Ch. 27 – Fluid, Electrolyte, and Acid-Base Balance These notes are a brief overview of the main themes of Ch. 27 only The new information in these notes and in Ch. 27 is FYI only, and will not be fair game for the Final Exam While Ch. 27 repeats a lot of information we have discussed during the past 9 months, it does a nice job of tying these topics together under the umbrella concept of homeostasis

Fluid (water) balance Water gain must = water loss Water ≈ 50-60% of our body weight There are no active transporters for water molecules, just water channels (aquaporins) “Water follows salt” by osmosis Major players in the maintenance of fluid balance: the renin-angiotensin system, ADH, aldosterone, natriuretic peptides, baroreceptors in the heart and blood vessels, and the thirst center in the hypothalamus Fig. 27-3, p. 1003

Electrolyte balance Electrolyte gain must = electrolyte loss Electrolytes = ions released when soluble inorganic compounds dissociate; they can conduct an electrical current in solution So essentially, electrolytes = ions in solution E.g. Na+, K+, Cl-, Ca2+, etc. Electrolytes are lost and gained in most (but not all) of the same ways as water In (gain): diet Out (loss): urine, feces, and sweat

Some important electrolytes in body fluids Fig. 27-2, p. 1001

Acid-base balance H+ production must = H+ loss Normal body fluid pH = 7.35-7.45 Major players in the maintenance of acid-base balance: The kidneys via the reabsorption and/or secretion of H+ and HCO3- Remember, HCO3- = bicarbonate, which acts with carbonic acid (H2CO3) as a buffer system: H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3- The elimination of CO2 via external respiration and exhalation at the lungs Since most of the CO2 in the blood is carried as bicarbonate, exhaling CO2 drives the above equation to the left, ↓ bicarbonate and H+ levels (which ↑ pH) Other buffer systems… See the next slide for examples of buffer systems including and in addition to the carbonic acid-bicarbonate buffer system

Buffer systems in body fluids Fig. 27-10, p. 1014

How an amino acid (and thus a protein) can act as a buffer Fig. 27-11, p. 1014

Acid-base imbalances Table 27-4, p. 1026 Severe acidosis causes ↓ neuron excitability (which can lead to disorientation, coma, and death) Severe alkalosis causes ↑ neuron excitability (which can lead to nervousness, muscle spasm, convulsions, and death)

Respiratory acidosis and alkalosis Respiratory acidosis is the most common type of acid-base imbalance Respiratory alkalosis is relatively rare Fig. 27-15, p. 1021

Metabolic acidosis This is the 2nd most common type of acid-base imbalance E.g. lactic acidosis and ketoacidosis Fig. 27-16, p. 1023

Metabolic alkalosis Is relatively rare The loss of HCl via severe vomiting is the most common cause Fig. 27-17, p. 1024

A diagnostic chart for acid-base disorders Fig. 27-18, p. 1025