Week 3 - Kidney

kidney

regulates extracellular fluid volume and blood pressure; regulates ECF osmolarity; maintenance of ion balance; regulates pH; excretion of wastes; production of hormones

extracellular fluid

blood plasma and interstitial fluid

280 mOsM

what osmolarity is maintained at

ions

Na⁺, K⁺, Cl^-, HCO₃^- - kept within normal range by kidney

creatinine and urea

excreted into urine by kidney; metabolic waste products

cortex

outer layer of the kidney

medulla

inner section of kidney composed of 8-15 renal pyramids

nephron

in each renal pyramid that deliver urine into the renal pelvis which transports it to the urinary bladder via the urethra

nephron

functional unit of kidney; over 1 million in each kidney

nephron

filters blood which then passes as fluid/filtrate into a series of tubules

tubules

reabsorb most of the constituents of the filtrate back into the blood; some substances are secreted from these into the filtrate

renal pelvis

remainder of filtrate forms urine which passes into this

modulation of rates of reabsorption

allows regulation of volume, osmolarity, ion balance, and pH of the ECF

cortical and juxtamedullary

two principal types of nephrons

cortical nephrons

glomeruli originate in the outer section of the cortex; loops of hence descend into the outer medulla

juxtamedullary nephrons

glomeruli originate in the inner cortex; have long loops o feeble that descend into the inner medulla; play central role in the production of concentrated urine

outer cortex

where glomeruli of cortical nephrons originate

inner cortex

where glomeruli of juxtamedullary nephrons originate

arterial blood

enters via renal artery and is delivered to afferent arterioles at the nephrons via interloper and arcuate arteries

afferent

what type of arterioles does arterial blood deliver to after entering the renal artery

renal artery

receives 20-25% of cardiac output

glomerular capsule

consists of a capillary bed (glomerulus) surrounds by a Bowman’s capsule

capillary bed

receives blood from afferent arteriole and drains into an efferent arteriole

glomerular filtration

fenestrated capillaries allow filtration of plasma, dissolved solutes, but not blood cells and platelets into the Bowman’s capsule

3

during glomerular filtration, plasma passes through how many barriers?

capillary fenestrations, glomerular basement membrane, inner Bowman’s capsule

3 barriers plasma passes through during glomerular filtration

capillary fenestrations

only exclude cellular components of blood and large proteins

inner Bowman’s capsule

consists of podocytes which wrap around capillaries with thousands of cytoplasmic extensions known as food processes/pedicels; slits between adjacent pedicels act as barriers

food processes/pedicels

cytoplasmic extensions that wrap around capillaries with podocytes

filtrate

fluid entering the Bowman’s capsule

filtrate

consists of plasma and a small amount of plasma protein (albumin)

leakage of plasma proteins

damage to the slit diaphrams causes what into filtrate and then into urine

proteinuria

damage to the slit diaphragms results in leakage of plasma proteins into filtrate and then into urine

capillary hydrostatic pressure

drives glomerular filtration

plasma oncotic pressure/Starling forces and Bowman’s capsule pressure

opposes glomerular filtration

glomerular filtration rate

volume of filtrate produced by both kidneys per minute

115 ml/min

normal GFR for females

125 ml/min

normal GFR for males

180 L/day

filtrate

most is returned to the vasculature in the tubules

renal clearance

volume of plasma completely cleared of the substance by kidneys/min

renal clearance

C_s x P_s = U_s x V

clearance rate of substance

C_s

plasma concentration of the substance

P_s

urine concentration of substance

U_s

urine flow rate

V

urinary excretion rate

U_s x V

urinary excretion rate

(glomerular filtration rate + secretion rate) - reabsorption rate =

inulin

used in research

creatinine

used clinically

C (creatinine)

urine x urine flow rate / plasma

amount filtered at glomeruli/min

if substance is not absorbed or secreted in the tubules then, amount excreted in urine/min is equal to what?

