MALE REPRODUCTIVE SYSTEM

MALE REPRODUCTIVE SYSTEM

The male reproductive system consists of the testes, genital ducts, accessory genital glands (seminal vesicles, prostate gland, and bulbourethral glands), and the penis.
Function.
The male reproductive system produces spermatozoa (sperm), testosterone, and seminal fluid. Seminal fluid transports and nourishes the sperm as they pass through the excretory ducts. The penis delivers sperm to the exterior and also serves as the conduit for excretion of urine from the body.
TESTES
Testes develop in the abdominal cavity and later descend into the scrotum, where they are suspended at the ends of the spermatic cords. They are the sites of spermatogenesis and production of the male sex hormones, primarily testosterone
Testicular tunicae (covering of the testes)
1. The tunica vaginalis is a serous sac derived from the peritoneum that partially covers the anterior and lateral surfaces of each testis.
2. Tunica albuginea
a. Tunica albuginea is the thick, fibrous connective tissue capsule of the testis.
b. It is lined by a highly vascular layer of loose connective tissue, the tunica vasculosa.
c. It is thickened posteriorly to form the mediastinum testis, from which incomplete connective tissue septa arise to divide the organ into approximately 250 compartments (lobuli testis).

Lobulitestis

1. The lobuli testes are pyramidal intercommunicating compartments that are separated by incomplete septa.
2. Each contains 1 to 4 seminiferous tubules. These tubules are embedded in a meshwork of loose connective tissue containing blood and lymphatic vessels, nerves, and interstitial cells of Leydig.
Interstitial cells of Leydig
1. Interstitial cells of Leydig are round to polygonal cells in the interstitial regions between seminiferous tubules.
2. They possess a large central nucleus, numerous mitochondria, a well-developed Golgi complex, and many lipid droplets. The lipid droplets contain cholesterol esters, precursors of testosterone.
3. They are richly supplied with capillaries and lymphatic vessels.
4. Function. Interstitial cells of Leydig are endocrine cells that produce and secrete testosterone. Secretion is stimulated by luteinizing hormone (LH; interstitial cell–stimulating hormone) produced in the pituitary gland. These cells mature and begin to secrete during puberty.


Seminiferous tubules
a. Seminiferous tubules are 30 to 70 cm long, with a diameter of 150 to 250 _m.
b. They are enveloped by a fibrous connective tissue tunic composed of several layers of fibroblasts and extensive capillary beds.
c. They form tortuous pathways through the testicular lobules and then narrow intoshort, straight segments, the tubuli recti, which connect with the rete testis.
d. They are lined by a thick complex epithelium (seminiferous or germinal epithelium). This epithelium consists of four to eight cell layers and contains spermatogenic cells, from which the germ cells eventually develop (spermatogenesis), and Sertoli cells, which have several functions.
Sertoli cells.
a. Structure
(1) Sertoli cells have a pale, oval nucleus that displays frequent indentations; they arehighly infolded and possess a large nucleolus.
(2) They have a well-developed smooth endoplasmic reticulum (SER), some rough
endoplasmic reticulum (RER), an abundance of mitochondria and lysosomes, andan extensive Golgi complex.
(3) Receptors for follicle-stimulating hormone (FSH) are present on their plasma
membranes.
(4) They form zonulaeoccludentes (tight junctions) with adjacent Sertoli cells near
their bases, thus dividing the lumen of the seminiferous tubule into a basal and an
adluminal compartment. These tight junctions are responsible for the blood-testis
barrier, which protects developing sperm cells from autoimmune reactions.
b. Function
(1) Sertoli cells support, protect, and nourish the spermatogenic cells.
(2) They phagocytose excess cytoplasm discarded by maturing spermatids.
(3) They secrete a fructose-rich fluid into the lumen that nourishes and facilitates thetransport of spermatozoa through the seminiferous tubules to the genital ducts.
(4) They synthesize androgen-binding protein (ABP) under the influence of FSH. ABPassists in maintaining the necessary concentration of testosterone in the seminiferoustubule so that spermatogenesis can progress.
(5) They secrete inhibin, a hormone that inhibits the synthesis and release of FSH by
the anterior pituitary.
(6) They establish a blood-testis barrier.
(7) They synthesize and release antimullerian hormone, which determines maleness.


