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Embryology > Development Of Limbs > Flashcards

Development Of Limbs Flashcards

1
Q

When do the limb buds first appear as small elevations of the ventrolateral body wall

A

End of fourth week

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2
Q

The upper limb buds are visible by day _ to ), where are the lower limb buds are visible when

A

262-27

1-2 days later

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3
Q

Each limb bud consists of a mass of mesenchyme covered by ___

A

Ectoderm

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4
Q

The mesenchyme is derived from the somatic layer of the __ ___

A

Lateral mesoderm

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5
Q

The limb buds elongate by proliferation of the ___

A

Mesenchyme

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6
Q

Although the early stages of limb development are alike for the upper and lower limbs, there are distinct differences. Why

A

Bc of their form and function

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7
Q

The upper limb buds develop opposite the __ ___ segments, whereas the lower limb buds form opposite the ___ and ___ ___ segments

A

Caudal cervical

Lumbar and upper sacral segments

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8
Q

At the apex of each limb bud, the ectoderm thickens to form an apical ectodermal ridge. What is the AER

A

Specialized multilayered epithelial structure, interacts with the mesenchyme int he limb bud, promoting outgrowth of the bud for which BMP is essential

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9
Q

Retinoids acid promotes the formation of the limb bud. How

A

By inhibiting FGF8 signaling

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10
Q

The AER exerts an inductive influence on the limb mesenchyme that initiates growth and development of the limbs in a proximodistal axis

A

Mesenchymal cells aggregate at the posterior margin of the limb bud to form a zone of polarizing activity

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11
Q

FGF from AER activate what, causing what

A

The zone of polarizing activity

Causing expression of Shh, which controls the patterning of the limb along tha AP axis

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12
Q

Expression of wnt7 from the dorsal epidermis of the limb bid and engrailed (En-1) fromt he ventral aspect is involved in specifying the dorsoventral axis

A

The AER itself is maintained by inductive signals from Shh and Wnt7

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13
Q

The mesehchyme adjacent to the AER consists of undifferentiated, rapidly proliferating cells, whereas the mesenchymal cells proximal to it differentiate into blood vessels and cartilage bone models

A

For cartilage formation, TGFB signaling plays. A key role. The distal ends of the limb buds eventually flatten into hand and foot plates

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14
Q

By the end of the 6th week of development, mesenchymal tissue in the hand plates has condensed to form what

A

Finger buds-digital rays

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15
Q

What are fingerbuds/digital rays

A

Outline the pattern of the digits

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16
Q

During the 7th week, similar condensations of mesenchyme in foot plated form what

A

Toe buds/digital rays

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17
Q

At the tip of each digital ray, a part of the __ induced development of the mesenchyme into the mesenchymal primordia of the bones in the digits

A

AER

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18
Q

The intervals between the digital rays are occupied by ___ ___

A

Loose mesenchyme

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19
Q

Soon the intervening regions of mesenchyme undergo ____ forming notches between the digital rays

A

Apoptosis

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20
Q

As epoptosis occurs, separate digits are produced by the end of the __ week

A

8th

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21
Q

What controls the cell apoptosis between digits

A

Anatagonism between TGFB and retinoids acid

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22
Q

What happens if you block cellular and molecular events during the apoptosis between digits

A

Webbing, fusion of the fingers or toes

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23
Q

Syndactylyl

A

Webbing, fusion of fingers or toes

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24
Q

The mesenchyme in a limb bud gives rise to what

A

Bones, ligaments, and blood vessels

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25
Q

As the limb bud elongate during the early part of the 5th week, mesenchymal models of the bones are formed by cellular aggregations

A

Ok

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26
Q

___ __ appear later in the fifth week

A

Chondrification centers

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27
Q

By the end of the sixth week, the entire limb skeleton is cartilaginous

A

Ok

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28
Q

Osteogenesis of th elong bones begins in the _ week from primary ossification centers in the diaphysis of the long bones

A

Diaphyses

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29
Q

Ossification centers are present in all long bones by the _ week

A

12th

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30
Q

Primary ossification of the carpal bones begins during the _ year

A

1st

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31
Q

From the dermomyotome regions of the somites, myogenic precursor cells also migrate into the limb bud and later differentiate into ___,

A

Myoblasts

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32
Q

As the long bones form, myoblasts aggregate and form a large muscle mass in each limb bud.

A

In general this muscle mass separated into dorsal (extensor ) and ventral (flexor) components

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33
Q

The muscle mass separates into __(extensor) and __(flexor)

A

Dorsal

Ventral

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34
Q

Early in the 7th week, the limbs extend centrally and the preaxial and postaxial borders are cranial and caudal,

A

Respectively

35
Q

The upper limbs rotate __ through 90 degrees on their longitudinal aces

A

Laterally

36
Q

The future elbows point ___ and the extensor muscles lie on the lateral and posterior aspects of the limb

A

Dorsally

37
Q

The lower limbs rotate __ through almost 90 degrees

A

Medially

38
Q

The future knees face __ and the extensor muscles lie on the __ aspect of the lower limb

A

Ventrally

Anterior

39
Q

Motor axons arising from the spinal cord enter the limb bud during the _ week and grow into the dorsal and ventral muscle masses

A

Fifth

40
Q

Sensory axons enter the limb buds after the motor axons and use them for guidance

A

True

41
Q

__ _ __, the precursors of Schwann cells, surround the motor and sensory nerve fibers into e limbs and form the neurolemmal myelin sheaths

A

Neural crest cells

42
Q

What is a dermatome

A

Area of skin supplied by a single spinal nerve and its spinal gangl

43
Q

During the _ week, the peripheral nerves grow from the developing limb plexuses into the mesenchyme of the limb buds

A

5th

44
Q

The spinal nerves are distributed in segmental bands, suppplying both the dorsal and ventral surfaces of the limb buds.

