3: RENAL PHYSIOLOGY

kidneys regulate the ______ and _______ of urine by filtering the blood

volume and composition

in the body extracellular fluid the kidneys regulate:

blood plasma filtration

blood pressure

osmolarity

explain each a little

blood plasma filtration- seperate wastes from blood stream

blood pressure- eliminate or conserve water

osmolarity- eliminate or conserve salts

the kidney controls osmolarity with 5 primary methods:

1. renin enzyme

2. erythropoeitin hormone

3. working with the lungs to secrete CO2

4. calciterol (vit D)

5. detox of drugs and free radicals

how does renin enzyme control osmolarity?

activates hormone mechanisms for BP and electrolyte balance (renin angiotestin system)

how does erythropoietin hormone control osmolarity?

controls RBC count and O2 carrying capacity

how do lungs help control osmolarity?

secrete CO2 and help acid base balance

how does calciterol (vit D) control osmolarity?

calcium homeostasis

loss of kidneys causes what condition? with what symptoms?

uremia

diarrhea, vomit, arrhythmia, toxic nitrogen wastes, dyspnea, convulison, death

if no kidney donor is avalible what do you need to do to survive renal failure?

homodialysis to remove nitrogenous wastes

the kidney along the medial concave surface has a slit called _________ where renal nerves, blood vessels, lymphatics and ureter connect

the hilum

what 2 main regions is the kidney parenchyma divided into? which sits closer to the renal sinus?

cortex

medulla (closer to sinus)

renal pyramids steming from the renal ________ exist between regions of medulla and end with paillae

cortex

what percent of blood supply does kidney recieve?

21%

describe the pathway of blood travel from the aorta up until the more distal interlobular arteries that supply the glomeruls of nephrons

aorta→renal artery→interlobular arteries→arculate arteries→interlobular arteries→ glomerulus of nephron

arterioles branching from the distal interlobular arteries supply ___ nephrons each

1

what is the angle of the arculate arteries

90 deg

where do arcutate arteries make a 90 degree turn?

when going from beside to above the medullary pryamids

they then branch off to smaller interlobular arteries in the cortex

what arterioles supply and drain the glomerulus? which is larger?

afferent (much larger)’

efferent (smaller)

where is the juxta glomerular apperatus? what is its purpose?

a part of the DCT that sits near the afferent and efferent arterioles of glomerulus, purpose to help glomerular autoregulation.

from the efferent arteriole leaving the glomerulus, it joins a plexus of ___________ surrounding the tubules and loop of henle

peritubular cappilaries

from the peritubular capillaries what route does blood travel eventually going back to the heart by inferior vena cava?

peritubular capillaries→interlobular veins→arculate veins→interlobular veins→renal vein→ inferior vena cava

the renal medulla recieves what percent of total renal blood flow?

1-2%

how does the renal medulla recieve blood supply?

the vasa recta-

a small portion of the peritubular arteries, capillaries and veins that is around the loop of henle (loop of henle dips into the medulla- other tubules in cortex)

how many nephrons per kidney?

1.2 mil

what are the names of two spatially diffrentiated nephrons? which produces more urine?

juxtamedullary- more urine production

cortical

what are the two components of a renal corpuscule?

glomerulus + bowman capsule

what is the outer layer of bowman capsule called?

squmous epithelium

what is the visceral layer of the bowman capsule called?

podocytes

podocytes wrap around ______

glomerular capillaries

glomerular filtrate (fluid filtered out of blood) enters the capsular space which is teh space between the _______ and _________ layers of bowman capusle

parietal (sqamous epithelium)

visceral (podocyte)

from the capsular space where does glomerular filtrate go?

renal tubule

the renal tubule is made of 3 main regions:

DCT, loop of henle, PCT

where do renal tubules from many nephrons dump into?

collecting ducts

which part of renal tubule is the most coiled

PCT

what type of epithelium covers all of the renal tubule?

cuboid

what part of the renal tubule has microvilli?