glomerular filtration rate

maintained at a rate sufficient to allow kidneys excrete wastes but not to use excessive water loss

vasoconstriction

causes a reduction in GFR

vasodilation

causes an increase in GFR

intrinsic renal autoregulation

kidneys maintain a constant GFR despite variations in MAP between 70-180 mmHg

myogenic response

increase in blood pressure triggers a reflex constriction of afferent arterioles; decrease in blood pressure causes a reflex dilation of afferent arterioles

constriction

increase in blood pressure triggers WHAT. of afferent arterioles

dilation

decrease in blood pressure triggers WHAT of afferent arterioles

glomerular filtration rate

not changed when MAP changes because of constant blood flow to glomeruli by vasodilation and vasoconstriction

juxtaglomerular apparatus

located between ascending limb of the loop of Henle and afferent arteriole; contains macula densa

macula densa

specialized cells within the juxtaglomerular apparatus

glomerular filtration rate

an increase in this causes increased filtration of NaCl into the tubules macula densa detect elevated tubular and NaCl and release ATP triggering constriction of afferent arterioles; reduces GFR

macula densa

detects elevated tubular NaCl after increased filtration of NaCl into the tubules and release ATP triggering constriction of afferent arteriole into the glomerulus

tubuloglomerular feedback

homeostasis of GFR within the nephron

renal sympathetic nerves

release noradrenaline to trigger constriction of afferent arterioles and REDUCE GFR

decreased urine production

prevents reduction in blood pressure and blood volume

1-2 L

amount of urine produced daily; but varies depending on hydration status

99%

percentage of filtrate that is reabsorbed in the nephron and returned to the vasculature

epithelial cells

line the inner wall of the nephron and reabsorb the filtrate

reabsorption of Na+

driving force for the reabsorption of all other filtrate constituents

active transport

how Na+ is reabsorbed

cytoplasm

what part of PT epithelial cells has a low [Na+] due to Na+/K+ ATPase pumps on the basolateral membrane?

basolateral membrane

where are Na+/K+ ATPase pumps located on the epithelial cells?

co-transport

energy released during movement of Na+ down gradient drives reabsorption of other molecules like glucose and amino acids

electrostatic gradient

movement of Na+ creates this for transport of Cl-

osmotic gradient

movement of Na+ creates this for transport of water

passive transport

how Cl- and water follow Na+

microvilli

specific transporters are expressed on these in the apical membrane

apical membrane

where specific transporters are expressed (Na+/H+ exchanger, Na+/PO₄- co-transporter, Na+/glucose co-transporter, Na+/amino acid co-transporter, aquaporin 1)

glomerular filtrate

blood plasma minus plasma proteins

isosmotic

how glomerular filtrate is with plasma because plasma is also 300 most

65%

percentage of salt and water in filtrate that is reabsorbed in the proximal tubule

loop of henle

reabsorbs ~20% of salt/water in tubular fluid

countercurrent multiplier system

determines osmolatiry of urine in the Loop of Henle

dehydration

low volume, concentrated urine produced

excess hydration

high volume, dilute urine produced

high

while urine concentration occurs in the collecting duct, osmolarity of interstitial fluid in the medulla should be WHAT

low

while urine concentration occurs in the collecting duct, osmolarity of tubular fluid should be WHAT

countercurrent multiplier system

tubular filtrate becomes increasing dilute, medullary interstitial fluid becomes concentrated with salt

juxtamedullary nephrons

in the ascending limb of loop of hence

descending limb

what part of the Loop of Henle is permeable to water but not to salt; cells express AQP1 but not Na+ transporters

ascending limb

what part of the Loop of Henle creates the high osmolarity of interstitial fluid

vasa recta

long blood vessels that parallel the loop of Henle

descending vasa recta

salt and urea move out of what

ascending vasa recta

salt and urea move into what

salt

this is extruded by the ascending limb and must remain in the interstitial fluid

water

this is extruded by the descending limb and must be removed by blood; moves into ascending vasa recta

early nephron

85% of glomerular filtrate is reabsorbed into this