Lecture 5 Flashcards
What week will our upper and lower limbs begin to form?
Week 4
What grows first: upper or lower limbs?
Upper limbs. Our body likes to shunt blood to our heads, thus, our upper limbs will grow and develop quicker.
When does primary ossification occur?
Week 12
For our limbs to be made, what do we need?
For our limbs to be made, we are going to need MUSCLE, CARTLAGE and CONNECTIVE TISSUE.
How do we form our limbs?
To form our limbs, we will begin with a layer of [limb forming mesoderm]. This layer of limb forming mesoderm will contain different kinds of mesoderm, because we need to form muscle, cartilage and connective tissue (mesenchyme). Thus, the mesoderm will have 1. Paraxial mesoderm (myotome), to form out muscles 2. Somatic layer of the lateral plate mesoderm to form our [cartilage, bone and connective tissue.] This limb forming mesoderm will release FGF10, causing the overlying ectoderm to thicken and become our AER (apical ectodermal ridge). The AER will then release FGF 8 and 4, which will stimulate the mesoderm to grow and proliferate PROXIMAL–> DISTAL.
we are trying to codense our cartllage
How does proximal –> distal growth occur?
The reciprocal signaling of limb forming mesoderm releasing FGF10 and apical ectoderm ridge releasing FGF8 and 4.
What is special about the mesoderm that becomes bones?
It is already fated to become certain bones via concentration gradients of FGF10 and FGF8 and 4.
What is the most proximal thing formed (which is formed first)?
Stylopod
Stylopod makes what?
Humerus and femur
What forms after the stylopod?
Zeugopod. In our upper: radius and ulna Lower: tibia and fibula
What is the most distal thing formed?
Autopod In our upper: carpals, metacarpals and digits Lower: tarsals, metatarsalsnd and digits
Order of things formed proximal–>distal
- Stylopod 2. Zeugopod 3. Autopod
SZA
(humerus, radius/ulna/metacarpals)
In limb development, what happens in week 5?
- Hand and foot plates form.
Hands before foot
- Chondrification centers form
In limb develpoment, what happens in week 6?
- Digital rays (bones) of the hand are formed because of the condensing of the somatic layer of the lateral plate mesoderm
Here, the entire limb is cartilaginous.
In limb develpoment, what happens in week 7?
- Digital rays (bones) of the FEET are formed
- Osteogenesis of long bones begin
- Limbs begin to rotate
In limb develpoment, what happens in week 8?
Seperate digits are formed VIA apoptosis due to BMP (not having webbed feet is due to BMP)
Limb musculature is derived from what part of the somite?
Dorsolateral Remember, are you DL? DM me.
After proximal–>distal growth, what happens?
Limb musculature will begin during the 5th week. Our muscles will be derived from our dorsolateral plate of the somites.
- Motor neurons (from NEURAL TUBE-neuroectoderm) will enter the bud in week 5. As our muscles grow, they will pull the cell with.
- Sensory neurons (from neural crest) will THEN FOLLOW
- Neural crest WILL ALSO give rise to schwann cells to myelinate.
When do sensory neurons enter?
Sensory neurons will enter following the entrance of motor axons. Neural crest cells travels in the same direction as the neural extoderm. Neural crest cells also give rise to schwaan to myelinate.
Limb rotation occurs when?
Week 7.
How do limbs move in week 5?
Upper and lower limbs grow out laterally and cephallicaly
How do limbs move in week 6?
Pals and soles of the feel will point medially
How do limbs move in week 7?
Limb rotation occurs. Upper limbs will rotate 90 degrees laterally. Lower limbs will rotate 90 degrees medially.
Blood supply of the limbs
Intersegmental arteries from the aorta will come off and go to the limb bud. There, they give rise to primary axial artery.
In the upper limbs, primary axial artery–> Brachial artery and the common interrosseous.
In the lower limbs, primary axial artery–> deep artery of the thigh and the posterior tibial artery
ia angiogenesis, we get the adult patter in the arm
