Sodium / Water / Urea

Primary Active Transport

Movement against electrochemical gradient via ATP hydrolysis

Secondary Active Transport

“Downhill” movement of one substance provides energy for “uphill” movement of another substance

Paracellular

Renal epithelia dependent on “tightness” of tight junctions (H20, Cl-, urea)

Transcellular

Renal epithelia dependent on presence of membrane transport systems (i.e. Na2+, Ca2+, glucose)

Luminal, cytosol, basolateral, interstitial, capillary

5 barriers for tubular renal absorption of substance

1. __ membrane (Deep)

2. Cell’s __

3. __ cell membrane

4. __ fluid

5. __ wall (Superficial)

Salts, water, excretion, reabsorption

The Kidney reabsorbs __ (i.e. sodium), and __ (liquid) passively follows

• Membrane must be permeable to water

•  Diuretic medications - Increase water __ by decreasing sodium __

Na+, urea, interstitium, out

In order to get H2O reabsorbed

• Need __ (ion) and __ (salt) gradient in the __

• High Na+ and urea draw H2O __ (in/out) of renal tubule

67%

Proximal convoluted tubule Na+ percentage (in nephron)

25%

Thick ascending limb - LOHen Na+ percentage (in nephron)

5, 3%

Distal convoluted tubule Na+ percentages (in nephron)

Less than 1(%)

Excretion of Na+ percentage from nephron

UT1

Urea protein channels allowing for movement of urea

High ADH

ADH condition where there is less water in nephron as there is net reabsorption of water to body

Ascending, distal, concentrated

High ADH

• Only the __ loop of Henle up to the __ convoluted tubule is impermeable to water

• Urine is __ (concentrated/dilute)

Low ADH

ADH condition where there is more water in the nephron than to body

Ascending, dilute

Low ADH

• Everything past the __ loop of henle is impermeable to water

• Urine is __ (concentrated/dilute)

1.5, 144

• 99% plasma ultra-filtrate is reabsorbed

  • Only __ L of urine produced daily

  • With GFR of 100, __ L  a day is filtered

67, H2O, urea, iso

Proximal convoluted tubule (PCT)

• __% of Na+ is reabsorbed and brings many other important solutes with it

• 65% of water follows Na+ as proximal tubule is permeable to __

• __ (Solute) follows water out

• Overall is an __-osmotic process

Na/K, HCO3-, H+, HCO3-

What transporter generates the driving gradient for most reabsorption in the proximal convoluted tubule?

• The __ pump

• Body reabsorbs __ by secreting _ ions and form CO2 + H2O

• Moves into cells and is converted back to __ via Na/K pump

Reabsorbed, ascending, urea, thick

Loop of Henle’s Thin Descending and Thick Ascending Tubules

• Water passively __ (reabsorbed/filtered) in thin descending, but entire __ limb is impermeable to water

• Some __ is secreted into thin descending limb and thick ascending limb

• However, __ ascending limb is impermeable to urea

Na+, countercurrent, Ca2+, Mg2+

Loop of Henle’s Thin Descending and Thick Ascending Tubules

• __ reabsorbed in thick ascending limb

• Na+ reabsorption when H2O is unable to follow is crucial to forming the __ gradient

• __ and __ (ions) reabsorption is largely dependent on electrical gradient between lumen and interstitial space

Countercurrent gradient

Electrical gradient between lumen and interstitial space

Na-2Cl-K, 25

The __ transporter is the primary method of Na+ reabsorption in thick ascending lumen, covering __% of Na+

5, H2O, urea

Distal Convoluted Tubule + Collecting Duct

• _-10% of Na+ reabsorbed in early distal tubule, late distal tubule, and collecting tubule

• __ and __ are not reabsorbed unless ADH is present

ADH, Aquaporin, ADH, UT

• H2O not reabsorbed unless __ is present

  • — upregulates __ channels → Increase permeability of H2O

• Urea is not reabsorbed unless __ is present

  • — upregulates __ (urea) channels → Increase permeability of urea

Thiazide

Medication keeps sodium and water in lumen of nephron --> allows for water excretion

Na+, K+, hypokalemia

“Potassium wasting effect”

• Extra __ concentration enters cell more → __ leaves frequently

• Potential of __emia

Potassium sparing diuretic

Medication where Na+ less frequently enters cell, meaning K+ leaves less frequently from cell

Vasa recta, solute, H2O, solute, 350

Interstitium

• __ __ necessary for reabsorbing H2O and solutes from interstitium

• With stable intake of Na+ and H2O, extra __ and __ entering interstitium is removed via Vasa recta

• More __ (solute/water) is typically re-absorbed

  • giving __ mOsm/L of blood leaving vasa recta

Counter current multiplication

The countercurrent gradient along with permeability allows for reabsorption of H2O and excretion of concentrated urine

Inhibiting, lower, less, more

Most diuretics act by __ (promoting/inhibiting) salt reabsorption into interstitium

• Makes the gradient __ (higher/lower)

• __ (more/less) H2O reabsorbed and __ H2O excreted

Natremia, water

Clinically observable hyper/hypo__ is in direct relation of too much or too little __

Na/H+, SNS, Na+, reabsorption

Na+ Regulation

• Sympathetic nervous system and Angiotensin II increase __ exchange

  • Decreased __ activity → Less __ (ion) present

  • Less water __ (excretion/reabsorption)

Hypothalamic, thirst, ADH, thick, baroreceptors, constriction

Osmolarity + Blood pressure for Water Regulation

• __ osmolarity receptors

• Control “__”

• __ (Hormone) to reabsorb more H2O

  • Increases Na+ reabsorption in the __ (thick/thin) ascending limb

• BP - use __ (receptors) and act by vaso__

V1, constriction, V2, reabsorption

Vasopressin Receptors

• __ promotes __ of blood vessels

  • Increased systemic vascular resistance

• __ promotes __ of kidneys

  • Increased blood volume

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

• Increased ADH that is abnormal → Excess water retention

• Causes - Lung cancers, pulmonary issues, intracranial issues, trauma, drugs

Restrict, hyper, V2 antagonists

Tx of SIADH -

• Fluid __ patient and administer __tonic solutions

• Medication choice: __ __