Urinary Flashcards
Describe the general location of the kidneys and ureters in the abdominal cavity.
Retroperitoneal
Which kidney is lower in the abdominal cavity and why?
Right. Depressed by the liver.
Which nerve roots do the two kidneys span each?
Left: T11-L3
Right: T12-L3
What are the two types of nephrons? What are their blood supplies like and their relative functions?
Cortical - has peritubular capillaries, primarily reabsorption
Juxtamedullary - has vasa recta, primarily creation of a concentration gradient to control concentration of urine
Relative to fluid in the tubule, which direction do the blood flow in the vasa recta and what is the significance of this?
Countercurrent,
Thick ascending limb is impermeable to water and pumps out Na+, K+ and Cl- ions into the intersticium to establish a concentration gradient. The blood in the vasa recta runs down this, becoming increasingly concentrated as water leaves to enter intersticium.
Thin descending limb contains plenty of water which moves out of the tubule, into the intersticium and the ascending vasa recta which have been concentrated by action of the thick ascending limb.
Urea is recycled in the nephron. Where, how and why?
The cycle is under ADH influence - this only works if aquaporins are present on the apical membrane of cells of the CD.
Urea leaves the collecting duct down its concentration gradient –> intersticium so water follows through aquaporins –> urea enters the vasa recta (more concentrated blood) –> water follows into vasa recta further concentrating the urine.
What does isosmotic reabsorption mean? Where does it happen and what ion is involved?
Reabsorption of solutes from a filtrate in a 1:1 ratio with water which results in no change in the osmolarity of the filtrate.
PCT
Na+
What is reabsorbed in the PCT?
Glucose, amino acids, Na+, Some Cl-
Give an example of a substance with a 100% clearance rate. What renal value can this give you?
Bile salts, inulin
Is equal to GFR value.
PAH (paraaminohippurate) is completely secreted by the kidneys. What can it be used as a direct measure of?
Renal Plasma Flow
Equation to calculate renal plasma flow?
RPF = plasma from haematocrit x renal blood flow
Equation to calculate filtration fraction?
FF = RPF/GFR
Equation to calculate clearance rate?
C = (Concentration of substance in urine x urinary flow rate)/Concentration of substance in plasma
Equation to calculate filtered load?
FL = concentration of substance in plasma x GFR
What is the typical value for GFR?
125 ml.min-1
Name the retroperitoneal organs.
SAD PUCKER
Suprarenal glands
Aorta/IVC
Duodenum
Pancreas Ureters Colon (except transverse which is intraperitoneal) Kidneys oEosophagus Rectum
What two main cell groups are found in the juxtaglomerular appartus?
Macula Densa cells
Juxtaglomerular cells
What do juxtaglomerular cells produce?
Renin in response to a drop in renal perfusion pressure in afferent arteriole of glomerulus (via stretch receptors in vasc walls)
How does renin act on the kidney? hint: RAAS
Activates RAAS –> renin cleaves angiotensinogen to angiotensin I. Angiotensin I enters blood and is carried to the lungs where angiotensin converting enzyme (ACE) cleaves to to form Angiotensin II. Angiotensin II is a vasoconstrictor and increases ADH and aldosterone release.
Concluding effect: indirectly increases blood volume via vasoconstriction, sodium retention and hormone-induced water reabsorption to increase renal perfusion and GFR.
Aldosterone is a part of the RAAS. Where is secreted from and what is its mechanism of action at its target organ?
Secretion from zona glomerulosa of adrenal cortex (mineralocorticoid secreting portion).
Action in the nephron DCT and CD on the principal cells to increase Na+ reabsorption and therefore water.
What ion channels of which cells does aldosterone act on and where are they located?
Action on principal cells of DCT and CD
Ion channels:
3Na+/2K+ antiporter (K+ lost to tubule)
ENaC
NB: it also acts on intercalated cells in cortical CD on the H+/Na+ antiporter (H+ lost)
What is one possible danger of hyperaldosteronism (Conn’s syndrome, adenoma)?
Hypokalaemia –> tachycardia and tachyarrhythmias
Where is the action of Thiazide diuretics? Give an example.
Inhibit Na+ reabsorption at the Distal Convoluted Tubule
Where do carbonic anhydrase inhibitors act? What patient indicator may make them the diuretic of choice?
Proximal Convoluted Tubule. They are potassium preserving and so useful for patients who may be hypokalaemic.
Spironolactone is another potassium sparing antidiuretic. What is its mechanism of action and where?
Site of action is distal convoluted tubule. It inhibits the action of aldosterone which otherwise acts on the Na+/H+ antiporter to conserve Na+
Where do loop diuretics act? Give an example.
Ascending limb of loop of Henle, on the Na+K+2Cl- symporter preventing establishment of a concentration gradient in the medulla for water to flow out into.
Furosemide
Where is the ENaC found and give an example of a diuretic that acts on it.
Distal convoluted tubule.
Amiloride
The macula densa is involved in which sensory renal feedback loop?
Tubuloglomerular autoregulatory feedback loop.
How do cells of the macula densa regulate GFR?
Detect NaCl concentration in ultrafiltrate. Salt enters cells, water follows and causes swelling.
GFR too high: cells swell too much –> cause vasoconstriction of afferent arteriole to reduce GFR
GFR too low: cells do not swell enough –> cause vasodilation of afferent arteriole to increase GFR AND release prostaglandins that act on the juxtaglomerular cells which then secrete renin –> RAAS to restore blood volume.
