Derivatives

Question 1

Ectoderm

Answer 1

1. CNS
2. PNS
3. Skin
4. Epidermis → hair, nails, lens, cornea, sebaceous glands
5. Neural crest cells → Schwann cells, neuroglia, adrenal medulla, melanocytes
6. Neural tube → brain, pituitary, retina, spinal cord

Question 2

Paraxial mesoderm

Answer 2

1. Sclerotome
2. Myotome
3. Dermatome

Question 3

Lateral plate mesoderm

Answer 3

1. Somatic mesoderm → parietal pleura
2. Splanchnic mesoderm → visceral pleura

Question 4

Intermediate mesoderm

Answer 4

1. Genito-urinary tract

Question 5

Endoderm

Answer 5

1. Liver
2. Alveolar parenchyma
3. Thyroid
4. Parathyroid glands

Question 6

Neural crest cells

Answer 6

1. CN ganglia
2. Melanocytes
3. Schwann cells
4. Adrenal medulla
5. Pia & Arachnoid mater
6. Islets of Langherhan
7. Enamel of teeth
8. Dentine pulp

Question 7

Cross-section @ 4th week of IUL

Answer 7

Question 8

Embryonic stem cells and their potencies

Answer 8

1. Totipotent → early morula, zygote
2. Pluripotent → inner cell mass, epiblast
3. Multipotent → mesenchymal, hematopoietic, adult stem cells, cells of all germ layers
4. Unipotent → their own cell type

Question 9

Embryonic period

Answer 9

1. Inner cell mass forms amniotic membrane
2. Bilaminar disc is formed by the second week of fertilization
3. Trophoblast differentiates into 2 layers: syncytiotrophoblast (outer) & cytotrophoblast (inner)
4. Neural crest cells develop from marginal layer of neural tube

IUL:
2nd week → formation of epiblast & hypoblast
3rd week → gastrulation, formation of neural tube, commencement of beating of ❤️, coelomic cavity has formed, brain
4th week → folding, all 3 germ layers complete, embryonic gut
6th - 10th week → development of hard palate, finger nails
End of 1st trimester → yolk sac disappears
After implantation → placenta

Question 10

Microscopy

Answer 10

1. Min. amount for light microscope is 500nm
2. Oil is added to surface of the slide to improve resolution
3. Diaphragm controls amount of light entering
4. Condenser converges light rays onto the slide
5. Phase contrast microscope is used to view living cells
6. Tissue sectioning is needed for TEM not SEM
7. Oocyte can be seen by the naked eye

Question 11

Cells of multicellular organism

Answer 11

1. Limited by diffusion as they have large SA
2. Have a longer life span tan unicellular organisms
3. Preserves cellular autonomy
4. Responds to neighboring cells of same tissue

Question 12

Epiblast

Answer 12

1. Comes from inner cell mass
2. Migrates and replaces hypoblast
3. Forms endoderm
4. Forms notochord
5. Are pluripotent cells
6. Trophoblast comes from outer cell mass

Question 13

Skeletal muscle vs. Cardiac muscle

Answer 13

Similarities:
1. Presence of cross striations
2. Presents of T-tubular system
3. Presence of neuromuscular junctions

Skeletal muscle:
→ multinucleated
→ unbranched fibers
→ type 1 = aerobic (type 2 = anaerobic)
→ contractile filaments are arranged parallely ( criss-cross in smooth muscles)
→ they are arranged as fascicules
→ nuclei are flattened + located at peripheries
→ A bands remain constant in with during contractions
→ perimysium contains dense connective tissue around fasciculi
→ circularly arranged fibres form sphincters

Cardiac muscle:
→ uninucleated
→ branched

Question 14

Karyotype

Answer 14

1. Describes the chromosome count and structure of an organism
2. A karyograph shows:
   → number of chromosomes
   → sex chromosome content
   → presence or absence of individual chromosomes
   → nature or extent of chromosomal aberrations
   → does not show phenotype
   → point mutation cannot be observed

Question 15

Embryonic stem cells

Answer 15

1. Better than adult stem cells for cloning
2. Diploid in nature
3. Contains the same genomic, genetic material as found in an adult somatic cell
4. Helps the embryo to increase in size
5. Cell Autonomy is lost during differentiation