proximal tubule

Question 1

Describe the structure of the proximal tubule

Answer 1

Microvilli, vertical mitochondria between fold of basolateral membrane. Leaky tight junctions- 20% paracellular 80% transcellular

Question 2

What is the proximal tubule permeable to?

Answer 2

Sodium, both directions

Question 3

Active transport is..?

Answer 3

primary (pumps) or secondary (co transport) transport against a concentration gradient, requiring energy

Question 4

Passive transport is..?

Answer 4

down an electrochemical gradient, can be bidirectional. Transporters facilitate not drive

Question 5

What is transcellular transport?

Answer 5

across the cell, two membranes, active or passive. may require transporter

Question 6

What is paracellular transport?

Answer 6

Passive, bidirectional transport. Between cells via tight junctions. Low specificity

Question 7

what does Inulin clearance suggest?

Answer 7

Glomerular filtration rate, because inulin is freely filtered and not reabsorbed or secreted

Question 8

What is the clearance rate of glucose?

Answer 8

0, because it is freely filtered and completely absorbed

Question 9

How do you calculate excretion?

Answer 9

Filtered- absorbed + secreted

Question 10

How would you know if a substance will be secreted?

Answer 10

Higher clearance rate than GFR

Question 11

Is the clearance of penicillin high or low?

Answer 11

High. Penicillin is a weak acid.

Question 12

Describe filtration of Urea

Answer 12

Plasma urea concentration; 15-45mg/100ml. 40-50% reabsorbed. Clearance is 60-65 ml/min. reabsorbed as a consequence of sodium reabsorption.

Question 13

How is PARA aminohippuric acid (PAH) helpful?

Answer 13

PAH is an organic acid, can be used to measure renal plasma flow because it is freely filtered, not reabsorbed, but IS secreted

Question 14

How much sodium and H20 does the proximal tubule reabsorb?

Answer 14

2/3. tubular fluid is close to isotonic.

Question 15

what is T Max?

Answer 15

The transport maximum, saturation of transport, working at max capacity but no increase in transport.

Question 16

How is HCO3- reabsorbed?

Answer 16

HCO3- combines with H+ in lumen to form H2CO3 (Carbonic acid) which is broken down by carbonic anhydrase to H2O and CO2. These enter the cell by passive diffusion and reform via CA to H2CO3. H2CO3 broken down to H+ ions and HCO3-. HCO3- leaves cell basolaterally down concentration gradient via HCO3-/Na+ co transporter.

Question 17

Are channels or transporters faster?

Answer 17

Channels. But transporters can carry larger molecules

Question 18

What is secretion?

Answer 18

Molecules move from the plasma of peritubular capillaries into the renal tubules to become part of the filtrate.

Question 19

What is reabsorbed in the proximal tubule?

Answer 19

Glucose, amino acids, urea, vitamins, ions.

Question 20

What is secreted back into the filtrate?

Answer 20

K+ and H+ ions, waste products; choline and creatinine, penicillin.

Question 21

What is the renal threshold?

Answer 21

plasma concentration of a solute at which spillover into the urine will occur. If plasma concentration if higher than renal threshold the rate of solute excreted into the urine will increase.

Question 22

What is clearance?

Answer 22

The rate at which a solute is excreted in ml/min. Excretion rate / plasma concentration.

Question 23

How do you calculate excretion rate?

Answer 23

concentration of urine x urine flow rate.

Question 24

Secretion transport on the basolateral membrane?

Answer 24

Na+ influx carries alpha ketoglutarate into the cell. A-ketoG efflux carries in anions like PAH. PAH exits into the lumen in exchange for chloride and bicarbonate

Question 25

Give examples of proteins picked up by endocytosis

Answer 25

Megalin and cubalin

Question 26

What volume does kidney filter per day?

Answer 26

180L!

Question 27

What is oncotic pressure?

Answer 27

also known as colloid pressure. osmotic forces according to the presence of proteins. denoted by Pi symbol. force fluid back into capillary bed

Question 28

What is hydrostatic pressure?

Answer 28

denoted by the letter P. Pressure that compels fluid to move out of a vessel. any fluid contained in a space exerts hydrostatic pressure on the boundaries. Blood in glomerulus has high hydrostatic pressure (55mmHg).