Histology of Male Reproductive System

Lecture Objectives

• Describe the histological features of the male reproductive system

Male Reproductive SystemThe 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

SpermatogenesisNote: 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

Spermiogenesisthere 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 epididymisStructure – 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 VesiclesStructure• 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 GlandStructure –• 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