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APS 136 > Lecture 1 > Flashcards

Lecture 1 Flashcards

1
Q

Define development.

A

A series of progressive changes in form and function that occurs during an organisms life cycle. Continues through juvenile stages until the organism can reproduce.

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2
Q

What is the difference between embryonic stages and development.

A

Embryonic stages precede birth and development continues after this.

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3
Q

What is the order of the key stages of development?

A 
Fertilisation
Cleavage
Gastrulation
Organogenesis 
Morphogenesis
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4
Q

How is cleavage stimulated?

A

Fertilisation that goes on to form the multicellular embryo.

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5
Q

Where do the cytoplasm and mitochondria in the embry come from?

A

The egg.

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6
Q

Where is the nucleus of the egg in the zygote?

A

The animal hemisphere (opaque).

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7
Q

Where do the nutrients accumulate in the zygote?

A

The vegetal hemisphere (clear).

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8
Q

When and where is the grey crescent exposed?

A

In amphibians, when the sperm enters at the animal hemisphere, the cortex rotates, exposing the grey crescent opposite the sperm entry site.

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9
Q

How is the form the cells will take determined at this stage?

A

By the proteins in the grey crescent.

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10
Q

Define cleavage.

A

Rapid series of mitotic cell divisions after fertilisation to form a blastula.

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11
Q

Where do cells divide during cleavage?

A

At the cleavage furrow.

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12
Q

What is the structure of each individual cell?

A

A blastomere with a animal and a vegetal pole.

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13
Q

How does the cell mass change during cleavage?

A

There is very little cell growth so the mass stays the same.

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14
Q

What is a morula?

A

A solid ball of cells.

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15
Q

What is a blastula?

A

A hollow ball of cells.

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16
Q

What are the 3 patterns of cleavage?

A

Complete
Incomplete- discoidal
Incomplete- superficial

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17
Q

What determines which pattern of cleavage an organism undertakes?

A

The amount of yolk and the orientation of spindles.

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18
Q

In what sort of animals does complete cleavage take place?

A

In embryos with no yolk, cells are equal in size and are completely and evenly divided.

19
Q

In what sort of animals does incomplete- discoidal cleavage take place?

A

In embryos with lots of yolk such as birds as yolk obstructs cleavage furrow, causing cells to divide asymmetrically.

20
Q

How does incomplete- discoidal cleavage take place?

A

Cleavage furrows can’t penetrate the yolk so a blastodisc forms on top of the yolk and produces the embryo and membranes.

21
Q

Describe incomplete- superficial cleavage.

A

Yolk is in the middle and multiple nuclei form but cytokinesis doesn’t occur so the nuclei migrate to the edge and the membrane grows inward, partitioning the nuclei into individual cells E.g. Insects.

22
Q

What are the 3 types of cleavage as determined by mitotic spindles?

A

Radial, spiral and roational cleavage.

23
Q

Describe these 3 types of cleavage.

A

Radial cleavage occurs when mitotic spindles occur at right angles or parallel to the animal-vegetal axis.
Spiral cleavage occurs when mitotic spindles occur at non-right angles (oblique) to the A-V axis.
Rotational cleavage occurs when the first division is parallel to the A-V axis and the second is at right angles.

24
Q

When do cells stop being totipotent?

A

At determination when they become structurally and functionally specialised.

25
Q

Describe gastrulation.

A

Blastula becomes an embryo with 3 tissue layers and body axes.

26
Q

What are the 3 tissue layers?

A

Ectoderm: Epidermis and nervous system.
Mesoderm: Bone, muscle, organs.
Endoderm: Digestive and respiratory tract and circulatory system.

27
Q

Describe gastrulation in a sea urchin.

A

Vegetal hemisphere invaginates into a blastocoel forming a blastopore, then an archenteron (primitive gut).

28
Q

What do mesenchyme cells do in the gastrulation in sea urchins.

A

Primary mesenchyme cells migrate to form mesoder at the base of the invagination.
Secondary mesenchyme cells attach to invagination and pull it up.

29
Q

What is the difference between deuterostome and protostome?

A

In deterostomes blastopore forms anus and mouth forms second.
In protostomes blastopore forms mouth and anus forms second.

30
Q

What makes up the blastodisc of a bird embryo?

A

Epiblast (embryo) and hypoblast (extraembryonic membranes). These are opposite each other.

31
Q

How does henson’s node move?

A

It moves along the blastodisc, creating the anterior and posterior as well as the primitve streak that is left in its wake.

32
Q

What is the function of the primitive streak?

A

Cells move to the midline of the epiblast and down through the primitive streak to become endoderm and mesoderm. Primitive streak becomes the blastopore.

33
Q

In mammals, what does the blastula become in mammal gastrulation.

A

Becomes the trophoblast (placenta) and the inner cell mass.

34
Q

What does the inner cell mass become?

A

The epiblast (embryo) and hypoblast (extraembryonic membranes)

35
Q

What makes up the blastocyst in mammals?

A

Trophoblast, epiblast and hypoblast.

36
Q

Where does the the blastocyst go?

A

Implanted in the uterus.

37
Q

What are the 2 processed in organogensis?

A

Neuralation and body segmentation.

38
Q

When does neuralation occur?

A

During early organogenesis.

39
Q

How does neuralation occur?

A

Thickeing ectoderm forms neural plates that thicken into ridges.

40
Q

How does the neural tube form.

A

Neural ridges fuse over the gap between the ridges.

41
Q

How does the brain form?

A

Thickening of the neural tube.

42
Q

What are the extraembryonic membranes in birds?

A

Yolk sac (nutrient transfer), amniotic sac (protection), chorion(water/gas exchange), allantois (waste storage).

43
Q

How does this compare with mammal embryos?

A

Placenta (nutrient transfer), amnion in amniotic sac (protection), chorion (fused to placenta), allantois (incorporated into the umbilical cord).

44
Q

What does the yolk sac do in mammal embryos?

A

Produces blood cells that migrate into the embryo.

APS 136 (17 decks)

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