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56 Cards in this Set

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  • Back
Functions of Calcium
muscle contraction
role in action potential-cardiac/smooth muscle and nueronal
second messenger
exocytosis of messenger
major bone mineral
blood clotting
Total body calcium input equal to...?
What regulates the distribution of Ca between bone and ECF
endocrine regulation
what % of calcium is found in the ECF?
What % of calcium is found in the body's cells?
Where is most calcium found?
98.8% in bones as a major bone mineral
Distribution of ECF calcium (that .1%)
41%: combined w/ plasma proteins and non-diffusible thru the capillary membrane (not filtered in kidneys)
9%: combined w/ plasma and ECF anionic substances (citrate/phosphate) and is non-ionized
50%: ionized and can freely diffuse through the capillary membrane: this ionic form is the most important form for most functions of calcium in the body
Normal calcium levels?
9.4 mg/dl
What kind of consequence does slight increase or decrease in calcium levels in the plasma/ECF have?
serious pysiological ones
Fxns of Phosphate
major bone mineral
acid-base buffer system
phosphorylation of proteins
Phophaate input=...?
what regulate the distribution of phosphate between bone, ICF, and ECF?
endocrine regulation
Distribution of Phosphate in the body?
85% as a bone mineral
14-15% found in cells
1% in ECF
Which ofrm of inorganic phosphate in more concrentrated in the ECF?
Average total quanity of inorganic phosphorus is ?
4 mg/dl
Large increases or decreases in ECF phosphate has what physiological effects on the body?
not that serious
Why is ECF precisely controlled?
alteration is plasma Ca levels affects the excitability of neurons, skeletal, smooth, and cardiac muscle cells
a decrease in the ECF concentration of Ca causes neuromuscular excitability by causing an increae in permeability to sodium and thus allowing easy initation of action potential. can cause hyypocalcemic tetany
hypocalcemic tetany
hyperexcitability of nuerons
ie.e carpopedal spasm or spans oof larynegeal muscles obstructing respiration
an increase in plasma levels of Ca depresses the nervous systema nd muscle activity. Can cause caridacdysrhytmias
3 hormones req'd for maintenance of normal calcium and phosphate ballace
Parathyroid hormone (PTH)
1,25-dihydroxycholecalciferol-Vitamin D3 aka Calcitriol
Synthesis of Vitamin D?
Sun--> choleaciferol (Pre-D) ingested--> 25-hydroxycholecalciferol, 1st hydorxulation and stored in liver--> 1,25 dihydroxycholecalciferol (Vit D3) 2nd hydroxylation and secreted from kidney, stimulated by PTH
Major effects of Ca++ dfinecientyc
goes into GI tract and increase Ca++ absorption across walls
Fxn of Bones
-Uptake and Release(absorb) Ca++ and phosphate
-Reservoir for Ca++
-Organic matrix of collagen fibers and ground stubstance of fluid/proteoglycans for toughness
-The primary crystalline bone salt forund in the bone matrix is deposited as hyroxyapatie
-Desposition of bone: osetoblasts (actives secrete alkaline phosphates), osteocytes are mature osteoblast embedded i matrix
-Bone absoption occurs by activation of osetoclas
-Depostion and absorption tightly coupled
GI tract
Absoprtion of calcium, phosphate, and Vit. D into the blood vs. Excreting
~35% of ingested Ca absorbed/day, Calcitriol inceases absoportion
~90% of the clacium presented to the GI tract is excreted (secretions add Ca++)
-Almost all ingested phosphate is absorbed into the bllod and later most is excreted by the kidney
-reasbosprtion of filtered calcium/phosphate vs. excretion in the urine
-Calcium bound to protein not filtered (40%) while the rest is ionized and bound and is filtered feely
99% of filtered calcium reabsorbed w/ final adjustment in late distal tubule
-2nd hydroxylation of d3 to 1,25-dihydroxylcholecalciferol
-secretes active form of D3 (calcitriol)
-Kidney excretes approx. 10% of the filtered load of phosphate
Fx on the skin
contails sterol (7-dehydrocholesterol)
UV rays convert sterol to cholecalciferol
Fxn of the liver
stores inactive form of Vitamin D
-hydroxylates cholecalciferol to 25-hydroxycholecalciferol
Fxn of thyroid gland
C cells secrete calcitonin
Parathyroid glads
secretes parathyroid hormone PTH
What are hte lines of defense agains out of control calcium leve/s?
