Embryology 5 - Development of Bone and Muscle Flashcards
What does the mesoderm give rise to?
Most of bones and muscles
Where does the mesoderm emerge from?
Primitive streak
What four things does the mesoderm further divide into?
- Notochord
- Somite (paraxial mesoderm)
- intermediate mesoderm (IM)
- lateral plate mesoderm (LPM)
____ form segmented blocks next to the neural tube.
Somites
What are the three layers of somite?
Dermatome
Myotome
Sclerotome
What structure does the dermatome form?
Dermis of skin
What structure(s) do the myotome form?
Skeletal muscles
What structure(s) do the sclerotome form?
Vertebrae, ribs
Where does the sclerotome develop and what does it eventually form?
Surrounds neural tube and forms vertebra
Where is the sternum derived from?
Lateral plate mesoderm
How many somite pairs have formed at day 20 of development?
1 (at occipital level)
How many somite pairs have formed at day 22 of development?
7-10 pairs
How many somite pairs have formed at day 24 of development?
13-17
How many somite pairs have formed during the 5th week of development?
42-44 (some occipital and coccygeal somite pairs later disappear)
What controls somite segmentation?
cyclic NOTCH signaling
A new somite pair appears every __ hours.
8
What is DELTA protein?
Surface protein on the signal-sending cell that binds to NOTCH protein on neighboring cell to activate NOTCH signaling
What is Lunatic Fringe?
A protein in the signal-receiving cell that mediates whether NOTCH mRNA is translated to NOTCH protein and whether the protein is expressed on the cell surface
What does the NOTCH Protein do?
When bound to delta protein, activates MESP2 gene transcription in signal-receiving cell
What is Spondylocostal dysostosis?
Vertebral defects (scoliosis, hemivertebra, rib fusion) caused by mutations in NOTCH signaling components
The identity of each vertebrae is determined by ____ gene code.
HOX
Loss of HOX10 gene results in ___.
Extension of thoracic-appearing vertebrae into lumbar and sacral regions
Expanded HOX10 expression results in ____.
Extension of lumbar-appearing vertebrae into thoracic region of spine
What are Cervical ribs?
Abnormal Extra rib formation from C7 vertebra
Lateral plate mesoderm gives rise to which bones?
Bones in arms, legs, shoulders, pelvis, and chest
Neural crest (ectoderm) gives rise to which bones?
Bones in the face and jaws
What are the Two Types of Ossification Processes?
- Intramembranous ossification
- Endochondral ossification
What is Intramembranous Ossification?
Osteoblasts deposit mineralized matrix → bone
What is Endochondral Ossification?
- Mesoderm cells come together to form mesenchyme that differentiates to chondrocytes
- Chondrocytes deposit matrix → formation of cartilage as template for future bone
- Osteoblasts invade cartilage via blood vessels at the primary ossification center and replace cartilage with mineralized matrix → bone
What bones do endochondral ossification occur in?
- Vertebrae
- Ribs
- Pelvis
- Limb bones
- skull base
What causes Achondroplasia?
Caused by precocious endochondreal ossification
Caused by mutations in fibroblast growth factor receptor 3 (FGFR3) gene
What bones do intramembranous ossification occur in?
Flat skull bones (frontal, parietal, occipital), clavicle
What Ossification process is involved in healing of bone fractures?
Intramembranous ossification
What gene is essential for ossification?
RUNX2 gene (CBFA1)
What does Cleidocranial dysplasia (CCD) affect?
RUNX2 heterozygous mutation → Intramembranous ossification is impaired
What causes Craniosynostosis?
Caused by premature ossification of skull bones
Skeletal muscle is derived from:
Somite (myotome)
Cardiac muscle is derived from:
Lateral plate mesoderm (cranial region)
Smooth muscle is derived from:
Lateral plate mesoderm
How does skeletal muscle differentiate?
Myogenic progenitor cells → Differentiate into myoblasts → Myoblasts line up to form myotube → Fuse to form muscle fiber (multi-nucleated cell)
What are Myosatellite Cells?
Myoblast-like stem cells that persist throughout life and proliferate and differentiate upon injury to regenerate skeletal muscle
What brings the cardiogenic mesoderm to the thorax?
Cephalic and lateral folding
What is Prune Belly Syndrome?
Defects in urinary system (bladder, urethra) → Degeneration of abdominal muscles
What is Poland Syndrome?
Underdevelopment of unilateral chest wall muscle
Often accompanied by finger defects on the same side
May be caused by an interruption of subclavian arteries during embryo development
