Renal physiology - kidney structure and function

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  • Created by: Alex
  • Created on: 02-06-13 17:29
Function of Kidney
Maintain water balance, regulate ocnc of ions, maintain plasma volume, excrete waste & foreign compounds, maintain osmolarity, Secrete compounds, convert Vitamin D to active form
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How is urine produced
1. filtration of plasma, 2.reabsorption of plasma 3.secretion directly into filtrate
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How many nephrons in each kidney?
1million
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Two types of nephorn in the kidney
cortical nephron and internal juxtamedullary nephron
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location and % of cortical nephron
85% small glomeruli - mainly in cortex and medulla
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location and % of internal juxtamedullary nephron
15% large glomeruli,long loop of henle extending deep into medulla
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function of bowmans capsule
cups arend glomerulus to collect fluid
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% of water and solutes removed by the blood by glomerular filtration
15-25%
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what does rate of glomerular filtration depend on?
net hydrostatic pressure, colloid pressure of blood plasma and hydraulic permeability of membranes
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osmotic pressure of glomerulus
-30mm Hg
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intracapsular pressure
-15mmHg (lower pressure so things pushed through)
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Layers of the glomerulus
Wall of glomerular capillaries, acellular basement membrane, inner layer of bowman's capsule
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renal clearance rate=
volume of blood plasma completely cleared of a substance per minute
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what is reabsorbed in the kidneys
filtered glucose and 1/2 ureas
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average clearance rate
125ml/min
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way to calculate renal clearance
1. infuse insulin and allow to mix 2.collect blood sample and determine plasma conc 3.determine rate of appearance in urine
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Types of transport
Passive and active
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Passive
no energy expended- down conc gradients
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active
requires energy, against electrochemical gradient - important substances
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what % of energy useage is taken up by sodium reabsorption?
80%
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what % of sodium is reasbsorbed in the PCT
67%
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what % of sodium is reabsorbed in the loop of henle
25%
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what % of sodium is reabsorbed in the DCT
8%
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What is reabsorbed in the PCT
Glucose, amino acids, water, urea and chloride ions
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how much phosphate can be reabsorbed?
up to normal plasma conc and no more - excess excreted
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what % of body weight is water?
60%
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where is water in the body?
2/3 intracellular fluid 1/3 extracellular(plasma and interstitial fluid)
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What is normal fluid balance in the body? - amount of water to substrate
300mm/Litre (isotonic)
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What is the max fluid concentration in urine?
1200 mosm/Litre
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what % of sodium is removed by active transport in the PCT?
75%
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what is the ascending loop of henle thin part permeable to?
Na+ and Cl- ions. low water permeability
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what is the ascending loop of henle thick part permeable to?
very low water permeabiity - Na+ and Cl- now activly transported out
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what is the descending loop of henle permeable to?
no active transport, impermeable to salts, highly permeable to water
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what does the DCT pump and what follows?
Transports K+, H+ and NH3 into lumen. Tranports Na+, Cl- and HCO3- out of lumen. As salts pumped, water follows
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what is the collecting duct permeable to?
water - flows from dilute urine to more concentrate interstitial fluid of renal medulla. reabsorbs NaCl by active transport. high permeability to urea
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Why concentrate and then dilute fluid in loop of henle in a counter current mechanism?
establishes vertical osmotic gradient in medulla to enable collecting tubule/duct to concentrate urine.
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what must exist for water to be reabsorbed?
osmotic gradient and tubule permeable to water
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what needs to be present for the collecting duct/tubule to be permeable to water?
antidiuretic hormone vasopressin
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where is vasopressin produced?
the hypothalamus
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where is vasopressin stored?
posterior pituitary gland
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what stimulates release of vasopressin
water deficiency- low BP, high plasma osmolarity
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how does vasopressin work
1. binds with receptor on basolateral membrane 2.activates cAMP 2nd-messenger system 3.cAMP increases luminal membrane permeability by inserting aquaporin2 water channels in the membrane
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cont
4.water enters tubular cell from tubular lumen through water channels 5. water exits cell through a different water channel (AQP2/3) permanently positioned on basolateral border and goes into the blood
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what triggers thirst and vasopressin release?
hypothalamic osmoreceptors. further input from volume receptors that monitor bp in left atrium of heart
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how much urine is produce a minute when normall hydrates?
1ml/min isotonic urine
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what controls exit of urine from bladder?
internal urethral sphincter(involuntary) and external urethral sphincter (volountary)
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micturition
urination
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what % of filtered Na+ is reabsorbed?
99.5%
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How is Na+ reabsorbed?
actively - Na+ - K+ ATPase carrier located in basolateral membrane of tubular cells. Moves Na+ against conc gradient
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what controls Na+ reabsorption?
the renin-angiotensin-aldosterone system
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renin-angiotensin-aldosterone system- how is controls Na+ reabsorption
1. renin secreted by kidney due to fall in ECF volume/BP 2.renin activates angiotensinogen to angiotensin1 3.Angiotensin1 is converted to angiotensin2 by angiotensin 4.angiotensin2 stimulates aldosterone secretion from adrenal cortex
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cont
5.aldosterone inserts additional Na+ and Na+ - K+ ATPase carries into luminal/basolateral membranes) 6. Increases flux of Na+ ito tubular cells and blood 7.cl- follows passively along electrical gradient
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is any NaCl secreted in presence of full aldosterone secretion?
no
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How much NaCl can be secreted a day in absence of aldosterone
20NaCl
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is potassium reabsorption in PCT regulated?
no
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what % of filtered K+ is excreted in urine?
10-15%
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Control of K+ secretion
Aldosterone - stimulates K+ secretion simultaneous to Na+ absorption Ac-d- normally K+ secreted, when body fluids too acidic, H+ secreted instead
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main factors controlling pH in mammals
excretion of CO2 via lungs and excretion of acid via kidneys
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Acid definition
Hydrogen containing substance that dissociate in solution to liberate free H+ (more free H+ = stronger acid)
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Base
Substance that binds with H+ to remove it from solution
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what generates H+?
carbonic acid (H2CO3) forms from CO2 and H2O and dissociates to give free H+, inorganic acids from food breakdown and organic acids from intermediary metabolism
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How kidneys regulate pH
Can conserve or eliminate HCO3- and H+ by H+ excretion, HCO3- excretion and NH3 excretion
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Card 2

Front

How is urine produced

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1. filtration of plasma, 2.reabsorption of plasma 3.secretion directly into filtrate

Card 3

Front

How many nephrons in each kidney?

Back

Preview of the front of card 3

Card 4

Front

Two types of nephorn in the kidney

Back

Preview of the front of card 4

Card 5

Front

location and % of cortical nephron

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