Spermatogenesis and Oogenesis
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Transcript of 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.
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#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.).
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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..
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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
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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:
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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.
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- #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.
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".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.
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- 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.
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- 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.
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- 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
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- 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.
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- 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.
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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. .
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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.
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%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)
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