Physiology (1-5) Flashcards
(126 cards)
1
Q
What is osmolarity?
A
Concentration of osmotically active particles in a solution
2
Q
What is the approximate osmolarity of the body’s fluids?
A
~300mosmol/L
3
Q
How can the osmolarity of a solution be calculated?
A
If the following are known:
- Molar concentration - Number of particles present
4
Q
What is the osmolarity of a 100mM solution of magnesium chloride?
A
Molar concentration = 100mM
Number of particles present = 3
Osmorality = 100 x 3 = 300mosmol/L
5
Q
What are the units of osmolality?
A
osmol/kg of water
6
Q
When are osmolarity and osmolality bascially interchangeable?
A
Weak solutions
Body fluids
7
Q
What is tonicity?
A
Effect a solution has on cell volume
8
Q
What effect does a hypotonic solution have on cells?
A
Cell lysis
9
Q
What effect does a hypertonic solution have on cells?
A
Cell shrinkage
10
Q
What does tonicity take into account?
A
Solute’s ability to cross cell membranes
11
Q
How much of the total body water is made up of ICF?
A
67%
12
Q
How much of the total body water is made up of ECF?
A
33%
13
Q
What forms the ECF?
A
Plasma (20%)
ISF (80%)
Lympha and transcellular fliud (Negligible)
14
Q
What tracer can we use to calculate total body water?
A
³H₂O
15
Q
What tracer can we use to calculate ECF?
A
Inulin
16
Q
What tracer can we use to calculate plasma volume?
A
Labelled albumin
17
Q
How can we calculate ICF?
A
TBW = ECF + ICF
We know TBW and ECF from ³H₂O and Inulin respectively
18
Q
How can we calculate the volume of distribution?
A
- Add a does of tracer (D) to an unknown volume of water (V)
- Allow tracer to mix evenly
- Take a small sample and measure [Tracer] (C)
- Calculate V as follows:
V(litres) = Does (D)/Sample
Where [Sample] = Mass/Volume in mg/L
19
Q
Calculate the volume of distribution for the following values:
- Dose given = 42mg
- Sample volume is 5ml
- Sample tracer mass is 0.01mg
A
[Tracer] in sample = 0.01/0.005 = 2mg/L
V = 42/2 = 21L
20
Q
Which of the following are sensible water losses and which are insensible:
- Sweat
- Faeces
- Skin
- Urine
- Lungs
A
Sensible:
- Sweat
- Faeces
- Urine
Insensible:
- Skin
- Lungs
21
Q
What sources of water loss are increased and decreased in hot weather?
A
Increased:
- Sweat
Decreased:
- Lungs
- Urine
22
Q
What sources of water loss are increased and decreased during prolonged heavy exercise?
A
Increased:
- Lungs
- Sweat
Decreased:
- Urine
23
Q
What is the main method of maintaining water balance?
A
Increasing water intake
24
Q
What is the ionic composition of ICF in regards to the following ions:
- Na+
- K+
- Cl-
- Bicarbonate
A
Sodium -> 10mM
Potassium -> 140mM
Cloride -> 7mM
Bicarbonate -> 10mM
25
What is the ionic composition of ECF in regards to the following ions:
- Na+
- K+
- Cl-
- Bicarbonate
Sodium -> 140mM
Potassium -> 4.5mM
Cloride -> 115mM
Bicarbonate -> 28mM
26
What are the main ions in the ICF?
Na+
Cl-
Bicarbonate
27
What are the main ions in the ICF?
K+
Mg²⁺
Negatively charged proteins
28
What causes water movement between the ICF and ECF?
Osmotic gradient
29
What results when there is a gain or loss of H₂O in regards to fluid osmolarity and ICF/ECF volumes?
Change in fluid osmolarity
| Similar change in ICF and ECF volumes
30
What results when there is a gain or loss of NaCl in regards to fluid osmolarity and ICF/ECF volumes?
