Male Reproductive System
TESTES
- The testes have both exocrine and endocrine functions
 Exocrine – seminiferous tubules
o Compound, coiled, tubular glands that “secrete” cells (i.e. spermatozoa)
o Lined by stratified epithelium made of developing spermatozoa and supportive sertoli cells
 Endocrine – interstitial (Leydig) cells
o Secrete hormones, testosterone, for development and maintenance of accessory organs
- Structure of the testes
 Carries the peritoneum during descent to form the tunica vaginalis
 Testis proper is surrounded by CT and vascular layers
o Tunica albuginea (CT)
o Tunica vasculosa (vessels)
 Tunica vasculosa projects a conical mass of CT – mediastinum testis – into the testis
 Mediastinum parenchyma subdivides testes into ~300 lobuli testis (lobules)
 Each lobule contains 1-4 convoluted seminiferous tubules
- Enclosed by basal lamina
- Surrounded by 3-4 layers of smooth muscle cells
 Myoid (peritubular) cells
- Each tubule is ~150-300 µm in diameter and 30-80 cm long
- Each tubule is U-shaped with ends opening into the rete testis
- Tubules lined with seminiferous epithelium for spermatogenesis
 Developing sperm cells
 Sertoli (Sustentacular) cells
 Each seminiferous tubule continues near the mediastinum and transitions into a straight
tubule – tubulus rectus
 Tubulus rectus continues into the rete testis
 Rete testes continues into excurrent ducts
SPERMATOGENESIS
- The process by which stem cells develop into mature spermatozoa
- Three phases
 Spermatocytogenesis (mitosis)
 Meiosis
 Spermiogenesis
- Spermatogenic cells
 Spermatogonia
o “Mitotic” Cells
o Stem cells that replenish and populate
o Lie along basement membrane
 Type A spermatogonia
o Stem cells that give rise to both type A (themselves) and Type B spermatogonia
o Have a rounded nuclei with very fine chromatin grains and one or two nucleoli
 Type B spermatogonia
o Are not stem cells
o Divide repeatedly
o Have rounded nuclei with chromatin granules of variable size and one nucleolus
 Chromatin granules often attach to the nuclear membrane
- Meiotic cells
 Primary spermatocytes
o Luminal and larger than spermatogonia
 Always visible in cross-sections
o Immediately enter prophase of the first meiotic division
 Extremely prolonged phase (22 days)
o Completion of the first meiotic division results in the formation of secondary spermatocytes
 Secondary spermatocytes
o Smaller than primary spermatocytes
o Rapidly enter and complete the second meiotic division
 Seldom seen in histological preparations
 Spermatids
o Closest to luminal part of the seminiferous epithelium
o Small (diameter ~10 µm) with a very light nucleus
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Spermiogenesis
 Terminal phase of spermatogenesis
 Consists of differentiation and maturation of the newly-formed spermatids into spermatozoa
 Golgi phase
o Formation of the acrosome vesicle from hydrolytic granules formed in the Golgi
 Cap phase
o Acrosomal vesicle forms the head cap over the nucleus
o Centrioles (2) assemble at the caudal pole of the nucleus and help organize spindle fibers
 Distal centriole gives rise to an outgrowing flagellum
 Acrosomal phase
o Nucleus elongates and chromatin condenses (stains darker)
o Spermatid rotates with head towards the basal lamina and tail towards the lumen
o Acrosome stains brightly with PAS stain due to its content of hydrolytic enzymes
 Maturation phase
o Completion of nuclear condensation
o Arrangement of mitochondria around the axoneme of the flagellum
o Release of the spermatid into the tubular lumen
o Spermatid reduces in size by extruding cytoplasm and organelles – forms a “residual body”
o Residual bodies are phagocytosed by Sertoli cells, lost in tubular lumen, and partly autolysed
Spermatogenic cycle
 Defined as the time it takes for the reappearance of the same stage within a given segment of the tubule
o ~ 48-60 days from meiosis to mature spermatozoa
 In testes cross-section, sperm cells can be seen to differentiate in distinct associations with other cells
o Each spermatogenic association is classified as a “stage” of the seminiferous epithelial cycle
 Number of stages within a spermatogenic cycle varies between species
 Number of cycles required for the completion of spermatogenesis varies between species
Sertoli cells
 Hormone responsive support cells
 Pleomorphic - two or more structural forms during a life cycle
 Provide nutrient support
 Secrete ABP, inhibin, activin
 Connected by tight junctions through which germ cells move
 Tight junctions form the blood-testis barrier
Interstital tissue
 Located between seminiferous tubules
 Composed of CT, blood vessels, lymphatics and Leydig (interstitial) cells
o Leydig cells secrete testosterone and estrogens
Sertoli Cells
Leydig Cells
DUCTS
- Excurrent ducts
 Tubulus rectus (straight tubule) – lined by low columnar cells
