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Guyton Physiology - Renal
Terms in this set (145)
what are the primary ions in the ECF?
sodium(+) and chloride(-)
what are the primary ions in the ICF?
potassium (+), phosphate (-), and proteins
what makes up the ECF?
plasma and interstitial fluid
same composition, except plasma has more proteins, phospholipids, and cholesterol.
it makes plasma more (-), thus having most colloid osmotic pressure than interstitial compartment.
how can you estimate the blood volume?
70ml/kg of LEAN body weight
% of RBCs in blood volume
Finish the equation: ICF =
TBW - ECF
net diffusion of water across a semipermeable membrane from a high concentration of water to an area of low concentration of water
high [water] = diluted solutes
low [water] = concentrated solutes
finish the equation: osmotic pressure =
concentration (g/L) / MW (g/mole) X 1000
if solution contains more than one ion (like NaCl) multiply the answer by the # of ions.
what happens to ICF and ECF in isotonic solution?
ECF expands only
what happens to ICF and ECF in hypotonic solution?
ICF and ECF both expand.
osmolarity decreases (diluted)
what happens to ICF and ECF in hypertonic solution?
ECF expands, ICF shrinks.
osmolarity increases (concentrated)
caused by loss of sodium or gain or water
low sodium causes an increase in ICF (hypotonic state)
if chronic, ions transport out of cell
vulnerable to osmotic injury if corrected to rapidly
causes by loss of water (DI) or gain of sodium
high sodium causes decrease in ICF (hypertonic state)
Edema occurs when...
when compliance in interstitial space is positive.
normally it is (-).
where are the kidneys located?
posterior wall of the abdominal cavity on the OUTSIDE of the peritoneal space.
Hilum of kidney
medial side that is an indented region.
it has the renal artery, renal vein, lymphatics, nerves, and ureter passing through it.
what parts of the kidney contains contractile smooth muscle?
calyces (minor and major), pelvis, and ureters
explain the anatomy of the renal pyramids
located in the medulla of the kidneys
inner most part is the papilla (tip of the pyramid)
How much of the cardiac output do the kidneys receive?
functions of the kidney
excretion of wastes, toxins, metabolites
water and electrolyte balance
BP regulation (RAAS)
acid-base regulation (acid secretion)
vitamin D3 regulation (forms calcitrol - or active form of vitamin D)
gluconeogensis during prolonged fasting
Anatomy of the blood vessels of the kidney
in terms of arterioles, what increases GFR?
think of it like this: GFR will increase if it prolongs the time spent in the glomerular capillaries (increasing the glomerular capillary pressure)
pathway of urine flow
Loop of Henle
what is the macula densa?
located between thick ascending limb of loop of Henle and DCT
runs between the afferent and efferent arterioles
what is the difference between cortical nephrons and juxtamedullary nephrons?
cortical nephrons are located in cortex and have short loops of Henle.
juxtamedullary nephrons located in medulla and have long loops of Henle.
what is the vasa recta?
specialized peritubular capillaries
they run parallel to the loop of Henle
play an important role in the formation of concentrated urine
what is the name of the muscle that makes up the bladder?
detrusor muscle - smooth muscle
allows action potentials pass easily along to allow the bladder to contract as one
how much pressure can the bladder produce?
40-60 mm Hg
what is the trigone?
inferior region of the bladder
ureters enter above, and urethra begins here
sphincters of the urinary tract
internal sphincter: smooth muscle with tone to prevent emptying until pressure in the bladder climbs
external sphincter: skeletal muscle located in the urogenital diaphragm (conscious control)
bladder is enervated by?
pelvic nerves of the parasympathetic system via the sacral plexus
what initiates the micturition reflex?
stretching of the bladder
what nerve controls the external sphincter of urethra?
what nerve controls the blood supply of the bladder?
hypogastric nerve (sympathetic control)
Explain the process of the micturition reflex
1. volume in bladder increases causing stimulation of stretch receptors
2. signals are sent to the sacral cord via PNS
signals are sent back down to the detrusor muscle
3. micturition contractions occur
4. "self-regenerative" characteristic causes stronger micturition contractions - which in turn cause more stimulation of stretch reflex.
5. reflex can fatigue out, then cycle begins again
positive feedback loop until person urinates.
what centers in the brain inhibit the micturition reflex?
also contracts external sphincter
what centers in the brain stimulate the micturition reflex?
also inhibits external sphincter to allow urination
caused by crush injury to sacral nerves (S2 and S3)
decreases sensory output and loss of micturition reflex
cord damage causes increased activity of sacral segments
micturition reflex INTACT! but NO conscious control
external stimulation can produce reflex (gives person some control...)
finish the equation: excretion =
filtration - reabsorption + secretion
the process by which the kidneys filter the blood, removing excess wastes and fluids.
