Lecture 13: Osteogenesis And Joints Flashcards Preview

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Flashcards in Lecture 13: Osteogenesis And Joints Deck (9):

List some characteristics about intramembranous bone formation.

- Aggregation of mesenchymal cells:
-- Controlled by following signals: Wnt, Hedghog, FGF, TGF-β
- Mesenchymal cells → osteoblasts
- Osteoblasts secrete osteoid, trapping some of the osteoblasts = blastema.
- Trapped osteoblasts → osteocytes: (through heat)
- Osteocytes form a functional syncytium
- Mineralization occurs via calcium ions.
- Osteoblasts form an epitheliallike covering over the surface of primary bone tissue and can secrete more osteoid on the surface:
-- Osteoid includes collagen I and non-collagen proteins.
- Primary ossification center becomes a trabecula.
- Numerous trabeculae fuse together to form spongy bone.
- Initial bone is woven bone:
-- Collagen fibers are arranged randomly.
- Collagen fibers become aligned:
-- Bone becomes lamellar.
- Lamellae may become symmetrically arranged around a blood vessel forming an osteon (Haversian system).
- Membrane bone usually consists of two layers of compact bone enclosing a layer of spongy bone (diploe).
- See Slides 6-13


List the steps of endochondral bone formation

- Cartilage is REPLACED by bone.
- Primary ossification center occurs in future diaphysis of cartilage model.
- Chondrocytes become hypertrophic.
- Chondrocytes secrete vascular endothelial growth factor.
- Blood vessels break through perichondrium, bringing in osteoprogenitor cells.
- Hypertrophic cartilage cells undergo apoptosis, leaving behind thin strands of calcified matrix.
- Osteoblasts use calcified strands as substrates for deposition of osteoid.
- Osteoid is calcified.
- Simultaneously, cells derived from initial perichondrium begin to secrete osteoid appositionally.
- Perichondrium now = periosteum.
- Secondary ossification centers occur in the epiphyses.
- Epiphyses and diaphyses are separated initially by epiphyseal plate (growth plate):
- Reserve zone
- Proliferative zone
- Hypertrophic zone
- Vascular invasion zone


THOROUGHLY go through slides 16-37. Seems like a lot, but...



What is the definition of a joint and what are the three types of joints called?

- A joint is where two bones come together.

Three Types:
1. Cartilaginous Joint
2. Fibrous Joint
3. Synovial Joint


Describe Cartilaginous Joints

- Bones are joined by hyaline or fibrocartilage
- Symphysis: Symphyses are joined by fibrocartilage:
--Examples of symphyses include intervertebral discs and the pubic symphysis
- Synchondrosis: Synchondroses are joined by hyaline cartilage:
-- Examples of synchondroses include epiphyseal plates and the first sternocostal joint.


Describe Fibrous Joints

- Bones are joined by collagenous and/or elastic fibrous CT. Types:
- Suture: Examples are the joints between the bones of the calvaria.
- Gomphosis: This is a “peg-in-the-socket joint such as the teeth in the alveoli.
- Syndesmosis: Bones are joined by an interosseous fibrous membrane such as the fibrous membrane between the tibia and fibula.


Describe Synovial Joints

- These are the movable joints exemplified by a connective capsule surrounding a fluid-filled joint space.
- Synovial joints are often reinforced by thickenings of the outer part of the capsule referred to as ligaments.
- Ligaments stabilize the capsule and the joint.
- Ligaments control and restrict direction and range of motion.


What are the three types of Synovial Joints

(Based on the type of movement of the joint)
- Joints allowing movement in one plane only are monaxial:
-- Hinge joints include the humeroulnar and knee joints.
-- Pivot joints include the atlantoaxial and radioulnar joints.
- Joints allowing movement in two planes are biaxial:
-- Condyloid joints include the metacarpophalangeal and atlantooccipital joints.
-- A saddle (sellaris) joint is exemplified by the first carpometacarpal joint.
- Joints allowing movement in three planes are triaxial:
-- These include the ball-and-socket joints such as the glenohumeral and the femoroacetabular joints.

(See Slide 43)


Describe the histology of the synovial joint

- Articular cartilage:
-- Hyaline cartilage
-- Lacks perichondrium
-- Not lined by synovial membrane
- Joint capsule
-- Vascularized dense CT
-- Lined by synovial membrane
-- Attached to edges of articular cartilage
- Synovial membrane:
-- Highly vascularized (fenestrated capillaries)
-- 1-3 layers of synovial cells
-- No basal lamina
- Synovial fluid:
-- Contains mucin (hyaluronic acid-protein complex)
-- Produced by synovial cells
-- Synovial cells: Type A: = Macrophage-like, Type B = Fibroblast-like

See Slides 46-51