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Flashcards in 13. Limb Devo Deck (55)
1

areas of somatic mesoderm located on each side of the
embryo.

The Limb Fields

2

Due to differential expression of_______ genes, the limb fields are localized at distinct axial levels, one for the upper limb and one for the lower limb

Hox

3

Specific transcription factors are expressed within the upper limb_____ and the lower limb ______

(Tbx5)
(Tbx4 & Pitx-1).

4

Limb bud outgrowth is initiated by signaling molecules
_______originating in the _______ mesoderm.

(FGF & Wnt)
intermediate

5

Limb bud outgrowth is initiated by signaling molecules
(FGF & Wnt) originating in the intermediate mesoderm. These signals induce ______ expression in the appropriate areas of ________ resulting in limb bud formation.

FGF 10
lateral plate mesoderm

6

forms skeletal elements, fibrous connective tissue and
dermis of the skin (probably vascular endothelium and smooth muscle)

Somatic mesoderm

7

forms the epidermis of the skin

Surface Ectoderm

8

migrates into the limb bud forming the skeletal muscle

Somitic (somite derived) mesoderm –

9

Nerve fibers from ________ of spinal nerves migrate into the limb and become surrounded by neural crest-derived Schwann cells.

ventral primary rami

10

Limb development occurs along three axes. Limbs elongate and limb segments are formed along the _______ axis.

proximal-distal

11

Muscles and nerves are organized in
compartments along a _______ axis.

dorsal–ventral

12

Digits are arranged along an _______ axis.

anterior-posterior

13

After limb outgrowth is initiated, Fgf 10 produced by the somatic mesoderm of the
bud initiates the secretion of______ (also Fgf4 & 2) in the distal ectoderm. This results in a thickening of the distal ectoderm called the _________

Fgf 8
apical ectodermal ridge(AER).

14

What defines the location of the ridge at the boundary between the dorsal and ventral surfaces of the limb? T

Differential gene expression in the dorsal and ventral surface ectoderm

15

acts as a signaling center for the underlying
mesenchyme (originating from somatic mesoderm).

AER

16

Signals from the AER (primarily Fgf 8) induce the adjacent mesenchyme to proliferate, which creates a
pool of mesenchyme cells that enable the limb ______

to elongate.

17

_____ signals also inhibit mesenchyme differentiation and is secreated from the mesenchyme adjacent to the AER
to maintain AER function until all limb segments
are formed.

Fgf
(Thus a positive Fgf feedback loop occurs between the mesenchyme (Fgf 10) and the AER (Fgf 8). )

18

The arrangement of the digits is achieved by signaling from the_________ on the posterior border of the limb just proximal to the AER.

Zone of Polarizing Activity (ZPA)

19

The ZPA is an area of somatic mesenchyme on the posterior side of the limb bud that secretes

Sonic hedgehog (Shh)

20

has been shown to mimic the action of Shh.

Retinoic acid

21

Expression of Shh from the ZPA initiates the expression of a subset of the Hox genes in the posterior
mesoderm... how does this cause normal digit formation

Expression occurs in an overlapping nested fashion. This expression pattern of Hox genes as well as other signaling molecules

22

The flat digital plate contains condensations of mesenchyme representing each digit called _____

digital rays

23

The phalanges and joints will form from digital rays and initially they are joined together by a web of condensed mesenchyme. The AER in the web areas disappears and

triggers apoptosis within the web mesenchyme. This results in digit separation. The AER remains at the
distal tip of the digital ray until all parts of the digit have formed.

24

How do we get vascular supply to developing muscles in the limbs?

Sprouts from several intersegmental arteries enter the limb bud and form a vascular network within the mesenchyme. Eventually one intersegmental
dominates as the primary axial artery. During development, the vascular network is remodeled into the mature vascular arrangement.

25

The Preaxial channel in the upper limb becomes the ______, while that in the lower limb becomes the

cephalic vein
saphenous vein

26

Nerve trunks from the _______ grow into thelimb bud and associate with the forming skeletal muscles, vessels and skin.,,,signals from mesenchyme at the base of the limb bud appear to direct nerve ingrowth.

forming brachial and lumbosacral plexuses

27

Overall dorsal and ventral pattering is set up by

competing signals for the dorsal and ventral ectoderm.

