Water Balance Flashcards
Describe the distribution of water in the body
60% body weight is water
40% water is intracellular fluid
20% water is extracellular fluid
Describe the distribution of extracellular fluid
1/4 is plasma
3/4 is interstitial fluid
Why must osmolarity be kept constant?
To maintain cellular specialisation
What is the role of the kidneys in water balance/
To ensure that the water intake and output is equal
What is osmotic clearance?
The volume of plasma that would contain all the combined solutes excreted in urine
How is osmotic clearance calculated?
Urine osmolarity/plasma osmolarity x urine volume
What is free water clearance?
The rate of solute free excretion
How is free water clearance calculated?
Urine volume - osmotic clearance
If urine is isotonic, what is free water clearance?
Zero
If urine is hypotonic, what is free water clearance?
Positive
If urine is hypertonic, what is free water clearance?
Negative
What stimulates ADH secretion?
Increasing osmolarity Decreasing plasma volume Nausea Hypoglycaemia Hypoxia Angiotensin II Stress Pain Temperature Hypercapnia
What inputs regulate thirst?
Osmoreceptors in hypothalamus detect plasma osmolarity
Hypovolaemia
Angiotensin
Oropharyngeal sensory receptors
Describe the role of oropharyngeal sensory receptors
It immediately removes thirst sensations as it takes time to decrease osmolarity
What drinks would heighten the satiety of oropharyngeal sensory receptors?
Cold, carbonated drinks