatocyte . It is diploid (2n). 5.The primary spermatocyte undergoes MEIOSIS I to produce two secondary spermatocytes . These are now haploid (n) but still contain two chromatids per chromosome

12. 1.Spermatocytogenesis: 6..Each of these secondary spermatocytes undergoes MEIOSIS II to each produce two spermatids . Spermatids are haploid (n) and each contain 1 chromosome that was previously a chromatid . The result is 4 total spermatids .

13. 2.Spermiogenesis: .Steps of Spermiogensis : 1.Spermatids modify to assume specific shape of the sperm.they elongate and reorganize internal structure to acquire the particular shape. 2. The changes include ; -Golgi apparatus forms acrosomal cap- proteolitic enzymes -Nucleus is condensed - Centriols : make collar around neck -Microtubules, forrm flagellum, -Mitochondria arrange as spiral around neck -Excess cytoplasm cast off as residual body - Cytoplasmic bridges break and sperms release from Sertoli cells to lie free in lumen of seminiferous tubules

14. 3.Spermiation: mature spermatids are released from Sertoli cells into the seminiferous tubule lumen prior to their passage to the epididymis. extensive restructuring and remodelling of the spermatid to produce a streamlined spermatozoan involves several discrete steps including 1. remodelling of the spermatid head and cytoplasm 2. removal of specialized adhesion structures 3. the final disengagement of the spermatid from the Sertoli cell.

15. Intra-Testicular Communication ( Regulation of spermatogenesis) cellular communication is categorized into: 1. Endocrine signaling is mediated by hormones. - Hormones are transported via the bloodstream from the site of production, and reach their cellular target through diffusion or mediated by receptor. - Albeit indispensable ,highly effective and relatively slow.

16. Intra-Testicular Communication 2. Paracrine signaling level of interaction exists between the neighbouring cellular elements. Not only signaling between neighboring cells but also between the testicular compartments occur between immune cells, fibroblasts and Leydig cells in the interstitiurn , between interstitial cells and peritubular cells, between peritubular cells and Sertoli cells, between Sertoli cells and germ cells and among germ cells themselves. 3. Autocrine signaling. the secreted molecules that act back on the cells from which they originate. A signaling molecule can functionally cover more than one category.

17. Rete testis Fully formed spermatozoa leave the seminiferous tubules by straight tubules and enter interconnected channels called rete testis within the mediastinum (bottom left). The rete testis lead into the efferent ductules (bottom right) that lead into the head of the epididymis . Note the cells of Efferent ductules have cilia, which beat to help move mature sperm to the epididymis .

18. Epididymis Definition :- a long, coiled tube. Transportation , Storage and maturation area for sperm. Efferent ductules empty into epididymis. Functions:. 1. Maturational changes of spermatozoa 2 . Stabilization of condensed chromatin. 3. Changes in surface charge of the plasma membrane. 4. New sperm surface proteins. 5. Sperm storage. 6. Sperm transport by peristalsis (sperm epididymal maturation requires 2-12 days). 7. Release of spermatozoa during ejaculation. 8. Elimination of aged Location : - a curved structure on the posterior (back) margin of each testis. -Scalloped outline.

19. Epididymis Epididymal Anatomy and Physiology: -The efferent ducts fuse to form the ductusepididymidis of the epididymis . Single highly coiled tube (4-6 m). The canal is surrounded by connective tissue and blood vessels. divided into four gross anatomical regions: the initial segment, head (caput ), body (corpus ), and tail ( cauda ) Caput Corpus Cauda

20. Ductus ( Vas) deferens Upon ejaculation the epididymis contracts, expelling sperm into the ductus deferens. Can also store sperm several months Ampulla of the vas deferens After the ductus deferens exits the deep inguinal canal, it heads superiorly towards the urinary bladder. Terminal portion of the vas deferens enlarges into an ampulla . Lumen of ampulla larger than vas deferens. After crossing the ureters, the ampulla of the ductus deferens joins the seminal vesicle.

