Fluid,Electrolyte, and Acid - Base Homeostasis

Question 1

Where is body fluid found?

Answer 1

Intracellular body fluid (ICF) - found within the cells, the boundary for the fluid is the plasma membrane of the cells. 2/3 of the body fluid is found in IFC. (40% of body weight) Extracellular body fluid (ECF) - found outside the cells, the compartments could be blood vessels, cavity or space in between tissues (interstitial fluids). ECF comprises 1/3 of the body fluids. (20% of the body weight. 80% of ECF is interstitial fluid, 20% is plasma. Smaller contributors are lymph, CSF, and serous fluids.
Body fluids varies with age and gender: Newborns - 75 -80% body fluid. Women - 50 - 55% (more soid in the form of adipose). Men - 55 - 60% Overall, the % of body fluids decrease with age.

Question 2

Fluid balance -

Answer 2

Normal fluid loss = fluid gain
Fluid gains: Ingested liquids, fluid in solid foods, metabolic water produced in condensation reactions.
Fluid losses: Lungs - in expired air (insensible loss) Skin - via diffusion (insensible loss) Skin - sweating , Kidneys - urination, GI tract - in feces.

Question 3

Regulation of fluid gain -

Answer 3

Fluid intake is determined by habit, sociological factors and thirst. When fluid loss is greater > than fluid gain dehydration results. Dehydration increases thirst in three ways: 1. Decrease in saliva production - stimulates the thirst center in the hypothalamus. 2. Increase in blood osmolarity - stimulates thirst center in the hypothalamus. 3.decrease in blood pressure - stimulates the thirst center in the hypothalamus via renin - angiotensin pathway.

Thirst is decreased after we drink by moisturizing the mouth, stretching in the GI tract from water, and decreasing the osmolarity.

Regulation of Fluid and Solute Loss - Regulated primarily by renal factors already discussed: RAA ( renin - angiotensin - aldosterone) pathway. ADH - antidiuretic hormone. ANP - atrial natriuretic peptide, works in opposition to ADH.

Question 4

Movement of Body Fluids -

Answer 4

Exchange between plasma and the interstitial fluid: Vesicular transport, diffusion, Bulk flow (filtration and absorption)
Exchange between interstitial fluid and intracellular fluid: Normally, the fluid exchange is at equilibrium so that cells neither shrink nor swell. Movement of water is by osmosis (water chases salt) Ions are mostly moved by primary and secondary active transport.

Question 5

Functions of Electrolytes -

Answer 5

electrolyte - a solute that dissociates in water to form charged ions that carry an electrical current. An electrical charge is important to nerve impulse conduction, muscle contraction, and release of neurotransmitters. Also, helps maintain acid/based balance. It acts as a cofactor for enzyme activity and influence the movement of water.

Question 6

Electrolyte differences in the fluid compartments -

Answer 6

Intracellular fluid : potassium is the most abundant cation, hydrogen phosphate is the most abundant anion and protein anions are the 2nd most abundant anions. Plasma: sodium is the most abundant cation, chloride is the most abundant anion, bicarbonate and protein anions are 2nd and 3rd most abundant anions respectively.
Interstitial fluid - sodium is the most abundant cation, chloride is the most abundant anion, bicarbonate ion and organic acids (not on table) are the 2nd and 3rd most abundant anion respectively. Very few proteins are found in the interstitial fluid.

Question 7

Sodium - functions-regulation

Answer 7

1. provides fluid and electrolyte balance. 2. flow depolarizes cell to generate a potential. Regulation: Aldosterone increases sodium reabsorption in the late DCT and collecting duct. * in the absence of ADH, water loss is maximized. Loss of water maintains sodium concentration in the blood. ANP increases the excretion of sodium and water.

Question 8

Chloride - functions - regulation

Answer 8

Function - Maintains the balance of negative charge in the compartment. Regulation: Indirectly via aldosterone, by increasing the reabsorption of sodium, the reabsorption of chloride is also increased because the negatively charged chloride is attached to the positively charged sodium.

Question 9

Potassium - function - regulation

Answer 9

Functions: 1. establishes the resting membrane potential 2. assist in acid-base balance by exchanging with H+. Regulation: High potassium in the blood stimulates the release of aldosterone which increases potassium secreation so an increases in potassium in the blood results in an increase in secretion of potassium.

Question 10

Bicarbonate - function - regulation

Answer 10

Function: maintain acid/base balance by combining with H+ (buffers). Regulation: There will be a high rate of reabsorption of bicarbonate via simple diffusion but bicarbonate can be excreted if the concentration is too high.

