W3 - Fetal Development

Question 1

Mesoderm

Answer 1

Differentiates into somites, intermediate mesoderm (IM), lateral mesoderm (LM)
Mesoderm gives rise to muscles, bones, cartilage, blood cells & vessels, dermis, urogenital system
Somites form… axial skeleton
IM forms… urogenital
LM forms…somatic… bones, ligaments, blood vessels, connective tissue (body wall)
….splanchnic… heart, smooth muscle and connective tissue of the respiratory and digestive tracts (around the gut)

Question 2

Dermatome

Answer 2

An area of skin supplied by a single spinal nerve. Nipple is T4 dermatome, bellybutton is T10 dermatome

Question 3

Myotome

Answer 3

A group of muscles innervated by a single spinal nerve

Question 4

Coelom

Answer 4

Is the cavity created by “cracks” in the lateral mesoderm. This cavity will become the three adult cavities.

• Pericardial cavity
• plural cavity
• peritoneal cavity

Question 5

Gastrulation

Answer 5

Occurs early W3
Is the process of the bilaminar disc (epiblasts and hypoblasts) forming the 3 primary germ layers and it marks the start of morphogenesis giving polarity to the embryo.
-epiblasts proliferate and travel medially forming the primitive streak which lengthens via additions to it’s caudal end at the cranial end of the primitive streak is the primitive node and pit
-while the primitive streak is forming epiblasts are also displacing hypoblasts, these will become the endoderm, other epiblasts are delaminating and begin forming the mesoderm
-these mesodermal cells expand and fill the space in all directions except the prechordal plate and cloacal plate, mesoderm cells move cranially through the primitive node to form the notochord.

Question 6

Ectoderm

Answer 6

Gives rise to CNS, PNS, epidermis, eyes, teeth

Question 7

Endoderm

Answer 7

Gives rise to lining of GI tract, liver, pancreas (except for islets), lining of respiratory tract, bladder

Question 8

Embryological development

Answer 8

Week 1
Fertilization - In ampulla
Zygote - has full complement of DNA, encased in zona pellucida to prevent polyspermy and early implantation
Morula - 12-32 blastomeres
Blastocyst - cavity forms in morula with a clump of cells at one end; these are embryoblasts and the ring of cells are trophoblasts. The zona pellucida begins to breakdown and the trophoblasts begin to implant in the endometrium
Week 2
-The embryoblasts form the bilaminar disc (epiblasts are the floor of the amniotic cavity, hypoblasts form the roof of the yolk sac)
-Clefts form around the bilaminar disc = chorionic cavity the connecting stalk keeps the embryo attached to the wall of the chorionic cavity - this will become the umbilical chord
-By the end of week 2 trophoblasts produce enough hCG to be detected in urine
Week 3
-Gastrulation
-Late week three neuralation begins - the notochord induces the ectoderm above to thicken forming the neural plate
Week 4
-the neural plate expands and forms to medial folds. These will converge and pinch off forming the neural tube, the ridges of the folds will pinch off creating the neural crest cells (PNS)
-mesoderm on either side of the neural tube forms two longitudinal columns that condense into blocks, basis for segmentation
-The embryonic disc undergoes concurrent lateral and cranial caudal folding that brings the endoderm to the centre, septum transversum and cardiogenic area onto the ventral surface and the cloaca to the ventral surface

Question 9

Neural Tube Formation

Answer 9

During Week 4 of embryological development the neural tube “zips up”. Failure to do so can cause varying degrees of mental and physical difficulty. There can be many causes of a neural tube defect. If isolated there is a recurrence risk of 4% which can be reduced to 1% with folic acid supplementation

• Multifactorial
• Maternal nutrition
• Medications
• Diabetes

Question 10

4 Basic Tissues

Answer 10

Epithelium
-skin, glandular epithelium, lining of GI tracts
Connective Tissue
-supportive and structure reflects function. A tendon is dense and highly regular while a basement membrane is looser to allow diffusion
Muscle
-smooth muscle, cardiac muscle, skeletal muscle
Nervous Tissue
-Neurons

Question 11

Inherited

Answer 11

A trait present in one or both parents that is passed on to their offspring.

Question 12

Congenital

Answer 12

A trait someone is born with.

Question 13

DNA structure and organization

Answer 13

Two strands of nucleotides make up DNA, which associates with histones which creates chromatin. One continuous length of DNA is a chromosome. Euchromatin confers gene expression while heterochromatin contains unexpressed DNA
Histone acetylation leads to gene expression by dissociating the histone from the DNA
Deacetylation leads to gene silencing
Methylation also leads to gene silencing (methylates a CG group so methylation patterns are maintained during DNA replication)