21. Accessory sex glands The male reproductive system includes three different accessory sex glands, namely a pair of seminal vesicles, a pair of bulbourethral glands and the prostate . Their secretions provides the bulk of semen. 4 Major Functions of Male Glands 1. Activating spermatozoa. 2. Providing nutrients spermatozoa need for motility. 3. Propelling spermatozoa and fluids along reproductive tract: mainly by peristaltic contractions. 4. Producing buffers: to counteract acidity of urethral and vaginal environments

22. 1. Seminal vesicles ( glandulae vesiculosae ) Definition :- Paired, elongated, saclike structures, and highly folded tubular gland. The duct of each joins with the distal end of the ductus deferens to form an ejaculatory duct. Empty its secretions into vas d eferens. Functions : 1. secrets a strongly acidophilic and constitutes 45-80 % of the ejaculate volume (2-2.5 mL). 2. Its secrets contains several proteins, enzymes, mucus and vitamin C. 3. Rich in Fructose ( major sourse of energy) Location : - On posterior wall of urinary bladder.

23. 2. Prostate Definition :- The largest accessory gland consisting of 30-50 branched tubuloalveolar glands. Empty its secresions in the urethra. Functions:- 1. Secretions are acidic (pH 6.5). 2. Prostatic fluid contributes 15-30 % or about 0.5 mL to the volume of the semen. 3. Contains a high citric acid content (maintain the osmotic equlibirium in semen) , acid phosphatase and zinc. 4. Contains enzymes required for liquefaction of the ejaculate coagulum. Location : - - surrounds and opens into the urethra where it leaves the bladder.

24. 3. Bulbourethral glands (Cowper´s glands) Definition :- pair of pea-sized structures Functions: 1. Secretions including galactose , sialic acid 2. has a lubrication function ( mucoprotiens ) and precedes emission of semen along the penile urethra. 3. forming a part of the ejaculate (0.1-0,2 mL = 5%) Location : - located in the urogenital diaphragm, close to the bulb of the penis.

25. Ejaculatory duct - Is a short passageway (2 cm ): at junction of ampulla and seminal vesicle duct. - Penetrates wall of prostate gland. - Empties into urethra. Urethra Passageway for urine and male reproductive fluids Extends 18–20 cm: Extends from urinary bladder to distal end (tip) of penis. Is divided into 3 regions: prostatic membranous spongy

26. Penis Contains urethra Passageway for ejaculation of semen and excretion of urine. Body of penis – 3 cylindrical masses of tissue with erectile tissue: Glans penis – terminal opening is external urethral orifice Prepuce or foreskin covers glans in uncircumcised men Root of penis is attached portion Erection – parasympathetic fibers release and cause local production of nitric oxide (NO) causing smooth muscle in arterioles to relax and dilate allowing large amounts of blood to enter penis

27. Points to Remember Sperm Summary Produced : Seminiferous tubules (Testis). Stored: Epididymis Transported through epididymis by rhythmic peristaltic contractions as they mature Epididymis  Vas Deferens  Ejaculatory duct (ampulla of vas deferens fuses with duct of seminal vesicle “ejaculatory duct”)  prostate  prostatic urethra (then passes the bulbourethral gland)  membranous urethra  penile urethra

28. Points to Remember

29. Spermatozoon - Each day about 300 million sperm complete spermatogenesis The human sperm cell is about 70 µm long Head Nucleus with 23 chromosomes (haploid or n) Acrosome – vesicle filled with oocyte penetrating enzymes It is the head which binds to the egg at fertilization Midpiece : the energy for motility is generated by mitochondria Tail : motility – the beat is initiated just behind the midpiece , and then propagated along the tail Once ejaculated, sperm do not survive more than 48 hours in female reproductive tract.

30. At the end of lecture you are able to Describe the structure of the testis and the process of spermatogenesis. What is spermatogenesis? Sperm production and pathway. Describe the sperm structure.

31. References 1. 2014 Andrology and Embryology Review Course Manual of the American Board of Bioanalysis (ABB). 2. Robaire B, Hinton BT, Orgebin -Crist M, The Epididymis. In: Knobil and Neill’s Physiology of Reproduction,Third Edition edited by Jimmy D. Neill. Elsevier © 2006. 1071-1148.

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