```
Change in fluid osmolarity
Increased ECF NaCl:
- Increased ECF volume
- Decreased ICF volume
Decreased ECF NaCl:
- Decreased ECF volume
- Increased ICF volume
```
31
What results when there is a gain or loss of isotonic fluid in regards to fluid osmolarity and ICF/ECF volumes?
No change in osmolarity
| Change in ECF volume
32
What does the kidney alter in terms of the ECF and what is this vital for?
Composition
Volume:
- Both aid in BP control
33
What affect can small leaks or increased cell uptake of K⁺ have?
Severe changes in [K⁺]p:
- Muscle weakness -> Paralysis
- Arrhythmias -> Cardiac arrest
34
What does the rate of excretion of any substance equal?
Filtration rate + Secretion rate - Reabsorption rate
35
What does the rate of filtration of a substance X equal?
[X]plasma x GFR
36
What does the rate of excretion of a substance X equal?
[X]urine x Vu (urine flow rate)
37
What does the rate of reabsorption of a substance X equal?
Rate of Filtration of X - Rate of Excretion of X
38
What does the rate of secretion of a substance X equal?
Rate of Excretion of X - Rate of Filtration of X
39
If there is net reabsorption of a substance, what must be true?
Rate of Filtration > Rate of Excretion
40
If there is net secretion of a substance, what must be true?
Rate of Filtration
41
What acts as a barrier to RBC filtration into the glomerulus?
Glomerular capillary endothelial cells
42
What acts as a barrier to plasma protein filtration into the glomerulus?
Basement membrane
| Slit processes of podocytes in glomerular epithelium
43
What is the approximate glomerular capillary BP/hydrostatic pressure (BPgc)?
55mmHg
44
What is the approximate Bowman's capsule hydrostatic pressure (Hpbc)?
15mmHg
45
What is the approximate capillary oncotic pressure (COPgc)?
30mmHg
46
What is the approximate Bowman's capsule oncotic pressure (COPbc)?
0mmHg
47
How can the net filtration pressure be calculated?
(BPgc + COPbc) - ( Hpbc + COPgc)
| (55 + 0) - (15 + 30) = 10mmHg
48
What is the balance of hydrostatic pressure and osmotic forces known as?
Starling forces
49
How can GFR be calculated?
Filtration coefficient (Kf) x Net filtration pressure
50
What is the filtration coefficient?
How 'hole-y' the glomerular membrane is
51
What is a normal GFR?
Approximately 125ml/min
52
What is the main determinate of the GFR?
Glomerular afferent capillary BP/hydrostatic pressure
53
How are renal blood flow and GFR maintained extrinsically?
Sympathetic control -> The baroreceptor reflex
54
How are renal blood flow and GFR maintained intrinsically?
Myogenic mechanism
| Tubuloglomerular feedback
55
What happens to BPgc if the afferent arteriole is:
- Constricted
- Dilated
Constricted -> Falls
| Dilated -> Rises
56
What does autoregulation of renal blood flow do?
Prevents short-term BP changes affecting the GFR
57
How does the myogenic mechanism aid autoregulation of renal blood flow?
If vascular smooth muscle is stretched (due to increased BP) it contracts -> Afferent arteriole constriction -> GFR reduced
58
How does Tubuloglomerular feedback aid autoregulation of renal blood flow?
Involves the justaglomerular apparatus:
- If GFR rises -> Tubular NaCl flow increases
- > Afferent arteriole constriction -> GFR reduced
59
What can cause an increased Bowman's capsule hydrostatic pressure and what effect does this have on GFR?
Kidney stone
| Reduces GFR
60
What can cause an increased glomerular capillary oncotic pressure and what effect does this have on GFR?
Diarrhoea
| Reduces GCR
61
What can cause a decreased glomerular capillary oncotic pressure and what effect does this have on GFR?
Severe burns
| Increased GFR
62
If the filtration coefficient is reduced, what happens to GFR?
Decreases
63
What is plasma clearance?
Volume of plasma completely cleared of a substance per minute (ml/min)
64
How can we calculate the clearance of substance X?
