Physiology 4 Tubular Reabsorption and Secretion

Question 1

Solute Movement: Electrical Coupling

Answer 1

Attraction of oppositely charged ions (ex: reabsorption of Na and you get lost of Cl going with it) Does NOT involve a carrier

Question 2

Solute Movement: Carrier Coupling

Answer 2

two solutes use a common carrier. Each solute promotes the movent of the other (symport or by antiport) DEPENDENT ON THE Na+ GRADIENT (due to Na-K-ATPase secondary active transport)

Question 3

Solute Movement: Osmotic Coupling

Answer 3

the movement of solutes creates an osmotic gradient that promites water flow by osmosis (ex: Na and glucose are reabsorbed and water follows)

Question 4

Solute Movement: Favorable Concentration Gradients

Answer 4

Reabsorption of solutes and water reduced the tubular volume and increases the tubular concentration of other solutes in the tubule (the ones left behind) Results in a generation of a favorable concentration gradient for the passive diffusion (reabsorption) of the other solutes. Ex: urea, Cl- and weak organic acids and bases

Question 5

where does reabsoprtion of organic solutes occur

Answer 5

Only occurs in the poximal tubule

Question 6

Tubular transport maximum

Answer 6

the maximum rate at which the proximal tubule can reabsorb a given solute when all carriers are saturated (i.e maximum filtered load that can be completely reabsorbed)

Question 7

What happens when filtered load excedes the transportation maximum

Answer 7

some solutes remain in the tubule and get excreted in the urine (ex: Diabetes- glucose excedes max transport) The presence of excess solutes in the tubule can hinder the reabsorption of water leading to diuresis (ex: glucose left behind in diabetes is acts as an osmol and retains water)

Question 8

Renal Threshold

Answer 8

The plasma concentration of the solute at which the solute just begins to apear in the urine (when the filtered load is so large that it saturates the transport system and exceeds transport max)

Question 9

Reabsorption of Glucose

Answer 9

Reabsorption of glucose occurs ONLY IN THE PROXIMAL CONVOLUTED TUBULE (normally everything that is filtered is reabsorbed) . SGLT-2 (Na-Glucose sympoter) and SGLT-1 (2Na-glucose symporter found in the late proximal tubule)

Question 10

At what concentration do we begin to see glucose in the urine

Answer 10

[300]

Question 11

Name subsance with tubular maxima and renal thresholds

Answer 11

glucose, amino acids, phosphate, uric acid, ketone bodies, vitamins

Question 12

Active secretion of Organic Solutes in the proximal tubule

Answer 12

Organic cation transporters and organic anion transporters located on the basolateral membrane

Question 13

Secretion and reabsorption of lipid soluble organic solutes

Answer 13

Passive diffusion: Non-ionized form is lipid soluble and can diffusse across the epithelium down its concentration gradient (ex: NH3 ammonia) Ionized forms: NOT freelu soluble and becomes diffusion trapped (stayes in the tubule ex NH4+ ammonia)

Question 14

Secondary Active Transport

Answer 14

Na moves down its gradient and supplies the energy to move the second solute against its gradient (NaKATPase Pump)

Question 15

Weak organic acids in acidic environement

Answer 15

Pushed the reaction toward the nonionized form which can freely diffuse across the membrane i.e GET ABSORBED (ex: if you want to absorb an acidic drug you would need to acidify the urine)

Question 16

Weak organic acids in alkaline environment

Answer 16

push reaction towards H + A (ionized form) and will be trapped in the lumen (DIFFUSION TRAPPED) Thus excretion of an organic acid can be acombilied by making tubular filtrate more alkaline

Question 17

How does the reabsorption of water affect a weak organic acid

Answer 17

creates a favorable concentration gradient for the reabsorbtion of nonionized diffusable form

Question 18

Weak organic base in acidic environment

Answer 18

more H+ will favor the HB+ and the weak base will therefore become diffusion trapped and will be eliminated

Question 19

Weak organic base in an alkaline environment

Answer 19

more HB will push the reaction towards B + H+ and therefore favors the reabsorption of B (nonionized form)

Question 20

in a hypovolemc state how will the excretion of a weak organic acid or a weak organic base be effected

Answer 20

In a hypovolemic state more water and solutes will be absorbed creating a favorable concentration gradeinet for the ABSORPTION of the nonionized form of the organic acid/base