Ca and PO4 metabolism Flashcards by kasia Tatara

What is the distribution of Ca and PO4 in the body?

 50% of the total calcium in serum is
present in the ionized form.
 99% of calcium and 85% of phosphore in
the organism are lacalised in bones.

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What regulates blood levels of Ca metabolism?

PTH and vitamin D

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What is the Ca concentration in the serum?

Total serum Ca: 2,1–2,6 mmol/l (8,5–10,5 mg/dl)

Ionized Ca: 1,1–1,3 mmol/l (4,4–5,2 mg/dl)

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How does PTH control Ca levels?

 Hypercalcemia

 Hypophosphatemia

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What regulates PTH secretion?

release is controlled by active vit D3

secretion is controlled by Mg and catecholamines

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What are the effects of PTH on the body?

 Bone – resorption of calcium and phosphate
from bones
 Intestinal mucosa – increase of intestinal
calcium absorption by renal production of 1,25-OH Vitamin D
 Kidney –increases the reabsorption of
calcium and inhibits the reabsorption of
phosphate (thus promotes renal phosphate
excretion). PTH stimulates vitamin D
hydroxylation in the kidney.

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How is calcitonin regulated in the body?

secreted by parafollicular C cells of the thyroid gland

regulated by serum calcium (increased Ca2+ level stimulate CT release)

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What are the effects of calcitonin (CT)?

 Hypocalcemia

 Hypophosphatemia

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What is the effect of excess secretion of CT?

Secretion of extremely high calcitonin levels by
medullary thyroid carcinoma has no effect on
mineral homeostasis.

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What are the biological effects of calcitonin on the body?

 Bones - the major effect of the hormone is
to inhibit osteoclastic bone resorption.
 Kidney – CT inhibits the reabsorption of
phosphate, increases the renal excretion of
calcium.
 It is important as a tumor marker in
medullary thyroid carcinoma.

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How is the medullary thyroid carcinoma test conducted?

Stimulation tests – up-regulation of
calcitonin production
Test with pentagastrin (0,5ug/kg body weight
(i.v.) in 5 sec.) or fast intravenous supplementation of gluconate calcium (2 mg of calcium/kg body weight iv over 1 minute).

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What vitamin controls the levels of calcium in the body?

1,25-OH Vitamin D is the most important

metabolite, and is the most biologically active.

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What are the effects of 1,25-OH Vitamin D

 Hypercalcemia

 Hyperphosphatemia

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How are the target tissues affected by 1,25-OH Vitamin D?

 Intestine – the transport of calcium through the
cytosol requires a vitamin-D-inducible protein
called calbindin.
 Bone – 1,25OH-D plays a role in regulating bone
formation and resorption (promotes phosphate
deposition).
 Kidney – it stimulates calcium and phosphate
reabsorption by the kidney tubules.
 Parathyroid glands – decreased vitamin D
production stimulates secretion of PTH.

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How is the presence of hypercalcemia defined by lab values?

Level of total calcium in blood > 2,7 mmol/l

or level of ionised calcium > 1,3 mmol/l

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What are some important causes of hypercalcemia?

 Primary hyperparathyroidism
 Tertiary hyperparathyroidism in chronic renal failure
 Malignancies
 Sarcoidosis – it increases 1,25OH-D production
 Endocrinopathies (thyrotoxicosis, adrenal
insufficiency, pheochromocytoma)
 Drug-induced (iatrogenic)– especially thiazide
diuretics which increase calcium reabsorption in the
kidney (and loss of potassium)
 Idiopathic hypercalcemia

What is a hypercalcemic crisis?

 Calcium level in blood over 3.5mmol/l
 Clinical symptoms: short QT interval,
polyuria, polydipsia, nausea, vomites,
shock, coma.
 Biochemical test: hypercalcemia,
hypophosphatemia, dehydratation,
electrolytes imbalance, metabolic acidosis

What is the etiology of primary hyperparathyroidism?

single parathyroid adenoma 80%,
primary hyperplasia 15%,
parathyroid carcinoma 1-2%

What are the symptoms of primary hyperparathyroidism? 5

 Kidney – renal stones, nephrocalcinosis, polyuria,
polydipsia, uremia
 Bone – osteitis fibrosa, osteoporosis
 Gastrointestinal tract – constipation, nausea, vomiting,
peptic ulcer, pancreatitis
 Psychiatric – lethargy, fatigue, depression, psychoses
and others
 Others - hypertension, itching, keratitis, soft tissue
calcification

What are the lab values indicating primary hyperparathyroidism? 6

 Calcium level in blood > 2,6 mmol/l
 Hypercalciuria – normally 6 mmol/24h
 Phosphor level- in lower norm range or
decreased
 PTH level – increased over 60pg/ml
 Alkaline phosphatase level – increased
 Tests of kidney function – creatinine,
clirens of creatinine.

