Devo Lect 6 - Implantation Flashcards
(23 cards)
Blastocyst
Embryo around day 5-7; contains blastocoel, inner cell mass (embryonic stem cells), trophoblast cells (form placenta)
Strypsin
Protease released from egg and uterus; breaks open the zona so the embryo can implant
Early implantation
Egg releases collagenases which break through ECM of the endometrium of the uterus
Placenta previa
Implantation occurs too close to cervix, placenta blocks the birth canal
Ectopic pregnancy
Implantation occurs not in uterus; in ovary; in abdomen (falls out); in oviduct; in deeper tissue of uterus; usually placenta doesn’t form so it gets reabsorbed
Timing of implantation
The embryo must have hatched, and the uterus must be ready to receive it
L-Selectin
Cell adhesin molecule found in leukocyte, allows them to adhere to capillary wall and roll; also found on embryo and binds to oligosaccharide in uterine wall; levels increase a lot after hatching;
L-Selectin and IVF possibilities
Perhaps in invitro fertilization embryo doesn’t produce L-selectin,
Trophoblast compared to cancer cells?
Secrete VEGF and such angiogenic molecules; invade tissues via enzymes. Cell division is controlled in trophoblast
Four possible mechanisms to prevent fetal rejection
- Anatomical separation; false. 2. Antigenic immaturity of embryo; kinda true, not developed early but will later. 3. Immunological tolerance of mother; true, mother suppresses their own immune cells. 4. Fetal tissue actively suppresses mother’s immune system; true (IDO)
IDO
Indolamine dioxygenase, breaks down tryptophan; Trp is limiting for T cells in mother; IDO needed for normal pregnancies so that the blastocyst is not rejected by the mother’s immune system (mouse experiment)
First animals thought to evolve when? (from reading)
about 540 million years ago in the Cambrian period
What is Burgess shale? Why important?
Best studied fossil bed; gives much insight into the early life of animals, many unique body plans in fossils of segmented vertebrates; many of them now extinct
Can we learn about the development of the animals from the Burgess shale?
Difficult since fossils form best from hard tissues (bone, exoskeleton); young usually don’t have hard shells;
Doushantuo formation
about 580 million years old; scientists discovered early embryos; easier to find these soft tissues because of phosphate levels in the region; embryos with smaller and smaller cells in the same size of envelope, early animal embryos; leads to paleoembryology
Twin types
Monozygotic: identical; Dizygotic: two eggs released and fertilized
What happens when twins divide before day 5?
Two trophoblasts, 2 chorions, 2 amnions
What happens when twins divide during day 5-9?
One trophoblasts with 2 inner cell masses, 1 chorion and 2 amnions
What happens when twins divide after day 9?
1 chorion, 1 amnion. More likely to have conjoined twins
Fetus in fetu
A rare form of conjoined twins where one develops inside the other, usually as a parasite
Meroblastic cleavage
Discoidal cleavage, birds, fish, reptiles; telolecithal eggs, early cell divisions occur on one side until they reach all the way around the yolk. Small patch divides, forms a blastocoel, top of it is called epiblast, bottom is hypoblast. Name of embryo is blastoderm
Blastomere, Blastula, Blastocoel, Blastocyst, Blastoderm
Blastomere: name after first cell divisions; Blastula: frog embryo, Blastocoel: fluid filled cavity, all have it; Blastocyst: mammalian embryo; Blastoderm: reptiles and birds embryo
Compare blastocyst, blastoderm, blastula** picture it!
Blastula and blastocyst are both hollow balls of cells; blastula has grey crescent; blastocyst has an inner cell mass; blastoderm is a disc on top
