This lecture relates to the learning outcomes covered in the lecture on regulation of urine volume and fluid balance. Good luck!
Reviewed by Daniel Mercer
Regulation of urine volume and fluid balance
1a. Which of the following is not a symptom of hypovoleamia?
Dizziness on standing
You are asked to see a patient that was discharged a week ago from your ward. During a quick end of bed inspection you notice that their JVP is raised, have effortful breathing, and appear to have enlarged calves. What do you suspect has occurred?
Due to a physiological abnormality, fluid from the blood vessels has moved into the interstitial fluid , creating an excess fluid in places where it is not normally present. In this case the patient has developed oedema in their calves and potentially in their lungs which can be leading to the shortness of breath.
The patient has a chest infection
The patient has gained weight, the excess fat is pushing on their chest, making is more difficult to breath
They are having a heart attack
Describe the purpose of regulating blood fluid volume
The body needs to change cellular fluid composition regularly
So that cells can maintain and isotonic solution for optimal functioning
So humans don’t carry around excess weight
So that waste can be excreted
Upon examination of a patient with kidney failure, you notice that they appear “puffy”. What could explain this observation?
Due to kidney failure, the patient is unable to excrete excess fluid from the blood and the fluid has thus diffused into their extracellular, giving them a swollen appearance
Due to a system wide inflammatory process, their entire body has become swollen
They have gained weight due to their inability to excrete cholesterol
They have lost the ability to utilise fat, so it is being inappropriately stored
What is the amount of waste solutes that must be excreted by the body daily?
What is the maximum possible concentration of urine?
What is the normal concentration of filtrate?
Given the equation Osmoles excreted/day (osmoles) = urine osmolarity (Osm/L) x urine output (L/day). What is the minimal urine output of a human in a day?
Which of the following is not a cause of polyuria?
Excess salt intake
Excess water intake
Excess fat intake
You are monitoring a patient’s urine output on the ward and notice that they have oliguria, what cannot explain this?
They are not drinking enough fluid
They have decreased renal perfusion
They are dehydrated
They have taken caffeine
Where is most water absorbed in the nephron?
Proximal convoluted tubule
Descending loop of Henle
Distal convoluted tubule
A patient that had previously been treated on the ward has made a GP appointment to investigate her unquenchable thirst and needing to use the toilet more than 10 times per day. What part of the uriniferous tubule is most likely to be affected?
Proximal convoluted tubule
Thick ascending loop of Henle
Thick descending loop of Henle
What are the main contributors to the hyper osmotic interstitium in the kidney that maintains the concentration gradient higher than that of the filtrate, allowing osmosis to occur?
sodium, potassium, chlorine
Sodium, calcium, chlorine
Urea sodium, chlorine
glucose, sodium, potassium
A patient is administered furosemide and you find that the osmolarity of their urine has increased. What are the consequences of this?
Furosemide breaks down into multiple ions in the kidney filtrate, rendering the filtrate more concentrated, thus less water will want to leave the filtrate
There are less ions that can now contribute to the counter current exchange system, leaving the interstitum more diluted.Now less water will thus flow out of the filtrate and diuresis occurs.
The patient will feel thirsty and want to drink more water in order to have enough fluid to excrete the right osmolarity of concentrated urine
Furosemide exerts its effect on the RAAS system and not on the kidney directly
What hormone is used to control the excretion of water in proportion to intake or restriction?
Your patient presents with polyuria and polydipsia. Which of the following is not a differential you would consider?
Where is ADH produced?
Paraventricular nucleus of the hypothalamus
Suprachiasmatic nucleus of the thalamus
Arcuate nucleus of the hypothalamus
Dosal nucleus of the hypothalamus
You are reading the results of a genetic screening and find that your patient has a mutation that codes for aquaporin 1. Which part of the nephron will have reduced water reabsorption capabilities?
Proximal convoluted tubule
Loop of Henle
Early distal convoluted tubule
Which of the following is not a main stimulus for ADH release?
Increased plasma osmolarity
Hypovoleamia or decreased blood pressure
A patient presents to you in clinic with headaches, vomiting, confusion, mood swings, hallucinations. Blood results: hyponatreamia and decreased blood plasma osmolarity. A year ago they underwent surgery to remove their pituitary adenoma. Urinalysis: increased urine sodium. How do you interpret these results?
A mutation in their sodium channels is causing an increased output of sodium
Inappropriate over secretion of ADH
A cranial infection such as Meningitis
A diuretic that is working above its therapeutic range
How would you distinguish cranial vs nephrogenic diabetes insipidus during a fluid deprivation test?
They are indistinguishable
During a fluid deprivation test you would see an increased concentration of urine if it was cranial relative to nephrogenic
During a fluid deprivation test you would see a decreased concentration of urine if it was cranial relative to nephrogenic
During a fluid deprivation test, you would see oedema with nephrogenic diabetes insipidus
What treatment is normally given for diabetes insipidus?