Calcium Balance

Question 1

Where is 1% of calcium found?

Answer 1

in the serum or plasma of the blood and the ECF

Question 1

Where is 99% of calcium in the body found and in what form is it?

Answer 1

it is found in bones and teeth as hydroxyapatite which is a calcium phopshate which is laid down on a collagen matrix

Question 2

What is a resevoir for calcium storage and release?

Answer 2

bones

Question 3

What is the normal concentration of free calcium in the plasma and what does this range indicate?

Answer 3

2.12-2.62 mM or 8.5-10.5mg/dL
-this range is very narrow which shows that meaning it is kept under tight regulation to ensure homeostasis

Question 4

What percent of calcium in the ECF or plasma is free calcium, what percent is protein bound calcium and what percent is chelated calcium meaning it is calcium bound to carbonate, phosphate, or oxalate?

Answer 4

50% is free calcium, 40% is protein bound calcium and 10% is chelated calcium

Question 5

What are some of the functions of calcium intracellular signal wise?

Answer 5

-it is important for muscle contraction by coming in via voltage gated calcium channels and binding to the calcium dependent calcium channel in the SR of the muscle causing a release of calcium stores so calcium can bind to troponin so it can move out of the way and actin and myosin can bind and cause contraction
-it is important for calcium dependent kinases
-it is important for exocytosis cause calcium in the presynaptic terminal causes binding of synaptic vesicles
-it is a cofactor for many enzymes
-it is needed for cell adhesion molecules to function at tight junctions
-important cofactor for coagulation cause it binds to prothrombin and makes it thrombin

Question 6

Calcium can affect neuronal and muscle excitability what does hypercalcemia cause?

Answer 6

causes hypoactivity like hyperpolarization because more calcium in the outside of the plasma membrane interacts with the negatively charged phosphate groups on the outside and this causes the inside of the membrane to be more negative than the outside causing hyperpolarization and less activity

Question 7

Calcium can affect neuronal and muscle excitability what does hypocalcemia cause?

Answer 7

hyperactivity like depolarization - this is because less calcium on the outside of the plasma membrane is available to interact with the phosphate groups on the plasma membrane which are negatively charged causing the outside to be more negative than the inside making the inside more positive to the outside which causes depolarization and hyperacitivy

Question 8

How is intracellular calcium conentration kept so low in the cell?

Answer 8

it is sequestered in the smooth er and the mitochondria and the calcium is the cytoplasm can be bound to calcium binding proteins which causes free calcium concentration inside the cell to be nM

Question 9

What is the serum?

Answer 9

the blood plasma with no serum proteins and this is the same as the ECF

Question 10

What does hypercalcemia cause symptomatically?

Answer 10

cessation of breath and coma

Question 11

What does hypocalcemia cause symptomatically?

Answer 11

seizures and muscular twitches and diaphragm paralysis

Question 12

What are the three hormones that control calcium balance?

Answer 12

parathyroid hormone
calcitonin, sometimes
calcitriol

Question 13

Calcium ECF concentration is 2.5mM what are three sources of this calcium?

Answer 13

1. small intestine absorption of calcium
2. bones which are a resevoir of calcium
3. kidney reabsorption of calcium - calcium is freely filtered across the glomerular capillaries in bowman’s capsule

Question 14

What is the main way to lose calcium from the body and another way you can also lose calcium from the body?

Answer 14

main way - urine produced by the kidneys
other way - feces via the small intestine

Question 15

What is the electrochemical gradient of calcium?

Answer 15

inward into the cells via passive transport and active transport is out of the cells

Question 16

What is the cell type that deposits calcium into the bone?

Answer 16

osteoblasts

Question 17

What is the cell type that removes calcium from the bone or bone resorption?

Answer 17

osteoclasts

Question 18

What is one of the hormones which raises plasma calcium?

Answer 18

parathyroid hormone

Question 19

In what three ways does parathyroid hormone increase plasma calcium?

