Topic 1 Part A Flashcards
Excretion= [formula]
Filtration–Reabsorption + Secretion
Filtration occurs in the
glomerulus
Reabsorption and secretion occur in the
Proximal tubule
loop of Henle;
distal tubule
collecting tubule
Filtration rate= [formula]
GFR x Plasma concentration
- -Glucose concentration = 1 g/L
- -GFR = 180 L/day
- -Filtration rate = (1 g/L) x ( 180 L/day) = 180 g/day
Kidneys has independent control over
exertion rate by changing appropriate reabsorption rate
Tubular Reabsorption-Mechanisms (4)
- From tubular lumen into tubular cells
- From tubular lumen into tubular interstitial space
- From interior of cell into tubular interstitial space
- From interstitial space into peritubular capillary
From tubular lumen into tubular cells is a
transcellular path
From tubular lumen into tubular interstitial space is a
paracellular path
From interstitial space into peritubular capillary is driven by
capillary filtration forces [bulk flow]–net movement into the capillaries
Tubular Reabsorption–Mechanisms (A): involves both
active and passive mechanisms
Tubular Reabsorption–Mechanisms (A): primary active transport (4)
Na-K ATPase
Hydrogen ATPase
H-K ATPase
Ca ATPase
Tubular Reabsorption–Mechanisms (A): Secondary active transport/co-transport (2)
Sodium-glucose
Sodium-amino acids
Tubular Reabsorption–Mechanisms (B): Secondary active/co-transport (1)
Sodium-hydrogen
Tubular Reabsorption–Mechanisms (B): Pinocytosis (requires energy) =
Proteins–once in cell broken down to component amino acids and amino acids reabsorbed
Tubular Reabsorption–Mechanisms (B): Passive (2)
Osmotic movement of water
Bulk flow into peritubular capillaries
Reabsorption rate % for glucose
100%
Reabsorption rate % for Bicarb
> 99.99%
Reabsorption rate % for Sodium
99.4%
Reabsorption rate % for Chloride
99.1%
Reabsorption rate % for Potassium
87.8%
Reabsorption rate % for Urea
50%
Reabsorption rate % for Creatinine
0%
Sodium Reabsorption (A): Sodium pumped out of tubular cells into the interstitial spaces and then…
Potassium pumped into tubular cells
- -Na-K ATPase on basolateral sides of tubular epithelial cells
- -Creates membrane potential-70 mV
Sodium Reabsorption (A): Sodium follows concentration gradient from tubular lumen into the
tubular cells (diffusion down concentration & electrical gradients) --Brush board of proximal tubule luminal membrane creates huge surface area for diffusion (20x increase)
Sodium Reabsorption (B): Sodium reabsorption also enhanced by
carrier proteins through luminal membrane
–Co-transport & counter-transport proteins
Sodium Reabsorption (B): Sodium quickly moves (along with water) from interstitial fluid into
peritubular capillary
Glucose Reabsorption (A): Co-transport mechanism tied to sodium gradient from \_\_\_\_\_\_\_ to \_\_\_\_\_\_\_ --So efficient that usually removes all filtered \_\_\_\_\_\_
Co-transport mechanism tied to sodium gradient from tubular lumen to interior of tubular cells
–So efficient that usually removes all filtered
glucose
Glucose Reabsorption (A):
Two luminal transporters– _____ and _____
– ____% glucose reabsorbed via _____ in early part of proximal tubule
– ____% reabsorbed in later part of proximal tubule via ____
Two luminal transporters–SGLT2 and SGLT1
- -90% glucose reabsorbed via SGLT2 in early part of proximal tubule
- -10% reabsorbed in later part of proximal tubule via SGLT1
Glucose Reabsorption (B):
Two basolateral glucose transporters– _____ and _____
–______ transport down glucose concentration gradient
– ______ early stages of proximal tubule with ____ in the later stages
Two basolateral glucose transporters–GLUT2 and GLUT1
- -Passive facilitated transport down glucose concentration gradient
- -GLUT2 early stages of proximal tubule with GLUT1 in the later stages
Glucose Reabsorption (B): Bulk flow moves glucose from \_\_\_\_\_\_\_\_ into the \_\_\_\_\_
Bulk flow moves glucose from interstitial spaces into the peritubular capillaries
Amino Acid Reabsorption:
Co-transport mechanism tied to sodium gradient from ________ to __________
–So efficient that usually removes all filtered ______
Co-transport mechanism tied to sodium gradient from tubular lumen to interior of tubular cells
–So efficient that usually removes all filtered amino
Amino Acid Reabsorption:
______ system pumps the amino acids into the cells
Luminal co-transporter
Amino Acid Reabsorption:
Amino acids diffuse out of the cells into the _______
interstitial spaces
Amino Acid Reabsorption:
Bulk flow moves the amino acids from ____ into the ____
interstitial spaces into the peritubular capillaries
Hydrogen Secretion
- -Counter-transport mechanism tied to sodium gradient from ______ to _______
- -Sodium-hydrogen exchanger is located in brush boarder of the ________
- -Counter-transport mechanism tied to sodium gradient from tubular lumen to interior of tubular cells
- -Sodium-hydrogen exchanger is located in brush boarder of the luminal membrane
Maximum Level of Active Reabsorption:
Transport maximum: Max amount of solute that
can be reabsorbed (transport max transport)
–Occurs when
tubular load (amount of solute delivered to tubule) exceeds transport capacity of carrier proteins
Maximum Level of Active Reabsorption: Filtered load versus transport maximum --Glucose Tmax = \_\_\_\_\_\_\_ --Glucose filtered load = GFR x [Glu] = 125 mls/min x 1 mg/ml = \_\_\_\_\_
–Glucose Tmax = 375 mg/min
–Glucose filtered load = GFR x [Glu] = 125 mls/min x 1
mg/ml = 125 mg/min
Maximum Level of Active Reabsorption: Threshold conc (approx. \_\_\_\_ mg/dL) is concentration where glucose first appears in urine
Threshold conc (approx. 200 mg/dL) is concentration where glucose first appears in urine
