Week 2.2 - structure & function (workbook)

Question 1

what does the kidney consist of microscopically?

Answer 1

outer cortex and inner medulla surrounding the renal pelvis

Question 2

what does the renal pelvis connect?

Answer 2

kidney to ureters

Question 3

what is the microscopic functional unit of the kidney?

Answer 3

the nephron

Question 4

what is the nephron?

Answer 4

a long tube, lined with epithelial cells, with the glomerulus at one end, and a connection to the renal pelvis at the other

Question 5

what is the filter of the nephron?

Answer 5

the glomerulus

Question 6

where is the glomerulus located?

Answer 6

in the kidney cortex

Question 7

where does filtrate formed by the glomerulus pass?

Answer 7

passes first through the proximal convoluted tubule (PCT) in the cortex

Question 8

what happens after filtrate passes through the PCT?

Answer 8

the nephron then dips down into the medulla forming a hairpin loop ‘loop of Henle’

Question 9

what comes after the loop of Henle?

Answer 9

as the nephron ascends it forms the distal convoluted tubule, in the cortex

Question 10

what comes after the distal convoluted tubule?

Answer 10

finally, the nephron joins the collecting duct that passes through the medulla to the renal pelvis

Question 11

what do specialised afferent and efferent arterioles do?

Answer 11

maintains the relatively high, constant filtration pressure in the capillaries at the glomerulus

Question 12

why is the high constant filtration pressure in the capillaries at the glomerulus necessary?

Answer 12

drives water and small molecules out of the plasma at a rate of about 125ml/min (180L/day) - glomerular filtration rate (GFR)

Question 13

what is the GFR?

Answer 13

180L/day or 125ml/min

Question 14

what is the function of the proximal convoluted tubule?

Answer 14

specialised section of the nephron reabsorbs about 70-80% of most ions and water, plus most or all of the small organic molecules not destined for secretion (e.g. glucose, amino acids)

Question 15

is reabsorption in the PCT regulated?

Answer 15

not tightly

Question 16

how does the filtrate remain isotonic with ECF?

Answer 16

water follows the reabsorption of solute

Question 17

how are the epithelial cells lining the nephron like?

Answer 17

polarised, with different properties on the membrane facing the filtrate (apical / luminal membrane) and that facing the extra-cellular space (basolateral membrane)

Question 18

what is the reabsorption of many substances linked to in the PCT?

Answer 18

linked to the active movement of sodium ions

Question 19

how are sodium ions moved?

Answer 19

by active transport across the basolateral membrane, so generating a concentration gradient between the intra-cellular fluid and filtrate

Question 20

why is the concentration gradient between the intra-cellular fluid and filtrate important?

Answer 20

this then drives the reabsorption of most ions and small molecules, with water following passively by osmosis

Question 21

what happens as filtrate passes through the loop of Henle?

Answer 21

solute is selectively reabsorbed

Question 22

how is the fluid leaving the loop of Henle like? why?

Answer 22

there is overall less reabsorption of water, so the fluid leaving the loop is hypotonic

Question 23

how does the fluid move through the loop of Henle?

Answer 23

first down the descending limb, then up the ascending limb

Question 24

how does a hypertonic environment come about within the kidney medulla?

Answer 24

a process of counter current multiplication (as fluid moves through loop of Henle) generates a very hypertonic environment within the medulla

Question 25

what happens in the distal tubule and collecting duct?

Answer 25

further reabsorption of both water and electrolytes from the ultra-filtrate in the distal nephron is now variable

Question 26

what does the amount of solute or solvent reabsorbed in the distal tubule / collecting duct depend on?

Answer 26

the fluid and electrolyte balance of the body

Question 27

what is diuresis?

Answer 27

when the body has too many of certain substances in the fluid that the kidneys filter

Question 28

what happens in diuresis?

Answer 28

ions are reabsorbed, but not the water, producing a large volume of dilute urine (where there is need to excrete a lot of water)

Question 29

what happens if water needs to be conserved?

Answer 29

water is absorbed with ions in the DCT, drawn out of the collecting duct into the hypertonic renal medulla - producing very small volumes of very concentrated urine