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the left kidney is higher than the right


left kidney more superior due to the liver on the right side


describe the structure and function of the kidney

RENAL CORTEX = outer layer, site of glomerular filtration and the convoluted tubules

RENAL MEDULLA = inner part, location of the longer loops of Henle, and the drainage of the collecting ducts into the renal pelvis and ureter

RENEL PELVIS = entry point for blood vessels and nerves


what is the individual functional unit of the kidney?

draw a diagram of its structure

individual functional units = “nephrons”

nephron made up of:
– a filtration component (renal corpuscle = the glomerulus and bowmans capsule)
– a complex set of renal tubules, which are further divided into structural and functional regions

glomerulus* → bowmans capsule → proximal tubule → thin descending + ascending limb of Henle → thick ascending limb of Henle → macula densa → distal tubule → connecting tubule → cortical connecting tubule → medullary connecting tubule → collecting duct

GLOMERULUS = filtration unit of nephron:
– tuft of interconnected capillaries (glomerular capillaries)
– a fluid filled capsule (bowmans capsule)


describe the flow through and excretion of urine from the nephron

1. plasma volume enters afferent arteriole
2. 20% volume filtered in glomerulus to bowmans capsule
3. 80% enters efferent arteriole and peritubular capillaries
4. 99% of filtered volume is reabsorbed into peritubular capillaries
5. >99% of plasma entering the kidney returned to systemic circulation, rest is excreted

EXCRETION = filtration - reabsorption + secretion

glomerular filtration:
– the movement of fluid and solutes from the glomerular capillaries into Bowman’s space

tubular reabsorption:
– taking fluids back into body
– movement of materials from the filtrate in the tubules into the peritubular capillaries

tubular secretion:
– removing fluid from body
– movement of solutes from the peritubular capillaries into the tubules


give a detailed description on how fluid is filtered through the glomerular filtration barrier

glomerular filtration barrier consists of 3 layers:
– single-celled endothelial fenestrations
– non-cellular basement membrane
– single-celled epithelial lining of Bowmans capsule (podocytes + slit diaphragm)

fluid forced through the barrier by hydrostatic pressure from cardiac pump

fluid is filtered from the blood through fenestra in the glomerular capillaries into slit pores between the foot processes of the podocytes


what is starlings law?

hydrostatic pressure from the heart FAVOURS filtration

Plasma osmotic pressure and hydrostatic pressure of the filtrate oppose it

increasing protein concentration inside glomerular capillary will oppose filtration


what is GFR and how does it depend on filtration pressure?

glomerular filtration rate (GFR) equals the volume of filtrate formed each minute

GFR is directly proportional to the net filtration pressure


why does GFR need to be kept constant?

GFR must be kept constant as reabsorption of H2O & other substances from filtrate partly dependent on rate of flow through tubules

↑ GFR = inadequate reabsorption = substances lost in urine
↓ GFR = reabsorption increased = wastes not excreted

small changes in GFR equal large changes in the
volume of filtrate that must be processed

10% increase in GFR equals 18L more filtrate to be processed


use a diagram to describe how P(G) / GFR is affected by:
1) arterial pressure
2) afferent arteriolar resistance
3) efferent arteriolar resistance

↑ AP = ↑ P(G) = ↑ GFR

↑ AAR = ↓ P(G) = ↓ GFR
↓ AAR = ↑ P(G) = ↑ GFR

↑ EAR = ↑ P(G) = ↑ GFR
↓ EAR = ↓ P(G) = ↓ GFR


how does GFR effect systemic blood pressure?

increased GFR = decreased urine output = reduced BP (vice versa)


in what MAP range is GFR auto-regulated?

GFR automatically maintained constant when MAP = 80-180mmHg


name the two types of autoregulation?

tubuloglomerular feedback mechanism

myogenic mechanism


describe how the tubuloglomerular feedback mechanism regulates glomerular filtration


as distal tubule passes through parent glomerulus, there are macula densa (MD) cells

