Spermatogenesis and Oogenesis

7/18/2019 Spermatogenesis and Oogenesis

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SPERMATOGENESISSPERMATOGENESIS

DefinitionDefinition: It is the different steps by: It is the different steps by

which spermatogonia are transformedwhich spermatogonia are transformed

into spermatozoa in the testis. It beginsinto spermatozoa in the testis. It beginsat puberty (13-16 years) and continuesat puberty (13-16 years) and continues

into old age. he whole process ta!esinto old age. he whole process ta!es

about 6" days.about 6" days.



#permatogenesis#permatogenesis

$ It is a process by which spermatogonia are transformedinto spermatozoa. It begins at puberty.

$ %t birth: germ cells in the male infant present in the se&

cords of the testis are surrounded by supporting cells

(#ertoli cells).$ %t this time the primordial germ cell di'ides to gi'e

spermatogonia.

$ #permatogonia gi'es rise to 1ry spermatocyte.

$ 1ry spermatocyte by 1st meiotic di'ision gi'es nd spermatocyte.

$ nd spermatocyte by nd meiotic di'ision gi'es haploid

spermatids (" in no.).



SpermiogenesisSpermiogenesis - It is the- It is the morphological changesmorphological changes through which the spermatid isthrough which the spermatid is

transformed into atransformed into a spermsperm..



The spermThe sperm

Fig. 8A: rawing showing the main parts

of the human sperm (*1+,). he head

composed mostly of the nucleus is partlyco'ered by the cap li!e acrosome (an

organelle containing enzymes). he tail of

the sperm consists of three regions: he

middle piece principal piece and an end

piece.

#canning electron

micrograph of human

sperms



OOGENESISOOGENESIS

$ ogenesis means differentiation of the

primordial germ cells (oogonia) that are

present in the corte& of the o'ary into

mature o'a. ogenesis passes into two

stages of maturation: prenatal and

postnatal maturation:



1. Prenatata mat!ration1. Prenatata mat!ration

- he primordial germ cells (oogonia) undergomitotic di'isions then they are arranged in clusters

surrounded by a layer of flat epithelial cells.he flat

cells are called follicular cells and are deri'ed from

the epithelium co'ering the o'ary.



- #ome oogonia differentiate into large primary

oocytes where /% replication occurs and they

enter the prophase of the first meiotic di'ision.- he sur'i'ing primary oocytes become

surrounded by flat epithelial cells. ogether they are

called primordial follicles.



".Postnata mat!ration

- /ear birth all the primaryoocytes ha'e started prophase

of the first meiotic di'ision then

they are arrested till puberty.

- he number of primaryoocytes at birth ranges from

0,,,,, to million. %t puberty

only ",,,,, primary oocytes

remain and about ",, only will

be o'ulated during the female

life time.



- ith the onset of puberty +-1+ primordialfollicles begin to maturate with each o'arian cycle.

- he primary oocyte begins to increase in sizeand the surrounding flat cells change from flat tocuboid and proliferate to produce a stratifiedepithelium of granulosa cells.



- he follicle is now called the primary follicle. hegranulosa cells rest on a basement membraneseparating them from the stromal cells of the o'ary

that form the theca folliculi .

- he granulosa cells and the oocyte secrete alayer of glycoprotein on the surface of the oocytecalled the zona pellucida.



- 2luid-filled spaces appear between the granulosacells then they coalesce together forming thefollicular antrum and the follicle is now called the

secondary follicle. .- he follicle enlarges and is called the Graafianfollicle



- he primary oocyte continues the firstmeiotic di'ision leading to two uneualdaughter cells with 3 chromosomes each( autosomes 4 *). he large cell is calledthe secondary oocyte and the small one(ha'ing little cytoplasm) is the first polar

body . he secondary oocyte and the firstpolar body enter the second meiotic di'isionwithout /% replication.

- he second meiotic di'ision is completedonly if fertilization occurs to gi'e fertilizedoocyte (mature ovum) and a second polarbody that soon degenerates.



- he primary oocyte continues the firstmeiotic di'ision leading to two uneualdaughter cells with 3 chromosomes each( autosomes 4 *). he large cell is calledthe secondary oocyte and the small one(ha'ing little cytoplasm) is the first polar

body . he secondary oocyte and the firstpolar body enter the second meiotic di'isionwithout /% replication (2ig. 5).

- he second meiotic di'ision is completedonly if fertilization occurs to gi'e fertilizedoocyte (mature ovum) and a second polarbody that soon degenerates.



The mat!re o#!mThe mat!re o#!m- It is a large o'al cell that

'aries from 110 1" 7 in

diameter. It has two

membranes8 the inner thin

one is the vitelline membrane and the outer one is the zona

pellucida.

- he corona radiata is two

or three layers of cellssurrounding the zona

pellucida e&ternally when the

o'um is shed from the

follicle. .



Fig. 1$: rawings (%-9) illustrating the mo'ement of the uterine tube

that occurs during o'ulation. /ote that the fimbriated infundibulim of

the tube becomes closely applied to the o'ary. Its finger li!e fimbriae

mo'e bac! and forth o'er the o'ary and sweep the secondary oocyte

into the infundibulum as soon as it is e&pelled from the o'arian follicle

and o'ary during o'ulation.



%omparison &et'een the%omparison &et'een the

mae an( femae gametesmae an( femae gametesSperm Oo)*te +o#!m,

- #ize small (+, u) large (110-1" 7)

- obility highly motile immotile

- embranes ------------------ co'ered by zona

pellucida and corona radiata

- 9ytoplasm ;ittle - abundant (contains

yol! granules fornutrition of

the embryo duringthe first

wee! of

de'elopment)

Spermatogenesis and Oogenesis

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