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LLU: Medicine: Anatomy: Histology Mentor: Reproduction
Histology Mentor
Reproductive System
Ovary, Oviducts, Uterus, Uterine Cervix, Vagina, Mammary Glands
I. OVARY - cellular cortex and vascular medulla.
The medulla consists of loose connective tissue and abundant spiraling blood vessels. Lymph drainage is abundant particularly from follicles and the corpus luteum.
The cortex has a very cellular stroma (fibrocytes) with a fine reticular fiber matrix surrounding follicles at different stages of development and derivatives of follicles. The actual number and types of follicles and their derivatives present depends upon the age of the individual and, in reproductively active women, the stage of the menstrual or reproductive cycle.
A. Surface - Covered by a simple cuboidal mesothelium this is some times erroneously called a germinal epithelium.
B. Follicles
1. Primordial (simple, inactive) follicles - Primary oocytes arise in the fetus by mitotic proliferation of oogonia (diploid somatic cells). This process is completed early in life so that the child's ovary contains about a million primary oocytes in primordial follicles. In these follicles the primary oocyte is arrested in prophase of 1st meiotic division and is surrounded by simple flat follicular cells. These follicles are most easily seen in prepubertal ovary but they are present until menopause.
2. Primary (developing) follicle - Beginning at puberty each menstrual cycle is initiated when a group of about 50 primordial follicles begin to differentiate as a result of an unknown stimulus. The oocyte enlarges as does its nucleus and the organelles become dispersed in the cytoplasm. Under the influence of activin from the oocyte the follicular cells become cuboidal and proliferate forming a multilaminar follicle. The amorphous zona pellucida consisting of glycoproteins secreted by the oocyte and the surrounding granulosa cells appears. Cytoplasmic processes of the oocyte and epithelial cells meet in the zona pellucida forming gap junctions.
The stroma differentiates to form two layers; theca interna, and theca externa. The theca interna becomes epithelial in nature having the characteristics of steroid secreting cells - lipid droplets, abundant smooth endoplasmic reticulum and mitochondria with tubular cristae. Under the influence of LH they secrete androstenedione which is taken up by the cells of the stratum granulosum and converted to estradiol.
3. Secondary (antral, vesicular) follicle - When an antrum containing the liquor folliculi appears it is called a secondary follicle. The continued proliferation of the follicular epithelium (stratum granulosum) depends upon the stimulation of FSH. The granulosa cells in turn produce, in addition to estradiol, molecules that regulate the release of LH and FSH from the pituitary gland.
4. Tertiary (mature Graafian) follicle - This follicle is about 2.5 cm. in diameter and forms a transparent bulge or stigma on the surface of the ovary. It has a fully developed cumulus oophorus, antrum, stratum granulosum, theca interna, and theca externa. A surge of luteinizing hormone from the basophils (gonadotrophs) of the pituitary gland triggers the rupture of the follicle and the oocyte with its surrounding corona radiata is forcefully expelled. As or before the follicle ruptures the oocyte completes the 1st meiotic division and becomes a secondary oocyte with a haploid number (23) of chromosomes. Meiosis is again arrested until fertilization takes place.
It takes about 5 cycles for a follicle to mature and ovulate. During that time most of the follicles that began to develop undergo atresia and of the few that reach the tertiary stage one becomes dominant and independent of further FSH stimulation. That follicle produces large amounts of inhibin which effectively shuts down FSH production.
C. Stroma consists of numerous spindle shaped fibroblast-like cells and sparse reticular fibers.
1. Tunica albuginea - least cellular layer just under the surface mesothelium.
2. Thecae of ovarian follicles differentiate from stroma.
a. Theca interna - most cellular and most vascular layer. Under the influence of FSH produces androstenedione that goes to the granulosa cells for aromatization to estrogens.
b. Theca externa - more fibrous, provides support.
D. Corpus luteum - Ovulation is triggered by a surge of LH from the pituitary gland and the follicle collapses trapping theca interna cells in folds between granulosa cells. . Then under influence of LH the granulosa cells enlarge and become eosinophilic. Numerous blood vessels penetrate the basement membrane to nourish the granulosa cells as that become lutein cells.
1. Granulosa lutein cells are derived from the stratum granulosum - large eosinophilic cells that produce progesterone and estrogen.
2. Theca lutein cells are derived from the theca interna - small cells along folds; produce precursors of estrogen and progesterone.
