NOTES NOTES BONES, JOINTS, & CARTILAGE SKELETAL SYSTEM ANATOMY & PHYSIOLOGY osms.it/skeletal-system-anatomy-physiology SKELETAL BASICS TYPES OF BONES Axial skeleton ▪ Vertical axis of body; 80 bones (22 in skull, 33 vertebrae, 24 ribs, 1 sternum) Long bones ▪ Length > width ▪ Humerus, radius, ulna (in arms); metacarpals, phalanges (hands, ﬁngers); femur, tibia, ﬁbula (legs); metatarsals, phalanges (feet, toes) ▪ Primarily responsible for height ▪ 206 bones in skeleton ▪ Separated into axial, appendicular skeleton Appendicular skeleton ▪ Supports limbs; pectoral girdle (clavicles, scapulae) holds humeri, pelvic girdle (hip bones) holds femora; 126 bones (4 in shoulders, 6 arms, 54 hands, 2 hips, 8 legs, 52 feet) Short bones ▪ Similar length, width ▪ Carpal bones (in wrists); tarsal bones (ankles) ▪ Support hands, feet Figure 48.1 Overview of skeleton. OSMOSIS.ORG 405
Flat bones ▪ Thin, sometimes curved ▪ Skull bones; scapulae, sternum, ribs ▪ Protect vital organs Sesamoid bones ▪ Embedded in tendons, shaped like giant sesame seeds ▪ Pisiform bone (in wrists); patella (knees) ▪ Support, protect, give additional leverage to tendons Irregular bones ▪ Facial bones; mandible; vertebrae; sacrum, coccyx SURFACE FEATURES OF BONES Sites of muscle, ligament attachment ▪ Tubercle, tuberosity: small bumps on bone, serve as attachment sites for muscles; large tubercle → tuberosity; deltoid tuberosity (on humerus) ▪ Process: bony prominence; xiphoid process (sternum) ▪ Crest: narrow ridge; iliac crest (ilium) Projections ▪ Part of joints ▪ Condyle: rounded, articular projection; lateral, medial condyles (femur); epicondyle → raised portion on/above condyle (lateral, medial epicondyles) ▪ Ramus: arm-like section; mandibular ramus (mandible) Openings, passageways, depressions ▪ Foramen: holes in bone, allow blood vessels/nerves through; foramen magnum (in occipital bone of skull) ▪ Canal/meatus: tunnels, allow blood vessels/ nerves through; optic canal (sphenoid bone); external auditory meatus (temporal bone of ear) ▪ Sinuses, cavities: empty spaces within/ between bones; nasal cavity, paranasal sinuses ▪ Fossa: depressions where other structures rest; hypophyseal fossa (sphenoid bone) 406 OSMOSIS.ORG Figure 48.2 Types of bones. STRUCTURE OF BONE Cortical/compact bone ▪ Surrounded by periosteum ▪ Contains pipe-like structures called osteons ▪ Osteons contain hollow centers (Haversian canals) for nerves, blood cells; connected laterally by Volkmann’s canals ▪ Osteon walls made of bone matrix (type I collagen reinforced with hydroxyapatite), produced by osteoblast cells ▪ Some osteoblasts get trapped in bone matrix → mature into osteocytes → repair old/broken bone ▪ Osteoclast cells secrete enzymes → break down bone matrix → release calcium, phosphate into blood Trabecular/spongy bone ▪ Similar material to cortical bone ▪ Looser structure; branching rods called trabeculae ▪ Contains bone marrow, consists of hematopoietic stem cells (“red marrow”), adipocytes/fat cells (“yellow marrow”) ▫ Appendicular bones often contain red marrow at tips, yellow marrow in hollow medullary cavity (center) ▫ Axial bones mostly red marrow
Chapter 48 Musculoskeletal Physiology: Bones, Joints, & Cartilage Figure 48.3 Bone cross-section showing structure which consists of cortical bone and spongy bone. Spongy bone contains two types of bone marrow, each made up of a different kind of cell. CARTILAGE osms.it/cartilage WHAT IS CARTILAGE? ▪ Strong, ﬂexible connective tissue ▫ Comprises part of nose, ears ▫ Provides cushioning between joints ▫ Supports/connects body parts (e.g. costal cartilage connects ribs to sternum) ▪ Perichondrium: connective tissue that wraps around cartilage ▫ Outer layer contains ﬁbrous connective tissue, blood vessels ▫ Inner layer contains chondroblasts → secrete proteins that make extracellular matrix ▪ Extracellular matrix: protein ﬁbers (collagen for strength; elastin for ﬂexibility) suspended in viscous gel (water, proteoglycan aggregates) ▫ Chondrocytes: chondroblasts trapped in lacunae (small holes) of matrix; maintain, repair extracellular matrix ▫ Proteoglycan aggregates: hyaluronan (long chain of hyaluronic acid molecules) with hundreds of proteoglycans (proteins + long chains of glycosaminoglycan sugars—GAGS) branching off OSMOSIS.ORG 407
Figure 48.4 Cross-section through cartilage showing its histological structure. Perichondrium wraps around extracellular matrix. Chondroblasts originally in perichondrium become chondrocytes as they become trapped in the extracellular matrix. TYPES ▪ Three main cartilage types Elastic cartilage ▪ Least common type ▪ ↑ chondrocyte density; ↓ protein ﬁber density (mostly loose elastin ﬁbers, some type II collagen ﬁbers) ▪ Softest, most ﬂexible cartilage ▪ Ear pinnae, throat epiglottis Hyaline cartilage ▪ Most common type ▪ Medium chondrocyte density; medium protein ﬁber density (mostly type II collagen ﬁbers, some loose elastin ﬁbers) ▪ Stronger, but less ﬂexible cartilage; ↓ friction surface ▪ Embryonic skeleton (eventually replaced by bone); nose; larynx walls; tracheal, costal cartilages; growth plates; articular cartilages Fibrocartilage ▪ ↓ chondrocyte density; ↑ protein ﬁber density (mostly type I collagen ﬁbers) ▪ Most tensile strength; resistant to compression, stretching; ↓ ﬂexible ▪ Meniscus of knee, spinal intervertebral discs 408 OSMOSIS.ORG Figure 48.5 Proteoglycan aggregate, found in viscous gel of the extracellular matrix.
