EMBRYOLOGY NOTES-Structure of Sperm

Sperm is the haploid male gamete .Normal sperm has Sperm has three parts ,namely head,middle piece and tail.
(1)  Head - Head contains two structures.
(a) Acroscime                 (b) Nucleus.

Acrosome is a vesicle like double membranous  structure which has hydrolytic enzymes. These  are combinely known as spermlysin. These  enzymes help in penetration of egg. Mammalia  acrosome has mainly hyaluronidase & proacrosine  enzyme. Both are combinely known as acrosomine.  Proacrosine is an inactive enzyme, but when it comes  in contact with egg, it converts into active acrosine.
These membranes of golgibody left on acrosome cap are  called as Galea capitis.
       A space between acrosome & nucleus is known as perforatorium. 
      Volume of nucleoplasm reduces due to compactness. Nucleolus disappear in nucleus of      sperm. According to few scientists Histone are also removed. Histones are replaced by protamines in sperm nucleus. These are the alkaline protein.
 (2) Middle piece- Its anterior part is narrow & called as neck of sperm. It has two centrioles.
      (i) Proximal centriole or anterior knob : Proximal centriole is situated in the base of nucleus in a pit. Proximal centriole stimulate the cleavage in fertilized egg.
      (II) Distal centriole or posterior knob : Distal centriole acts as a basal granule & produces axonema filament. Axonema is surrounded by 9 solid protein fibres in middle piece of sperm.
      In middle piece many mitochondria are arranged spirally around to axonema.
      This spiral sheath of mitochondria around the axonema is known Nebenkern sheath.
      At the end part of middle piece sperm has another centriole which is known ring centrioles. The function of ring centriole is unknown. Basal part of head & middle piece has a thin layer of cytoplasm which is called as Manchette.
(3) Tail - It is a long flagellum, its basal body is distal centriole. Tail is divided into two parts-
      (a) Main piece                                   (b) End piece
      Main piece of axonema surrounded by two solid protein fibres.  A Thin layer of cytoplasm present in main piece of the tail.  End piece of tail consist of only axonema and 9 + 2 arrangement.
In humans sperm formation is completed in 74 days.
 In one ejaculation 4 ml semen have 400 million sperms.
 If sperm count is less = Oligospermia,
 If there are dead sperms = Necrospermia.
 If there are no sperm = Azoospermia.
Shape & size of sperms
(a) SHAPES OF SPERM HEAD:
Spherical head e.g, Teleost fishes
 Lanceolate e.g. Amphibia & Reptilia
 Cork screw (Spiral) e.g. Birds
 Spoon shaped e.g. Mammals (man)
 Hook shaped e.g. Rat
(b) TAIL OF SPERM
Tailless sperm (Non flagellated sperm)
   e.g.   (a)  Ascaris-Amoeboid
             (b) Cray fish (Astacus) – Star shaped
             (c)  Crab & lobster – Small, rod like, apex has three hooks
Toad fish -Biflagellated.
 In Grasshopper and many arthropods. Many heads of sperms are combined and form a sperm boat. After reaching to egg the sperms become separate.
 In Pila - Two types of sperms are found
(1) Eupyrune (one tail)
 (2) Oligopyrene (4-6 tail)
(c) SIZE OF SPERMS
Smallest sperm -Crocodile and Amphioxus (.02 mm).
 Longest sperms of chordata are present in Discoglossus (2mm).
 Longest sperm of Animal kingdom present in Drosophila bifurca (5.8 cm)