[filtered substance] in filtrate = [substance] in plasma
when substances travel from filtrate back to blood through the peritubular capillaries
water and specific solutes are reabsorbed
when substances are added to the urine from the blood like hydrogen and potassium
What happens to potassium and hydrogen ions in kidney failure?
kidneys do a bad job at secreting potassium and hydrogen into the urine
patient at risk for acidosis and hyperkalemia
excretion of creatinine is equal to...
it is only filtered
it is not secreted or reabsorbed
excretion of sodium and other electrolytes are equal to...
amount filtered - amount reabsorbed
they are filtered and PARTIALLY reabsorbed
excretion of glucose and amino acids are equal to...
they are filtered and COMPLETELY reabsorbed
(under normal conditions)
excretion of hydrogen ions and potassium are equal to...
amount filtered + amount secreted
they are filtered and remaining partially or totally secreted
An increase in plasma creatinine equals to...
a decrease in GFR
kidneys are not doing a good job at filtering creatinine out.
in the body, the [H+] is tightly regulated at...
4 x 10^-8 mEq/L
a molecule containing H+ and can easily release H+ into solutions
example: HCl ionizes in water to form H+ and Cl-
a molecule that can easily accept H+ ions.
example: HCO3- can combine with H+ to form H2CO3-
RBCs and proteins are some of the most important bases within the body.
in terms of [H+], finish the equation: pH =
what is the relationship between [H+] and pH?
high [H+] = low pH
low [H+] = high pH
what are the three major defense mechanisms of the body?
1. buffering of H+
2. removal of CO2 by the lungs
3. adjustment of urine pH by the kidneys
Bicarb buffer system
reacts within SECONDS
most important system
takes CO2 and combines it with water to form H2CO3 and that breaks down and forms H+ and HCO3-
H+ can be secreted into the urine.
bicarb can combine with sodium to make sodium bicarb (acts as a reserve in the blood for when it is needed)
what is the Henderson hasselbach equation?
pH = 6.1 + log( ([HCO3 / 0.03 X CO2) )
the ratio of bicarb and CO2 determines pH.
acute respiratory acidosis vs. chronic respiratory acidosis
narcotics vs. progressive disease like COPD
when are buffers most effective?
when pK = pH, where 50% is bicarb and 50% is CO2 (or H2CO3)
phosphate buffer system
important intracellular and urine buffer
excess H+ (that can't bind with bicarb) can bind with phosphate to form H2PO4- and can be excreted as urine when formed with sodium to make NaH2PO4- (carrying with it, all the excess H+)
protein buffer system
important intracellular buffer
helps prevent changes in ECF by functioning as acids or bases (whichever the body needs to be buffered with)
albumin and globulins are major plasma proteins
respiratory control of pH
lungs can speed up or slow down elimination of CO2 based on ventilation
increased CO2 in body stimulates chemoreceptors to increase MV in respirations - brings CO2 level back to normal
max response = 12-24 hours (then kidneys must take over to maintain homeostasis)
increased ventilation = decreased CO2 = increased pH (alkalosis)
decreased pH = increased ventilation
either the body can drive the RR or the RR can drive the pH.
kidneys regulate [H+] in ECF through:
1. secretion of H+
2. Reabsorption of HCO3-
3. Production of HCO3- (through breakdown of glutamine and phosphate buffer)
excretion of bicarb alters in response to acidosis and alkalosis
responds with hours to DAYS, but most powerful
HCO3- reabsorption mostly occurs in the?
but throughout tubules EXCEPT thin segments of the loop of Henle
for each bicarb reabsorbed, a H+ ion is excreted
bicarb travels to renal interstitial fluid to peritubular capillaries then back to blood.
H+ secretion with HCO3- reabsorption occurs where?
PCT and thick ascending loop of Henle
What mechanism allows H+ to be secreted into urine?
sodium-hydrogen secondary active transport
what enzyme is required to combine CO2 and H2O into H2CO3 (to later form H+ and HCO3-)?
Primary active secretion of H+ occurs where?
DCT and collecting tubule
in Type A intercalated cells
net effect: bicarb reabsorbed, H+ secreted
what is the minimum pH that urine can be?
this severely limits the amount of H+ that can be excreted alone
that is why it binds with phosphate and ammonium so it can excreted without making the pH more acidic.
Glutamine's role in urine
amino acids break down into glutamine.
Glutamine is filtered by the kidney and is metabolized into 2 NH4 molecules and 2 bicarbs.
process stimulated by acidosis
inhibited by alkalosis
NH4 is secreted into urine (getting rid of H+)
NEW bicarb that is formed is reabsorbed into the blood.
