-
what are the fuxns of the kidneys
- make urine
- regulate osmotic pressure of plasma and other extracellular fluids
- regulate the excretion of sodium and water
- regulate the individual concentration of numerous electrolytes
- regulate plasma bicarbonate concentration
- eliminate metabolic waste products
- produce hormones, proteolytic enzymes, paracrines, active D, and glucose
-
what is the outer part of the kidney
cortex
-
what is the inner part of the kidney
medulla
-
what is the basic unit of kidney structure and fuxn.
nephron
-
- A - Proximal Convoluted Tubule
- B - Loop of Henle
- C - Distal Convoluted Tubule
- D - Collecting Duct
-
what are the two types of nephrons
-
how do you id a cortical nephron
loop of Henle is short
-
how do you id a juxtamedullary nephron
long loop of henle
-
what is the ratio of cortical to juxtamedullary in humans
- 85% cortical
- 15% juxtamedullary
-
what are the major structures of a proximal tubular cell
- microvilli
- brush border
- tight junction
- basolateral cell membrane
- basement membrane
-
-
what is the flow of blood through the kidneys
- artery
- afferent arterioles
- glomerulus
- efferent arteriole
- peritubular capillaries
- vein
-
what is the vasa recta
capillaries that descend into and ascend from the medulla in parallel with the tubular structrures
-
where is blood flow/pressure highest in the nephron and why
glomerulus b/c filtration happens there
-
where is blood pressure/flow lowest and why
- peritubular capillaries for uptake of fluid reabsorbed by the tubules
- maintain higher osmotic pressure
-
what is the extrinsic mechanism in the kidney vessels
innervation by SNS releases NE that binds to alpha receptors causing vasoconstriction of the afferent arterioles
-
how are kidneys regulates without the sympathetic nerve fibers
intrinsic mechanisms/renal auto regulation
-
how does renal autoregulation fuxn
- if BP/flow increases, the afferent arterioles constrict
- if BP/flow decreases, the afferent arterioles dilate
-
how does changes in BP/flow affect filtration and excretion
changes in BP/flow = changes in filtration = big changes in excretion
-
what can happen if BP/flow remains high
permanent constriction of afferent arterioles leads to kidney failure
-
what is the juxtaglomerular apparatus
structure in the kidneys consisting of macula densa, extraglomerular mesangial cells, and granular cells, located in the region where the distal tubule touches afferent and efferent arterioles of its parent glomerulus
-
what are granular cells
cells embedded in the smooth muscle walls of afferent arterioles responsible for synthesizing and releasing renin
-
where is renin released
by the granular cells of the juxtaglomerular apparatus
-
what is the fuxn of renin
if BP/flow decreases to the kidneys then renin released end result is angiotensin II is formed that stims adrenal cortex to secrete aldosterone
-
what is the fuxn of aldosterone
stims Na reabsorption by the collecting ducts
-
what are macula densa cells
epithelial cells in the DCT
-
what are extraglomerular mesangial cells
messenger cells b/t the granular and macula densa cells
-
what is the tubuloglomerular feedback
NaCl composition of tubule fluid in DCT is relayed bact to afferent arterioles, changes in blood flow changes filtration
-
what is the fuxn of the nephron
form urine
-
what are the steps of urine formation
- glomerular filtration
- tubular reabsorption
- tubular secretion
-
what is glomerular filtration
- the first step in the formation of urine that is non-selective filtration of plasma
- allows passage of anything w/ mw <10,000 out of blood into lumen of Bowman's capsule
-
what is GFR
the # of ozs. filtered out of blood at given amt. of time
-
what is tubular reabsorption
process whereby substances are transferred out of the tubular fluid and returned to the peritubular capillaries; much more selective
-
where does the bulk of reabsorption occur
PCT
-
what is tubular secretion
mvmt of substances across tubule epithelium in a direction opposite to reabsorption
-
how much is excreted, filtered, and reabsorbed daily
- excrete 1.5 -2L/day
- filter 180 L/day
- reabsorb 178L/day
-
what is the fuxn of glomerular filtration
always takes out of blood into lumen of tubule
-
what is the glomerular filtration membrane
three layers capillary endothelium, glomerular basement membrane, podocyte cell layer
