Question

a)Mention two mechanisms the human body can use to raise a drop in blood pressure due to a hemorrhage. b) Can the transport through the capillaries in the right foot be affected by an edema? Explain. c) Mention the respiratory and urinary adjustments to acidosis and alkalosis.

Answer 1

a) Following mild acute blood loss as in hemorrhage, the human body compensates for the drop in blood pressure using 2 mechanisms: vasoconstriction, and baroreceptor reflex (atrial reflex).

Vasoconstriction is the narrowing of blood vessels. This reduces the diameter and volume of blood vessels. As pressure and volume of fluids are inversely related, reduction in volume increases the blood pressure to compensate for the hemorrhage.

Baroreceptors are special stretch receptors located in the walls of the right atrium and the venae cavae of the heart. A drop in blood pressure reduces the stretch and decreases the rate of baroreceptor firing. This stimulates the heart and increases cardiac output to compensate for the reduced blood flow that follows as a result of reduced blood volume.

b) Yes, transport through capillaries can be affected by edema. Edema is the result of excessive fluid accumulation within the collagen-mucopolysaccharide matrix present in the interstitial space between cells. The excess fluid build-up and swelling associated with edema negatively impacts the diffusion of oxygen and other nutrients, as well as the removal of toxins from the tissue. Additionally, the pressure exerted by the excess fluid build-up on the capillaries physically compresses capillaries and reduces nutritive tissue perfusion. This way, transport through capillaries is affected by edema.

c) Acidosis and alkalosis can be respiratory or metabolic. Respiratory acidosis occurs when the lungs do not clear the CO₂ produced by the body. Metabolic acidosis occurs when the kidneys are not removing enough acid (H⁺) from the body, resulting in an accumulation of acid in the body fluids. The opposite (hyperventilation, or too much bicarbonate in blood due to kidney disease) causes alkalosis.

During acidosis, when CO₂ and H⁺ accumulate, their dissolution in body fluids produces carbonic acid, whose acidic nature lowers the pH of blood and other body fluids. Lungs respond by hyperventilation, to reduce the partial pressure of CO₂. As CO₂ is cleared, the amount of carbonic acid in the blood falls, increasing the pH and restoring it to around 7.4. The kidneys excrete the excess protons while reabsorbing HCO₃⁻ in response to acidosis.

During alkalosis, CO₂ is very rapidly cleared, reducing the amount of carbonic acid and H⁺ in blood below normal, which increases the pH of blood and other body fluids. In this case, pulmonary compensation through hypoventilation leads to the accumulation of carbonic acid and H⁺, which lowers the pH, bringing it closer to the set point of 7.4. Kidneys (specifically, a subpopulation of intercalated cells (type B) in the cortical collecting tubules) respond to alkalosis by excreting HCO₃⁻ during ultrafiltration while reducing H⁺ secretion.