Lecture 33: Body water - distribution and regulation

Question 1

What % of our body weight is water?

Answer 1

55-60% of our body weight

• Males 60%
• Females 55%

Question 2

What proportion of our TBW is ECF?

Answer 2

1/3

Question 3

What proportion of our TBW is ICF?

Answer 3

2/3

Question 4

What proportion of ECF is plasma?

Answer 4

1/5

Question 5

What proportion of ECF is interstitial fluid?

Answer 5

4/5

Question 6

What is osmolarity based on?

Answer 6

The number of osmotically active ions or solutes

Question 7

What can osmolarity be estimated by?

Answer 7

Specific gravity

Question 8

What does iso-osmotic mean?

Answer 8

Same osmolarity

Question 9

What does hypo-osmotic mean?

Answer 9

Lower osmolarity

Question 10

What does hyper-osmotic mean?

Answer 10

Higher osmolarity

Question 11

What is tonicity based on?

Answer 11

The effect of a solution on cells

Question 12

What does an isotonic solution not do?

Answer 12

Change water homeostasis between cells

Question 13

What is the sodium concentration in the ECF?

Answer 13

145 mmol/L

Question 14

What is the potassium concentration in the ECF?

Answer 14

4-5 mmol/L

Question 15

What is the sodium concentration in the ICF?

Answer 15

15 mmol/L

Question 16

What is the potassium concentration in the ICF?

Answer 16

150 mmol/L

Question 17

What is particular about the osmolarity between the the ICF/ECF

Answer 17

They are the same/similar

Question 18

Total body water remains relatively what?

Answer 18

Constant

Question 19

Intake and loss of water must be in what?

Answer 19

Balance

Question 20

Urine output is adjusted to do what?

Answer 20

Maintain balance

Question 21

What is water output most effected by?

Answer 21

Kidneys producing urine

Question 22

What are the 4 important places within the nephron where sodium is reabsorbed?

Answer 22

• Proximal convoluted tubule(PCT)
• Thick ascending loop (TAL)
• Distal convoluted tubule (DCT)
• Collecting duct (CD)

Question 23

What % of sodium is reabsorbed in the PCT?

Answer 23

67%

Question 24

What % of sodium is reabsorbed in the TAL?

Answer 24

25%

Question 25

What % of sodium is reabsorbed in the DCT?

Answer 25

5%

Question 26

What % of sodium is reabsorbed in the CD?

Answer 26

3%

Question 27

What are the 3 important places within the nephron water is reabsorbed?

Answer 27

- PCT - Thin descending loop (tDL) - CD

Question 28

What % of water is reabsorbed in the PCT?

Answer 28

67%

Question 29

What % of water is reabsorbed in the tDL?

Answer 29

25%

Question 30

What % of water is reabsorbed in the CD?

Answer 30

2-8%

Question 31

What % of water is excreted as urinary secretion?

Answer 31

0.5 - 8% of the filtered load

Question 32

What is needed to make you own Powerade? | 4

Answer 32

- Water - Sugar - Sodium - Flavour/vitamins

Question 33

What is water reabsorption in the proximal tubule driven by?

Answer 33

Sodium reabsorption

Question 34

What do transporters such as the sodium glucose-cotransporter use to reabsorb glucose?

Answer 34

The sodium gradient

Question 35

The thick ascending loop reabsorbs sodium into the interstitial generating what?

Answer 35

A high osmotic medullary gradient (HOMG)

Question 36

`The thin descending loop is leaky epithelium facilitating what?

Answer 36

Water reabsorption

Question 37

Water reabsorption in the thin descending loop can occur how? (2)

Answer 37

- Via aquaporins (transcellular) | - Via the paracellular pathway

Question 38

Obligatory water reabsorption is not what?

Answer 38

Regulated

Question 39

Obligatory water reabsorption account for what % of total water reabsorption

Answer 39

92% of total water reabsorption

Question 40

Facultative water reabsorption in the CD has what type of epithelium?