Ammonia in the collecting tubules
Any ammonia that reaches the collecting tubules can be combined with H+ to form NH4 and is excreted from body.
another way to expel H+ from body..
H+ secretion is stimulated by:
H+ secretion is inhibited by:
why can't fatty acids and calcium filtered through the kidney?
because they are bound to proteins
GFR is about 20% of what?
renal plasma flow
GFR is determine by:
1. Starling's forces
2. capillary filtration coefficient (Kf)
GFR = Kf X NFP
net filtration pressure = capillary hydrostatic pressure - (bowman's capsule pressure + capillary COP)
increase in hydrostatic pressure and Kf equals...
increase in GFR
layers of the glomerular capillary membrane
all layers are negative, all repel proteins
endothelium: has fenestrations that increase filtration rate
basement membrane: proteoglycans are (-)
epithelium (podocytes): have slits pores that allow water movement (but not proteins)
the relationship between MW and filtration
Increased MW decreased filtration
the relationship between negativity and filtration
the more negative, the less filtration occurs
Conditions that decreased GFR
UTI, kidney stones (increase bowman's capsule pressure)
DM, CKD, HTN (decreased Kf)
A decrease in renal blood flow causes...
decreased sodium filtration
decreased sodium reabsorption
decreased oxygen consumption
normal renal blood flow (in ml/min)
Kidney's auto regulation of BP can compensate for?
BP between 80-170 mm Hg
so BP changes usually has little effect on RBF and GFR
finish the equation: renal blood flow =
(renal artery pressure - renal vein pressure) divided by the total renal vascular resistance
SNS on RBF and GFR
causes constriction of afferent and efferent arterioles
decreases RBF and GFR
increases sodium and water reabsorption
Angiotensin II on RBF and GFR
release of Ang II is stimulated by a decrease in RBF and decrease in filtration pressure
so the EFFERENT arteriole constricts to increase filtration pressure and increase RBF
increases sodium and water reabsorption
Prostaglandins on RBF and GFR
dilates AFFERENT arteriole
NSAIDS block prostaglandins so they constrict afferent arterioles causing a decrease in RBF and GFR
tubulo-glomerular negative feedback and auto regulation of GFR
alters [NaCl] to regulate arterioles
decreased glomerular hydrostatic pressure
decreased flow through loop of Henle
increased NaCl reabsorption
decreased [NaCl] in macula densa
dilation of afferent arteriole & renin release
increased hydrostatic pressure, Ang II release
efferent arteriole constriction
kidneys regulate excretion by regulating...
Reabsorption of a substance requires?
paracellular (through spaces) or transcellular (through) movement across 2 cell membranes
by active or passive (diffusion)
what is bulk flow?
movement into peritubular capillaries by ultrafiltration
driven by osmotic pressure and hydrostatic pressure
Primary active transport
moves substances against a [ ] gradient
sodium-potassium pump: reabsorbs sodium, secretes potassium
creates and maintains RMP of -70.
sodium and water moves from interstitial space to capillary through bulk flow
secondary active transport
when 2 substances move together
glucose and amino acids both use Na+ to diffuse into capillaries.
SGLT 1 & 2
Na+ glucose co-transporters
allows glucose to transport with sodium.
SGLT 2 blockers are useful in DM.
sodium hydrogen exchanger
protein responsible for exchanging H+ for Na+
secretes H+ into tubule when taking Na+ into capillaries
transporters can be maxed out and too saturated to carry any more molecules out of filtrate and into blood.
when glucose is too high, SGLT is used up and glucose spills into urine
Chloride and Urea
wherever sodium goes, chloride follows.
urea does the same, but to a MUCH LESSER extent
proximal convoluted tubule
main goal: reabsorption of sodium (and water for that matter) via Na/K+ ATPase
osmolarity remains the same during this phase.
drug and toxins are cleared here.
descending limb of loop of Henle
filtrate becomes VERY concentrated.
thin ascending limb of loop of Henle
ions start to be reabsorbed and not water
thick ascending limb of loop of Henle
impermeable to water
filtrate becomes very diluted here.
uses Na/K ATPase
HIGH metabolic activity
where does lasix work
on the thick ascending limb of loop of Henle
Early distal convoluted tubule
reabsorbs solutes, but not water (like thick LOH)
called the "diluting segment"
uses Na/Cl co transporter and Na/K ATPase
Late distal convoluted tubule
uses principal cells to reabsorb Na and secrete K
driven by Na/K ATPase
passive channels in luminal membrane
intercalated cells actively secrete H+ and reabsorb bicarb
what does aldosterone do in the nephron?
