Physiology of kidney I

Question 1

What are the two types of nephrons in the kidney

Answer 1

Cortical nephrons (80%)
Juxtamedullary nephrons (20%)

Question 2

What is renal corpuscle

Answer 2

combination of glomerulus and Bowman’s capsule

Question 3

What is filtration in kidney

Answer 3

Movement of fluid from blood into the lumen of the nephron
Takes place in the renal corpuscle
Once filtrate is in the nephron it is destined for excretion

Question 4

What is reabsorption in kidney

Answer 4

Process of moving substances in the filtrate from the lumen of the tubule back into the blood

Question 5

What is secretion in the kidney

Answer 5

Selectively removes molecules from the blood and adds them to the filtrate in the tubule lumen
Secretion uses membrane proteins to move molecules across the tubule epithelium

Question 6

Where does reabsorption happen in kdiney

Answer 6

Occurs when proximal tubule transports solutes out of the lumen and water follows
As it passes through loop of henle, more solute than water is reabsorbed
Then passes into distal tubule where regulation of water and salt balance occurs

Question 7

Primary function of proximal tubule

Answer 7

Isosmotic reabsorption of solutes and water

Question 8

What is formed at the end of filtration

Answer 8

Creates a filtrate with a composition similar to plasma

Question 9

What is filtration fraction

Answer 9

Percentage of renal plasma flow into the tubule

Question 10

How much of the plasma that flows through renal corpuscle gets filtered

Answer 10

1/5 (20%)

Question 11

3 filters of the renal corpuscle

Answer 11

Glomerular capillary endothelium - Glomerular capillaries are fenestrates aloow most plasma coponents to filter through
Basment membrnae - layer of extracellular matrix seperating the two endotheliums
Bowman’s capsule epithelium - Consists of podocytes that surround each glomerular capillary

Question 12

What is capillary blood pressure

Answer 12

Hydrostatic pressure of blood flowing through glorerular capillaries forces fluid through endothelium
Filteration takes place along the near entire lenght of glorerular capillaries due to high pressure

Question 13

What is colloid osmotic pressure

Answer 13

Higher inside glomerular cappilaries than the fluid in Bowman’s capsule

Question 14

What is Bowman’s capsule pressure

Answer 14

Enclosed space, presence of fluid creates hydrostatic fluid pressure opposing fluid moving into capsule
Fluid foltering out of the capillaires must displace the fluid already in the capsule lumen

Question 15

What is glomerular filtration rate

Answer 15

Volume of fluid that filters into bowman’s capsule per unit time
Average GFR is 125ml/min or 180l/day

Question 16

What affects glomerular filtration rate

Answer 16

net filtration pressure and filtration coefficient

Question 17

What are the two components of filtration coefficient

Answer 17

Surface area of glomerular capillaries available for filtration
Permeability of the filtration slits

Question 18

What is tubuloglomerular feedback

Answer 18

Paracrine signalling mechanism through which changes in fluid flow through the loop of Henle influence GFR

Question 19

How does macula densa regulate GFR

Answer 19

If salt delivery past the macula densa increases due to increased GFR, the macula densa sends a paracrine message resulting in constriction of afferent arteriole and GFR decrease

Question 20

What is the macula densa

Answer 20

Modified portion of the tubule epithelium

Question 21

What does granular cells do

Answer 21

Secrete renin and other paracrine molecules

Question 22

How does reabsorption occur in proximal tubule

Answer 22

Active transport creates a gradient, lumen more negative than ECF
Anions follow Na+ out of lumen
This dilutes laminal fluid and increases ECF concentration, allowing water to leave by osmosis
Loss of volume in lumen increases its solute concentration
Luminal solute conc. is higher than ECF, so solutes diffuse out of the lumen

Question 23

Transcellular vs paracellular transport

Answer 23

Transcellular - substances cross apical and basolateral membranes of tubule epithelial cell to reach interstitial fluid

Paracellular - substances pass through spaces between two adjacent cells

Question 24

What does the transport route taken depend on

Answer 24

Permeability of epithelial junctions and electrochemical gradient for the solute

Question 25

How is basolateral transport of Na+ done

Answer 25

Done in exchange for K+ by Na+-K+-ATPase

Question 26

How is urea concentration gradient built

Answer 26

When Na+ and other solutes are reabsorbed from the proximal tubule, transfer of osmotically active particles makes the ECF more concentrated than remaining filtrate in the lumen
Water moves via osmosis
This increases urea concentration in lumen

Question 27

What is saturation in renal transport

Answer 27

Max rate of transport that occurs when all available carriers are occupied by substrate