Anatomy Lecture 13_Limb Development Flashcards
What levels of mesoderm give rise to which structure in developing limbs?
Paraxial mesoderm gives rise to somites that migrate and give rise to muscle Lateral plate mesoderm gives rise to the cartilage that is eventually calcified into bone
Describe the axises of growth
Describe the apical ectodermal ridge (AER)
It is the area of elongating limb growth. It is driven by growth factor FGF 10 and FGF 8
What is the Zone of Polarizing activity (ZPA)
It is the region where the posterior/anterior axis is established in the limb bud. Sonic Hedghog (SHH) consentrates in the ZPA which is located at the posterior aspect of the limb bud. This establishes an SHH gradient across the forming limb bud.
Define Stylopod, Zeugopod, and Autopod
Stylopod - Upper arm, area of the Humerous,
Zeugopod - Lower arm, area of the radius and ulna
Autopod - Area of the hand
What is the purpose of SHH
Consentrations of SHH determins which bones form. Low consentrations form the radius in the Zeugopod and the thumb in the auto pod. Medium consentrations give rise to the second and third digits. High concentrations give rise to the ulna in the zeugopod and the 4th and 5th digits in the autopod.
Define Amilia and what causes it
It is the complete absense of limbs. It is often caused by a failure in FGF 10 which prevents the AER froming and thus prevents the ZPA.
Define polydactyly. What casues it?
Polydatyly is the presence of extra fingers. It is often the result of an atypical SHH gradient.
What is Syndactyly and what causes it?
Syndactyly is webing between the digits. It is a result of signaling problems between SHH and bone morphogenic protein (BMP). Typically the webing is removed by apoptosis and is directied by normal BMP signaling
What governs which HOXD genes are expressed?
HOXD genes are expressed based on their proximal distal position on the limb. More proximal locations express fewer of the HOXD9-13 genes while the most distal (metacarples and digits) express all of them.
Define Meromelia and what causes it
Meromelia is the partial absense of limbs. It is typically a result of problems with HOXD genes
How is the Dorsal/Ventral axis established?
WNT-7a is expressed in the dorsal ectoderm while EN-1 is expressed in the ventral ectoderm. EN-1 suppresses the expression of WNT-7a ventrally and thus establishes a WNT-7a dorsal ventral gradient which establishes the anterior nad posterier compartments of the arm.
