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Capillaries Flashcards

1
Q

What does H2O solution contain in + out cells?

A

IN: O2, glucose, AA, hormones, immune response etc.
OUT: metabolic end products CO2, urea

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2
Q

Role of cell membranes + eg?

A

Support and protection
Cell-to-cell recognition eg immune system
Controls what enters or leaves the cell eg ion movement in nerves
Regulates cell function eg Insulin-mediated glucose uptake

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3
Q

What are the two layers of amphipathic phospholipids?

A

polar phosphate head (hydrophilic)

non-polar FA tails (hydrophobic)

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4
Q

eg of passive transport processes?

A

Diffusion: conc gradient, O2 uptake from lungs into blood
Convection: pressure gradient, circulation
Osmosis: osmotic pressure gradient, water uptake by cells
Electrochemical flux: electrical + conc gradient, ion flow during an AP in a nerve

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5
Q

Describe capillaries

A

Small diameter
Extension of inner lining of arterioles
Endothelium only – 1 cell thick
Semi-permeable

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6
Q

Role of capillaries?

A

Connect terminal arterioles to venules
Higher density in active tissue (muscles, liver, heart, kidneys, brain)
Solute exchange (passive diffusion, filtration): O2, glucose, AA, hormones, 💊
Fluid exchange (flow down pressure gradients): regulation of plasma + interstitial fluid volumes

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7
Q

What controls rate of solute transport?

A

Properties of passive diffusion
Properties of solutes + membranes (Fick’s law)
Properties of capillaries
Permeability

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8
Q

Properties of passive transport?

A

No ATP
Molecules move randomly
Move from high -> low conc
Transport of lipid-soluble solutes over short distances

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9
Q

Why does passive transport only work over short distances?

A

Time taken (t) for a randomly moving molecule to move net distance (x) in 1 specific direction increases when distance squared
t = x² / 2D
D : diffusion coefficient for molecule within medium
eg D for O2 in water vs air are diff

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10
Q

Properties of the solute?

A

Conc gradient
Size
Lipid solubility

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11
Q

Properties of the membrane?

A

Thickness/composition
Aq pores
Carrier-mediated transport
AT mechanisms

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12
Q

What’s Fick’s law?

A

Jₛ = - DA (ΔC/x)
D : Diffusion coefficient of solute-ease via solvent
A : Area
ΔC/x : Conc gradient (C1-C2) across distance x
Jₛ : Solute movement, mass per unit time m/t

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13
Q

Why’s Fick’s law negative?

A

flowing ‘down’ a conc gradient

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14
Q

3 types of capillaries?

A 
Continuous capillaries (least permeable)
Fenestrated capillaries
Discontinuous capillaries (most permeable)
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15
Q

Describe continuous capillaries

A

Moderate permeability
Tight gaps between neighbouring cells
Constant basement membrane

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16
Q

eg of continuous capillaries?

A

BBB

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17
Q

Describe fenestrated capillaries

A

High water permeability
Fenestration structures
Disrupts basement membrane

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18
Q

eg of fenestrated capillaries?

A

‘high water turnover’ tissues:

salivary glands, kidney, synovial joints, choroid plexus (CSF)

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19
Q

Describe discontinuous capillaries

A

Large fenestration structures

V disrupted basement membrane

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20
Q

eg of discontinuous capillaries?

A

When movement of cells is required:

🔴 in liver, spleen, bone marrow

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21
Q

What’s an intercellular cleft?

A

10-20 nm wide

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22
Q

What’s a glycocalyx?

A 
covers endothelium
-ve charged
blocks solute permeation+access to transport mechanisms
regulated
controls movement of molecules
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23
Q

What are caveolae + vesicles?

A

large pores system

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24
Q

Define permeability

A

rate of solute transfer by diffusion across unit area of membrane per unit conc diff
’how freely a solute crosses a membrane’

