Cholera

Question 1

What is meant by tonicity

Answer 1

Tonicity refers to the ability of a solution to cause water movement across a semipermeable membrane due to differences in solute concentration. It is determined by the concentration of non-permeable solutes in the solution. Tonicity influences the direction of water flow, which will move to balance the osmolarity across a cell membrane, potentially causing cells to shrink, swell, or remain the same size

Question 2

Name the type of dehydration caused by cholera. (1 mark)

Briefly outline the changes that occur in volume and osmolality in the main fluid compartments with this type of dehydration

Answer 2

In isotonic dehydration, such as that caused by vomiting or diarrhea, there is an equal loss of sodium and water. This results in a decrease in the volume of the extracellular fluid (ECF) compartment, as both water and sodium are lost from this space. Because the loss is isotonic, the osmolarity of the ECF does not change.

Consequently, there is no osmotic gradient to drive water movement between the intracellular fluid (ICF) and ECF compartments, so the volume of the ICF remains unchanged. Overall, the main effect is a reduction in the volume of the ECF without any change in osmolarity across the fluid compartments

Question 3

What way does h20 move in hypo, iso and hypertonic dehydration

Answer 3

hypotonic dehydration
- electrolyte loss from ECF > water loss
- water moves from ECF -> ICF

Hypertonic dehydration
- Water loss from ECF > electrolyte loss
- water moves from ICF -> ECF

Question 4

Outline how kidneys respond to low blood pressure

Answer 4

Low blood pressure/loss of fluid results in reduced stretching of the afferent arteriole of the kidney -> Juxtaglomerular cells secrete Renin into blood.

Angiotensinogen released from liver converts Renin to Angiotensin 1.

Angiotensin Converting Enzyme (lungs) converts Angiotensin 1 to 2.

Angiotensin II has the following effects:

(i) Increases sodium resorption in the tubules (PCT mostly) by increasing activity of Na+/H+ ATPase.

(ii) Stimulates the release of aldosterone from the zona glomerulosa of adrenal cortex -> further increases sodium resorption + H+ secretion.

(iii) stimulates the release of ADH from posterior pituitary - inserts aquaporins into collecting tubules.

(iv) Increases blood pressure by binding to angiotensin II receptors on blood vessels -> vasoconstriction.

(v) vasoconstricts the renal arterioles which encourages more sodium/water resorption.