Renal system Flashcards
what are the conditions in the internal environment controlled by the kidneys
concentration of waste products
concentration of ions
pH
volume and pressure
what are the functions of the renal system
regulates water homeostasis
regulates ECF volume
regulates concentration of most ECF ions
excretes waste products
regulates pH by adjusting urinary acid excretion
produces and activates hormones
how does the kidney react to hypoxia conditions
as blood carries RBC to kidneys, low O2 levels detected by Hif-alpha subunit > combines with Tif-beta to form hypoxia response element > produce erythropoietin > stimulate RBC production in bone marrow > increase O2 carrying capacity
structure of aquaporin 1
6 transmembrane domains
exists as tetramer with each subunit having its own water pore
what are the defence mechanisms against changes in ECF [H+]
buffer system: reversible reaction between HCO3- and H+
respiratory control: controlling concentration of CO2 in the blood > in turn control [H+]
renal control: regulate pH by excreting excess H+ and reabsorbing bicarbonate ions
how to find plasma clearance rate of a substance
(urine conc of a substance x urine flow rate) / plasma conc of a substance
commonly used substances for plasma clearance test
inulin, creatine, para-aminohippuric acid
causes of kidney failure
high blood pressure and diabetes
infection, toxic substances, autoimmune response
urinary tract obstruction
types of kidney failure
acute: rapid loss of renal function, condition may be reversible
chronic: progression in disease of kidneys; gradual loss in renal function; condition is not reversible
major consequences of renal failure
uremia: accumulation of waste products
salt and water retention
metabolic acidosis
anemia
endocrine disorder
disorder of mineral metabolism
difference between cortical and juxtamedullary nephrons
glomeruli of cortical lie in outer layer of cortex, while that of juxtamedullary lie on inner layer
loop of henle of cortical dip slightly into medulla while that of juxtamedullary plunges entirely through medulla
peritubular capillaries of juxtamedullary forms vasa recta, but not for cortical
what are the 3 basic renal processes
glomerular filtration > tubular reabsorption > tubular secretion
what is the pathway of substances to be filtered
pores between and fenestrations within endolethial cells of glomerular capillary > acellular basement membrane > filtration slits between the foot processes of podocytes in inner layer of Bowman’s capsule
what are the forces involved in glomerular filtration
glomerular capillary blood pressure (55): pressure exerted by blood within glomerular capillaries
plasma-colloid osmotic pressure (30): since plasma proteins cannot be filtered > conc of H2O in bowman’s capsule greater than glomerular capillaries > osmosis down concentration gradient > opposes filtration
bowman’s capsule hydrostatic pressure (15): pressure exerted by fluid in bowman’s capsule against glomerular capillaries
what are the mechanisms regulating GFR
auto regulation: prevent spontaneous changes in GFR
extrinsic sympathetic control: aimed at long term regulation of arterial blood pressure
mechanisms responsible for autoregulation of GFR
kidneys can maintain constant blood flow into glomerular capillaries despite changes in driving arterial pressure by altering arteriolar caliber > adjust resistance
if GFR increase as direct result of increase in arterial pressure, net filtration pressure and GFR can be decreased by constriction of afferent arteriole
mechanisms contributing to auto regulation of GFR
myogenic mechanism and tubuglomerular feedback
what is myogenic mechanism
arteriolar vascular smooth muscle stretches due to increase in pressure in vessel > smooth muscle contracts and afferent arteriole constricts > limit blood flow into glomerulus despite increasing arteriole driving pressure
what is tubuglomerular feedback
smooth muscle cells within walls of afferent arteriole specialised to form granulose cells > collectively known as macula densa > detect changes in Na+ levels of fluid flowing past them
when GFR increase > more fluid flow through distal tube > increase in salt level > macula densa cells release atp adenosine > cause afferent arteriole to constrict > reduce GFR
what is the role of baroreceptor reflex in extrinsic control of GFR
decrease in blood pressure > detected by baroreceptors > afferent arteriole undergoes sympathetically induced vasoconstriction so that there will be more resistance and thus blood pressure will increase > decrease GFR and urine output > more H2O and salt conserved for body > restore plasma volume so that short term cardiovascular adjustments are not needed
how is GFR influenced by changes in Kf
each tuff of glomerular capillaries held together by mesangial cells
sympathetic stimulation > mesangial cells contract > closes off portion of filtering capillaries > decrease SA for filtration > decrease kf > decrease GFR
how much is sodium reabsorbed in each of the different tubules
proximal: 67%
loop of henle: 25%
distal and collecting ducts: 8%
what are the 3 inputs for renin secretion
granulosa cells detect fall in BP
macula densa cells detect fall in Na+ in fluid flowing past the distal tubules
baroreceptor reflex detects fall in BP > increase sympathetic activity > stimulate granulosa cells to secrete more renin
what is tubular maximum
each carrier is specific for the type of substance it can transport across plasma membrane > limited number of each carriers > Tm is the maximum amount of a substance that can be actively transported from tubular fluid in a given time > any quantity filtered beyond its Tm escapes into urine
only Na+ does not have Tm
how to calculate filtered load of a substance
plasma conc x GFR of substance
what is renal threshold
the plasma conc at which Tm of a particular substance is reached and substance starts appearing in urine
how is Cl- reabsorbed
-vely charged Cl- passively reabsorbed down electrical gradient created by active reabsorption of +ve Na+
Cl- passes BTWN, not THROUGH tubular cells
amount of Cl- reabsorbed is determined by rate of active reabsorption of Na+
how are the 2 types of aquaporins different
AQ1 in proximal is always open > high permeability
AQ2 in principal in distal parts of nephron regulated by vasopressin
how is water reabsorbed
basolateral pump activity of extrusion of Na+ > [Na+] diminishes in tubular fluid and and tubular cells while it increases in lateral spaces > osmotic gradient formed induces passive net flow of H2O from lumen into lateral spaces > accumulation of fluid in lateral space > buildup of hydrostatic pressure > flush H2O out of lateral space into interstitial fluid and into peritubular capillaries
what is the mechanism for K+ secretion
basolateral pump simultaneously transports Na+ into lateral space and K+ from peritubular capillary into tubular cell
increase in plasma [K+] stimulates adrenal cortex to secrete aldosterone > secretion and urinary excretion of excess K+
what are the properties of the descending and ascending loop of henle
descending: highly permeable to H2O but does not reabsorb Na+
ascending: actively transports NaCl out of tubular lumen into surrounding interstitial fluid but is never permeable to H2O
what is the mechanism of vasopressin
vasopressin binds to receptor on basolateral membrane of principal cell in distal/collecting tube > activates cAMP 2nd messenger pathways > promotes insertion of AQ2 into opposite luminal membrane > increase permeability > water enters tubular cell from tubular lumen
what is osmotic and water diuresis
osmotic diuresis: involves increased excretion of both water and solute caused by excess ubreabsorbed solute in tubular fluid (occurs in untreated diabetes mellitus)
water diuresis: increased urinary output of water with little or no increase in excretion of solutes