-
what is characteristic of the 1st layer of the glomerular filtration membrane
fenestrae pores of about 50 -100 nm
-
what is characteritic of the 2nd layer of the glomerular filtration membrane
meshwork of fine fibrils embedded in a gel-like matrix
-
how is the epithelium of the bowman's capsule
has slit pores
-
what does all three layers of the glomerular filtration membrane contain and what do they do
contain glycoproteins that are negatively charged, which repel negative charged plasma proteins
-
why is the measurement of GFR important
valuable indication of renal fuxn
-
what is necessary to measure GFR
a cmpd that is not secreted or reabsorbed, allows the amt filtered to = amt excreted
-
what cmpd is meets the requirements for GFR measurement
inulin
-
what is inulin
cmpd form onion/artichoke
-
what is the formula for clearance
C = (U * V)/ P
-
what is renal plasma clearance
the rate of excretion of a substance divided by its plasma concentration
-
what are the symbols in C=(U*V)/P
- u - urine concentration
- p - plasma concentration
- v - urine flow rate
-
what is the urine flow rate
2ml/ min
-
what is the clearance rate of inulin
120ml/min
-
what are the types of reabsorption
-
how much water do we excrete a day
2L/day
-
what is obligatory water loss
the amt of we need to excrete a day which is 400ml/day
-
what is actively reabsorbed
- glucose
- Na
- uric acid
- phosphate
-
how is glucose reabsorbed
- in PCT
- coupled transport tw/ Na out of lumen
- into PCT cell out basolateral membrane by facilitated diffusion
-
how is Na reabsorbed
- in PCT
- coupled to glucose, some amino acids, phosphate, Cl, and water
-
how is uric acid reabsorbed
in PCT
-
what causes gout
high plasma levels of uric acid
-
what is a symptom of gout
big toe pain b/c crystal build up in the vessels of that region
-
what is given to gout patients
uricosuric agent to lower uric acid levels in plasma by blocking reabsorption of uric acid
-
what is a uricosuric agent
Probenecid
-
what is passively reabsorbed
-
what is tubular secretion
out of peritubular capillaries into tubule fluid
-
why is tubular secretion necessary
supplements filtration process
-
-
what blocks reabsorption and secretion
probenecid
-
what is given to patients with penicillin and why
- probenecid
- to help patients that don't come back for next shot
- inhibits peniciliin secretion
-
what is related to Na reabsorption
H and K secretion by antiport transport
-
-
what causes acidified urine
H in urine
-
where is potassium secreted
early in collecting ducts
-
how is potassium secreted
assoc. w/ Na/K ATPase pump
-
what cmpd is necessary to measure total renal plasma flow
PAH
-
what happens to PAH
almost completely cleared from the blood in 1 pass thru
-
what is the total renal plasma flow rate
625 ml/min
-
why is Na reabsorption in the kidney important
- Na reabsorption causes water reabsorption
- Na reabsorption coupled to reabsorption of organic and inorganic ions
- Na reabsorption related to secretion of H and K
- 80% of energy supports Na reabsorption
-
where is 70% of water and Na reabsorbed
PCT
-
how is Na reabsorbed in the PCT
- enters lumen by Na/solute cotransporters
- exits by basolateral Na/K ATPase pumps
-
what drives Na into the blood
peritubular capillary Starling forces
-
how does peritubular capillary starling forces fuxn
tubules pressure is low do to the blood passing thru other vessels, favors the uptake of Na
-
how much Na and water is reabsorbed in the Loop of Henle
20% of Na and 10% of water
-
why is less water reabsorbed in the loop of henle
the ascending loop is impermeable to water
-
how is Na reabsorbed in the loop of henle
- reabsorption occurs through coupled transport of Na/K/Cl
- exits by Na/K ATPase pump from the basolateral membrane
-
why is less Na reabsorbed in the DCT and collecting ducts
b/c of tight epithelial
-
how much Na and water is reabsorbed in the DCT and collecting ducts
9% of Na and 19% of water
-
what controls the collecting ducts
hormones
-
what hormone stims Na reabsorption in the collecting duct
aldosterone
-
what is the reabsorption of Na in the collecting duct linked to
Na/K exchanger
-
what is the fuxn of ADH
increase collecting duct permeability, causes more water reabsorption
-
how does the lack of ADH affect Diabetes insipidus patients
- less water reabsorbed causing freguent urination
- 15-20L/day = polyuria
