MSS_Devo Flashcards
From what embryonic tissues are skeletal tissues derived?
Initial progenitor tissue is mesenchyme (STFM)
What is the is the STFM for the vertebrae/ribs, sternum and skull dervived from?
Vertebrae: Scleratome tissue of somites
Sternum: somatic mesoderm of ventral body walla
Skull: head mesoderm, scleratome tissue of occipital somites, neural crest ectomesenchyme
What tissue is the appendicular skeleton derived from?
Somatic mesoderm
What are the developmental phases for skeletal tissues?
Mesenchyme cells condense into PMC (pre-skeletal mesenchyme condensations) with inductive signals
What are the similarities and differencnes between intramembranous and endochondral ossification?
Intramembranous: bone is formed directly from mesenchyme. Mesenchyme condense–>differentiation into osteoblsts–> osteoblasts produce osteoid–> mineralization of osteoid
Endochondral: cartilage intermediates. Mesenchyme–> pre-skeletal mesenchymal condensation–> Sox-9–> differentiation into chondrocytes. Chondrocytes secrete cartilage matrix. Mesenchymal cells form perichondrium and express RunX2 –> osteoblasts. vascular tissues invade.–> ossification
What is the role of RunX2 in bone development? Sox-9 in cartilage development?
RUNX2 and Sox9 encode transcription factors
Expression of RunX2–> osteoblast.
Expression of Sox-9–> chondroblast
What is the difference between a primary and secondary ossification center?
Primary ossification center: area of pre-skeletal mesenchyme condenation that is first to ossify. (long bones; usually center of shaft)
Secondary ossification center: additional areas of ossification that appear in pre-natal, post-natal or post pubertal period. ( usually in epiphysis)
How can ossification centers be used to identify the bone age of a patient?
Bone age= amount of epiphyseal cartilage retained in skeleton. Bone age is useful as an indicator of skeletal growth and maturation
1. appearance of calcified material in diaphysis/ epiphysis
2. appearance of dark lines representing epiphyseal cartilage plates that indicate that epiphysis has closed. (no cartilage)
What is the difference between a pituitary dwarf and ahondroplastic dwarf?
Achondroplasia: short proximal extremiteis and shortened skull base because epiphyseal cartilage clsoes early. Pituitary based drawfism is due to interupted bone growth from insufficient production of growth hormones.
What is defected in achondroplasia?
Fgf Receptor 3 gene that affects cartilage formation
How can you differntiate between gigantism and acromegaly?
Giagantism: condition of overgrowth caused by overproduction of pituitary hormones. Before epiphyseal growth plate closure= increased stature. If after closure- increased soft tissue growth in forehead and extremities ( acromegly)
Marfan’s syndrome
Results from defect in fibrillin production. Thin, elongated, spider-like digits on hands and feet. Tall stature. Aortic aneurysms are associated with this condition
Mucopolysaccharidoses
Defect in lysosomal enzymes that degrade proteoglycan molecules. See distortion of face and skull. CNS anomalies
Osteogenesis imperfecta
results from defect in type I collagen. Bones are brittle and easily fractured. May see blue sclera, hearing loss, growth restriction, kyphoscoliosis, macrocephaly.
How does the sclerotome form?
Sclerotome forms during somite differentiation. Neural tube and notochord produce Shh to induce cells in ventral half of somite to undergo epithelium to mesenchyme transformation.
How does the sclerotome mesenchyme become a vertebrae?
Precursor tissues for vertebrae is derived from sclerotome mesenchyme of somites in trunk of embryo. During 4th week of development, scleratome mesenchyme migrates towards notochord and neural tube. Cranial half remains loose while caudal half is tightly packed. During resegmentation, the caudal half of one sclerotome fuesse with the cranial half of sclerotome below it.
Scleratome compartments have been shown to have distinct contributions to vertebra formation. What are they?
Central
Ventral
Dorsal
Lateral
Somitocoel cells
Central: Pedicle, proximal rib
Ventral: vertebral body, intervertebral disc
Dorsal: dorsal part of neural arch, spinous process
Lateral, distal rib
Somitocoel cells: Vertebral joints, intervertebral disc, proximal rib
What structures allow a vertebra to grow?
Neurocentral junction: cartilage between neural arch and centrum that allos for longitudinal growth
what controls axial patterning of vertebrae?
Differential expression of Hox genes along axis of embryo mediates regional patterning of vertebral column in cranio-caudal axis.
How do ribs form?
Costal processes of forming vertebrae grow ventraolaterally forming the Ribs.
How does the sternum form?