Question 11

Calcium - function - regulation

Answer 11

Functions: Contributes to hardness of teeth and bones, blood clotting, triggers neurotransmitter release, contributes to muscle contraction. Regulation: Parathyroid hormone (PTH) low calcium in the blood stimulates osteoclast activity to increase levels of calcium in the plasma. PTH also activates vitamin D to form calcitriol. Calcitriol - increases the adsorption of calcium in the GI tract and reabsorption in the renal tubule. Calcitonin released by the thyroid gland inhibits osteoclast activity and decreases plasma calcium levels( minor effects)

Question 12

Phosphate - function - regulation

Answer 12

Functions: Calcified salt in bones and teeth, important buffer (hydrogen phosphate mostly), found as a part of necleic acids, ATP, lipids, carbohydrates and proteins. Regulation: PTH releases HPO42- from bone into blood. Calcitriol increases absorption of phosphate as well as calcium but inhibits reabsorption of phosphate inthe renal tubule.

Question 13

Magnesium - function - regulation

Answer 13

Function : Key cofactor for enzyme function. Important to neuromuscular activity and cardiac function. Regulation : Increased secreation of magnesium if extrcellular fluid or magnesium level is high. PTH inhibits magnesium reabsorption.

Question 14

Acid - Base Balance -

Answer 14

ECF is maintained tightly at 7.35 to 7.45 in health. Plasma proteins work best at pH 7.4. Control mechanisms to remove H+ : Buffer systems that act within seconds but have a limit to their buffering capacity. Exhalation of carbon dioxide - altering the rate of respiration, effects seen in minutes. Renal mechanisms - in the kidneys, may take hours to days to excrete enough H+.
Buffer- a substance that accepts hydroxyl (combining with OH-) or releases H+ to prevent the pH of a solution from changing dramatically when acid or base is added.
Protein buffer systems - amino terminus, carboxy terminus and the side chains of amino acids can act as buffers by accepting or releasing H+. Carbonic Acid - Bicarbonate buffer system - bicarbonate ion acts as a weak base and carbonic acid acts as a weak acid. Phosphate Buffer system - dihydrogen phosphate can act as a weak acid and monohydrogen phosphate can act as a weak base.

Question 15

Exhalation of Carbon Dioxide -

Answer 15

When we exhale carbon dioxide, we decrease the acid potential of the blood. Because carbonc acid is a volatile acid. Remember the equation and what happens when the equilibrium shifts.
Hyperventilation - more carbon dioxide is released, this decreases the H+ and therefore increases the pH (respiratory alkalosis). Hypoventilation - less carbon dioxide is released, this increases the H+ and therefore decreases the pH (respiratory acidosis).
Acid - Base Imbalances :
acidosis - blood pH below 7.35 or alkalosis - blood pH above 7.45.

Question 16

Acid - Base Imbalances -

Answer 16

Acidosis - blood pH below 7.35 , Alkalosis - blood pH above 7.45. The body has mechanisms for compensation but compensation does not correct the underlying problem. The Characteristics are in the uncompensated condition.
Respiratory acidosis - less carbon dioxide is exhaled could be due to air way obstruction, inhibition of gas exchange as in emphysems, or injury to medulla. Characteristics- the partial prssure of carbon dioxide in the blood would be greater than 45 mm Hg , pH less than 7.35. Compensation - compensation occurs in the renal tubule in the renal tubule and collecting duct by increasing reabsorption of bicarbonate ion (buffer) and increasing secreation of H+( via intercalated cells).

Respiratory alkalosis -more carbon dioxide is exhaled than normal. This could be due to high altitude, stroke or severe anxiety. Characteristics - partial pressure of carbon dioxide in the blood is less than 35 mm Hg, the pH is greater than 7.45. Compensation - occurs in the renal tubule by increasing the secretion (and excretion) of bicarbonate ion and increasing the reabsorption of H+ ( via intercalated cells).

Metabolic acidosis - excess acid production could be due to diabetic ketoacidosis, loss of bicarbonate due to diarrhea, kidney disease. Characteristics - less 22mEq/liter of bicarbonate, pH is less than 7.35. Compensation - hyperventilation (increase in breathing rate), restores the pH but the bicarbonate is still low.

Metabolic alkalosis - could be due to the loss of acid or gain of base, loss of acid from vomiting and gain of base from to much ingestion. Characteristics - greater than 26 mEq/liter of bicarbonate, pH is greater than 7.45. Compensation - hypoventilation (decrease in breathing rate), the pH is restored but bicarbonate is still high.