Kidney physiology

Question 1

what are some examples of problems thatmess with homeostasis of water and electrolytes?

Answer 1

-haemorrage
-unusual eating or drinking behaviour
-severe dehydration, rapid fluid loss from the gut or after burns
-unintended consequences of drug actions

Question 2

what is the water and electrolyte homeostasis?

Answer 2

-intake/loss must be in balance

Question 3

what is the typical input of water?

Answer 3

2.5L day
1200ml water
1000ml food
300ml metabolic

Question 4

what is the typical output of water?

Answer 4

2.5L per day
1500ml urine
100ml swear
200ml faeces
700ml insensible loss

Question 5

what can affect the output of water?

Answer 5

temperature
humidity
activity

Question 6

what happens during periods of heavy exercise or in hot/humid conditions?

Answer 6

sweat loss can >2L/hour, >10L/day
urine output reduced in these conditions

Question 7

what are the daily recommendations of salt?

Answer 7

6g/day
3.75g/day if 51 or older or have high BP, diabetes or chronic kidney disease

Question 8

how much CO goes to kidneys?

Answer 8

25% supplies the 200g of tissue
625ml/100g/min

Question 9

what is the blood pressure in glomerular capillaries?

Answer 9

50-60mmHg

Question 9

how do we achieve high BP in glomerular capillaries?

Answer 9

renal artery is short and has a relatively large radius

Question 10

what are the sequence of blood vessels in the glomerular capillaries?

Answer 10

afferent arteriole
glomerular capillaries
efferent arteriole
tubular capillaries
venule

Question 11

what are the 2 types of nephrons?

Answer 11

superficial and juxtamedullary

Question 12

which type of nephron is water reabsorption more effective?

Answer 12

longer jjuxta-medullary nephrons

Question 13

what are the 4 sections of the nephron?

Answer 13

PCT
loop
DCT
collecting duct

Question 13

what is reabsorption?

Answer 13

active pumping from filtrate in tubules
(substances that are retained are water, glucose, amino acids and electrolytes)

Question 14

what is secretion?

Answer 14

active pumping into tubules
for substances to be eliminated faster than filtration alone allows (H+, ammonia, uric acid and some drugs)

Question 15

what else can affect pumping rates?

Answer 15

hormones
eg aldosterone can adjust the rates of Na and K excretion

Question 16

where does filtration of small molecules and water occur?

Answer 16

between podocytes
cut off is 67KD

Question 17

what are some small molecules that can filter through podocytes?

Answer 17

ions, urea, glucose, amino acids and small proteins

Question 18

what is the normal glomerular filtration rate?

Answer 18

90-140ml/min

Question 19

what is the brush border?

Answer 19

-active resporption of glucose, amino acids, NA and K ions
-co transporters, aqueous channels, membrane pumps
-substantial water reabsorption

Question 20

what has happened by the end of the PCT?

Answer 20

-complete reabsorption of glucose and amino acids
-substantial reabsorption of Na and water
volume of filtrate reduced by 2/3rds

Question 21

which wall of the loop of henle is thicker?

Answer 21

thinner wall descending into the medulla
thicker wall ascending from the medulla

Question 22

why is the wall ascending thicker?

Answer 22

so it can pump the solute up

Question 23

what occurs at the loop of henle?

Answer 23

Solute diffuses into descending tubule: Counter-current mechanism ‘recycles’ solutes. Ion pumping develops high osmotic pressure at the tip of the loop. No net re-absorption here.

Question 24

what happens in the Distal Convoluted Tubule?

Answer 24

Similar structure and function to Proximal Tubule. Compare A and C. No need for glucose transporters Less intense electrolytes and water re-absorption DCT ion pumping can be controlled by hormones like aldosterone to ‘fine tune’ Na + and K + exchange

Question 25

what happens in the collecting duct?

Answer 25

concentration of urine CDs pass close to tips of Loop If CDs are permeable to water, then moves out of the duct to concentrate filtrate. Duct permeability set by ADH/AVP. When ADH/AVP is present Aquaporins are inserted into the luminal membrane to allow water movement. Rapid insertion/removalallows quick responses

Question 26

what is the normal plasma osmolarity?

Answer 26

300mOsm

Question 27

what happens when water intake is restricted?

Answer 27

When water intake is restricted, plasma osmolarity ↑. More ADH/AVP is secreted by the hypothalamus. ADH ↑ the water permeability of Collecting Ducts. More water is reabsorbed. Concentrated urine is produced.

Question 28

what is the max conc of urine?

Answer 28

1200 mOsm.

Question 29

what is the minimum urine output?

Answer 29

1ml/min

Question 30

what happens when excess water is consumed?

Answer 30

If excess water is consumed, plasma osmolarity falls Hypothalamus secretes less ADH/AVP. Collecting Duct walls loose permeability to water. Dilute urine is produced.

Question 31

what is the max urine output?

Answer 31

20ml/min

Question 32

how is filtration pressure controlled?

Answer 32

Hypo-filtration initiates secretion of Renin by the Juxtaglomerular apparatus. Renin splits Angiotensinogen to makeAngiotensin I which is converted to Angiotensin II a powerful vasoconstrictor. This system regulates renal blood flowand glomerular filtration rate (low BP, low renal flow, hypofiltration, etc)

Question 33

what enhances the system that increases BP?

Answer 33

sympathetic NS

Question 34

where is renin released from?

Answer 34

juxtaglomerular cells

Question 35

what is angiotensin II a?

Answer 35

a powerful vasoconstrictor

Question 36

what triggers the RAAS system?

Answer 36

hypofiltration

Question 37

what happens when electrolyte concentrations fall?

Answer 37

aldosterone levels increase

Question 38

where is aldosterone released from?

Answer 38

secreted by golmerulosa cells of the adrenal cortex

Question 39

what is reabsorbed in the proximal tubule?

Answer 39

water NaCl amino acids glucose potassium bicarb

Question 40

what moves into the proximal tubule?

Answer 40

H+ ammonium

Question 41

which part of the nephron is rich in aquaproins?

Answer 41

descending loop water reabsorbed

Question 42

what is reabsorbed in the distal tubule?

Answer 42

NaCl, water and bicarb

Question 43

what is absorbed into the tubule in the distal tubule?

Answer 43

H+ ammonium potassium

Question 44

what is the structure of transitional epithelium?

Answer 44

lower cells - cuboidal/ columnar apical cells - cuboidal when not stretched