Male Anatomy and Function Flashcards
What is the penis / scrotum
- Penis: Copulatory organ, root, shaft, glans penis (tip), foreskin (prepuce), corpus spongiosum (surrounds urethra) and corpus cavernosa (paired dorsal erectile bodies)
- Scrotum: Sac of skin and superficial fascia, hangs outside abdominopelvic cavity, contains testes, midline septum divides scrotum in two
Describe aspects of the testes
- Testes: Within the scrotum, surrounded by two tunics, tunica vaginalis (outer layer derived from peritoneum) and tunica albuginea (inner layer forms fibrous capsule)
- Septa: Divides the testis into ~250 lobules
- Seminiferous Tubules: Each lobule contains 1-4 tubules, germ cells (form sperm) and sertoli cells (support, protection, maturation), no blood supply
- Spermatogonium: Sperm ripens from this into mature sperm
- Interstitial Tissue: Leydig cells (secrete testosterone / androgens), peritubular myoid cells (peristaltic movement) and capillary cells of BV
What is the blood testis barrier
- Structure: Separates testes from normal circulation, tight junctions between adjacent sertoli cells
- Function: Prevent blood and other fluids entering the lumen of seminiferous tubules, protects developing sperm from immune system, restrict passage of drugs to sperm
What are the features of the male duct system
- Seminiferous Tubules: Produce, maintain and store sperm, lined by stratified epithelium, germ cells (form sperm) and sertoli cells (support, protection, maturation)
- Straight Tubules: Form due to converging of seminiferous tubules, convey sperm into rete testis
- Rete Testis: Tubular network on inner seminiferous tubules
- Efferent Ductules: Sperm leave the testis to enter the head of epididymis
- Epididymis: Single highly coiled tube, about 6m long, maturation of sperm, passage of sperm 2-6 days, microvilli absorb testicular fluid and pass nutrients to stored sperm (head, body, tail)
- Vas / Ductus Deferens: Sperm transport, smooth muscle in walls propels sperm from epididymis to urethra, sperm storage, palpable, about 45cm long
- Ejaculatory Duct: Enters prostate, and there it empties into the urethra
- Urethra: terminal portion of the male duct system, conveys both urine and semen
What is the male HPG axis and hormonal regulation
- Testosterone: Development of male genitalia during foetal development, maintenance of spermatogenesis, accessory glands and ducts, development of secondary sexual characteristics, anabolic effects
Hormonal Regulation:
1. Hyp releases GnRH, stimulates AP to release FSH and LH
2. LH stimulates leydig cells to stimulate testosterone synthesis which binds to androgen receptors stimulating spermatogenesis
3. FSH stimulates sertoli cells to secrete inhibin and ABP (binds to testosterone) which stimulates spermatogenesis
4. Inhibin -ve feeds back to AP inhibiting further release of FSH
5. Testosterone -ve feeds back to hyp and AP inhibiting release of GnRH, FSH and LH
What are the cells in the testes
Sertoli Cells:
- Sustentacular cells, in seminiferous tubules, large (basement to lumen)
- Deep fold / pockets in cytoplasm house maturing spermatids, tight junctions form blood testis barrier, glycogen containing, simple columnar, avascular
- Provide nourishment, aid spermatid maturation, phagocytose excess cytoplasm, support germ cell progenitors and help to transfer nutrients from the nearby capillaries
- Production of testicular fluid, growth factors (transforming GF and activin), secrete hormones and proteins (androgen binding protein, mullerian inhibiting factor, inhibin, oestrogen)
Leydig Cells:
- Interstitial cells, in interstitial tissue (connective) outside seminiferous tubule, secrete testosterone in response to LH
- Pale cytoplasm (cholesterol-lipid droplets), cholesterol used in first step of testosterone production
Peritubular Myoid Cells:
- Surround the basement membrane of seminiferous tubules, squamous contractile cells, generate peristaltic waves in tubules
Capillary Cells:
- Surrounding blood vessels
What is spermatogenesis
- Spermatogenesis: Diploid chromosome set reduced to achieve haploid chromosome set, formation of haploid spermatids from diploid spermatogonia during meiosis, requires low levels of testosterone
Process: - Spermatogonium (diploid) undergo mitosis to produce primary spermatocyte (diploid) during prophase 1
- First meiotic division to produce two secondary spermatocytes (haploid)
- Second meiotic division to produce four spermatids (haploid)
What is spermiogenesis (phases)
Spermiogenesis:
- Four phases of remodelling and maturation of spermatids into mature spermatozoa (sperm) in epididymis
- Takes ~74 days, requires testosterone
Phases:
- Golgi (acrosomal vesicle)
- Cap (developing axonemal complex, acrosomal cap)
- Acrosome (cap migrates posterior, spermatid elongates, microtubules, centriole elongates to form tail)
- Maturation (residual body, annulus)
What are the genital reflexes
Erection:
- Vascular event, nerves release nitric oxide, vasodilation, BF to corpus cavernosa, compression of veins and venules to maintain erection / vasocongestion / engorgement
Emission:
- Movement of semen into the posterior urethra due to contraction of prostate, vas deferens, seminal vesicles and bulbourethral glands
- Mediated mainly by sympathetic fibres via the hypogastric nerve
- Integrated in upper lumbar segments of the spinal cord
Ejaculation:
- Propulsion of semen out of the penis by contraction of the smooth muscles of the urethra and striated muscles of bulbospongiosus
- Reflex contraction of bulbospongiosus, pulsatile release of semen
What are the male accessory glands
Prostate Gland:
- Encircles urethra inferior to bladder, size of peach pit, single gland
- ~30% of seminal fluid, contains enzymes
- Secretes milky, acidic fluid
Seminal Vesicles:
- Paired glands, posterior bladder surface
- ~65% of seminal fluid, alkaline, prostaglandins, clotting proteins, fructose (ATP)
- Smooth muscle contracts during ejaculation, duct of seminal gland joins ductus deferens to form ejaculatory duct
Bulbourethral Gland:
- Cowper’s gland, pea-sized glands inferior to prostate, paired glands
- <5% of seminal fluid, lubricate glans penis (tip)
- Alkalinity neutralises acidic urine in urethra, pre-ejaculatory fluid, produce thick, clear mucus during sexual arousal
What is semen
- Milky-white mixture of sperm / accessory gland secretions, contains fructose (ATP)
- Protects & activates sperm, and facilitates sperm movement
- Alkalinity neutralises acidity of male urethra
- pH 7.35-7.5, 2 to 6 mL, 40 million sperm / mL, 60% motility / morphology, liquefaction time 5-20 min
- Early fraction (rich in acid phosphatase, prostate), mid fraction (rich in spermatozoa, vas deferens) and late fraction (rich in fructose, seminal vesicle)
Describe structure of spermatozoa
- Head, acrosome for enzymatic penetration of the egg at fertilisation
- Mid-piece containing the mitochondrion
- Tail for forward propulsion, stored in epididymis till needed
What is meiosis 1 vs meiosis 2
- Meiosis 1: Reduction division, diploid to haploid, primary to secondary spermatocyte
- Meiosis 2: Equational division, haploid to haploid, secondary spermatocyte to spermatids
