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Human Phys
Bone Physiology
| Question | Answer |
|---|---|
| Bones | Mineralized connective tissue Collagen and calcium phosphate. Calcium phosphate -firmness. Compact or spongy- light weight |
| Joints | Site where two or more bones or other skeletal components are joined together |
| Cartilage | Fibrous connective tissue Cartilage provides flexible support i.e. the nose, trachea, ears. Cushion/ low friction movement |
| Tendons/ligaments | Tendon: tough connective tissue connects muscle to bone. Ligament: fibrous connective tissue holds bones together |
| Support | Limbs and vertebral column support the body Jaw supports the teeth Some organs are supported by nearby bones |
| Protection | Brain, spinal cord, bone marrow and internal organs (flat bones) |
| Movement | Limb movements, breathing by actions of muscles on bones (movement) |
| Electrolyte balance | Storage of calcium and phosphate ions |
| Acid based balance | Bone tissue buffers the blood against excessive pH changes by absorbing or releasing alkaline phosphate |
| Blood formation | Red bone marrow is the major producer of blood cells and cell of the immune system |
| Energy reserve | Yellow bone marrow acts as a potential energy reserve for the body, consists of adipose cells which store triglycerides |
| Long bone anatomy | - living cells (osteoblasts, osteoclasts, and osteocytes) embedded in organic matrix Diaphysis- Length/ leverage Epiphysis- strengthens joint/ tendons/ ligaments The articular cartilage hyaline cartilage Ephiphyseal line- remainder of growth plate |
| Types of bone tissue | Cortical bone Cancellous/ spongey bone Blood Red/ yellow bone marrow Cartilage Adipose tissue Nervous tissue Fibrous connective tissue |
| Flat bones function | - skull protects brain - sternum protects ribs/lungs/heart - scapula allows arm rotation |
| Flat bones structure | Flat bones are made up of a layer of spongy bone between two thin layers of compact bone Periosteum-Compact bone- Spongey bone Most do not have marrow cavity Meet at unique structures called sutures (immobile) |
| Compact bone | The periosteum- Tough outer membrane Tendons and ligaments attach to the outer layer vascular Volkmann’s canals: blood and lymph vessels/ nerves Endosteum- thin connective tissue, contains preosteoblasts Intracortical bone structural units |
| Spongey bone | End of long bone and just under cortical bone Arranged in an irregular lattice structure Trabeculae oriented along the lines of stress to help resist forces and reduce the risk of fracture Contain red or yellow bone marrow-RBC are made |
| Bone marrow | - stem cells - RBC/ platelets/ lymphocytes (red marrow) - more fatty and contains mesenchymal stem cells (yellow marrow) fat, cartilage, muscle and bone cells |
| Mature Lamellar bone 1) | Made up of functional units with canals at the centre (OSTEON) Series of lamellae (concentric/ interstitial/ circumference Collagen fibres run in opposite directions with minerals in between |
| Mature Lamellar bone 2) | Withstands torsion (twisting force) Central canal has nerve fibres and blood vessels Perpendicular canals: connects the blood and nerves to reach from periosteum to the medullary region |
| Mature Lamellar bone 3) | Where the lamella meet, small gaps: lacuna Contain osteocytes Lacuna connected by canaliculi |
| Bone compartments: osteoid matrix | 0% Type I Collagen fibres, 10% other proteins such as proteoglycans-secreted by the osteoblasts. Forms the framework for bones, which are hardened through the deposit of the calcium and other minerals around the fibres |
| Bone compartments: inorganic mineral content | Hydroxyapatites Mineral salts are deposited between gaps in the collagen layers, minerals then accumulate around the collagen fibres, crystallising and causing the tissue to harden; this process is called ossification - 25% water |
| Bone cells 1) | Osteogenic cells Stem cells Bone marrow |
| Bone cells 2) | Osteoblast Surface of the bones Builds bones Secretes matrix |
| Bone cells 3) | Osteocyte Mature bone cells Maintains bone tissue |
| Bone cells 4) | Osteoclast Derived from circulating monocytes/ bone marrow Dissolve bone |
| Bone remodelling | - bone is a highly dynamic organ that is continuously resorbed by osteoclasts and neo-formed by osteoblasts Normal bone remodelling is necessary for 1) Calcium homeostasis 2) Skeleton adaptation to mechanical use 3) Fracture repair |
| Calcium | - not made in the human body (from dietary intake and bone tissue exchange) CaP04 salts – hydroxyapatite’ (bones and teeth) - free calcium involved in action potentials, muscle contraction, cell division |
