Renal Flashcards
internal sphincter
smooth muscle, autonomic control
external sphincter
skeletal muscle, voluntary control
renal function (kidney)
only connected to sympathetic neurons
where are most of the nephrons found?
80% in the cortex, 20% dip down into medulla (juxtamedullary nephrons)
effective circulating blood volume
determined by cardiac output, peripheral resistance, and actual blood volume (kidney function)
body % of water
55-60%
total body weight
ICF volume (2/3) + ECF volume (1/3)
intracellular fluid
2/3, water inside all cells of the body
extracellular fluid
1/3, subdivided into plasma (1/4) and interstitial (3/4)
sodium
low intracellular, high extracellular
potassium
high intracellular, low extracellular
blood flow in renal portal system
afferent arterioles -> glomerulus -> efferent arterioles > peritubular capillaries
vasa recta
in juxtamedullary nephrons, these are the long peritubular capillaries that dip into the medulla
parts of nephron (in order of movement)
Bowman’s capsule -> proximal tubule -> loop of henle (tDHL, tALH, TALH) -> distal tubule -> collecting duct
filtration
blood -> lumen of nephron
only occurs in renal corpuscle, Bowman’s capsule allows bulk flow
reabsorption
lumen -> blood
occurs primarily in proximal tubule
also occurs in loop of henle, distal tubule, and collecting duct
secretion
blood -> lumen of nephron
molecules in peritubular capillary blood enter lumen of nephron
excretion
lumen -> external environment
thick ascending limb
osmolality drops, “diluting segment” (salt removed)
impermeable to water
most common site of kidney failure
glomerular filtration
filtration fraction
20% of renal plasma flow (80% stays in circulation)
that is about 1/5 of cardiac output
FF = GFR/renal plasma flow
podocytes
cell type surrounding capillaries, “foot” cells
help maintain structural integrity
have high pressure
mesangial cell
can contract to change the surface area
may be involved in paracrine function
3 filtration barriers
- glomerular capillary endothelium: fenestrated and allow most components of plasma in
- basal lamina: basement membrane, negatively charged
- epithelium of bowman’s capsule: podocytes and mesangial cells
hydrostatic pressure
begins to drop due to resistance but then remains constant
oncotic pressure
slowly increases, does not hit equilibrium point inside glomerular capillary
net filtration
hydrostatic pressure > oncotic pressure
always in glomerular capillary
Kf (filtration coefficient)
the higher this value, the easier to be filtered
diabetics have a low Kf
GFR is influenced by?
net filtration pressure and Kf (SA and permeability)
vasoconstriction of afferent arteriole
decrease renal blood flow, decrease hydrostatic pressure, decreased GFR
vasoconstriction of efferent arteriole
decrease renal blood flow, increase hydrostatic pressure, increase GFR
GFR autoregulation
myogenic (bayless)
tubuloglomerular feedback
myogenic response
smooth muscle in afferent arterioles stretches due to increased pressure, ion channels open, cells depolarize, muscle contracts
-vasoconstriction increases resistance to flow, thus filtration pressure decreases
tubuloglomerular feedback
macula densa: when senses increased NaCl going past, send paracrine message to afferent arterioles to constrict
- these are at end of loop of henle and beginning of distal tubule
- this increases resistance, and decreased GFR
transcellular transport
substances pass apical and basolateral membrances
paracellular transport
substances pass through cell junction
active transport of sodium
this is the driving force of most renal reabsorption
- sodium enters the cell down the electrochemical gradient
- sodium is pumped out of the cell by NaKATPase (primary active transport)
Na-Glucose transporter
secondary active transport
symport on apical membrane, brings in Na and glucose
glucose facilitated diffusion transporter
glucose passively leaves cells through basolateral membrane while the sodium is pumped is pumped out by the NaKATPase
mechanisms of sodium reabsorption in proximal tubule
- solute and water reabsorption
- bicarbonate reabsorption
- sodium-coupled solute reabsorption
bicarbonate reabsorption
