Investigation of salt/water and acid/base balance Flashcards
What percentage of body weight is body fluids?
Total body fluids = 60% of body weight
What are obligatory losses of water?
§ Obligatory losses
□ Skin (sweat)
□ Lungs
What are controlled losses of water dependent on?
§ Controlled losses – these depend on:
□ Renal function
□ ADH
□ Gut (main role of colon)
What are the intakes of sodium?
○ Intake
□Dietary (unless vegan and doesn’t add salt)
What are obligatory losses of sodium?
§ Obligatory loss
-Skin
What are controlled losses/excretion of sodium?
§ Controlled losses/excretion
□ Kidneys
□ Aldosterone – fine controlling of Na balance
□ GFR
□ Gut – most sodium is reabsorbed; loss is pathological
Where is aldosterone produced and what does it regulate?
Aldosterone produced in the adrenal cortex: regulates sodium and potassium homeostasis and hydrogen ion balance
What do natriuretic hormones promote and decrease?
○ Natriuretic hormones (ANP cardiac atria, BNP cardiac ventricles) promote sodium excretion and decrease blood pressure
Where is ADH/Vasopressin synthesised in and what does its release cause?
ADH/vasopressin: synthesised in hypothalamus and stored in posterior pituitary. Release causes increase in water absorption in collecting ducts
Where is AQP1(Aquaporin 1) located and not under the control of?
Located on the proximal tube
Where are AQP2 and 3 present and what are they under the control of?
AQP2 and 3 present in collecting duct and under control of ADH
What is the response to increased ECF osmolality due to water loss?
○ Stimulation of vasopressin release causing renal water retention allowing the restoration ECF osmolality
○ Stimulation of hypothalamic thirst centre which leads to increased water intake allowing restoration of ECF osmolality
○ Redistribution of water from ICF which leads to increased ECF water allowing the restoration of ECF osmolality
Where is 85% of Na reabsorbed in renal tubules?
85% Na is reabsorbed in PCT
What is fine tuning of Na reabsorption under the influence of?
Fine tuning of Na reabsorption under influence of aldosterone in exchange for hydrogen and potassium ions
What does the kidney sense and so what signal does it send and cause the release of what?
• Kidney senses reduced perfusion so sends signal from adrenal cortex to release renin
What does renin convert angiotensin into and what does it cause?
• Renin converts angiotensinogen to angiotensin I in lungs
○ This goes back to adrenal cortex to stimulate aldosterone from adrenal cortex
○ Signal to start reabsorbing more Na
What converts angiotensin I into angiotensin II?
• Angiotensin I is converted to Angiotensin II by ACE
What does dehydration mean?
Dehydration means less water perfusing the kidney
How is there a difference in handling of urea and creatinine in dehydration?
○ Creatinine is excreted
○ Urea, if perfusion rate drops, starts being reabsorbed in kidney
- Mismatch between urea and creatinine
What would happen to the Na, urea and creatinine levels in psychogenic polydipsia?
They would be low
BP in psychogenic polydipsia
Normal
Why is there low urine sodium in psychogenic polydipsia?
Low urine sodium because too much water so kidney needs to reabsorb all sodium to match the water intake
What happens if you drop your Na really quickly?
• If you drop your Na really quickly, can get violent and aggressive
What history do you take when assessing patients with fluid/electrolyte disturbance?
○ Fluid intake/output
○ Vomiting/diarrhoea
○ Past history
○ Medication
-Drugs that may predispose them to imbalances in Na
