Biology Today — January 2018

Post acrosomal sheath

Fibrous sheath

Axial

filament

(9+2 fibrils)

Ring centriole (Annulus)

Head

Neck

Very short, contains proximal centriole and distal centriole.

End piece

The part behind the main piece, consists of

naked filament.

Mitochondrial spiral

Provides energy for the movement of sperm.

Acrosome

Anterior portion of sperm, covered by cap-like structure,

derived from Golgi body of spermatid, contains sperm

lysins, e.g., hyaluronidase, proteolytic enzymes.

Plasma membrane

Envelops the entire body of sperm.

Nucleus

Contains chromosomal material.

Middle piece

Contains mitochondria coiled around axial filament and a

ring centriole at its end.

Tail

Several times longer than head. In its first part called main

piece, the axial filament is surrounded by thin layer of

cytoplasm. Sperm swims about by its tail in fluid medium.

Proximal centriole

Present towards nucleus, takes part in first cleavage of zygote

Distal centriole

Gives rise to axial filament of sperm.

Fig.: Mammalian spermatozoan

HORMONAL CONTROL OF MALE REPRODUCTIVE SYSTEM

• Spermatogenesis starts in male only
  at puberty due to increased secretion
  of gonadotropin-releasing hormone
  from hypothalamus of brain.


• Though the gonadotropic hormones
  secreted by pituitary gland, i.e., FSH
  and LH are named so for their action
  in females, they both are also involved
  in regulating male reproductive
  functions also.


• LH stimulates the Leydig’s cells to
  secrete testosterone and FSH
  stimulates the Sertoli cells to secrete
  androgen binding protein (ABP)
  and inhibin.


• Testosterone and inhibin, in turn exert
  negative feedback inhibition on the
  secretion of LH and FSH respectively.

Hypothalamus

produces GnRH.

Hypothalamus

Anterior

pituitary

gland

GnRH stimulates

release of LH and

FSH from anterior

pituitary gland.

Testosterone inhibits

production of GnRH

and LH.

LH stimulates

interstitial cells

to produce

testosterone.

FSH (and testost-

erone) stimulates

sperm production.

Testosterone stimulates

sperm production.

High sperm count

stimulates production

of inhibin.

Inhibin inhibits the

production of GnRH

and FSH.