3 - renal + GI Flashcards
TRUE OR FALSE
the left kidney is higher than the right
TRUE
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
- plasma volume enters afferent arteriole
- 20% volume filtered in glomerulus to bowmans capsule
- 80% enters efferent arteriole and peritubular capillaries
- 99% of filtered volume is reabsorbed into peritubular capillaries
- > 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
ARTERIAL PRESSURE
↑ AP = ↑ P(G) = ↑ GFR
AFFERENT ARTERIOLAR RESISTANCE
↑ AAR = ↓ P(G) = ↓ GFR
↓ AAR = ↑ P(G) = ↑ GFR
EFFERENT ARTERIOLAR RESISTANCE
↑ 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
TUBULOGLOMERULAR FEEDBACK
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
MYOGENIC MECHANISM
– 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
insulin
give an example of a substance that is filtered, completely reabsorbed, but not secreted
glucose
give an example of a substance that is filtered, some reabsorbed and some secreted
electrolytes
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