Answer 19

1. causes osteoclasts to recruit calcium from bones
2. INDIRECTLY stimulates the absorption of calcium through the small intestine
3. stimulates the calcium resorption from the kidney tubule

Question 20

What is another hormone which increases plasma calcium?

Answer 20

calcitriol

Question 21

In what two ways does calcitirol raise plasma calcium?

Answer 21

-DIRECTLY stimulates calcium uptake from the intestine
-stimulates osteoclasts to recruit calcium from bone

Question 22

What organ is involved in the synthesis of calcitriol?

Answer 22

kidney

Question 23

What hormone lowers calcium concentration?

Answer 23

calcitonin

Question 24

What three ways does calcitonin lower calcium concentration?

Answer 24

-stimulates osteoblasts to recruit calcium into the bones
-opposes reabsorption of calcium by the kidney
-increases calcium reabsorption from the kidney

Question 25

When does calcitonin play a role in life?

Answer 25

not much in adult life but during growth in children when bones are growing and in pregnant and lactating women to give calcium to fetus or put it in the milk

Question 26

How does parathyroid hormone raise plasma calcium indirectly via increasing intestinal absorption of calcium?

Answer 26

indirectly via vitamin D - parathyroid hormone is needed to stimulate the kideny to make calcitriol which is what causes the increase in intestinal absorption of calcium directly

Question 27

From what glands is parathyroid hormone released from and are these glands needed for life?

Answer 27

released from the parathyroid glands which are on the back of the thyroid glands and they are needed for life because in Graves disease when they try to remove the thyroid gland they cannot remove the parathyroid gland cause that causes immediate death

Question 28

In a PTH cell what is the control mechanism or pathway that controls the PTH release?

Answer 28

1. Caclium ions in the ECF bind to the plasma membrane CSR or calcium sensing receptor
2. this causes the GPCR CSR receptor to activate PLC
3. PLC inhibits the exocytosis of PTH which is a peptide hormone

this means a fall in calcium concentration would release the inhibition of PTH causing PTH to be released

Question 29

In what two ways can vitamin d be acquired?

Answer 29

from the diet or from cholesterol which is an endogenous precursor which with sunlight can be made into vitamin d

Question 30

What does the liver transform vitamin d into?

Answer 30

25-hydroxycholecalciferol (25(OH)D3)

Question 31

Where does 25-hydroxycholecalciferol made by the liver go to and what happens there?

Answer 31

goes to the kidney - in the presence of low calcium plasma concentration PTH will stimulate the kidney to make 25-hydroxycholecalciferol into calcitriol or 1,25-dihydroxycholecalciferol also known as vitamin D3 which can then increase the calcium concentration

Question 32

How does calcitriol work in the small intestine to recruit calcium to the plasma?

Answer 32

calcitriol promotes the ECaC or epithelial calcium channel a voltage gated channel to open to allow calcium to come into the intestinal epithelium from the intestinal lumen via an inward current of calcium which is super strong due to the presence of calcium binding proteins like callbindin which keep calcium concentration inside the intestinal epithelium low so it can come in from the intestinal lumen
-calcitriol then stimulates the calcium ATPase a primary actuve transporter to get calcium into the ECF and also stimulates the 3 sodium in 1 calcium out secondary active transport antiporter to get calcium into the ECF as well

Question 33

How does the kidney specifically the distal nephron work in the kidney to recruit calcium to the plasma?

Answer 33

it stimulates the synthesis of callbindin which is a calcium binding protein which keeps the internal calcium concentration low

Question 34

How does calcitonin lower plasma calcium concentration?

Answer 34

-it inhibits the osteoclast activity in the bone and stimulates osteoblast activity
-it inhibits calcium reabsorption from the tubular fluid in the kidney

Question 35

From what cells in the thyroid gland does calcitonin come from?

Answer 35

c - cells or parafollicular cells in the thyroid gland which are near thryoid follicles

Question 36

What are the functions of calcitonin in humans?

Answer 36

important in bone growth in childhood - has no known funciton in adults - important in bone preserving action in pregnancy and lactation