Endocrine Lecture 5: Calcium and Parathyroid Flashcards
What functions in the body does Calcium contribute to?
- Nerve conduction
- Bone formation
- Muscle function
- Blood coagulation (factor IV is Ca ion)
- Cerebral and cardiac function Capillary permeability
- Cell growth and division
- Neurotransmitter action
Where and in what ways is Ca stored or present in the body?
Body contains 1-2 kg of calcium
- 98% in skeleton
- 1% in cells
- 0.1% in ECF
- 0.03% in plasma
Plasma Ca is present in the following forms in the body:
-50% Ionized (active form)
Most important form for calcium functions on heart, the nervous system, and bone formation
-41% protein bound (primarily albumin)
-9% combined with anions (diffusible)
Equilibrates with bone Ca++, but only 0.5% of bone calcium is readily exchangeable
Rest is slowly exchangeable
How does HYPOcalcemia manifest?
Nervous system excitement
• Increased neuronal permeability to Na, easy action potentials • 50% ion/ 35% total decrease leads to spontaneous discharges • Tetany, seizures
– Most common in hand: carpopedal spasm
-Or face:Chvosteks sign:tapping facial nerve leads to twitching
• Longer QT
How does HYPERcalemia manifest?
Chief manifestation is skeletal muscle weakness
– Nervous system depression
• Short QT, long PR interval, constipation, anorexia
– Treatment:
• Maintain UOP, hydrate, administer mithramycin in severe cases
Where and in what ways is Phosphorus stored or present in the body?
Body contains 1 kg of phosphorus
• 85% skeletal, 15% muscle/tissue, 1% ECF
– Circulates in plasma 12% protein bound
– Levels fluctuate significantly more than Ca++ because Ph moves between ECF and bone as well as between ECF and ICF
Where is the major control site of Phosphorus balance?
Major control site is kidney:
– Urinary excretion balances GI intake
– PTH increases urinary excretion
• Calcitonin to a lesser extent
– GI absorption increased by 1,25 D3The Parathyroid consists of __ glands located behind the upper and lower poles of the ___ gland.
4
Thyroid
The Parathyroid glands are very small, they contain mainly ___ cells and ___ cells.
Chief and oxyphil cells
Chief cells secrete _____.
Parathyroid Hormone
Synthesis and secretion of parathyroid hormone is related to _____ concentrations in the blood.
Calcium
These 3 conditions can cause enlargement of the parathyroid gland:
Prolonged stimulation
Pregnancy
Lactation
Decreases in ECF concentration of ____ increases the secretion of Parathyroid Hormone (PTH)
Calcium
Likewise:
Increases in calcium concentration in the extracellular fluid decreases the activity of the parathyroid gland
Vitamin D (Cholecalciferol) and Calcitonin both help with reabsorption of Ca from the ______ of the kidney?
Proximal tubules
What are the main actions of PTH?
- Major stimulus is low serum Ca++ level
- Increases bone resorption to mobilize calcium and phosphate
-Increases reabsorption of Ca++ in the kidney’s distal tubules
• Decreases reabsorption of phosphate in the renal tubules
• Increases the production of 1,25-dihydroxycholecalciferol
Increased release of PTH results in:
-Increases the excretion of phosphate, potassium, and sodium by increasing the calcium/magnesium/hydrogen reabsorption
(largely in the distal tubules and collecting ducts)
Serum: Increased calcium, decreased phosphate
Urine: Decreased calcium, increased phosphate
Where is Calcitonin produced?
parafollicular (clear or C cells) of the thyroid
What are the main effects of Calcitonin?
-In general it has the opposite effect of parathyroid hormone
Secretion is controlled by serum calcium level
• Increased Ca++ leads to in creased secretion
Serum:
– Decreased calcium
– Decreased phosphate
Urine:
– Increased calcium excretion
– Increased phosphate excretion
What is the active form of Vitamin D and how/where is it converted to it’s active form?
Vitamin D is not itself an active substance, but must be converted to its active product 1,25-dihydroxycholecalciferol
Vitamin D3 is converted to 1,25-dihydroxycholecalciferol by the liver
What are the main functions of vitamin D (D3/1,25-dihydroxycholecalciferol)?
Vitamin D has a potent effect to increase calcium absorption from the intestinal tract
Vitamin D has important effects on both bone deposition and bone absorption
GI absorption of Ca++ is increased by Vitamin D
Calcium regulation:
Urinary excretion of Ca is decreased by ____ and increased by ____.
decreased by PTH (parathyroid hormone)
increased by calcitonin
Calcium regulation:
Bone respiration is increased by _____ and inhibited by _____.
Increased by PTH
inhibited by Calcitonin
What is the primary cause of HYPOparathyroidism?
Usually a result of surgical damage to the gland during thyroid surgery
Calcium levels fall below normal in 24-72
surgical damage to the parathyroid gland during thyroid surgery causes Calcium levels to fall below normal in 24-72 hours which results in:
- Tetany: calcium ion interferes with membrane transport and interferes with the relaxation of the muscle
- Muscle cramps
- Grand mal seizures
- Cardiovascular collapse
