Unit V: DevelopmentMale Reproductive System

Chapter 25: 909-921

Male Reproductive System

Scrotum

• Pouch holding testes

– divided into 2 compartments by median septum

• Sperm not produced at core body temperature

– cremaster muscle

– dartos muscle

– pampiniform plexus

• countercurrent heat exchanger

Scrotum

Cremaster muscle

Skin

Dartos muscleSuperficial fascia

Scrotal cavity

Epididymis Efferent ductule Ductus deferens

Seminiferous tubule

Septa

Rete testis Rete testis

Testes

• Oval organ, 4 cm long x 2.5 cm in diameter• Seminiferous tubules

– thick germinal epithelium

• Sustentacular cells/nurse cells – promote germ cell development– secrete inhibin

• Interstitial cells

2 months

3 months

Birth

Developingtestis

Connectivetissue band

5 mm 5 mm 5 mm

The connective tissue bands do not get longer as the fetus grows.

Late in fetal development, hormones cause the connective tissue band to contract.

TestisScrotum

Testes

• 3% born with undescended testes (cryptorchidism)

• Location outside pelvic cavity essential for low temperatures needed for sperm production

• Blood-testis barrier

– Formed by tight junctions between sustentacular cells -- separating sperm from immune system

Spermatic Ducts1. Efferent ductules

– 12 small ciliated ducts

2. Epididymis– Reabsorbs 90% of testicular fluid– site of sperm maturation and storage (fertile for 60 days)

3. Vas (ductus) deferens– muscular tube 45 cm long– sympathetic nerve fibers– peristalsis during orgasm

4. Ejaculatory duct– 2 cm duct empties into urethra

Male Duct System

Accessory Glands

• Seminal vesicles/glands– pair of glands

– empty into ejaculatory duct

• Prostate gland– aggregate of glands

– empty into urethra

• Bulbourethral glands– near bulb of penis; empty into spongy urethra

– lubricating fluid

– neutralizes acid of urine

LM 35Seminal gland

LumenSecretorypockets

Smooth muscle

LM 35Prostate gland

Connectivetissue andsmoothmuscle

Prostaticglands

Smooth muscleCapsule

Mucousglands

Bulbo-urethral gland

Lumen

LM 140

Membranous urethra

Bulb of penis

Right crus of penis

Corpus spongiosum

Corpora cavernosa

Scrotum

Pubic symphysis

Root of penis

Body (shaft) of penis

Neck

Glans of penis

External urethral orifice

Penis

• Internal root; external shaft and glans– skin over shaft loosely attached allows expansion

• extends over glans as prepuce (foreskin)

• 3 cylindrical bodies of erectile tissue– Fill with blood during sexual arousal

Penis

• 3 cylindrical bodies of erectile tissue– corpus spongiosum

• encloses spongy urethra• bulbospongiosus muscle

– corpus cavernosa (2)• diverge like arms of a Y• ischiocavernosus muscle

Spermatogenesis

• Spermatogonia (diploid)

1. type A - produce more daughter cells until death

2. type B differentiate into primary spermatocytes

• cells must pass through BTB

3. meiosis I 2 secondary spermatocytes

4. meiosis II 4 spermatids

2

3

4

5

1

n nn

n

Secondary spermatocyte

Sustentacular cell

Spermatid

Spermiogenesis

Meiosis II

Meiosis I

Sperm

n n

Blood–testis barrier

Lumen ofseminiferous tubule

Primaryspermatocyte

Type B spermatogonium

Tight junction

Type A spermatogonium

Basement membraneof seminiferous tubule

2n

2n

2n

Spermiogenesis

• Changes that transform spermatids into spermatozoa

• 400 million per day

Spermatozoon

• Head

– containing the nucleus, acrosome and basal body of the tail flagella

• Tail (flagellum)

– midpiece contains mitochondria

Semen / Seminal Fluid

• 2-5 mL of fluid expelled during orgasm

– 60% seminal vesicle fluid, 30% prostatic, 10% sperm

• normal sperm count 50-120 million/mL

• Other components of semen:

– fibrinogen - causes clotting seminogelin

– prostatic fluid - is a base stabilizing sperm pH at 7.2 to 7.6

– prostaglandins - stimulate female peristaltic contractions

For capacitation:

– serine protease - liquefies semen within 20-30 minutes

– fructose - energy for sperm motility

Excitement

• Erection of penis is due to parasympathetic triggering of nitric oxide (NO) secretion

– dilation of deep arteries and filling of lacunae with blood

Orgasm

• Orgasm (climax) is 15 second reaction that includes the discharge of semen (ejaculation)

• Ejaculation– emission = peristaltic contractions propel sperm through ducts

as glandular secretions are added– expulsion = semen in urethra activates muscular contractions

that lead to expulsion

Resolution

• Sympathetic signals reduce blood flow to penis– penis becomes soft and flaccid

• Cardiovascular and respiratory responses return to normal• Refractory period (10 minutes to few hours)