Chapter 48 Musculoskeletal Physiology: Bones, Joints, & Cartilage Figure 48.6 Histology, characteristics of the three main cartilage types. GROWTH PATTERNS ▪ Two cartilage growth patterns ▪ Both growth patterns present in growing bones of children, teenagers (e.g. femur) ▫ Chondrocytes in growth plate → interstitial growth → cartilage lengthens → osteoblasts turn cartilage into bone ▫ Articular cartilage on tips of bone experience both appositional, interstitial growth Appositional growth ▪ Chondroblasts secrete new matrix on existing surfaces → cartilage expands, widens Interstitial growth ▪ Chondrocytes secrete new matrix within cartilage → cartilage grows in length Figure 48.7 The two cartilage growth patterns. Both types of growth occur in articular cartilage. In the growth plate, only interstitial growth occurs. OSMOSIS.ORG 409
BONE REMODELING & REPAIR osms.it/bone-remodeling-repair BONE REPAIR ▪ Old bone removed/resorbed (broken down) before new tissue replaces it 1. Osteoblasts sense microcracks, secrete receptor activator of nuclear factor κβ ligand (RANKL) 2. RANKL binds to RANK receptors on monocytes → causes them to fuse, form multinucleated osteoclast cells 3. Osteoclasts secrete lysosomal enzymes (mostly collagenase) → digest collagen in bone matrix → create surface holes Figure 48.8 Summary of bone repair. 410 OSMOSIS.ORG (Howship’s lacunae), hydrochloric acid → dissolves hydroxyapatite into soluble calcium, phosphate 4. Osteoblasts secrete osteoprotegerin → deactivates RANKL, slows down osteoclast activity (before osteoclast apoptosis), osteoid seam (mostly collagen) → ﬁll in Howship’s lacunae 5. Calcium, phosphate deposit on seam forming hydroxyapatite 6. Some osteoblasts get trapped within lacunae → turn into osteocytes
Chapter 48 Musculoskeletal Physiology: Bones, Joints, & Cartilage REMODELING FACTORS ▪ Hormonal ▫ Parathyroid hormone enhances bone resorption ▫ Calcitonin inhibits bone resorption ▫ Vitamin D (→ ↓ calcitonin) enhances bone resorption ▪ Mechanical (physical stress) ▫ Wolff’s law: bones that bear more weight remodel more FIBROUS, CARTILAGE, & SYNOVIAL JOINTS osms.it/fibrous-cartilage-synovial-joints TYPES ▪ Classiﬁcation based on movement of three main groups ▫ Fibrous joints: no movement ▫ Cartilaginous joints: some movement ▫ Synovial joints: freely movable FIBROUS JOINTS ▪ Synarthrosis/ﬁxed joints ▪ Bones are connected by ligaments Three main categories (based on location) ▪ Sutures: junctions between adjacent skull bones; Sharpey’s ﬁbers connect bones; ﬁxed (non-fused in babies → partially movable) ▪ Gomphoses: peg-and-socket joints for teeth; periodontal ligaments connect roots of teeth to sockets; slightly movable ▪ Syndesmoses: remaining ﬁbrous joints; connected by interosseous membrane (e.g. between radius, ulna); slightly movable Figure 48.9 Three main categories of ﬁbrous joints. OSMOSIS.ORG 411
CARTILAGINOUS JOINTS ▪ Hyaline cartilage connects bones, stretches to allow some movement ▪ Synchondrosis: costochondral joint, where cartilage attaches rib to sternum; growth plates between bone diaphysis, epiphysis ▪ Symphysis: symphysis pubis in pelvic bone (ﬁbrous cartilage) ▫ ↑ strength, ↓ ﬂexibility SYNOVIAL JOINTS ▪ Joint capsule connects bones ▫ Composed of outer ﬁbrous capsule, inner synovial membrane ▫ Filled with synovial ﬂuid: lubricates joint, absorbs shock; made of hyaluronic acid, lubricin, proteinases, collagenases ▫ Articular cartilage covers tips of bones (same function) ▪ Allow for abduction, adduction, rotation about axis Six main categories (based on structure, movement) ▪ Hinge joints: allow movement only in one axis (e.g. between humerus, ulna) ▪ Pivot joints: allow for rotation (e.g. between head of radius, groove of ulna) ▪ Plane (gliding) joints: allow ﬂat bones to glide across one another (e.g. in carpal, tarsal bones) ▪ Ball and socket joints: allow all movements (e.g. shoulder joint) ▪ Condyloid (ellipsoid) joints: allow most movements, but not rotation (e.g. metacarpophalangeal, metatarsophalangeal joints) ▪ Saddle joints: allow most movements, with limited rotation (e.g. carpometacarpal joint) 412 OSMOSIS.ORG Figure 48.10 The two categories of cartilaginous joints (with examples). Figure 48.11 Synovial joint cross-section showing joint capsule.
Chapter 48 Musculoskeletal Physiology: Bones, Joints, & Cartilage Figure 48.12 The six categories of synovial joints (with examples). Joints circled in green. OSMOSIS.ORG 413