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
