Embryogenesis part 1

Question 1

What are weeks 1-8 of human pregnancy known as? What happens? What follows embryogenesis?

Answer 1

Embryogenesis/organogenesis, when organ primordia are established; fetal period of continued differentiation and growth

Question 2

After fertilization, what does the zygote undergo? When will blastocyst begin implantation in uterine wall? Without fertilization, what happens to the oocyte?

Answer 2

Cleavage (e.g. morula is multicellular); By the end of the first week; within 24 hours the oocyte degens

Question 3

After which cleavage do cells max contact with each other? What is this process called and what does it entail? What are the cells known as at this point? What happens to the embryo about 3 days after fertilization?

Answer 3

3rd; compaction, when the inner and outer cells begin to segregate; blastomeres; division into a 16-cell morula

Question 4

Given the process of compaction, what do inner cells of morula become? Outer cells? What penetrates the intercellular spaces of ICM, and what is the embyro known as at this point?

Answer 4

Inner cell mass (tissues in embryo proper); trophoblasts (placenta); Fluid, forming a blastocoel; aka a blastocyst

Question 5

What types of cells are in the ICM?

Answer 5

Pluripotent cells, aka embryonic stem cells, giving rise to any cell type in the body

Question 6

What is the difference between totipotent and pluripotent?

Answer 6

Pluripotent cells can divide into any cell type in the body, whereas totipotent cells can differentiate into any cell type including extraembryonic tissue

Question 7

When blastocyst is prepared to implant in the uterine wall, what interacts with what? Around what day does this occur? What does the blastocyst hatch from?

Answer 7

L-selectins on trophoblasts with carbohydrate receptors on uterine epi; approx one week (7th day); the zona pellucida!!

Question 8

What happens if the embryo implants somewhere besides the A or P wall of the uterus? Where can these occur?

Answer 8

Ectopic pregnancy; fallopian tube, cervix, abdominal, Cesarean scar

Question 9

On what day does the trophoblast differentiate into two layers? What are these two layers? Which of these layers continues to expand into uterine wall?

Answer 9

Day 8; cytotrophoblast (inner layer of mononucleated cells) and syncytiotrophoblast (outer multinucleated layer with indistinct cell boundaries); syncytiotrophoblast

Question 10

On what day do ICM cells differentiate? Into what two layers? What do these layers form? What does trophoblast invasion mean?

Answer 10

9; hypoblast and epiblast; flat bilaminar disc; Means uterooplacental circulation (into maternal capillaries)

Question 11

From the blastocyst, what actually will make up the three germ layers? What gives extraembyronic tissues?

Answer 11

Epiblast; hypoblast and trophoblast

Question 12

What are the three goals of gastrulation? When are these three layers made? What does gastrulation first start with?

Answer 12

1. Form endodermal organs by bringing in embryo areas 2. Surround embryo with capable cells for ectoderm 3. Place mesodermal cells in between; third week; primitive streak on surface of epiblast

Question 13

What does the primitive streak become?

Answer 13

Groove with the primitive node surrounding a primitive pit at the cephalic end

Question 14

What happens after primitive streak formation?

Answer 14

Epiblast cells move toward primitive streak, detach from epiblast, and slip beneath the streak (ie invagination)

Question 15

What happens after invagination?

Answer 15

Some cells displace hypoblast (endoderm), some come between epiblast and endoderm to make mesoderm; those remaining in epiblast are ectoderm

Question 16

What does endoderm help form? Mesoderm? Ectoderm?

Answer 16

Lining of gut and other internal organs; Muscle, skeletal system, circulatory system; skin, brain, nervous system, other external tissues

Question 17

If we move the primitive (Hensen’s) node around, what can be established?

Answer 17

New body axis (it’s an ORGANIZER of gastrulation)

Question 18

Define neurulation; when does establishment of body axes occur?

Answer 18

process by which neural plate forms the neural tube; before and during gastrulation

Question 19

Four steps of neurulation?

Answer 19

1. Form and fold neural plate 2. Neural crest elevated 3. Neural folds converge 4. Close neural tube once neural folds are brought into contact with each other

Question 20

What will divide ectoderm? What are the three major domains, and what do they give rise to?

Answer 20

Neurulation; internally positioned neural tube (forms brain and spinal cord), externally positioned surface ectoderm (skin/epidermis), NCC’s will go to new locations to give rise to many cell types

Question 21

How many sites are there for neural tube closure? How does fusion proceed? What happens if you can’t close posterior neuropore? What if you can’t close at the other two sites (ie anterior neuropore)? What happens if you can’t close along the entire neural tube?

Answer 21

3; bidirectionally; Spina bifida; anencephaly; craniorachischisis

Question 22

What can help prevent neural tube defects?

Answer 22

Folic acid (form of folate, the water-soluble B-complex vitamin)

Question 23

What systems can NCC’s have a contribution to?

Answer 23

Neural, skin, teeth, head, fact, heart, endocrine, GI

Question 24

What do NCC’s undergo before migrating to contribute to different tissues?

Answer 24

Epi-to-mesenchymal transition at the dorsal neural tube

Question 25

What are the four regions that neural crests can give rise to along AP axis?

Answer 25

Cranial/cephalic neural crest; cardiac neural crest (septum of cardiac outflow tract and pulmonary artery and aorta separated); trunk (form DRG and symp ganglila); enteric (vagal and sacral): parasymp ganglia of the gut

Question 26

What can human cardiac NCC’s do specifically?

Answer 26

Migrate to pharyngeal arches 3, 4, and 6 and enter the truncus arteriosis (cardiac outflow tract) to generate the septum