Reproduction in lower and higher animals

 

Human Reproduction

Human Male Reproductive System

The human male reproductive system consists of:

• Testes
• Accessory ducts
• Accessory glands
• External genitalia

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I. Primary Sex Organs – Testes

a. Structure and Function

• Testes are a pair of primary sex organs.
• They are mesodermal in origin.
• Their main function is the production of sperms.

b. Location

• Testes are located outside the abdominal cavity in a pouch called the scrotum.

c. Development and Descent

• Testes develop in the abdominal cavity during early foetal life.
• Later, they descend into the scrotal sac through the inguinal canal.

d. Suspension

• Testes are suspended in the scrotal sac by the spermatic cord.

e. Attachment

• Testes are connected to the wall of the scrotum by a short fibromuscular band called the gubernaculum.

f. Shape and Size

• Testes are oval in shape.
• Approximate size:
  • Length: 4–5 cm
  • Width: 2–3 cm

g. Covering

• The outermost covering of the testes is a fibrous membrane called the tunica albuginea.

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II. Accessory Sex Organs

Accessory sex organs include:

• Accessory ducts
• Accessory glands

A. Accessory Ducts

1. Rete Testis

• Seminiferous tubules of the testes form a network of tubules called the rete testis.
• The rete testis opens into the vasa efferentia.

2. Vasa Efferentia

• Vasa efferentia are 12–20 fine tubules.
• They arise from the rete testis.
• They carry sperms from the testes to the epididymis.

3. Epididymis

• Epididymis is a long and highly coiled tube.
• It is differentiated into:
  • Caput (upper part)
  • Corpus (middle part)
  • Cauda epididymis (lower part)
• Sperms undergo maturation in the epididymis.

4. Vas Deferens

• Each vas deferens travels upward into the abdominal cavity.
• It loops over the ureter and opens into the urethra.
• The vas deferens joins the seminal vesicle to form the ejaculatory duct.

5. Ejaculatory Ducts

• Each ejaculatory duct passes through the prostate gland.
• It opens into the urethra.

6. Urethra / Urogenital Duct

• The urethra provides a common passage for urine and semen.
• In males, the urethra is long and extends through the penis.
• It opens outside through the urethral meatus or urethral orifice.

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B. Accessory Glands

The accessory glands associated with the male reproductive system are:

• Seminal vesicles (paired)
• Prostate gland (unpaired)
• Cowper’s glands / Bulbourethral glands (paired)

Functions of Accessory Glands

• Protect gametes
• Facilitate movement of sperms
• Nourish sperms

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III. External Genitalia

A. Penis

• Penis is the male copulatory organ.
• It is cylindrical and muscular.
• It contains three bundles of erectile tissue:
  • Two lateral corpora cavernosa
  • One median corpus spongiosum

Glans Penis

• The swollen tip of the penis is called the glans penis.

Foreskin / Prepuce

• The glans penis is covered by a loose fold of skin called the foreskin or prepuce.

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B. Scrotum

• Scrotum is a loose pouch of pigmented skin located behind the penis.
• It is divided into right and left scrotal sacs by a septum called the tunica dartos.

Functions of Scrotum

• Maintains the testes at a temperature 2–3°C lower than body temperature.
• This lower temperature is necessary for spermatogenesis.

Muscles Involved

• Cremaster muscles and dartos muscles help move the testes closer to or away from the body.

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Cryptorchidism

• Failure of the testes to descend into the scrotum is called cryptorchidism.

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Functions of Male Accessory Glands

I. Seminal Vesicles

• Seminal vesicles are a pair of small fibromuscular pouches present on the posterior side of the urinary bladder.
• They secrete an alkaline seminal fluid containing:
  • Fructose
  • Citric acid
  • Fibrinogen
  • Prostaglandins

Functions

• About 60% of semen volume is formed by seminal fluid.
• Fructose provides energy for sperm movement.
• Fibrinogen helps in coagulation of semen after ejaculation.
• Prostaglandins stimulate reverse peristalsis in the vagina and uterus, helping faster sperm movement toward the egg.

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II. Prostate Gland

• The prostate gland consists of 20–30 lobes.
• It is located below the urinary bladder and surrounds the urethra.
• It secretes a milky white alkaline fluid called prostatic fluid.

Composition

• Contains:
  • Citric acid
  • Acid phosphatase
  • Various enzymes

Functions

• Prostatic fluid forms about 30% of semen volume.
• Acid phosphatase protects sperms from the acidic environment of the vagina.

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III. Cowper’s Glands / Bulbourethral Glands

• These are pea-sized glands located on either side of the membranous urethra.
• They secrete a viscous alkaline mucus-like fluid.

Functions

• Acts as a lubricant during copulation.

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Semen

• Semen is a viscous, alkaline, milky fluid ejaculated by the male reproductive system.
• pH: 7.2–7.7
• Volume per ejaculation: 2.5–4.0 mL
• Contains approximately 400 million sperms.

Functions of Seminal Components

• Fructose → Nourishes sperms
• Calcium and bicarbonates → Neutralize acidity
• Prostaglandins → Activate sperm movement

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Path of Sperm

Seminiferous tubules → Rete testis → Vasa efferentia → Epididymis → Vas deferens → Ejaculatory duct → Urethra

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Prostate Cancer

• Prostate cancer is cancer of the prostate gland.
• Men above 50 years of age with high daily fat consumption have a higher risk.

Symptoms of Prostate Cancer

Early stages usually show no symptoms. Advanced stages may show:

• Weak or slow urinary stream
• Frequent urination, especially at night
• Blood in urine or semen
• Erectile dysfunction (ED)
• Pain in hips, back, chest or ribs
• Weakness or numbness in legs or feet
• Loss of bladder or bowel control

These symptoms are not specific only to prostate cancer and may occur in other conditions.