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42 Cards in this Set
- Front
- Back
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when extracellular Ca2+↓ , PTH release is (a) stimulated (b) inhibited? |
↑PTH release when extracellular Ca2+↓ |
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How is extracellular Ca2+ concentration detected by the parathyroid gland? |
G-protein coupled calcium-sensing receptor on the surface of chief cells (PTH-secreting cells) |
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What effect does excess PTH have on serum concentration of calcium & phosphate? |
excess PTH increases serum calcium & reduces serum phosphate |
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Outline PTH effects on bone (1) & in kidney (3). |
bone: PTH stimulates bone-building osteoblasts, which stimulate bone-resorbing osteoclasts net bone resorption with calcium & phosphate release kidney, PTH has 3 effects: increases vit D synthesis reduces proximal tubular phosphate reabsorption, increasing phosphate excretion (↓phosphate levels) increases distal tubular calcium reabsorption by activating calcium channels (↑Ca2+ levels) |
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Outline the vit D conversion pathway |
1. converted by 1ɑ-hydroxylase in the cells of the renal proximal tubule to 1,25-dihydroxycholecalciferol (principal active form of vit D)
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Outline actions of vit D on cells in the gut, bone & kidney |
* inhibits PTH secretion from parathyroid glands
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What effect does vit D have on calcium & phosphate levels? |
raises levels of both calcium & phosphate |
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Name hormones that promote renal phosphate reabsorption ↑PO42- |
GH insulin thyroxine |
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What effect do corticosteroids & chronic acidosis have on phosphate reabsorption? |
inhibit phosphate reabsorption ↓PO42- |
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What are phosphatonins & how do they effect phosphate levels? What effect do they have on vit D levels? |
phosphatonins are peptides which promote renal phosphate excretion by inhibiting phosphate reabsorption by the NPT2 sodium phosphate transporter in the proximal tubule ↓PO42- some phosphatonins also inhibit the activity of the renal 1ɑ-hydroxylase enzyme & so reduce vit D synthesis in the kidney ↓vitD |
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What does severe vs moderate hypophosphataemia indicate in terms of the mechanism? |
severe - indicates phosphate deficiency
moderate - often due to movement of phosphate into cells |
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What is the mechanism causing phosphate to move into cells, resulting in moderate hypophosphataemia? Give medical situations where this occurs. |
Movement occurs if intracellular phosphate is used up to generate phosphorylated metabolic products e.g. glucose-6-phosphate & ATP. Plasma phosphate can fall if glycolysis increases suddenly e.g. * respiratory alkalosis
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Give 4 situations in which hypophosphataemia occurs. |
* vit D deficiency (impaired absorption + calcium absorption)
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What happens to cells in severe phosphate deficiency? |
lowers cellular ATP levels, which can impair cellular function |
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Outline the clinical features of hypophosphataemia |
weakness of skeletal, cardiac & smooth muscle causing: * impaired myocardial contractility* coma |
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How can hypophosphataemia be treated? |
* IV phosphate can cause severe hypocalcemia - only used in severe phosphate depletion
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Give the 3 situations where hyperphosphataemia can occur & give examples in each. |
reduced urinary phosphate excretion * renal failure (phosphate retention) - most common* vit D excess (promotes absorption from gut) * chemotherapy, tumour lysis, rhabdomyolysis |
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What are the clinical features of hyperphosphataemia?
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Hypocalcaemia features (if present) including tetany.
If Phos high and calcium normal - soft tissue calcification occurs |
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How can hyperphosphataemia be treated?
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Hydration with saline can promote phosphaturia if renal function normal.
Phosphate-binding agents |
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Outline the roles of magnesium
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Req. by essential enzymes
Stabilises excitable membranes (heart) Regulates K+ and Ca2+ channels Stimulates Na+/K+ ATPase, promoting intracellular K+ retention |
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What can cause hypomagnesaemia?
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Loss from gut/kidneys
Inadequate intake e.g. Alcoholism |
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What are the clinical features of hyperphosphataemia?
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Hypocalcaemia features (if present) including tetany.
If Phos high and calcium normal - soft tissue calcification occurs |
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How can hyperphosphataemia be treated?
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Hydration with saline can promote phosphaturia if renal function normal.
Phosphate-binding agents |
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Outline the roles of magnesium
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Req. by essential enzymes
Stabilises excitable membranes (heart) Regulates K+ and Ca2+ channels Stimulates Na+/K+ ATPase, promoting intracellular K+ retention |
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What can cause hypomagnesaemia?
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Loss from gut/kidneys
Inadequate intake e.g. Alcoholism |
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Clinical features of hypomagnesaemia?
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Neuro & muscular - similar to hypocalcaemia: tetany, seizures, cardiac dysrhythmia (especially ventricular)
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What are the ECG changes in hypomagnesaemia?
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Prolonged PR
QRS widening T-wave inversion Prominent U waves |
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What can hypomagnesaemia lead to?
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Hypokalaemia
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What is Chvostek's sign?
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Facial twitch when facial nerve tapped below the zygomatic bone
Sign of tetany seen in hypocalcaemia |
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What is Chvostek's sign?
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Facial twitch when facial nerve tapped below the zygomatic bone
Sign of tetany seen in hypocalcaemia |
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What is Trousseau's sign?
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Spasm with hyperextended fingers & MCP flexion when a sphygmomanometer cuff is inflated for 3 min around the upper arm
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What is Chvostek's sign?
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Facial twitch when facial nerve tapped below the zygomatic bone
Sign of tetany seen in hypocalcaemia |
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What is Trousseau's sign?
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Spasm with hyperextended fingers & MCP flexion when a sphygmomanometer cuff is inflated for 3 min around the upper arm
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What are the clinical features of hypermagnesaemia?
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Bradycardia
Hypotension Reduced consciousness resp depression |
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What is Chvostek's sign?
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Facial twitch when facial nerve tapped below the zygomatic bone
Sign of tetany seen in hypocalcaemia |
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What is Trousseau's sign?
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Spasm with hyperextended fingers & MCP flexion when a sphygmomanometer cuff is inflated for 3 min around the upper arm
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What are the clinical features of hypermagnesaemia?
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Bradycardia
Hypotension Reduced consciousness resp depression |
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How is hypermagnesaemia treated?
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Furosemide + hydration or dialysis to remove excess Mg
Calcium reversed dangerous effects of Mg on the heart |
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What is Chvostek's sign?
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Facial twitch when facial nerve tapped below the zygomatic bone
Sign of tetany seen in hypocalcaemia |
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What is Trousseau's sign?
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Spasm with hyperextended fingers & MCP flexion when a sphygmomanometer cuff is inflated for 3 min around the upper arm
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What are the clinical features of hypermagnesaemia?
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Bradycardia
Hypotension Reduced consciousness resp depression |
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How is hypermagnesaemia treated?
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Furosemide + hydration or dialysis to remove excess Mg
Calcium reversed dangerous effects of Mg on the heart |