What is hungry bone syndrome?

 In patients with severe hyperparathyroid
bone disease after successful parathyroidectomy.
 Increased uptake of calcium and
phosphate by the bones.

What is secondary hyperparathyroidism?

increased PTH secretion is associated with hypocalcemia

 Decreased resorption of calcium from the
intestine
 Chronic kidney failure (decreased vit D
production, hyperphosphatemia)
 Decreased concentration of vit D in blood

What is renal osteodystrophy?

 Chronic renal diseases result in reduced
circulating levels of vitamin D metabolites,
and high levels of phosphate in the serum.
They bound calcium (soft tissue calcification)
– two reasons for hypocalcaemia.
 Hypocalcaemia and low levels of 1,25OH-D
stimulate PTH production – secondary
hyperparathyroidism.
 bones gradually become thin and weak with
increased risk of bone fractures

Secondary hyperparathyroidismbiochemical parameters?

 Increased PTH level
 Hypocalcemia eventually calcium level at
the low normal range
 Hyperphosphatemia
 Increased level of alkaline phosphatase
 Parameters of renal function

What are the blood parameters of hypocalcemia?

Level of total calcium in blood < 2,2 mmol/l, | or level of ionised calcium < 1,1 mmol/l

What are the causes of hypocalcemia?

 Normal magnesium level in blood  Hypoparathyroidism  Resistance to PTH action – pseudohypoparathyroidism, renal insufficiency (secondary hyperparathyroidism)  Vitamin D deficiency or resistance to vitamin D action  Acute hyperphosphatemia, transfusion of citrated blood  „Hungry bones syndrome” – idiopatic increased uptake of calcium and phosphate by the bones.  Decreased magnesium level  Impaired intestinal absorption  Alcoholism

What are the symptoms of hypocalcemia?

```  Neuromuscular manifestation – tetany, paresthesias, laryngeal spasm, latent tetany, generalized seizures, pseudotumor cerebri,  Cardiac effect – prolongation of the QT interval  Subcapsular cataract  Skin – is dry and flaky and nails are brittle ```

What is primary hypoparathyroidism?

 Lack or not efficient production of biological active from of PTH.  Pathophysiology:  Hypocalcemia – decreased calcium mobilisation form the bones, decreased absorbtion form the digestive syndrome, decreased production of metabolites of vit D3 in kidney; inhibited renal readsorption of calcium  Hyperphosphatemia – inhibits production of vit D3 metabolites in kidney; accumulation of calcium phosphate in soft tissues.

What are the lab results of hypoparathyroidism?

 Hypocalcemia in blood  Hyperphosphatemia with phosphaturia  Low PTH concentration in blood  Decreased level of 1,25(OH)2D3

What is pseudohypoparathyroidism?

Rear inherited syndrome characterized by end-organ resistance to PTH. Types:  1A – lack of 1 allel of gene for subunit of protein G (inheritance AD); 50% reduction of effectiveness of PTH binding to adenyl cyclase (resistance to PTH). Often is correlated with resistance to TSH, LH, FSH. Biochemical parameters: hypocalcemia, hyperphosphatemia, increased level of PTH.  1B – isolated resistance to PTH

How is phosphate metabolized?

 Phosphor is deposited in skeleton as hydroxyapatite,  15 % is distributed among extra skeletal sites like phosphoproteins, phospholipids, and nucleic acids  In blood, phosphorus exists as the phosphates, H2PO4 - and HPO42-, but its concentration is measured as phosphorus, with a normal range of 0,87 – 1,45 mmol/l (2.5 -4.5 mg/dl).

How is phosphate metabolism hormonally controlled?

 Kidney - PTH and CT increase phosphorus excretion, and Vitamin D decreases its excretion.  Intestine - Vitamin D increases absorption as well as PTH.  Bone – PTH stimulates phosphor release into the blood

What phosphate level indicates hypophosphatemia?

Phosphate level of less than 2.5 mg/dl (0.87 | mmol/l).

What are causes of hypophosphatemia?

```  hyperparathyroidism,  Hypothyroidism,  impaired kidney function,  diuretics for a long time,  severe undernutrition,  diabetic ketoacidosis,  severe alcohol intoxication, ```

What phosphate level indicates hyperphosphatemia?

Phosphate level of higher than 4.5 mg/dl (1.45 mmol/l).

What are causes of hyperphosphatemia?

```  kidney failure  primary hypoparathyroidism  bone diseases (fractures, neo)  acromegaly  sarcoidosis  severe burns ```