Lec 35

Question 1

Initially , the mesodermal germ layer form a —— sheet of loose tissue on each side of the midline
The reign where cells close to the midline form a second plate known as ——— future somites / small bodies
The reign where more laterally the mesoderm layer remains thin is known as ——
———— connects paraxial and lateral plate mesoderm

Answer 1

thin
paraxial mesoderm
lateral plate
intermediate mesoderm

Question 2

By beginning of 3 week , —— mesoderm begins to organise as segments / somites

Answer 2

Paraxial

Question 3

Somites first appear in the —— region on — day and their formation proceeds ——— , — pairs / day

Answer 3

Cephalic
20
Craniocaudally
3

Question 4

By the end of — week , 42-44 somites develop

Answer 4

Fifth

Question 5

No.somites developed over a period can be correlated to the —— of the embryo

Answer 5

approximate age

Question 6

each somite has 3 parts :

Answer 6

1- sclerotome
2- myotome
3- dermatome

Question 7

What is sclerotome ?

Answer 7

cells of the sclerotome migrate medially to surround the neural tube to give rise to [ vertebrae and ribs ]

Question 8

What is the dermatome ?

Answer 8

cells migrate to the under surface of ectoderm to give rise to the [ dermis of the skin of the back ]

Question 9

What is the myotome ?

Answer 9

they give rise to [ skeletal muscles ] of the body wall and limbs

Question 10

intermediate mesoderm contributes to the formation of —— and —— ( Gonads “ testes / uterus “ & ducts ) systems
example: —— but not the —— , gonads and their ducts

Answer 10

urinary , genital
kidneys , urinary bladder

Question 11

head and tail folds are the result of ——— of notochord and neural tube moving —— structures ventrally and caudally

Answer 11

Elongation , cranial

Question 12

The establishment of body forms occurs in —— planes

Answer 12

2

Question 13

the major structures that moved ventrally and caudally by head folding are :

Answer 13

1- septum transversum -> future diaphragm ( central part )
2- cardiogenetic region and future pericardial cavity
3- oropharyngeal membrane

Question 14

the tail folding brings ——— and ventrally

Answer 14

cloacal membrane , connecting stalk

Question 15

Folding of what results in upper part of YS York being incorporated into embryo as the primitive gut tube ?

Answer 15

Head & tail

Question 16

What are the results of formation of The head fold ?

Answer 16

1- reposition of organs { brain , oropharyngeal membrane , heart , septum transversum }
2- endoderm of YS is incorporated into head fold to form foregut

Question 17

What with the septum transversum become after formation of head fold?

Answer 17

Central part of diaphragm

Question 18

What are the results of formation of tail fold ?

Answer 18

• Folding of the caudal end of the embryo results from growth of the distal part of the neural tube
• the tail region to project over the cloacal membrane ( future site of the anus)
• The terminal part of the hindgut dilates to form the cloaca, the precursor of the urinary bladder and rectum

Question 19

Lateral folding is produced by ?

Answer 19

rapidly growing somites

Question 20

lateral edges of the embryonic desk move ventrally and medially to form a ?

Answer 20

cylinder shaped embryo

Question 21

lateral folding results in the formation of ventral body wall and ?

Answer 21

part of the endoderm is incorporated into the embryo as the midgut

Question 22

Initially there is a wide communication between the —— and the —— , But this will be —— with folding

Answer 22

midgut , yolk sac , reduced

Question 23

the connection that remains between the midgut & YS is called the ———

Answer 23

vitelline duct

Question 24

the attachment of the amnion to the —— surface is reduced to the —— region

Answer 24

ventral , umbilical

Question 25

on day 21 - 28 small spaces appear in the —— mesoderm , which will merge to form a larger cavity called [ ———— ]

Answer 25

lateral plate intraemberyonic coelom

Question 26

The intraembryonic coelom splits the lateral plate mesoderm into 2 parts :

Answer 26

splanchnic and somatic

Question 27

somatic mesoderm gives rise to ?

Answer 27

bones , ligaments , blood vessels , connective tissue of the limbs

Question 28

the mesoderm that surrounds the gut is [ splanchnic mesoderm ] , which forms ?

