Early Embryonic Development and Cell Types

Question 1

Describe the structure and embryonic origin of the umbilical cord

Answer 1

Umbilical Cord formed in area of dotted line on left-hand diagram

The Vitello-intestinal duct is the area connecting the gut tube to the remnants of the yolk sac

Question 2

Describe the 3D shape of the horseshoe intraembryonic coelom as the embryo develops

Answer 2

The 3D shape changes so the horseshoe is bent

Divisions occur to allow the pericardial cavity to form; then eventually on either side to allow the formation of the pleural cavities and peritoneal cavities

Connection between intra- and extra- embryonic coeloms shrinks and gets smaller to eventually separate

*** Note that picture is ‘upside down’

Question 3

What is housed in the peritoneal cavity

Answer 3

Gut Tube, Liver, other organs (except heart and lungs)

Question 4

What happens to the ectoderm that surrounds the embryo and the mesoderm directly below it in an adult

Answer 4

Becomes the skin;

Mesoderm becomes the dermis

Question 5

How do the peri-cardio and peritonial canals look from a cross section of an embryo (just see the picture)

Answer 5

Question 6

What does a transverse cross section of the almost pinched off yolk sac look like

Answer 6

Hands could theoretically meet across peritoneal cavity

Question 7

What are derivatives of the Ectoderm

Answer 7

**Neuroectoderm and External Epithelia

Question 8

What are derivatives of the Mesoderm

Answer 8

**Paraxial are the somites

Question 9

What are derivatives of the Endoderm

Answer 9

**Internal Epithelia

Question 10

How do embryos develop

Answer 10

**Be vaguely aware of this, don’t fuss over details

Question 11

Two main characteristics of stem cells

Answer 11

Unspecialised and can divide repeatedly over long periods

Can be induced to differentiate into cells with special function

Question 12

How to isolate embryonic stem cells

Answer 12

Isolating the inner cell mass of a cultured blastocyst and putting them into special culture conditions where they divide by mitosis and undergo treatment with specific factors to specialise

Question 13

What are the pathways where mitosis and differentiation occur relative to each other by stem cells

Answer 13

• They continuously divide into more stem cells
  (e. g. blastocyst formation)
• They divide into stem cells then differentiate into the same cell type
  (e. g. haematopoeisis)
• They divide then one daughter specialises and the other remains a stem cell
  (e. g. skin/basal cells)

Question 14

Why can even the least differentiated adult stem cells not be used to make all cell types

Answer 14

They differentiate as desired in-vitro but are not stable to behave in such ways when implanted into the body

Question 15

Totipotent

Answer 15

Stem cells that can give rise to all cell types found in the adult organism, as well as extraembryonic cells

e.g. Zygote

Question 16

Pluripotent

Answer 16

Stem cells that can give rise to all 3 germ layers but not extraembryonic cells

e.g. Cells of inner cell mass of blastocyst

Stem cells may lose their pluripotency as they divide

Question 17

Multipotent

Answer 17

Stem cells that can give rise to a restricted nu,ber of different cell types

e.g. Adult stem cells of the bone marrow

Question 18

What can happen to stem cells left to a petri dish (think of the heart)

Answer 18

They have an inclination to become cardiomyocytes and can often just differentiate into beating cardiomyocytes overnight

Question 19

What can Adult Stem Cells be used to treat

Answer 19

Replacing neurons damaged by spinal cord injury, stroke, Alzheimer’s or other neurological problems

Producing insulin to treat diabetics

Heart muscle cells that could repair damage after heart attack

Potentially replace virtually any tissue or organ that is injured or diseased

Question 20

Issues with using Embryonic Stem cells

Answer 20

Ethical considerations

Potential for immune rejection

Question 21

Somatic nuclear transfer

Answer 21

Obtaining nuclei from adult cells and introducting them into enucleated oocytes which are stimulated to differentiate into blastocysts to derive ES cells

They are genetically compatible with host; less controversial as fertilisation is not involved

Question 22

What is the estimate of pregnancies that end in spontaneous abortion; of those how many are as a result of chromosomal abnormalities

Answer 22

50% of pregnancies end in spontaneous abortion

Of those, half are from chromosomal abnormalities

Question 23

What percentages of foetuses would have birth defects as opposed to current estimates

Answer 23

12% instead of 2-3%

Many extremely minor that have no real effect

Question 24

What happens to the ectoderm that surrounds the embryo and the mesoderm directly below it in an adult

Answer 24

Becomes the skin;

Mesoderm becomes the dermis