3. Cytology of steroid producing cells - much smooth ER, many mitochondria with tubular cristae and lipid droplets.
E. Corpus albicans - hyaline scar results after several months of degeneration of corpus luteum.
F. Atretic follicles - Of the 2 million primordial follicles present at birth 3/4ths undergo atresia during childhood. Only about 450 are ovulated. Atresia of primordial and developing follicles leave hardly a trace; vesicular follicles go through a glassy membrane stage to eventually form a small scar. Some of the granulosa cells may remain to form interstitial glands secreting small amounts of androgens.
II. OVIDUCTS (Fallopian or uterine tubes) - potential "portal of entry" (Opens into peritoneal cavity)
A. Fimbriated end (infundibulum)- free motile fimbria. The epithelium lining the entire uterine tube consists of simple columnar ciliated and secretory (peg) cells that respond to hormonal cycles. Ciliated cells are the most numerous in the infundibulum and the peg cells are most numerous in the intramural part. The motile fimbria and cilia sweep up oocyte and directs it into the uterine tube. The peg cells produce a secretion that is rich in carbohydrates that nourish the gametes in their transit and facilitates capacitation of the spermatozoa.
B. Ampulla - highly branched folds of mucosa that do not anastomose with each other- muscularis is loose and consists mostly of the inner circular layer. Inflammation caused by gonorrhea often results in sterility due to adhesions between the complex mucosal folds. A carrier state results from chronic asymptomatic infection.
C. Isthmus - low simple mucosal folds; muscularis of isthmus is the pacemaker in labor contractions.
D. Intramural - that portion passing through the wall of the uterus.
III. UTERUS - fundus, body and cervix. Fundus is the broad part of the uterus superior to the point of entry of the oviducts. The body and fundus are histologically similar
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1. Perimetrium 2. Myometrium 3. Endometrial stroma 4. Endometrial epithelium (simple columnar epithelium lines inner surface and forms simple tubular glands) 5. Endometrium |
A. Perimetrium - fibrous c.t. covered by mesothelium (serosa) on the sides and posterior aspect. The anterior aspect rests on the urinary bladder and is therefore covered by an adventitia or fibrosa (no mesothelium).
B. Myometrium - thick, three indistinct layers, middle is thickest and very vascular, it is called the stratum vasculare and gives rise to short straight and long coiled arteries to supply endometrium. Myometrium of cervix has high content of fibrous c.t., therefore firm.
C. Endometrium - epithelium is simple columnar with mucous and ciliated cells. There are different arrangements in the cervix and body of the uterus.
1. Body and fundus- have simple tubular uterine glands that extend from the basal layer through the functional layer to the lumen. The basal layer has the most cellular stroma. It is supplied by straight arteries. The functional layer is supplied by coiled arteries.
The simple columnar epithelium lining the fundus and body has both ciliated and secretory cells but the glands do not have the ciliated cells. During menses the functional layer is sloughed when the spiral arteries constrict causing it to die. But the basal layer remains intact and the cells in the glands and the stroma proliferate to regenerate the functional layer during the estrogenic or proliferative phase of the menstrual cycle.
2. Cervix - lined by a simple columnar mucus-secreting epithelium that is continuous with its highly branched clefts (glands) between folds of mucosa.
Cervical canal is limited by the internal (opening into cavity of the uterus) and external os (opening into vagina). In response to changes in hormone levels at mid cycle the mucus secreted is more abundant and less viscous allowing easy penetration by sperm. The epithelium changes from simple columnar to stratified squamous at the endocervical junction a short distance from the external os. The stratified squamous non keratinized epithelium is the site where most cervical cancers begin.
IV. VAGINA - fibro-muscular sheath. It is lined by stratified squamous epithelium which is thin in children and post-menopausal women. Estrogen stimulates growth of epithelium and accumulation of glycogen in the cells so that the sloughed cells provide bacterial substrate to produce lactic acid. There are no glands in the vagina, but the lamina propria and ill-defined submucosa contain many large blood vessels. Bartholin (vestibular) glands secrete mucus into the vestibule. Its stroma contains smooth muscle.
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1. Stratified squamous pseudo keratinized epithelium 2. Smooth muscle (a few strands) 3. Large blood vessels 4. Dense irregular connective tissue |
V. MAMMARY GLANDS
A. Organization - compound alveolar gland
1. Lobes - 5 to 9 functional lobes, each opening at the tip of the nipple by its own lactiferous duct, lined by stratified squamous epithelium.
