L24 Physiology of the Kidney Flashcards
What is GFR?
- Glomerular Filtration Rate - gold standard for measuring kidney function. Normal is 100-120 mls/min/1.73m2 . This is measured using an injection of a radioactive tracer. It is used on live kidney donors to make sure the donor has enough kidney function for themselves and the donor.
What is creatinine clearance?
- Creatine clearance - it is an estimate of glomerular filtration rate. Creatine is released from muscle at a relatively constant rate. Creatine that you generate is dependent on your muscle mass. Therefore you must look at the patient when using creatine clearance. Creatinine is filtrated easily by kidneys. Creatinine is filtered by the kidneys into the tubule but the tubule level secretes creatinine into the tubule. If the tubule is not functioning well, the creatine level will increases also. Creatinine does not correlate completely with glomerular filtration rate as some is filtered as well secreted. Can use a blood test or 24-hour urine collection (not very accurate and rarely used).
What is the purpose of measuring serum creatinine?
Assessing kidney function by assessing whether the kidney is filtering it. Creatinine accumulates if kidney disease but it is not specific for site of injury. It is a delayed in rise following acute kidney injury. For chronic injury, it happens over months to years.
What is eGFR?
Used instead of creatinine clearance alongside creatinine. Calculated using the age of the patient, sex, ethnicity and serum creatinine you can estimate the glomerular filtration rate and so you can give an estimate of kidney function. eGFR is also used to categorise chronic kidney disease (and the amount of protein released). Patients will need to commence dialysis around 7-8 mls/min/1.73m2.
What is the relationship between creatinine and eGFR?
As creatinine rises, creatinine clearance decreases. When creatinine goes above the normal value, you have lost around 50% of the function.
What is the function of the proximal convoluted tubule?
The proximal convoluted tubule • recovers 70% of glomerular filtrate • Water – (aquaporins = water channels) • Electrolytes • Glucose • Amino acids recovery and generation of bicarbonate - function of acid base balance. Acidaemia can occur as a result of the proximal convoluted tubule being damaged or issues with filtering of the glomerular due to chronic injury or acute damage.
Bicarbonate in the tubule binds to hydrogen and carbonic anhydrase in the apical part of the tubule cell breaks this down to carbon dioxide and water. The carbon dioxide moves across into the cell leading to the regeneration of bicarbonate which can enter the blood.
What is the function of the ascending loop of Henle?
Ascending loop of Henle Uptake of • Na+ • K+ • 2Cl- - to maintain electro-neutrality H20
There is a sodium, potassium, 2 chloride cotransporter which takes up the electrolytes and water follows also.
What is the function of the medullary collecting duct?
Site of urinary concentration Antidiuretic hormone (ADH) works here acts to↑ water reabsorption. It does this by plugging in aquaporins into the membrane. Mechanisms are triggered that ADH goes up in dry conditions to conserve water. It also acts on urea and sodium reabsorption.
What is the function of the cortical collecting duct?
Site of reabsorption of Na+ (with H2O, Cl) in exchange for K+
Controlled by aldosterone
What is the normal value for urine osmolarity?
Plasma osmolality maintained at 285 mOsm/L
What is the counter-current mechanism?
The kidneys concentrate urine during periods of decreased fluid intake they conserve salt and water to maintain circulating volume and blood pressure. The mechanism responsible is referred to as: counter current mechanism. It establishes a high concentration gradient in the medulla. When the ADH works, by a process of concentration gradient, the water moves across as it is very concentration down the medulla. This enables reabsorption of water from the filtrate
○ Proximal tubule
○Collecting duct
