Week 3 Embryonic Dev. - Ach Flashcards
What are the functions of a notochord?
define axes
mechanical role in folding process
Induces signaling for the neural tube
What does the neural tube induce?
formation of the somites
What is mesenchyme?
embryonic connective tissue
multipotent
derived from mesoderm and neural crest
What week do limb buds appear??
WEEK FOUR!
Why is week 4 a critical period?
Neural tube begins to close
Appearance of somites
Limb buds appear
Organ systems start developing
How are somites formed? How many pairs are formed?
Somitomeres become compacted and bound by epithelium to become somites.
42-44 paris are formed
Which pairs remain somitomeres and do not compact into somites?
Pairs 1- 7
What are somitomeres?
paired blocks of loose mesoderm derived from paraxial mesoderm. They form segmentally along each side of neural tube at the end of the 3rd week
What happens in intramembranous ossification?
Mesenchymal cells differentiate directly into osteoblasts
EX: flat skull bones
What happens in endochondral ossifications?
- long bone formation
- Mesenchymal cells transforms into chondroblasts
-chondroblasts hyaline cartilanginous model
- deposition of ca+
- Osteoblasts in diaphysis form primary ossification center
- osteoblast replace cartilage with bone
- Growth plate (epiphyseal) continues to lay down hyaline cartilage, lengths bone from diaphysis toward epiphysis
- Secondary ossification centers are in epiphysis (most form postnatally). Growth toward daiphysis
How is bone age determined?
presence/absence of ossification centers and status of growth plate
Achondroplasia
can’t covert all the cartilage into bone
most common form of dwarism (limbs short)
Acromegaly
excess growth hormone secretion after closure of growth plates. INCORRECT PORPORTIONS. Big head, feet, and hands
Gigantism
excess growth hormone before growth plase closure. NORMAL PORPORTIONS. Big overall
Marfan Syndrome
Mutations in fibrillin-1
Affects connective tissue
Results in long limb, cardio and lung problems (Abe lincoln)
Osteogenesis imperfecta
Type 1 collagen gene
Extreme bone fragility
Sponateous fractures
Congenital Hip DYsplasia/ Dislocation
Incomplete formation of acetabulum (femurs can’t stay in place). Legs help at different positions, less movement, uneven leg length
Where do smooth muscles of the gut and respiratory come from?
Originates from splanchnic mesoderm of the lateral plate
Explain resegmentation of the vertebral column during development
- sclerotome cells surround notocord.
- Each segment is divided by an intersclerotomic fissure (von Ebner’s)
- this is where the spinal nerves will go through
- then each vertebra is formed by the dense part of one somite and the loose of another
Describe formation of the intervertebral discs
The von ebners fissures become the discs.
Nucleus pulposis is derived from the notochrod.
The annulus fibrosis derived from the sclerotome
Spinda bifida
failure of the neural tube to close. (occulta, meningocele, meningomyelocele)
Spinda bifida occulta
least severe
marked by tuft of hair
Spina bifida meningocele
meninges protrude through defect in spindal cord or skull
cyst, but cord is not in cyst
Spinda bifida meningomyelocele
meninges and spinal cord protrude through defect. Most severe
Congenital dermal sinus
neural ectoderm fails to completely separate from the surface ectoderm. Spinal cord may be tethered
hemivertebra
caused by failure of ossification center on one side of vertebral body (can cause congenital scoliosis)
Congenital brevicollis
shortened neck due to non-segmentation of cerical vertebrae. Limited movement of neck, low hairline.
Pectus excavatum
excess cartilage in sternum. Repairable. Concave chest
Thoracic outlet syndrome
C7 forms rudimentary rib that can compress neurovascular structures
What do myoblasts in epimere form? What innervates them?
deep muscles of the back. Erector spinae
-innervated by the dorsal primary rami
What do myoblasts in the hypomere from? what innervated them?
the trunk wall.
-ventral primary rami
Poland syndrome
underdevelopment of absence of pectoralis muscles
Prune belly syndrome
poor development of abdominal muscle wall causing skin to wrinkle
Congenital torticollis
spasm of shortening of one side of sternocleidomastoid muscle. Head twisted to one side.
apical ectodermal ridge (AER)
growth proximal to distal
cells further from AER differentiate
-AER also induced apoptosis to get rid of webs between fingers
Zone of polarizing activity (ZPA)
- responds to FGFs from AER
- determines anterior vs. posterior (thumb vs. little finger)
Amelia
absence or malformation of one or more limbs
Meromelia or Phocomelia
partial absence of one or more limbs. Reduction in long bone length
Polydactyly
duplication of digits
most common is little finger
Syndactyly
failure of apoptosis resluts in webbed finers and or/toes. Can be inherited or develop in isolation.
Clubfoot
unusal positioning of foot
