Tubular Reabsorption & Secretion Flashcards
Paracellular Path of reabsorption
Filtrate travels from the LUMEN through the Intercellular Space into the capillary
Transcellular Path or Reabsorption
Filtrate travels from the LUMEN through the CELL and then to the capillary
Aquaporin-1 location?
WIDESPREAD
Including the Renal tubules
Aquaporin-2 location?
- Present in APICAL membranes of COLLECTING Tubule cells
- Controlled by ADH
Aquaporin-3 location?
Present in BASOLATERAL membranes membranes of Collecting Tubule cells
Role of ATPases in the Nephron?
- Establish IONIC gradient across nephron
- Gradients drive reabsorption/secretion of many other solutes
- Transported by SECONDARY active transport
Most Primary Active Transporters have what characteristic?
ATPase attached to the name
Sodium enters the cell via ____ and exits the cell via ____.
Diffusion
Active Transport Pumps
Ion gradient determines what pathway for ____ concentration.
Sodium
What are examples of SECONDARY active transport?
- Reabsorption of GLUCOSE by the Renal tubule
2. Reabsorption of AA by the Renal Tubule
Sodium-glucose co transporter on the _______ of the ______ tubule.
- Brush Border
- Proximal
SGLT2
- Reabsorbs 90% of Glucose in EARLY Proximal Tubule
SGLT1
Reabsorbs 10% of Glucose in the LATE Proximal Tubule
Substances that are ACTIVELY secreted into the Renal Tubules.
- Creatinine
2. Para-aminohippuric Acid
PAHA
Transport max for glucose reabsorption
VS
Filtered Load for glucose
375mg/min
VS
125mg/min
Reasons that some passively reabsorbed substances do not have a Transport Maximum?
- Diffusion determined by E-chemical gradient
- Permeability of membrane
- TIME that the fluid remains in the tubule
Excretion will occur when [BG] exceeds how much?
250mg/min
Filtered load for glucose
- What you CONSUME is what you FILTER
- LINEAR on a graph
Rate of transport depends on what?
- E-Chemical gradient
- TIME in the tubule
- FLOW RATE
Proximal Tubule
- Highly metabolic w/ LARGE # of Mitochondria
- Extensive brush borders
- Extensive IC and Basal channels on interstitial surfaces
Purpose of a brush border?
To increase SURFACE AREA
What does the Proximal Tubule Reabsorb
- 65% of Filtered
- Na+
- Cl-
- Bicarbonate
- K+
“NaCl BiK (Nickel back)”
- ALL filtered glucose and AA
What is being SECRETED into the Proximal tubules?
- H+
- Organic Acids
- Bases
Anything with a Fluid/Plasma [ ] ABOVE 1 will be _____.
Excreted
Anything with a Fluid/Plasma [ ] BELOW 1 will be _____.
Almost completely Reabsorbed
Sodium reabsorption in the FIRST half of the Proximal tubule.
Via CO-transport along with
- glucose
- AA
- other Solutes
Sodium reabsorption in the SECOND half of the Proximal tubule.
Mainly with CHLORINE ions
Electrochemical gradient of the Tubular Lumen
-3 mV
Luminal [Na+]
140 mOsm
Cytoplasmic [Na+]
30 mOsm
Most Na+ entry is via the ____ with _____ Ions.
- ANTIPORT
- H+
H+ + Bicarbonate = ?
Carbonic Acid
CO2 + H2O =
Carbonic Acid
Descending segment of the Loop of Henle
- Highly permeable to WATER
- Moderately permeable to Most solutes
(Urea and Sodium) - Reabsorbs about 20% of filtered water
The defending limb reabsorbs about ___ of filtered water.
20%
Thin ascending segment of the loop of Henle.
IMPERMEABLE to Water
Thick ascending loop of Henle
- Impermeable to water
- Na/K Pump pumps K+ into the cell against [ ] gradient
- Co-transporter of
(1 Na+, 2 Cl-, 1 K1+) - Slight BACK Leak of K+ into Lumen
What does the slight back leak of K+ into the lumen of the thick ascending limb do to the lumen?
- Creates a POSITIVE charge of 8+ mV
- Forces Mg++ and Ca++ to diffuse through tubular lumen through PARA- cellular space of the IF
The first portions of the Distal Tubule form what?
The Macula Densa
Distal Tubule
- Impermeable to WATER
- Impermeable to UREA
- Highly Convoluted
- Similar to the THICK ascending limb
(They are attached to each other)
Where are Principal Cells Located?
- Located at the LATE Distal Tubule/ Cortical Collecting tube
Role of Principle cells?
- Reabsorbs Na+ and Water
- Secreted K+ into Lumen
- Uses Na/K pump
- Primary site of K+ diuretics
Intercalated cells in the Late Distal Tubule/ Cortical Collecting tube
- Reabsorbs K+ from the Lumen
- Reabsorbs Bicarbonate
- Secretes H+ into tubular lumen
The histology of the Medullary Collecting Duct
- Epithelial cells are cuboidal
- Smooth surface
- Few Mitochondria
Medullary Collecting Duct
- Permeable to Water
(Controlled by ADH) - Permeable to UREA
(Via transporters) - Capable of secreting H+ against a LARGE [ ] gradeint
Aldosterone
- Source
- Fxn
- Site of action
- Adrenal cortex
- Increase SODIUM reabsorption & Increase POTASSIUM secretion.
- On the Principal cells in the Cortical collecting duct
Addison’s Disease
- Absence of Aldosterone
- Marked loss of Na+ and accumulation of K+
Conn’s Syndrome
Hypersecretion of Aldosterone
Angiotensin II
- Fxn
- Increase Na+ and Water reabsorption
- Returns BLOOD PRESSURE and EC volume toward normal
Angiotensin II
- Effects
- Stimulates ALDOSTERONE secretion
- Constricts EFFERENT arterioles
- Directly stimulates Na+ reabsorption in the
- PROXIMAL tubule
- Loops of Henle
- Distal Tubule
- Collecting ducts
ADH
- Source
- Fxn
- Effects
- Aka Vasopressin
- Secreted from POSTERIOR pituitary
- Increase Water reabsorption
- Increase the formation of cAMP
(Makes the Tubule LEAKY)
ANP
- Found in Cardiac atrial cells
- Responds to DISTENSION
- Inhibits the REABSORPTION of Na+ and water
PTH
- Found in the Parathyroid gland
- Increases CALCIUM reabsorption
Renal clearance of a substance
- The volume of plasma that is completely cleared of the substance by the kidneys per unit TIME
- units of mL/min
Renal Clearance Equation
Cs x Ps = Us x V
- Cs = (Us x V)/(Ps)
Cs - Clearance rate of substance “s”
Ps - [Plasma] of substance “s”
Us - [Urine] of substance “s”
V - Urine volume
GFR equation
GFR x Ps = Us x V
- GFR = (Us x V)/(Ps)
Ps - [Plasma] of substance “s”
Us - [Urine] of substance “s”
V - Urine volume
SIMILAR to RENAL CLEARANCE
