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Foundations of Biomedical Sciences 1 > PPP: Body Fluids, Flow + Pressure > Flashcards

PPP: Body Fluids, Flow + Pressure Flashcards

1
Q

What is the percentage of water in a typical 70kg man?

A

60%

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2
Q

What is the cation that determines intracellular fluid and what does this control?

A

K+ - controls cell volume

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3
Q

What is the cation that determines extracellular fluid and what does this control?

A

Na+ - controls blood volume

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4
Q

What is the extracellular space/fluid?

A

The interstitial space + blood plasma - the plasma connects all of the extracellular spaces in the body

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5
Q

What are the 3 main fluid compartments?

A

1) blood plasma
2) intracellular space
3) interstitial space

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6
Q

What is the total body water (TBW) in humans?

A

42L

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7
Q

How is the TBW distributed between the 3 main fluid compartments?

A 
Intracellular = 28L (40%)
Interstital = 10.5L (15%)
Plasma = 3.5L (5%)
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8
Q

What does the water content of tissues depend on?

A

The fat content of the tissue (more fat, less water)

- water content of lean tissue = 0.17L/kg

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9
Q

What are 6 other fluid compartments (transcellular) ?

A

1) cerebrospinal fluid (CSF)
2) aqueous and vitreous humours of the eye
3) synovial fluid (joints)
4) amniotic fluid (pregnancy)
5) GI tract secretions
6) lymph

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10
Q

What are transcellular fluids?

A
  • Special variants of the extracellular space that may have slow diffusion to and from plasma
  • They are not accessed by capillaries as closely as the typical extracellular space
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11
Q

What are compartments?

A

Physiological collections of organs and tissues containing water, divided by cell membranes

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12
Q

Describe the dilution method to measure the volume of fluid compartments?

A

1) add a known amount of substance (s) to an unknown volume (v) in the body - use substances that only inhabit a specific compartment (don’t diffuse into others) and are non-toxic
2) measure the concentration in grams/litre
3) obtain a sample determine the volume using the formula V = S / C

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13
Q

What substances could you use to measure plasma volume?

A

e.g. Evan’s Blue (dye), labelled inulin/albumin - large and does not cross capillaries into interstitial space

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14
Q

What substances could you use to measure extracellular space volume?

A

e. g. 24Na (can recognise it from other Na), sucrose (not transported into cells with GLUT transporters
- these can easily cross capillaries but not enter cells

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15
Q

What substances could you use to measure TBW?

A

Heavy water (2H2O) - distributes with all water

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16
Q

How would you measure volume of interstitial/intracellular space?

A 
Interstitial = extracellular - plasma
Intracellular = TBW - extracellular
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17
Q

What are the 4 major constituents of body fluids?

A

1) ions
2) proteins - more in intracellular and plasma than extracellular
3) dissolved gases, nutrients, metabolites
4) cells in blood - intravascular space

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18
Q

Describe the main ions in the extracellular and intracellular fluid

A
  • main ions = Na+, Cl- and K+

- high [K+] intracellular, low [K+] extracellular (vice versa with Na+)

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19
Q

Why does the intracellular and extracellular fluid have to be isotonic?

A

To maintain osmotic pressure (osmolarity) and ∴ the shape and function of the cells

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20
Q

What is osmolarity determined by?

A

The total number of freely diffusible entities i.e. ions in a solution

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21
Q

What are the units of osmolarity and osmolality?

A 
Osmolarity = osmole/L (10mM CaCl2 = 30 mosm/litre)
Osmolality = osmole/kg
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22
Q

What is osmotic pressure?

A

The pressure with which water is drawn across the semi-permeable membrane (directly proportional to osmolarity)

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23
Q

Why is it important that osmolarity is directly proportional to osmotic pressure?

A

It means that osmolarity of the plasma/cell controls plasma/cell volume bc if osmolarity increases, it draws water into plasma
- ∴ this affects pressure of a cell/plasma

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24
Q

What are the two types of osmotic pressure?

A

1) crystalloid

2) oncotic (colloidal)

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25
Q

What is crystalloid osmotic pressure (cells)?

A
  • Osmotic pressure created by small diffusible ions
  • It sets the important equilibrium between the intracellular and interstitial space
  • As the cell membrane is largely impermeable to ions, water moves
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26
Q

What is oncotic (colloidal) osmotic pressure (plasma)?

