Early embryonic development and cell differentiation (5th week of development)

Question 1

Formation of umbilical chord up until week 5

Answer 1

By the end of the 3rd week, the embryo joins t the placenta via the connecting stalk
By the 4th week, the yolk sac pinches off to form the Vitello-intestinal duct
By the end of the 5th week the primitive umbilical ring contains a umbilical ring , 2 umbilical arteries and 1 vein, the vitello-intestinal duct and a canal which connects the intra- and extraembryonic coelomic cavities

Question 2

Formation of body cavities

Answer 2

Body cavities formed by splitting of the intraembryonic coelom (gap in the mesoderm)

future pericardial cavity lies ventrally(frontal).

the pericardiaco-peritoneal canals lie dorsal (backward) to the septum transversum and eventually form the pleural cavities.

Question 3

Function of umbilical chord

Answer 3

Permits blood flow between placenta and embryo

Question 4

The septum transversum becomes the

Answer 4

Diaphragm

Question 5

label this cross section happening during body cavity formation

Answer 5

Question 6

label this crossection hapenning during body cavity formation

Answer 6

Question 7

label this crossection happening during body cavity formation

Answer 7

Question 8

Derivatives of the mesoderm

Answer 8

Paraxial mesoderm (skeletal muscles, skeleton , dermis , CT)

head mesoderm (skull, CT, dentin)

intermediaries mesoderm (urinogenital system, gonads, ducts, accessory glands)

lateral mesoderm (CT , organ muscles, serous membranes , heart, blood , spleen , adrenal cortex)

Question 9

Derivatives of endoderm

Answer 9

Epithelial of internal surfaces e.g respiratory, digestive, urinary

Question 10

Derivatives of ectoderm

Answer 10

Neuroectoderm (neural crest and neural tube)

surface of body e.g skin, hair , nails, mammary glands , anterior pituitary gland

Question 11

Define totipotent

Answer 11

Can give rise to all cell types plus extraembryonic cells

refers to cells within a zygote

Question 12

Define pluripotent

Answer 12

Can give rise tail all 3 germ layers but not extraembryonic cells

Refers to the innner cell mass of blastocyst )

embryonic stem cells derives from inner cell mass

Question 13

Define multipotent

Answer 13

Can give rise to a restricted number of different cell types e.g adult stem cells

Question 14

Abnormal zygotes

Answer 14

Usually lost within 2-3 weeks of fertilisation before woman realises she is pregnant so are not detected

50% if pregnancies are estimated to end in spontaneous abortion - half due to chromosomal abnormalities

Without this , far more babies would be born with defects

Question 15

What are the three relation between mitosis and subsequent differentiation

Answer 15

Once a cell has differentiated, it loses its ability to undergo mitosis

Question 16

what is the septum transversum?

Answer 16

derived from the mesoderm; gives rise to the diaphragm and ventral mesentery of gut