Deck 15: B--Fluid and Acid-Base Balance

Question 1

Describe the means by which the body regulates water content.

Answer 1

The body regulates water volume primarily through the regulation of salt balance. Decreasing the amount of water in blood causes a decrease in blood pressure, which then initiates the renin-angiotensin-aldosterone system. Aldosterone causes the kidneys to conserve Na⁺ ions, thus preventing a severe decrease in the blood's osmolarity. Keeping more salt in the blood "attracts" water and this keeps more water in the body and reduces its loss in the urine. In addition, low blood pressure causes the release of vasopressin and this hormone causes the kidneys to conserve water. When the body's water content rises above optimum, less aldosterone and ADH are secreted allowing the kidneys to excrete more Na⁺ and water.

Question 2

Often patients experiencing sympathetically induced hyperventilation are told to breath in a paper bag. Why?

Answer 2

Hyperventilation results in the removal of excess CO₂, which causes the carbonic acid reaction to proceed to the left in an attempt to replace the CO₂ molecules lost to the atmosphere:
CO₂ + H₂O $\rightarrow$ H₂CO₃ $\rightarrow$ H⁺ + HCO₃^-

According to the equation above, the more CO₂ that is lost, the more H⁺ are removed from the solution, and fewer are formed from the reaction of CO₂ and water. This causes the blood to become more basic; this phenomenon is called respiratory alkalosis. Breathing into a paper bag causes the exhaled CO₂ to re-enter the lungs and prevents the chemical reaction above from proceeding too rapidly to the left. The result is maintenance of sufficient numbers of H⁺ in the blood to prevent respiratory alkalosis.

Question 3

Describe how sodium and blood pressure balance are interconnected. Mention the renin-angiotensin-aldosterone system and ANP in your answer.

Answer 3

Blood pressure is directly affected by blood volume; i.e., the higher the volume, the higher the pressure. A decrease in blood volume, as would happen with severe blood loss, causes a drop in blood pressure. The drop in blood pressure initiates the renin-angiotensin-aldosterone system in which the kidneys secrete renin that converts a plasma compound into angiotensin. After some modification, a form of angiotensin causes the release of aldosterone, which then causes the kidneys to conserve sodium. Since sodium contributes significantly to the ECF's osmotic pressure, conserving sodium causes more water to be conserved as water follows Na⁺ ions osmotically. In turn, conserving water raises the blood volume, which raises blood pressure. When blood pressure is too high, the heart secretes ANP, which causes the kidneys to excrete more water. This causes more water to be excreted, which lowers the blood volume, thereby decreasing blood pressure.

Question 4

Use this figure to answer the corresponding questions.
This figure depicts the process

Question 5

Use this figure to answer the corresponding questions.
Identify the number(s) for bicarbonate ions: ____________________.

Question 6

Use this figure to answer the corresponding questions.
In this figure ____________________ is labeled number ____ and is being reabsorbed, while ____________________ labeled number ____ is being secreted.

Question 7

Define chemical buffer system and describe specifically how the body's four chemical buffer systems help maintain homeostasis.

Question 8

Use this figure to answer the corresponding questions.
Which numbers identify substances that can act directly as bases in the body to increase a fluid's pH? ____________________

Question 9

Compare and contrast uncompensated and compensated respiratory acidosis.