Renal Physiology Lecture 3: Integrated Control of Blood Volume & Osmolarity

Question 1

How are blood volume & osmolarity well controlled?

Answer 1

• Both parameters controlled within an optimal range
• Disturbance in fluid & electrolyte levels shift blood volume & osmolarity
• Homeostatic adjustments compensate and correct for the disturbance

Question 2

Blood volume & osmolarity both increased:

Answer 2

• Salt intake exceeds fluid intake
• ECF volume & osmolarity increase
• Hypertonic urine produced

Question 3

Blood volume increased, plasma osmolarity normal:

Answer 3

• Salt & water was ingested simultaneously
• Only volume increases
• Isotonic urine produced

Question 4

Blood volume increased, osmolarity decreased:

Answer 4

• Pure water ingested
• ECF diluted
• Large volume of dilute (hypotonic) urine
• salt appetite may be stimulated

Question 5

Blood volume unchanged, plasma osmolarity increased

Answer 5

• Solute consumed in absence of fluid intake
• Thirst triggered
• Small volume of concentrate durine

Question 6

Blood volume unchanged, plasma osmolarity decreased:

Answer 6

• Dehydration, only ingest pure water
• ECF diluted

Question 7

Reduced blood volume, increased osmolarity:

Answer 7

• i.e. diarrhea, excessive sweating
• more water lost than solute

Question 8

Reduced blood volume, osmolarity unchanged

Answer 8

• i.e.hemorrhage
• Blood transfusion or isotonic saline infusion i.v.

Question 9

Goal in response to dehydration

Answer 9

restore blood pressure, extracellular fluid volume and plasma osmolarity by conserving fluid and preventing losses so we activate rapid cardiovascular reflexes to increase blood pressure and stimulate thirst to increase fluid intake

Question 10

Systems involved in deyhydration

Answer 10

• Cardiovascular mechanisms
• RAAS
• Renal mechanisms
• Hypothalamic mechanisms