2. Lobules - consists of small ducts, alveolar ducts, and alveoli.
3. Connective tissue -
a. Interlobar and interlobular - dense c.t. with considerable adipose tissue.
b. Intralobular - fine collagen and reticular fibers loosely arranged; many free cells - especially lymphoid and plasma - no adipose cells.
B. Functional states
1. Inactive - few alveoli; lobules consist mostly of ducts
2. Active - lobules greatly expanded by the addition of alveoli, which consist of cuboidal epithelium and abundant myoepithelial cells. Secretion is both by the merocrine (protein) and the apocrine (fat) mechanisms. It contains large amounts (1/4-1/2g/day) of secretory IgA, which is important in the protection of the infant from infection - especially intestinal.
3. Senile - alveoli disappear and ducts become highly attenuated.
C. Hormonal control is complex.
1. Development of ducts is stimulated by estrogen.
2. Development of alveoli requires both estrogen and progesterone.
3. Prolactin and somatotropin contribute to this development and prolactin is required for initiation and maintenance of secretion.
4. Minor effects of adrenal corticoid, insulin, and thyroxin have been observed.
I. MENSTRUAL CYCLE - morphological responses through the typical 28-day cycle (few are typical). Day one is the beginning of menses which is 14 days following ovulation. The cycle consists of a complex set of hormonal and tissue interactions.
A. Menses (2-6 days).
1. Going into menses, low levels of pituitary (FSH) and ovarian (estrogen and progesterone) hormones are found.
2. Necrotic functional layer of endometrium is sloughed. This is the result when the coiled arteries temporarily open and blood is liberated from the necrotic vessels into the stroma. The menstrual fluid consists of blood, necrotic tissue and secretion of uterine glands and does not normally clot.
3. Low levels of estrogen and progesterone are not adequate to inhibit release of FSH releasing factor - thus FSH increases.
B. Proliferative (follicular or estrogenic) phase (5-14 days).
1. Several follicles begin to develop under the influence of FSH and begin to secrete estrogen into the follicle and bloodstream. One follicle becomes independent of FSH and its follicular cells begin to secrete inhibin which decreases secretion of FSH. As FSH declines, the other follicles which began to develop are either arrested or undergo atresia.
2. Increased estrogens stimulate repair and proliferation of endometrial low columnar epithelium. Stromal cells enlarge with stored glycogen becoming decidual cells of the maternal placenta should pregnancy occur. Otherwise they are called predecidual cells and are sloughed during menses.
3. Mucus secretion by the cervix increases and becomes less viscous. The epithelium of the vagina becomes thicker and accumulates increased amounts of glycogen.
4. About 24 hours before ovulation, there is an LH surge; FSH levels are declining because of estrogen and inhibin inhibition of tuberal nuclei in the hypothalamus.
C. Secretory (luteal or progestational) phase (12 days), is the fully developed secretory phase. Glands are highly folded and contain secretions.
1. Increasing LH levels and possibly prolactin, stimulate differentiation of ruptured follicle to form corpus luteum.
2. Estrogen levels are maintained while progesterone levels increase markedly - progesterone causes uterine glands to accumulate glycogen-rich secretions in the base of cells and then release them from the apex. The glands are pleated and have a ragged luminal border
3. Stroma becomes edematous due to increased permeability of capillaries (progesterone) and predecidual cells may appear.
D. Premenstrual phase (1-2 days).
1. High levels of estrogen, progesterone and inhibin inhibit release of gonadotropin releasing factors, thus FSH and LH levels decline and subsequently estrogen and progesterone also decline.
2. Corpus luteum fails if pregnancy does not occur. If pregnancy does occur, chorionic gonadotropin maintains corpus luteum in the face of declining levels of pituitary gonadotropins. Estrogens are also produced by the placenta.
3. Endometrium shrinks because of fluid loss with failing levels of progesterone - coiled arteries constrict, causing ischemic necrosis of functional layer of endometrium. This prepares the way for menses. The coiled arteries go through cycles of constrictions and relaxation and blood is released into the stroma of the functional layer separating it from the basal layer. The menstrual flow thus consists of blood, necrotic tissue and tissue fluid. It does not normally clot.