Answer 28

the smooth muscles of the wall of the GIT

Question 29

blood cells & blood vessels arise from ?

Answer 29

mesoderm

Question 30

Between the 17th and 28th days , growth of the —— and lengthening of the —— causes both the head and tail regions to move —— forming head and tail folds

Answer 30

brain , neural tube ventrally

Question 31

Simultaneously , the —— of the embryo begin to fold ventrally to form 2 lateral body wall folds

Answer 31

sides

Question 32

The ectoderm + mesoderm + future coelomic cavities + endoderm from opposite sides fuse ; However in the —— region the ventral body wall does not close completely leaving a connection between YS and the gut called ———

Answer 32

umbilical , vitelline duct

Question 33

body folding results in the formation of endoderm lined gut tube :

Answer 33

1- foregut 2- Midgut 3- Hindgut

Question 34

What’s the foregut ?

Answer 34

- endodermal tube projecting cranially into region formed by head fold - dorsally it will form -> digestive portion which will form { pharynx , esophagus , stomach } - ventrally it will form -> respiratory portion that forms { trachea and lungs }

Question 35

What’s the midgut ?

Answer 35

- primitive midgut is not a complete tube -opens by vitelline duct into YS through umbilical ring -forms most of small intestine and part of colon

Question 36

What’s the hindgut ?

Answer 36

-endodermal tube projecting caudally into the tail fold -caudal portion expands to form cloaca -Allantois projects off cloaca into connecting stalk - forms remaining part of { rectum and urinary bladder }

Question 37

The coelom forms the —— cavities

Answer 37

body

Question 38

The ectoderm forms :

Answer 38

CNS , PNS , epidermis of skin , enamel of teeth , sensory epithelium of sense organs epidermis [ hair and nails ]

Question 39

endoderm forms :

Answer 39

digestive tract, respiratory tract , tympanic cavity , Eustatian tube , Liver , pancreas, gallbladder , tonsils, thyroids , thymus

Question 40

the mesoderm forms :

Answer 40

bone , cartilage, connective tissue, blood , walls of blood vessels, heart , spleen, muscle tissue , kidneys

Question 41

clinical correlations of body wall defects are

Answer 41

1- extrophy of the bladder 2- Gastroschisis

Question 42

What are the major structures derived from the endoderm?

Answer 42

1- Epithelial lining of gastrointestinal tract 2- Epithelial lining of urinary bladder , gallbladder , liver 3- trachea 4- lungs 5- thyroid gland 6- pancreas

Question 43

What are the major structures derived from the mesoderm ?

Answer 43

1- all skeletal & cardiac muscle + smooth muscle tissue 2- cartilage & bone & connective tissue 3- blood & blood vessels 4- dermis of skin 5- gonads & genital ducts

Question 44

What are the major structures derived from the ectoderm ?

Answer 44

1- all nervous system 2- epidermis of skin 3- hair follicles & nails 4- skin glands ( sebaceous & sudoriferous ) 5- mammary glands 6- pituitary gland

Question 45

What is teratology ?

Answer 45

A branch of embryology that studies the causes, mechanisms, patterns of abnormal development

Question 46

What is the literal meaning of teratology ?

Answer 46

the study of monsters

Question 47

what is a teratogen?

Answer 47

Any agent that may cause birth defects

Question 48

The major causes of congenital malformations from 50 - 60% are ——— , 20 - 25% are ——— , 6 - 7% ———— , ——— mutant genes , 7 to 10% ————

Answer 48

Unknown etiology Multifactorial inheritance chromosomal abnormalities 7 - 8% environmental agents

Question 49

Birth defect, occur —— live births

Answer 49

1/16

Question 50

The most vulnerable period for induction of birth defects is ——— period ( 3 to 8 weeks ) , which is known as the ————

Answer 50

embryonic critical period

Question 51

Death of embryo may occur from week —— from week 3 to 8 formation of the —— begin , so malformation of the embryo may occur ( heart defect ) The period from —— weeks ,growth and maturation of organ systems occur so most functional disturbance of fetus may occur (—-)

Answer 51

0 to 3 organs 8 to 38 mental retardation