Lecture 33: Tubular Reabsorption and Secretion

Question 1

nephron reabs rate

Answer 1

99% filtrate
proximal convouted tubule does most reabs
rest of nephron does fine tuning

Question 2

nephron filtrate fine tuning

Answer 2

solutes reabs by active and passive processes
water follows solutes (osmosis)
small proteins move across blood by pinocytosis.

Question 3

tubular secretion

Answer 3

transfers materials from blood to tubular fliud

helps control blood pH b/c H secretion
helps eleimaten substances (NH4, creatine, K)

Question 4

Paracellular reabsorbtion

Answer 4

50% reabs matreial moves beteween cells by diffusion in some parts of tubule

cross ONE membrane

Question 5

Transcellular reabs

Answer 5

material moves through both basal and apical membranes of tubule by ACTIVE TRANSPORT

Question 6

reabs of Na+

Answer 6

important!!!
several transport system exist for it
Na/K ATPase pumps sodium from tubule cell cytosal th BASOLATERAL membrane only

Question 7

water reabsoprtion

Answer 7

Osmosis ONLY

Question 8

obligatory water reabsorption

Answer 8

water “obliged” follow solutes being reabsorbed

moving ions from chamber A to B

Question 9

facultative water reabsorption

Answer 9

in collecting duct under control of ADH

Question 10

Reabs in PCT: Na symporters

Answer 10

help reabs materials from tubular filtrate
glucose, Amino acids, lactic acid, water sol vitamins

intracellular sodium levels kept low due to Na+/K+ pump on basolateral side

Question 11

PCT functions

Answer 11

reabs of nutrrients
isosmotic reabsorption (at same osmotic level of blood)

Question 12

Glucosuria

Answer 12

when renal symporters cant reabs glucose fast enough
happens when blood glucose above 200 mg/mL–> some glucose stays in urine

caused often by diabetes mellitus b/c insulin activity defcient and blood glucose too high

Question 13

osmolytes

Answer 13

characteristic renal threshold valules
renal clerance rates
inulin, creatinine)

Question 14

symporters in loop of Henle

Answer 14

thick asceding has Na, K-, Cl- symportes that reabs ions. Immpermeable to water!!!!

K+ moves back into filtrate through K+ leach channles

Na pumped out on basolateral side

Cl- diffuses across cell

Question 15

symporters in loop of Henle: why cations do what they do

Answer 15

cations passively move to vasa recta

drawn to neg charge in capp

Question 16

Formation of Dilute Urine

Answer 16

drinking water-> dec blood osmolarity-> ADH inhibited

goal: removed excess fluid from blood by making dilute urine

Question 17

formation of dilute urine in depth

Answer 17

blood plasma: 300 mOsm/L conc (normal for blood)

this is when we have low blood osmolarity

filterate osmolaraity INCREASES as it moves down desc. loop of henle

filtrate osmolarity decs as it moves up as loop of henlee

dec in collecting duct (impermeable to water) -> dilute urine

Question 18

Formation of concentrated urine

Answer 18

water deprivation-> inc blood osmolarity-> ADH stim

goal: prevent water loss and make concentrated urine

Question 19

formation of concentrated urine in depth

Answer 19

JG LHs (long ones)

in LH: similar to making dilute BUT: we are losing a lot of water so we need to get rid of solutes so we can get back to being isosmotic with blood. So we do the extra suff

in the CD: reabs more water when we have ADH (makes aquporins) (also principle cells reabs mor water when ADH present

ALSO:::: Urea RECYCLING: builds up in RENAL MEDULLA (not in tubule fluid)

Question 20

ADH actions

Answer 20

stim Na, K, CL symporters in thick ascending loop of henlee: builds osmotic gradient in intersitial fluid

stim water reabs in upper collecting ducts

stim water reabs and urea recycling in lower collecting ducts builds osmotic gradient in ISF

result: concentrated urine

Question 21

countercurrent mechanism descending loop

Answer 21

descending loop of henle is very permeable to water

high osmolarity of ISF outisde descending loop= water move out of tubule by osmosis,
at hairpin turn ,osmolarity of filtrate can reach 1200 mOs,/L

Question 22

countercurrent mechanism ascending loop

Answer 22

ascending loop impermeable to water, so ions move OUT

BUT: symporters reomve Na, Cl so osmolarity of filtrate drops to 100 mOsm/L, but less filtrate left in tubule

Question 23

slide 4

Answer 23

slide 4

Question 24

which part of LH is impermeable to water?

Answer 24

thick ascending limb

Question 25

apical membrane permeability

Answer 25

impermeable to water

Question 26

chloride

Answer 26

diffuses into basolateral side fluid

Question 27

potassium

Answer 27

goes into fluid on apical side

Question 28

ISF charge

Answer 28

more negative than fluid in lumen

Question 29

in depth concentrated urine part 2

Answer 29

urea recycling=urea build up in renal medulla. it passes through CD into ALH and DLH

b/c three things running in parallel loops
1. loop of henlee
2. peritubular capillaries
3. vasa recta
then put it in medulla, which has lots of urea