kidney 2

Question 1

blood in the Bowmans capsule entering proximal convoluted tubules

Answer 1

blood without cells, platelets, or big proteins

still has the same osmolarity, ions, glucose, amino acids, small proteins, urea etc.

Question 2

tubular reabsorption

Answer 2

highly selective

• 100% of sugars and 99.5% of salts reabsorbed
• only excess amounts of required substances are not reabsorbed
• waste products are not reabsorbed and eliminated as urine

Question 3

paracellular path

Answer 3

fluid and solutes can squeeze between cells
free reabsorption when pulled through osmotic gradients
common in the proximal convoluted tubule

Question 4

transcellular path

Answer 4

goes across apical and basal membrane

may be facilitated fission or osmosis, may also be active transport, may also be secondary active transport

Question 5

active transport

Answer 5

sodium, hydrogen, potassium, calcium, magnesium

mostly sodium, gradient used to drag things coupled with sodium

Question 6

secondary active transport

Answer 6

glucose, amino acids
sodium used to power glucose and amino acids co transporters
also used for chloride and proton balance

Question 7

pinocytosis

Answer 7

when small proteins leak through glomerular capillaries
reabsorption of amino acids
active - uses ATTP
by receptors and also random

Question 8

active transport is saturable

Answer 8

Tmax
anything involving a carrier or pump has a maximum rate of activity
important for diabetes mellitus - saturated glucose transporters which causes glucose to be lost to urine
only important in pathological states

Question 9

passive transport

Answer 9

CL, urea, phosphate, sodium, calcium, magnesium, water
cannot be saturated, rate dictated by
- electrochemical gradient
- permeability
- time
anion drag NA+ created passive Cl- reabsorption
urea
- resorption of everything else in the tubule creates a urea gradient, favouring urea resorption

Question 10

osmosis

Answer 10

• leafiness is regulated by tight junctions and aquaporins

- PCT - very leaky so water follows quickly, no time to establish osmotic gradient from Na pumping

Question 11

ascending loop of Henle

Answer 11

has no aquaporins
has tight junctions between cells
osmolarity can be changes

Question 12

DCT/CT/CD

Answer 12

distal convoluted tubule, collecting tubule and collecting duct variable permeability

Question 13

segmentation of nephron function - Na reabsorption

Answer 13

most reabsorbed immediately passively and actively at proximal convoluted tubule
1/4 reabsorbed at the loop of henle - obligatory, not regulated
regulated by hormonal control at the distal tubule, small portion of sodium reabsorption

Question 14

reabsorption of glucose, amino acids and small proteins in the nephron

Answer 14

all nutrients reabsorbed in the proximal tubule

endocytosis also occurs here to recapture proteins

Question 15

H2O reabsorption

Answer 15

mostly reabsorbed in the proximal tubule because it follows sodium
loop of henle dilutes the renal filtrate by reabsorbing more sodium than water
water may be reabsorbed in the distal tubule or collecting duct - depending on hormonal ocontrol

Question 16

proximal convoluted tubule

Answer 16

2/3 of sodium, chloride, potassium, water
100% of glucose and amino acids
secretes wastes, and protons
extensive brush border to increase surface area for exchange

Question 17

heterogeneity of the PCT

Answer 17

first half - Na resorbed by co-T with glucose, amino acids

second half - little glucose and AAs remain, Na reabsorbed with Cl

Question 18

secretions at the proximal convoluted tubule

Answer 18

NH3, bile salts, oxalate, urate, catecholamines, penecillin, salicylates, creatinine, etc

Question 19

does omolality change across the PCT

Answer 19

no

reabsorbing sodium but equally reabsorbing water so osmolality doesn’t change

Question 20

loop of henle

Answer 20

• descending - thin - no brush borders, few mitochondria, and minimal levels of metabolic activity, highly permeable to water, doesn’t not pump any salts only water moves due to many aquaporins
• ascending - thick - no aquaporins, impermeable to water, active resorption of sodium, chloride, and potassium

Question 21

thick ascending limb

Answer 21

powered by sodium potassium pumps
sodium 2 chloride potassium co transporter - drags 2 chlorides and 1 potassium when a sodium is allowed through
a leaky potassium channel lets a lot of potassium out
an electrical gradient is established which its used to drag cations through paracellular diffusion - brings magnesium, calcium

Question 22

sodium 2 chloride potassium co co transporter

Answer 22

drags 2 chloride and 1 potassium for every sodium that is allowed through
is a salt sensor - what is used to sense salts to regulate tubular glomerular feedback

Question 23

dilution of tubular fluid

Answer 23

impermeable to water and losing ions - therefore becomes very dilute

Question 24

distal convoluted tubule

Answer 24

2 cell types

• intercalated cells - secrete protons
• principle cells - reabsorb sodium and secrete potassium

Question 25

later distal collecting tube and cortical collecting duct

Answer 25

1. reabsorb sodium, secrete potassium - aldosterone
2. H+-ATPasse secretes H+
3. H2O permeability controlled by ADH - impermeable->permeable
4. impermeable to urea - almost all the urea that enters these segments passes on to CD - excreted in the urine (exc. some urea reabsorption in medullary CDs)

Question 26

medullary collecting duct

Answer 26

• reabsorbs <10% off the filtered water/Na
• final site for processing urine
• same functions of DCT/CCT, variable H2O permeability (ADH), can secrete H+
• unlike the cortical CT - urea is permeable
• urea is reabsorbed into medullary interstitium, increased osmolarity in this region - concentrated urine

Question 27

producing dilute urine

Answer 27

thick ascending limb is waterproof and salts are reabsorbed, when kept waterproof, urine will be dilute

Question 28

producing concentrated urine

Answer 28

• open aquaporins
• obligatory urine volume - some fluid required
• selective waterproofing - leaky distal collecting tubule, collecting tubule and collecting duct - so H2O is reabsorbed from the normally impermeable tubule segments
• a hyper osmotic renal medullary interstitial - provides the osmotic gradient for H2O resorption

Question 29

generating hyper osmotic medullary interstitium

Answer 29

• urea impermeable ascending loop of henle, distal collecting tubule, collecting tubule
• water reabsorbed from distal collecting tubule, rapidly increases concentration of urea
• urea permeable inner medullary collecting ducts
• urea diffuses into the renal interstitium
• urea transporters

maintains increased urea concentration in the tubular fluid even though urea is being reabsorbed

Question 30

why don’t peritubular capillaries dilute the medullary gradient

Answer 30

• the medullary blood flow is low - if there was normal flow salts would be picked up and carried out of the kidney
  vasa recta blood flow is so slow that the blood is able to equilibrate
• vasa recta countercurrent exchange - minimises solute washout