–Less than T max because each individual nephron is
different–chart represents action of both kidneys so
Tmax reached when ALL nephrons have reached their
max
Transport max: glucose=
375 mg/min
Transport max: amino acids=
1.5 mM/min
Transport max: plasma protein=
30 mg/min
Transport max: creatinine (actively secreted)=
16 mg/min
Transport max: para-aminohippuric acid (activley secreted)=
80 mg/min
Two excretion rates: #1
Before secretion Tmax is reached, so the amount excreted is the sum amount of…
filtered and amount secreted (steepest slope of excretion curve)
Two excretion rates: #2
After secretion Tmax is reached, the rate of excretion…
parallels filtration rate (slope of excretion curve matches slope of filtration curve)
Gradient-Time Transport:
Solute that is reabsorbed _______ and some ______
reabsorbed solute may not show maximum rate of
transport
Solute that is reabsorbed passively and some actively
reabsorbed solute may not show maximum rate of
transport
Gradient-Time Transport:
Rate of transport depends on: (4)
Electrochemical gradient for solute
Membrane permeability for solute
Time fluid containing solute remains in tubule
Transport rate inversely related tubular flow rate
Sodium Reabsorption: Proximal Tubule
Sodium does not show a transport maximum even though it is
actively reabsorbed
Sodium Reabsorption: Proximal Tubule
Capacity of _____ usually much greater than rate of net ______
-Significant amount of transported sodium leaks back into the ______
–Permeability of _______ between cells
–Forces controlling bulk flow of water & solute into ____
Capacity of Na-K ATPase usually much greater than rate of net sodium reabsorption
- Significant amount of transported sodium leaks back into the tubular lumen
- -Permeability of tight junctions between cells
- -Forces controlling bulk flow of water & solute into peritubular capillaries
Sodium Reabsorption: Proximal Tubule
As plasma concentration of sodium ______, sodium
concentration in proximal tubule ______ and sodium
reabsorption _______
As plasma concentration of sodium increases, sodium
concentration in proximal tubule increases and sodium
reabsorption increases
Sodium Reabsorption: Proximal Tubule
A decrease in tubular flow rate will also increase
sodium reabsorption
Sodium Reabsorption: Distal Tubule
Sodium reabsorption shows classic
tubular max transport
Sodium Reabsorption: Distal Tubule
Capacity of Na-K ATPase does not exceed rate of _____
-Minimal back leak of ____ into tubular _____
-Tighter (less permeable tight junctions) ____ transport of much smaller amount of ____
Capacity of Na-K ATPase does not exceed rate of net sodium reabsorption
- Minimal back leak of sodium into tubular lumen
- Tighter (less permeable tight junctions) coupled transport of much smaller amount of sodium
Sodium Reabsorption: Distal Tubule
Aldosterone increases the
Tmax level
Passive Reabsorption: Water
Driven by _______ created by movement of solute (mainly sodium) from ______ to the _______
Driven by osmotic differences created by movement of solute (mainly sodium) from tubular lumen to the tubular interstitial spaces
Passive Reabsorption: Water
Affected by cellular ______ (cell membranes and tight junctions)
-Increased permeability means increased _____ and decreased _______
Affected by cellular permeability (cell membranes and tight junctions)
-Increased permeability means increased reabsorption and decreased water excretion
Passive Reabsorption: Water
Permeability of proximal tubule
high
Passive Reabsorption: Water
Permeability of Loop of Henle (ascending loop):
low
Passive Reabsorption: Water
Permeability of Distal tubule / Collecting tubules / Collecting ducts
variable
Passive Reabsorption: Water: Proximal tubule
- ____ movement so overall solute gradient across cell is ____
- Solvent drag: water carries significant amount of (5) because of _____ permeability
- Rapid movement so overall solute gradient across cell is minimal
- Solvent drag: water carries significant amount of sodium, chloride, potassium, calcium, magnesium because of high permeability
Passive Reabsorption: Water: Loop of Henle (ascending loop):____ movement of water even though there is a large ________
Little movement of water even though there is a large osmotic gradient
Passive Reabsorption: Water: Distal tubule / Collecting tubules / Collecting ducts:
Cellular permeability depends on presence of ______
-Permeability _____ related to ______
-Changing water permeability only affects amount of water reabsorbed not the amount of ____ due to ____ solute permeability
Cellular permeability depends on presence of antidiuretic hormone (ADH)
- Permeability directly related to [ADH]
- Changing water permeability only affects amount of water reabsorbed not the amount of solute due to low solute permeability
Passive Reabsorption: Chloride & Urea
Sodium diffusion into cells creates
electrical gradient that pulls negative chloride ions into the cell
Passive Reabsorption: Chloride & Urea
Movement of water into cells concentrates
chloride creating concentration gradient into cell
Passive Reabsorption: Chloride & Urea
Chloride also linked to co-transport mechanism with
sodium across the luminal membrane
Passive Reabsorption: Chloride & Urea
Movement of water into cells concentrates urea creating
concentration gradient into cell
-but urea not nearly as permeable as water
Passive Reabsorption: Chloride & Urea
Inner medullary collecting duct contains specific
passive urea transports which facilitates reabsorption
Passive Reabsorption: Chloride & Urea
Only ___% of filtered urea is reabsorbed
50%
