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BIOL 124 > 8 - Embryogenesis and Development > Flashcards

8 - Embryogenesis and Development Flashcards

1
Q

Cleavage

A

cell division in early embryo

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2
Q

Gastrulation

A

cell movements which produce gut and 3 primary germ layers

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3
Q

difference between early embryonic and somatic cell cycle

A

somatic cycle: 4 phases

early embryonic: alternates between S and M phases without intervening G1 and G2

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4
Q

What is morphogenesis?

A

• The regulation of the pattern of anatomical development.

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5
Q

What is organogenesis?

A

• Formation of organs.

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6
Q

What is a morula?

A

• Tight collection of 32 cells at the beginning of differentiation.

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7
Q

What is a blastula?

A

• An animal embryo at the early stage of development when it is a hollow ball of cells.

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8
Q

What is a blastocoel?

A

• The fluid-filled cavity of a blastula.

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9
Q

What is a blastomere?

A

• (After the first division) it’s a cell formed by cleavage of a fertilized ovum.

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10
Q

What is meroblastic cleavage?

A

• Incomplete division of the egg, occurs in species with yolk-rich eggs, such as reptiles and birds.

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11
Q

What is holoblastic cleavage?

A

• Cleavage that completely divided an egg.

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12
Q

What happens in the cleavage of sea urchins?

A
  • Fertilised sea urchin eggs have vitelline membranes.
  • Rapid divisions of blastomeres (all the same size) create a morula.
  • Cells move around the outside and start to condense at one side of the structure (the bottom); these grow into a hollow structure.
  • Equal holoblastic cleavage (divides entire cell into 2).
  • Blastomeres become smaller with each division.
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13
Q

why is there unequal holoblastic division in amphibians?

A

Blastomeres in animal pole are smaller than blastomeres in vegetal pole because of presence of yolk in vegetal hemisphere.

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14
Q

amphibian cleavage steps

A

● Cleavage 1 and cleavage 2 are perpendicular and (equal holoblastic) but nuclei are displaced ‘animal-ward’

● Cleavage 3 is perpendicular/equatorial but (unequal holoblastic)

● Gives rise to a more rapidly dividing animal pole

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15
Q

What happens in the gastrulation of sea urchins?

A

• We have a blastula with a single layer of cells on the outside and a centrally located blastocoel.

  • Cells at the vegetal pole thicken to form the vegetal plate and these fold inwards to form a tube called the archenteron which will form the endoderm (giving rise to the gut).
  • Some cells detach and migrate into the blastocoel.
  • These are called mesenchyme cells and will form the mesoderm.
  • Cells remaining on the surface form the ectoderm. The open end of the tube at the vegetal pole is called the blastopore.
  • Contractions of filopodia of mesenchyme cells pull the tube through the blastocoel.
  • Eventually this tube fuses with the wall of the embryo giving rise to the mouth.
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16
Q

chick cleavage

A

meroblastic = cleavage plane doesn’t bisect yolk

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17
Q

what occurs after the cleavage stage

A

blastula formation

18
Q

what occurs after the blastula formation

A

gastrulation

19
Q

what does gastrulation form

A

primary germ layers: ectoderm, mesoderm, endoderm

20
Q

ectoderm

A
  • Epidermis of Skin
  • Nervous system
  • Pituitary gland
  • Adrenal medulla
  • Jaws and teeth
  • Germ cells
21
Q

mesoderm

A
  • Notochord
  • Muscular system
  • Skeletal system
  • Circulatory and lymphatic systems
  • Excretory and reproductive systems
  • Dermis of skin
22
Q

endoderm

A
  • Epithelial lining of gut and associated organs

- Epithelial lining of respiratory, excretory and reproductive tracts

23
Q

gastrulation in sea urchins

A

begins w/ small invagination in blastula =>
cells continue moving toward invagination =>
elimination of blastocoel => gastrula

24
Q

gastrulation in amphibians

A
  • blastopore begins to form
  • involution
  • mesoderm insinuates itself between ectoderm and endoderm (no outpocketing)
  • chordamesoderm forms notochord
25
Q

Gastrulation in chicks

A
  1. Cells move through the streak and replace hypoblast cells
  2. Cells moving through the streak move into the space to create mesoderm
26
Q

First cleavage division

A

The first cleavage division 24-30 hours after fertilisation. Holoblastic division. Two blastomeres are formed.

27
Q

What happens during implantation?

A
  • Once the blastocyst forms, it begins to attach itself to the wall of the uterus (approx. day 6-7).
  • Blastocyst secretes enzymes to burrow into the endometrium.
  • Inner cell mass next to the endometrium.
28
Q

What is the structure of human blastocysts?

A
  • Inside of blastocyst is called the Inner Cell Mass (ICM).
  • ICMs will become the embryo, which is identifiable at 4-6 days of human gestation.
  • Outside of blastocyst have cells called trophoblasts.
  • Trophoblasts go on to become the placenta.
  • Blastocyst begins to implant into the uterus and continues to develop.
  • Next stage is the formation of two cell layers: epiblast + hypoblast
29
Q

Epiblast

A
  • Outer layer: these cells go on to form the embryonic tissue.
  • Surrounded by an amniotic cavity.
30
Q

Hypoblast

A
  • Primitive endoderm (endo meaning inner).
  • Gives rise to extraembryonic tissues.
  • Faces onto the yolk sac.
31
Q

What happens during gastrulation of human blastocysts?

A
  • Around days 12-16, gastrulation results in the formation of a trilaminar embryo.
  • Primitive streak forms in dorsal epiblast & this structure defines anterior/posterior and left/right of embryo.
  • Epiblast cells (top layer) converge on the primitive streak/groove.
  • Individual proliferating cells move through PS (C) and displace the hypoblast to create the endoderm.
  • Later cells move through to create the mesoderm.
  • Cells spread out laterally and anteriorly (B).
32
Q

Day 0

A

fertilization

33
Q

day 1

A

2 blastomere cells

34
Q

day 2

A

4 cell stage

35
Q

Day 3

A

early morula forms

36
Q

Day 4

A

embryo has progressed to a morula to develop a blastocyst, 32 cell stage

37
Q

Day 5

A

hatching

  • the blastocyst digests a hole in the zona pellucida and emerges.
38
Q

Day 6

A

Blastocoel formation: the fluid-filled cavity inside a blastula

39
Q

Days 7-10

A

implantation in uterine wall

40
Q

Blastocyst

A

stage of early development in mammals that consists of a hollow ball of cells

41
Q

days 12-15

A

Gastrulation

  • Primitive streak forms in dorsal epiblast and defines anterior/posterior and left/right of embryo.
  • Cells from primitive node produce the notochord

BIOL 124 (12 decks)

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