PCT

the cells of the loop of henle have high amounts of _____ due to a lot of active transport

mitochondria

is DCT or PCT longer?

PCT

from DCT where does filtrate head?

collecting duct→ papillary duct→minor calyx

where does each process of urine formation occur?

1. filtration

2. tubular reabsorption

3. tubular secretion

4. water conservation

1. filtration- renal corpsule (glomerulus and bowman capusle)

2. tubular reabsorption- renal tubule

3. tubular secretion- renal tubule

4. water conservation- collecting duct

filtration in teh glomerulus occurs by a process called

capillary fluid exchange

the corpuscule has 3 layers of filtration what are they?

1. fenestrated endothelium of capillaries

2. basement membrane (proteoglycan gel)

3. filtration slits (podocytes)

what does fenestrated epithelium of capillaries filter for?

70-90nm -exclusion of blood cells so blood doesnt enter urine

what is basement membrane made of? what does it filter for?

proteoglycan gel

molecules >8nm cant pass, and proteins held back by negative charge of the gel

what percent protein is blood? what percent protein is glomerular filtrate?

7%, 0.03%

what do filtration slits filter for?

podocytes surrounding capillaries have neg charge and slits of 30nm. large anion obstacle

moleucles of size _____ or less pass into glomerular filtrate and therefore have similar concentration in filtrate as in blood

<3nm

kidney disease where blood and albumin is found in urine is likely a dammage in what?

glomerular capillary fenestrated epithelium

endurance exersizers can get temporary protenuria and hematuria why?

reduced perfusion and glomerular deterioration with hypoxia

what is glomerular blood pressure vs normal capillary pressure?

60mmHg

10-15mmHg

what is capsular space pressure?

18mmHg

what is the 60mmHg pressure opposed by? what net pressure?

60mmHg- hystrostatic inward 18mmHg (capsule)- colloid 32mmHg= net of 10mmHg

why are kidneys so prone to failure in low blood pressure?

the net 10mmHg is enough to keep glomerular filtrate going but little margin of error when blood pressure drops

how is blood pressure in glomerulus maintained when bodily blood pressure drops a bit

autoregulatory mechanisms

in most capillaries osmosis overrides filtration (too low pressure on venous end) so stuff isnt pushed out of capillary any more or less than it is taken in.

how does glomerulus ensure that stuff only filtrates out and not back into capillaries?

keeps a higher blood pressure

hypertension effect in kidney

potential glomerular rupture and scaring or kindey

(increased athrerosclerssis- narrowing over time can cause)

what happens when filtration too fast vs too slow?

too fast- too fast to reabsorb water and solutes (everything just goes through)

too slow- wastes that should be excreted may be reabsorbed

three mechanisms can adjust GFR by adjusting glomerular BP:

renal autoregulation, sympathetic control, hormonal control

renal autoregulation is controlled by the ________ which is a part of the DCT(and loop of henle) that presses against the glomerular afferent and efferent arterioles

macula densa

macula densa cells are located in the ______

thick ascending limb

macula densa senses _____ levels and is then able to contract efferent and afferent arterioles

NaCl

if GFR rate is too high (too much NaCl absorbed) the macula densa acts as a paracrine messenger and stimulates _______ cells to constrict the _______ arteriole

juxtaglomerular, afferent

if GFR is too low (not enough NaCl absorbed) macula densa secretes a different paracrine messenger to relax the arteriole and ________ cells

mesngial

what rang of arterial blood pressure is the renal autoregulation system able to compensate for?