Spermatogenesis
Spermatogenesis to proceed normally, the testes must be maintained at 35°C, the temperature insidethe scrotum, a level that is slightly below normal body temperature.Spermatogenesis takes 74 days to be completed, andit occurs in a cyclic but asynchronous fashion along the length of the seminiferous tubule. These cycles of the seminiferous epithelium consist of repeated aggregates of cells in varying stages of development. Each aggregateis composed of groups of cells that are connected to one another by intercellular bridges, forming a synchronized syncytium that migrates toward the lumen ofthe seminiferous tubule as a unit. The three phases o f spermatogenesis are spermatocytogenesis, meiosis, and spermiogenesis.
Spermatocytogenesisis a process involving mitosis, in which pale type A spermatogonia divide to form two types of spermatogonia, more pale type A as well as type B spermatogonia, both of which are diploid.
Dark type A spermatogonia represent a reserve population of cells that normally do not undergo cell division, but when they do, they form pale typeA spermatogonia.
Type B spermatogonia divide via mitosis to form diploid primary spermatocytes. All spermatogonia are located in the basal compartment, where asprimary spermatocytes migrate into the adluminal
compartment.
Meiosis phase starts when primary spermatocytes(4CDNA content) undergo the first meiotic division,forming two short-lived secondary spermatocytes(2CDNA content).
Secondary spermatocytes do not replicate theirDNA but immediately start the second meiotic division,and each forms two haploid (N) spermatids.
Spermiogenesis(is the process of cyto differentiationof the spermatids into spermatozoa and involves no cell division.
The spermatid loses much of its cytoplasm (which is phagocytosed by Sertoli cells), forms an acrosomal granule, a long cilium, and associated outer dense fi bers and a coarse fibrous sheath.
The spermatozoon that is formed and released into the lumen of the seminiferous tubule is non motile and is incapable of fertilizing an ovum.
ermatozoa remain immoThe sptile until just before they leave the epididymis. They become capable of fertilizing once they have been capacitated in the female reproductive system.

Intratesticular ducts

1. Tubuli recti are short, straight tubules lined by a simple cuboidal epithelium with microvilli and a single flagellum.
2. Rete testis is a labyrinth ine plexus of anastomosing channels lined by a simple cuboidal epithelium; many of the cells possess a single luminal flagellum.
Extratesticular ducts
1. Ductuli efferentes
a. Ductuli efferentes are a collection of 10 to 20 tubules leading from the rete testis to the ductus epididymis.
b. They possess a thin circular layer of smooth muscle beneath the basal lamina of the epithelium.
c. They are lined by a simple epithelium composed of alternating clusters of non ciliatedcuboidal cells and ciliated columnar cells.
d. Function. Ductuli efferentes reabsorb fluid from the semen.
2. Ductus epididymis
a. Ductus epididymis, together with the ductuli efferentes, constitutes the epididymis.
b. It is surrounded by circular layers of smooth muscle that undergo peristaltic contractions,which assist in conveying sperm toward the ductus deferens.
c. It is lined by a pseudostratified columnar epithelium, which is supported by a basal lamina and contains the following two cell types:
(1) Basal cells are round and appear undifferentiated; they apparently serve as precursors of the principal cells.
(2) Principal cells, which are columnar and posses non motile stereocilia (long, irregular microvilli) on their luminal surfaces
(a) These cells possess a large Golgi complex, RER, lysosomes, and many apical
pinocytotic and coated vesicles; the latter suggest that these cells function influid resorption.
(b) They secrete glycerophosphocholine, which inhibits capacitation (the process
whereby a sperm becomes capable of fertilizing an oocyte). Thus, capacitation occurs only after the sperm enters the female genital tract.


