Male Reproductive System Detailed Notes

Organs:
- Urinary bladder
- Ureter
- Large intestine
- Seminal vesicle
- Ejaculatory duct
- Prostate gland
- Urethra
- Corpus cavernosum
- Corpus spongiosum
- Penis
- Bulbourethral gland
- Anus
- Glans penis
- Prepuce
- Epididymis
- Testis
- Scrotum
- Superior pubic ramus (cut)
- Ductus (vas) deferens

Structure:
- Sac of skin, fascia, Dartos muscle, and Cremaster muscle.
- The spermatic cord extends from each testis, containing:
  - Vas deferens (ductus deferens)
  - Testicular arteries and veins
  - Lymphatic vessels
- Each chamber contains a:
  - Gonad (testis) and epididymis.
- Lined with a serous membrane (tunica vaginalis).

Temperature Regulation:
- Important for proper spermatogenesis.
- Cremaster and dartos muscle maintain the temperature of the testicles at approximately $3°C$ cooler than body temperature.
- Cremaster muscle:
  - Regulates the vertical position of the testicles.
- Dartos muscle:
  - Regulates the horizontal position of the testicles.

Function:
- Directs and delivers semen.
- Contains the urethra and erectile tissue.
Structures:
- Corpora cavernosa:
  - Paired.
  - Located dorsally.
  - Enables penile erection.
- Corpus spongiosum:
  - Singular.
  - Located ventrally.
  - Surrounds the urethra.
  - Prevents urethral compression during erection.
  - Expands distally to form the glans penis, which is important for sexual sensation.

Tunics:
- Tunica vaginalis:
  - Serous membrane.
  - Reduces friction.
- Tunica albuginea:
  - Fibrous connective tissue.
  - Provides structural support.
  - Compartmentalizes the testis into lobules.
Seminiferous tubules:
- Ducts made of:
  - Sertoli cells
  - Spermatogenic cells
  - Stem cells.
Sertoli (sustentacular) cells:
- Nourish cells undergoing spermatogenesis.
Leydig (interstitial) cells:
- Located surrounding the seminiferous tubules.
- Produce testosterone.

Hypothalamus releases Gonadotropin-Releasing Hormone (GnRH).
Anterior pituitary releases Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
FSH causes Sertoli cells to release androgen-binding protein (ABP).
LH causes Leydig cells to release testosterone.
ABP concentrates testosterone in the seminiferous tubules.
Testosterone stimulates spermatogenesis.
Testosterone enters the bloodstream and stimulates male sexual characteristics.

Erection:
- Sexual stimulation triggers the parasympathetic nervous system to release nitric oxide (NO).
- Nitric oxide (NO) causes vasodilation of arteries of the corpora cavernosa.
- Vasodilation leads to erection.
Ejaculation:
- The sympathetic nervous system releases norepinephrine (NE).
- Smooth muscle relaxation via NE.
- Smooth muscle contraction.
- Contraction of bulbourethral glands, prostate glands, and seminal vesicles.
- Peristalsis of the epididymis and vas deferens.
- Rhythmic contractions of muscles around the corpus spongiosum.
- Contraction of the internal urethral sphincter.

Testis → Epididymis → Vas deferens → Seminal vesicle → Ejaculatory duct → Prostatic Urethra (within the Prostate Gland) → Membranous Urethra → Penile Urethra → Bulbourethral Gland

Seminal vesicles:
- Produce approximately 60% of semen.
- Provide nourishment and transport media for sperm.
- Contain Fructose for energy.
- Prostaglandins to stimulate smooth muscle contractions in the female reproductive tract.
Prostate gland:
- Produces 20-30% of semen.
- Provides protection.
- Secretes prostatic fluid containing antibiotic enzymes.
Bulbourethral gland (Cowper’s Gland):
- Produces approximately 5% of semen.
- Provides protection and transport media.
- Acts as a pH buffer to approximately 7.5.
- Secretes lubricants.
Sperm:
- Approximately 10% of semen volume.
- Normal concentration: 50-120 million sperm/ml.
- Infertility is likely with sperm concentrations less than 25 million/ml.