Control of Water and Electrolytes

Question 1

how do we gain water?

Answer 1

ingested water (food and drinks), water formed in metabolism

Question 2

how do we lose water?

Answer 2

excretion: urine, faces, and evaporation: sweat, expired air

Question 3

how much water do we take in and lose everyday?

Answer 3

2400ml on average

Question 4

what control is urinary excretion under?

Answer 4

homeostatic control

Question 5

what are the parts of the nephron?

Answer 5

glomerulus, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting ducts

Question 6

what is the glomerulus involved in?

Answer 6

renal blood flow, filtration of plasma, glomerular filtration rate, filtration pressures

Question 7

what is renal blood flow in ml/min

Answer 7

1200ml/min

Question 8

what is glomerular filtration rate (GFR) in ml/min?

Answer 8

120ml/min

Question 9

in the glomerular capillary whereabouts do the filtration pressures vary?

Answer 9

from the afferent arteriole to the efferent arteriole

Question 10

what the capillary hydrostatic (blood) pressure in the glomerulus?

Answer 10

45-50mmHg

Question 11

what is the plasma protein oncotic pressure in the glomerulus?

Answer 11

25-35mmHg

Question 12

what is the capsular pressure in the glomerulus?

Answer 12

10mmHg

Question 13

what is the net filtration pressure in the glomerulus?

Answer 13

10-15mmHg

Question 14

what does the proximal convoluted tubule do?

Answer 14

obligatory reabsorption of 60-70% of the glomerular filtrate, secretion of hydrogen

Question 15

what are absorbed in the proximal convoluted tubule?

Answer 15

ions, small organic molecules

Question 16

what type of transport can be seen in the proximal convoluted tubule with regards to ion movement?

Answer 16

active transport; facilitated diffusion

Question 17

what is the loop of henle important for?

Answer 17

concentration of urine (countercurrent exchange mechanism)

Question 18

what does the concentration of urine depend on?

Answer 18

the active transport pumps in thick, ascending limbs of loop of Hnele

Question 19

what does the length of the loop of Henle correlate with?

Answer 19

the ability to concentrate urine

Question 20

what is the distal convoluted tubule involved in?

Answer 20

reabsorption of water, sodium, chlorine and calcium, and secretion of hydrogen and potassium

Question 21

what is the activity of the distal convoluted tubule controlled by?

Answer 21

hormones

Question 22

what hormones control the distal convoluted tubule?

Answer 22

aldosterone, atrial natriuretic hormone, ADH, parathyroid hormone

Question 23

what are the collecting ducts responsible for?

Answer 23

water reabsorption

Question 24

what influences water reabsorption?

Answer 24

ADH

Question 25

where does ADH go in the collecting ducts and for what purpose?

Answer 25

membrane channels for water reabsorption

Question 26

describe the movement of water in the collecting ducts

Answer 26

it moves along the osmotic gradients created by the counter current exchange mechanism

Question 27

what hormones control the regulation of water and electrolytes?

Answer 27

antidiuretic hormone, renin-angiotensin-aldosterone, atrial natriuretic hormone

Question 28

what is the main control of water?

Answer 28

ADH

Question 29

what is ADH also known as?

Answer 29

vasopressin

Question 30

where is ADH produced and released?

Answer 30

produced in the hypothalamus and released from posterior pituitary gland

Question 31

where does ADH act on to increase water permeability?

Answer 31

distal convoluted tubules and collecting ducts

Question 32

what helps ADH control water?

Answer 32

aquaporin channels

Question 33

what parts of the nephron does the water move between?

Answer 33

tubule lumen and interstitial fluid

Question 34

what triggers the release of ADH?

Answer 34

decreased plasma volume and increased plasma osmolarity

Question 35

what does decreased plasma volume do to the baroreceptor distension?

Answer 35

decreases it

Question 36

what does increased plasma osmolarity do to osmoreceptor activation?

Answer 36

increases it

Question 37

what does increased ADH release result in?

Answer 37

increased water permeability of collecting ducts

Question 38

what is ADH secretion increased by?

Answer 38

lower ECF volume (low pressure receptors in atria and great veins) and increased ECF osmolarity (osmoreceptors in hypothalamus)

Question 39

where are ions present

Answer 39

in the ICF and ECF

Question 40

what controls ions?

Answer 40

homeostatic control

Question 41

name the ions

Answer 41

sodium, potassium, hydrogen and calcium

Question 42

what organ does ion control operate through?

Answer 42

kidneys

Question 43

what controls sodium?

Answer 43

renin-angiotensin-alodsterone system and atrial natriuretic hormone

Question 44

what does the renin-angiotensin-aldosterone system do?

Answer 44

promotes reabsorption of Na (and water) in DCT in exchange for K and H

Question 45

what is angiotensin?

Answer 45

potent vasoconstrictor

Question 46

what does the atrial natriuretic hormone

Answer 46

increases excretion of Na (and water) and has the opposite effect to aldosterone

Question 47

describe the renin-angiotensin-aldosterone system

Answer 47

stimulus releases renin from juxta-glomerular apparatus - renin joins with angiotensinogen to make angiotensin I - angiotensin converting enzyme (ACE) acts on angiotensin I to make angiotensin II - angiotensin II travels to the adrenal cortex - increased aldosterone release - increased Na reabsorption in cortical collecting ducts

Question 48

what is the atria natriuretic hormone secretion pathway?

Answer 48

increased plasma volume - increased atrial distension - increased ANH release - increased glomerular filtration rate (GFR) and decreased sodium reabsorption - increased sodium excretion

Question 49

what do cell membrane potentials depend on?

Answer 49

ECF of potassium

Question 50

what is potassium regulated by?

Answer 50

aldosterone, Na is swapped for K or H

Question 51

what can hyposecretion of ADH result in?

Answer 51

diabetes insipidus - large volumes of insipid (tasteless) urine

Question 52

what is hyersecretion of ADH

Answer 52

syndrome of inappropriate ADH

Question 53

what does excess ADH lead to?

Answer 53

water retention

Question 54

what does increasing ECF of potassium do to nerve function?

Answer 54

depolarises, causing axons to fire axon potentials and remain in a refractory period

Question 55

why are potassium salts used in toothpastes?

Answer 55

to desensitise hypersensitive dentine

Question 56

how does the potassium salts in toothpaste work?

Answer 56

the ions diffuse along tubules and there is a raised potassium concentration at the inner end of the tubule, this depolarises the nerve, sodium channels are inactivated for a prolonged refractory period

Question 57

what is the problem with potassium salts in toothpase?

Answer 57

the potassium build up does not persist

Question 58

with regards to renal blood flow what events lead to the increased renin secretion from the juxta-glomerular apparatus?

Answer 58

decreased plasma volume - increased sympathetic nerve activity - decreased renal BF - decreased stretch of J-G baroreceptors - juxta-glomerular apparatus - renin secretion

Question 59

with regards to decreased glomerular filtration rate, what events lead to the increased renin secretion from the juxta-glomerular apparatus?

Answer 59

decreased plasma volume - increased sympathetic nerve activity - decreased renal BF - decreased GFR - decreased Na in tubular fluid - macula densa - juxta-glomerular apparatus - increased renin secretion