Etiology & Pathophysiology 8% Flashcards
(123 cards)
What are fibrous joints?
Bones connected by fibrous connective tissue with little to no motion
e.g. SI joints, sutures of skull
What are cartilaginous joints?
Bones connected by cartilage with little to no motion
e.g. intervertebral discs, pubic symphysis, sternomanubrial joints
What are synovial joints?
Bones connected by hyaline cartilage and separated by a joint space lined with synovium and filled with synovial fluid, allowing for FREE MOVEMENT
e.g. most joints
What factors contribute to joint stability?
Shape of joint
Joint capsule and ligaments prevent hypermobility
Muscles and tendons actively guide and stabilize
Adhesive properties of synovial fluid
What types of cells make up the synovial membrane?
Type A synovial membrane cells (20%)
Type B synovial membrane cells (80%)
Synovial membrane is the same thing as synovial lining or synovial intima.
What are Type A synovial membrane cells?
Macrophages
20% of synovial membrane cells
Express CD45, MHC class II, CD68 - macrophage cell surface markers
Remove debris from synovial space
What are Type B synovial membrane cells?
Fibroblasts
80% of synovial membrane cells
Produce matrix components
What are the principle components and functions of synovial fluid?
Synovial fluid is a filtrate of plasma with similar concentrations of small molecules and lower concentrations of large molecules (e.g. proteins)
Functions to lubricate and allow free movement
Does not have any components of coagulation pathway. Doesn’t clot.
Albumin 1.2 g/dL
Total protein 1.7-2.1 g/dL
IgG 13% of serum, igM 5% of serum
Hyaluronic acid 300 mg/dL - provides viscosity
What are the principle components of articular cartilage?
Chondrocytes - derived from MESODERM
Extracellular matrix components
How is articular cartilage organized?
Into cartilage ZONES
Zone 1: most superficial and contacts synovial lining. Chondrocytes in zone 1 synthesize LUBRICIN. More cellular in zone 1.
Zone 2
Zone 3
Zone 4: separated by zone 3 by “tidemark” a blue line on H&E. Where calcification of matrix starts.
What do chondrocytes of the articular cartilage synthesize?
Chondrocytes of the articular cartilage synthesize:
- Proteoglycans and collagen of the extracellular matrix
- Proteases to degrade ECM components to maintain cartilage regulation
What are the principle components of the extracellular matrix of articular cartilage?
Proteoglycans - protein core to which glycosaminoglycans (chondroitin sulfate and keratan sulfate) attach. Primary proteoglycan is aggrecan.
Collagens
- Type II collagen
- Type IX, Type X collagen
What are the classifications of bone based on mechanism of ossification?
Intramembranous ossification - facial, cranial, clavicular bones
Endochondral ossification - mostly appendicular and axial skeletal bones
What is bone matrix primarily made of?
90% Type I collagen
What cells make and degrade bone?
Mesenchymal stem cells
Osteoblasts
Osteocytes
Osteoclasts
What is the function of mesenchymal stem cells?
Differentiate into cells of bone (osteoblasts, osteocytes, osteoclasts), cartilage (chondrocytes), muscle (myocytes, or fat (adipocytes)
Located in inter-trabecular loose connective tissue next to vascular channels and in the periosteum
What is the function of osteoblasts?
Produce organic components of bone, mainly COLLAGEN but also OSTEOCALCIN and OSTEOPONTIN
After becoming entrapped in formed bone, become OSTEOCYTES within lacunae
What is the function of osteocytes?
Mineralizes hydroxapatite, bone’s organic matrix
Most abundant bone cell that preserves bone integrity and mediates remodeling in response to mechanical stress
Connected by cytoplasmic tendrils that deliver nutrients and metabolites to keep the osteocytes alive
What is the function of osteoclasts?
Bone resorption
Converts trabecular bone to compact bone
Degrade bone by secreting lysosomal enzymes that cause Ca release
What are the differences between cortical (compact) and trabecular (cancellous, spongy) bone?
Cortical (compact) bone - outer layer of thick cortical bone
Trabecular (cancellous, spongy) bone - inner layer of interlacing ossified trabeculae. Alignment of trabecular network with long axis of the bone confers maximal tensile strength and compressive tolerance so that less bone mass is required
Bones subject to mostly tensile and compressive forces (e.g. vertebrae) have thin cortical bone and exert their support by their shape and trabecular architecture
Bones subject to torsion, bending, and shearing forces (e.g. bones of the leg) are usually cylindrical with thick collar of cortical bone and a marrow cavity
What type of collagen is bone predominantly made of?
Type 1 collagen (bONE)
What type of collagen is articular cartilage predominantly made of?
Type 2 collagen (carTWOlage)
What type of collagen is the glomerular basement membrane predominantly made of?
Type 4 collagen (basement has a floor = four)
What is a DEXA scan?
Dual Energy X-ray Absorptiometry
- preferred methods for measurement of bone mineral density (BMD)
- lowest radiation (1/10th of CXR)
- need to adjust for bone size
- osteopenia z score -1 to -2.5
- osteoporosis z score < 2.5