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25
How does a porous membrane interfere with diffusion of lipid insoluble solute?
reduction in area for diffusion (A), increased path length through membrane (x), restricted diffusion in pore produces hydraulic issues (D) ALL FACTORS = permeability (P)
26
What's the modified Fick's law for a porous membrane?
``` Jₛ = -PAₘΔC Jₛ : Rate of solute transport P : Permeability [pore size, length (x), diffusion coefficient (D)] Aₘ = SA of capillary ∆C = Conc gradient ```
27
How do large lipophobic proteins get transported?
big gaps in inflammation, trans-cellular channels, vesicles (endocytosis + exocytosis)
28
How do lipophilic O2, CO2 diffuse?
trans-cellular
29
How do small lipophobic glucose get transported?
filtration via inter-cellular, fenestral route
30
How does water get transported?
filtration via inter-cellular, fenestral route, water channels
31
How much of glucose is transported by diffusion?
98% of glucose transport into interstitial space | via passive diffusion – via GLUT transporter system
32
How much of glucose is transported by filtration?
2% glucose transport via fenestrations/intercellular gaps
33
Why's filtration of glucose much less than diffusion?
[glucose] in plasma is 1 g / L Daily volume of plasma filtrate flowing into tissues = 8 L Max filtration of glucose = 8 g / day but glucose consumption of adult is 400 g / day
34
What controls diffusion rate?
Increased blood flow Fall in interstitial conc (more solute used, metabolism) Recruitment of capillaries
35
How increased blood flow controls diffusion rate?
- increased conc of solutes in capillaries - more exchange along capillaries in lungs - less time for eq of O2/CO2 to occur between interstitial spaces + capillaries - reduces exchange
36
How a fall in interstitial conc controls diffusion rate?
- use more O2 - increases conc diff for O2 to move in - metabolism increases blood flow - metabolic hyperaemia - more O2 delivery
37
How a recruitment of capillaries controls diffusion rate?
- dilation of arterioles - more capillaries perfused - increases SA for diffusion - shortens diffusion distance - faster diffusion
38
Why does O2 transport from blood to muscle | increases over 40 times during exercise?
- increase CO (blood flow) - use more O2 (fall in tissue concentration) - open up more capillaries (recruitment)
39
Importance of fluid exchange?
Normal physiological function H2O for chemical reactions Abnormalities --> oedema/tissue swelling Controlling blood, interstitial, cell volumes after drop in BP/poor end organ perfusion eg haemorrhage, sepsis, during surgery, dehydration
40
What's hydraulic pressure?
Pressure exerted when fluid moves across membrane into interstitial space due to blood flow OUUUUUTTTTTTTT
41
What's oncotic pressure?
pressure exerted by plasma proteins that cannot pass through membrane, which creates suction force to move fluid from interstitial space into capillary INNNNN
42
What's Starling’s principle of fluid exchange?
Fluid movement depends on balance between hydraulic + oncotic pressures across the capillary wall
43
What are the Directions of Fluid Movements dominated by?
P꜀ and πₚ P꜀: capillary BP πₚ: plasma proteins
44
Why does the hydraulic pressure mean easy movement across the membrane?
P꜀ > Pᵢ P꜀: capillary BP Pᵢ: interstitial fluid pressure
45
Why does the osmotic pressure mean movement via intercellular gaps?
πₚ > πᵢ πₚ: plasma proteins πᵢ: interstitial proteins
46
Equation of Starling’s principle of fluid exchange?
``` Jᵥ = Lₚ A [ (P꜀ - Pᵢ) - σ(πₚ - πᵢ) ] Jᵥ ∝ (P꜀ - Pᵢ) - (πₚ - πᵢ) Jᵥ: net filtration Lₚ: Hydraulic conductance of endothelium, how Leaky endothelium is to fluid A: wall area σ: Reflection coefficient for intercellular gaps (P꜀ - Pᵢ): hydraulic pressure diff (πₚ - πᵢ): osmotic pressure diff ```
47
What does it mean if σ for a plasma protein is 0.9?
10% plasma proteins are conducted across capillary wall into interstitial space
48
What happens to σ if small gaps?
plasma proteins stay in lumen exerting osmotic pressure = 1
49
Equation of effective osmotic pressure?
effective osmotic pressure = σ x potential osmotic pressure
50
What does Starling's principle tells us
- constant osmotic p πₚ=25 - first part of capillary P꜀=35mmHg so filtration - lose pressure down capillary - P꜀=πₚ both 25mmHg - more drop so P꜀=10mmHg so reabsorption
51
Problems with Starling's principle?