Sternal bars appear in the somatic mesoderm forming the ventral body wall of thorax. Sternal bars fuse in midline. Several primary ossification centers from cartilage model of sternum form sternebrae ( xiphoid). Joint that remains between the manubrium and body of the sternum= sternal angle.
Klippel Feil sequence
Possibly due to defect of Hox gene expression. Characteristics: short neck, low hairline, restricted neck morevments, number of cervical vertebral bodies is less than normal.
Spina Bifida
Failure of fusion of halves of vertebral arch. Spina Bifida occulta: one or two vertebrae are involved ( usually asymptomatic)
Accessory ribs
Result from extension of costal processes of cerivcal or lumbar vertebrae. Cervica rib on C7 can put traction on trunk of brachial plexus.
Hemi-vertebrae
results from failure of one of the chondrification centeres of centrum to form. Results in a vertebrae with a wedge shaped body that sets up imblance in spine–> result sin scholiosis
Rachischisis
vertebrae have unfused spinous process (Open spine)
Lumbarization
Sacral vertebrae fails to fuse with the sacrum and remains free as 6th lumbar vertebra
Sacralization
5th lumbar vertebra becomes incorporated into sacrum
Scoliosis
condition where abnormal lateral curvature forms in the spine
Sternal clefts
abnormal fusion of sternal bars. Precuts Excavate: concave depression. Precuts Cranium: convex elevation of sterum
From what embryonic tissues are the 3 types of muscle tissues derived?
Skeletal muscle: myotome tissue of somites; head mesoderm
Visceral smooth muscle: splanchnic mesoderm
Vascular smooth muscle: local mesoderm; neural crest ectomesenchyme
iris muscles: ectoderm
ciliary muscle: neural crest
cardiac muscle: splanchnic mesoderm of heart fields
How does muscle tissue develop?
Skeletal muscle forms from somites. Wnt signaling at the dorsal half of somite remains epithelium= dermomyotome (DM). Cells of the Medial edge of DM (wnt, shh) undergo mesenchyme transformation. Cells of lateral mesoderm (Bmp) also undergo EMT and migrate under DM. Cells become myogenic ( skeletal m. precursoe) and express myogenic regulatory factors (myf5 and myoD). Myogenic cells eventually become myoblast. Myoblasts fuse to form multinucleated myotubes. Myotubes differntiate into primary muscle fibers. Secondary muscle forms later.
What is the lateral somite frontier?
LSF is located between paraxial and lateral mesoderm. Boundary is created by gradient of signaling molecules. Medial= primaxial domain. Lateral domain= Abaxial domain
what are some mechanisms used to form named skeletal muscles from myoterm derived muscle precursors?
Fusion of adjacent myotomes, splitting longitudinally into parts or into layers, by changing fiber direction, by atrophy of portions of muscle mass.
How could alternations of muscle development mechanisms lead to normal variations of muscle morphology?
Failure of pre-muscle mass to split properly could result in absence of a muscle or muscle belly. Excessive splitting could result in extra bellies for a particular muscle?
What is the basic plan for innervation of skeletal muscle?
Skeletal muscle derived from myotomes in trunk are innervated by spinal nerves.
Skeletal muscle derived from head mesoderm or occipital somites are innervated by cranial nerves. Myotomes in trunk are subdivided into Epaxial ( dorsal primary rami) and Hypaxial (ventral primary rami)
What is a body wall segment?
A section of spinal cord level that includes the skeletal muscle, skin and pair of spinal nerves.
What is muscular dystrophy?
Progressive deterioration of skeletal muscle. Duchenne is most common form. X-linked and affects boys in early childhood. Myocytes are suspectible to damage due to lack of dystrophin.
What is congenital torticollis?
Fixed rotation of the head to the side cause by defect in SCM. Acquired due to birth injury to SCM.
What is prune belly syndrome
Condition in which muscles of the abdominal wall are absent. Associated with anomalies of urinary bladder and urinary tract or urethral obstruction.
What is poland sequence?
condition characterized by absence of petoralis major and pectoralis minor muscles. More common on right. Associated anomalies include absent of breast tissues, hypoplasia of rib cage and upper limb defects.
How does the limb begin its development?
Limb fields are areas of somatic mesoderm located on each side of the embryo. Hox gene expression controls localization of limb fields. Specific transcription factors are expressed in upper (TBX5) and lower limb (TBX4 and Pitx1) Limb bud outgrowth is initiated by signaling molecules (FGF and Wnt). These signals induce FGF 10 expression–> limb bud formation.
