Bones and Skeletal JALALT Tissues
Cartilage in Intervertebral disc Cartilage in external ear Cartilages in nose Articular Cartilage of a joint Costal cartilage Epiglottis Thyroid cartilage Cricoid cartilage Larynx Trachea Lung Respiratory tube cartilages in neck and thorax Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Bones of skeleton Axial skeleton Appendicular skeleton Cartilages Hyaline cartilages Elastic cartilages Fibrocartilages Figure 6.1
Basic Structure, Types and Locations 1.Hyaline cartilages Articular cartilages[which cover the ends of most bones at movable joints] Costal cartilage [which connect the ribs to the sternum breastbone Respiratory cartilages which from the skeleton of the larynx voice box and reinforce other respiratory passageway Nasal,which support the external nose
Basic Structure, Types and Locations 2.Elastic Cartilages they are found in only two skeletal locations, shown in green,the external ear and the epiglottis(the flap that bends to cover the opening of the larynx each time we swallow ) 3.Fibrocartilages occur in sites that are subjected to both pressure and stretch, such as the pad like cartilage (menisci) of the knee and the discs between vertebrae, coloured red
Growth Cartilage First - Appositional growth, cartilage forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage tissue. Second Interstitial growth the lacunae-bound chondrocytes divide and secrete new matrix, expending the cartilage from within.typically,cartilage growth ends during adolescence when the skeleton stops growth. Note,however, that calcified cartilage is not bone; cartilage and bone are always distinct tissues.
Bones perform several important functions 1. Support 2.Protection 3.Anchorage 4.Mineral and growth factor storage 5.Blood cell formation 6.Triglyceride ( fat ) storage 7.Hormone production
Bones are classified by their location and shape The 206 named bones of the human skeleton are divided into two groups: Axial ( long axis of body orange) Appendicular (collared gold) Bones are classified by their shape as long, short, flat, or irregular
The gross structure of all bones consists of compact bone sandwiching spongy bone Gross Anatomy This external layer is Compact bone. Internal to this is Spongy bone ( also called trabecular bone ). In living bones the open spaces between trabeculae are filled with red or yellow bone marrow. Structure of Short, Irregular, and Flat Bones They all consist of thin plates of spongy bone covered by compact bone. They contain bone marrow ( between their trabeculae ),but no well defined marrow cavity.
Structure of a Typical Long Bone Diaphysis surrounds a central Medullary cavity is called yellow marrow cavity Epiphyses cartilage covers the joint surface of each epiphyses cushioning the opposing bone end during movement and absorbing stress. Hematopoietic tissue - Red marrow is typically found within the trabecular cavities of spongy bone of long bones and in the diploe and flat bones.
Microscopic Anatomy of Bone Cells of bone tissue Osteogenic cell Osteoblast Osteocyte Osteoclast Compact Bone - The structural unit of compact bone is called either de osteon or Haversian. Each matrix tube is a lamella (lah-mel ah; little plate), called often Lamellar bone.
Chemical composition of bone Organic Components include its cells[ osteogenic cells, osteoblast, osteocytes, bone-lining cells, and osteoclast] and osteoid,the organic part of the matrix./composed of proteoglycans glycoprotein/ and collagen fibres, both of which are secreted by osteoblasts. This substances contribute to the flexibility and tensile strength Inorganic Component the balance of bone tissue 65% by mass consists of inorganic hydroxyapatites or mineral salts, largely calcium phosphates present tiny, tightly packed. needle like crystals in and around collagen fibres in the extracellular matrix.
Bones develop either by intramembranous or endochondral ossification Formation of the Bone Skeleton Endochondral Ossification-the stages for ossification 1. Bone collar forms around the diaphysis of the hyaline cartilage model 2. Cartilage in the centre of the diaphysis calcifies and then develop cavities 3. The periosteal bud invades the internal cavities and spongy bone forms 4. The diaphysis elongates and medullary cavity form 5. The epiphyses ossify. When completed, hyaline cartilage remains only epiphyseal plates and articular cartilages.