A
  • Pressure exerted by proteins in capillaries (ions cross capillaries easily ∴ no crystalloid osmotic pressure diff)
  • The oncotic pressure is 25mmHg and draws water into the plasma space, offsetting the hydrostatic pressure that would otherwise remove the water from the plasma into the interstitial space (maintains eqm between plasma and interstitial space)
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27
Q

Describe what normally happens with pressure throughout a capillary

A

1) at the arterial end of the capillary bed, there is a higher hydrostatic pressure than plasma oncotic pressure ∴ fluid moves out of the plasma into the surrounding tissues
2) at the venous end of the capillary bed, the hydrostatic pressure decreases ∴ the oncotic pressure exceeds the hydrostatic pressure and fluid from the tissues is reabsorbed into the plasma
(problems with this = oedema)

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28
Q

What are the concentrations of ions in plasma (mM/L)?

A 
Na+ = 140
K+ = 4
Ca2+ = 2
Cl- = 110
HCO3- = 24
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29
Q

What are the concentrations of ions in intracellular space (mM/L)?

A

Na+ = 10
K+ = 120
Ca2+ = 100 nM/L
(+ aa, bit of Cl-, proteins)

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30
Q

What does plasma contain?

A

1) plasma proteins (albumin, globulins, fibrinogen)
2) cells (RBCs, WBCs, granulocytes)
3) platelets (type of blood cell)

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31
Q

Describe albumin (main plasma protein)

A
  • The protein responsible for the oncotic pressure
  • Transport function: drugs and other compounds can be absorbed into the albumin and bind to it ∴ disappearing from solution
  • Contributes to buffering
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32
Q

Describe globulins

A
  • Three types of specific protein with specific functions (alpha, beta, gamma)
  • Small, spherical proteins
  • Diff functions: clotting factors (haemostasis), transferin transports iron harvested from decaying RBCs, gamma globulins are ABs
33
Q

Describe fibrinogen

A
  • Substrate for blood coagulation
  • Lies in wait for the coagulation cascade to be set off + to coagulate blood when there is a leak in the vascular system (haemostasis)
34
Q

What is the packed cell volume (PCV)?

A

The total volume of all RBCs (normally 45% of total blood volume)

35
Q

What can be problems with RBCs?

A

1) too many RBCs = problem for circulation bc blood needs to have a low viscosity to flow freely through capillaries
2) anaemia = too few RBCs/low Hb per cell/defective Hb/low Hb production ∴ transport of oxygen is not optimum - can diagnose by counting the number of RBCs and looking at their size

36
Q

Describe erythrocytes (RBCs)

A
  • Short lifespan in the circulation (120 days) bc they have no nucleus (mostly just Hb)
  • Generated in the bone marrow, removed by the spleen (cannot regenerate or repair themselves)
  • RBC count (RBCC) on avg = 5 x 10^12 / litre
  • Function: transport of oxygen and buffering of blood pH
37
Q

Describe leucocytes (WBCs)

A
  • They use the blood for transport as they mainly fulfill their function in the periphery elsewhere
  • Defend against foreign materials and involved in inflammation/allergic responses
  • Monocytes migrate to tissues and form macrophages which phagocytose
  • Granulocytes are the largest group (neutrophils, eosinophils, basophils)
38
Q

Describe platelets

A
  • Fragments of cells (no nucleus) generated in the bone marrow by flaking of their precursor (megakaryocytes)
  • They are the first response when there is a leak in the blood vessel (plug the leak) as they are attracted to tissue different from the normal endothelial tissue lining the blood vessel (i.e. an injury) - haemostasis
  • Here, they release the contents of their dense granules which attract more platelets, helping to set off and maintain the coagulation of the blood at the place of injury
39
Q

Describe human circulation

A
  • It is a closed system with two pumps (right and left ventricle) in series (as there are two circulations)
40
Q

Describe the two circulations

A

1) pulmonary - between the lungs and heart
- low resistance and low pressure
2) systemic - between the rest of the body and heart
- high resistance and high pressure
- most of the branches are in parallel with each other

41
Q

What are the exceptions to normal circulation patterns?

A

1) GI tract circulation does not drain directly into the venous circulation, it first goes to the liver ∴ here the liver and GI tract systemic circulations are in series with each other
2) Bronchiole circulation - the tissues of the airways require their own branch of the systemic circulation bc diffusion from the air within the airways is not sufficient to provide oxygen to the airways
- this drains into the pulmonary venous circulation (not directly into the systemic venous circulation) ∴ deoxygenated blood coming from bronchiole vasculature is acc partially diluting the oxygen returning from the lungs to the heart

42
Q

What is the terminology to describe flow out of the heart?

A

1) stroke volume = volume per beat (70ml)
2) cardiac output = volume per minute (5L/min)
∴ CO = SV x heart rate (HR) ∴ flow is movement of a volume of liquid over a period of time

43
Q

Where does resistance to flow come from?

