pregnancy Flashcards
define the term capacitation
changes in the sperm cell membrane which increase its fluidity allowing the acrosome reaction to occur
outline the journey of the sperm
1 )the sperm are released from the epididymis and travel along the vas deferens out the penis
2) they swim through the cervix and along the lining of the uterus into the oviduct where it meets the secondary oocyte
3) capacitation of the sperm occurs as it moves through the fluid of the uterus
outline the process of capacitaion
1) enzymes in the uterus cause the cell membrane of the sperm to become more permeable to calcium ions
2) this occurs by altering levels of glycoproteins and cholesterol in the sperm membrane
3) the acrosome membrane fuses with the cell surface membrane which starts the release of acrosomal hydrolytic enzymes
outline the process of fertilisation and the acrosome reaction
1) fertilisation occurs at the beginning of the fallopian tube
2) the sperm reaches the secondary oocyte and the acrosome releases proteases which digest the corona radiata and the zona pellucida
outline the cortical reaction
1) the sperm attaches to the membrane of the secondary oocyte and calcium ions make cortical granules fuse with the cell membrane
2) enzymes are released by exocytosis
3) enzymes change the chemical composition of the zona pellucida making it expand and harden forming a fertilisation membrane
4) entry of the sperm head causes the completion of meiosis II forming an ovum and second polar body
5) the nucleus of the ovum fuse with the nucleus of the sperm forming a diploid zygote
what does the cortical reaction ensure
that polysermy doesnt occur
outline the formation of a blastocyst
1) the zygote divides (cleavage) by mitosis to form a solid ball of cells called a morula
2) cleavage continues and the cells move in relation to one another forming a hollow ball of cells called a blastocyst
3) the cells on the outside of the blastocyst are trophoblast and divide to make an inner cell mass
what is a trophoblast
cells forming the outer layer of a blastocyst
outline implantation
1) after around 9 days protrusions from the trophoblast cells called trophoblastic villi penetrate the endometrium which increases the surface area for nutrients
2) the embryo will derive nutrients from the endometrium for the next 2-4 weeks
3) the trophoblast develops into the chorion
4) cells of the chorion move into the trophoblastic villi to form larger chorionic villi
define chorion
the outer membrane surrounding the embryo formed from the development of the trophoblast
what do the cells of the chorion do
they move into the trophoblast villi to form a larger chorionic villi
what are the 5 major roles of the placenta
1) secretion of hormones ie progesterone and oestrogen
2) material exchange ie oxygen, nutrients, waste
3) barrier to high blood pressure and blood born pathogens or toxins in the mothers blood
4) allows maternal antibodies to protect foetus by passive immunity
5) protection from mothers immune system by preventing WBC from the mother entering fetal blood circulation
describe the placental structure
- two umbilical arteries carry fetal blood to the placenta and 1 umbilical vein carries blood back to the fetus
- fetal blood is carried over a large surface area of chorionic villi which have microvilli to increase the area in contact with mothers blood
describe the movement of maternal blood in the placenta
- flows into the intervillous space in the endometrium from the uterine artery and flows out through the uterine vein in a counter-current flow
where does the material exchange between the mother and fetus occur
the chorionic villi