-exchangable clacium
-regulatory mechanisms to elevate ECF Calcium
Exchangable Calcium
-released inf decrease in Ca++
-in the form of CaHPO4
-represents .5-1% of total bone clacium
-exchangable Ca++ slats are easily dposited and released, so they are a bufferent in sudden temporary increaes/decrease in calcium
Regulatory mechanisms ot Elecate ECF Ca
PTH stiumlates osteocytes to propmote release of exchangable clacium-(hours)
-PTH stiumaltes prolifecation of osteocytes (weeks)
-PTH stimulates increased osteoclastic absorption most likely by seding a signal via the osteoblasts and osteocytes (can weaken bone)
-PTH increases Renal reabsorption of Ca+ in the TAL and distal tubule
-PTH increases renal excretion of phosphate
-PTH stimulates the final hydroxylation of D3 and secretion of DF
-Calcitrol (D3) stimulates increased absorption of Ca++ and phosphate in the GI tract
Role of Clacitonin in Regulation of calcium levels
-effects overriden by effets of PTH
-decreases osteoclastic absorption of Ca==
-shits the balance of absoption vs. deposition towards deposition
-decreaes the formation of osteocytes
-Still not a huge deal at all for humans
Calcium/phosphate in the GI tract
1000 mg/day from duct
150 mg/day from secretion
90% lost in feces
-absorb 350mg/day
100% PO4 absorbed
Ca++ and phosphate
old age, biased towards females
-disenegrating bones
Fxn of Bone: overview of bone structure and fxn?
-Specialized calcified connective tissue
-Dynamic tissues that changes depending on the stresses placed upon it
-provides protection of the organs
-supports the muscular system
-reservoir for several minerals of the body
-highly vascular tissue
-consists of cells and an intercellular matrix
vocers the external surface of the bone, except the synovial articulations
-outer layer of dense, fibrous connective tissue
-inner layer of osteoprogenitor cells
Osteoprogenitor cells
derived from embryonic mesenchyme and can undergo mitosis
derived from the osteoprogenitor cell
-resposbsible for the syntehsis fo the organic components of the bone matrix, collagen, proteoglycans, and glycoproteins
What do osteoblasts secrete during active bone formation?
high levels of alkaline phosphatase, a marker for monotoring the rate of bone formation
Key parts of osteoblasts
receptors-bind to PTH and sitmulates osteoclasts
-enzymes that make it easier for the osteocytes to make contact w/ the mineralized bone surface
-integrins on their surface
multinucleated cells that arise in the bone marrow from the granulocyte-monocyte lineage. Osteoclasts secrete enzymes that decrade the organic calcified matrix of the bone
mature bone cells derived from osteoblasts
-found in lacunae w/ the clacified bony matrix
-canliculi-narrow tunnels that radiate out in all directions, house the cytoplasmic processes of the osteocyte. For gap jxns w/ neighboring osteocytes
Hormones the stimulate bone growth and help maintain bone mineral density
GH, IGF-1, Thyroid, Insulin, Testosterone, Estrogen, Vit D3, Paracrine/autorcine growth factors (IL-1, IL-6)
Inhibitors of bone growth and bone mineralization
-Excess PTH and Cortisol
-Lack of Weight bearing/inactivity
disease and injury
excess thyroid hormone
decreased PTH leased to decreased ECF clacium, can lead to hypocalcemic tetany
excess secretion of PTH causes increased osteoclastic activity
-Primary: due to oversecretion of PTH from a tumor
-Secondary: due to increased secretion of PTH secondary to derangements in calcium balace (kidney failure, Vit D dficiency)
What can elivated calcium levels cause>
depressed neuronal activity
muscle weakness
depressed relaxation of the heart
GI problems (constipation, pain, lack of appetite)
-Normally due to a lack of D3 in the diet of children (no sun)
-plasma levels of Calcium and phosphate decrease
-PTH rises causes increased absorption and weakend bones
-Increased osteoclastic activity stimulates increased osteoblastic activity and new bone is formed, but lack of appropriate levels of clacium result in the formation of new bone that is not properly clacified
Osteomalacia-adult rickets
problem maybe GI malabsorption
-Vitamin D deficiency in elderly populations
Renal rickets
renal faiilure = decreased secretion of 1,25 D3 and therefore decreased absorption of GI calcium
Osteoperosis-real definition
diminished organic bone matrix
rate of osteoblastic activity less than norman
Causes: protein malnutrition, lack of physical activity, postmenopausal lack of extrogen in females, old age, cushing's syndrome (excess cortisol)
vitamin D deficiency in children and elderly caused by
lack of sunlight
poor nutrition
dietary restrictions
Poor Bone heath ain children and adolesces caused by
lack of sunlight
poor nutrition
lack of physical activity
dietary restrictions