MD cells sense NaCl concentration inside tubule
——> NKCC2 cotransporter transports Na, Cl and K into MD cells

increase GFR, increase sodium filtration —> detected by MD

ATP passes through basolateral membrane, converted to AMP —> adenosine

binds A1 receptor on extraglomerular cells —> activates Gi —> inhibits adenylate cyclase
—> also activates Go —> increases intracellular calcium

calcium spreads to surrounding smooth muscle cells via junctions

calcium causes contraction —> afferent arteriole constriction —> reduce GFP

MD sends signal to afferent arteriole to constrict = reduce GFR


describe how the myogenic mechanism regulates glomerular filtration


– increased pressure in afferent arteriole is detected by smooth muscle = stretch = arteriole dilates
– stretching opens stretch-activated ion channels in arteriole membrane
– sodium ions enters cell —> depolarisation
– this opens Ca2+ channels on SR reticulum
– intracellular calcium facilitates muscle contraction —> membrane returns to normal shape

this mechanism helps maintain normal GFR despite fluctuations in BP
constrict afferent arteriole = GFR decrease = less blood is entering glomerulus


give an example of a substance that is not filtered

large proteins


give an example of a substance that is filtered but not reabsorbed or secreted



give an example of a substance that is filtered, completely reabsorbed, but not secreted



give an example of a substance that is filtered, some reabsorbed and some secreted



where is sodium reabsorbed?
(give percentages)

64% in proximal tubules

28% in loop of Henle

7% in distal tubule and collecting duct

1% excreted


where is water reabsorbed?
(give percentages)

67% in proximal tubules

10% in loop of Henle

9% in distal tubule and collecting duct

<1% excreted


what is the transport maximum?

point at which carrier proteins are saturated i.e. no more can be reabsorbed

at transport maximum, solute begins to be excreted


the reabsorption of which particular solute drives reabsorption of other solutes?

sodium reabsorption drives other substances to be reabsorbed


draw a diagram depicting the ion flow across the proximal tubule

1) at the basolateral membrane, Na is pumped into the interstitial space by the Na+-K+ ATPase. active Na+ transport creates concentration gradients that drive:

2) “downhill” Na+ entry at the apical membrane

3) reabsorption of organic nutrients and certain ions by cotransport at the apical membrane

4) reabsorption of water by osmosis through aquaporins. water reabsorption increases the concentration of the solutes that are left behind. these solutes can then be reabsorbed as they move down their gradients:

5) lipid-soluble substances diffuse by the transcellular route.

6) various ions (e.g., Cl−, Ca2+, K+) and urea diffuse by the paracellular route.


draw a diagram depicting the ion flow across the thick ascending loop of henle



draw a diagram depicting the ion flow across the cortisol collecting ducts



how is urine concentration regulated?

describe this process at each point in the nephron

remember: water diffuses from HYPO-osmotic compartment to HYPER-osmotic
i.e. water follows sodium

for example:
1. in the ascending limb, NaCl is actively transported out of the tubule
2. medullary interstitial fluid becomes HYPERosmotic
3. water diffuses out from the descending limb of the Loop of Henle (simple diffusion) into the hyperosmotic medullary ISF

proximal tubules:
– always reabsorb sodium and water in the same proportions

ascending limb:
– Na+ and Cl- are reabsorbed from the tubule into the medullary interstitium
– requires energy = active transport
– impermeable to water
– medullary interstitial fluid becomes hyperosmotic

descending limb:
– highly permeable to water
– dilutes concentrated fluid


which four receptors detect changes in ECF and where are they found?

– hypothalamus
– changes in composition

– zona glomerulosa
– changes in composition

– aortic arch + carotid artery
– changes in volume

– atrium + pulmonary vessels + ventricles
– changes in volume


how does ADH respond to excess water intake?

1) excess water ingested

2) ↓ ECF osmolarity

3) ↓ firing by hypothalamic osmoreceptors

4) ↓ ADH secretion by post. pituitary

5) ↓ plasma ADH

6) collecting ducts ↓ permeability to H2O = ↓ reabsorption

7) ↑ H2O excretion


what is the body's response to dehydration?


2) ↑ ECF osmolarity

3) a) thirst
b) osmoreceptors shrink and the supraoptic and paraventricular nuclei and send neural signal to post. pituitary to ↑ ADH secretion

4) ↑ plasma ADH

5) ADH stimulates V2 receptors in collecting ducts = actvate adenylate cyclase = insertion of aquaporins into luminal membrane= ↑ permeability to H2O = ↑ reabsorption

6) ↓ H2O excretion


what is the action of atrial natriuretic peptide?

atrial natriuretic peptide is a hormone released by the cardiac atria

it is a potent vasodilator which acts on post. tubule to inhibit sodium reabsorption
= regulates sodium balance and blood volume

can also increase GFR – further contributes to increased sodium excretion