 Rete testes – lined by flattened to cuboidal epithelium
 Ductus efferens (efferent duct)
o Lined by pseudostratified columnar epithelium with cilia
o Carry spermatozoa from the testes to the epididymis
o Absorptive cells
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Ductus epididymis
o Spermatozoa-carrying duct that forms the epididymis
o Organized into head (caput), body (corpus), and tail (cauda)
o Lined by tall, pseudostratified stereociliated columnar epithelium and basal epithelium
o Spermatozoa are stored within the epididymis while they mature to become sperm
Epididymis
Epididymis
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Vas deferens (ductus deferens)
o Carry sperm from the epididymis to the ejaculatory duct in anticipation of ejaculation
o Transverses the inguinal canal toward urethra
o Lined by pseudostratified columnar epithelium with sterocilia
o Lamina propria and thick muscularis with inner and outer layers
o Terminates at the ampulla (enlargement of the duct) near the prostate
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Ejaculatory duct
o Short duct formed via joining of distal ductus deferens and a duct from the seminal vesicle
o Carries sperm and semen through the prostate gland, emptying into the urethra
o Lined by simple or pseudostratified epithelium
o Wall is composed of fibrous tissue
ACCESSORY GLANDS
- Functions of accessory gland products
 Nourish and activate the spermatozoa
 Clear urethral tract prior to ejaculation
 Transport vehicle for spermatozoa in the female tract
 Plug female tract after placement of spermatozoa to help ensure fertilization
- Gland structure varies highly in organization and distribution among species
 Usually described as branched tubular or branched tubuloalveolar
- Seminal vesicles (vesicular gland)
 Develop from vas deferens
 Elongated sacs (~4 cm long, ~2 cm wide) that taper
where they unite with the vas deferens
 Each seminal vesicle consists of one coiling tube
(~15cm long)
 Mucosa is composed of thin-branched columnar or
pseudostratified epithelium
 Muscularis layer on inner and outer walls
Seminal vesicles
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Prostate gland
 Largest accessory sex gland
 Equivalent to the mammary gland in females
 Empty into excretory ducts of urethra
 Promotes movement of spermatozoa
 Helps form a vaginal plug that ensures fertilization
 Secretions help neutralize vaginal secretions
o More serous (dogs)
o More mucous, contains high levels of fructose and citric acid (bull)
 Stromal cells have 5-alpha reductase to produce dihydrotestosterone
 Structure
o Compound tubuloalveolar gland lined by low cuboidal to low columnar epithelium
 Epithelium contains secretory and basal cells
o Grossly divided into two parts (development varies with species) – body, disseminate part
o Secretory ducts lined by simple columnar to transitional epithelium
 Secretions empty directly into urethra
o Concretions (solid masses) may be present in secretory end pieces and parts of the duct system
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Bulbourethral glands
 All domestic species (not dog) have these glands
 Small, paired tubular or tubuloalveloar glands
o Composed of simple columnar and secretory
epithelium
 Capsule of dense CT contains smooth and skeletal m.
of the bulbocavernous and urethral mm.
 Have separate ducts that enter the urethra
 Functions of mucous secretions
o Clears the urethra of urine
o Lubricates urethra and vagina
o May be energy source for spermatozoa
Urethra
 Connects bladder and passage for spermatozoa
 Structure
o Has prostatic, membranous (pelvic), and
spongiose (penile) portions
o Mostly lined with transitional epithelium
 Tip is squamous epithelium
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Bulbourethral gland (boar)
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Penis
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Propria submucosa contains erectile tissue of cavernous sinuses
 Also has branched tubular mucous glands and the urethral glands (species variable)
Colliculus Seminalis
 Openings for ductus deferens, prostate and vesicular glands
Tunica muscularis near bladder consists of striated urethral muscle
Tunica muscularis of membranous region consists of smooth muscle
 Cavernous erectile tissue – corpus cavernosum – is found in CT beneath epithelium
Erectile tissue – corpus spongiosum – is more pronounced in the penile urethra
Shared outlet for urine and spermatozoa
Copulatory organ
Mostly consists of erectile tissue
Structure
o Paired corpora cavernosa
 Dorsal columns of erectile tissue surrounded by dense CT (tunica albuginea)
 Erectile tissue consists of trabeculae of irregular cavernous blood spaces lined by
endothelial cells and surrounded by smooth muscle cells, nerves and dense CT
o Corpus spongiosum
o Glans penis – erectile tissue, bone, fibrocartilage