Calcium

Question 1

How is calcium absorbed?

Answer 1

Absorbed in both small and large intestine

Most efficient in the upper duodenum where it is slightly more acidic as it keeps the calcium in 2+ form

Only about 25-30% absorption from foods

Question 2

What increases calcium absorption?

Answer 2

Absorption increases to about 75% in pregnancy and childhood when needs are elevated

Calcitrol (Vit D3) increases absorption by up-regulating of calcium transporters

Lactose and presence of protein also increases absorption

Question 3

What factors limit calcium absorption?

Answer 3

• phytic acid, oxalic acid, polyphenols and tannins particularly effect calcium
• Fat mal-absorption: the fat binds with calcium and gets excreted
• dietary phosphorus

Question 4

How is calcium transported through the body?

Answer 4

Can travel through the blood as free ionised calcium or bound to proteins

Question 5

Where is calcium stored in the body?

Answer 5

99% is stored in the skeleton and teeth

Question 6

How is calcium excreted?

Answer 6

Urine, sweat, faeces

Question 7

How does calcium help bone maintenance and development?

Answer 7

1- Bone development and
maintenance:
- Forms calcium-hydroxyapatite
along with phosphate:
- Strong lattice-like structure that
binds to collagen
- Hydoxyapatite allows strength
of bone
- Collagen allows flexibility
- Bone remodeling: total
skeleton replaced every 10
years

Question 8

Explain what mechanisms occur when blood calcium levels fall below homeostatic levels?

Answer 8

The parathyroid gland recognises this and secretes parathyroid hormone which:

• stimulates calcium release from bones
• increases calcium uptake in the intestines
• increases retention from kidneys

Question 9

Explain what mechanisms occur when blood calcium levels rise above homeostatic levels?

Answer 9

The thyroid gland recognises this and releases calcitonin which:

• decreases the calcium release from bones
• increases the excretion of calcium by the kidneys

Question 10

What is the role of calcium in the body?

Answer 10

• forming calcium hydroxyapatite
• involved in blood clotting cascade
• muscle contractions: Ca release when nerve transmission reaches the muscle and triggers proteins to contract
• transmission of nerve impulses: influx of Ca ions when impulse reaches the cell
• smooth muscle vasodilator

Question 11

What is caused by a calcium deficiency?

Answer 11

Bone loss

• osteopenia: normal to low bone mass
• osteoporosis: very low bone mass