Kidney Flashcards
Kidney’s main functions
- Eliminate nitrogenous waste
- Water balance (i.e. concentrate urine)
- pH balance
- Set the concentration of extracellular fluids (i.e. Na+, K+, etc)
Typical blood plasma concentration
300 mOsm
Typical concentration of urine
1200 mOsm
UP ratio
The concentration of urine/concentration of plasma. For us it’s about 1200mOsm/300mOsm = 4
Fluid pathway in body
Blood–>kidney–>ureter–>bladder–>urethra–>out
Major portions of the kidney
- cortex - outer portion
- medulla - inner portion
- renal pelvis - collects urine that goes to the ureter
cortex and medulla
–osmolarity changes b/w cortex and medulla are most important way kidney regulates shit
renal pelvis
collects the urine that goes to ureter
nephron
- -the functional unit of the kidney
- -about 1 million nephrons per kidney
afferent arteriole
carries blood TO the glomerulus
efferent arteriole
carries blood AWAY from the glomerulus
Functions of the nephron
- Filtration
- Reabsorption
- Secretion
- Excretion
Filtration
Occurs in the glomerulus in Bowman’s capsule
glomerulus
the capillary bed in bowman’s capsule where blood first gets filtered into the kidney
What goes into the kidney and what stays out?
- -Big things do not go into the kidney: red blood cells, white blood cells, big proteins
- -what goes into the kidney: everything else
GFR
glomerular filtration rate
Numbers
- -600 ml of plasma goes into afferent arteriole
- -120 ml goes into bowman’s capsule
- -a good amount of this 120 ml gets reabsorbed and the rest goes out as urine
reabsorption
- -occurs in the proximal tubule
- -most occurs by active transport
- -Sodium is pumped out of proximal tubule
- -Water follows sodium due to osmotic gradient (when sodium is pumped out, you increase solutes in extracellular space, so water follows)
- -the concentration of other solutes inside the proximal tubule increases as a result of water leaving
- -small molecules can diffuse out of proximal tubule according to the concentration gradient
glomerulus vs. peritubular capillary bed
- -glomerulus is filtration only
- -peritubular capillary bed is reabsorption only
vasa recta
–branches off the peritubular capillary to carry blood into the medulla
podocyte
- -a special cell with long finger-like projections that wraps around the capillaries
- -function to do the size-selecting for what gets through the glomerulus into the kidney
collecting duct
- -this is where urine gets really concentrated
- -water leaches out of the collecting duct as it moves down b/c of the osmotic gradient that is in the interstitial space
- -(the loop of henle has set up this osmotic gradient in the medulla)
ADH
- -anti-diuretic hormone
- -This hormone acts on the collecting duct
- -When ADH is present, it increases permeability of the collecting duct to water –> more water reabsorption –> less urine
- -Caffeine and beer are ADH blockers, which means you decrease the permeability of the collecting duct to water –> more urine excreted
- -Uses cAMP transduction mechanism
osmoreceptors
- -found in the hypothalamus
- -they take account of the osmolarity of the blood and regulate whether ADH is released from the posterior pituitary
vasopressin
- -ADH is the same thing as vasopressin. They are named differently for the different functions
- -ADH works on collecting duct to increase permeability to water
- -Vasopressin acts on the arterial side to increase smooth. muscle contraction –> increase in blood pressure
- -Uses IP3 transduction mechanism
counter current multiplier
- -the loop of henle
- -applies the single effect, which creates a static gradient, to a dynamic system where fluid is continually moving through the loop of henle
- -Basically the result of the single effect combined with the fact that fluid is constantly moving through the loop of henle means that a concentration gradient is established where solute is very very concentrated at the bottom of the loop of henle (and in the medulla) and least concentrated at the top of the ascending limb
- -the vasa recta’s role is to pick up water on the descending side of the loop of henle and to pick up salt on the ascending side of the loop of henle
single effect
- -the process by which active transport of solute by pumps in the wall of the thick ascending loop of the Loop of Henle creates a concentration gradient
- -result is that solute is more highly concentrated outside the tubule (in the medulla) than inside the tubule (in the filtrate)
- -Water cannot diffuse out of the ascending loop so the gradient depends entirely on the active pumping of solutes. Water CAN diffuse out of the descending limb.
