L1: First week of development Flashcards
what are the primary male sex organs?
the testis (2 in number).
where are the testes?
In the scrotum.
what is the function of testes?
produce sperms and secretes male sex hormone.
what are secondary male sex organs?
the epididymis, the vas deferens, the seminal vesicles, the ejaculatory ducts, the urethra and the accessory glands (seminal vesicle, prostate and bulbourethral glands).
what are male external sex organs?
(scrotum & penis; male copulatory organ).
what are female primary sex organs?
the ovaries (2 in number).
where are the ovaries?
In the pelvis
what is the function of the ovaries?
produce ova and secretes female sex hormones.
what are female secondary sex organs?
Uterine tube, uterus, and vagina
what are female external sex organs?
the vulva
what are the parts of the uterine tube?
formed of 4 parts; infundibulum, ampulla (widest part), isthmus (narrowest part) and intramural part.
The uterus
pear-shaped, lies in the pelvis, formed of 3 parts (fundus, body and cervix) and its wall consists of 3 layers (endometrium, myometrium & perimetrium).
The vagina
acts as female copulatory and birth canal, its upper end surrounds the cervix which divides it into 4 fornices (anterior, posterior, and 2 lateral).
what does a mature sperm consist of?
The mature sperm consists of:
ο· Head:
- Contains nucleus (has the haploid number of chromosomes; 22 X or 22 Y).
- Covered by acrosome (head cap) which contains enzymes for penetration of the coverings of the ovum.
ο· Neck.
ο· Tail: consists of:
- Middle piece (contains mitochondrial sheath which produces energy needed for sperm motility).
- Principal piece (responsible for sperm motility).
- End piece.
what does a mature ovum consist of?
ο Usually released from the ovary in the stage of 2ry oocyte (contains a haploid number of chromosomes; 22X).
ο Surrounded by zona pellucida & corona radiata
what is fertilization?
it is the union of the male and female gametes to form the zygote.
Where does fertilization take place?
In the ampulla.
process of fertilization
deposition
transport of sperms
capacitation
acrosome reaction
Deposition
about 200 β 600 million sperms are deposited in the posterior fornix of the vagina during sexual intercourse
transport of sperms
about 200 β 300 sperms reach the fertilization site while other sperms die.
capacitation
process by which the sperm acquires the capacity to fertilize the ovum and it takes place in the femaleβs genital tract for 7 hours.
what is the mechanism of capacitation?
removal of the seminal plasma proteins from the cell membrane of the head of sperm.
acrosome reaction
process by which the sperm releases the contents of its acrosome and it takes place around the ovum.
what is the mechanism of acrosome reaction?
release of the following substances:
ο Hyal-uronidase enzyme: penetrates the corona radiata.
ο Trypsin-like substance: digest the zona pellucida.
ο Zona lysine: help the sperm to penetrate the zona pellucida
what are the steps of fertilization?
1) Penetration of corona radiata: by hyal-uronidase enzyme.
(2) Penetration of zona pellucida: Trypsin-like substance digests the zona then zona lysine help the sperm to penetrate the zona.
(3) Fusion of the cell membrane of the sperm and ovum: while the head and tail enter the oocyte.
(4) Zona reaction: once the sperm penetrates the zona this reaction occurs make the zona pellucida impermeable to other sperms.
(5) Completion of the 2nd meiotic division: after entry of the sperm the oocyte completes the 2nd meiotic division to give mature ovum (female pronucleus) and 2nd polar body.
(6) Formation of male pro-nucleus: by the nucleus of the sperm.
(7) Union of the pro-nuclei: to form zygote with 46 chromosomes
what are the results of fertilization?
- The 2ry oocyte completes the 2nd meiotic division.
- Restoration of the diploid number of chromosomes.
- Determination of the sex of the embryo (if the sperm is Y male and if the sperm is X female).
- Determination of the state of health and disease of the embryo.
- The zygote starts cell division (cleavage).
what is dispermy(triploidy)?
it is the fertilization of the ovum with two sperms (69 chromosomes)
what is parthenogenesis?
it is the dividing of the ovum to form the zygote.
what is cleavage?
repeated mitotic divisions of the zygote to increase the number of cells (blastomeres).
what is the site of cleavage?
during passage of the zygote in the uterine tube towards the uterus.
what are the steps of cleavage?
- Repeated cell division: the zygote gives 2 then 4 then 8 blastomeres.
- Formation of morula: after 3 days 16 β 32 blastomeres are formed. They are surrounded by zona pellucida which has the following functions:
ο Keep the dividing cells together.
ο Prevent adhesion between the dividing cells and the uterine tube. - The morula reaches the uterine cavity: about the 4th β 5th day.
- Formation of blastula (blastocyst):
- Small cavities filled with fluid (from the uterine cavity) appear in between the dividing cells.
- The cavities fuse together to form one large cavity (Blastocele), which separates the blastomeres into 2 groups:
ο· Trophoblast: thin outer layer which will form the fetal part of the placenta.
ο· Inner cell mass: an inner group of cells that will give rise to the embryo.
ο The zona pellucida degenerates and disappears.