A. Development - the outer layer of the trophoblast (syncytiotrophoblast) surrounding the embryo invades the endometrium forming a mass within which lacunae develop. This leaves an outer shell of trophoblastic cells through which maternal blood vessels open into the lacunae surrounding chorionic villi. Three regions of the endometrium (decidua) are now defined: 1) decidua capsularis - that portion covering the trophoblast and embryo; 2) decidua basalis - that portion deep to the trophoblast, forming the maternal part of the placenta; and 3) decidua parietalis - that portion lining the remainder of the uterus. Decidual cells are particularly numerous in the stroma of the decidua.
B. Chorionic villi - consist of a core of embryonic mesenchyme covered by two cell layers, the cytotrophoblast and the syncytiotrophoblast. The syncytiotrophoblast lines the intervillous spaces. It is also the major source of placental hormones: chorionic gonadotrophin, peptide placental lactogen (somatomammotropin), chorionic thyrotropin and relaxin (a hormone that causes a softening of the symphysis allowing expansion of the pelvis during parturition). Estrogen and progesterone are also products of the trophoblast (cytotrophoblast and/or syncytiotrophoblast). Since the trophoblast lacks the capacity to produce estrogen precursors these are provided by the adrenal fetal cortex and maternal blood.
Testis (semineferous tubules, straight tubules, rete testis), efferent ductules, epididymis, vas deferens, seminal vesicles, prostate gland, ejaculatory ducts, bulbourethral glands, urethra and penis
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1, Tunica albuginea (C.T. capsule and septa) 2. Seminiferous tubule (a coiled stratified epithelial tube cut in many planes) 3. Interstitial cell clusters (endocrine epithelium) |
A. Scrotum and Spermatic cord
1. Scrotum - a sac composed of thin skin with smooth muscle (tunica dartos) in its dermis. The dartos reflexly regulates the temperature of the testis slightly below body temperature.
2. Spermatic cord - the testis forms in the abdomen and migrates through the inguinal canal into the scrotum bringing with it loops of skeletal muscle (cremaster), its vascular supply (testicular artery and pampiniform plexus of veins), a peritoneal sac (tunica vaginalis) and its excretory duct (vas deferens).
B. Lobulation - the condensation of connective tissue forming the capsule of the testis is called the tunica albuginea. The thickened portion of this at the hilus is called the mediastinum testis, which contains the rete testis. The latter consists of numerous spaces lined by cuboidal epithelium into which the seminiferous tubules, via the tubuli recti (straight tubules), open. Incomplete c.t. septa extend from the mediastinum to the tunica albuginea to divide the testis into lobules. Mesothelium is found on the anterior and lateral aspects of the testis where the visceral layer of the tunica vaginalis is adherent.
C. Seminiferous tubules - each of these highly convoluted tubules (1-4 per lobule) forms a loop with a straight tubule at each end. They consist of a stratified epithelium containing two populations of cells and surrounded by a specialized c.t. sheath.
1. Sustentacular (Sertoli) cells - these cells are columnar with very irregular borders. They extend through the entire thickness of the germinal epithelium, forming a mesh work in which the developing germ cells are embedded and nourished. These cells respond to FSH by producing an androgen-binding protein, which is released into the luminal (adluminal) compartment. This provides the high level of testosterone needed by the developing germ cells. They also produce inhibin which has a negative feed back effect on FSH secretion. Their large, pale ovoid nuclei have a prominent nucleolus and are frequently seen in groups of 2 or 3 just superficial to the basal layer of nuclei. Occluding junctions between Sertoli cells segregate the developing germ cells in an adluminal, immunologically protected, compartment from the spermatogonia in the basal compartment, and are the basis of the blood-testis barrier.
2. Germinal cells - most of the basal layer of cells are cuboidal with prominent, very round nuclei. These cells are the spermatogonia. They are somatic cells with 22 pair of chromosomes plus the X and Y chromosomes and are continually proliferating (mitosis). The larger cells superficial to the spermatogonia are the primary spermatocytes. These cells have a tetraploid amount of DNA and each chromosome consists of 2 chromatids. Many of these are seen to be in various stages of the first meiotic (reductional) division, which results in the separation of paternal and maternal chromosomes, and in the formation of two smaller secondary spermatocytes - one of which has an X chromosome and one a Y chromosome. Very few secondary spermatocytes can be seen, because they pass very quickly through the second meiotic (equational) division with the formation of spermatids. Clusters of spermatids may be seen in the luminal portion of the epithelium. These are in various stages of spermiogenesis (the change from spermatids to fully formed seprmatocytes). They develop in a clonal fashion, all cells arising by mitosis of a single spermatogonium form a syncytium being connected by intercellular bridges. This clone becomes primary spermatocytes and moves from the basal to the adluminal compartment.
