Histology of Male Reproductive System
Lecture Objectives Describe the histological features of the male reproductive system
Male Reproductive System The male structures of reproduction include the: testes, a system of ducts ductus epididymis ductus deferens ejaculatory duct urethra accessory sex glands seminal vesicles prostate gland bulbourethral glands supporting structures penis
Testis: General Organization Tunica vaginalis extension of peritoneum Tunica albuginea dense CT layer Mediastinum projection of the tunica albuginea Lobules formed from septa from the tunica albuginea
Seminiferous Tubules General structure 200-500 m in length Tunica propria lamina propria surrounding the seminiferous tubules Myoid cells 3-5 layers thick, synthesize collagen, contractions help move sperm through the tubules Basal lamina Seminiferous epithelium complex stratified epithelium composed of spermatogenic cells and sertoli cells
Spermatogenic cells Type A spermatogonia ovoid nuclei, can be either type A dark (stem cells) or type A pale (committed to become sperm) Type B spermatogonia formed by mitotic division of type A pale cells, connected to each other by cytoplasmic bridges Primary spermatocytes result from the mitotic division of type B spermatogonia, large nuclei with dark staining condensed chromatin Secondary spermatocytes formed from the first meiotic division of primary spermatocytes Spermatids formed following the second meiotic division Spermatozoa formed following spermiogenesis
Sertoli (Supporting) Cells Structure Long cytoplasmic processes extending between spermatogenic cells Contain inclusion bodies of Charcot-Böttcher Functions Blood-testis barrier formed from unique tight junctions, separates sperm from immune system Hormones release inhibin, androgen binding proteins Respond to FSH and testosterone Support support and nourish spermatocytes, therefore, also known as supporting or sustentacular cells Other characteristics do not replicate
Leydig Cells Structure large, polygonal, acidophilic Contain lipid droplets & Reinke crystals Location interstitium of seminiferous tubules Function secrete testosterone in response to LH Do not replicate Produce testosterone during early fetal life but are inactive until puberty
Spermatogenesis Note: during spermatogenesis, the developing sperm are connected to each other by cytoplasmic bridges. This ensures synchronous development of each clone Spermatogonial phase (mitosis) Type A dark Type A pale Type A pale Type B primary spermatocytes Spermatocyte phase (meiosis) Meiosis I primary spermatocyte forms two secondary spermatocytes (separation of chromosomes) Meiosis II secondary spermatocyte forms two spermatids containing haploid DNA (separation of chromatids) mitosis mitosis mitosis mitosis
Spermiogenesis there are four phases: Golgi phase Proacrosomal granules contain glycoproteins (enzymes); granules fuse to form the acrosomal vesicle Acrosomal vesicle located near the nuclear membrane; its location determines the anterior pole of the developing sperm Axonal complex migration of centrioles to the posterior pole to initiate synthesis of axonemal complex of sperm tail Cap phase Acrosomal cap acrosomal vesicle condenses and covers the anterior half of nucleus Acrosome phase Reorientation of spermatid with head pointed down into Sertoli cell Lengthening of flagellum Manchette organization of cytoplasmic microtubules Centrioles migrate back to nucleus to initiate formation of the neck region Maturation phase Residual body excess cytoplasm is pinched off and phagocytized by Sertoli cells
Structure of a Mature Sperm Head nucleus & acrosomal cap Neck centriole, excess nuclear envelop, striated columns Tail Middle piece 9 outer doublets, central doublet of MTs, 9 outer dense fibers, mitochonderial sheath Principle piece outer dense fibers gradually decrease in number and are surrounded by a fibrous sheath Tail end piece microtubules, no dense fibers
Intratesticular Ducts Straight Tubules (Tubuli recti) Location immediately after seminiferous tubule Epithelial lining Sertoli cells only at junction with seminiferous tubules becoming simple cuboidal near rete testis Function transport of sperm Rete Testis Location interconnecting within CT of mediastinum Epithelial lining simple cuboidal to low columnar Function transport Efferent Ductules Location rete testis connects to 20 efferent ductules Epithelial lining pseudostratified columnar (sawtooth appearance due to presence of tall ciliated columnar cells used for moving sperm and low columnar cells with microvilli used for fluid absorption; basal cells are also present) Muscle layer first appearance of a layer of smooth muscle; elastic fibers are interspersed among the muscle cells Function transport of sperm
