packet 24 Flashcards
Nephrons and collecting ducts perform 3 basic processes
micro essay
- glomerular filtration
- tubular reapbsorption
- tubular secretion
a portion of the blood plasma is filtered into the kidney
–happens one time
glomerular filtration
water & useful substances are reabsorbed into the blood
–happens over and over
tubular reabsorption
wastes are removed from the blood & secreted into urine
–happens over and over
tubular secretion
rate of secretion =
filtration + secretion - reabsorption
Blood pressure produces ____
Filtration fraction is 20% of plasma
48 Gallons/dayfiltrate reabsorbedto 1-2 qt. urine
glomerular filtration
glomerular Filtering capacityenhanced by:
maybe micro essay
- thinness of membrane & large surface area of glomerular capillaries
- glomerular capillary BP is high due to small size of efferent arteriole
Filtration membrane does what 3 things?
***micro essay?
#1 Stops all cells and platelets #2 Stops large plasma proteins #3 Stops medium-sized proteins, not small ones
endothelial fenestration stops…
all cells and platelets
basal lamina stops…
large plasma proteins
slit membrane stops…
medium-sized proteins, not small ones
total pressure that promotes filtration
= 10mm Hg
net filtration pressure
BP increases to above 70 =
BP that decreases to lower than 40 =
increase filtration
decrease filtration
low BP and low filtration =
no filtration
Amount of filtrate formed in all renal corpuscles of both kidneys / minute
–average adult male rate
is 125 mL/min
Glomerular Filtration Rate
Homeostasis requires GFR that is constant
–if too high…
substances are lost due to the speed of fluid passage through nephron
Homeostasis requires GFR that is constant
–if too low…
waste products may not be removed from the body
Changes in net filtration pressure affects GFR by
--filtration stops if GBHP drops to 45mm Hg --functions normally with mean arterial pressures 80-180
Mechanisms that maintain a constant GFR despite changes in arterial BP
—myogenic mechanism
—tubuloglomerular
feedback
Renal Autoregulation of GFR
- systemic increases in BP, stretch the afferent arteriole
2. smooth muscle contraction reduces the diameter of the arteriole returning the GFR to its previous level in seconds
myogenic mechanism
- elevated systemic BP raises the GFR so that fluid flows too rapidly through the renal tubule & Na+, Cl- and water are not reabsorbed
- macula densa detects that difference & releases a vasoconstrictor from the juxtaglomerular apparatus
- afferent arterioles constrict & reduce GFR
tubuloglomerular feedback
Blood vessels of the kidney are supplied by sympathetic fibers that cause vasoconstriction of afferent arterioles
At rest, renal BV are maximally dilated because sympathetic activity is minimal
–renal autoregulation
prevails
With moderate sympathetic stimulation, both afferent & efferent arterioles constrict equally
—decreasing GFR equally
With extreme sympathetic stimulation (exercise or hemorrhage), vasoconstriction of afferent arterioles reduces GFR
—lowers urine output &
permits blood flow to
other tissues
neural regulation of GFR
hormonal regulation of GFR
- atrial natriuretic peptide (ANP)
2. Angiotensin II
increases GFR
---stretching of the atria
that occurs with an
increase in blood
volume causes
hormonal release
--relaxes glomerular
mesangial cells
increasing capillary
surface area and
increasing GFRatrial natriurectic peptide
ANP
reduces GFR
potent vasoconstrictor that narrows both afferent & efferent arterioles reducing GFR
Angiotensin II
Normal GFR is so high that volume of filtrate in capsular space in half an hour is greater than the total plasma volume
Nephron must reabsorb 99% of the filtrate
- -PCT with their microvilli do most of work with rest of nephron doing just the fine-tuning
- -solutes reabsorbed by active & passive processes
- -water follows by osmosis
- -small proteins by pinocytosis
tubular reabsorption and secretion
Important function of nephron is tubular secretion
transfer of materials from blood into tubular fluid
- –helps control blood pH because of secretion of H+
- –helps eliminate certain substances (NH4+, creatinine, K+)
reabsorption routes
paracellular
transcellular
50% of reabsorbed materialmoves between cells bydiffusion in some parts oftubule
Paracellular reabsorption
material moves throughboth the apical and basalmembranes of the tubulecell by active transport
Transcellular reabsorption
water is only reabsorbed by
water follows salt
osmosis
Reabsorption of Na+ is important because
- several transport systems exist to reabsorb Na+
2. Na+/K+ ATPase pumps sodium from tubule cell cytosol through the basolateral membrane only
Renal symporters can not reabsorb glucose fast enough if blood glucose level is above 200 mg/mL
—some glucose remains in the urine
-Common cause is diabetes mellitis because insulin activity is deficient and blood sugar is too high
glucosuria
–Na+ symporters help reabsorb materials from the tubular filtrate
–Glucose, amino acids, lactic acid, water-soluble vitamins and other nutrients are completely reabsorbed in the first half
–Intracellular sodium levels are kept low due to Na+/K+ pump
Reabsorption in the Prox. Con. Tubule
