Lecture 33: BODY WATER - DISTRIBUTION AND REGULATION Flashcards
1
Q
What is TBW?
A
55-60% of body weight
2
Q
What is ECF?
A
1/3 of TBW
3
Q
What is ICF?
A
2/3 of TBW
4
Q
What is plasma?
A
1/5 of ECF
5
Q
What is interstitial fluid?
A
4/5 of ECF
6
Q
What is osmolarity based on?
A
The number of osmotically active ions or solutes (which attract water)
7
Q
What is the concentration of NaCl?
A
145mM = 145mM Na+ + 145mM Cl- = 290mosmol/L
8
Q
What can osmolarity be measure by?
A
Specific gravity
9
Q
What does iso-osmotic mean?
A
The same osmolarity
10
Q
What does hypo-osmotic mean?
A
Lower osmolarity
11
Q
What does hyper-osmotic mean?
A
Higher osmolarity
12
Q
What is tonicity based on?
A
The effect of a solution on cells
13
Q
What does an isotonic solution do?
A
Not change the water homeostasis between cells
14
Q
What is the concentration of sodium in the ECF?
A
145 mmol/L
15
Q
What is the concentration of sodium in the ICF?
A
15 mmol/L
16
Q
What is the concentration of potassium in the ECF?
A
4-5 mmol/L
17
Q
What is the concentration of potassium in the ICF?
A
150 mmol/L
18
Q
What is the osmolarity of the ECF?
A
275-295 mosmol/L
19
Q
What is the osmolarity of the ICF?
A
275-295 mosmol/L
20
Q
What remains relatively constant?
A
Total body water
21
Q
What must balance?
A
Intake and loss of water
22
Q
What is adjusted to maintain water balance?
A
Urine output (so the kidneys are the most important in water balance)
23
Q
Where does reabsorption of sodium occur?
A
PCT, thick ascending limb, DCT and collecting duct
24
Q
What amount of sodium is absorbed in the PCT?
A
67%
25
What amount of sodium is absorbed in the thick ascending limb?
25%
26
What amount of sodium is absorbed in the DCT?
5%
27
What amount of sodium is absorbed in the collecting duct?
3%
28
Where does reabsorption of water occur?
In the PCT, thin descending limb and collecting duct
29
What is reabsorption of water in the PCT driven by?
Sodium reabsorption in order to make isosmotic solution
30
What do transporters such as the sodium glucose transporter use?
The sodium gradient to reabsorb glucose
31
What does SGLT do?
Sodium/glucose - cotransporter from the filtrate to the cell
32
What are aquaporins?
Channels for water to get from filtrate into the cell and then into the blood
33
What does a glucose transporter do?
Transport glucose from the cell to the blood
34
What does Na+/K+ ATPase do?
Transport sodium into the blood from the cell
35
What does the thick ascending limb do?
Reabsorbs sodium into the interstitial generating a high osmotic medullary gradient (HOMG)
36
What is the thin descending limb like?
Leaky epithelium, facilitating water reabsorption via aquaporins (transcellular) and the paracellular pathway
37
What is the thin descending limb permeable to?
Water and impermeable to solutes so it causes the solute concentration to increase (in urine)
38
What is the thick ascending limb permeable to?
Impermeable to water and selectively permeable to na+ and cl- so solute concentration decreases (in urine)
39
Where does obligatory reabsorption occur?
In the PCT and thin descending limb
40
Is obligatory reabsorption regulated?
no
41
What portion of water reabsorption does obligatory reabsorption account for?
92%
42
Where does facultative reabsorption occur?
In the collecting duct
43
What is the epithelia at facultative reabsorption?
Tight (so only transcellular)
44
What is facultative reabsorption regulated by?
ADH
45
What portion of water reabsorption does facultative reabsorption account for?
2-8%
46
What does changing water content do?
Change osmolarity
47
What happens to equalise?
Fluid shifts between ECF and ICF
48
What also changes when water content changes?
Volume of compartments
49
What happens when volume of compartments change?
Cell size changes, cell structure altered and cell functions become impaired
50
What are red blood cells dependent on?
An isotonic environment
51
What changes the function of red blood cells?
Hypertonic environment (shrivel) or hypotonic environment (burst)
52
What do total body water changes alter?
Plasma (ECF) osmolarity
53
What is change in plasma osmolarity detected by?
Osmoreceptors in the hypothalamus (brain)
54
What do osmoreceptors stimulate?
Pituitary gland to secrete more/less ADH
55
What does ADH do?
Alters the permeability of the renal collecting duct so that water is retained/excreted to balance the initial change in TBW
56
What does the effect of ADH mean?
Plasma osmolarity and cell volume become stable
57
What happens when dehydration (increased sodium levels) occurs?
Increased ADH secretion, thirst and water reabsorption, water into the ECF to decrease Na+ levels
58
What happens when hyper hydration (decreased sodium levels) occurs?
Decreased ADH secretion, thirst suppressed and water loss, water decreases in ECF to increase sodium levels
59
What happens without ADH (diuresis)?
Small amount of water reabsorption and a large volume of dilute urine is produced
60
What happens with ADH (antidiuresis)?
Large amount of water reabsorption and a small volume of concentrated urine is produced
61
What does ADH in the bloodstream do?
Finds its receptor in the basolateral side of collecting duct cells
62
What does ADH do once bound to the receptor?
Via intracellular signalling cascades increases the number of aquaporins in the apical membrane increasing water permeability of the apical membrane of the collecting duct
63
What can the macula densa cells do?
Sense changes in sodium reaching the distal tubule and therefore perfusion of the nephron; if it is too low this leads to a release of renin from juxtaglomerular cells
64
what regulates changes in ECF volume?
ANP or aldosterone (renin-All-Aldosterone-System)
65
What is the receptor when increased ECF volume by fluid gain (or fluid and Na+ gain)?
cardiac muscle cells
66
What does the receptor stimulate when increased ECF volume by fluid gain (or fluid and Na+ gain)?
release of ANP
67
What are the effectors when increased ECF volume by fluid gain (or fluid and Na+ gain)?
hypothalamus, kidney and blood vessels
68
What is the response when increased ECF volume by fluid gain (or fluid and Na+ gain)?
Increased sodium lossed in urine and increased water lost inurine
69
What is the result when increased ECF volume by fluid gain (or fluid and Na+ gain)?
Decreased ECF volume
70
What are the receptors when decreased ECF volume by fluid loss (or fluid and Na+ loss)?
baroreceptors and kidneys
71
What do kidneys stimulate when decreased ECF volume by fluid loss (or fluid and Na+ loss)?
RAAS - renin release leads to angiotensin ll activation and increased aldosterone release
72
What do baroreceptors stimulate when decreased ECF volume by fluid loss (or fluid and Na+ loss)?
sympathetic activation
effectors - hypothalamus, heart and blood vessels
response - increased ADH release
73
What is the response when decreased ECF volume by fluid loss (or fluid and Na+ loss)?
Decreased sodium lost in urine and decreased water lost in urine
74
What is the result when decreased ECF volume by fluid loss (or fluid and Na+ loss)?
Increased ECF volume
