unit v: development male reproductive system chapter 25: 909-921
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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)