K4 - The Proximal Tubule and Loop of Henle

Question 1

how much of the plasma that enters the glomerulus is filtered?

Answer 1

20%

Question 2

what is glomerular filtrate?

Answer 2

modified filtrate of the blood containing ions and solutes at plasma concentrations but lacks RBCs, large plasma proteins

Question 3

how much of the filtered fluid is reabsorbed in the proximal tubule?

Answer 3

80ml/min

Question 4

what is the relationship between the the fluid reabsorbed in te proximal tubule and the filtrate?

Answer 4

iso-osmotic - same osmolarity

Question 5

what does the proximal tubule reabsorb?

Answer 5

• Sugars
• Amino acids
• Phosphate
• Sulphate
• Lactate

Question 6

what is secreted in the proximal tubule?

Answer 6

• H+
• Hippurates
• Neurotransmitters
• Bile pigments
• Uric acid
• Drugs
• Toxins

Question 7

what is trasncellular reabsorption?

Answer 7

reabsorption across cell layer

Question 8

what is paracellular reabsorption?

Answer 8

reabsorption through tight junctions between epithelial cells

Question 9

what is primary active transport?

Answer 9

Energy is directly required to operate the carrier and move the substrate against its concentration gradient

Question 10

what is secondary active transport?

Answer 10

The carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)

Question 11

what is facilitated diffusion?

Answer 11

Passive carrier-mediated transport of a substance down its concentration gradient

Question 12

where is the Na+/K+ ATPase found?

Answer 12

basolateral membarne

Question 13

why is the Na+/K+ ATPase at the basolateral membrane important?

Answer 13

it is essential for Na+ reabsorption into the peritubular capillary

Question 14

how is O2 and CO2 transported across the membrane?

Answer 14

Diffusion through the lipid bilayer

Question 15

how is Na+ trasnported across membrane?

Answer 15

Diffusion through channels

Question 16

How is glucose transported across the epithelial cell?

Answer 16

Facilitated diffusion

Question 17

How is Na+ and K+ transported across the epithelial cell?

Answer 17

Primary active transport

Question 18

How is Na+ and glucose transported across the epithelial cell?

Answer 18

Secondary active transport

Question 19

Isoosmotic fluid reabsorption across “leaky” proximal tubule epithelium due to?

Answer 19

(1) Standing Osmotic Gradient

(2) Oncotic Pressure Gradient

Question 20

how does Na+ move across the tubular epithelium to be reabsorbed?

Answer 20

1. Na enters the cell via a symport with glucose, amino acids and a countertarasnporter with H+.
2. Na then moves across the tubular cell to the basolateral membrane
3. Exits the cell to be reabsorbed into the blood via the Na/K ATPase

Question 21

How is glucose and amino acids reabsorbed?

Answer 21

move across luminal membrane with sodium in symport

glucose then leaves the cell via facilitated diffusion

Question 22

how is water reabosrbed across tubular epithelium?

Answer 22

Osmotic gradient between Na and Cl will be set up.

water moves down this gradient via paracellular transport

absorbed into peritubular capillary by osmosis

Question 23

what is the transport maximum?

Answer 23

max amount of substrate that can be reabsorbed before the transporter proteins become saturated

Question 24

what is the renal threshold?

Answer 24

concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine

Question 25

why would glucose not be absorbed and when would this happen?

Answer 25

- when transport maximum has been reached | - then renal threshold has been reached (around 10-12 mmol/l

Question 26

why does the osmolarty of tubular fluid not change along the proximal tubule

Answer 26

salt and water are absorbed in equal amounts

Question 27

what % of salt and water are reabsorbed in the proximal tubule?

Answer 27

67%

Question 28

what % of glucose is reabsorbed in the proximal tubule?

Answer 28

100%

Question 29

What is tubular fluid when it leaves the proximal tubule?

Answer 29

iso-osmotic

Question 30

what is the function of the loop of henle?

Answer 30

- Generates a cortico-medullary solute concentration gradient which enables the formation of hypertonic urine

Question 31

what is the Opposing flow in the two limbs of the loop of henle?

Answer 31

countercurrent flow

Question 32

what establish a hyper-osmotic medullary interstitial fluid?

Answer 32

loop of henle and the vasa recta

Question 33

Describe what happens on the ascending limb of the loop of henle

Answer 33

- along the entire length of the ascending limb Na+ and Cl- are being reabsorbed (thick upper AL is achieved by active transport, in the thin lower AL this is passive) - the ascending limb is relatively impermeable to water - little or no water follows salt reabsorption

Question 34

Describe what happens on the decending limb of the loop of henle

Answer 34

does not reabsorb NaCl and is highly permeable to water

Question 35

describe the process of the triple co-transporter?

Answer 35

- Na, Cl and K ions all pas through a triple transporter on the luminal end - Na and Cl are transported though the basolateral membrane where they are absorbed into the interstitial fluid as aCl - K ions are recycled

Question 36

Describe the 5 stages that occur in the loop of henle

Answer 36

1. Solute removed from lumen of ascending limb (water cannot follow) 2. Tubular fluid is diluted and osmolality of interstitial fluid is raised 3. Interstitial solute cannot enter the descending limb 4. Water leaves the descending limb by osmosis 5. Fluid in the descending limb is concentrated

Question 37

what type of fluid leaves the proximal tubule?

Answer 37

iso-osmotic

Question 38

what type of fluid enter sthe distal tubule?

Answer 38

hypo-osmotic

Question 39

what is the purpose of countercurrent multiplication?

Answer 39

To concentrate the medullary interstitial fluid to enable the kidney to produce urine of different volume and concentration according to the amounts of circulating antidiuretic hormone

Question 40

What runs alongside the long loop of Henle of juxtamedullary nephrons and acts as a countercurrent exchanger?

Answer 40

vasa recta

Question 41

What features of the vasa recta reduce NaCl and urea being washed away?

Answer 41

- vasa recta capillaries follow hairpin loops - vasa recta capillaries are freely permeable to NaCl and water - blood flow to vasa recta is low

Question 42

what happens to blood osmolarity as it dips down into the medulla?

Answer 42

rises

Question 43

what happens to blood osmolarity as it rises up into the cortex?

Answer 43

falls