Renal Physiology Flashcards
Functions of Kidney?
-Regulation of ECF (blood plasma and interstitial fluid) volume and blood pressure
-Regulation of ECF osmolarity (Osmolarity maintained at 280mOsM
-Maintenance of ion balance
-Regulation of pH (7.4)
-Excretion of wastes
-Production of hormones (EPO)
Anatomy of Kidney?
-Outer layer known as cortex
-Inner section (medulla) composed of 8-15 renal pyramids
-Multiple nephrons in each pyramid deliver urine into renal pelvis which transports it to urinary bladder via ureter
What does the nephron do?
Filters blood which passes as fluid/filtrate into series of tubules
-Tubules reabsorb most of constituents of filtrate back into blood (some substances are secreted from tubules into filtrate)
-Remainder of filtrate forms urine which passes into renal pelvis
What does modulation of rates of reabsorption allow?
Regulation of volume, osmolarity, ion balance and pH of ECF
What are the 2 principal types of the nephron?
1) Cortical nephrons -Glomeruli originate in outer section of cortex - loops of Henle descend into outer medulla
2) Juxtamedullary nephrons
-Glomeruli originate in the inner cortex
-Have long loops of Henle that descend into the inner medulla
-Play central role in production of concentrated urine
How does arterial blood get into kidney?
-Enters via renal artery and is delivered to afferent arterioles at the nephrons via interlobar and arcuate arteries
-Renal artery receives 20-25% of cardiac output
What is the route of bloodflow in the kidneys?
Afferent arteriole - glomerular capillaries - efferent arteriole - peritubular capillaries
What does the glomerular capsule consist of?
A capillary bed (Glomerulus) surrounded by Bowmans capsule
-Capillary bed receives blood from afferent arteriole ans drains into an efferent arteriole
What are the 3 barriers that plasma passes through during glomerular filtration?
- Capillary fenestrations - plasma and dissolved solutes but not blood cells, platelets, large proteins into Bowmans capsule
- Glomerular basement membrane
- Inner layer of Bowmans Capsule
-Consists of podocytes which wrap around capillaries w thousand of cytoplsmic extensions known as foot processes or pedicels
-Slits (slit diaphragms) between adjacent pedicels act as barriers
What can lead to linkage of plasma proteins into filtrate and then into urine?
Damage to slit diaphragms
What is filtration driven and opposed by?
Driven by capillary hydrostatic pressure and opposed by plasma oncotic pressure (starling forces) and Bowmans capsule pressure
What is average GFR for men and women?
-Vol of filtrate produced by both kidneys per minute
Female: 115ml/min
Male: 125ml/min
What is renal clearance?
Volume of plasma completely cleared of substance by kidneys/min
Clearance rate of substance = Urine conc of susbtsnace x urine flow rate (ml/min) / plasma conc of the substance
What is urinary excretion rate?
Glomerular filtration rate + secretion rate - reabsorption rate
Inulin vs Creatinine usage?
Inulin is used in research
Creatinine is used clinically
What does vasoconstriction/dilation of afferent arterioles affect?
Blood flow to glomeruli and affects GFR
-Vasoconstriction - reduction in GFR
-Vasodilation - increase in GFR
Example of Intrinsic Renal Autoregulation regarding MAP and GFR?
-Kidneys maintain a constant GFR despite variations in MAP (mean arterial pressure) between 70-180mmHg
(vasoconstriction/vasodilation result in constant blood flow to glomeruli and no change in GFR)
What is the myogenic response?
-Increase in blood pressure triggers a reflex constriction of afferent arterioles
-Decrease in blood pressure causes a reflex dilation of afferent arterioles
-despite cjanges in MAP, vasoconstriction/vasodilation results in constant blood flow to glomeruli, no change in GFR
Intrinsic Renal Autoregulation - Juxtaglomerular apparatus?
Juxtaglomerular apparatus is located between acending limb of the loop of Henle and afferent arteriole and contains specialized cells called macula densa
-An increase in GFR causes increased filtration of NaCl into the tubules - macula densa detects elevated tubular NaCl conc and releases ATP which triggers constriction of afferent arteriole into glomerulus - reduces GFR
Examples of external regulation of GFR?
-Renal sympathetic nerves release noradrenaline which trigger constriction of afferent arterioles which reduces GFR
-Decreased urine production prevents reduction in blood volume and blood pressure
-Counteracts drop in blood pressure caused by shock or blood loss
What cells reabsorb the filtrate?
Epithelial cells lining the inner wall of the nephron
What ion is the driving force for reabsorption of all other filtrate consitituents?
Na+
-is reabsorbed by active transport
How does Na+ cause reaborption in proximal tubule?
-Cytoplasm of PT epithelial cells has a low Na+ conc due to Na+/K+ ATPase pumps on basolateral membrane
-Creates a conc gradient for movement of Na+ from filtrate in lumen in cells
-Energy released during movement of Na+ down gradient also drives reabsorption of other molecules (glucose, aa), co-transport
-Movement of Na+ creates electrostatic gradient for transport of Cl-
-Movement of Na+ creates osmotic gradient for transport of water
-Cl- and water follow Na+ by passive transport
Where are specific transporters found? (in proximal tubule for reasborption)
-Expressed on microvilli in apical membrane