A

As the limbs elongate, the cutaneous distribution of the spinal nerves migrates along the limbs an no longer reaches the surface in the distal part of the limbs

45
Q

Although the original dermatome pattern changes during growth of the limbs, an orderly sequence of distribution can still be recognize din the adult

A

Ok

46
Q

In the upper limb, the areas supplied by _ and _ adjoin the areas supplied by _ - and _, but overlap between them is minimal at the ventral axial line

A

C5 and c6

T2, T1, and C8

47
Q

Bc there is overlapping of dermatomes, a particular area of skin is not exclusively innervated by a single segmental nerve

A

The limb dermatomes may be treated progressively down the lateral aspect of the upper limb and back up its medial aspect

48
Q

The limb buds are supplied by branches of the __ arteries

A

Intersegmental

49
Q

The intersegmental arteries arise from the dorsal aorta and from a fine capillary network throughout the ___

A

Mesenchyme

50
Q

The primordial vascular pattern consists of a primary axial artery and its branches which drain into a peripheral marginal sinus

A

Blood int he sinus drains into a peripheral vein

51
Q

The vascular pattern changes as the limbs develop, chiefly as a result of vessels sprouting fro existing vessels (angiogenesis)

A

The new vessels coalesce with other sprouts to form new vessels

52
Q

The primary axial artery becomes the brachial artery in the arm and the ulnar and radial arteries in the forearm, its terminal branches of the brachial artery

A

As the digits form, the marginal sinus breaks up and the final venous pattern, represented by the basilica and cephalic veins and their tributaries develops

53
Q

In the thigh the primary axial artery is represented by the deep artery of the thigh

A

In the leg, the primary axial artery is represented by the anterior and posterior tibial arteries

54
Q

Ectrodactylyl

A

Cleft hand or cleft foot where one or more central digits are absent

55
Q

What causes ectrodactylyl

A

Failure of one or more digital rays to develop

So hand or foot is divided into two parts that oppose each other

56
Q

Syndactyly

A

Remaining digits are partially or completely fused

57
Q

Congenital absence of radius

A

Radius is partially or completely absent. Hand deviates laterally (radially) and the ulna bows with the concavity on the lateral side of the forearm.

58
Q

What causes congenital absence of the radius

A

Failure of the mesenchymal primordium of the radius to form during the 5th week
Or genetic factors

59
Q

Polydactylyl

A

Supernumerary digits
Common
Usually incompletely formed and lacks proper muscular development , rendering it uselesss

60
Q

Are extra digits medial or lateral on hand and feet

A

Medial or lateral hand

Usually lateral foot

61
Q

Polydactylyl is inherited how

A

AD

62
Q

What is the most common limb defect

A

Cutaneous syndactylyl

63
Q

What is cutaneous syndactylyl

A

Simple webbing of digits

64
Q

Is cutaneous syndactylyl more common in hand or foot

A

Foot

65
Q

Syndactylyl is most frequently observed between _ and _ fingers, and between te _ and _ toes

A

3,4

2,3

66
Q

How is cutaneous syndactylyl inherited

A

Simple dominant or simple recessive.

67
Q

What causes cutaneous syndactylyl

A

Failure of the webs to degenerate between two or more digits

68
Q

In some cases of syndactylyl there is synostosis. What is synostosis

A

Fusion of bones

69
Q

Osseous syndactylyl

A

When the notches between the digital rays do not develop during the seventh week as a result of separation of the digits does not occur

70
Q

Arthrogryposis muliplex congenita

A

Heterogenous group of MSK disorders characterized by multiple contracture, and immobility of two or more joints from birth

71
Q

Incidence of arthrogryposis multiplex congenita

A

1/300

More males in sex linked cases

72
Q

Cause of arthrogryposis multiplex congenita

A

Neurologic (central and peripheral nervous system defects

Non-neurologic (cartilaginous defects and restricted movement in utero)

73
Q

Congenital talipes

A

1/1000

74
Q

Talipes equinovarus

A

Most common
Males
Sole of foot is turned medially and the foot is inverted

75
Q

Cause of talipes

A

Hereditary
Environmental

Follows multifactorial pattern of inheritance :intrauterine position that results in abnormal positioning of the feet may cause talipes if the fetus is genetically predisposed to this deformity

76
Q

Amelia

A

Complete absence of limb

77
Q

Meromelia: hemimelia

A

Partial absence of a limb

78
Q

Meromelia:phocomelia

A

Hands and feet are attached close to the body

79
Q

Suppression of limb bud development in early part of fourth week

A

Amelia

80
Q

Arrest or disturbance of the differentiation or growth of the limbs during the 5th week results in what

A

Meromelia

81
Q

HOW, BMP, SHH, WNT7, EN1, others

A

Brachydactylyl or osteogenesis imperfecta

MUTANT GENES

82
Q

Thelidomide

A

Teratogen

83
Q

Combination of genetic and env factors

A

Congenital dislocation of the hip

84
Q

Vascular disruption and ischemia

A

Limb reduction defects

Embryology (12 decks)

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