Calcium/Phosphate/Magnesium Metabolism And Disorders Flashcards
Describe the distribution of body calcium
99% is part of bone
1% is in the blood and ECF
•45% as free Ca2 ions
•40% bound to proteins like albumin
•15% to anions like HCO3, citrate, PO4 and lactate
What is the reference interval for total plasma calcium❓
2.15-2.55mmol/L
- Ca> 3.5mmol/L can lead to cardiac arrest/arrhythmias
- Medical emergency
What is the reference interval for free ionized calcium in plasma❓
1.1-1.4mmol/L
Free ionized calcium is physiologically ________ and the calcium bound to albumin is physiologically ________
Active
Inactive
What are the factors involved in the control of calcium❓
- Diet
- Vitamin D
- Parathyroid glands
- Thyroid glands
- Normal functioning intestines
- Normal functioning kidneys
The parathyroid hormone is a single chain polypeptide containing ____ amino acids
The amino acid on the ____ terminal mediates it’s biological activity
84
34N
What are the actions of parathyroid hormone❓
On bones:
⬆️plasma concentration of Ca and Ph
⬆️osteoclastic bone activity
On the kidneys:
⬆️plasma concentration of Ca by increasing reabsorption
⬇️plasma concentration of Ph by ⬇️Ph reabsorption and causing phosphaturia
The control of PTH depends on:
- Free ionized calcium conc in plasma
2. Extracellar magnesium conc
How is PTH affected in severe chronic hypomagnesaemia❓
PTH conc. is reduced
The parathyroid hormone related protein is seen in what disease state❓
⬆️in certain tumors
Causes humoral hypercalcaemia of malignancy
b/c it has a similar amino acid sequence with PTH at the biologically active end
What is calcitonin❓
What is it’s role in calcium metabolism❓
A hormone secreted by the medullary cells of the thyroid gland
Secreted in ⬆️blood calcium
🚫PTH
🚫Vit D
What are the two forms of vitamin D❓
Where are obtained❓
VitD2 Ergocalciferol
From plants in diet
Vit D3 Cholecalciferol
Formed on skin by the action of UV light on 7-dehydrocholestrol
Speak briefly on the metabolism of Vitamin D
•Transported bound to vitamin D binding protein
•7-dehydrocholesterol ⬇️UV Cholecalciferol (Liver) ⬇️25-hydroxylase 25-hydroxycholecalciferol* (Kidney) ⬇️1-alpha-hydroxylase 1,25-dihydroxycholecalciferol
What can stimulate the action of 1-alpha-hydroxylase❓
⬇️plasma phosphate
⬆️PTH
What can inhibit the action of 1-alpha-hydroxylase❓
Hyperphosphataemia
⬆️free ionized calcium
What can inhibit the synthesis of 1,25-dehydroxycholecalciferol❓
What can it lead to❓
Renal disease
Hypocalcaemia
What the functions of 1,25-dehydroxycholecalciferol❓
On intestinal mucosal cells:
⬆️Ca and Ph reabsorption
On bones:
⬆️Ca by stimulating osteoclastic activity with PTH
Describe the synergistic effect of PTH and VitD
- The action of PTH on bone is impaired in the absence of 1,25-(OH)Vit D
- PTH enhances 1-hydroxylase activity and therefore promotes 1,25-(OH)Vit D synthesis
What are the effects of hypercalcaemia❓
Renal:
Renal calculi (ppt of Ca Ph stones)
Polyuria
Renal damage
Hypokalemia:
⬆️Ca 🚫K reabsorption
Neuromuscular effects:
Hypotonia
CNS: Nausea Vomiting Anorexia Depression
GIT:
Constipation
Peptic ulceration
Abdominal pain
Cardiac:
Shortened Q-T interval
Broadened T waves
What are the causes of hypercalcaemia?
Thiazide diuretics
Bony metastasis
Hyperthyroidism
High bone turnover in thyrotoxicosis and immobilization
⬆️Vit D
Primary hyperparathyroidism is caused by an ⬆️PTH due to an adenoma/hyperplasia/carcinoma of the PTH gland
True or false
True
What happens in tertiary hyperparathyroidism❓
- PTH gland have been subjected to chronic +ve feedback by hypocalcaemia of secondary parahyperthyroidism which has been corrected
- Hypertrophy of PTH gland
- PTH secretion is partly autonomous and isn’t suppressed by -ve feedback of hypercalcaemia
In malignant disease of the bone…
- bony metastasis from tumors of breast, lungs etc
- malignant deposits stimulate local osteoblastic reaction
- plasma alkaline phosphatase activity is raised
- ⬆️plasma phosphate
What protein is involved in humoral hypercalcaemia of malignancy❓
Parathyroid Hormone related protein is involved in humoral hypercalcaemia of malignancy
It is not subject to normal feedback control
Results in hypercalcaemia
Hypercalcaemia can be drug-induced.
