Manual 126-129: Embryology

Question 1

when precisely do limb buds start to develop?

Answer 1

during the later part of the 4th week (as soon as teh trilaminar embryo completes its lateral foldin)

Question 2

where on the embryo do limb buds form?

Answer 2

along the ventrolateral side of the cylindrical embryonic body

Question 3

which appears first upper or lower limb buds?

Answer 3

upper (day 26-27) – lower about 2 days later

seen at the inferior segment of the developing cervical region (C5-T1)

Question 4

The ________ limb buds originate from a slightly larger segment than the _______ limb buds.

Answer 4

lower limbs originate from slightly larger segment than the upper limb buds

L2- S2 (6) compared with C5-T1 (4)

Question 5

what is the mesenchymal core of the limb bud derived from?

Answer 5

somatic component of the lateral mesoderm layer of embryo

Question 6

Further development and enlargement of the limb buds initially begins by a very fast division of the mesenchymal cells. Evidence has shown that this cell division is under direct control of _________ gene.

Answer 6

HOX homeobox-containing

also responsible for patterning of the limbs (distal ends of buds flatten into paddle-like hands and ffet)

Question 7

At the distal segment of the limb bud (apex) the ectodermal cells undergo cell proliferation and show consideral thickening known as the _______

Answer 7

apical ectodermal ridge AER

Question 8

responsible for proximal to distal limb bud growth

Answer 8

AER (inductive influence is a result of expression of fibroblast growth factor)

limbs will not develop in absence of AER
moving location of AER will move location of limb

Question 9

by the end of the ___ week, the hand paddles show presence of digital rays which will eventually gice rise to fingers

Answer 9

6th week

Question 10

during early part of ______ week, toe rays can be seen in the foot plates

Answer 10

7th week

Question 11

Separation of individual digits takes place during the ___ week by the process of apoptosis in the __________ tissue between digital rays

Answer 11

8th week; mesenchymal tissue

Question 12

the mesenchyme of limb buds gives rise to following components of the limbs:

Answer 12

bones
joints
cartilage
fascial layers
blood vessels
lymphatic vessels

Question 13

the cells of the cartilage models are derived from the original mesenchymal cells of the embryo begining by the ___ week of development

Answer 13

5th week

by the 6th week the entire cartilaginous skeleton is complete

during the 7th week, the cartilage models start to undergo endochondral ossification whereby the chondrocytes are replaced by bone producing cells

Question 14

endochondral bone formation begins where?

Answer 14

diaphysis of long bones as the primary center of ossifications

long bones also develop secondary ossification centers in the epiphysis

Question 15

each long bone has _____________ ossification centers

Answer 15

3 total

one primary and two secondary

Question 16

cervical myotomes give rise to _______ muscles.

lumbosacral myotomes provide precursor cells for the _______.

Answer 16

pectoral girdle

pelvic girdle

Question 17

these cells derived from the somites provide cells tat stay deep to the ectoderm and gice rise to dermis of skin

Answer 17

dermatomal cells

Question 18

eventually become established as nerves of limbs

Answer 18

axonal processes

Question 19

the supporting cells of the nervous system ( schwann cells) are derived from the ____________.

Answer 19

neural crest cells

Question 20

name the migrant cells

Answer 20

myogenic
dermatomal
axonal
neural crest cells

there is evidence which indicates that the mesenchymal cells of the limbs organize the migrant cells and control their expression

Question 21

regarding limb rotation …

the area of the limb superior (cranial) to the axial line is the _____ compartment.

the area inferior (caudal) to the axial line is the _________ compartment.

Answer 21

preaxial; postaxial

Question 22

the superior border of the preaxial compartment is the preaxial border and the inferior border of the postaxial compartment is the postaxial border.

preaxial border is along the same line as _____.
postaxial border corresponds to the location of the __________.

Answer 22

preaxial border = same line as the thumb or the great toe

postaxial border = location of the 5th toe or the little finger

Question 23

preaxial compartments contain _____ muscles and the postaxial compartments contain the __________ muscles.

Answer 23

pre - flexor

post - extensor

Question 24

when do the limbs undergo a rotation along their __________ axis?

Answer 24

7th week

long axis

Question 25

upper limbs rotate _____; lower rotate _______

Answer 25

lateral

medial

Question 26

the flexor compartment/ preaxial of the upper limb faces _______ in the anatomical position

Answer 26

anteriorly

the extensor compartment is located posterior to the longitudinal axis

Question 27

limb defects appear in how many births?

Answer 27

2/1000

Question 28

early 60s birth defects were traced back to what drug

Answer 28

thalidomide

Question 29

most susceptible time for producing limb defects

Answer 29

between day 24-36

Question 30

extra digits resulting from having extra digital rays

Answer 30

polydactyly

Question 31

attached digits. malformation in the act of apoptosis will result in two or more digits that remain attached

Answer 31

syndactyly

Question 32

absence of limbs

Answer 32

amelia

Question 33

absence of a part of a limb

Answer 33

meromelia

Question 34

failure of development of one or more digital rays. the hand or the foot appears to be split down the middle.

Answer 34

cleft foot

Question 35

short digits

Answer 35

brachydactyly

Question 36

defect applying to any abnormality of the foot involving the talus

Answer 36

congenital club foot ( 1/1000 births)

the affected individual walks on the ankle rather than the foot. the sole of the foot is usually tuned medially and the foot is inverted.