| Calcium absorption | - absorbed in gut, excreted in urine - transported in blood freely, protein bound - levels regulated by PTH, vitamin D and calcitonin |
| PTH (parathyroid hormone) | - polypeptide hormone synthesised and stored in parathyroid glands - released into response to low blood calcium CHIEF CELLS- Synthesise & Store PTH OXYPHIL CELLS- Calcium sensing function Calcium Sensing Receptors regulate synthesis |
| Effect of PTH on bones | Stimulates osteoblasts to increase expression of RANKL Inhibits osteoprotegerin (normally inhibits RANKL) Osteoblast-osteoclasts Bone is broken down, Ca2+ and Pi released into blood stream |
| Effect of PTH on kidneys | PTH targets the distal convoluted tubule and collecting duct, increasing calcium reabsorption from urine Stimulates kidney tubule to release Vit D/(calcitriol) |
| Effect of PTH on gut | Vit D/ Calcitrol- stimulates the intestines to absorb calcium from the digested food |
| Calcitriol | Produced by sequential action of the skin, liver and kidneys |
| Calcitriol | Keratinocytes use UV to convert a steroid to a pre-vitamin D Over three days converted to Vitamin D- transported to blood stream The liver adds hydroxyl group- calcidiol Kidneys add another hydroxyl group- calcitriol |
| Calcitriol | Behaves like a hormone- raises blood calcium Increases absorption by the intestine Increases release from the bones Promotes the reabsorption by the kidneys |
| What is Calcitriol? | Hormone secreted by parafollicular cells (C-cells) of the thyroid gland Secreted when the blood calcium concentrations rise to high Antagonistic to PTH Lower the calcium concentration |
| What is Calcitriol? | Inhibits osteoclasts: Liberate less calcium from the bone Osteoblast stimulation: deposit calcium into the bone Inhibits reabsorption from the gut and kidneys |
| Calcium negative feedback loops | Correction for hypercalcemia (muscle weakness) Excess blood Ca2+ Release calcitonin from thyroid gland Less bone resorption (reduced osteoclast activity) More bone deposited (increased osteoblast activity) Ca2+ levels reduce |
| Calcium negative feedback loops | Correction for hypocalcemia Ca2+ deficiency PTH released More bone resorption (increased osteoclast activity) Less bone deposited ( (reduced osteoblast) Less urinary excretion of calcium |
| Bone remodelling | Osteoclasts and osteoblasts can alter bone mass and geometry through bone remodelling to enable the skeleton to be as light as possible, while meeting biomechanical needs |
| Remodelling cycle | - reabsorption: osteoclasts/monouclear cells - reversal: pre-osteoblasts - bone formation: osteoblasts - osteocytes: mineralisation - resting bone surface: pre-osteoclasts |
| Signalling pathways controlling absorbtion and formation | Receptor activator of nuclear factor-κB (RANK) RANK ligand (RANKL) Osteoprotegerin (OPG) Canonical Wnt signalling |
| RANKL formation | RANKL is a protein signalling molecule that plays a key role in bone metabolism Produced by osteoblasts, stimulated by hormones (PTH), VitD, cytokines, mechanical stress Stimulates the differentiation, activation of osteoclasts |
| RANK/ RANKL/ OPG pathway 1) | Osteoclasts recruited to bone surface Osteoblasts secrete RANKL |
| RANK/ RANKL/ OPG pathway 2) | RANKL binds to receptor, RANK osteoclast precursor cells |
| RANK/ RANKL/ OPG pathway 3) | Fuse together to form osteoclasts |
| RANK/ RANKL/ OPG pathway 4) | Secrete collagenase HCL dissolves hydroxyapatite into Ca2+ and PO43- |
| RANK/ RANKL/ OPG pathway 5) | Osteoclast phagocytose osteocyte Osteoblasts secrete osteoprotegerin (OPG), OPG acts as a decoy to balance over destruction of bone |
| RANK/ RANKL/ OPG pathway 6) | Osteoclast apoptosis |
| RANK/ RANKL/ OPG pathway 7) | Osteoblasts secrete collagen Absorb Ca2+ and P from blood Deposit on collagen |
| Spongey bone | Delicate lattice of spicules and trabeculae Filled with red marrow between trabecula Not random structure, imparts strength to regions under most stress |
| Spongey bone | More surface area exposed to osteoclasts Therefore, most reabsorption comes from the spongy bone Larger remodelling area and higher turnover rate |
| Compact bone | Haversian system Blood vessels, lymphatics, nerves, connective tissue Arranged in concentric rings (lamellae) surrounding each Haversian canal |
| Woven bone (non-lamellar) | Deposited during embryonic development before being replaced by mature bone Seen at sites of fracture healing Randomly ordered collagen fibres The criss-cross appearance of the fibrous matrix Mechanically weak, but forms quickly |
| Lamellar mature bone | Normal adult bone Collagen fibres arranged in lamellae Orderly distribution Mechanically strong |
Created by:
reub8n
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