a. Head - very condensed nucleus capped by the acrosome, a vesicle derived from the Golgi apparatus, containing digestive enzymes.
b. Neck - a short constricted region between the head and the middle piece of the tail.
c. Tail -
1. Middle piece - consists of mitochondria wrapped around the core of the flagellum provide the energy needed for movement resulting from interaction of microtubules bridged by dynein. Mutation of dynein and other proteins required for ciliary and flagellar motility results in immobile sperm and frequent respiratory infections.
2. Main and end pieces of tail are similar to cilia in their arrangements of microtubules but have additional features that are unique to sperm flagella.
4. Connective tissue (c.t.) sheath - it is obvious that this sheath is very well organized in the adult with the fibrocytes (blasts) oriented circularly. Since the thin sheets of cytoplasm are interposed between the tubules and the vasculature, it would appear that these fibrocytes are potentially capable of modifying the nutritive environment of the seminiferous tubules. They also contain actin and have myoid-like activity. This c.t. sheath becomes fully organized only at puberty. In the prepubertal testis spermatogenesis does not take place, and the c.t. sheath is very poorly organized. In certain cases of testicular dysfunction, the c.t. sheath may remain in a prepubertal state, in others it may be overly developed or fibrotic.
D. The interstitial cells (of Leydig) - these nests of cells found between the seminiferous tubules produce testosterone under the influence of interstitial cell stimulating hormone - ICSH (same as LH). Testosterone is responsible for stimulating the development and function f the male reproductive organs and the appearance of the male secondary sexual characteristics. These cells are large having an eosinophilic finely granular cytoplasm. With the EM they are seen as typical steroid-producing cells in that they have an abundance of smooth endoplasmic reticulum and mitochondria with tubular cristae. Lipid droplets and crystalline structures may also be seen in these cells. Abundant lymph vessels and fenestrated capillaries among the interstitial cells help in transporting the testosterone to the circulation. Interstitial cells are well developed in the fetus between 4 months and birth. It is believed that testosterone produced at this time under the influence of chorionic gonadotropin stimulates the development of the scrotum, the opening of the inguinal canal, the descent of the testis and the differentiation (masculinization) of the fetal brain.
II. MALE GENITAL DUCTS. The spermatozoa produced in the testis are propelled by population and fluid pressure out of the rete testis into the efferent ductules. These ductules (15-20 of them) become coiled as they leave the upper part of the mediastinum and empty into the duct of the epididymis. They modify the fluid environment of the stored spermatozoa by processes of secretion and absorption. Phagocytes may also enter the fluid to remove cellular debris and dead and dying spermatozoa.
A. Efferent ductule - the epithelium of these ducts is characterized by a smooth outer border, but an irregular luminal border. This configuration is produced by alternating groups of tall columnar ciliated cells and cuboidal cells. The pits thus formed in this simple epithelium are probably absorptive in function. The cilia are functional and sweep toward the epididymis. These ductules change gradually to take on the characteristics of the duct of the epididymis. The ductules are surrounded by a thin layer of smooth muscle.
The efferent ductules have two main functions, transport of sperm to the epididymis and reabsorption of testicular fluid..
B. Duct of the epididymis. Large ducts with smooth regular contours where sperm are stored and mature. The epithelium may be considered pseudostratified having tall columnar cells bearing tufts of stereocilia and small rounded basally-placed cells. The nuclei of these two cell types occupy different levels and are easily distinguished. The duct is embedded in a fibrous stroma and is surrounded by a thick basement membrane and a sheath of circular smooth muscle. The process of maturation (capacitation) progresses in this duct but may not be complete until the sperm are exposed to secretions of the female tract. This is also the site of sperm storage.
C. Spermatic cord and ductus deferens (vas deferens).
1. Spermatic cord - surrounded by fascia and skeletal muscle, which forms fascicles of the cremaster. The spermatic cord contains the cremaster muscle, testicular artery, the pampiniform plexus of veins, (which cools the arterial blood by counter-current exchange), nerves, lymph vessels and the ductus deferens.
