Anatomy and Physiology of the

Male

Topics

• Anatomy• Physiology• Spermatogenesis• Hormonal regulation• Development

Anatomy

• Scrotum• Testes• Penis• Glands

Scrotum

• Maintains 34°C (93.2°F)• Dartos muscle –

wrinkles the skin• Cremaster muscles –

draw scrotum toward abdomen

Testes

• Coverings• Tunica vaginalis• Tunica albuginea

• Lobules• Seminiferous

tubules• Tubulus rectus

• Rete testis• Epididymis

Testes Blood Supply

• Countercurrent heat exchange• Testicular artery• Pampiniform

venous plexus

Testes Blood Supply

• Varicocele• Varicose vein like condition• 15-20% of males• 40% of infertile males

Penis external anatomy

• Foreskin• 60% in US

are circumcised

• 15% worldwide

• Shaft• Glans penis

Penis internal anatomy

• Corpus spongiosum• Bulb of

penis

• Corpora cavernosum• Crura of the

penis

Male Duct System

• Epididymus• 20 feet!• 20 days for

sperm to mature

• Smooth muscles expel sperm during ejaculation

• Cells have microvilli

Male Duct System

• Epididymus• Smooth

muscles expel sperm during ejaculation

• Cells have microvilli

Male Duct System

• Ductus (vas) deferens• 18”• Very muscular• Ampulla

Male Duct System

• Vasectomy• Almost 100%

effective• Reversal about

50% success rate

Male Duct System

• Ejaculatory duct• Urethra

• Conveys both urine and semen

• Prostatic• Membranous • Penile

• Urethral glands secrete mucus prior to ejaculation

Glands• Seminal vesicles• Size of little

finger• Surrounded by

smooth muscle• Seminal fluid

• Fructose• Ascorbic acid• Coagulating

enzyme• Prostaglandins• Other factors

that enhance sperm mobility

Glands• Prostate• Size of peach pit• Several ducts into the

prostatic urethra• Surrounded by

smooth muscle• Secretions

• Citrate• Enzymes (fibrinolysin,

hyaluronidase, acid phosphatase)

• Prostate specific antigen (PSA)

• activate sperm

Glands

• Bulbourethral glands• Pea sized• Mucus

• Lubrication• Neutralizes

acidic urine prior to ejaculation

Semen

• 2-5ml• Composed of

• Sperm (10%)• Testicular fluid• Gland secretions

Semen• Functions

• Transport, activation and protective medium• Nutrients for sperm (fructose)• Neutralizes vaginal tract• Prostaglandins reduce viscosity of mucus at

cervix• Enzymes enhance motility• Antibiotics• Chemicals that suppress the female immune

system• Clotting factors that coagulate semen so it

sticks to vagina• Fibrinolysin then dissolves that mass

Physiology

• Erection• NO (nitric oxide) released (in penis

tissue)• Causes arterioles (normally constricted)

to relax/dilate• Blood flows into the corpora cavernosa• Compresses veins to prevent flow out• Corpus spongiosum also expands but

maintains open urethra• Bulbourethral glands secrete lubricant

Physiology• Ejaculation

• Spinal reflex• Bladder sphincter muscle constricts• Reproductive ducts and glands contract

• Contents enter urethra

• Muscles around the blub of penis – series of rapid contractions

• Other systemic changes• Rapid heartbeat• Elevated blood pressure• Generalized muscle contraction

Erectile dysfunction• Deficient NO release

• Viagara, Cialis and Levitra increase effects of NO

• Possible factors• Psychological factors• Alcohol or drugs

• Antihypertensives, Antidepressants

• Diabetes mellitus• Arteriosclerosis• Varicose veins• Nervous system issues

• Stroke, Penile nerve damage, MS

Spermatogenesis

Spermatogenesis

• Meiosis• Sertoli cells

• Nourish and “clean”

• Secrete testicular fluid

• androgens

• Tight junction• Blood-testis

barrier• prevents sperm

antigens from the immune system

Spermatogenesis

Spermatogenesis

• Spermatogenic cell• 64-72 days

Infertility• 1/7 of Americans; most due to sperm

issues• Estrogen-like compounds• Antibiotics (tetracycline)• Compounds that lead to abnormal sperm

• Radiation, marijuana, lack of selenium, alcohol

• Lack of a specific Ca++ channel (for motility)

• Anatomical obstruction• Hormonal imbalance• Oxidative stress (damages DNA)• overheating

Hormonal Regulation• Hypothalamic-

Pituitary-Gonadal Axis• Hypothalamus• Anterior pituitary• Testes

Hypothalamic-Pituitary-Gonadal Axis

• Hypothalamus• GnRH –

gonadotropin releasing hormone

• Stimulates the anterior pituitary

Hypothalamic-Pituitary-Gonadal Axis

• Anterior Pituitary• LH – luteinizing

hormone• Released in response

to GnRH• Stimulates interstitial

cells (Leydig cells) to secrete testosterone

Hypothalamic-Pituitary-Gonadal Axis

• Anterior Pituitary• FSH – follicle

stimulating hormone• Released in response

to GnRH• Stimulates Sertoli

cells• ABP – androgen-

binding protein: Keeps concentration of testosterone high

Hypothalamic-Pituitary-Gonadal Axis

• Testosterone• meiosis of

spermatogenic cells• development and

maintenance of secondary sex characteristics

• Libido• Feed back to

pituitary and hypothalamus

Hypothalamic-Pituitary-Gonadal Axis

• Inhibin• Secreted by Sertoli

cells• produced in

response to sperm count

• Inhibits release of GnRH and FSH

Hypothalamic-Pituitary-Gonadal Axis

• Absence of GnRH, FSH and LH• Testicular atrophy• Accessory organs

atrophy• Testosterone

production declines (or ceases)

Secondary sex characteristics• Pubic and axillary hair• Facial and chest hair• Larynx enlarges• Skin thickens and becomes

oilier• Bones grow and increase

density• Skeletal muscle increases• Basal metabolic rate increases• Development of libido• Brain development

Reproductive System Development

5 weeks•gonadal ridges•Mullerian ducts – female•Wolffian duct – maleGerm cells migrate to gonad

Reproductive System Development

7 weeks – ductus deferens forms•Seminiferous tubules form in gonadal ridges•Join the Wolffian ducts

•Testes secrete MIF – Mullerian Inhibitory factor•Mullerian ducts degenerate

Reproductive System Development

8 weeks – presence of testosterone•Genital tubercle enlarges

• forms penis•Urethral folds fuse

• Forms spongy urethra•Labioscrotal swellings fuse

• Form scrotum

Reproductive System Development

•• At 7 months G stops growing and becomes fibrous• Rapid growth of fetus causes G to pull testis into the

scrotum

Gubernaculum (G) (blue) – connects testis to floor of scrotum