Histology of Male Reproductive System · 2019-04-15 · –skin extends over the glans penis...
Transcript of Histology of Male Reproductive System · 2019-04-15 · –skin extends over the glans penis...
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