Calcium Balance Flashcards
What are the effects of hypercalcemia?
progressive depression of the nervous system
constipation and lack of appetite
What does a decrease in calcium concentration cause?
nervous system is more excited
What percent of of total body calcium is in the extracellular fluid?
0.1%
What percent is in the cells and organelles?
1%
Where is the majority of calcium stored?
in the bones
What percent of phosphate is stored in the bones?
85%
What percent of phosphate is stored in the cells?
14-15%
What percent of phosphate is stored in extracellular fluid?
less than 1%
How is inorganic phosphate in the plasma?
HPO4 and H2PO4
T/F Large changes in the level of phosphate in the ECF do not cause major immediate effects on the body
T
T/F Slight changes in extracellular calcium does not cause extreme immediate physiological effects
F, does cause extreme effects
How does the body react to hypocalcemia
causes nervous system excitement and tetany
Why does the nervous system become more excitable
increased neuronal membrane permeability to sodium
Why does hypocalcemia cause seizures?
first sign is tetany in the hand
When does tetany occur?
hypocalcemia
lethal amouth in 4mg/dl
What are the usual rates of intake for calcium each day
1000mg/day
What effect does vitamin D have on calcium absorption?
increases
What happens to calcium when it isn’t absorbed?
excreted in feces (250mg/day- 90% of daily intake)
How much calcium is excreted in urine?
10% - 100mg/day
What percent of plasma calcium is bound to plasma proteins?
41%
What percent of calcium do the renal tubules reabsorb?
99%
What is the purpose of exchangeable calcium?
rapid buffering mechanism (goes back to normal in about 30 minutes)
How does vitamin D increase calcium absorption?
by intestines, kidneys, and bones to absorb calcium into ECF and contribute to feedback regulation
Where are vitamin D receptors in most cells?
nuclei of target cells
What are the characteristics of vitamin D receptors
Have hormones binding and DNA binding
What is calbindin?
calcium-binding protein in intestinal epitheial cells
help transport calcium into the cell cytoplasm
How does 1,25 dihydrocycholecalciferol promote calcium absoprtion
- calcium stimulated ATPase in brush border
2. alkaline phosphatase
What is the affect of extreme quantities of vitamin D?
absorption of bone
What happens when vitamin D is in small quantities?
bone calcification
What happens if there is excess PTH?
rapid absorption of calcium salts from bones
What does hypofunction of PTH glands cause?
hypocalcemia and tetany
What is the process of synthesis of PTH?
Location- ER and gogi
preprohormone –> prohormones –> hormone
What occurs during the rapid phase of PTH?
begins in minutes- activation of already existing bones to promote Ca and phosphate absorption
What occurs during the slower phase of PTH?
begins in days or weeks
through proliferation of osteoclasts, reabsorption of bone itself
T/F osteoclasts have membrane receptor proteins for PTH?
F- they do not
What is the major secondary signal in osteoclasts to activate preosteoclast cells?
osteoprotegerin ligand
What are the two stages of the osteoclastic system?
- Immediate activation of osteoclasts
2. Formation of new osteoclasts
What affect does PTH have on renal calcium reabsorption?
rapid loss phosphate in urine
increase renal tubular reabsorption
What are three conditions that decrease calcium ion concentration?
- Rickets
- Pregnancy
- Lactation
What conditions increase calcium ion concentration above normal?
- excess calcium in diet
- increased vitamin D in diet
- bone absoprtion
What are the characteristics of calcitonin?
- peptide hormone
- decreases calcium concentration
- secreted by thyroid gland
Where is calcitonin synthesized?
parafollicular cells (C cells)
What is occurring during Paget disease?
osteoclastic activity is greatly accelerated
calcitonin is more potent
When does hypoparathyroidism occur?
when PT glands dont secrete enough PTH
osteoclasts become totally inactive
signs of tetany- spasms can obstruct respiration
What is primary hyperthyroidism?
abnormality of parathyroid gland cause excess PTH
*more prevalent in women
What is secondary hyperthyroidism?
High levels of PTH
Can be cause by vitamin D deficiency
Aldosterone is the major mineralocorticoid and is secreted by which of the following regions of the adrenal cortex?
Zona glomerulosa
Coritsol secretion is controlled by which of the following factors?
ACTH
Which of the following is not a characteristic of lack of aldosterone?
hypernateremia
Adrenal diabetes may occur due to excess of which of the following
Glucocorticoids
Addisons disease is due to a deificiency in what?
GLucocorticoids and mineralocorticoids
