Osteology Study of bone structure and function Bones are organs Organs are tissues working together Bones are made up of osseous (bone) tissue, cartilage, connective tissue, cardiovascular tissue, adipose (fat) tissue, and nervous tissue

Structure of Bone Tissue Each bone is a living organ made up of tissue There are two types of bone tissue, which differ in their density Compact bone – heavier; gives bones hardness and strength Spongy bone - lighter, less dense

Functions of Bone Tissue 1. Support Support soft tissues Provide attachment sites for tendons of muscles 2. Protection Cranium protects brain Ribs protect heart and lungs Pelvic girdle protects reproductive organs 3. Movement Bones provide sites for muscle attachment Bones and muscles work together to produce movement

Functions of Bone Tissue (continued) 4. Mineral Homeostasis Bone stores 99% of body’s calcium Normal calcium levels 9-11 mg/dl When Ca+2 blood levels are low, Ca+2 is released from the bone Blood Ca levels are maintained by two hormones: Parathyroid hormone- if blood Ca levels are too low, PTH pulls Ca from the bone to increase blood Ca levels Calcitonin- if blood Ca levels are too high, CT decreases blood Ca levels by depositing calcium into the bones

Functions of Bone Tissue (continued) 5. Hemopoiesis Process of blood cell formation (red blood cells, white blood cells and platelets) Takes place in red bone marrow 6. Triglyceride Storage Fat is stored in yellow bone marrow Red bone marrow is present at birth…it is gradually replaced by yellow marrow in adults

Parts of Long bones 1. Diaphysis – shaft of long bone; compact bone 2. Epiphysis- proximal and distal ends of long bones; spongy bone 3. Metaphysis-where diaphysis joins the epiphysis Location of epiphyseal plate (growth plate) Where bone replaces cartilage 4. Articular cartilage- covers the epiphysis Forms joints Reduces friction and absorbs shock

Parts of Long Bones (cont) 5. Periosteum - connective tissue Covers the outer surface of the long bone Important for growth and repair, thickens bone, attachment point for tendons 6. Medullary Cavity - hollow space in diaphysis Contains yellow marrow 7. Endosteum - inner surface that lines the medullary cavity Contains bone forming cells

Bone (Osseous)Tissue Contains four types of cells suspended in a matrix that is 25% H2O, 25% protein, 50% mineral salts 1. Osteogenic cells – unspecialized stem cell Undergo cell division Mature into osteoblasts Found in periosteum, endosteum & canals in bone that contain blood vessels 2. Osteoblasts – bone forming cells Secrete collagen fibers for the matrix Deposit calcium which makes bone hard (calcification)

Bone (Osseous) Tissue (cont) 3. Osteocytes - mature bone cells Trapped in the matrix Maintain cellular activity of bone tissue (exchange of nutrients with blood) 4. Osteoclasts – breaks down and reabsorbs bone helps keep Ca and P in the blood stream at a constant level

Matrix Contains calcium carbonate & calcium phosphate Also contains magnesium hydroxide, fluoride & sulfate (mineral salts) Minerals are deposited in a framework of collagen fibers, which gives flexibility Calcification – mineralization The minerals crystallize and then harden to become bone

Two Types of Bone 1. Compact Bone – 80% 2. Spongy Bone – 20%

Compact Bone External layer of all bones Makes up most of diaphysis Provides support & protection Osteon – also known as Haversian system Functional unit of compact bone Allows nutrients and O2 to reach osteocytes Removes waste

Structure of Compact Bone 1. Perforating Canals- where blood vessels and nerves enter 2. Central Canals- run longitudinally through bone 3. Concentric Lamellae- encircle the central canals 4. Lacunae- space on lamellae where osteocytes are trapped 5. Canaliculi- small channels; connect lacunae with each other and with central canals

Structure of Compact Bone (cont) 6. Circumferential lamellae – encircle the bone beneath the periosteum 7. periosteal vessel – what lets nutrients and blood get into the bone

Structure of Spongy Bone Lightweight Where hemopoiesis takes place Does not have true osteons Lamellae are arranged in trabeculae, which is a thin, irregular lattice of bone with red marrow found in the spaces Osteocytes get nutrients and oxygen directly from blood in the medullary cavity

Effect of Exercise on Bone Bones alter their strength in response to mechanical stress When placed under stress, bone tissue adapts by becoming stronger through increased mineral salt deposits and production of collagen (the converse is also true…with no stress, bones become weaker)

Effects of Age on Bone Birth to Adolescence More deposition than reabsorption Bone building phase Young Adults Deposition equals reabsorption Bone maintenance Middle Age More reabsorption than deposition Bone loss

Reasons for Bone Loss 1. Demineralization -loss of calcium and other minerals from the bone matrix Females – starts ~ age 30 Lose 8% bone mass every 10 years Males – starts ~ age 60 Lose 3% bone mass every 10 years

Reasons for Bone Loss (cont) 2. Brittleness –results from a lowered rate of protein synthesis, which decreases the strength of bone Decreased collagen production causes fractures, pain, stiffness, deformity, loss of height & teeth