- -Once the moderate gradient is set up by the pumping of the ascending limb, water moves out of the descending limb and into the medulla until these two areas have equal concentrations
- -Net result of the single effect is diluting filtrate in the ascending limb while concentrating it in the medulla AND concentrating filtrate in the descending limb of the loop of Henle (b/c the descending limb is permeable to water whereas the ascending limb is not)
countercurrent exchanger
- -the vasa recta
- -allows the needs of the medulla to be met while avoiding disruption of the balance of solutes described above
urea loop
- -contributes to the osmotic gradient
- -we only use it when we are dehydrated
- -Urea loop kicks in when ADH is present
- -The collecting duct becomes more permeable to urea as you move down the duct
- -Urea diffuses out of collecting duct and into ascending limb
Afferent arteriole dilation
–Leads to more blood flow –> increased GFR
efferent arteriole constriction
- -generates back pressure in glomerulus –> increased GFR
- -decreased pressure in peritubular capillary –> increased reabsorption
myogenic mechanism
- -a property of the smooth muscle in the afferent arteriole
- -If blood pressure increases, the smooth muscle contracts to decrease GFR
tubuloglomerular feedback
- -a way of monitoring salt
- -renin angiotensin cascade
juxtaglomerular cells
- -make renin
- -distal tubule
distal tubule
- -where reabsorption of Na+ and Ca2+ occurs
- -secretion of K+, H+, HCO3-
Signals that result in the release of renin
- Decrease in sodium chloride in the distal tubule
- sympathetic nerve stimulation
- decrease in pressure in afferent arteriole
macula densa cells
- -keep track of sodium and chloride concentrations in the distal tubule
- -if sodium or chloride drops too low, it indicates that we are not getting enough filtration, so our GFR is too low
- -macula dense cells signal juxtaglomerular cells to release renin
angiotensinogen
- -made in the liver and circulates in the blood
- -activated by renin to angiotensin 1
renin
–activates angiotensinogen to angiotensin 1
ACE
- -angiotensin converting enzyme
- -converts angiotensin 1 to angiotensin 2 in the LUNGS
angiotensin 2
- -active component in the blood
- -vasoconstriction of efferent arteriole –> increased GFR
- -acts on hypothalamus to increase thirst, salt hunger, ADH
- -increase aldosterone secretion
aldosterone
- -triggered by low GFR
- -increased sodium retension
- -increase potassium excretion
- -Increases sodium channels on proximal tubule cell membrane
- -pumps sodium back into blood and brings potassium into cell using ATP pump; potassium can go into urine
- -Acts on mitochondria to increase ATP
- -We regulate aldosterone through renin and the renin-angiotensin cascade.
aldosterone secretion
- -occurs in response to renin-angiotensin cascade
- -also occurs in response to high levels of potassium, which the adrenal gland can sense directly
11BHSD2
- -converts cortisol to cortisone
- -the mineral corticoid receptor has a much lower affinity for cortisone. Since the mineral corticoid receptor also binds aldosterone, it is helpful to metabolize cortisol and keep it from binding mineral corticoid receptor
- -11BHSD2 allows us to maintain the mineral corticoid receptor as being primarily for aldosterone
Conn’s syndrome
- -adrenal gland makes too much aldosterone
- -results in an increase in sodium in the blood –> increased water retention –> increased blood volume –> increased blood pressure
- -results in decreased potassium levels inside the cell –> imports H+ into cell from the blood to balance charge –> basic blood pH
ANF
- -atrial naturitic factor
- -released by the HEART
- -target organs: kidney, adrenal gland, hypothalamus
- -causes naturiesis, an increase in sodium excretion and consequently an increase in urine output
- -mechanism: inhibits renin, decreases aldosterone, decreases ADH secretion
- -occurs in response to increased blood volume
secretion
- -occurs in proximal tubule
- -negatively charged organic ions come in to proximal tubule cell from blood and are exchanged with alpha-keto-glutarate
- -negatively charged organic ion is then secreted from proximal tubule cell out to lumen of kidney (into proximal tubule)
