3rd lecture morphological changes during maturation o te gametea

7/27/2019 3rd Lecture Morphological Changes During Maturation o Te Gametea

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Morphological changes

duringmaturation of the gametes

Dr. Eman khammas al-sadi

Embryology lecturer


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Maturation of the oocyte begins before birth:

Once the primordial germ cells have arrived in the gonads of the genetically female

1- they differentiate in to oogonia & undergoes no. of mitotic divisions

3- by the end of the3rd month are Arrange in clusters surrounded by a layer of

epithelial cells.


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At4 month

The majority of oogonia continue to divide by mitosis, but some ofthem differentiate in to much larger primary oocyte,Immediately

they replicate their DNA and enter the prophase of the 1st

meioticdivision

by the 5th mont: Oogonia increase in number&reaches its maximum (7million) At this time many oogonias become etretic as well asprimary oocytes.


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By 7mo.

The majority of oogonias have degenerate except few near thesurface ,

All surviving primary oocyte have entered the 1st meiotic division

,most of them are surrounded by a layer of flat epithelial cells

primordial follicle

The primary oocyte, together with it is surrounding flat

epithelium, is known as aprimordial follicle


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At birth:

((oocyte have entered the diplotine stage of prophase)), in

which they remain until (just before ovulation) at the puberty

when only then do they enter. metaphase of the 1st meiotic

division).


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the gowing follicle

the follicular cells become cuboidal & begin to secrete the zuna

pellucida,(irregular patches on the surface of the oocyte).

(primary follicle),

the follicular cells form a stratified layer of granulosa cells&the zuna

pellucida is well defined


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Maturing follicle1-The oocyte surrounded by the zuna pellucida, the follicle is off-

center=(the antrum) which has developed by fluid accumulation

between intercellular spaces.

3- charectrized by the arrangement of cells of the (theca interna&

theca externa.)


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Mature vesicular or graffian follicle1- the antrum

A-has been enlarged considerably, filled with follicular fluidsurrounded by stratified layer of granulosa cells.

2- the oocyte is embedded in amount of granulosa cells, the cumulus

oophorus


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Week 1 and 2 Human Development Overview

An overview of development of following fertilization during the first week and into

the second week of development. The first week of development occurs floating

freely within the uterine tube and body.

Note the timing is only approximate, it is the sequence of events that is importantto understand.

Day 14 of menstrual cycle - Oocyte released from ovary about the midpoint of the

menstrual cycle.

Day 0 - The haploid oocyte and spermatozoa fuse at fertilization to form a diploidzygote, the first cell. Fertilization occurring generally in the first third of the uterine

tube (uterine horn, fallopian tube).

Day 1 to 3 - Cell division by mitosis forming a solid ball of cells, the morula.

Day 3 to 5 - Cell compaction forming a fluid-filled space and two cell populations,

the blastocyst (1-chambered conceptus).

Day 5 to 7 - blastocyst "hatches" from the surrounding zona pellucida.

Day 7 to 9 - Implantation commences and continues through the second week of

development.
http://php.med.unsw.edu.au/embryology/index.php?title=Oocyte_Developmenthttp://php.med.unsw.edu.au/embryology/index.php?title=Menstrual_Cyclehttp://php.med.unsw.edu.au/embryology/index.php?title=Oocyte_Developmenthttp://php.med.unsw.edu.au/embryology/index.php?title=Spermatozoahttp://php.med.unsw.edu.au/embryology/index.php?title=Fertilizationhttp://php.med.unsw.edu.au/embryology/index.php?title=Zygotehttp://php.med.unsw.edu.au/embryology/index.php?title=Cell_Division_-_Mitosishttp://php.med.unsw.edu.au/embryology/index.php?title=Morulahttp://php.med.unsw.edu.au/embryology/index.php?title=Blastocysthttp://php.med.unsw.edu.au/embryology/index.php?title=Blastocysthttp://php.med.unsw.edu.au/embryology/index.php?title=Zona_pellucidahttp://php.med.unsw.edu.au/embryology/index.php?title=Implantationhttp://php.med.unsw.edu.au/embryology/index.php?title=Week_2http://php.med.unsw.edu.au/embryology/index.php?title=Week_2http://php.med.unsw.edu.au/embryology/index.php?title=Implantationhttp://php.med.unsw.edu.au/embryology/index.php?title=Zona_pellucidahttp://php.med.unsw.edu.au/embryology/index.php?title=Blastocysthttp://php.med.unsw.edu.au/embryology/index.php?title=Blastocysthttp://php.med.unsw.edu.au/embryology/index.php?title=Morulahttp://php.med.unsw.edu.au/embryology/index.php?title=Cell_Division_-_Mitosishttp://php.med.unsw.edu.au/embryology/index.php?title=Zygotehttp://php.med.unsw.edu.au/embryology/index.php?title=Fertilizationhttp://php.med.unsw.edu.au/embryology/index.php?title=Spermatozoahttp://php.med.unsw.edu.au/embryology/index.php?title=Oocyte_Developmenthttp://php.med.unsw.edu.au/embryology/index.php?title=Menstrual_Cyclehttp://php.med.unsw.edu.au/embryology/index.php?title=Oocyte_Development