2.Intramembranous Ossification About week 8 of development forms the cranial bones of the skull frontal, parietal, occipital and temporal bones and the clavicles, flat bones. Ossification begins within fibrous tissue membranes formed by mesenchyme Cells. This process involves four major steps: 1. Ossification centres appear in the fibrous Connective tissue membrane 2. Osteoid is secreted within the fibrous membrane and calcified.
2.Intramembranous Ossification 3.Woven bone and periosteum form. 4.Lamellar bone replaces woven bone,just deep to the periosteum. Red marrow appear.
Growth in Length of Long Bones 1. Proliferation zone-these cells divide quickly pushing the epiphysis away from the diaphysis. 2. Hypertrophic zone. 3. Calcification zone. 4. Ossification zone.
Growth in Length of Long Bones Longitudinal bone growth ends when the bone of the epiphysis and diaphysis fuses. This process, called epiphyseal plate closure, happens at 18 years of age females and 21 years of age males. Growth in width and thickness are normal there is slightly more building up than breaking down.
Hormonal regulation of Bone Growth During infancy and childhood. the single most important stimulus of epiphyseal plate activity is growth hormone released by the anterior pituitary gland (thyroid hormone) At puberty,sex hormones (testosterone in males end oestrogen in females) are released amounts. For example hypersecretion result excessive height (gigantism) and deficits characteristics types dwarfism.
Bone remodelling involves bone deposit and removal 1. Bone remodelling - Packets of adjacent osteoblasts and osteoclasts called remodelling units coordinate bone remodelling (with help from the stress-sensing osteocytes ). Bone Deposit 2.The precise trigger for calcification is still controversial, but mechanical signals are definitely involved. One critical factor is the product of de local concentrations of calcium and phosphate in the endostea cavity. Other factors involved are matrix proteins that bind and concentrate calcium and enzyme alkaline phosphatase ( shed in matrix vesicles by the osteoblasts ), which is essential for mineralization.
Bone Resorption As noted earlier, the giant Osteoclasts accomplish Bone Resorption. The ruffled border of osteoclast clings tightly to the bone sealing off the area of bone destruction and secreting protons (H+) and Lysosomal enzymes that digest the organic matrix. Osteoclasts may also phagocytize the demineralized matrix and dead osteocytes. There is much to learn about osteoclast activation, but parathyroid hormone and proteins secreted by T cells of the immune system appear to be important.
Control of remodeling The increased When activated, they break down both old and new matrix. As blood concentrations of calcium rise the stimulus for PTH release end.
Bone repair involves hematoma and callus formation,and remodelling. Fracture Treatment and Repair 1.A hematoma forms 2.Fibrocartilaginous forms 3.Bony callus forms 4.Bone remodelling occurs.
Bone disorders result from abnormal bone deposition and resorption
0steomalacia and Rickets Osteomalacia includes in which bones poorly mineralized. Osteoid is produced, but calcium salts are not adequately deposited,so bones are soft and weak. The main symptom is pain when weight is put on the affected bones. Rickets is analogous disease in children,because young bones are still growing rapidly, rickets is much more severe than adult osteomalacia. Bowed legs and deformities of the pelvis, skull, and rib cage are common. Osteomalacia and rickets are caused by insufficient calcium in the diet Or by a vitamin D deficiency.increasing vitamin D intake and exposing the skin to sunlight usually cure these disorders.
Osteoporosis The composition of the matrix remains normal but bone mass declines, and the bones become porous and light.
RISK FACTORS FOR OSTEOPOROSIS Petite body form Insufficient exercise to stress the bones A diet poor in calcium and protein Abnormal Vitamin D receptors Smoking (which reduced oestrogen levels) Hormone related conditions such as hyperthyroidism, low blood level of thyroid stimulating hormone, diabetes mellities.