POTASSIUM (K+)

Dominant Intracellular Electrolyte Normal level of plasma in

extracellular fluids is 3.5-5.1 mEq/l

Potassium Function

Potassium is responsible for control intracellular fluid osmolarity

Maintaining resting membrane potential, nerve impulse and muscle contraction

Play role in acid/base balance

Potassium

K is filtered through glomerulus K is reabsorbed to plasma at

proximal convoluted tubule (PCT) and the loop of Henle

Aldosterone reabsorb Na in the plasma and secret K in the distal convoluted tubule (DCT)

Mostly K excreted in the urine

Hypokalemia: A below level of K in the extracellular fluids of less than 3.5 mEq/l, may cause skeletal muscle weakness, respiratory arrest

Hyperkalemia A high level of K in the extracellular fluid of more than 5.1 mEq/l may cause diarrhea, restlessness, muscle weakness

Calcium

Total Ca level in the plasma 9 – 11 mEq/l

Hypercalcemia: Excess of Ca in the extracellular fluid fatigue, confusion, coma,

Hypocalcemia: A low concentration of Ca in the extracellular fluids of less than 9 mEq/l muscle spasm occur

Effect of calcitonin

When Ca concentration too high. Thyroid gland releases calcitonin in the blood

Calcitonin stimulate osteoblast which caused bone formation

Calcitonin reduces Ca concentration

Effect of parathyroid hormone

When Ca concentration too low parathyroid gland releases parathyroid hormone

PTH increases the activity of osteoclast which increases the Ca concentration in the plasma

Parathyroid hormone increase the uptake of Ca from the filtrate in the kidney into the plasma

Acid/Base Balance

Homeostasis of hydrogen ion content Body fluids are classified as either acids or

bases depending on H ion concentration Acid is an H donor and elevates the

hydrogen ion content of the solution to which it is added

Base is an H acceptor and can bind hydrogen ions

Measure the acidity and alkalinity of a solution in units of pH, which is the measurement of free H ion in solution

Normal pH of blood is 7.35-7.45 (alkaline)

Acids

During the process of cellular metabolism acids are continually being formed and excess hydrogen ions must be eliminated

There are two types of acids formed: volatile acids are excreted by the lungs and nonvolatile acids are excreted by the kidney

Volatile acids can be excreted from the body as gas. Carbonic acid produced by the hydration of carbon dioxide is a volatile acid

Normally carbon dioxide is excreted by the lungs as fast as metabolism produces it, so carbonic acid is not allowed to accumulate and alter pH

Some electrolyte found in the plasma:

Basis: HCO3, HPO4, SO4 Acid: H2CO3, H2PO4

Regulation of pH

Three methods control pH 1. chemical buffers-when Hydrogen is

removed a buffer replaces it 2. regulation of carbon dioxide by

respiratory system 3. regulation of plasma bicarbonate

concentration by the kidneys-slower, second line of defense

Chemical buffers

These are the first line of defense against changes in pH

Act within a fraction of a second for immediate defense against H+ shift

Buffers are composed of weak acid and weak base pairs

Convert strong acids into weak acids and strong bases into weak bases

Chemical Buffer System

H2CO3/HCO3 buffer system H2PO4/HPO4 buffer system Proteins buffer

Chemical Buffers

Carbonic acid-bicarbonate system is most important extracellular buffer because it can be regulated by both lungs and kidneys

Carbonic acid/bicarbonate ratio is usually 1:20

Phosphates act as a buffer like the bicarbonate system does and protein buffers are the most abundant buffers in body cells and blood

Regulation of pH through respiratory system Decreases respiration rate causes 1. Increase CO2 in the plasma2. Less CO2 is exhaled3. Results in hypoventilation4. Accumulate CO2 results in increase

H2CO3 and H concentration 5. pH decreases

Renal control of pH

If acid increases kidney regulate pH by:1. Re-absorption of bicarbonate in proximal

convoluted tubule2. Generate bicarbonate in the renal tubule

3. Secreting H ions. In urine, hydrogen ion is buffered by phosphate and ammonia

If the pH is high, bicarbonate is not re-absorbed in the renal tubule and eliminated

pH decreases