Physiology week 13 Flashcards
What is calcium important for
- muscle contraction, nere impulse transmission and blood clottin
What are the effects of abnormal levels of calcium
Hypercalcemia: Depresses the nervous system.
Hypocalcemia: Increases nervous system excitability.
Explain the distibution of calcium
- ECF - 0.1%
-Cells and organelles 1%
-Stored in bones 99%
Explain phosphate distribution
- Bones - 85%
-Cells- 14-15%
-ECF - less than 1 %
Name the three forms in which calcium exists as in the plasma
- Whether they are diffusible or nont
-Bound to plasma proteins , non-diffusible
-Bound to anionic substances , diffusible
-Ionized calcium , diffusible
Name the 2 forms in whcih inoranic phosphate exists as in the plasma
- HP04 2-
-H2P04 2-
and alkaline pH Explain the effect of an acidic pH on the 2 forms of inorganic phosphate
Acidic pH: Increases H₂PO₄⁻, decreases HPO₄²⁻.
Alkaline pH: Opposite effect.
Large changes in extracellular phopshate levels lead to..
- Minimal psyhcological effects
Changes in calcium levels cause..
- Significant immediate effects
What is the effect of Hypocalcemia
- Tetany
What is calcium absorption facilitated by
- Vitamn D
How is phosphate absorbed
- Absorbed into the blood from the gut
What happens to phosphate during excretion
- Phospate is combined with non absorbed calcium in the feces
Name the 2 types of bone
-Cortical(compact) bone
-Trabecular(spongy) bone
What is the structure of cotical (compact) bone
Where is it found
- Has a dense outer layer forming 80% of bone mass
- SHafts of long bones
What is the function of the cortical(compact bone)
supports body weight
Where is the Trabecular bone found
- At the ends of long bones,joints and vertebrae
What is the structure of the Trabecular(Spongy)bone +
What does it contain
- Has a porous inner bone, forming 20% of bone mass
-Red bone marrow for RBC production
What is the bone composed of
- Organic Matrix
What is the organic matrix in the bone composed of and functions
- 90-95% of collagen fibers, providing tensile strength
- The remainder is groundsubstances ( proteoglycans like chondroitin sulfate ) that aid calcium salt deposition and bone repair
Name the 2 types of bone strength
- Tensile strength
-Compressional strength
What provides tensile strength
- Collagen fibers alligned along tension lines
What provides compressional strength
- Calcium salts
What causes precipitation of hydroxyapatite
- High enough calcium and phosphate concentrations
What prevents precipitation in tissues other than the bone
- Inibitiors such as : Pyrophosphate
Explain the initial stage of bone calcification
-Osteoblasts secrete collagen monomers and ground substance (proteoglycans).
-Collagen fibers form, creating osteoid
-Some osteoblasts become trapped in osteoid, becoming osteocytes.
What happens after the initial stage of bone calcification
- Calcium salt precipitates
Explain the calcium salt precipation step in bone calcifictaion
Begins on collagen fibers, forming minute nuclei that grow into hydroxyapatite crystals over time.
Initial salts deposited are amorphous (noncrystalline) compounds.
Amorphous salts can quickly supply calcium when needed.
What is the role of pyrophosphate in bone precipitation
- Inhibits hydroxyapatite crystalization
What is pyrophosphate regulated by
-TNAP
-NPP1
-ANK
What is the function of TNAP as a regulator of pyrophosphate
- Breaks down pyrophosphate allowing calcification
What is the function of NPP1 as a regulator of pyrophosphate
- Produces extracellular pyrophosphate
What is the function of ANK as a regulator of pyrophosphate
- Transports pyrophosphate fromm the cell interior to the surface
What is the effect of low TNAP in relation to calcification
Results in poor bone mineralization
What is the effect of low NPP1 and ANK on calcification
- Leads to excessive calcification
What is the role of Exchangeable calcium in bone
Maintains equillibrium with extracellular calcium ions
Where is exchangeable calcium present
- Tissue cells like the ones in the liver and gastrintestinal tract
Where are osteoblasts found
on bone surfaces and trabecular cavities
What is the function of osteoblast cells
- Bone depostition
What is the function of osteoclasts
- Bone resorption
Explain the mechanism of Bone resorption by osteoclasts
- Form a ruffedl border to secrete:
-Proteolytic enzymes
-Acids - Then the bone particles are phagocytosed,dissolved and released into the blood
What is the function of PTH in relation to bone resporption and deposition
- PTH indirectly stimualtes osteoclasts activity by acting on osteoblasts
What is the function of Osteoprotegrin(OPG) in relation to bone resorption
+ what produces it
- Inhibits bone resorption by binding to to RANKL preventing osteoclast maturation
- Produced y Osteoblasts
What is the function of RANKL and what is it secretd by
Binds to RANK receptors on osteoclacts promoting osteoclasts maturation
Name 4 hormones that have influences on bone remodelling
-PTH and vitamin D
-Glucocorticoids
-Estrogen
What is the funcion of the hormones PTH and vitamin D togther
- Stimulates RANKL production and inhibits (osteoptoegrin ) OPG
What is the function of Glucoorticoids
-Increases RANKL and decreases OPG increasing bone resorption
What is the function of Estrogen
-Increases OPG reducing bone , decreasing bone resorption
