week 2 mixture Flashcards
at what week is the limb buds visible as outpouchings from the ventrolateral body wall?
week 4
what does the mesoderm give rise too?
skeleton, skeletal muscle, circulating system, genitalia system
what does the endoderm give rise too?
give rise to the respiratory and GI tract
what did the ectoderm give rise too?
CNS?
which 2 germ layers give rise to limbs
mesoderm and ectoderm
explain the origions of the limb buds?
the buds contain a core of tissue derived from lateral plate mesoderm which is covered by a layer of ectoderm.The mesoderm core differentiates and condenses into mesenchyme – this will form the bones and connective tissue of the limbs
what is the skeletal muscle dervived from?
paraxial mesoderm
what does paraxial mesoderms form on either side of the neural tube?
somites
what do somites form?
muscle of the limbsg and they go from the somites to the developning limb buds
what does the somites differentiate too?
somties divide into a ventral part called sclerotome forms –> vertebral column
also divide in a dorsalateral part forms a dermomyotome which divides into a dermatome and a myotome.
dermatome –> give rise to the dermise of the skin and
myotome gives rise to skeletal
what do the myotome differentiate too and what are there functions?
form dorsal epimere –> dorsal part will form the muscle of the dorsum ( near the vertebrate)
form ventral hypomere –> travels ventrally and forms the muscle of teh thorax and abdomen
When ventral hypomere migrate too the limb buds what do they form?
skeletal muscle in the limb buds
what nerves innervate the epimere ?
dorsal rami of spinal nerve?
What nerves innervate the structures formed by the hypomere? ( muscle of thorax and skeletal muscles of teh limb buds
ventral rami of the spinal nerve
where do limb skeletal muscle originate from?
hypomere region adjacent to the level of the developing upper (C5-C8) and lower (L3-L5) limb buds
are the hypomere migrate to the imb buds they divide into 2 parts. What are these 2 parts?
Posterior condensation: –> Extensors and supinator’s of the upper limbs and Extensors and abductors of lower limb.
Anterior condensation: Flexors and pronators of the upper limbs
Flexors and adductors of the lower limb
what nerves supply the upper limb?
C5 -T1 –> brachial plexus
what nerves supply the lower limb?
lumbosacral plexus –> L4-S3
between which weeks does limb rotation occur?
weeks 6 and 8
how do the upper limbs rotate in embroyinic development?
they rotate 90° laterally (outwards) so flexors lie anterioly
how do the lower limbs rotate in embroyinic development?
Lower limbs rotate 90° medially ( move to middle) so flexors lie posteriorly
what do flexor and extensor muscles do?
flexor muscle –> contract you muscles
extensor muscles –> straighten your muscles
how many nerves supply a dermatome?
one pair of nerves
why is dermatomes important?
You can use it to see if there is any damage for a particular part of the spinal cord
what are the 3 axes in which the limbs develop?
proximidistal axis, craniocaudal and Dorsoventral axis
how to the apical ectodermal ridge (AER) form?
lateral plate mesoderm secrets Fgf 10 which induces thickening of the overlining ectoderm along the tip of the limb bud
what growth factors does AER produce and what does it affect?
produces Fgf 4 and 8 –> promote the growth of underlining mesenchymal
what is the zone of progress ?
is the zone of the growth of the limb bud
what does the dorsal and ventral ectoderm express?
dorsal ectoderm express wnt7 while the ventral ectoderm expresses Engrailed 1 which inhibit wnt7 –> dorsoventral axis
what is formed with high levels of wnt7?
growth of nails
what does high level of engrailed 1 promote?
formation of your palms
how is the craniocaudal axis determined?
small region of mesenchyme in the caudual part of the limb bud –> contain zone of polarising activity wheree contain the sonic hedgehog protein (shh) is expressed
what direction does shh move and what is the outcom of this movement?
the shh moves cranially away from the zhh and the concentration of shh decreases the further away from the zhh. –> craniocaudal patterning
what does high and low concentration of shh induce?
high concentration of shh induces the foramtion of caudual structures such as little finger while low concetration of shh induces the formation of cranial structures such as big toe or thumb
what occurs in week 6 of limb formation
terminal parts of the limb flatten to form hand and food plates
how are fingers and toes formed?
appoptosis occurs in the apical ectodermal ridge to divide AER into 5 fingers or toes of each hand or foot and the AER keep growing to form fingers or toes.
what week does apoptosis of the fingers and toes occur?
week 8
what is the malformation of amelia and what is the couse ?
is the complete absense of limbs and this is caused by the absense of fibroblast growth factors (FGF) very early on which means there is no promotion of limb buds outgrowth
what is maromelia and what is the course?
it is the partial growth of the limbs but absense of fgf later on causes the lack of full formation of the limbs
what is phocomelia and what is the course?
it is premature development of digits and affect either upper or lower limb. Can be due to either genetic factors or teratogens –> Thalidomide inhibits Fgf 10 and 8 expression
what is syndactyly? How is it fixed?
is it the fusion of digits –> lack of apopotisis between the AER in the hands
surgically easy to fix as the hands have fully formed
what is polydactyly?
extra formation of digits? over expression of shh
what is Ectrodactyly ?
split of the hands and feet. It is the failure for the middle of AER to form properly.