A

Vascular beds in the systemic circulation

44
Q

What is the total peripheral resistance (TPR)?

A

The total resistance in the systemic circulation
- this determines the afterload = pressure against which the left ventricle has to pump in order to maintain flow through the systemic circulation (pressure load on the left heart)

45
Q

What is the venous return?

A

The volume of blood that flows into the heart through the venous circulation per minute (5L/min)
- venous return must equal CO as it is a series flow of blood ∴ the same volume of blood leaves and returns to the heart per minute

46
Q

What is the central venous pressure (CVP)?

A

The pressure of the blood returning in the venous circulation to the heart (filling pressure) = preload

  • determines the filling of the heart with blood
  • this is what stretches the ventricle of the heart and ∴ helps determine how hard the muscle then contracts back to generate cardiac output
47
Q

What is bulk flow?

A

Transport within the blood or air due to pressure differences which determine movement
- the blood + everything dissolved and carried in it moves with the blood

48
Q

What is Fick’s Law about?

A

The rate of diffusion in a solution

49
Q

What does Fick’s Law say that the rate of diffusion depends on?

A
  • Variable factors:
    1) the area over which diffusion occurs (A)
    2) the conc difference of a diffusing substance (ΔC)
    3) the distance the substance has to travel (ΔX)
  • Constant factors (affect how easily a substance diffuses):
    4) temp (normally 37 degrees)
    5) solubility of a substance in plasma/tissue fluid (depends on temp but temp is constant)
    6) the square root of Mr of a substance
50
Q

What is Fick’s Law of Diffusion?

A

rate of diffusion = ΔC x A/ΔX x solubility/sqrt(Mr)

51
Q

What does Fick’s Law show?

A

1) diffusion is proportional to ΔC and permeability (rest of equation)
2) diffusion is too slow over large distances (if ΔX is very large, rate is very slow) ∴ ΔX is a rate limiting factor and flow is required to transport substances around the body

52
Q

Describe Darcy’s Law

A
  • In a tube with a pressure difference where P1 > P2, the fluid in the tube will flow from P1 to P2
  • The rate of flow is proportional to the pressure difference (P1-P2) and inversely proportional to the resistance to flow
  • R is an independent variable ∴ if pressure changes, flow changes and vice versa but resistance does not change in response to these changes (changes independently)
  • When R changes, it influences both pressure and flow
53
Q

What is Darcy’s Law?

A

Flow = (P1-P2)/R

54
Q

What does Poiseuille’s Law determine?

A

Resistance to flow

55
Q

What is Poiseuille’s Law?

A

R = 8VL/πr^4 (V = viscosity of fluid, L = length of tube)

56
Q

Combine Darcy’s and Poiseuille’s Law

A

Flow = ((P1-P2) x πr^4)/8VL

57
Q

What is the significance of Darcy’s and Poiseuille’s Law combined?

A
  • Flow is proportional to r^4 as radius is the most important component in determining resistance and ∴ flow (R is proportional to 1/r^4)
  • ∴ a small change in diameter causes a large change in resistance and ∴ flow
58
Q

Describe the effect of viscosity on flow

A
  • The thicker the fluid, the higher the viscosity (RBCs and plasma proteins make blood very viscous)
  • ∴ this higher viscosity alone would reduce flow compared to the flow of water through the same tube
  • But the reduction in flow is not as significant as this bc blood is a non-Newtonian fluid (relationship less simple)
59
Q

What is laminar flow?

A

Flow in a straight, single direction (the ideal situation)

60
Q

Describe the process of axial streaming

A

1) viscous drag at the sides of the tube due to friction between the flowing blood and endothelium of the blood vessel slows the fluid (influenced by viscosity)
2) there is more drag at the sides of the tube than in the middle ∴ the fastest movement (most flow) is in the centre
- this difference between flow in the middle and at the sides becomes more apparent as the radius becomes smaller
3) ∴ the RBCs tend to align themselves in the middle of the tube so that they can flow through the fastest moving stream of fluid and avoid contact with the sides of the tube
4) in small vessels, this effectively reduces viscosity of the blood (Fahraeus-Lindqvist effect)

61
Q

Describe flow in capillaries

A
  • RBCs are 7μm in diameter and capillaries are 6μm in diameter to absolutely minimise diffusion distance
  • ∴ RBCs fit the capillary like a plug but are very deformable ∴ they easily flow through the capillary
62
Q

How is laminar flow disrupted?

