-peptie hormone produced by parathyroid glands - key role in Ca homeostasis....also regulates phosphorus - parathyroid gland contains a protein that acts as a SENSOR of blood calcium -dec blood Ca (sensor PRO detects this, inc PTH synthesis)

- parathyroid gland tumour - high blood Ca...bone will be broken down

- removal of parathyroid or thyroid glands - Ca not being homeostatic

Vit D and Ca Flashcards by Amy Gerditschke

is Vit D a water soluble vitamin

no, it is fat soluble

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where is Vit D synthesized
what is it synthesized from
what does it require

in the skin, from cholesterol…need sunlight

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what is the main form of Vit D that is utilized by humans

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what is the active form of Vit D

calcitriol

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Vit D food sources

found naturally in very few foods
…..fatty fish, fish liver oils
….mushrooms
….milk and a lot of dairy products are fortified

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Vit D absorptions and transport

absorbed involves incorporation into chylomicron
transported in plasma BOUND to a PROTEIN (DBP-vitamin D Binding Protien)
converted to active form (calcitriol) in kidney

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where can Vit D be stored

in liver, other tissues, especially adipose (bc its fat soluble)

vit D produced in the skin in the spring summer and fall can be stored for winter

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Overall metabolic role of Vit D

maintain calcium and phosphorus homeostasis

ensure Ca and Phosphorus are available in the blood that “bathes” the bones
acts as a STEROID hormone
sometimes referred to as the Vit D Endocrine System

main thing it keep Ca in check…Phosphorus follows along

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Vit D as steroid hormone

targets specific organs and their Vit D Receptor (VDR)

main target organs are INTESTINE and BONE
Also, brain and nervous system, pancreas, muscle, cartilage, repro organs, cancer cells

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list the steps of Vit D acting as a steroid hormone

(1) 1,25(OH)2-D3 travels to specific cell
(2) enters cell and binds to nuclear VDR
(3) binds to the actual DNA
(4) alters transcription rate of mRNA which code for synthesis of specific proteins, which will alter metabolic function

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Vit D and Ca homeostasis

tight regulation of Ca important for:

bone growth
maintenance of bone density
nervous system
blood clotting

also important to keep phosphorus in normal range
comple system..involved:
-vit D (steroid hormone)
-parathyroid hormone (PTH)

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PTH

-peptie hormone
produced by parathyroid glands

key role in Ca homeostasis….also regulates phosphorus
parathyroid gland contains a protein that acts as a SENSOR of blood calcium

-dec blood Ca
(sensor PRO detects this, inc PTH synthesis)

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PTH Effects…what is the goal

GOAL:

to restore normal blood Ca and maintain phosphorus homeostasis via negative feeedback loop

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what are the primary target organs of PTH and what happens

KIDNEY
(A) stimulates activation o fVit D
(B) inc Ca reabsorption
  -dec urinary Ca
  - inc blood Ca
(C) dec phosphate reabsorption
   -prevents hyperphosphatemia; whic can inhibit conversion of Vit D to its active form 
-when Ca removed from bone, P is as well
-inc urinary phosphate

BONE
(A) inc osteoclast activity
   -inc bone resorption (breakdown)
   -Ca and  P are released
  -inc blood Ca and P

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Hyperparathyroidism

parathyroid gland tumour

- high blood Ca…bone will be broken down

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hypoparathyroidism

removal of parathyroid or thyroid glands

- Ca not being homeostatic

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what is the goal of Calcitriol 1,25(OH)2-D3?

-to restore normal blood calcium

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where is calcitriol produced and what is production stimulated by

kidney

PTH

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where in the body does calcitriol act?

intestine and bone

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what are the effects of calcitriol on the intestine?

