Lecture 19: Skeletal System and Bones References: • Eizenberg, Briggs, et al. 2008, ‘General Anatomy: Principles and Applications’. Ch 4, pp 25-35 • Anatomedia CD ROM: General Anatomy: Systems Frames 1-9 • Drake et al. 2010: Gray’s Anatomy for Students: Ch 1, pp 14-20 Skeletal Framework of Body: Subdivided into: Axial Skeleton: - Forms the axis of the body - Made of: Skull, vertebral Column, ribs, sternum Appendicular Skeleton: - The “appendages” that attach to the axial - Includes: limbs and limb girdles (what attaches the limbs to the axial skeleton) - Eg. pelvic girdles—made up the pelvis (part of the appendicular skeleton) - Eg. shoulder girdle—made up of scapula and clavicle Skeletal system: - Made up of bones and cartilage Function of skeletal system: - Supports the body and muscles - Protects and encloses visceral organs (organ surrounded by bones) eg. brain, heart, lungs - Helps movement – because muscles attached to bones - Blood formation in bone marrow (RBC) - Stores minerals & salts: o Eg. calcium, phosphorous o Provides electrolyte balance and releases them when body is needed - Removes foreign and toxic heavy metals o The minerals and salt in bones can attract heavy metals o Immune can recognize toxic metals and remove it Types of Bones 206 Bones in adult body—children have greater number of bones that adult because individual bones have not fused yet Bones of appendicular system: Long: Flat bones: - Arm, leg, digits bones - Enclose structures - Long hollow tubular structure - Cranial bones—enclose brains Short bones: - Sternum, mandible - Carpal bones—bones in wrist Irregular shaped bones - Vertebrae - Tarsal bones—bones in ankles - Bones of the face - They are cuboidal in shape (not metacarpals/tarsals though—long bone) Other bones that are a mix of all of these: - Pneumatic bones: o air filled so these bones are very light o eg. bones that circle the nasal cavity – near sinus circled in blue—the grey part o eg. Head bones—otherwise head will be too heavy for us to hold up - Sesamoid bones o Typically small bones embedded in tendons o These tendons work on distal elements o Eg. the patella—in the knee, to let the bending of our knees - Accessory bones: o May show up in radiographs o Don’t show any functional impairment eg. circled Bone Composition: Composition: Bone cells (osteoblasts, osteoclasts), EM 2 types of bone cells: Osteoblasts: - Cells that produce bones Osteoclasts: - Cells that dissolve bone/ break down bones There is also a component that lays around the bones: Extracellular matrix: - 2/3 of EM in bone – of inorganic materials o it is made of mineralised ground substance: 85% hydroxyapatite (crystallised calcium phosphate) 10% calcium carbonate Other minerals o mineralised elements give bone strength - 1/3 – organic o of collagen fibres, protein, carbs - mix of organic & inorganic: o gives bone strength & resilience o strength: due to minerals—resist compression and breaking down o Resilience: due to collagen—resists tension and gives elasticity Structure of: Long Bones Long bones do not necessarily have to be long but must contain a shaft with specific endings at each end All of bone is covered by a connective tissue—lines the whole outer layer of bone This connective tissue is called the periosteum – it forms a “collar” surrounding the bone Periosteum: • It is usually continuous with the connective tissue of muscles It is made up of 2 layers: • Outer layer: the fibrous part • inner layer: made up of collagen and osteogenic cells Osteogenic cells/Osteocytes: Include: Osteoblasts and osteoclasts. Osteoblasts: cells that produce bone by depositing extracellular matrix down. Osteoclasts are cells that dissolve bone, freeing the minerals present in the matrix. They might be active in response to a drop in blood calcium levels—breaks down bone to release calcium Long bones also made up of: Compact bone: • Makes up 3/4th of weight of bone • Found on outer edges of bone • Where bone is tightly packed together Spongy bone: • On the inner sides of the bone • Forms a latticework (criss cross pattern) of bone – called trabeculae • This pattern makes bone light • Makes up 1/4th of the weight Diaphysis: • Shaft of the bone • Does not grow On either ends of diaphysis… Epiphysis: • Usually has 2 epiphyses –eg femur • But metacarpals and some others only have 1 • Leads growth of bone Between epiphysis and diaphysis there is a plate of cartilage… Epiphyseal Plate: • Plate of cartilage • It is where growth takes place • When bone stops growing, the epiphyseal plate will be replaced with bone • The epiphysis will then join with the diaphysis • Then vasculature of the diaphysis and the epiphyses can join up • As you age—the epiphyseal plate is worn down, disintegrates There is an opening at the diaphysis… Nutrient foramen: • Or “nutrient opening” • Nutrient vessel/artery will go through there • Brings into bone osteogenic cells—the osteoblasts and osteoclasts • Has an oblique pathway—it doesn’t go perpendicularly into bone On the inside part of bone there is a hollow tube called Medullary cavity… Medullary cavity: • Inner lining of it – endosteum – fibrous tissue • Outer lining of it—periosteum • Medullary cavity Important for production of bone marrow Bone Marrow: Full of haemopoeitic cells that help produce RBC • In a growing long bone: o medullary cavity produces red bone marrow o Red marrow is present in all bones at the start of development • Once growth competed: o ie. when diaphysis and epiphysis fuse o Then bone marrow progressively becomes yellow bone marrow o Around 18-20 yo Diff b/w yellow and red bone marrow • Red bone marrow - responsible for the production of blood cells • Yellow marrow- mainly made up of fat (adipose tissue) - not useful in terms of the production of blood cells • Bones in the axial skeleton will always contain red marrow • Yellow bone marrow has capacity to return back to red bone marrow if needed o Eg. if got a fracture in long bone, yellow bone marrow changes to red and begins to heal bone Note: Long Bone Rearrangement follows the “properties of bones” section explored below Structure of: Flat bones: Eg. Forms the sternum -- image à Flat bones have 3 layers: 2 layers of compact bone 1 layer of spongy bone—trabeculae layer (called dipole specifically in flat bones) 2 layers of compact bone: • Inner and external layer Between those layers…. • Layer of spongy bone (Called dipole in flat bones)—made up trabecular • The spaces in spongy bone is called trabeculae Note: • Flat bone has no specific cavity that houses bone marrow • Has No marrow cavity (medullary cavity)—but they still hold bone marrow • In flat bones: keep red bone marrow as lifetime depository – always has Red BM .