Histology of the Male Reproductive System

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Male reproductive system includes:

Penis:

• Intomittent organ.

Testis:

• site of genesis of sex cells.

Duct System:

• conduit to outside.

Accessory Glands:

• nourish sperm & provide bulk of semen.

Primordial Germ Cells (PGC):

They arise in the 3rd week from yolk sac endoderm. They migrate via ameboid locomotion to the genital ridge and arrive by end of the 4th or beginning of the 5th week. Primordial germ cells proliferate via mitosis. Coelomic epithelium proliferates to form sex cords. The swellings produced are the genital ridges.

Formation of Primordial germ cells (PGC):

In the second month, sex cords invest the primordial germ cells. In females, cortical sex cords near the surface form follicle cells. In males, medullary sex cords form pre-Sertoli cells which at puberty will become Sertoli cells of the seminiferous tubules.

Action during Meiosis I and II:

• Meiosis I. homologous chromosomes pair and when they separate chiasma occur where blocks of genes are exchanged.

• Meiosis II. yields 2 secondary spermatocytes in males; 1 secondary oocyte & 1 polar body in females. The 2nd meiotic division yields 4 spermatids in males; 1 oocyte & 2 more polar bodies in females.

Meiosis halves the number of chromosomes & DNA in preparation for fertilization.

Significance of Meiosis:

• Chiasma allows genetic mixing & recombination of genetic material.

• Constancy of chromosome number from generation to generation is maintained by producing haploid germ cells.

Function of Prepuse:

Prepuce with glands of Tyson which are sebaceous glands not associated with hairs.

Contribute to Smegma:

• Thick, cheesy, odiferous material chiefly composed of desquamated cells around external genitalia, especially clitoris & under prepuce.

Phimosis:

• If aperture of glans is too small for prepuce to be withdrawn easily to reveal glans.

Penile Raphe:

• Remnants of urethral folds.

Detumescence:

• Loss of erection.

Circumcision:

• Both males & females.

Testis is both endocrine (testosterone) & exocrine (spermatozoa)

Accessory Glands:

Prostate:

• Secretions are more alkaline than the acid pH of the vagina.

Seminal vesicles:

• Fructose & prostaglandins.

Cowper's (bulbourethral):

• Mucous.

Glands of Littre:

• Mucous glands in urethra.

Parts of Urethra:

• Prostatic.

• Membranous.

• Penile (spongy) with glands of Littre.

Formation of Sperm:

Spermatogonia:

• A & B differentiate.

Primary spermatocytes:

• Prolonged prophase followed by rapid completion of Meiosis I.

Secondary spermatocytes:

• Short lived, rarely seen.

Spermatids:

• Connected by cytoplasmic bridges.

Spermatozoa:

• Released from Sertoli cell, immature & flagellum cannot beat.

Sertoli cell:

• Tall & irregular in shape, blood-testis barrier, nourish, secrete serous fluid, phagocytose excess cytoplasm of spermatids.

Testosterone from interstitial cells of Leydig initiate puberty & cause seminiferous tubules to function.

Primordial Germ Cells Development:

Spermatogonia A:

• Mitotically active stem cell population.

Spermatogonia B:

• Differentiate into primary spermatocytes in a process called spermatocytogenesis.

Functions of Sertoli Cells:

• Sertoli cells nourish sex cells.

• Phagocytose excess cytoplasm of spermatids.

• Secrete large volumes of fluid to wash non-motile sperm.

• Provide proper environment for development of sex cells.

• Blood-testis barrier.

• Contain Charcot- Bottcher crystals; function unknown.

Spermatogenesis takes 64 days.

Steps in Spermiogenesis:

Spermiogenesis:

• Maturation & transformation of spermatids into spermatozoa.

• Formation of acrosome from Golgi

• Condensation of nucleus.

• Formation of neck, midpiece & tail.

• Shedding excess cytoplasm as the residual body.

Sertoli Cells Secrete:

• Androgen-binding protein (ABP) which binds testosterone in seminiferous tubules.

• Inhibin which regulates FSH and aids in regulating the number of cells entering spermatogenesis.

• A substance similar to LH-releasing factor that may function as intercellular messenger between Sertoli & Leydig cells.

• Anti-Mullerian hormone which acts during embryonic development to promote regression of Mullerian ducts in males.

Capacitation:

• Obligate period of time sperm must spend in the female tract before they can fertilize an egg.

• Glycoproteins are removed from the acrosome & sperm become active (hyperactivated).

• Most likely occurs in the isthmic sperm reservoir.

