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Y1S2 Biochemistry > Calcium-phosphorus & PTH metabolism > Flashcards

Calcium-phosphorus & PTH metabolism Flashcards

1
Q

What is a calcium?

A

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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2
Q

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

A

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

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3
Q

What is the main source of calcium?

A

Milk

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4
Q

What are the functions of calcium?

A

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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5
Q

What are the compounds that regulates the calcium levels?

A

1) Vitamin D
2) PTH
3) Calcitonin

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6
Q

What are the organs that regulates calcium levels?

A

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

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7
Q

What is the recommended daily intake of calcium?

A

1000mg

  • Plasma conc 2.2-2.6mmol/L
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8
Q

What is the composition of the bone?

A

1) 40% Organic compound (collagen & proteoglycan)

2) 60% Inorganic compound (calcium hydroxyapatite)

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9
Q

How is calcium regulated?

A
  • 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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10
Q

What is the main function of vitamin D?

A

Regulation and absorption of calcium

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11
Q

Deficiency in vitamin D will lead into which condition?

A

Rickets in children & Osteomalacia in adults

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12
Q

What is the normal dietary form of vitamin D?

A

Cholecalciferol (calciol)

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13
Q

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

A

1 Alpha

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14
Q

What is the form of vitamin D in skin?

A

7-dehydrocholesterol

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15
Q

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

A

Cholecalciferol

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16
Q

Cholecalciferol then goes into which organ?

A

The liver

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17
Q

The liver converts cholecalciferol into what?

A

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

18
Q

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

A

Kidneys

19
Q

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

A

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

  • Activated by low phosphate, and parathyroid hormone
20
Q

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

A

Intestine and blood

21
Q

What is the effect of calcitriol on the intestine?

A

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

22
Q

What is the effect of calcitriol on the bones?

A

It increases reabsorption

23
Q

Overall what is the function of vitamin D?

A

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

24
Q

What are the hormones/vitamins that controls hypocalcemia?

A

1) Vitamin D
2) PTH

25
Q

Describe the composition of the PTH

A

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

26
Q

How does PTH affect the levels of calcium?

A

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)

27
Q

What are the target organs and effects of the PTH?

A

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

28
Q

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

A

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

29
Q

How does our body deal with hypercalcemia?

A

1) Calcitonin

30
Q

What gives the bone and teeth their rigid structure?

A

The density and hardness of calcium and phosphate

31
Q

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

A

Yes

32
Q

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

A

Dairy, bakery, eggs, meat food additives

  • The recommended intake is 1000mg/day
33
Q

Describe the calcitonin hormone

A

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

34
Q

What is the function and mechanism of calcitonin?

A
  • 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

35
Q

What is osteoporosis?

A
  • Reduced bone mass leading to reduced strength
36
Q

What is the function of estrogen in bone resorption?

A

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

37
Q

What causes osteoporosis?

A

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

38
Q

What is the scan used to scan bone density?

A

DEXA

39
Q

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

A

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)

40
Q

What is the importance of intracellular calcium?

A
  • 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)
41
Q

How are calcium levels kept low?

A

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

Y1S2 Biochemistry (4 decks)

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