Early Development Lecture Sep 27

Question 1

WHere does implantation usually occur?

Answer 1

the superior posterior wall of the uterine cavity, but implantation can occur at other abnormal sites

Question 2

WHat are the two possible causes of twinning during development?

Answer 2

1. 2 eggs released in ovulation and fertilized (non-identical)
2. Separation of pluripotent inner cell mass resulting in the production of two genetically identical fetuses

Question 3

What two major developmental events occur when the embryo is in the morula stage?

Answer 3

1. Formation of inner and outer cells
2. Compation - tight junctions and gap junctions form between adjacent blastomers and cells flatten together to form a tight ball.

Question 4

What adhesion molecules have a big role in compaction?

Answer 4

cadherins

Question 5

what does a blastocyst have that a morula doesn’t?

Answer 5

a blastocoel - a fluid-filled space

Question 6

What happens when the embryo implants in the uterine epithelial lining?

What has to happen to the embryo before that can occur.

Answer 6

THe embryo first has to hatch out of the zona pellucida.

Then part of the outer trophoblast cells fuse together to form the syncytriotrophoblast, which invades the epithelial tissue.

Question 7

What are two things improper implantation can cause?

Answer 7

ectopic pregnancy

placenta previa

Question 8

What hormone does the syncriotrophoblast does to signal for continued secretion of estrogen and progesteron by the corpus luteum?

What effect does this happen?

Answer 8

Human chorionic gonadotropin (HCG)

It represses sloughing of the endometrium and maintains the pregnancy

Question 9

What happens in the decidual reactions?

Answer 9

The invasion of synctriotropobloast into the endometrium treiggers a reaction by the uterine stromal cells to swell and accumulate glycogen and lipid.

The transformed cells are called decidual cells and they’ll form a distinct layer that surrounds the torphoblast called the decidue.

This may serve as a protection of the fetus from mother immune attack

Question 10

What does delamination result in?

Answer 10

The inner cell mass cells pull away from the adjacent trophectoderm to form a fluid space called the amniotic cavity

Question 11

The inner cell mass cells flatten and form two layers of cells. WHat are the layers?

Answer 11

1. epiblast (the cells closest to the amniotic cavity - they’re tall and columnar)
2. Hypoblast (cuboidal)

Question 12

THe hypoglast cells proliferate and extend below the embryonic disc to enclose a space known as what?

Answer 12

the yolk sac

Question 13

What calles form the connecting stalk which will eventually become the umbilical cord?

Answer 13

cells that break off the wall of the primary yolk sac to fill the space between the yolk sac and trophoglast (they are called extraembryonic mesoderm cells)

Question 14

What is the first sign of gastrulation?

Answer 14

The development of the primitive streak and node.

This is from cells that proliferate and migrate to the midline of the epiblast

Question 15

How are the mesoderm and endoderm formed?

Answer 15

THe primitive streak of the epiblast invaginates and as cells from the epiblast moves toward the streak, they will be laid down between the hyphoblast and the epiblast - first the endoderm and then th emesoderm

Question 16

Cells that remain in the epiblast after gastrulation are called what?

Answer 16

ectoderm

Question 17

How does the notochord develop?

Answer 17

Many cells which migrate through the primitive node will descend into the mesoderm and then migrate rostrally and form a thick cord ot cells called the notochord.

The notochord is important for mechanical support and as an inducer ot nervous system development.

Question 18

How does neurulation occur?

Answer 18

Ectoderm cells directly over the notochord are induced to proliferate and form a thickening called the neural plate

the neural plate begins to buckle and form the neural folds

the neural folds curve around and fuse with the opposite side to form a tube, called the neural tube.

the neural tube is then completely surrounded by ectoderm.

Question 19

What do neural crest cells eventually develop into?

Answer 19

They are sometimes called thd 4th germ layer because they develop into spinal and autonomic ganglia, schwann cells, the meninges, adrenal medulla and malanoctyes

Question 20

What are the two major subdivision of mesoderm?

Whichin one of the mesoderms, what are the sub categories?

Answer 20

1. extraembryonic mesoderm
2. Embryonic mesoderm (arises from the epiblast)

THe embryonic mesoderm is further divided by the third and fourth week ino:

paraxial mesoderm

intermediate

lateral mesoderm

Question 21

What gives rise to somites? what are somites?

What do the somites give rise to?

Answer 21

THe paraxial mesoderm has two thickenings near the notochord/neural tube

they form in pairs (we usually get about 42-44)

They give rise to most of the axial skeleton and associated musculatur and adjacent dermis of the skin

Question 22

What will the intermediate mesoderm participate in the formation of?

Answer 22

the urogenital system

Question 23

What happens to the lateral mesoderm?

Answer 23

the lateral mesoderm will begin to display fluid spaces which will coalesce to split the lateral mesoderm into dorsal and vental wings

the dorsal wing is called somatic mesoderm (this will help form lateral and bentral bodywall.

THe ventral wings, or splanchnic mesoderm, will surrounde the gut and form mesentery.

Question 24

the fluid-filled space that separates the two leaves of lateral mesoderm are called what?

Answer 24

coelom

Question 25

Where do blood cells and blood vessels begin to form during the 3rd week. What is this process called?

Answer 25

Angiogenesis occurs in the extraembryonic locations, specifically the yolk sac, extraembronic mesoderm, connecting stalk and chorion

most start out as blood islands on the surface of the yolk sac.

Question 26

what does embronic cirulation begin?

Answer 26

end of the 3rd week

Question 27

how is the heart brought to its adult location during development?

Answer 27

the cephalo-caudal folding that occurs in week 4

Question 28

Embryo FOlding is extremeley important for these three reasons:

Answer 28

1. It converts the three flat germ layers into a cylinder of central endoderm, medial mesoderm, and peripheral ectoderm
2. it seals off the intraembryonic coelom from extraembyronic coelom, and…
3. rolls endoderm into the tubular gut, surrounded by mesentary and forms the ventral body wall

Question 29

As the lateral wings of the somatic mesoderm extend ventrally to pinc the yolk sac into a narrow projection, what does the yolk sac eventually become?

Answer 29

It developes into the umbilical cord (this, it includes the connecting stalk)

Question 30

What will the somatic mesoderm (dorsal layer) give rise to?

Answer 30

the ventral body wall,

parietal pritoneam

blood vessels

limbs

Question 31

what will the splanchnic mesoderm generate?

Answer 31

adrenal cortex, visceral peritneum, heart and blood vessle

Question 32

What will the ectoderm form?

Answer 32

epidermis, hair, nails, cutaneous and mammary glands, CNS and PNS

Question 33

What does the paraxial mesoderm develop into?

Answer 33

muscles of the head,

trunk

limbs

axial skeleton

dermis

connective tissue

Question 34

what will the endoderm develop into?

Answer 34

epithelium of lung, bladder and gastrointestinal tract

glands associated with GI tract (like liver and pancreas)