Lecture 17- Development II

Question 1

What happens to the cell cycle after cleavage?

Answer 1

The cell cycle resumes normal functions. Cell division slows.

Question 2

Morphanogenesis

Answer 2

Cellular & tissue-based process by which animal body takes shape. Occurs during gastrulation and organogenesis.

Question 3

Gastrulation

Answer 3

Hollow blastula becomes gastrula (layered embryo)
3 germ layers:
Ectoderm
Endoderm
Mesoderm

Question 4

Gastrulation in Sea Urchins

Answer 4

Involves cell migration, invagination- infolding
Forms archenteron- early gut tube
Blastopore- open end of archenteron- becomes anus
2nd opening becomes mouth
Cells at vegetal pole (bottom) migrate into blastocoel
Vegetal plate forms-> cells flatten, fold inwards
Archenteron forms-> cells at tip extend toward opposite wall, contact opposite wall
Archenteron fuses with blastocoel wall-> digestive tube formed. present: 3 germ layers
mouth
anus
cilia

Question 5

Gastrulation in Birds

Answer 5

Doesn’t occur like we see in echinoderms because there is too much yolk. Instead we have an active cap where gastrulation takes place. Meroblastic cleavage.

2 layers in active cap: Hypoblast and epiblast
(Epiblast is on outer part, furthest from egg, hypoblast is closest to egg)

Epiblast cells migrate inward. They either go up and push the hypoblast (becomes endoderm), move laterally and go to the sides (becomes mesoderm), or stay at the bottom of the epiblast (becomes ectoderm).

Question 6

Primitive Streak

Answer 6

Blastopore, directs movements associated with gastrulation

Question 7

Involution

Answer 7

Cell Migration

Question 8

Hypoblast Cells

Answer 8

Contribute to sac around yolk
Connection between yolk and embryo
Do not contribute to embryo itself

Question 9

Gastrulation in Humans

Answer 9

End of cleavage-> blastocyst has formed
Mammalian version of blastula
Arrive at uterus ~6 days after fertilization

Blastocyst
100 cells around central cavity
Trophoblast: Outer single layer of cells
Inner cell mass: Cluster of cells. The inner cell mass becomes the embryo, and is the source of embryonic cell lines.

Implantation
Trophoblast contacts uterine lining- secretes enzymes
-> Erode area of endometrium
-> Embryo penetrates
-> Thickens, extends projections into endometrium

Gastrulation
Takes 1 week- 2nd-3rd week of pregnancy
Inner cell mass forms flat disc- 2 layers (Epiblast and Hypoblast)

Cell Fates
Some epiblast stays in place
-> Ectoderm
Some epiblast migrates in between
-> Mesoderm
Some epiblast migrates & mixes with hypoblast
-> Endoderm

Human Gastrula
3 layers
- Ectoderm
- Endoderm
- Mesoderm
Also contains extraembryonic membranes: Chorion, amnion, yolk sac, allantois
Functions:
- Contain fluid
- Form blood vessels (Gas exchange, food/waste)

Question 10

Organogenesis (basic)

Answer 10

Process of organ formation
Embryo begins to increase in size
Nervous system 1st to develop in most vertebrates

Question 11

Neurulation

Answer 11

Process of forming nervous system
Cells of dorsal mesoderm (notochord) induce dorsal ectoderm to flatten and thicken.
Dorsal ectoderm becomes neural plate, then folds inward to become neural tube
Becomes central nervous system. Anterior portion is brain, and remainder is spinal cord.
Folic acid deficiency can cause problems with development.

Question 12

Cells of neural crest

Answer 12

Form nerves, teeth, and skull bones

Question 13

Somites

Answer 13

Blocks of mesoderm cells lateral to notochord
- Segmented/serially repeated structures
- Ribs, vertebrae, associated muscles

Question 14

Early Human Development

Answer 14

Most radical changes for mother and embryo
Implanted embryo secretes hCG (Human chorionic gonadotropin)-> Acts like LH
Maintains progesterone and estrogen from corpus luteum during 1st trimester

Question 15

Placenta

Answer 15

1st 2-4 weeks, nutrients directly from endometrium. Trophoblast mixes with endometrium -> placenta.

Placenta
Organ of exchange between mother and embryo
Provides nutrients, O2
Removes waste, excreted by mother
Umbilical cord connects embryo to placenta

Question 16

Twins

Answer 16

Identical (Monozygotic)- Shared placenta

Fraternal (Dizygotic)- Separate placentas

Inner cell mass can split during 1st month-> 2 groups of cells-> identical

Question 17

Birth

Answer 17

Begins with labor
Uterine contractions- push fetus, placenta out of body
Regulated by prostaglandins, hormones (estradiol, oxytocin)

Question 18

Positive or negative feedback during labor?

Answer 18

Positive

Question 19

What is the function of human chorionic gonadotropin (hCG)?

Answer 19

Promotes the maintenance of the corpus luteum which allows the corpus luteum to secrete progesterone.

Question 20

Which type of cleavage pattern do sea urchins undergo?

Answer 20

Holoblastic

Question 21

The ____ is the bag of waters in which a human fetus develops.

Answer 21

Amniotic sac

Question 22

_____ is the process whereby an embryo develops neural folds.

Answer 22

Neurulation

Question 23

In which region of the body does cleavage occur in humans?

Answer 23

Oviduct

Question 24

What is the early blastocyst composed of?

Answer 24

Inner cell mass / Trophoblast / Blastocoel

Question 25

When is the first time an embryo physically grows following gastrulation?

Answer 25

Neurulation

Question 26

The _____ is a layer of cells forming the outer ring of the blastocyst that combines with the maternal endometrium to form the placenta.

Answer 26

Trophoblast

Question 27

During neurulation, the mesoderm gives rise to the _____.

Answer 27

Notochord

Question 28

The _____ secretes proteolytic enzymes to break down the endometrial extracellular matrix to allow for implantation of the blastocyst in the uterine wall.

Answer 28

Trophoblast

Question 29

The notochord induces the formation of the _____ .

Answer 29

Neural plate

Question 30

The neural plate undergoes a series of folds and becomes the _____.

Answer 30

Neural tube

Question 31

_____ is the process whereby the trophoblast thickens and extends fingerlike projections into the endometrium.

Answer 31

Implantation

Question 32

What does the neural tube develop into?

Answer 32

Anterior → brain / Posterior → spinal cord

Question 33

_____ are blocks of cells that lie in the mesoderm, bilateral to the neural tube (notochord) and contribute to repeating, segmented structures.

Answer 33

Somites

Question 34

Which germ layer does the neural crest develop from?

Answer 34

Ectoderm

Question 35

What is the main function of the placenta?

Answer 35

Gas exchange (both oxygen and waste)

Question 36

The placenta and the developing fetus are connected by the _____.

Answer 36

Umbilical cord

Question 37

_____ is a hormone for the maternal recognition of pregnancy produced by trophoblast cells that are surrounding a growing embryo, which eventually forms the placenta after implantation.

Answer 37

Human chorionic gonadotropin (hCG)