(A) stimulates Ca absorption

also need Mg
inc blood Ca

(B)stimulates phosphorus absorption
-inc blood phosphorus

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what are the effects of calcitriol on bones

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increased osteoclast activity (same as PTH)

inc bone resorption (breakdown)
Ca and P are released
inc blood calcium and P

what is the most abundant mineral in the body

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calcium

outline the two types of Ca absorption

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PASSIVE

does not depend on Vit D
concentration dependent
we can absorb Ca without vit D, but we dont always get enough, or sources are being inhibited

ACTIVE TRANSPORT absorption

Depends on Vit D
requires a transporter and energy
requires calbindin (Ca binding protein)
Vit D increases synthesis of calbindin therefore increases Ca absorption

what is the purpose of Calbindin

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free Ca is very toxic to inside of cells so the Ca needs to move across cell. The Ca needs to be BOUND in order to shuttle it across the cell
CALBINDIN binds Ca and acts as a shuttle for Ca through the cell
Calbindin facilitates Ca absorption across the intestinal cell

VIT D INCREASES CALBINDIN SYNTHESIS

Factors enhancing Ca absorption

``` Vit D presence of calbindin stomach acid supplements best absorbed with a meal optimal ratio of Ca to Phosphorus ```

factors inhibiting Ca absorption

Vit D deficiency - lack of stomach acid - excess phosphorus - high fiber diet - phytic acid - oxalate

metabolic role of Ca

bone health - Ca's major role - bone is dynamic....losing and gaining minerals all the time - goal is balance regulator of cellular processes (minor role) - muscle contraction, blood clotting - transmission of nerve impulses - membrane excitability - second messenger

Ca as a second messenger

- signal transduction - intracellular messenger of hormone action - peptide hormone action - calmodulin is an intracellular protein (Ca receptor) that binds Ca allowing for activation of intracellular proteins and enzymes

Calmodulin

- intracellular protein/Ca receptor - also called Ca-dependent regulatory protein - found in all cells - binds intracellular Ca - allows for signal transduction to occur - activated proteins and enzymes - key in the mechanism of action of numerous peptide hormones

calcitonin acts in the opposite of _____

PTH

what are the hormones involved in the regulation of Ca homeostasis

PTH calcitriol calcitonin

Calcitonin

- peptide hormone - produced in thyroid gland - acts in OPPOSITION to PTH - production stimulated by INC in blood calcium - production inhibited by derease in blood calcium overall hypocalcemic effect

where in the body does calcitonin act

kidney and bone

what are the effects of calcitonin in kidney

inhibits activation of Vit D -inhibits 1-hydroxylase stimulates Ca excretion OR decreases Ca reabsorption -inc urinary Ca

what are the effects of Calcitonin on bone

inhibits activity of osteoclasts - inhibits bone resorption - hypocalcemic effect

what hormone is used to treat diseases with high rates of bone resorption

calcitonin

in a vit D deficiency, | production of _____, and _____ absorption is decreased

calbindin Ca

list 3 syndromes related to Vit D and Ca deficiencies

Rickets(children) osteomalacia osteoporosis

rickets

vit D deficiency low blood Ca impaired mineralization of growing bones muscle weakness and nervousness

factors contributing to development of rickets

poor diet | low UV light exposure

Osteomalacia

Vit D deficiency low blood Ca looking at composition and quality of bone (remember bone is in constant state of turnover) new bone matrix is laid down but NOT mineralized properly (amount not affected, COMPOSITION affected) RARE softening of bones defect in mineralization of the bone matrix

osteoporosis

Ca deficiency looks at AMOUNT of bone reduced bone density

what are the 2 compartments of bone

cortical - 80% of skeleton - dense bone tissue, shafts of long bone, outer hard shell of flat bones - Ca loss is slow trabecular - inner structural matric - at ends of long bones, inside the cortical shell of flat bones - loses Ca readily (faster)

Type I osteoporosis

rapid bone loss 50-70y/o due to rapid loss of estrogen in women following menopause due to dec in testosterone in men with advancing age more common in women primarily TRABECULAR BONE wrist and spine fractures

Type II osteoporosis

``` slower bone loss >70y/o due to aging factors -reduced Ca absorption -inc risk of falling -increased bone mineral loss ``` BOTH trabecular and cortical bone hip fractures

what is used as an indicator of Vit D and Ca status?

bone health

what is Vit D and Ca toxicity called

hypervitaminosis D

Vit D and Calcium- toxicity

results in Ca absorption Symptoms: -hypercalcemia** -Calcinosis -not due to excess sun (this is self limiting)

what is calcinosis

results from Vit D and Ca- toxicity - deposition of Ca in soft tissues - blood vessels - heart kidney lungs - kidney stones - tissues around joints

Ca and disease prevention

osteoporosis colon cancer hypertension -inverse relationship between Ca and blood pressure obesity

Vit D and Ca Flashcards

(50 cards)