2. Ductus deferens - it is a very thick-walled tube in comparison to the lumen size. The wall is composed of inner and outer longitudinal layers and a middle circular layer of smooth muscle. The lumen is stellate-shaped and is lined by an epithelium consisting of tall columnar cells with stereocilia and a prominent basal layer of small rounded cells. At the time of sexual arousal sympathetic stimulation induces peristaltic activity in the vas deferens to move the sperm from the epididymis to the ampulla of the vas deferens and prostatic urethra. This is called emission. Then ejaculation occurs when a parasympathetic discharge results in the coordinated contraction of the muscles of the ampulla of the vas deferens, the seminal vesicles and the prostate gland.
D. Ampulla of the ductus deferens. Thin, branching and anastomosing folds of mucosa lined by a pseudostratified epithelium, fill the lumen and form blind pouches, some of which extend into the muscularis. The thick muscularis consists of interwoven fascicles of smooth muscle, but layers are not distinct.
E. Ejaculatory ducts - formed by the union of the ampulla of the vas deferens and the seminal vesicle. They pierce the connective tissue near the midline of the posterior part of the prostate gland to open on the sides of the colliculus seminalis. They have a highly folded mucosa with a simple columnar to pseudostratified secretory epithelium.
III. AUXILIARY GENITAL GLANDS - prostate, seminal vesicles, and bulbourethral glands.
A. Prostate gland - the fibro-elastic capsule contains about 50% smooth muscle and is continuous with the stroma, which is similarly composed, and which together account for 1/4 of the organ's mass. The parenchyma comprises two types of glands: 1) periurethral glands (mucosal and submucosal); and 2) prostatic glands proper. The latter tubuloalveolar glands are large and contain many complex folds of epithelium. The epithelium is cuboidal to columnar and may give evidence of an apocrine style of secretion. The secretion is thin, slightly acidic, and contains acid phosphatase as well as enzymes that liquefy the coagulated semen (fibrinolysin). Prostate specific antigen (PSA) is a serine protease. Acidophilic concretions, corpora amylacea, may be present in the gland.
B. Seminal vesicle - this is a convoluted tube with a well-developed muscularis. The glandular lumen is fairly large with many mucosal folds lined by a pseudostratified secretory epithelium. These are similar to those of the ampulla of the ductus deferens. The secretion is thick, rich in fructose and contains semenogelin that coagulates the semen after ejaculation. It is expelled at the time of ejaculation. Fructose is an important nutrient for spermatozoa.
C. Bulbourethral gland (Cowper's gland) corresponds to, and is structurally like, the major vestibular glands of the female. It is a pure mucous gland with smooth muscle in its stroma.
D. Hormonal relations - development of these glands is dramatically influenced by hormones. Castration results in regressive changes, particularly in the seminal vesicle and prostate. Hypertrophy, which frequently occurs in older age, may be related to hormonal imbalances. In addition to the male steroid hormones, prolactin is also known to contribute to the development of these glands.
A. Erectile tissues - consist of dense connective tissue containing large cavernous venous spaces associated with smooth muscle bundles that can prevent the spaces from filling with blood. In the flaccid state sympathetic and smooth muscle tone is continuous. During sexual arousal parasympathetic activity releases nitric oxide that causes cyclic GMP-dependent relaxation of arterial and venous smooth muscle. Since venous drainage is limited, the spaces become engorged and being surrounded by a very dense connective tissue sheath erection occurs. Viagra is a phosphodiesterase inhibitor.
1. Corpora cavernosa are two erectile bodies that form the bulk of the dorsal part of the penis. They are enclosed by the very dense tunica albugenia.
2. Corpus spongiosum is not enclosed by a capsule and therefore does not become rigid during erection. It is enlarged distally where it forms the glans penis and surrounds the navicular fossa. It contains the urethra that is mostly lined by pseudostratified columnar epithelium except in the navicular fossa that is lined by stratified squamous nonkeratinized epithelium. Mucus-secreting glands of Littre are found throughout the length of the penile urethra. Catheters sometimes get lodged in their wide ducts.
B. Prepuce - the fold of skin that covers the glans in the flacid state. Its inner surface is lined by nonkeratinized epithelium and many sebaceous glands are present.
C. Glans penis - the expanded distal end of the penis. When the prepuce is present the glans is covered by stratified squamous nonkeratinized epithelium supported by dense connective tissue containing sebaceous glands. When the prepuce has been removed by circumcision the epithelium is keratinized.
Note: the nonkeratinized sites are prime sites for HIV infection. Circumcised men have a 2-7 fold less chance of being infected
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