- Fluid filtration throughout length of capillaries - No reabsorption - vital for fluid replacement - πᵢ not small, πₚ = πᵢ - Glycocalyx central to fluid exchange - Starling’s principle states that increasing πₚ + reabsorption with colloid fluids should increase blood volume but they don't expand plasma volume
52
What's the revised equation of Starling’s principle of fluid exchange?
Jᵥ = Lₚ A [ (P꜀ - Pᵢ) - σ(πₚ - πg) ] Jᵥ: net filtration Lₚ: Hydraulic conductance of endothelium, how Leaky endothelium is to fluid A: wall area σ: Reflection coefficient for intercellular gaps (P꜀ - Pᵢ): hydraulic pressure diff (πₚ - πg): osmotic gradient
53
Role of glycocalyx?
Glycocalyx acts as a barrier so plasma proteins move from lumen into interstitial space via vesicle system not via intercellular spaces as
54
Why's πₚ = πᵢ ?
Stream of fluid filtration from endothelium carries plasma proteins into interstitial space creating low πg (subglycocalyx region) - πₚ = πᵢ
55
Why's there filtration at venous end despite low P꜀?
Filtration occurs across length of capillaries | Less P꜀ at venous end means πᵢ moves into πg – less (πₚ - πg) osmotic gradient
56
Why colloid fluid doesn't expand blood volume in sick patient?
shedding of glycocalyx
57
Why's there brief reabsorption during haemorrhage?
- less CO, less BP - sympathetic so vasoconstriction - low P꜀ (hypovolemia) - less blood volume - increased osmotic pressure>25mmHg - so fluid reabsorption to lower osmotic pressure - reabsorb 500ml over 0.5hr - stops when osmotic p normal
58
Purpose of brief reabsorption during haemorrhage?
``` Life-preserving Supports CVP Increases CO Rises BP Greater end organ perfusion ```
59
Role of lymphatic circulation?
returns excess tissue fluid/solutes back to the cardio-vascular system
60
Features of lymph vessels?
valves + smooth muscle
61
What contributes to lymph flow?
Spontaneous contractions of smooth muscle | Surrounding skeletal muscle contractions / relaxation
62
Organization of lymphatic thoracic duct system?
- initial lymphatic plexus - collecting lymphatic - afferent lymphatic - high endothelial venule - lymphocyte - lymph node - efferent lymphatic - cysterna chyli - lacteal - thoracic duct
63
What does overall control of ECF balance depend on?
Capillary filtration Capillary reabsorption Lymphatic system
64
What changes happen if imbalance of ECF?
Starling’s factors Efficiency of lymphatic system Influence fluid balance between intravascular + interstitial spaces
65
What causes oedema?
Excess interstitial fluid by imbalance between | filtration, reabsorption, lymphatic function, glycocalyx function
66
Factors that promote filtration?
increased P꜀ increased πg increased Lₚ decreased πₚ
67
Factors that promote reabsorption?
decreased P꜀ | increased πₚ
68
Eg of clinical scenarios where there's increased P꜀?
Dependent (gravitational) oedema – ‘standing up for long periods’ Deep venous thrombosis Cardiac failure
69
Describe DVT
- prevention of venous return - increases venous pressure --> ‘back-up’ of pressure - increased P꜀ across capillaries - increased filtration
70
What causes decreased πₚ?
Malnutrition/malabsorption, hepatic failure, nephrotic syndrome
71
What's Nephrotic syndrome?
protein lost in urine that isn't replaced by liver production
72
How does liver disease decrease πₚ
insufficient endogenous albumin produced
73
Describe how kwashiorkor happens
- reduced plasma protein conc - reduced oncotic pressure πₚ - greater P꜀ - fluid from capillaries -> interstitial fluid - oedema
74
eg of how inflammatory-mediated oedema occurs?
Insect bites/stings, infection, trauma, autoimmune disease
75
Describe how inflammation causes oedema?
- local chemical mediators of inflammation cause swelling - increase capillary permeabilty Lₚ - decreased σ - increased protein permeability - so πₚ = πg = πᵢ - increased P꜀ - more filtration
76
What's filariasis/elephantitis?
nematode infestation, larvae migrate to lymphatic system grow/mate/form nests – block lympathetic drainage
77
What's lymphoedema?
from surgery to treat testicular cancer – removal of lymphatics
78
eg of what causes dysfunctional glycocalyx
inflammation, sepsis, during surgery
79
What happens if there's dysfunctional glycocalyx?
- giving fluids (crystalloids or colloids) causes movement of plasma proteins via intercellular gaps - so πₚ = πg = πᵢ - increased P꜀ - more filtration - oedema

CVS II (19 decks)

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