- sodium-hydrogen coupling: sodium in, hydrogen out
- protons pumped out bind with filtered bicarbonate and become CO2 which is lipid soluble and can reenter cell
- the proton is not excreted, just recycled
- the sodium that enters is pumped out by NaK pump
- when CO2 reenters cell and combines with water will make bicarbonate and then be facilitated out of cell
Tm (transport maximum)
saturation occurs and we cannot transport anymore substrate
inulin
not reabsorbed or secreted, it is 100% excreted
inulin clearance is gold standard for measuring GFR
typical GFR
100-120 mL/min
para-amino hippurate (PAH)
used to measure renal plasma flow
- not natural, must be infused
- it is filtered and then secreted by proximal tubule
- clearance of PAH will be greater than inulin, because inulin is only filtered
Cx > Cin
net secretion
Cx < Cin
net reabsorption
plasma solute that is only filtered
inulin
plasma solute that is filtered and reabsorbed
glucose
plasma solute that is filtered and secreted
penicillin and PAH
plasma solutes that are filtered, reabsorbed, and secreted
potassium and urea
hyperosmotic
has higher concentration of solute (less water)
hyposmotic
has lesser concentration of solute (more water)
hypertonic
cell will shrink
hypotonic
cell will swell
osmoreceptors
- respond to an increase is osmolarity
- when receptors receive signal will send APs down axon to posterior pituitary
- ADH (anti diuertic hormone) at these terminals
- will also go to brain to stimulate thirst centers
ADH (vasopressin)
- decreases urine flow
- targets late distal tubule and collecting duct
- will bind to V2 receptor and increase cAMP in target cell
- this stimulates insertion of water pores (AQP2) into apical membrane
- increased water reabsorption to conserve water
baroreceptors
in aorta and carotid bodies, respond to drop in blood pressure
diuerisis
excreting water
-absence of vasopressin, collecting duct impermeable to water and urine is dilute
anti-diuresis
conserving water
-presence of vasopressin, water is being withdrawn into interstitial space
volume depletion hypovolemia
decrease amount of sodium, contracts the volume
volume expansion hypervolemia
increase amount of sodium, expand the volume
how do we measure volume in the body
volume sensors = baroreceptors
low pressure: cardiac atria, pulmonary vasculature
high pressure: carotid sinus, aortic arch, juxatglomerular appartus
sodium excretion is altered by what?
changes in GFR: if you don’t filter it, don’t have to reabsorb it
changes in tubular reabsorption
RAAS (Renin-Angiotensin-Aldosterone System)
- liver constantly producing Angiotensin
- drop in BP sensed by granular cells, renin is released
- renin + angiotensin = angiotensin 1
- angiotensin 1 comes in contact with ACE enzyme which cleaves off AA and makes angiotensin 2
- as angiotensin 2 circulates it causes increase the BP
Angiotensin 2 circulation causes
OVERALL: increase BP
-vasoconstriction of arterioles
-directly tells medulla to increase CO
-hypothalamus: release vasopressin and increase thirst signal
-adrenal cortex: increase aldosterone, increase Na+ reabsorption
this maintains osmolality and conserves ater
loop diuretics
very powerful, blocks the sodium 2 chloride potassium mechanism
-without gradient, water cannot be reabsorbed
chlorothiazide
in distal tubule, blocks sodium chloride reuptake
-loss of sodium = loss of volume
amiloride
(gentlest) in the collecting duct, blocks the sodium channel found on the epithelium
atrial natriuretic peptide (ANP)
-produced in atria
-when volume overloads, is activated
-decrease tubular Na+ reabsorption
-increase renin release
-vasodilate afferent arterioles
-decrease sympathetic nervous system
OVERALL: increase sodium excretion
buffers
1st line of defense against acid input, act like sponges to resist sudden pH change
ex) bicarbonate, protein, hemoglobin , phosphates, ammonia
net excretion of acid in two forms
- ammonium (NH4+)
2. titratable acid (mostly phosphoric acid)
volatile acids
excreted by respiratory system
-most important volatile acids come from carbohydrate metabolism
non-volatile acids
excreted by renal system (cannot be respired off)
