2. Male Reproductive Anatomy

2.1 External Genitalia

  • Penis: urethra, glans, erectile tissue (corpora cavernosa & corpus spongiosum).
  • Scrotum: houses testes; temperature regulation (≈34°C).

2.2 Internal Reproductive Structures

  • Testes: seminiferous tubules (sperm production), Leydig cells (testosterone).
  • Epididymis: sperm maturation & storage.
  • Vas deferens: transport of sperm.
  • Accessory glands:
    • Seminal vesicles (60% semen volume)
    • Prostate gland (enzymes, citrate)
    • Bulbourethral glands (lubrication)

2.3 Blood-Testis Barrier

  • Formed by tight junctions of Sertoli cells.
  • Protects germ cells from immune system.
  • Maintains specialized microenvironment for spermatogenesis.

2.4: Male Sexual Response

  • The main phases of the male sexual response are:
    • erection
    • emission and
    • ejaculation.

2.4.1 Erection

  • Erection results from engorgement of the erectile bodies with blood.
  • Can occur due to conscious sexual thought
  • hypothalamus sacral region of the spinal cord penis), or
  • sensory stimulation: penis spinal cord penis
  • Parasympathetic (S2–S4) → nitric oxide release → vasodilation → erection.
    • Activation of parasympathetic nerves to the penis increases local nitric oxide (NO) release
    • NO results in increased blood flow into and engorgement of the erectile tissues of the penis.
    • This results in an erection, which allows the penis to penetrate the vagina.
  • Inhibited by stress, sympathetic activity.

2.4.2      Emission and Ejaculation

  • Emission is the movement of semen into the urethra
  • Ejaculation is the forceful expulsion of semen from the urethra due to rhythmic contraction of pelvic muscles.
    • Both are under sympathetic nervous system control.
    • Contraction of smooth muscles in the tubules, seminal vesicle, prostate, and muscles at base of penis is involved in ejaculation.
  • Detumescence
    • erection subsides: sympathetic constricts arterioles
    • latent period: new ejaculation not possible (min-hrs)

2.5      Semen

§  Semen, also known as seminal fluid or ejaculate, is the whitish-gray fluid released by males during sexual climax (ejaculation).

§  These fluids originate from the testicles, seminal vesicles, and prostate gland.

§  Function:

o   Semen's primary role is to carry sperm to the female reproductive tract for fertilization.

o   It also provides a nutrient-rich environment for sperm survival and motility.

§  2-5ml/ejaculation contains;

o   60% seminal fluid from seminal vesicles (fructose, amino acids, citric acid, phosphorus, potassium, and prostaglandins)

o   30% prostatic fluid from the prostate gland (citric acid, acid phosphatase, calcium, sodium, zinc, potassium, enzymes, and fibrolysin);

o   10% testicular fluid from testes (50-300million sperm/ml; less than 60 million total = sterile).

§  Characteristics

o   Appearance: Typically grey-opalescent, it initially clots and then liquefies over time.

o   Volume: The average volume is about 1 to 5 milliliters per ejaculate. 

o   Smell/Taste: It can have a chlorine-like or slightly fishy odor and a slightly sweet taste due to fructose.

o   pH: It is slightly alkaline, with a pH range of 7.2 to 7.8, which helps protect sperm in the acidic environment of the vagina.

§  Everyday a healthy adult male produce about 400 million sperm.

2.6    Clinical Note

  • Fertility and sexual function decline with age due to declining levels of sex hormones
  • age 50 men go through a period of physical and psychological change = climacteric
  • older men are also more likely to father children with autism, epilepsy or schizophrenia
  • A sperm count < 20 million/ml semen is called oligospermia and is considered less fertile. May be caused by heat, drugs, or anabolic steroids
  • Erectile dysfunction: vascular, neurogenic, endocrine, or psychogenic causes.