It is a macromolecule that is highly abundant in our body, composing 40% of our bodies minerals - Absorbed by simple diffusion or active transport, and excreted by the kidneys

Calcium-phosphorus & PTH metabolism Flashcards by Youssef El Soussi

What is a calcium?

It is a macromolecule that is highly abundant in our body, composing 40% of our bodies minerals

Absorbed by simple diffusion or active transport, and excreted by the kidneys

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What is the percentage of distribution of calcium in our body?

99% of it is in our bones and 1% is in our blood

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What is the main source of calcium?

Milk

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What are the functions of calcium?

1) Muscle contraction
2) Nerve conduction
3) Hormonal release
4) Blood clotting
5) Main component of bones
6) Regulator of a lot of metabolic pathways
7) Works as a second messenger
8) Insulin secretion from the pancreas

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What are the compounds that regulates the calcium levels?

1) Vitamin D
2) PTH
3) Calcitonin

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What are the organs that regulates calcium levels?

1) Liver
2) Kidney
3) Skin
4) Intestine
5) Bones

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What is the recommended daily intake of calcium?

1000mg

Plasma conc 2.2-2.6mmol/L

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What is the composition of the bone?

1) 40% Organic compound (collagen & proteoglycan)

2) 60% Inorganic compound (calcium hydroxyapatite)

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How is calcium regulated?

There is three hormones/vitamins that are involved in calcium homeostasis:

1) Vit D
2) PTH
3) Calcitonin

They affect the kidneys, intestine & bones

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What is the main function of vitamin D?

Regulation and absorption of calcium

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Deficiency in vitamin D will lead into which condition?

Rickets in children & Osteomalacia in adults

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What is the normal dietary form of vitamin D?

Cholecalciferol (calciol)

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What is the name of the medication given to renal failure patients that cannot synthesize vitamin D?

1 Alpha

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What is the form of vitamin D in skin?

7-dehydrocholesterol

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UV-Light converts 7-dehydrocholesterol that is found in the skin into what?

Cholecalciferol

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Cholecalciferol then goes into which organ?

The liver

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The liver converts cholecalciferol into what?

With the help of 25-hydroxylase it converts it to 25-OH-D3 (calcidiol)

Calcidiol (25-OH-D3) is then transferred into which organ?

Kidneys

The kidneys coverts calcidiol (25-OH-D3) into what?

With the help of 1-hydroxylase, (PTH) it converts it into 1,25-dihydroxy-D3 (calcitriol)

Activated by low phosphate, and parathyroid hormone

1,25-dihydroxy-D3 (calcitriol) is then transferred into which organ?

Intestine and blood

What is the effect of calcitriol on the intestine?

It increases the transcription of calbindin which is a calcium absorption protein that absorbs calcium from exogenous sources

What is the effect of calcitriol on the bones?

It increases reabsorption

Overall what is the function of vitamin D?

1) Increases the uptake of calcium by the intestine (via calbindin)

2) Minimizes the loss of calcium by the kidney via increasing reabsorption

3) Stimulates resorption (demineralization) of bone when blood calcium is low

What are the hormones/vitamins that controls hypocalcemia?

1) Vitamin D
2) PTH

Describe the composition of the PTH

It is a linear polypeptide containing 84 amino acids that is secreted from the parathyroid gland, monitoring the calcium concentration in blood and is secreted during hypocalcemia

How does PTH affect the levels of calcium?

1) Increases bone resorption 2) Increases calcium reabsorption in the kidney 3) Increases the formation of calcitriol (1,25-dihydrohy-D3) which will in turn increase the concentration of calbindin (calcium binding protein in the intestine)

What are the target organs and effects of the PTH?

1) Bone: increases Ca & PO4 release from the bones 2) Kidneys: increases the reabsorption of calcium from the kidney, and increases the kidney's excretion of PO4 3) GUT: increases dietary calcium reabsorption indirectly by the activation of vitamin D

What are the factors that might decrease the absorption of calcium?

1) Vitamin D deficiency (decrease gut absorption of Ca) 2) Kidney failure (no hydroxylation of vitD) 3) Hepatic failure (no hydroxylation of vitD) 4) High fats and fiber content of food (locks Ca) 5) Excess phosphorus 6) Polyphenols (tannins in tea) inhibits calcium absorption 7) Menopause (estrogen suppress bone resorption) 8) Aging

How does our body deal with hypercalcemia?

1) Calcitonin

What gives the bone and teeth their rigid structure?

The density and hardness of calcium and phosphate

Does vitamin D enhance the absorption of phosphorus in the intestine?

Yes

What are the sources of phosphorus and its daily recommended intake?

Dairy, bakery, eggs, meat food additives - The recommended intake is 1000mg/day

Describe the calcitonin hormone

It is a 32 amino acid polypeptide secreted by the thyroid gland

What is the function and mechanism of calcitonin?

- It decreases the serum concentration of calcium by: 1) Inhibition of bone resorption 2) Increasing renal calcium excretion FYI it has no role in the intestine

What is osteoporosis?

- Reduced bone mass leading to reduced strength

What is the function of estrogen in bone resorption?

It suppresses the bone resorption which will decrease in women after postpartum

What causes osteoporosis?

1) reduced estrogen in postpartum women 2) Inadequate calcium 3) long term immobilization FYI- Osteoporosis leads to 1.5 million fracture per year in the USA

What is the scan used to scan bone density?

DEXA

What are the biochemical tests done for bone and mineral metabolism?

1) Serum Ca & Phosphorus 2) Ca & Phosphorus excretion 3) Alkaline phosphate (osteoblast activity) 4) PTH test 5) Vitamin D test 6) Proline and hydroxyproline excretion (determines collagen status)

What is the importance of intracellular calcium?

- Major regulator of many cell function - Many drugs and physiological mechanisms operates, directly or indirectly by influencing Ca+2 - Most of the Ca2+ in a resting cell is sequestered in organelles (endoplasmic reticulum or sarcoplasmic reticulum)

How are calcium levels kept low?

1) Active transport mechanism that ejects cytosolic Ca+2 through the plasma membrane and pumps it into the ER 2) Normally low plasma and ER membranes permeability to calcium