Lecture 15 | Development II

Question 1

What happens after Cleavage?

Answer 1

Normal cell cycle resumes (G1, S, G2, M)
Cell division slows
Morphanogenesis

Question 2

What is morphanogenesis and when does it occur?

Answer 2

Cellular & tissue-based process by which the animal body takes shape
Occurs during next two stages of development (gastrulation, organogenesis)

Question 3

What is Gastrulation?

Answer 3

Process by which hollow blastula becomes layered embryo (gastrula)

embryonic layers are: ectoderm, endoderm, mesoderm

Question 4

What is the Gastrulation process in Sea Urchins?

Answer 4

Involves cell migration, invagination (infolding)
Forms archenteron (early gut tube)

Question 5

Why is Gastrulation in Birds different from that in sea urchins?

Answer 5

Too much yolk (can’t be divided entirely through) - meroblastic cleavage
Occurs on Active Cap

Question 6

What are the 2 layers of the active cap?

Answer 6

Epiblast (upper layer, embryo derived from epiblast)
Hypoblast (lower layer)

both on top of yolk

Question 7

How do Epiblast cells migrate?

Answer 7

Involution
Epiblast cells migrate inward and downward toward hypoblast (toward midline)

Question 8

What is the primitive streak?

Answer 8

Crease between epiblast cells that runs down center of the active cap
Functional equivalent of blastopore

Question 9

What are the Epiblast Cell Fates?

Answer 9

Ectoderm (cells that stay on top)
Mesoderm (cells that end up in between)
Endoderm (cells that migrated downward)

Question 10

What is the role of the Hypoblast cells?

Answer 10

Contribute to membranes around yolk
Connection between yolk and embryo

NOT part of embryo itself

Question 11

What forms in Humans after cleavage?

Answer 11

Blastocyst (100 cells around central cavity, mammalian version of blastula)

Question 12

What is the structure of a blastocyst?

Answer 12

Trophoblast (out single layer of cells)
Inner cell mass (cluster of cells, becomes embryo, source of embryonic germ layers)

Question 13

What occurs in the Implantation step of the Gastrulation process in humans?

Answer 13

Blastocyst arrives in uterus about 6 days after fertilization
Trophoblast contacts uterine lining - secretes enzymes
Erodes area of endometrium
Embryo penetrates
Thickens, extends projections into endometrium

implantation is unique to mammals

Question 14

What does the Gastrulation process look like in humans?

Answer 14

Takes about a week (2nd-3rd week of pregnancy)
Inner cell mass forms flat disc (epiblast and hypoblast)
Involution causes gastrulation

Question 15

What are the Epiblast Cell Fates in Humans?

Answer 15

Ectoderm (cells that stay on top)
Mesoderm (cells that end up in between)
Endoderm (cells that migrated downward)
Epiblast cells mix with hypoblast to become endoderm

Question 16

What differentiates Gastrulation in Humans from Birds?

Answer 16

Epiblast cells mix with hypoblast to become Endoderm

Question 17

How is the Human Gastrula different from others?

Answer 17

Missing yolk
Contains extraembryonic membranes

Question 18

What are the functions of the extraembryonic membranes?

Answer 18

Contain fluid
Form Blood Vessels (gas exchange, food/waste - prior to formation of placenta)

Question 19

What is organogenesis?

Answer 19

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

Question 20

What is Neurulation?

Answer 20

Prcoess of forming nervous system

Question 21

How is the Nervous System formed?

Answer 21

Cells of dorsal mesoderm become notochord
Notochord induces ectoderm (thickens, forms neural plate)

Question 22

What is Induction?

Answer 22

Process by which cells stimulate or influence differentiate of neighboring cells

Question 23

What is the Neural Plate?

Answer 23

Embryonic Region
Neural plate rolls up becomes neural tube (why nerve cord is hollow)
Develops into Central Nervous System (anterior portion is brain, remainder is spinal cord)

Question 24

What is Cell Migration in Organogenesis?

Answer 24

Involves local & local range cellular interactions & migration

ex: somites

Question 25

What are Somites?

Answer 25

Blocks of mesoderm cells lateral to notochord Segmented/serially repeated structures | ex: ribs, vertebrate, associated muscles

Question 26

What occurs in the 1st trimester of human development?

Answer 26

Most radical changes for embryo and parent Implanted embryo secretes hCH (acts like LH) Maintains progesterone, estrogen from corpus luteum Placenta develops

Question 27

What makes the Placenta and what does it replace?

Answer 27

1st 2-4 weeks, nutrients directly from endometrium Trophoblast mixes with endometrium = makes placenta

Question 28

What is the Placenta?

Answer 28

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

Question 29

How are Monozygotic (identical) twins formed?

Answer 29

Inner cell mass split during 1st month into 2 groups of cells Shared placenta

Question 30

How are Dyzygotic (fraternal) twins formed?

Answer 30

2 sperm, 2 eggs, fertilization happens at the same time with seperate placentas | more common, same relatedness as regular siblings

Question 31

What is Birth?

Answer 31

takes about 9 months Simple, positive feedback loop Begins with labor, uterine contractions (push fetus and placenta out of body) Regulated by prostaglandins, hormones (estradiol, oxytocin)

Question 32

What type of feedback loop is birth?

Answer 32

Positive Feedback Loop Oxytocin causes contractins and placenta to release prostaglandins Prostaglandins cause more contractions of uterus Amplifies until pressure goes away