What drugs do you know that could cause ⬆️Ca❓
Thiazides (⬇️Renal Ca excretion)
Lithium
Vitamin A
How is Ca metabolism affected in sarcoidosis❓
What other conditions can produce the same effect❓
- Granulomatous tissue synthesize 1,25(OH)2 Vit D
⬆️Ca reabsorption from GIT
- Histoplasmosis and leprosy
How would you treat hypercalcaemia❓
- Rehydration
- Bisphosphonates (bind calcium) eg pamidronate
- Steriods esp. in Vit D intoxication and sarcoidosis
- Calcitonin
What are the clinical effects of hypocalcaemia❓
Tetany Carpo-pedal spasm Generalized seizure Laryngospasm Hyperreflexia Cataract Cardiac arrhythmias Paraesthesiae hypotension Prolonged Q-T interval on ECG
What are the clinical signs of hypocalcaemia❓
Trousseau’s Sign
Chvosteks’s Sign
Describe the Trousseau’s Sign
When is it observed❓
Carpopedal spasm and tetany by inflating a BP cuff to 10-20mmHg above systolic BP for 3-5minutes
It is observed in hypocalcaemia
Chvosteks’s Sign is seen in hypocalcaemia. Give a brief description
It is elicited by tapping the facial nerve anterior to the ear, ipsilateral facial muscle contraction may occur
Classify hypocalcaemia
Hypocalcaemia with hypophosphataemia
Hypocalcaemia with hyperphosphataemia
What are the causes of hypocalcaemia with hypophosphataemia❓
Inadequate intake of Ca, Vit D and phosphate
Secondary parahypothyroidism
Steathorhoea (impaired absorption of Vit D)
Renal disease (impaired metabolism of 1,25-(OH) Vit D)
Anticonvulsant therapy (increased inactivation of Vit D)
Renal tubular disorders of phosphate disorders
What are the causes of hypocalcaemia with hyperphosphataemia❓
Renal dysfunction (acute and chronic renal failure- 1-alpha-hydroxylase is affected)
Primary hypoparathyroidism causes by surgical damage to parathyroids
Pseudohypoparathyroidism (in-born error, end organ resistance)
How would you treat hypocalcaemia❓
Mild hypocalcaemia:
Oral calcium
Vit D supplements
OR
IV calcium- 10mls of 10% calcium gluconate over 5 minutes
Continue with oral supplement
Describe the distribution of body phosphate
Major intracellular divalent anion
80% in skeleton
20% in soft tissues and muscle
90% excreted via renal route
Causes of hyperphosphataemia❓
⬆️phosphate intake, esp. IV
⬆️tissue breakdown
Tumor lysis syndrome
Malignant hyperpyrexia
Crush injuries
ARF or CRF
Acidaemia
DKA
Acromegaly
⬆️Vit D intake
How would you treat hyperphosphataemia❓
Use of oral phosphate binding agents eg magnesium hydroxide or calcium carbonate
Hemodialysis or peritoneal dialysis
Causes of hypophosphataemia❓
Poor intake
Malabsorption states
Chronic alcoholism
Renal tubular acidosis
Hyperparathyroidism
Cellular redistribution
- IV glucose
- Alkalemia
- Insulin administration
Describe the distribution of body magnesium
Major intracellular divalent cation
Cereals, nuts and vegetables are dietary sources
Absorbed in upper small intestine w/o Vit D
Eliminated in faeces and via the kidney
Magnesium acts as an antagonist to calcium in cellular responses
True or false❓
True
Causes of hypermagnesaemia❓
Increased intake of:
Antacids
Purgatives
Parenteral nutrition
Renal failure (Impaired renal excretion)
Hypothyroidism
Adrenal insufficiency
What the clinical consequences of hypermagnesaemia❓
Mg>2mmoles/L
Cardiac arrhythmias Cardiac arrest Seizures Hyporeflexia Paralytic ileus Nausea Respiratory depression Hypotension
How would you manage severe hypermagnesaemia❓
10ml of 10% calcium gluconate given slowly
Insulin/ glucose infusion
Dialysis
The symptoms of hypomagnesaemia are not similar to those of hypocalcaemia
True or false
List them
False
Tetany Carpo-pedal spasm Generalized seizure Laryngospasm Hyperreflexia Cataract Cardiac arrhythmias Paraesthesiae hypotension Prolonged Q-T interval on ECG
Hypomagnesaemia can result in…
Cardiac arrhythmias
Digoxin sensitivity
Abdominal discomfort
Anorexia
Neuromuscular sequelae: Parasthesia Vertigo Tetany Seizures Irritability
Will severe hypomagnesaemia lead to hypercalcaemia or hypocalcaemia❓
Why❓
Hypocalcaemia
⬇️PTH release and activity
Long term magnesium deficiency may be a risk factor for coronary artery disease
True or false
True
⬆️Mg intake is associated with hypertension and insulin resistance
True or false
False
⬇️Mg intake is associated with hypertension and insulin resistance