Answer 40

Tight epithelia

Question 41

What 2 types of water reabsorption can occur in the CD?

Answer 41

- Obligatory water reabsorption | - Facultative water reabsorption

Question 42

Facultative water reabsorption uses only what type of pathway?

Answer 42

Transcellular

Question 43

What is regulated reabsorption in the CD regulated by?

Answer 43

ADH

Question 44

Facultative water reabsorption account for what % of total water reabsorption?

Answer 44

2-8% of total water reabsorption

Question 45

Changing water contents does what?

Answer 45

Changes osmolarity

Question 46

What does fluid shift between to equalise osmolarity?

Answer 46

ECF - ICF

Question 47

What does changing water contents do to a cell?

Answer 47

Changes the size of the cell

Question 48

What does a change in the size of cell do? | 2

Answer 48

- Cell structure altered | - Cell functions become impaired

Question 49

What does a hypertonic solution do to red blood cells?

Answer 49

Causes water to move out of the cell and it to shrivel

Question 50

What does an isotonic solution do to red blood cells?

Answer 50

Causes water to move in/out at a constant rate

Question 51

What does a hypotonic solution do to red blood cells?

Answer 51

Causes water to move into the cell and it to swell

Question 52

What are red blood cells dependent on?

Answer 52

An isotonic environment

Question 53

What do hypertonic/hypotonic environments to to red blood cells?

Answer 53

Alter their function

Question 54

What does TBW changes alter?

Answer 54

Plasma (ECF) osmolarity

Question 55

What are changes to osmolarity of ECF detected by?

Answer 55

Osmoreceptors in the hypothalamus (Brain)

Question 56

When changes to osmolarity of ECF are detected what happens?

Answer 56

It stimulates the pituitary gland to secrete more/less ADH

Question 57

What does ADH alter the permeability of?

Answer 57

The renal collecting duct

Question 58

When the permeability of the renal collecting duct is altered by ADH what happens?

Answer 58

Water is retained or excreted to balance initial change in TBW

Question 59

What happens to water re-absorption and urine production without ADH?

Answer 59

Diuresis - Large volume of dilute urine

Question 60

What happens to water re-absorption and urine production with ADH?

Answer 60

Anti-diuresis - small volume of concentrated urine

Question 61

ADH in the blood stream finds what?

Answer 61

Its receptor on the basolateral side of CD cells

Question 62

What does ADH via intracellular signalling cascades increase the number of?

Answer 62

Aquaporins in the apical membrane of CD

Question 63

What does an increase in aquaporins in the apical membrane of CD do?

Answer 63

Increases water permeability of the apical membrane

Question 64

What can macula dense cells sense?

Answer 64

Changes in sodium reaching the distal tubule and therefore perfusion of the nephron

Question 65

If sodium levels reaching the distal tubule is too low what happens?

Answer 65

It leads to a release of renin from juxtaglomerular cells

Question 66

What is a decrease in ECF volume by fluid loss detected by?

Answer 66

Baroreceptors/kidney

Question 67

What does a decrease in ECF volume detected by the kidneys causes the kidneys to do? (2)

Answer 67

- Renin release leading to angiotensin II activation | - Increased aldosterone

Question 68

What does renin release leading to angiotensin II activation and increased aldosterone lead to? (2)

Answer 68

- Decrease sodium loss in urine | - Decreased water loss in urine

Question 69

What is an increase in ECF volume or fluid gain detected by?

Answer 69

Cardiac cells

Question 70

What is an increase in ECF volume detected by cardiac cells to do?

Answer 70

Cause the release of natriuretic peptides

Question 71

What do natriuretic peptides have an effect on? | 3

Answer 71

- Hypothalamus - Kidneys - Blood vessels

Question 72

What does the hypothalamus, kidneys and blood vessels cause when activated by natriuretic peptides? (2)

Answer 72

- Increase in sodium loss in urine | - Increased water loss in urine