Limb Development in Embryology

<p>Nail folds (A)</p> Signup and view all the answers

<p>Without them, development stops (B)</p> Signup and view all the answers

<p>Fibroblast growth factor (FGF) 10 (A)</p> Signup and view all the answers

<p>TBX5 (B)</p> Signup and view all the answers

<p>Day 26 (D)</p> Signup and view all the answers

<p>Limb bud (B)</p> Signup and view all the answers

<p>Parietal layer of lateral plate mesoderm (C)</p> Signup and view all the answers

<p>Paddle-shaped (C)</p> Signup and view all the answers

<p>HOX genes (C)</p> Signup and view all the answers

<p>Opposite cervical segments (C)</p> Signup and view all the answers

<p>Sonic hedgehog (SHH) (A)</p> Signup and view all the answers

<p>Apical Ectodermal Ridge (AER) (A)</p> Signup and view all the answers

<p>Formation of extra digits (polydactyly) (A)</p> Signup and view all the answers

<p>Bone segments (A)</p> Signup and view all the answers

<p>Hox genes, BMP, and WNT-7 (D)</p> Signup and view all the answers

<p>By inducing cell proliferation in the mesenchyme (D)</p> Signup and view all the answers

<p>Keep cells in the progress zone proliferating (C)</p> Signup and view all the answers

<p>Regulation by sonic hedgehog (SHH) (C)</p> Signup and view all the answers

The process of limb development begins with the activation of mesenchymal cells from the lateral mesoderm. These cells form limb buds, which are elevations or swellings on the ventrolateral body wall.

The HOX genes, particularly HOXB8, regulate the positioning of the limbs along the craniocaudal axis. These genes play a critical role in patterning the bones of the limbs.

The transcription factor TBX5 is crucial for the specification of the forelimb, while TBX4 regulates the development of the hindlimb. These factors determine the identity of each limb.

Fibroblast growth factor 10 (FGF10) is secreted by the lateral plate mesoderm in the limb-forming regions. This growth factor plays a critical role in initiating limb outgrowth.

The upper limb buds appear lower on the embryo's trunk because the cranial half of the embryo develops earlier. This leads to the upper limbs developing opposite the caudal cervical segments.

The lower limb buds develop opposite the lumbar and upper sacral segments. The timing of their appearance is slightly later than the upper limb buds, making them appear slightly lower on the embryo's trunk

The mesenchymal core of the limb bud forms the bones and connective tissues of the limb. This core is surrounded by a layer of cuboidal ectoderm.

The paraxial mesoderm contributes to the formation of muscles in the limbs. This mesoderm develops along the sides of the neural tube and plays a critical role in muscle formation.

The proximal part of the limb develops before the distal part, forming a paddle-like structure for the hand or foot, separated by a constriction.

Fingers are formed by indentations in the hand plate, with mesenchymal condensations appearing as digital rays. Webs between fingers regress as development progresses.

Limb muscles are derived from myotomes of the somite that migrate into the limb, with specific segmental levels providing cells for specific limbs.

The ventral muscle mass of the limb forms the flexor and pronator groups in the upper limb and flexor and adductor groups in the lower limb.

The dorsal muscle mass of the limb forms the extensor group of muscles in both the upper and lower limbs.

The apical ectodermal ridge (AER) is a thickened area of ectoderm at the tip of each limb bud that is essential for limb development along the proximodistal axis. It secretes signaling molecules, primarily FGF, which stimulate proliferation of underlying mesenchyme, leading to outgrowth of the limb in a proximal-to-distal direction.

The area beneath the AER in the limb bud composed of rapidly dividing mesenchymal cells. Cells in the progress zone differentiate into cartilage and bone as they move away from the AER's FGF influence.

A specialized region of mesenchyme located on the posterior side of the limb bud that secretes Sonic hedgehog (Shh) signaling molecules. The ZPA controls the pattern of digits along the anteroposterior axis, ensuring the correct order of digits (thumb to little finger) from anterior to posterior.

A signaling molecule secreted by the ZPA that plays a crucial role in regulating digit formation and patterning along the anteroposterior axis of the limb. Shh is essential for establishing the correct order and number of digits.

The development of the limb from proximal to distal (shoulder to fingers). This process is regulated by the AER and the progress zone.

Development of the limb from anterior to posterior (thumb to little finger) and is controlled by the ZPA and its Shh signals.

The development of the dorsal/ventral (back of the hand/palm) axis of the limb. This is regulated by specific gene expression in the dorsal and ventral ectoderm.

One of three major segments of the limb: stylopod (humerus/femur), zeugopod (radius/ulna or tibia/fibula), and autopod (hand/foot components).