Clearance of X = Rate of Excretion of X / [X]p
| Clearance of X = [X]u x Vu / [X]p
65
What is the clearance of a substance which is filtered, completely reabsorbed and not secreted? Give an example?
Zero
| Glucose
66
When else is the clearance of a substance 0?
If substance is not filtered and not secreted
67
What is the clearance of a substance which is filtered, partly reabsorbed and not secreted? Give an example?
Clearance
68
What is the clearance of a substance which is filtered, secreted and not reabsorbed? Give an example?
Clearance > GFR
All of filtered plasma cleared
Peritubular plasma also cleared
H+
69
If clearance
Substance is reabsorbed
70
If clearance = GFR?
Substance neither reabsorbed or secreted
71
If clearance
Substance secreted
72
What can Para-amino Hippuric Acid (PAH) be used to calculate?
Renal plasma flow
73
What is a normal renal plasma flow?
650ml/min
74
WHich of the following is not a feature of PAH:
- Freely filtered at glomerulus
- Produced in small (but quantifiable) amounts by the body
- Secreted into tubule
- Not reabsorbed at all
- Completely cleared from plasma
Produced in small (but quantifiable) amounts by the body
75
True or False; All PAH which escapes filtration is secreted from peritubular capillaries?
True
76
What is the filtration fraction?
Fraction of plasma flowing through glomeruli which is filtered into tubules
77
What properties should a clearance marker have?
Non-toxic
Inert (not metabolised)
Easy to measure
78
What additional features should a GFR marker have?
Freely filtered
Not:
- Secreted
- Reabsorbed
79
What additional features should a RPF marker have?
Freely filtered
AND
Completely secreted
80
Why is inulin not a convenient substance to use to estimate GFR?
Requires a constant infusion to maintain [Inulin]p
81
How is the filtration fraction calculated?
GFR/Renal Plasma Flow
82
What is the normal filtration fraction?
~20%
83
How is renal blood flow calculated?
RPF x 1/1-HCT (Where HCT is the Haematocrit):
- HCT is the % of blood which is RBCs
-> ~45% in males
-> ~40% in females
RBF = 650/1-0.45 = 650 x 1.85 = 1200ml/min
84
What rate is the filtrate absorbed in the PCT?
~80ml/min
85
What rate is the filtrate absorbed in the Loop of Henle?
~45ml/min
86
Is reabsorbed fluid hypotonic, isotonic or hypertonic to the glomerular filtrate?
Isotonic
87
Which of the following is not reabsorbed in the PCT:
- Sugars
- Amino acids
- Na⁺
- PO₄³⁻
- SO₄²⁻
- Lactate
Na⁺
88
Which of the following is not secreted into the PCT:
- H⁺
- Hippurates
- Neurotransmitters
- Bile pigments
- K⁺
- Uric acid
- Drugs
- Toxins
K⁺
89
What are the two routes by which a substance can be reabsorbed from the tubule?
Transcellular (mainly)
| Paracellular
90
How does primary active transport work?
Energy required to operate carrier
| Substance moved AGAINST its concentration gradient
91
How does secondary active transport work?
Carrier molecule transported coupled to the concentration gradient of an ion -> Usually Na⁺
92
How does facilitated diffusion work?
Passive carrier-mediated transport
| DOWN its concentration gradient
93
What chemicals can diffuse through the lipid bilayer?
Oxygen and Carbon dioxide
94
Give an example of a compound that is carried through a membrane by facilitated diffusion?
Glucose
95
Give an example of a primary active transport
Na+/K+ ATPase:
- Na+ reabsorbed
- K+ secreted
96
Give an example of secondary active transport
Na+/Glucose co-transporter:
| - Glucose carried coupled to Na+
97
What is the approximate renal threshold for glucose?
[Glucose]p 10-12mmol/L
98
What is the transport maximum for glucose?
~2.0mmol/min
99
What happens once glucose filtered > glucose reabsorbed?
Excretion = Filtration = Reabsorption
100
What happens to the clearance of a substance that is reabsorbed or secreted once Tm (Transport maximum) is reached?