A
  • There may be situations where there are obstructions (sharp edges, natural branching points or atherosclerotic plaque) which produce a narrowing at certain points in arteries or arterioles
  • These obstructions or high velocity, esp in large tubes, can disrupt laminar flow, leading to turbulence
  • This can lead to problems as turbulent flow is not good for the health of arteries/arterioles
63
Q

What are the effects of turbulent flow?

A

1) the turbulence significantly increases resistance as it increases friction with the endothelium and causes vibrations
2) high velocity blood flow due to narrow heart valves causes murmurs (oxidative stress)
3) high velocity airflow due to narrowed airways causes wheezes (oxidative stress)
4) turbulence can also cause damage to the vessel wall and/or activate clotting mechanisms esp if the endothelium is damaged

64
Q

Why is Poiseuille’s Law an idealised situation?

A

It assumes that the tube is rigid and not flexible

- ∴ if the tube is rigid, there is a linear relationship between flow and pressure

65
Q

Why is it significant that veins (+arteries and arterioles) are flexible tubes?

A
  • It means that the relationship between flow and pressure can change depending on how the structure of the vessel changes
  • They are distensible vessels ∴ when pressure increases, the vessel passively dilates
  • ∴ as pressure increases, there is a disproportional increase in flow as the radius increases, reducing resistance and increasing flow
  • e.g. pulmonary circulation - when CO increases, to maintain flow through the lungs, pulmonary arteries expand
66
Q

What is the effect of a distensible vessel having myogenic tone?

A
  • It allows parts of the body to maintain flow at the same rate regardless of changes in pressure (increases in MABP/CO)
  • e.g. in cerebral circulation - the brain only needs a certain amount of blood regardless of what else is happening in the body
  • ∴ these vessels are distensible but are able to contract in response to increases in pressure to maintain flow at a steady rate (myogenic tone)
67
Q

How do you calculate total resistance of a circuit in series?

A

Rtotal = R1 + R2 + R3 etc (sum of individual resistances)

68
Q

How do you calculate total resistance of a circuit in parallel?

A

1/Rtotal = 1/R1 +1/R2 + 1/R3 (total resistance decreases when more resistance is added)

69
Q

What happens as total resistance increases in a series circuit?

A

Pressure decreases stepwise - initial pressure drop determined by R1, second determined by R2 etc
- first pressure drop < second pressure drop

70
Q

How is blood flow controlled in the body?

A
  • Changing perfusion pressure changes flow (Darcy’s Law)
  • However, blood flow through each organ/tissue can be regulated independently of others/of MABP by independent regulation of resistance in different parts of the body
  • ∴ if blood pressure is kept constant, then flow through any tissue is controlled independently by its own resistance (dilation/constriction of its blood vessels) as systemic circulation is in parallel
71
Q

What happens to flow when blood pressure is not being maintained by regulating CO?

A

A decrease in flow in one tissue increases flow in other tissues so that total flow doesn’t change

72
Q

What is the equation for MABP?

A

MABP = CO x TPR

73
Q

What are the two levels of regulation of MABP?

A

1) flow control (by the pump) - controls CO and ∴ HR + SV

2) controlling TPR through resistance control by changing radius of arterioles

74
Q

What happens during the cycle of blood flow in the systemic circulation?

A

1) When the left ventricle contracts, pressure oscillates between 0 and 120mmHg (systolic pressure)
2) Blood is then expelled into the aorta and large arteries (still oscillations between systolic and diastolic pressure -afterload)
3) Blood flows into the resistance arteries and arterioles - pressure drops as blood needs to flow from a region of high pressure to low pressure as resistance increases
4) Blood flows into capillaries and pressure decreases towards the venules, great veins and right ventricle - pressure in the capillaries is sufficient to maintain flow into the venules

75
Q

What is the difference in blood flow in the pulmonary circulation?

A
  • Similar situation but pressures are a lot lower

- This low resistance facilitates pumping of the whole cardiac output through the lungs

76
Q

Describe the changes in resistance through the blood vessels

A

1) aorta and large arteries - very low as very wide
2) arterioles - high as narrow
3) capillaries - low as more branches ∴ more resistance in parallel
4) venules - high as fewer branches (capillaries merge into venules which merge into veins)
5) great veins - low as wide

77
Q

What is diastolic pressure determined by?

A

The resistance to flow in vasculature downstream
- for a given cardiac output to be achieved, the contracting heart muscle must generate sufficient force to ‘overcome’ to afterload

78
Q

What is true about flow in the two circulations even though their overall pressures and resistances are different?

A

Total flow (cardiac output) is the same as the two circulations (systemic and pulmonary) are in series

Foundations of Biomedical Sciences 1 (9 decks)

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