Male Reproductive System: Structure, Function, and Evolution

Posted on Mar 21, 2025 in Biology

Male Reproductive System: Structure and Function

Solution:

Male Reproductive System

The male reproductive system has two main parts: the reproductive organs and accessory glands. The main organ, or male gonad, is the testis, which is located in the scrotum.

  1. Scrotum: The scrotum is a pouch of pigmented skin arising from the lower abdominal wall. It protects the testes and acts as a thermoregulator.
  2. Testes: Testes are the primary sex organs and are extra-abdominal in position. Each testis contains about 200 to 300 lobules composed of germinal epithelial cells. Seminiferous tubules consist of spermatogonia (sperm mother cells) and nurse cells (Sertoli cells). Interstitial cells, or Leydig cells, secrete the hormone testosterone after puberty.
  3. Vasa Efferentia: Vasa efferentia are a pair of ducts that start from the rete testis and enter the epididymis.
  4. Epididymis: The epididymis is a paired structure with a highly coiled duct about 6 meters long, situated on the posterior border of each testis. It is differentiated into three regions:
    • Caput epididymis: The upper, wider head that receives the vasa efferentia. Here, sperm undergo physiological maturation, acquiring increased motility and fertilizing capacity.
    • Corpus epididymis: The middle, narrower body.
    • Cauda epididymis: The lower duct or tail. Sperm remain in the tail for a short period before entering the vas deferens.
  5. Vasa Deferentia: A pair of tubular structures, about 40 cm long, arising from the cauda epididymis.
  6. Ejaculatory Duct: The duct of the vas deferens and a duct of the seminal vesicle form the ejaculatory ducts. Both ejaculatory ducts open into the urethra near the prostate gland. The ejaculatory duct carries seminal fluid containing sperm to the urethra.
  7. Urethra: The urethra has three parts: the prostatic urethra, the membranous urethra, and the penile urethra. The urethra carries both urine and semen.
  8. Penis: The penis is the copulatory organ used for insemination, or the deposition of sperm in the female genital tract. The urethra passes through the length of the penis.

Accessory Sex Glands

  1. Seminal Vesicles: Two small fibromuscular pouches located on the posterior side of the urinary bladder. They have seminal ducts that join with the vas deferens to form the ejaculatory ducts. Seminal fluid secreted by the seminal vesicles makes up about 60% of the total volume of semen.
  2. Prostate Gland: Secretes prostatic fluid, which makes up about 30% of the total volume of semen. Prostatic fluid is a whitish, alkaline liquid that neutralizes the acidity of vaginal secretions.
  3. Cowper’s Glands (Bulbourethral Glands): Pea-sized glands situated on either side of the membranous urethra. They secrete an alkaline, viscous fluid.

Diagram of the male reproductive system

Structure and Function of the Lac Operon

Solution:
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Lac Operon

The lac operon (where “lac” refers to lactose) is a polycistronic structural gene regulated by a common promoter and regulatory genes. This arrangement is common in bacteria and is referred to as an operon. The lac operon consists of:

  1. One regulatory gene (the i gene – where “i” is derived from the word “inhibitor”)
  2. Three structural genes (z, y, and a).

Functions:

  1. The i gene codes for the repressor of the lac operon.
  2. The z gene codes for beta-galactosidase (β-gal), which is primarily responsible for the hydrolysis of the disaccharide lactose into its monomeric units, galactose and glucose.
  3. The y gene codes for permease, which increases the permeability of the cell to β-galactosides.
  4. The a gene encodes a transacetylase.

All three gene products in the lac operon are required for lactose metabolism. In most other operons as well, the genes present in the operon are needed together to function in the same or related metabolic pathway.

Origin and Evolution of Man

Solution:
  • The origin of human beings is called human evolution.
  • All human beings belong to the same species, Homo sapiens.
  • The species originated in Africa and spread to different parts of the world (proven by fossils obtained in Africa).

Stages of Human Evolution

  1. Parapithecus: An Oligocene fossil from the Fayum province in Egypt.
    • About the size of a squirrel.
    • Adapted to running and leaping.
    • Ancestors of Old World monkeys.
  2. Aegyptopithecus: Larger in size, canopy dwellers, and had a tail.
    • Forerunners of Dryopithecus.
  3. Dryopithecus: A common ancestor of humans and apes.
    • Semi-erect posture with similarly sized hind limbs and forelimbs.
    • Hands and skull were monkey-like; forehead like humans.
  4. Ramapithecus: The earliest human-like primates.
    • Walked on legs.
    • Fossils reported from Africa, Hungary, and Greece.
  5. Australopithecus: More human-like below the neck and ape-like above the neck.
    • Cranial capacity: 400-600 cubic cm.
    • Larger brain size compared to body size.
    • Incisors were vertical, and canines were spatulate.
    • Ilium was broad, and the foot was arched, indicating bipedalism and running.
  6. Homo habilis: This early true man had perfect bipedal locomotion; height: 150 cm, weight: 40-50 kg.
    • Cranial capacity: 680 cubic cm.
    • Used chipped stone tools.
    • Carnivorous-omnivore who hunted small animals.
    • Male to female ratio: 1:2.
  7. Homo erectus: Walked erect on long legs; height: 150 cm.
    • Brain size: 775 to 1225 cubic cm.
    • Prognathous face with prominent brow ridges.
    • No chin, massive jaws, and large teeth.
    • First hominid to move out of Africa.
  8. Homo sapiens: The parent species to which modern man belongs.
    • Evolved from H. erectus in Africa.
    • Developed three subspecies:
      • Neanderthal Man
      • Cro-Magnon Man
      • Modern Man
    • Modern man evolved 25,000 years ago.
    • Moved to different parts of the world about 10,000 to 11,000 years ago.
    • Man has undergone cultural evolution: Paleolithic Age, Mesolithic Age, Bronze Age, Iron Age, etc.