Ductus epididymus Efferent ductules coalesce to form a single ductus epididymis Structure highly coiled; 4-6 m long Divisions head, body, tail Tail is the principle reservoir of mature sperm Epithelium pseudostratified columnar with stereocilia Muscular layer gradually thickens the tail has three layers: inner and outer longitudinal and middle circular layer. The muscle of the head and body move sperm by peristaltic contraction; sperm is ejected during ejaculation by muscle of the tail Function Sperm reservoir (tail region) Fluid absorption and phagocytosis of remaining residual bodies and damaged sperm Secretion Further development of sperm addition of surface glycosides to inhibit sperm binding to egg Ejection of sperm during ejaculation
Vas deferens Structure Epithelium pseudostratified columnar with microvilli Three muscle layers inner & outer longitudinal, middle circular Ampulla enlargement of the distal end where it is joined by the duct of the seminal vesicle Functions secretory; transport Ejaculatory ducts Structure continuation of the vas deferens through the prostate gland Epithelium - pseudostratified columnar with microvilli Other features NO muscle layers except fibromuscular tissue of the prostate Empties into the prostatic urethra Functions secretory; transport
Epididymis vas deferens
Seminal Vesicles Structure One primary lumen; numerous primary and secondary folds that increase surface area Pseudostratified columnar epithelium Inner circular and outer longitudinal muscle layers which contracts during emission adding stored secretions to seminal fluid Function produces and secretes 60% of the volume of semen secretion is viscous, whitish-yellow containing fructose, simple sugars, ascorbic acid, amino acids and prostaglandins. Secretion requires testosterone
Prostate Gland Structure Consists of 30-50 tubuloalveolar glands lined with pseudostratified or simple columnar epithelium. The glandular components are arranged in three layers: Mucosal layer (central zone) empty directly in the urethra Submucosal layer (transition zone) glands empty first into the prostatic sinus and then into the urethra Peripheral layer (peripheral zone) the main prostatic glands, empty into prostatic sinuses Prostatic concretions (corpora amylacea) precipitated secretory material that may be calcified, found in alveoli particularly in older men Capsule fibroelastic CT and smooth muscle, contracts during emission Function produces 30% of semen volume. Secretion is milky fluid containing citric acid, cholesterol, acid phosphatase, fibrinolysin, and electrolytes Benign prostatic hypertrophy (BPH) & cancer BPH normally occurs in older men in the mucosal and submucosal glands malignancies occur in the epithelium of the main peripheral glands
Bulbourethral Glands Structure tubuloalveolar, mucus secretory glands lined with simple columnar epithelium Surrounded by intermixed smooth & skeletal muscle Function secretes preseminal fluid that lubricates the penile urethra prior to ejaculation Glands of Littre (urethral glands) Structure predominantly around penile urethra Function mucus secretion protects epithelium from urine
Penis Structure Erectile tissue three cavernous bodies surrounded by loose elastic connective tissue with an outer covering of thin skin skin extends over the glans penis (prepuce or foreskin) unless removed by circumcision. A thick fibrous sheath called the tunica alboginea surrounds each cavernous body. The cavernous bodies consist of irregular vascular spaces separated by trabeculae of dense fibroelastic tissue. The 3 bodies are: Corpora cavernosa two dorsal erectile tissues of the penis Corpus spongiosum (corpus cavernosum urethrae) ventral erectile tissue, surrounds urethra
Erection Results from parasympathetic postganglionic efferent impulses which cause penile arteries to dilate, more blood enters cavernous spaces, cavernous body distends compressing veins, engorgement results in erection arterial dilation also mediated by nitric oxide produced by endothelial cells Note: Viagra enhances the effects of nitric oxide resulting in vasodilation Emission Results from adrenergic (sympathetic) stimulation stimulation causes movement of sperm from the tail of the epididymis and contractions of the vas deferens, seminal vesicle and prostate gland Ejaculation Results from contraction of skeletal muscle surrounding the corpora cavernosa (the ischiocavernosis) and the corpus spongiosum (the bulbospongiosus) muscle contraction ejects semen out of the urethra