Lecture 22

Question 1

Histogenesis

Answer 1

Process where different tissues form undifferentiated cells in an embryo. Undifferentiated cells arise from 3 germ layers incl. ectoderm, mesoderm and endoderm

Question 2

Fertilisation to implantation

Answer 2

Ovum released and meets with sperm for fertilisation. It becomes a diploid and undergoes cleavage to form multiple cells to form morula. Morula hatches out to form blastocyst which embeds in the uterine wall.

Question 3

Implantation

Answer 3

Blastocyst has trophoblast as external cell layer, inner cell mass is made of epiblast and hypoblast. Trophoblasts form extra embryonic tissue (supports embryo proper) after invading wall. Inner cell mass forms foetus. Epiblast and hypoblast forms bilamina germ discs.

Question 4

Bilamina germ disc

Answer 4

Top is epiblast, bottom is hypoblasts. Epiblast cells migrate into the disc to form the primitive streak medially. This displaces the hypoblasts and form endoderm. Triggered by signals from hypoblasts. Endoderm sends signals to the epiblast to cause more cells to migrate

Question 5

Gastrulation

Answer 5

Movement and selective differentiation of specialised cells to form trilamina germ disc. Endoderm from epiblast, mesoderm from migratory cells and ectoderm from epiblast cells.

Question 6

Ectoderm

Answer 6

Gives rise to skin, CNS and neural crest (PNS)

Question 7

Neurulation

Answer 7

The primitive streak forms a groove, which flattens to become the neural plate. The surrounding epidermal ectoderm moves inward, promoting the formation of the neural tube, which eventually pinches off from the epidermal ectoderm. The neural tube is made of neuroectoderm. Cells in the ‘hinge’ region migrate to become PNS.

Question 8

Mesoderm

Answer 8

Different mesoderms. Gives rise to blood, muscles, bones and specialised kidney cells.

Question 9

Endoderm

Answer 9

Innermost layer. GIT and respiratory tract.

Question 10

Germ cells

Answer 10

Germ cells don’t originate from germ layers. Primordial germ cells found in yolk sac. They migrate to where future genitals are

Question 11

Epithelial-mesenchymal transition

Answer 11

Stationary epithelial cells to migratory mesenchymal cells. Signals change surface molecules and epithelial characteristics (e.g adherens junctions) disappear. It breaks through basal lamina and away from epithelial cells. They can invade tissues and establish colonies that become organs. Part of mesoderm and neural crest cell formation.

Question 12

EMT durung gastrulation

Answer 12

Formation of mesoderm by mesenchymal cells. Delamination from epiblast.

Question 13

EMT during neurulation

Answer 13

Neural crest cells form from dorsal region of the neural tube.

Question 14

EMT in adulthood

Answer 14

Involved in wound healing, cancer metastasis or fibrotic pathologies.