K, Ca, Mg, PO4 Endocrinology Flashcards
Which of the following has the highest potassium distribution within its cells?
A. Liver
B. Bone
C. Muscle
D. Kidneys
C. Muscle
Potassium plays an important role in cell volume maintenance. What would the effects be of:
- Net loss of K+
- Net gain of K+
Net loss of K+ = cell shrinkage
Net gain of K+ = cell swelling
Potassium plays an important role in intracellular pH regulation. What would the effects be of:
- Low plasma [K+]
- High plasma [K+]
Low plasma K+ = cell acidosis
High plasma K+ = cell alkalosis
What effect does lack of potassium have on protein synthesis?
Reduced protein synthesis and stunted growth
What effect do changes in the transmembrane [K+] ratio have on resting cell membrane potential?
Reduced [K]in:[K]out = membrane depolarization
Increased [K]in:[K]out = membrane hyperpolarization
What effect do changes in the transmembrane [K+] ratio have on neuromuscular activity?
Low plasma [K] = muscle weakness, muscle paralysis, intestinal distension, respiratory failure
High plasma [K] = initially increased muscle excitability, later muscle weakness (paralysis)
What effect do changes in the transmembrane [K+] ratio have on cardiac activity?
Low plasma [K] = prolonged repolarization; slowed conduction; abnormal pacemaker activity, leading to tachycardia
High plasma [K] = enhanced repolarization; slowed conduction, leading to bradyarrhythmias and cardiac arrest
What effect do changes in the transmembrane [K+] ratio have on vascular resistance?
Low plasma [K]: vasoconstriction
High plasma [K]: vasodilation
99% of calcium is stored in ________, and 90% is excreted in _____
Bone; feces
Which of the following is important in the formation of bone from the body calcium pool?
A. Calcitonin
B. PTH
C. Calcitriol
D. Both PTH and calcitriol
A. Calcitonin
What is the effect of hypocalcemia on neuromuscular excitability?
INCREASES in neuromuscular excitability (hypocalcemic tetany/spacsticity)
What is the effect of hypercalcemia on neuromuscular excitability?
DEPRESSES neuromuscular excitability (threshold shifts away from resting membrane potential)
Primary hyperparathyroidism and malignancy are related to which of the following?
A. Low serum calcium
B. Low serum potassium
C. Elevated serum calcium
D. Elevated serum potassium
C. Elevated serum calcium
Hypoparathyroidism, renal disease, and vitamin deficiency are associated with which of the following?
A. Low serum calcium
B. Low serum potassium
C. Elevated serum calcium
D. Elevated serum potassium
A. Low serum calcium
Where is the majority of phosphate stored in the body?
Bone (85%)
The rest is in cells (14%) and serum (1%)
Fine-tuning of circulating phosphate levels is mostly under the control of renal excretion. Reabsorption depends on the _______ ________
Transport maximum (Tm)
What are the 4 main known regulators of phosphate metabolism?
Dietary
Calcitriol
PTH
Renal tubular reabsorption of phosphorus
What percent of total magnesium is considered free (unbound) serum Mg2+?
69%
Depletion of which of the following is associated with migraines, depression, epilepsy, SIDS, arrhythmia, preeclampsia, and muscle cramps?
A. Calcium
B. Phosphate
C. Magnesium
D. Potassium
C. Magnesium
What effect does PTH have on serum calcium and serum phosphate levels?
Increases serum Ca
Decreases serum Pi
What effect does calcitonin have on PTH, Ca and Pi concentrations?
Calcitonin opposes PTH
Decreases serum Pi and Ca concentrations
What effect does calcitriol have on serum Ca and Pi levels?
Increases serum Ca and Pi levels
Action of PTH on bone
Increases osteoclastic resorption
Action of PTH on intestine
Increases Ca/Pi absorption indirectly via Vit D (calcitriol) production
Action of PTH on the kidney
Increased reabsorption of Ca primarily in DCT
Decreased reabsorption of Pi in PCT
Decreased activity of Na/H antiporter
Decreased bicarb reabsorption
Excess PTH can cause what conditions?
Hypercalcemia
Hypophosphatemia
Hypercholermic metabolic acidosis
T/F: Calcitonin is inhibited by hypercalcemia
False: calcitonin is stimulated by hypercalcemia
Action of calcitonin on bone
Inhibits osteoclastic-mediated bone resorption
Action of calcitonin on kidney
Promotes phosphate excretion
Promotes calcium excretion
Pharmacologic doses of calcitonin are used in what types of conditions?
Osteoporosis
Paget’s disease
Hypercalcemia
Action of calcitriol on bone
Promotes osteoid mineralization
Osteoclastic mediated bone resorption
Action of calcitriol in the intestine
Increases calcium absorption (30% dietary calcium is absorbed)
Increases phosphorus absorption
Action of calcitriol on kidney
Increased phosphate reabsorption
Increased Ca reabsorption
Stimulus for secretion and action on kidneys of:
PTH
Stimulus for secretion: decreased plasma [Ca]
Action on kidneys:
Decreased Pi reabsorption (PT)
Increased Ca reabsorption (DT)
Stimulus for secretion and action on kidneys of:
ADH
Stimulus for secretion:
- increased plasma osmolarity
- decreased blood volume
Action on kidneys:
-increased H2O permeability (late DT and CCD principal cells)
Stimulus for secretion and action on kidneys of:
Aldosterone
Stimulus for secretion:
- decreased blood volume (via RAAS)
- increased plasma [K]
Action on kidneys:
- increased Na reabsorbtion (ENaC in DT principal cells)
- increased K secretion (DT principal cells)
- increased H secretion (DT alpha-IC cells)
Stimulus for secretion and action on kidneys of:
ANP
Stimulus for secretion:
-increased atrial pressure
Action on kidneys:
- increased GFR
- Decreased Na reabsorption
Stimulus for secretion and action on kidneys of:
Angiotensin II
Stimulus for secretion:
-decreased blood volume (via renin)
Actions on kidneys:
-Na/H exchange and HCO3 reabsorption (PT)