70-180 mmHg

what happens when BP under 70

glomerular filtration stops efferent arteriole dialates

what happens if blood pressure >180

glomerulus dammage and efferent constriction

sympathetic control in exersize or circulatory shock (low BP) or epinephrine constrict ____ arterioles to direct more blood supply to brain heart and muscles and away from kidney

afferent

(decrease GFR)

when is renin angiotestin system activated?

when low BP and reduced NaCl and water in filtrate

what cells senses when low BP and reduced NaCl and water in filtrate? what do they secrete?

juxtaglomerular cells

secrete renin

renin ats on what plasma protein ?

angiotestin

renin +angiotestin protein=

angiotestin I peptide

in the lungs angiotestin I becomes

angiotestin II peptide

what does angiotestin II do?

vasoconstriction to raise BP, afferent and efferent arteriole constriction (decreases GFR), adrenal cortex stimulation to release aldosterone

what does aldosterone do?

increase NaCl and H2O retention in kidney

(increases BP and volume, and stimulates thirst)

renin is secreted when blood pressure is high (T/F)

F- renin is secreted by juxtaglomerular cells when blood pressure is too low

in kidney what specifically does angiotestin II do?

vasoconstriction- decrease GFR and Na excretion in glomerulus

reabsorpion of Na+ transport in tubules

what percent of glomerular filtrate is reabsorbed in the PCT?

65%

PCT alone use up ____% of resting calories and ATP

6

what part of nephron reabsorbs greatest variety of chemicals?

PCT

what are the two routes of reabsorption by PCT

transcellular (active or facillatated)

paracellular (passive)

what is most abundant cation in glomerular filtrate

Na+

[Na+] in PCT is ______

[Na+] in epithelial cells is _______

gradient favours sodium movement into _______

140mM

12mM

epithelial

glomerular filtrate is reduced to what fraction of original volume of blood from capillary

1/3

glomerular filtrate remains isomotic with glomerular capillaries (T/F)

T

Na+ is absorbed in the first half of the PCT by _______ proteins

symport

(bind and transport sodium along with glucose, AA, phsophate or lactate)

the sodium glucose symporter is on what side of the PCT epithelial cell? (filtrate facing/ blood facing)

filtrate facing

how is soduim concentration gradient from filtrate into PCT epithelial cell maintained?

Na+/K+ ATPase actively transporting sodium fout of epithelial cell an into blood stream

Na+ enters epithelial cell by _______ and leaves by _______

facillitated diffusion (symporter)

active transport (ATPase)

the mechanism of Na+ reabsorption is based on active transport therefore there is a transport maximum (Tm)

when Tm exceeded what happens?

solutes are too high so reabsorption is not fast enough

(often the case in diabeties and why we see glucose in diabetic urine- cannot be absorbed fast enough with teh Na+glucose symporter due to concentrations exceeding the Tm)

bicarbonate ions are recovered by first by reacting with water in tubular fluid to make _______

HCO3- + H2O→ H2CO3 (carbonic acid)

carbonic acid (H2CO3)→ CO2 + H2O by what enzyme in tubular fluid

carbonic anhydrase

recovery of bicarbonate ions makes urine more _______ (acidic/basic) due to ______

acidic, H+ moving into tubular fluid as bicarbonate moves out

CO2 enters epithelial cell and then is converted by ______ back to H2CO3 and then to HCO3- + H+

carbonic anhydrase

what are the fates of HCO3- and H+ produced from CO2+H2O in the epithelial cell?

HCO3- is released back into blood stream by facillitated diffusion, H+ goes back into the tubular fluid by secondary active transport to decrease pH of urine and help move in more CO2

how does H+ move out of the cell back into tubular fluid?

Na+/H+ transporter (secondary active)

how does epithelial cell stay polarized to keep bicarbonate reabsorption occuring?

Na+/K+ ATPase keeps moving sodium from epithelial cell into blood stream to keep sodium coming in

where does bicarbonate reabsorption occur?

PCT

what part of nephron secretes urea, uric acidm drug metabolites into tubular fluid for excretion?

kidney

Loop of Henle (urine concentration system) is also known as ________________

counter current multiplier system

what part of evolution did the loop of henle help us with?

water→ land

no constant water source need tubular fluid to not be isomolar with plasma or we would excrete all of our water