Renal Flashcards
What is the function of the kidneys?
Excrete metabolic waste, foreign chemicals Secrete and metabolise hormones Regulate pH Control blood pressure Gluconeogenesis Regulate water and electrolyte excretion
What waste products are excreted by the kidneys?
Urea
Creatinine
Bilirubin
Hydrogen
What hormones are secreted by the kidney?
Erythropoetin
Renin
Why is erythropoetin secreted by the kidneys?
In response to low blood O2 in the kidneys, to increase erythrocyte production
What ions do the kidneys regulate?
Sodium Chloride Potassium Hydrogen Calcium Phosphate Magnesium
What are the nephrons function?
Filtration
Reabsorption
Secretion
Excretion
What determines capacity for filtration?
The size and charge of the barrier
Name 4 reasons why proteinuria is clinically significant
Hypertension
Diabetes
Pre-eclampsia
As an annual check-up
What can cause microalbuminuria?
Early diabetes
Hypertension
Glomerular hyperfiltration
What is microalbuminuria?
Urine excretion of 30-150mg albumin per day
What 3 factors determine glomerular filtration rate?
+ Glomerular hydrostatic pressure
- Glomerular colloid osmotic pressure
- Bowman’s capsule pressure
What is hydronephrosis?
Dilation of the renal pelvis caused by urinary retention due to the obstruction of the free flow of urine
What factors affect the glomerular capillary hydrostatic pressure?
Constriction of afferent and efferent arterioles
How much of the cardiac output is directed to the kidneys?
22%
Why is so much oxygen and nutrients directed to the kidneys?
It is used for renal tubular sodium reabsorption
What are the key regulators of GFR?
Sympathetic nervous system
Hormones
Autocoids
How does the sympathetic nervous system control GFR?
Innervation of vasculature
Noradrenaline
What is EDNO and what does it do?
Endothelial-Derived Nitric Oxide
Protects against excessive vasoconstriction
What is the role of prostaglandins in the kidneys?
Increased glomerular filtration rate
What is the myogenic mechanism?
Autoregulation of GFR and renal blood flow
The response to increased arterial pressure
> stretch of blood vessels
> increased Ca++ entry and intracellular Ca++
> increased vascular resistance
» increased blood flow and GFR
What is the macula densa?
A collection of cells in the wall of the distal convoluted tubule.
Sensitive to sodium chloride concentration, increasing renin release and decreasing the blood flow in the afferent arteriole to decrease the GFR etc.
What are the 2 reabsorption (transport) pathways?
Paracellular
Transcellular
Outline the primary active transport of Na+ in the proximal tubule
- Active transport via the Na+/K+ pump across the basolateral surface
- Establish concentration and electrochemical gradient for Na+
- Na+ transport into the epithelial cell from the lumenal surface
Outline the 2 secondary active transport mechanisms
Co-transport of glucose and amino acids with Na+ ions driven by electrochemical gradient
Counter-transport driving a movement of a 2nd substrate in the opposite direction
Why can creatinine be used as diagnostic tools for assessing kidney function?
All creatinine should be excreted
What is transported in the proximal tubule?
Out: Na+, Cl+, HCO3-, K+, H2O, glucose, amino acids
In: H+, organic acids, bases
What are the transport characteristics of the thin and thick loops of Henle?
Both ascending limbs impermeable to water
Thin descending limb permeable to water.
How is tubular reabsorption regulated?
Hormones - aldosterone, angiotensin, ADH Sympathetic nervous system Arterial pressure Glomerulotubular balance Peritubular physical forces Osmotic factors
How does aldosterone regulate tubular absorption?
Acts in the collecting tubule and duct:
Increase NaCl and H2O reabsorption, and K and H secretion
How does angiotensin II regulate tubular reabsorption?
Acts in the proximal and distal tubules, collecting tubule
Increase NaCl reabsorption, and H secretion
How does ADH regulate tubular reabsorption?
Acts in the distal tubule onwards
Increases H2O reabsorption
What is hydronephrosis?
When there is a blockage in the kidneys/ureters, so urine builds up, changing the pressure in the glomeruli.
What is polyuria?
When too much urine is being passed
What is glucosuria?
When glucose is found in the urine
What is the macula densa sensitive to?
Concentrations of NaCl in the distal convoluted tubule
Where is the macula densa?
In the wall of the thick ascending arm of the loop of Henle, at the transition to the distal convoluted tubule
Where is renin secreted?
By the kidneys
Name the systems/organs responsible for fluid output
Kidneys Lungs Feces Sweat Skin
Outline the response to low oxygen levels received by the kidneys
Stimulated to release erythropoietin
Increased erythrocyte production
Increased oxygen delivered to kidneys
Outline the blood supply to the kidneys
Aorta > renal arteries > segmental arteries > interlobar arteries > arcuate arteries > interlobular arteries > glomerulus > intertubular capillaries
What (approximate) percentage of the cardiac output is taken by the kidneys?
22%
What is the role of juxtaglomerular cells?
Secrete renin in response to a drop in blood pressure; stimulated by the macula densa cells
