OVULATION & OVUM

STD-12      UNIT-6     CHA-3

HUMAN REPRODUCTION

OVULATION & OVUM

OVULATION

• In humans , ovum is released from the ovary in the secondary oocyte stage . 
• Thus in human being , ovulation is the release of the secondary oocyte from the ovary 
• The wall of the ovary gets ruptured to release the oocyte . 
• In humans ovulation occurs about 14 days before the onset of the next menstruation . 
• Ovulation is induced by LH . 
• The maturation of the ovum is completed in the mother's Fallopian tube usually after the sperm has entered the secondary oocyte during fertilization . 

OVUM

• The mature ovum or a female gamete is spherical in shape . 
• The human ovum is almost free of yolk and is said to be alecithal . 
• Its cytoplasm is called ooplasm containing largenucleus , termed the germinal vesicle . 

• The nucleus contains a prominent nucleolus . 
• There are no centrioles in the ovum . 
• The cytoplasm is enveloped by the plasma membrane ( cell mem brane ) .
• Very small vesicles called cortical granules are present under the plasma membrane .
• A narrow perivitelline space is present outside the plasma membrane .
• Just outer lo perivitelline space , there is thick , acellular zona pellucida probably secreted by the follicular cells . 
• Outer to the zona pellucida there is very thick cellular corona radiata . 
• The latter is formed of radially elongated follicular cells . 
• The side of ovum which extrudes polar bodies is termed as animal pole . The opposite side is called vegetal pole . 
• Human ovum ( egg ) loses its ability to be fertilized about 24 hours after ovulation . 
• In human beings ovum is released from the ovary as secondary oocyte 

Similarities in Spermatogenesis and Oogenesis 

• Both processes consist of three main phases , viz . multiplication , growth and matu ration phases.
• In multiplication phase , the primordial germ cells of testes and ovaries proliferate mitotically , forming numerous gametogonia (spermatogonia/oogonia ) in both processes . 
• In the growth phase , the cells accumulate food reserves and grow to primary gametocytes (spermatocytes / oocytes ) in both processes . 
• Maturation phase in both processes comprises two successive divisions , first meiotic and second meiotic , resulting in the formation of secondary gametocytes and gametes respectively .

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