test 8 part 2

Question 1

Reabsorption – Proximal Tubule

Answer 1

 65% of filtered load of sodium & water reabsorbed

 Little less percentage for chloride

Question 2

Proximal Tubule Cellular Ultrastructure

Answer 2

• Contain large number of mitochondria to support extensive active transport activity
• Luminal (apical) brush border
   Provides huge surface area for rapid diffusion
   Contains extensive number of protein carrier molecules
• Basolateral border
   Contains extensive number channels in between cells providing huge surface area
   Contains extensive amount of N-K ATPase

Question 3

First half of tubule of proximal reabsorption

Answer 3

 Extensive co-transport of sodium with glucose and amino acids
 Sodium reabsorption carries glucose, bicarb, organic ions leaving chloride resulting in increasing [Cl-]
 105 mEq/L increases to 140 mEq/L

Question 4

Second half of tubule of proximal reabsorption

Answer 4

 Most glucose & amino acids have been reabsorbed –
 Electrochemical gradient
 Sodium reabsorption drives chloride reabsorption
 High chloride concentration favors chloride diffusion

Question 5

Sodium concentrations thorugh the tubule vs quantity

Answer 5

 Total quantity of sodium in tubule changes but concentration does not change because water reabsorption matches sodium reabsorption
 Total osmolarity does not change for the same reason
 Proximal tubule highly permeable to water

Question 6

Glucose & amino acid concentrations through proximal tubule

Answer 6

• decrease due to extensive reabsorption

Question 7

Creatinine & Urea concentrations through the proximal tubule

Answer 7

• concentrated because they are not reabsorbed

Question 8

Total amount of Na+, Cl-, HCO3-,glucose, amino acids in tubule

Answer 8

decreases

Question 9

Total amount of creatinine and urea in tubule

Answer 9

does not change

Question 10

Secretion of Organic Acids & Bases

Answer 10

 Many end products of metabolism are secreted by proximal tubule
catecholamines
 Many drugs & toxins secreted
 Para-aminohippuric acid also secreted
 90% of PAH in renal blood flow is removed
-PAH can be used to determine renal blood flow

Question 11

Functional Segments of the Loop of henle

Answer 11

1. Thin descending segment
2. Thin ascending segment
3. Thick ascending segment

Question 12

Thin Descending & Ascending Segment

Answer 12

 Thin epithelial membrane
 No brush border
 Few mitochondria
 Minimal metabolic level

Question 13

Thin Descending Segment

Answer 13

 Highly permeable to water
 Moderately permeable to most solute
 Allows diffusion of water and solutes (No active reabsorption)
 20% of water reabsorption occurs in the loop of Henle

Question 14

Thick Ascending Segment

Answer 14

 Thin and thick ascending segment impermeable to water (lumen is hypo-osmotic)
 Part of mechanism for concentrating urine
 Thick epithelial cells with high concentration of mitochondria
 High level of metabolic activity
 Able to reabsorb sodium, chloride, & potassium (Approx 25% of filtered load)
 Also reabsorbs calcium, bicarb, and magnesium

Question 15

Thick Ascending Segment: Sodium Reabsorption

Answer 15

 Driven by N-K ATPase in basolateral border of tubule cells
 Two transport mechanisms move sodium from tubular lumen
 1 Na-2Cl-1K co-transport mechanism (all move into the cell) (PRIMARY MEANS OF MOVING SODIUM OUT OF LUMEN INTO TUBULAR CELLS)
 Na-H counter-transport mechanism

Question 16

Loop Diuretics

Answer 16

 Loop diuretics inhibit the action of the 1Na- 2Cl-1K co-transport mechanism
- Less sodium reabsorption
 Less water reabsorption in later segments of the nephron
 Less potassium reabsorption with potential loss of potassium

Question 17

Paracellular reabsorption of what solutes

Answer 17

 Sodium
 Potassium
 Magnesium
 Calcium

Question 18

Na-Cl-K co-transport mechanism

Answer 18

 Isoelectric BUT K able to diffuse back into lumen via potassium channels creating +8 mV positive charge in tubule lumen