-
what does the bowman's capsule surround
glomerulus
-
what causes the activation renal autoregulation
BP/flow increases
-
what refers to the rate of excretion of a substance divided by its plasma concentration
renal plasma clearances
-
where does active of absorption of Na occur
PCT
-
what does aldosterone and ADH act to increase
reabsorption of Na and water
-
secretion
a. dependent upon Na/K ATPase pump
b. requires both the descending and ascending limbs
c. K is controlled by this process
d. urea shows this
e. is decreased with low MAP
K is controlled by this process
-
active reabsorption
a. dependent upon Na/K ATPase pump
b. requires both the descending and ascending limbs
c. K is controlled by this process
d. urea shows this
e. is decreased with low MAP
dependent upon Na/K ATPase pump
-
countercurrent multiplication
a. dependent upon Na/K ATPase pump
b. requires both the descending and ascending limbs
c. K is controlled by this process
d. urea shows this
e. is decreased with low MAP
requires both ascending and descending limbs
-
filtration
a. dependent upon Na/K ATPase pump
b. requires both the descending and ascending limbs
c. K is controlled by this process
d. urea shows this
e. is decreased with low MAP
is decreased with low MAP
-
passive reabsorption
a. dependent upon Na/K ATPase pump
b. requires both the descending and ascending limbs
c. K is controlled by this process
d. urea shows this
e. is decreased with low MAP
urea show this
-
principal
a. releases renin
b. has microvilli
c. responds to ADH
d. has fenestrae
e. has foot processes
responds to ADH
-
tubular epithelial
a. releases renin
b. has microvilli
c. responds to ADH
d. has fenestrae
e. has foot processes
has microvilli
-
glomerular capillary
a. releases renin
b. has microvilli
c. responds to ADH
d. has fenestrae
e. has foot processes
has fenestrae
-
granular
a. releases renin
b. has microvilli
c. responds to ADH
d. has fenestrae
e. has foot processes
releases renin
-
podocyte
a. releases renin
b. has microvilli
c. responds to ADH
d. has fenestrae
e. has foot processes
has foot processes
-
how much body water is contained in the ECF and ICF
- ECF - 1/3 of body water
- ICF - 2/3 of body water
-
what determines water distribution
osmotic pressure
-
what is the largest contributor to osmotic pressure of body fluids
electrolytes
-
what is osmotic pressure directly related to
osmolality
-
what is osmolality
total solute conc.
-
what is directly related to the amt of water in a compartment
the amt of solute in that compartment
-
what happens if solute conc. increases
osmolality increases
-
how does water move
- water moves from lower osmolality to higher osmolality
- water moves from lower osmotic pressure to higher OP
-
what is equal in humans
the OP of ECF and ICF
-
what determines the volume of water in the ECF
Na and its accompanying anions accounts for 90%
-
what determines the volume of water in ICF
K
-
what do kidneys have a major role in
balancing water, electrolytes, protons, and some organic cmpds.
-
what are the 2 mechanisms of water balance
hormonal and thirst
-
how does hormonal water balance work
ADH controls renal excretion of water
-
how does the thirst mechanism of water balance work
- osmoreceptors in the hypothalamus detect cellular hydration
- signal cerebral cortex
- you feel thirsty
-
what may also stim thirst
- blood vol receptors in CV system and kidneys
- causes hypovolemia and
- you fell thirsty
-
what is responsible for 95% of total Na output
urine
-
what is closely related to Na balance
ECF
-
what controls Na excretion
negative feedback system
-
what mechanisms responds to changes in ECF vol
- GFR
- plasma aldosterone levels
- renal SNS activity
- Plasma ANP
- peritubular capillary starling forces
- intrarenal blood flow distribution
-
how does GFR respond to changes in ECF vol
increase of ECF <increase of GFR < increase in sodium excretion
-
how does aldosterone react to changes in ECF vol
decrease ECF vol <renin release<leads to angiotensin II< aldosterone< Na reabsorption
-
how does ECF vol affect renal sns activity
decrease of renal sodium excretion
-
how does ECF vol affect ANP
increase Na excretion
-
how does ECF vol affect peritubular capillary starling forces
increase Na excretion with increase in hydrostatic pressure or decrease of colloid osmotic pressure
-
how does ECF vol affect intrarenal blood flow
|
|