Devo Lect 6 - Implantation

Question 2

Blastocyst

Answer 2

Embryo around day 5-7; contains blastocoel, inner cell mass (embryonic stem cells), trophoblast cells (form placenta)

Question 3

Strypsin

Answer 3

Protease released from egg and uterus; breaks open the zona so the embryo can implant

Question 4

Early implantation

Answer 4

Egg releases collagenases which break through ECM of the endometrium of the uterus

Question 5

Placenta previa

Answer 5

Implantation occurs too close to cervix, placenta blocks the birth canal

Question 6

Ectopic pregnancy

Answer 6

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

Question 7

Timing of implantation

Answer 7

The embryo must have hatched, and the uterus must be ready to receive it

Question 8

L-Selectin

Answer 8

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;

Question 9

L-Selectin and IVF possibilities

Answer 9

Perhaps in invitro fertilization embryo doesn’t produce L-selectin,

Question 10

Trophoblast compared to cancer cells?

Answer 10

Secrete VEGF and such angiogenic molecules; invade tissues via enzymes. Cell division is controlled in trophoblast

Question 11

Four possible mechanisms to prevent fetal rejection

Answer 11

1. 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)

Question 12

IDO

Answer 12

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)

Question 13

First animals thought to evolve when? (from reading)

Answer 13

about 540 million years ago in the Cambrian period

Question 14

What is Burgess shale? Why important?

Answer 14

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

Question 15

Can we learn about the development of the animals from the Burgess shale?

Answer 15

Difficult since fossils form best from hard tissues (bone, exoskeleton); young usually don’t have hard shells;

Question 16

Doushantuo formation

Answer 16

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

Question 17

Twin types

Answer 17

Monozygotic: identical; Dizygotic: two eggs released and fertilized

Question 18

What happens when twins divide before day 5?

Answer 18

Two trophoblasts, 2 chorions, 2 amnions

Question 19

What happens when twins divide during day 5-9?

Answer 19

One trophoblasts with 2 inner cell masses, 1 chorion and 2 amnions

Question 20

What happens when twins divide after day 9?

Answer 20

1 chorion, 1 amnion. More likely to have conjoined twins

Question 21

Fetus in fetu

Answer 21

A rare form of conjoined twins where one develops inside the other, usually as a parasite

Question 22

Meroblastic cleavage

Answer 22

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

Question 23

Blastomere, Blastula, Blastocoel, Blastocyst, Blastoderm

Answer 23

Blastomere: name after first cell divisions; Blastula: frog embryo, Blastocoel: fluid filled cavity, all have it; Blastocyst: mammalian embryo; Blastoderm: reptiles and birds embryo

Question 24

Compare blastocyst, blastoderm, blastula** picture it!

Answer 24

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