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Maturation of the oocyte continue at

pubertyPrimary oocyte remain in the diplotene stage of the prophase &

do not finish their 1st meiotic division before puberty is reached

at birth

Primary oocyte(700,000-2 million)

At puberty(400,000) will remain

500 only will be ovulated.

Some oocyte remain 40 yrs or more before they reach maturation

so it may increase risk of chromosomal abnormalities


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At puberty1. 5-15 primordial follicles begin to mature with each ovarian cycle.

Continue to grow forming the primary follicle

2. granulosa cells rest on a basement membrane separating themfrom surrounding stromal cells that form the theca folliculi)

1. Inner layer: secretary cells theca interna

2. outer layer: connective tissue containing fibroblast-like

cells, the theca externa.

3. Small, finger-like processes of follicular cells extend across

the zuna pellucida. these are important for transport of

materials from follicular cells to the oocyte.

3. both (granulosa cells & the oocyte) will secrete a layer ofglycoproteins on the surface of the oocyte, forming the( zuna

pellucida)

4. The Follicle called secondary follicle when contain the antrum.

&cumulus oophorus


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At maturity :

The follicle which may be 10mm or more in diameter is

called tertiary or vesicular or graffian follicle:Surrounded

by

1- theca interna:

A-cch. By steroid secretion,

B-rich in blood vessels.2-theca externa which gradually merges with the ovarian

stroma.

With each ovarian cycle a number of follicles begin to

develop, but usually only one reaches maturity. Others

degenerate and become atretic


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The 1st meiotic division resumes shortly before

ovulation, then enter meiosis2

ovulation occurwhen the2ndry oocyte show

spindle formation & the oocyte shed from the

ovary

meiosis 2 completed only if the oocyte is fertilized:

otherwise, the cell degenerates approximately 24

hrs after ovulation


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Spermatogenesis: Maturation of the sperms starts at puberty:

At birth

germ cells :in the sex cord of the testis as, large, pale cellssurrounded by supporting cells which become Sertoli cells.

Shortly before puberty

the sex cords acquire a lumen &become the seminiferous

tubules.

at same time the primordial germ cells give rise tospermatogonia which consist of 2 types:


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Types of spermatozoa:2types Type A

divided by mitosis, to provide continuous reserve of stem cells Type B

Spermatogonia give rise to primary spermatocytes

I l t


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In normal eventssome of type A cells

leave the stem population & give rise to successive

generations of spermatogonia each more

differentiated than the last

on completion of type B spermatigonia form

When these cells undergoes mitosis

primary spermatocyte are created


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Primary spermatocyte enter the prolonged prophase(22 days )

followed by rapid completion of meiosis1 & the formation of 2ndry

spermatocytes

During the 2nd meiotic division these cells immediately begin to form haploid

spermatids


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They are embedded in deep recesses of Sertoli cells through out theirdevelopment

Functions of Sertoli cells are:

1-support & protect the germ cells

2-participate in their nutrition.

3-assist in release of mature spermatozoa.


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spermatogenesis

The series of changes resulting in the

transformation of spermatids intospermatozoa

spermatogenesis which includes:

1-formation of acrosome, which covers halfof the nuclear surface & contains enzymes

to assist in penetration of the egg & it is

surrounding layers during fertilization

2- shedding of the most of the cytoplasm.


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In human the time required for a spermatogonium to develop in to a

mature spermatozoon is approximately 74 days.When fully developed

spermatozoa enters the lumen of the seminiferous tubules, then to the

epididymis by contractile elements in the wall of the seminiferous

tubules.

Although initially only slightly motile, spermatozoa obtain full motility inthe epididymis.


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Abnormal germ cells

1. In human one ovarian follicle occasionally

contains 2 or 3 clearly distinguishableprimary oocyte, they usually degeneratebefore reaching maturity

2. In rare cases one primary oocyte contain 2 oreven 3 nuclei, they die before reachingmaturity.


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Abnormal spermatozoa1-are seen frequently,& up to10% of all spermatozoa have observable

defects

2-The head, or the tail may be abnormal

3-May be giant or dwarf.

4-Or may be joined.

5-They usually lack normal motility

6-Probably not fertilize oocyte.


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Thank you

3rd lecture morphological changes during maturation o te gametea

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