7. Regulation and disorders of calcium and phosphate metabolism (PTH, calcitonin, D-hormone) Flashcards
Give the total plasma Ca2+ concentration
2.5mmol/l
Give the divisions of Ca2+ concentration in the plasma
- Ionised form - 40% (1.2mmol/l)
- Albumin bound - 50%
- In complex molecules - 10%
List the functions of Ca2+
- Structure of bones and teeth
- Co-factor for blood clotting
- Muscle contraction
- Hormone: Secretive function of cell receptors
List the determining factors of the distribution of calcium
- Demand
- Intake
- Blood phosphate content
- The function of Parathyroid C-cells
- Alkalosis
- Acidosis
How does demand affect calcium distribution?
Related to body productivity:
- Egg laying
- Lactation
How does intake affect calcium distribution?
- Grains + Grasses = Low Ca2+
- Clover + alfalfa = High in Ca2+
- Overfeeding of alfalfa → Underfunction of the parathyroid gland
- Postpartum → Decrease of Ca2+ = Milk fever
How does blood phosphate affect calcium distribution?
Blood phosphate is inversely related to the blood calcium level
How does parathyroid C-cell function affect calcium distribution?
- C-cells release PTH (responsible for Ca2+ conc.)
- Parathyroid gland stimulates osteoclasts to break down bone
- Calcium release → ↑ Blood Ca2+
Parathyroid C-cell function has an indirect effect on…
- Vitamin D - Responsible for Ca2+ and PO43- absorption
- Hypoalbuminaemia → Causes decrease in total Ca2+
How does alkalosis affect calcium distribution?
- Causes an increase in protein-bound calcium
- This occurs at the expense of ionised calcium
How does acidosis affect calcium distribution?
- Causes an increase in ionised calcium
- This occurs at the expense of protein-bound calcium
Give the factors regulating calcium and phosphate absorption
- Demand of the organism
- Age
- Body weight
- Intestinal peristalsis
- Intestinal circulatory disorders
- Fat, Mg, F, Phytin
- Protein
How does demand of the organism affect the regulation of calcium and phosphate absorption?
The greater the need, the more efficient absorption is
How does ageing affect the regulation of calcium and phosphate absorption?
↑ Age = ↓ Absorption
How does body weight affect the regulation of calcium and phosphate absorption?
↑ Body weight = ↓ Absorption
How does intestinal peristalsis affect the regulation of calcium and phosphate absorption?
↑ Intestinal peristalsis = ↓ Absorption
How do intestinal circulatory disorders affect the regulation of calcium and phosphate absorption?
↑ intestinal circulatory disorders = ↓ Absorption
How does Fat, Mg, F and Phytin intake affect the regulation of calcium and phosphate absorption?
↑ Fat, Mg, F and Phytin = ↓ Absorption
How does protein intake affect the regulation of calcium and phosphate absorption?
↑ Protein intake = ↑ Absorption
List the hormones responsible for phosphate and calcium regulation
- PTH
- Calcitonin
- D-Hormone
How does PTH regulate phosphate and calcium?
PTH release:
- ↑ Kidney P → ↓Plasma P
- P + C is mobilised from bones → ↑ Plasma P + C
- Doesn’t result in P concentration change due to compensation
- Results in ↑ plasma C
How does calcitonin regulate phosphate and calcium?
- ↑ renal excretion → ↓ Plasma P level
- Causes ↓ mobilisation of C from the bones → ↓ plasma C
- Results in ↓ plasma C + P
How does D-hormone regulate phosphate and calcium?
- Facilitates intestinal C, P and Mg absorption
- Stimulates several transport proteins
- Provides proper balance of C + P to support mineralisation
- Improved utilisation of phytin
In the kidney, vitamin D is converted to…
D-hormone
List the causes of Vitamin D-deficiency
- Genetic defects in vitamin D receptor
- Severe liver/kidney disease
- Insufficient exposure to sunlight
- Improper intake
Give the consequences of D-hormone deficiency
- Osteoporosis
- Rickets
- Osteomalacia
- Osteoarthritis
- Abnormalities of PTH
- High BP
