Male Reproductive System — Overview

Parts

• Testes

• Vas deferens

• Urethra

• Accessory reproductive glands

• Penis

The Testes

• The male gonads

• Male reproductive cells are formed in the testes

• Testes located outside the body in the scrotum

Functions of the Testes

• Spermatogenesis — spermatozoa produced in seminiferous tubules of the testes

• Hormone production

  • Androgens (male sex hormones) produced in interstitial cells of the seminiferous tubules

  • Principal androgen = testosterone

    • Secondary sex characteristics

    • Libido

    • Anabolic effects (such as protein building)

Spermatozoa

• Long, thin cells

• 3 main parts (head- covered by caplike acrosome, midpiece, tail)

Development of Testes

• Begin development in the abdomen near the kidneys before birth

• Gubernaculum — band of connective tissue that attaches testes to scrotum

• Testes gradually pulled caudally and ventrally

• Pass through inguinal rings down into the scrotum

The Scrotum

• Sac of skin that houses the testes

• Helps regulate temperature of testes

  • Must be kept cooler than body temperature

• Cremaster muscle passes down through inguinal ring and attaches to the scrotum

  • Adjusts position of testes depending on temperature

The Spermatic Cords

• Tube-like, connective tissue structures

  • Contain blood vessels, nerves, lymphatic vessels, and vas deferens

• Link the testes with the rest of the body

• Form heat-exchange mechanism: pampiniform plexus

The Tunics

• 2 layers of connective tissue that surround the testes and spermatic cord

  • Visceral vaginal tunic = proper vaginal tunic

  • Parietal vaginal tunic = common vaginal tunic

• Tunics become significant when animal has an orchiectomy

Tunica Albuginea

• Lies beneath the tunics

• Fibrous connective tissue capsule that encloses each testis

• Septa divide each testis into tiny lobules that contain the seminiferous tubules

Seminiferous Tubules

• Spermatogenesis takes place in U-shaped tube = rete testis

• Interstitial endocrine cells produce androgens

• Sertoli cells support developing spermatids and shield them from the body's immune system

The Epididymis

• The storage site for spermatozoa and a place for them to mature

• Flat ribbon-like structure that lies along the surface of the testis

  • Head

  • Body

  • Tail

The Vas Deferens

• Moves the spermatozoa from the epididymis up to the urethra when ejaculation occurs

• Spermatozoa mixed with secretions from accessory glands = semen

The Urethra

• 2 functions in the male:

  • Urinary

  • Reproductive (ejaculation) — urine flow blocked during this function

• 2 portions in the male:

  • Pelvic portion

  • Penile portion

Accessory Reproductive Glands

• Ducts of glands enter the pelvic portion of the urethra

• Different species have different combinations of glands

• Produce alkaline fluid to help counteract acidity of the female reproductive tract

  • Electrolytes

  • Fructose

  • Prostaglandins

• Seminal vesicles — present in every species except dogs and cats

• Prostate gland — completely surrounds urethra; larger in dogs because it's the only one they have

• Bulbourethral glands = Cowper's glands — secrete mucus-containing fluid that helps clear and lubricate the urethra for semen passage

The Penis

• Male breeding organ

• Composed of muscle, erectile tissue, connective tissue, a large blood supply, and many sensory nerve endings

• Urethra runs down the center

• 3 main parts:

  1. The roots — 2 bands of crura attach penis to brim of pelvis

  2. The body — 2 bundles of erectile tissue

     • Sinuses engorge with blood = erection

     • Corpus cavernosum urethrae = corpus spongiosum

     • Corpus cavernosum penis

  3. The glans

     • Distal end of penis with numerous sensory nerves

     • Prepuce = sheath of skin that encloses the penis when not erect

       • Paraphimosis = penile prolapse, often due to inflammation of prepuce

• Lots of species differentials!

The Canine Penis

• Urethra runs through groove on os penis

• Bulb of the glans remains swollen after ejaculation... "the tie"

  • Often mistaken for testes by clients!

Canine Stages of Coitus

• First Stage Coitus (1–2 min)

• The Turn (2–5 sec)

• Second Stage Coitus (5–45 min)

The Equine Penis

• Diverticulum or fossa on dorsal aspect of penis 

• Sebaceous glands regularly produce sebum

• When mixed with dead skin debris = smegma, which can form "beans"

Sigmoid Flexure

• Seen in bulls

• Erection results from straightening the S shape of the non-erect penis

• Penis protrudes from prepuce for breeding

• Retractor penis muscle pulls penis back to non-erect, S shape