Body Water Compartments, Osmolality, and Electrolyte Regulation in Physiology

What are the two main compartments of total body water?

Extracellular fluid (ECF) 1/3 and intracellular fluid (ICF)-2/3

What is the significance of the osmolality of body fluids?

All body fluids have an equal osmolality of approximately 280-290 mmol/kg, except urine

What regulates water balance?

hypothalamus, posterior pituitary, and kidneys

What is osmolality?

A measurement of how concentrated a compartment is (the proportion of solutes-to-water that is in a compartment's fluid).

If the ICF has an lower osmolality that the ECF then there's a

Decrease in water excretion (the kidneys retain the water)

If the ICF has a greater osmolality than the ECF then there's a

increase in water excretion

What is the principal extracellular cation and its normal range?- also the primary contributor to ECF osmolality.

Sodium (Na+), 135-145 mmol/L

What is the calculated serum osmolality formula?

2 x serum [Na+] + [Glucose]/18 + [BUN]/2.8

What condition is characterized by a measured serum osmolality greater than calculated serum osmolality?

Osmolal gap

What hormones work in sodium balance?

Aldosterone and Atrial natriuretic peptide

How does aldosterone work in sodium balance?

it promotes sodium retention and potassium excretion

What is ADH?

Anti-diuretic hormone - it controls the concentration of urine and is released into the bloodstream by the pituitary gland

How does atrial natriuretic peptide work in sodium balance?

It promotes sodium excretion and vasodilation

Hypernatremia due to a normal sodium content and water loss is due to

renal H20 loss and diabetes insipidus

Hypernatremia due to decreased sodium content and water loss is due to

Osmotic diuresis and diabetes mellitus

Hypernatremia due to a normal water content and increase sodium content is due to

Conn's syndrome, and Cushing's syndrome

What are the clinical features of hypernatremia?

Salt gain, fluid loss, raised jugular venous pressure, and pulmonary edema

What is hyponatremia and its common causes?

Low sodium levels due to fluid retention or sodium deficit

What is the syndrome of inappropriate antidiuresis (SIAD)?

A condition with non-osmotic ADH secretion leading to water retention and hyponatremia

What are examples of non-edematous hyponatremia?

decreased water excretion due to SIAD and renal failure or increased water intake due to compulsive water intake or psychogenic

What are examples of edematous hyponatremia?

decreased water excretion due to CHF, liver disease, nephrotic syndrome or increased water intake due to inappropriate IV saline

Sodium retention can lead to_____

potassium loss

What are common causes of hypokalemia?

Deficient intake, gastrointestinal losses, adrenergic stimuli, renal losses, drug usage, high aldosterone levels and systemic alkalosis

Symptoms of hypokalemia

severe weakness, tachypnea, hyporeflexia, cardiac arrhythmias

How is alkalosis and hypokalemia related?

Hypokalemia causes alkalosis primarily because it shifts hydrogen ions into cells, stimulating the kidneys to retain bicarbonate by secreting more hydrogen ions to maintain the balance.

What is the normal range for serum potassium (ECF) ?

3.5-5.0 mmol/L

What are the main functions of potassium in the body?

Essential for nerve and muscle activity, maintaining resting membrane potential, and muscle function

What is the best way to gain potassium through diet?

by eating meats, beans, fruits,and vegetables and potatoes

Homeostasis of potassium is mainly through

regulation of renal excretion

What are causes of hyperkalemia?

renal failure, mineralocorticoid deficiency, certain drugs, excessive potassium intake, diabetes, systemic acidosis, damaged cells, and pseudohyperkalemia

What can cause pseudohyperkalemia?

Hemolysis during blood collection

Potassium levels less than 6 mmol/L are

usually asymptomatic

Potassium levels greater than 6 mmol/L is

an electrolyte emergency that can lead to cardiac arrest

Potassium levels greater than 7 mmol/L can cause

muscle weakness, impaired speech, flaccid paralysis, and respiratory arrest

An ECG with flatten T waves, U waves in all leads, and ST depression can be a sign of

hypokalemia

What is the primary function of calcium in the body?

Mitosis, muscle contraction, nerve function, and cofactor for clotting factors

An ECG with tall peaked T waves, prolonged PR interval, depressed P wave amplitude, and widening of QRS complex can be a sign of

hyperkalemia

What is the normal range the total calcium in the blood?

2.4 mmol/L

_____ makes up 40% of total calcium in the blood

protein-bound calcium (albumin)

_______ makes up 60% of total calcium in the blood

ultra filterable calcium

_________ of ultra filterable calcium is ionized

50% (1.15-1.27 mmol/L)

What hormone regulates calcium homeostasis?

Parathyroid hormone (PTH)

How does PTH regulate calcium levels?

increases blood calcium via osteoclasts, renal tubules resorption, vitamin D3 activate to increase small intestine absorption

Acidemia

Increased in ionized (unbound) calcium

Alkalemia

decreased in ionized (unbound) calcium

What are common causes of hypocalcemia?

renal disease (High PTH, BUN, creatinine), hypoparathyroidism (Low PTH), vitamin D deficiency (high PTH)

What are the clinical manifestations of hypocalcemia?

Neurological symptoms like tingling, tetany, mental changes, and cardiovascular issues, bone diseases, and poor wound healing

What are common causes of hypercalcemia?

Hyperparathyroidism( high PTH) and hypercalcemia of malignancy (low PTH)

What is the 2nd most abundant intracellular cation?

magnesium

What is the role of magnesium in the body?

Cofactor for over 300 enzyme systems, essential for transmembrane transport of K+ and Ca++, influences PTH hormone secretion from parathyroid glands, maintain electrical properties of cell membranes

What is the normal range for serum chloride (Cl-)?

98-108 mmol/L

How do kidneys maintain extracellular fluid electrical neutrality?

By exchanging Cl- with HCO3-

What is the relationship between sodium and chloride levels?

Conditions that increase or decrease serum [Na+] will cause the same imbalance in [Cl-], except during metabolic acidosis or alkalosis

A decrease in bicarbonate causes an _______ in chloride and vice versa for an increase in bicarbonate.

increase