W17 64 renal physiology and chronic kidney disease Flashcards
How much of cardiac output do the kidneys receive?
25%
What is blood supply of a nephron?
From an afferent arteriole that opens onto the glomerular capillary bed
To an effect arteriole, supplying the peritubular capillaries and medullary vasa recta
What are the 2 main roles of kidneys?
Homeostasis
Metabolic/endocrine function
What homeostasis do the kidneys maintain?
Elimination of waste
Water homeostasis
Electrolyte homeostasis
Acid base homeostasis
Blood pressure control
How are kidneys affected by blood pressure?
Kidneys auto regulate their own blood flow when systolic BP is between 80-180.
In extreme hypotension or hypertension, this can lead to acute kidney injury and subsequently chronic kidney disease.
As part of the metabolic/endocrine function of kidneys, they synthesise hormones and excrete drugs and drug metabolites. What hormones do the kidneys synthesis?
Vitamin D
Erythropoietin
Renin
What does vitamin D do?
Promotes intestinal absorption of calcium and renal reabsorption of phosphate
When is erythropoietin release and what does it do?
Release in response to hypoxia
Stimulates the production of RBCs in bone marrow
What does renin do?
Regulates the angiotensin and aldosterone levels to control blood pressur
Pg610 don’t really get watch a YouTube vid. How ions are transported through the nephrons!
Read it and watch a YouTube vid pls. Need to understand.
What should the arterial blood pH be?
7.35-7.45
Hydrogen ion concentration in blood is maintained within narrow limits
What is the formula for the maintenance of acid-base balance in the blood?
H+ + HCO3- <-> H2CO3 <-> CO2 + H2O
The kidneys and lungs maintain acid-base homeostasis. What is the role of the kidneys?
Reabsorb and regenerate bicarbonate from urine
Excrete hydrogen ions and fixed acids (anions of acids) into urine
What is the RAAS system? SEE IMAGE PG611!
Angiotensinogen produced by the liver —> turned into angiotensin I (promoted by renin) —> ACE converts this to angiotensin II —> angiotensin II promotes alosterone secretion from kidneys
What does renin do?
Hydrolysed angiotensinogen to produce angiotensin I
What blood pressure effects do angiotensin II and aldosterone have?
Both increase the kidneys absorption of sodium chloride, thereby expanding the extracellular fluid compartment and raising blood pressure.
How does renin increase or decrease blood pressure?
When renin levels are raised, concentrations of angiotensin II and aldosterone increase, leading to increased sodium chloride reabsorption, expansion of the extracellular fluid compartment, and an increase in blood pressure
Conversely when renin levels are reduced, angiotensin II and aldosterone levels decrease, contracting the extracellular fluid compartment, and decreasing blood pressure.
What factors increase renin secretion?
Low blood pressure (causing reduced renal perfusion), low sodium level, synthetic nerve stimulation
What drugs affect renin secretion and lower blood pressure?
Beta blockers and NSAIDs (eg ibuprofen)
When is erythropoietin released?
In response to hypoxia in the renal circulation
Eg in anaemia, pt have a low RBC concentration, so have a low oxygen carrying capacity in the blood so tissues become hypoxic
What does erythropoietin do?
Stimulates erythropoiesis (production of RBCs) in the bone marrow, to help return the pt back to normal RBC concentration
What is measured in urea and electrolytes test (U&E)?
Sodium, potassium, urea, creatinine, eGFR
What is glomerular filtration rate (GFR) and how is it measured in practice?
Glomerular filtration rate (GFR) = (urine concentration (mmol/L) x urine volume) / plasma concentration (mmol/L)
Total volume of plasma per unit time leaving the capillaries and entering the Bowman’s capsule. In clinical practice creatinine is used because it is subjected to very little proximal tubular secretion.
What is estimated glomerular filtration rate (eGFR)?
Calculated from creatinine, age, gender, ethnicity
Good measure in stable renal function (but can be affected by the extremes of body mass)
What is renal clearance?
Renal clearance is the volume plasma from which a substance is removed per minute by the kidneys.
What is measured in drug clearance?
Glomerular filtration
Tubular secretion
Passive reabsorption
Urine excretion