3. Ductus (vas) deferens
a. The ductus deferens has a thick muscular wall with inner and outer layers of longitudinal smooth muscle, which are separated from one another by a middle circularlayer.
b. It possesses a narrow, irregular lumen lined by pseudostratified columnar epithelium similar to that of the ductus epididymis.
4. Ejaculatory duct
a. The ejaculatory duct is the straight continuation of the ductus deferens beyond where it receives the duct of the seminal vesicle.
b. It lacks a muscular wall.
c. It enters the prostate gland and terminates in a slit on the colliculus seminalis located in the prostatic urethra.

Seminal vesicles

1. Epithelium
a. Epithelium of the seminal vesicles is pseudostratified columnar, with a height that varies with testosterone levels; it lines the extensively folded mucosa.
b. It contains many yellow lipochrome pigment granules and secretory granules, a large Golgi complex, many mitochondria, and abundant RER.
2. The lamina propria consists of fibroelastic connective tissue surrounded by an inner circularand outer longitudinal layer of smooth muscle.
3. The adventitia is composed of fibroelastic connective tissue.
4. The seminal vesicles secrete a yellow, viscous fluid containing substances that activatesperm (e.g., fructose); this fluid constitutes about 70% of the human ejaculate.

Prostate gland

a. The prostate gland surrounds the urethra as it exits the urinary bladder.
b. It consists of 30 to 50 discrete branched tubuloalveolar glands that empty their contents via excretory ducts into the prostatic urethra. These glands are arranged in three nconcentric layers (mucosal, submucosal, and main) around the urethra.
c. The gland is covered by a fibroelastic capsule that contains smooth muscle. Septa
from the capsule penetrate the gland and divide it into lobes.
Epithelium of prostate
a. The epithelium of the prostate gland is simple or pseudostratified columnar and lines the individual glands that constitute the prostate.
b. It is composed of cells that contain abundant RER, a well-developed Golgi complex,numerous lysosomes, and many secretory granules.
Corpora amylacea are prostatic concretions, composed of glycoprotein, which may become calcified; their numbers increase with age.
The prostate secretes a thin whitish fluid, a part of the semen containing proteolytic enzymes, citric acid, acid phosphatase, fibrinolysin, and lipids. The prostatic secretion serves to liquefy the coagulated semen after it is deposited in the female genital tract. Itssynthesis and release are regulated by dihydrotestosterone.


Bulbourethral (Cowper) glands
1. Bulbourethral glands are adjacent to the membranous urethra.
2. They empty their secretion into the lumen of the membranous urethra to lubricate it.
3. They are lined by a simple cuboidal or columnar epithelium.
4. They are surrounded by a fibroelastic capsule containing smooth and skeletal muscle.
PENIS
A. Corpora cavernosa
1. Corpora cavernosa are paired masses of erectile tissue that contain irregular vascularspaces lined by a continuous layer of endothelial cells. These spaces are separated fromeach other by trabeculae of connective tissue and smooth muscle.
2. The vascular spaces decrease in size toward the periphery of the corpora cavernosa.
3. During erection, the vascular spaces become engorged with blood as a result of parasympathetic
impulses, which constrict arteriovenous shunts and dilate the helicine arteries,
thus increasing flow to the vascular spaces of the two corpora cavernosa and the single corpus spongiosum.
B. Corpus spongiosum
1. The corpus spongiosum is a single mass of erectile tissue that contains vascular spaces of uniform size.
2. It possesses trabeculae that co
ntain more elastic fibers and less smooth muscle than those of the corpora cavernosa.
C. Connective tissue and skin
1. The tunica albuginea is a thick, fibrous connective sheath that surrounds the paired corporacavernosa and the corpus spongiosum. The arrangement of dense collagen bundlespermits extension of the penis during erection.
2. Glans penis
a. The glans penis is the dilated distal end of the corpus spongiosum.
b. It contains dense connective tissue and longitudinal muscle fibers.
c. It is covered by retractable skin, the prepuce, which is lined by stratified squamous
lightly keratinized epithelium.
3. Glands of Littre are mucus-secreting glands present throughout the length of the penileurethra.