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Flashcards in Calcium Metabolism Deck (52)
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1

_____ of calcium is located in bones and teeth`

99%
- hydroxyapatite

2

How much calcium is intracellular?

1%

3

How much calcium is extracellular?

0.1% in ECF and plasma
- 30-40% is protein-bound
- ionized (50-60%) (unbound) --> biologically active form, fraction dependent on pH
- complexed (10%) --> citrate, lactate, bicarb, phosphate

4

Ionized calcium makes up ____ of intracellular plasma

55%

5

3 functions of calcium

- nerve impulses via membrane stabilization
- muscle contraction via release of Ach and NMJ (affects skeletal, smooth, and cardiac)
- coagulation

6

Clinical signs of hypocalcemia in dogs

- due to stabilization of sodium channels
- anxiety
- tremors
- tetanic concentration
- seizures
- paw chewing
- facial rubbing

7

Phosphorus concentrations

- 85% in bone
- 15% intracellular (cell membrane, nucleotides)
- <1% extracellular fluid (buffer)

8

Site of calcium regulation

- GIT
- kidney
- bone
- parathyroid gland

9

Hormones of calcium metabolism

- PTH
- vitamin D (active form)
- calcitonin

10

How much calcium is excreted in the feces

90%

11

Bone is in constant _____

Equilibrium
- balance of calcium resorption and deposition
- calcium reservoir

12

______ of ingested Ca is absorbed thru the intestine

35%
- via activated calcitriol

13

Almost all dietary P is absorbed from the ___

Gut

14

Where does calcium reabsorption occur in the kidneys?

90% reabsorbed in the proximal tubules, loops of Henle and early distal tubules
- reabsorption of remaining 10% is selective!! --> dependent on blood ionized Ca concentration

15

Bone cells

Osteoclasts
- monocyte derivatives
- bone resorption
Osteoblasts
- bone deposition

16

Vitamin D inhibits ________

Release of Ca from bone

17

Parathyroid hormone

- chief cells of PT
- maintains plasma ionized calcium concentration
- regulates plasma phosphorous concentration

18

PTH and the set point

Set point is the calcium concentration required to produce half of the max inhibition of PTH secretion
- small change in [Ca] = large change in [PTH]

19

PTH effect on bone

Resorption, release of Ca, P from bone
- effect on blood levels
- increased blood calcium, increased phosphorous
- rapid phase of bone resorption (min-hrs)
- slow phase of bone resorption (days-weeks)

20

PTH effect on kidney

Reabsorption
- increased calcium
Excretion
- decreased phosphorous

21

PTH effect on small intestine

Indirectly increases active vitamin D
- increase Ca, increase P

22

Rapid phase of bone resorption

Osteocytic membrane system
- osteoblasts, osteocytes
- bone fluid between osteoblast membrane and bone containing Ca and P salts

23

Osteocytic pump

Pumps Ca from bone fluid to ECF
- activated by PTH

24

Slow phase of bone resorption

Osteoclasts
- requires activation and proliferation
- days to weeks

25

Net effect of PTH on bone

- increased serum Ca
- increased serum P

26

PTH stimulates calcium reabsorption from the ______ and _____ (fine tuning)

Distal tubules; collecting ducts

27

_______ stimulates P excretion

Proximal tubules
- has more of an impact that resorption of bone!!!!
= overall decrease in phosphorous concentration

28

Net effect of PTH on kidneys

- increase serum Ca
- decrease serum P

29

Proximal tubules stimulates synthesis of _____

Active form of vitamin D
- increases activity of 1-alpha hydroxylase to catalyze vitamin D reaction

30

What is the net effect of PTH in the blood?

- increase calcium
- decrease phosphorous