28

The upper limbs rotate______ and the lower limbs rotate _________

laterally
medially

29

On average limb defects occur in

two per thousand live births

30

When is limb development most sensitive to teratogenic development?

between the 4th to 9th weeks of development.

31

is a potent teratogen that causes significant limb defects.

Thalidomide

32

What is the difference between a defect and a deformation?

defect = morphological abnormality resulting from abnormal developmental mechanisms or processes, thus it is inherent to the process of development.
deformation=abnormal form, shape or position of a normally formed body part. Mechanical forces that impact the child as it develops cause deformations.

33

These types of limb defects would be similar to
amputations along the proximal–distal axis. That is segments or parts of segments are missing distal to the “amputation”.

Transverse Type –

34

The most severe form of Transverse type is
the absence of an entire limb, a condition called

Amelia

35

Transverse type condition where only a segment or part of a segment is missing, e.g. a forearm and hand or a foot. These types of truncation are called

Meromelia.

36

This subset includes defects were there are parts
missing within one or more segments of the limb. For example, the radius and
some digits, along the anterior-posterior axis may be missing or the fibula may be absent.

Longitudinal Type

37

where the missing parts are in the median aspect of the distal limb segment, such as the middle digits, which creates a “lobster claw-like” deformity.

Oligodactyly

38

(seal limb) where the most distal limb segment(s) is (are) attached to the limb girdle, e.g. the hand is
attached to the shoulder girdle or the foot to the pelvic girdle.

Phocomelia

39

Syndactyly and Sirenomelia are both examples of

Failure of Differentiation or Separation of Limb Parts

40

Digits may be completely or partially fused. Fusion may involve only the skin or may include fusion of the bones.

Syndactyly

41

fusion of complete lower limbs or lower limbs represented by a conical stump, is the most extreme case of this type of anomaly.

Sirenomelia

42

a condition where there is one or more extra digits. This may occur unilaterally or bilaterally.

Polydactyly

43

where several digits as well as part of the hand or foot are duplicated.

Diplopodia

44

bands of amnion can break free and wrap around portions of the fetus. Amniotic bands can wrap around a normally formed limb causing a severe constriction or amputation

Congenital Constriction Band Syndrome

45

Clubfoot (also called talipes) is any defect involving the ____ bone.

talas

46

the foot is plantar-flexed (like a horse’s
foot), inverted and adducted (varus). This type is twice as common in boys as in girls.

talipes equinovarus,

47

Cause of Clubfoot

Some believe that most instances of
clubfoot represent a defect the repair of which may involve some surgical as well
as casting procedures. A clubfoot may also be acquired when the foot becomes
located in an abnormal position within the uterus. Clubfoot is often isolated but it
is part of some syndromes. Multifactorial inheritance may also play a role.

48

Developmental Dysplasias: The major problem is that the hip is for some reason

more susceptible to dislocation after birth.

49

Reasoning for Developmenta Hip Dysplasia

This is compounded by the fact that normally at birth the hip joint is somewhat immature and malleable to aid in
the birth process. The thinking regarding this defect is that the hip joint is more insufficiently formed than usual. Congenital hip dysplasia is often associated
with breech births and with a syndrome of generalized joint laxity.

50

What conditions during pregnancy and birth may also contribute to developmental hip dysplasias?

Hormones that make the maternal connective tissue soft at childbirth

51

Pattern of susceptibility for developmental hip dysplasias?

more common in females and may be unilateral or bilateral. The defect tends to run in families

52

characterized by an undescended scapula.
Normally the scapula is located between T2-T7. In this
deformity it is located at C4-T2. The muscles associated with the scapula are hypoplastic or atrophic which limits shoulder movement and is disfiguring.

The Sprengel Deformity

53

Sprengle deformity shows a 3:1 predominance in_____. Usually there are associated anomalies of the_____.

males
spine

54

People with this deformity have a variety of anomalies that include hypoplasia or aplasia of the clavicles, large head, small face, long neck, and a short narrow chest. They also have short fingers and dental problems.

Cleidocranial Dysplasia

55

Cause of Cleidocranial Dysplasia

defect in Runx-2.