It is not constant
101
How is Cl- reabsorption driven in the PCT?
Na+ reabsorption drives Cl- reabsorption via the paracellular pathway
102
How is water reabsorbed in the PCT?
Osmosis
103
What is the osmolality of the tubular fluid when it leaves the PCT?
~300mosmol/L (ie isotonic to plasma)
104
What are the main functions of the Loop of Henle?
Generates a corticomedullary solute concentration gradient
| Helps form hypertonic urine
105
What sort of flow does the Loop of Henle have?
Countercurrent
106
What runs alongside the Loop of Henle that helps establish a hyperosmotic medullary ISF?
Vasa recta
107
What is reabrosbed in the ascending limb of the Loop of Henle?
Na+ and Cl-
108
How does reabsorption occur in the thick upper part of the ascending limb of the Loop of Henle?
Active transport
109
How does reabsorption occur in the thin lower part of the ascending limb of the Loop of Henle?
Passive transport
110
How permeable is the ascending limb of the Loop of Henle to water?
Very impermeable (little/no water follows Na+)
111
What processes do and don't occur in the descending limb of the Loop of Henle?
Highly permeable to water -> Reabsorbed
| NaCl is NOT reabsorbed
112
What transporter is present on the apical/lumenal membrane of the PCT?
Na+/K+/2Cl- co-transporter
113
What transporters are present on the basolateral membrane of the PCT?
K+/Cl- co-transported
| Na+/K+ exchanger
114
What does K+ recycling in the PCT do?
Allows NaCl to be absorbed into the ISF
115
The following steps are the first part in setting up the corticomedullary solute concentration gradient via the triple co-transporter, put them in order:
- ISF can't enter DL of Loop of Henle
- Fluid in DL is concentraed
- Tubular fluid diluted and ISF osmolarity rised
- NaCl removed from AL (and water can't follow)
- Water leaves DL by osmosis
1. NaCl removed from AL (and water can't follow)
2. Tubular fluid diluted and ISF osmolarity rised
3. ISF can't enter DL of Loop of Henle
4. Water leaves DL by osmosis
5. Fluid in DL is concentraed
116
After the initial corticomedullary solute concentration gradient via the triple co-transporter is set up, what happens next?
1. Fluid enters descending limb of Loop of Henle
2. Fluid moves into ascending limb
3. Hypotonic fluid enters DCT
117
What is the third step in setting up the corticomedullary solute concentration gradient?
1. Solute pumped out of ascending limb
2. ISF osmolarity rises
3. Passive water efflux from descending limb
4. Flow occurs
118
How does countercurrent multiplication finish the set-up of the corticomedullary solute concentration gradient?
1. Iso-osmotic fluid leaves the PCT and enters the descending limb of the Loop of Henle
2. Hypo-osmotic fluid enters the DCT
3. Horizontal gradient multiplied into a large vertical gradient
119
What are the steps in the urea cycle throughout the nephron?
1. PCT and Loop of Henle relatively impermeable to urea -> Concentration in tubule rises
2. DCT is totally impermeable to urea -> [Urea]t rises
3. ~50% of urea absorbed into ISF at the collecting duct
4. Urea diffuses passively into Loop of Henle
120
Why is a corticomedullary solute concentration gradient set up?
Enables the kidnesy to produce urine of varying volumes and concentrations
121
What is the Vurine on normal fluid intake?
~1ml/min
122
Which nephrons does the vasa recta run alongside?
Juxtamedullary nephrons
123
What happens to the blood in the vasa recta?
Equilibrates with ISF due to the 'leaky' endothelium
124
What happens to the blood osmolarity as the vasa recta enters the medulla?
It increases:
- Water leaves
- Solute enters
125
What happens to the blood osmolarity as the vasa recta rises back into the cortex?
It decreases:
- Water enters
- Solute leaves
126
The vasa recta blood flow tends to wash away the concentration gradient set up in the medulla, how is this reduced?
1. Vasa recta follows hairpin turns
2. It is freely permeable to NaCl, water and urea
3. Vasa recta blood flow is low