From what embryonic tissues is the limb derived from?
Somatic mesoderm: skeletal elements, connective tissue, dermis
Surface ectoderm: epidermis
Somitic mesoderm: migrate sinto limb bud–> forms skeletal muscle
Nerve fibers from ventral primary rami migrate into limbs and surrounded by neural crest derived schwann cells
What are the major axes for pattern formation and growth?
Proximal-distal: limb elongation
Dorsal-ventral: muscle and nerves organization into compartments
Anterior-posterior: digits
How do limb progenitor tissues interact to elongate?
FGF10 (somatic mesoderm of bud) initiates secretion of FGF 8 in distal ectoderm–> thickening to form apical ectodermal ridge (AER). AER acts as a signaling center for underlying mesenchyme (fgf8) induces mesenchyme to proliferate. Mesenchyme adjacent to AER continues to express FGF 10 to maintain AER function until all limb segments are formed.
How did the digits become arranged? What are the key signaling molecules?
Signaling from Zone of polarizing activity (ZPA) on posterior border of limb secrestes SHH–> initiates expression of HOX genes in over lapping nested fashion. Large digit develops on preaxial (cranial) border.
what is the role of apoptosis?
AER in web of condensed mesenchyme between digital rays triggers apoptosis for digit separation.
How are skeletal muscle, vascular, and neural precursors patterned during limb development?
Skeletal muscles are derived from somitic mesoderm. Influenced by mesenchyme cells at limb bud. Sprouts from intersegmental arteries enter limb bud form vascular networks. Pre-axial channel of upper limb becomes cephalic vein while in lower limb, becomes the saphenous vein. Nerve trunks from brachial and lumbosacral plexuses grow into limb bud.
Expression of what genes control dorsal and ventral patterning during limb devo?
Dorsal ectoderm expresses wnt and radical fringe (Rf) that induce expression of Lmx-1 in underlying mesoderm of dorsal half of limb. Engrailed-1 expression (by ventral mesoderm) inhibits Lmx-1
In which direction does each limb rotate?
upper limbs rotate laterally.
Lower limbs rotate medially
What is the frequency of limb anomalies?
2 per 1000 live births
When is limb development most sensitive to tertogenic development?
4th and 9th week.
What is a teratogen that causes limb defects?
Thalidomide
What is the difference between defect and deformation?
Defect is morphological abnormality from abnormal development process. A deformation is an abnormal form, shape or position of normally formed body part.
What is Amelia?
Absence of an entire limb
What is meromelia?
Segment or part of a segment is missing (forearm, hand or foot)
What is Oligodactyly?
Missing parts are in median aspect of distal limb segment ( middle digits– lobster claw)
What is phocomelia?
Seal limb– most distal limb is attached to limb girdle ( hand to shoulder)
What is syndactyly?
failure of separation of limb parts where digits are fused
What is sirenomelia?
Complete fusion of lower limbs
What is polydactyly?
Condition where there is one or more extra digits
What is diplopodia?
Several digits, part of hand or foot are duplicated
What is clubfoot?
Defect involving talas bone. Talipes equinovarus: foot is plantarflexed, inverted and adducted
What is developmetal dysplasia of the hip?
Hip is more susceptible to dislocation after birth. Insufficiently formed. Associated with breech birth and syndrome of generalized joint laxity.
Sprengel deformity?
Chracterized by undescended scapula. Muscles associated with scapular are hypoplastic or atrophic.
Cleidocranial dysplasia
Believed to be due to defect in Runx-2. Characterized by hypoplasia of clavicles, large head, small face, long neck and short narrow chest, short fingers and dental problems.
What is a potential problem with gluten free diets? Why is it important?
Folate deficiency. Folate is essential for normal cell differentiation. Deficiency can result in spina bifida, ancephalopathy
What is the recommendation intake for folate?
Women: 400 mcg; during pregnancy: 600 mcg
What is the risk with fish oil supplements?
Vitamin A toxicity. Retinol form is stored in liver and can be teratagenic during pregnancy
What is the risk with babies who are exclusively breast fed?
Vitamin D deficiency. Breast milk is inadequate in vitamin D. Recommended to supplement with 200 IU vit D daily
What is the risk of babies on TPN w/o fat emulsion?
Essential fatty acid defiency. Symptoms: compromised wound healing, slowed growth and dry scaly skin
What is the risk of lactose intolerance in adolescence?
Calcium deficiency. Phytates in grains, iron supplements can interfere with calcium absorption. Requirements: 1300 mg 9-18 yo. 1000mg 19-50.