Question 19

Early Distal Tubule

Answer 19

 Macula densa forms first part of tubule
 Provides feedback control for GFR and blood flow (for its own nephron)
 Solute reabsorption: Yes
 Water reabsorption: NO
 Diluting segment of distal tubule
 5% of filtered load for sodium & chloride reabsorbed here
 Driven by Na-K ATPase in basolateral border of tubular cells
 Na-Cl co-transport mechanism moves Na+ and Cl- into cell down [Na+] gradient
 Chloride diffuses out of cell via chloride specific channels

Question 20

Thiazide diuretics

Answer 20

• inhibit this Na-Cl co-transport mechanism in the early distal tubule
   Reduces sodium and chloride reabsorption
   Ultimately reduces water reabsorption in later segments of nephron

Question 21

Functional Characteristics – Late Distal Tubule and Cortical Collecting Tubule

Answer 21

 Membranes impermeable to urea
 Some reabsorption of urea will occur in medullary collecting ducts
 Sodium reabsorption and potassium secretion controlled by various hormones especially aldosterone
 Able to secrete hydrogen ions against large concentration gradient (1000:1)
 Proximal tubule moves hydrogen ions against small gradient (4:1 to 10:1)
 Water permeability controlled by concentration of antidiuretic hormone (ADH, aka vasopressin)
 No ADH - no water permeability – excrete dilute urine

Question 22

Principal cells

Answer 22

 Reabsorb sodium & water

 Secrete potassium

Question 23

Intercalated cells

Answer 23

 Reabsorb potassium

 Secrete hydrogen

Question 24

two types of cells in the Late Distal Tubule and Cortical Collectin Tubule

Answer 24

 Principal cells

 Intercalated cells

Question 25

Principal Cell Activity

Answer 25

 Na-K ATPase in basolateral borders of tubule cells drives activity  Sodium follows concentration gradient into the cell through Na specific channels  Potassium follows concentration gradient out of cell into tubular lumen through K specific channels

Question 26

Potassium Sparing Diuretics - Aldosterone antagonists

Answer 26

 Mineralocorticoid receptor antagonists  Compete with aldosterone receptor sites which inhibits sodium reabsorption and potassium secretion  Spironolactone & eplerenone

Question 27

Potassium Sparing Diuretics - Sodium Channel Blockers

Answer 27

 Inhibit entry of sodium into cell which reduces amount of sodium transported by Na-K ATPase  Also reduces secretion of potassium as action of Na-K ATPase decreases  Amiloride & triamterene

Question 28

Intercalated Cell Activity – Hydrogen Ions

Answer 28

 Secretion controlled by H-ATPase transporter – tubular border  Presence of carbonic anhydrase allows conversion of CO2 and H2O to hydrogen and bicarb ions  Chloride also secreted following electrochemical gradient  Bicarb reabsorbed using Cl-HCO3 - counter-transport mechanism following the Cl- gradient into the cell – basolateral border  CO2 moved freely between cell and interstitial fluid  Potassium is also reabsorbed

Question 29

Meduallary Collecting Ducts

Answer 29

 Reabsorb approximately 10% of filtered water and sodium  Determines final concentration of solutes and urine concentration  Epithelial cells smooth with few mitochondria  Water permeability controlled by ADH  Urea is reabsorbed via specific urea transporters which moves urea into the interstitial spaces thus affecting osmolarity  Secretes hydrogen ions (like cortical collecting tubule)

Question 30

Solute Concentrations graph

Answer 30

- anything above one = tubular concentration is higher than plasma concentration - Less reabsorption - more secretion - or both

Question 31

Inulin

Answer 31

- neither secreted or reabsorbed (plasma concentration and inulin concentration in boweman's capsule is the same)  Provides indication of water reabsorption  [Inulin] of 3 means that 1/3 of the water remains in the tubule (2/3 has been reabsorbed)