• 200-300 million sperm in a 3.5 ml ejaculate.

• 300-500 move through the cervix, uterus & oviduct.

Leydig Cells:

• Located between seminiferous tubules.

• Produce testosterone.

• Large, light & frothy.

• Occur in clumps.

• Target is seminiferous tubules.

Efferent ductule, about 3 inches long with ciliated columnar cells alternating with cuboidal microvillar cells. A thin band of smooth muscle surrounds each ductule. This is the only place with motile ciliated cells.

Epididymis:

This is 20 feet long with stereocilia on pseudostratified columnar epithelium. Sperm pass through slowly, about 6 weeks. 90% of all fluid from Sertoli cells resorbed here. Smooth muscle contracts during ejaculation. If ejaculation does not occur, sperm degenerate.

Vas (ductus) deferens with thick smooth muscle layers (3). Epithelium is pseudostratified columnar.

Pampiniform Plexus:

Temperature of blood entering testicular artery must be cooled below normal prior to entering the testis. Testicular artery is surrounded by Pampiniform plexus which cools the blood. Epithelium of prostatic urethra is transitional. Further down it is variable (stratified or pseudostratified). In penile urethra epithelium is stratified squamous.

Seminal Vesicle:

• Seminal vesicle with smooth muscle.

• Epithelium is honeycombed and irregular.

• Function is to supply viscous mucous with fructose.

• Supplied by sympathetic fibers that fire during ejaculation.

Functions of Prostate Gland:

Prostate surrounds prostatic urethra. Smooth muscle and irregular epithelial lumen. Secretes serous material rich in acid phosphatase and makes up 70% of seminal fluid. Secretions are slightly acidic (ph 6.5) but are alkaline when compared with the vagina. Secretions liquefy coagulated sperm after it has been deposited in the female. Prostatic concretions, lamellar bodies, amyloid bodies or corpora amylacea are secretion deposits & sloughed epithelial cells. Can become calcified.

Benign Prostatic Hypertrophy (PUG):

• Periurethral glands are enlarged& compress the urethra (U).

• Present in 50% of males over 50 & 95% of men over 70.

• Clinical symptoms in 5-10%.

2 corpora cavernosa 1 corpus spongiosum; All are surrounded by tunica albuginea.

Blood Supply to the Penis:

• Flaccid - supplied by dorsal artery.

• Erection - blood is supplied by deep arteries which give off helicine arteries that enter lacunae.

• In flaccid state helicine arteries have a longitudinal intimal pad of smooth muscle that closes the vessels.

• During excitation leading to erection, the muscles relax allowing blood to flow into the lacunae.

• This compresses the veins beneath the tunica albuginea that drain the penis and an erection is achieved.

• After ejaculation, the helicine muscles contract and the veins drain the blood from the lacunae.

Ejaculation:

• During erotic stimuli, glands of Littre adds mucous to the urethra.

• Bulbourethral (Cowper's) secretes mucous to lubricate and clean out urethra.

• Friction on the glans reinforced by other afferent impulses results in discharge along sympathetic fibers to smooth.

• Muscle of epididymis, vas deferens, prostate and seminal vesicles.

• Smooth muscle contractions ejects sperm and matrix to prostatic urethra.

Bulbospongiosus Muscle

• Bulbospongiosus muscle ejects fluid & sperm from prostatic urethra.

• Bulbospongiosus muscle is supplied by pudendal nerve, (S2, 3, 4 keeps the penis off the floor).

• Sphincters of the bladder contract & prevent reflux of sperm into the bladder.

"Point and Shoot"

• Arousal.

• Erection = p = parasympathetic = point.

• Ejaculation - s = sympathetic = shoot.

Additional Reading:

Basic Histology

1. Introduction to Histology
2. Basic Cell Physiology
3. Actin, Microtubules, and Intermediate Filaments
4. Mitochondria, Nucleus, Endoplasmic Reticulum, Golgi
5. Epithelium (Epithelial Tissue)
6. Connective and Adipose Tissue
7. Types of Cartilage
8. Osteogenesis
9. Nervous Tissue
10. Muscle Tissue
11. Cardiovascular System
12. Blood and Hematopoiesis
13. Lymphoid Tissue
14. Digestive Tract I: Oral Cavity
15. Digestive Tract II: Esophagus through Intestines
16. Liver, Pancreas, and Gall Bladder
17. Respiratory System
18. Integument
19. Urinary System
20. Endocrine System
21. Male Reproductive System
22. Female Reproductive System
23. Eye and Ear

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