Bone Tissue - Chapter 7 PDF

Functions of Bone Support: Framework for body Protection (what body parts are protected?) Movement (interacts with muscles) Mineral and Fat storage (Ca and P) Hematopoiesis (blood cell formation)  What Type of Tissue is Bone? Connective Tissue: Cells: Osteogenic: bone stem cel...

Functions of Bone Support: Framework for body Protection (what body parts are protected?) Movement (interacts with muscles) Mineral and Fat storage (Ca and P) Hematopoiesis (blood cell formation)  What Type of Tissue is Bone? Connective Tissue: Cells: Osteogenic: bone stem cells Osteoblasts: Bone forming cells Osteocytes: Mature bone cells Osteoclasts: Bone destroying cells Fibers: Collagen Matrix: Calcium phosphate salts The cells make and secrete the fibers The cells make and secrete the matrix Chemical Components of Bone 1/3 Organic Compounds Cells, collagen Resists tension 2/3 Inorganic Compounds Calcium phosphate (hydroxyapatites) Resists compression Bone matrix is hardened by deposition of calcium phosphate and is called calcification. 2 Types of Bone Based on Density Compact and Spongy Spongy Compact Compact is solid. Spongy has holes in it, like a sponge. Microscopic Structure of Compact Bone  Have lamellae, Red bone marrow Osteocytes and Is found weaving canaliculi Through spongy bone Spongy or Cancellous Bone Parts of a Long Bone Metaphysis: between diaphysis and Epiphysis Periosteum: see slide 6 Nutrient artery enters bone and supplies diaphysis and red marrow. Periosteal artery supplies periosteum. Metaphysial and Epiphysial arteries supply red marrow and epiphyses CONCEPT CHECK Bone Development/Ossification Bone Development in utero: intramembranous and endochondral Bone Growth in Length Bone Remodeling Intramembraneous Ossification Skull bones and clavicles form this way Intramembranous Ossification in Utero Fontanels Soft spots on a baby’s head Will become sutures Endochondral Ossification Most of skeleton forms this way. All bones other than skull except clavicle  Endochondral Ossification Most bones begin as a cartilage model, with bone formation spreading essentially from the center to the ends Periosteum develops and enlarges to produce a collar of bone Secondary ossification centers appear in the epiphysis, and bone growth proceeds toward the diaphysis The epiphyseal plate remains between the diaphysis and each epiphysis until bone growth in length is complete 17 Endochondral Bone Formation 12 weeks 18 Endochondral Ossification of the Hand and Wrist Fetal hand specimen showing primary ossification centers in the bones of the hand and fingers. Radiograph of endochondral ossification in the hand and wrist. 19  Endochondral Ossification Epiphyseal plate is composed of four layers: “Resting” cartilage cells Zone of proliferation Zone of hypertrophy Zone of calcification 20 Growth Plate  Epiphyseal or Growth Plate The epiphyseal plate can be a site of bone fractures in young people Long bones grow in both length and diameter If no growth plate, Bone can’t grow longer 22 Bone Remodeling Bone is dynamic; it is constantly being remodeled Spongy bone replaced ever 3-4 yr; compact bone every 10 yr 2 processes affect bone remodeling: bone deposition (making bone tissue) and bone resorption (bone tissue removal) Bone remodeling Osteoblasts: “build” or make bone tissue (deposition) Osteoclasts: “chip away” or break down bone tissue (resorption) Factors that affect bone remodeling Vitamins A, C, D Growth Hormone Thyroid Hormone Sex Hormones Stress on skeleton (swinging a tennis racket or lifting weights) Calcium levels in body CONCEPT CHECK Stresses Placed Upon the Bone Regulation of Blood Calcium Levels in the Skeletal System Helps maintain constancy of blood calcium levels: During bone formation, osteoblasts remove calcium from blood and lower circulating levels During breakdown of bone, osteoclasts release calcium into blood and increase circulating levels Hypercalcemia: too much calcium Hypocalcemia: too little calcium 29 Regulation of Blood Calcium Levels in the Skeletal System Homeostasis of the calcium ion concentration is essential for: Bone formation, remodeling, and repair Blood clotting Transmission of nerve impulses Maintenance of skeletal and cardiac muscle contraction 30 Mechanisms of Calcium Homeostasis Parathyroid hormone Primary regulator of calcium homeostasis Stimulates osteoclasts to breakdown bone matrix and increase blood calcium levels Increases renal absorption of calcium from urine Stimulates vitamin D synthesis Calcitonin Protein hormone produced in the thyroid gland Produced in response to high blood calcium levels Stimulates bone deposition by osteoblasts Inhibits osteoclast activity 31 Calcium Homeostasis Osteoporosis Bone reabsorption faster than bone deposition Esp. spongy bone of vertebrae Loss of estrogen in menopause Lack of exercise (stress on bone) Low Ca++ /protein uptake Abnormal Vitamin D receptors Diabetes Smoking (lowers estrogen levels) Consume lots of Ca++ while bone density is still increasing (up to 35-40 years old) Bone Fractures Most common cause is trauma Pathological (spontaneous) fractures Weakness results in breakage despite very little stress Stress fractures Occur in the absence of any clinically visible damage Displaced (open) fracture Complete and incomplete 34 Clinical Application green stick Types of Fractures fissured comminuted transverse oblique spiral Avulsion Colles Hairline Impacted Pott Pathologic Stress CONCEPT CHECK