acts on the late DCT to reabsorb Na+ (and water) by acting on principal cells
stimulated by: hyperkalemia, and Ang II
where does spironolactone work?
late DCT and inhibits the reabsorption of Na+ (and water)
what does amiloride do?
blocks Na+ channels in the late DCT
where do K+ sparing diuretics work?
what do principal cells do and where are they?
what controls water permeability in the late DCT?
binds to V2r
activates protein kinases and phosphorylates aquaporins
increases water permeability
increases water reabsorption
Type A intercalated cells
type A = acid
actively secretes H+ via H+ transporter and H+/K co-transporters
reabsorbs bicarb and reabsorbs K
Type B intercalated cells
type B = bicarb
secretes bicarb and K+
active in alkalosis
when are type B intercalated cells active?
because they secrete the extra bicarb and pick up acid
medullary collecting duct
may or may not reabsorb water (depends on ADH)
secretes H+ and urea
what prevents the overload of distal nephrons?
when tubular fluid load increases, reabsorption will increase
increased GFR = increased water reabsorption
Peritubular capillary pressure
decreased arteriolar resistance =
increased peritubular pressure =
decreased reabsorption =
an increase in filtration fraction causes...
increased capillary COP =
increased reabsorption =
= decreased reabsorption
= increased UO
creatinine clearance is indicative of GFR
requires 24 hour collectoin
finish this equation: FENa =
urine Na X plasma Cr / plasma Na X urine Cr
how does ADH control urine concentration?
increased serum osmo
= increased ADH
= increased water reabsorption
= water conserved, urine concentrated
osmolarity through the nephron
(osmo is 300 to begin with)
descending limb of LOH: 600 (concentrated due to water reabsorption)
ascending limb of LOH: 100 (dilute due to solute reabsorption
DCT: varies depending on ADH
when ADH is present, where is water best reabsorbed?
cortical collecting tubule
(more than the medullary collecting tubule)
increased specific gravity is equal to an increase in...
how does urea get diffused out of the medullary CT?
urea transporters (UT A1 and UT A3)
ADH activates UT A3
20-50% of filtered urea is excreted in urine
Countercurrent exchange in vasa recta
blood enters and leaves vasa recta at border of cortex and medulla
blood picks up solutes as it descends and gives it up as it ascends back to cortex
reason?? it provides blood flow to meet metabolic needs of medulla without taking away solutes from interstitium
Where is ADH synthesized?
in supraoptic and paraventricular nuclei in hypothalamus
its packaged into vesicles and shipped to posterior pituitary where it is released
causes water and sodium retention
ADH release stimulants
increases plasma osmo or decrease in volume = increased release
increase in osmotic = sharp increase
large decrease in volume = HUGE increase
other: nausea, hypoxia, and MS
inhibition caused by alcohol
what stimulates thirst?
angiotensin II release
increased Na+ intake
K+ uptake is stimulated by?
uptake decreases plasma K (goes into the cells)
insulin (increase K after a meal is greater in DM)
beta adrenergic stimulation
K+ release from cells is stimulated by?
release increases plasma K (leaves ICF and goes into ECF)
stimulates Na/K pump, aldosterone secretion - increases permeability of principal cells
increased plasma osmo
Renal K+ excretion
filtered at glomerulus (rate constant with GFR)
reabsorbed at PCT and thick ascending limb of LOH
secreted in DCT and CT (rate varies) - occurs in principal cells
uptake from interstitium by Na/K pump
diffuses passively into urine
what happens in Addison's disease?
decreased aldosterone (blockage of negative feedback system)
loss of regulation of K
renal secretion of K is decreased
how is calcium presented in the body?
bound to plasma proteins
complexed to ions
relationship between acidosis and calcium
acidosis causes a decrease in calcium binding to albumin = increased ionized calcium
regulation of calcium
decreased calcium causes a release of PTH
PTH increases renal reabsorption, activated vitamin D (increases GI reabsorption), and osteoclast activation
so PTH = increased plasma calcium
Calcium excretion by the kidney
only ionized calcium can be filtered (99% reabsorbed)
most reabsorption occurs in PCT
diffuses into cell via primary and secondary active transports
Loop of henle and DCT: can be reabsorbed in thick limb (stimulatated by PTH and vitamin D)
at low levels, 100% is reabsorbed
at high levels, phosphate spills into urine
(PTH can cause an increase of phosphate in blood)
Magnesium control by the kidney
filtered and mostly reabsorbed in loop of henle
excretion controlled by reabsorption
increased capillary pressure
fluid goes to interstitial
What happens at the Pulmonary vein?
What are the two main functions of cholesterol?
What are three functional groups of muscles?
What type of molecules use simple diffusion?
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