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Body Systems > Capillary Exchange and Localised Control of Circulation > Flashcards

Capillary Exchange and Localised Control of Circulation Flashcards

1
Q

What does capillary exchange refer to?

A

the exchange of materials from capillary blood vessels into the surrounding tissues. The processes that facilitate capillary exchange are principally by diffusion, bulk transport and transcytosis

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2
Q

Why are capillary vessels and capillary beds ideal for the process of exchange?

A
  • 8 um in diameter
  • Thin walls – facilitate diffusion
  • Large intercellular clefts
  • Fenestrations (pores)
  • Blood flow through capillaries is slow (low blood pressure)
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3
Q

Give a brief overview of what is absorbed into the body cells in capillary exchange and what is reabsorbed into the blood?

A
  • Water, oxygen, amino acids, glucose, ions etc. absorbed into the body cells
  • Water, CO2, water molecules, ions ect. reabsorbed into the blood
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4
Q

What are the cellular mechanisms for filtration and reabsorption in the capillaries?

A
  • Filtration pores e.g. albumin
  • Transcytosis e.g. fatty acids, albumin, insulin etc
  • Diffusion: O2, CO2, steroids
  • Intercellular clefts in capillary walls (bulk flow): glucose, ions, water
  • Active transport
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5
Q

What is the capillary hydrostatic pressure?

A

‘blood pressure’, adds a force to the wall of capillaries and tends towards ‘pushing; water and solutes out of capillaries into the interstitial fluid

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6
Q

What is the blood colloid osmotic pressure (BCOP)?

A

osmotic forces arising from the interstitial fluid that oppose the CHP

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7
Q

What is the net filtration pressure (the overall drive) determined by?

A

both hydrostatic and osmotic pressure values

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8
Q

What is the equation to work out the net filtration pressure?

A

Net CHO - Net BCOP

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9
Q

Capillary blood pressure declines from the arterial end to the venous end. What consequences does this have?

A

This has functional consequences related to the rates of filtration as blood passes along the length of a capillary

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10
Q

What is the net hydrostatic pressure?

A
  • The Net hydrostatic pressure contains the capillary hydrostatic pressure CHP (ranging from 35mmHg (arterial end) to 18mmHg (venous end))
  • CHP is counteracted by a hydrostatic pressure generated by the interstitial fluid. Has a very low value and is somewhat negligible (usually valued as 0)
  • net hydrostatic pressure is the difference between the capillary hydrostatic pressure and the interstitial fluid’s hydrostatic pressure
  • Effectively the net hydrostatic pressure is the capillary hydrostatic pressure as the interstitial fluid pressure is negligible
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11
Q

What is the net osmotic pressure?

A
  • Net osmotic pressure = Blood colloid osmotic pressure (BCOP) – Interstitial Fluid Colloid Osmotic Pressure (ICOP)
  • BCOP = 25 mmHg
  • ICOP – interstitial fluid has few proteins in suspension therefore this is low and negligible
  • So Net Osmotic pressure becomes equivalent to the blood colloid osmotic pressure
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12
Q

How do you work out the net filtration pressure?

A
  • Net filtration Pressure (NFP) = Net hydrostatic pressure (35 to 18 mmHg) – Net Colloid Osmotic Pressure (about 25 mmHg)
  • Net filtration pressure = Net CHP – Net BCOP
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13
Q

Give features of blood pressure in the capillary bed?

A
  • Blood flow in capillaries is extremely slow due to low bp

* Declining blood pressure through capillary bed

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14
Q

What happens at the arterial end of the capillary bed?

A
  • the hydrostatic pressure will exceed the blood colloid osmotic pressure difference
  • NFP = 35 mmHg – 25 mmHg = +10 mmHg
  • CHP > BCOP
  • Fluid forced out of the capillary
  • Filtration
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15
Q

What happens at the venous end of the capillary bed?

A
  • the BCOP will exceed the hydrostatic pressure
  • NFP = 18 mmHg – 25 mmHg = -7 mm Hg
  • BCOP > CHP
  • Fluid moves into capillary
  • Net reabsorption
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16
Q

What happens when the hydrostatic and osmotic pressures are equivalent?

A
  • NFP = 25 mmHg – 25 mmHg = 0
  • No net movement of fluid
  • Takes place in venous end of capillary bed
17
Q

Why does more filtration take place across the capillary than reabsorption?

A

Because the max filtration pressure is greater than the maximal absorption pressure, the transition point (when hydrostatic and osmotic pressures are equivalent) is located towards the venous end of the capillary and not in the centre

18
Q

Why is elevated hydrostatic pressure problematic?

A
  • High blood pressure results in poor capillary exchange
  • If CHP is increases or if BCOP decreases fluid balance is altered there is net exit into peripheral tissue:
     Fluid collects in extremities
     Systemic Oedema
19
Q

What is different about pulmonary circulation?

A

• Pulmonary vascular resistance is very low
- Arterioles thinner, wider and shorter
- Arteries thinner walled, less elastin
• Pulmonary arterial BP is lower than the systemic BP – 10 mmHg vs 35 mmHg
• Increased distensibility means these vessels can readily accommodate increased cardiac output without significant increases in pressure
• Importantly, fluid can also be continually absorbed along the entire capillary length. This prevents any interference with gas diffusion

20
Q

What happens with high blood pressure in pulmonary circulation?

A

the opposite dynamic dominates and fluid build up affects respiration as fluid builds up in the lung tissues (alveoli) as opposed to the extremities
- Leads to pulmonary oedema

21
Q

How much CO does the brain consume for what % of body mass?

A
  • Consumes 12% of CO for 2% body mass

* Flow rate 750 ml/min

22
Q

What happens with the brain and blood flow?

A

• Four arteries used to supply brain and anastomoses inside the cranium
• Blood flow is constant and preserved even in emergencies
• Under extreme conditions peripheral circulation will be constricted but cerebral circulation will be maintained (vasodilation)
• So during any temporary loss of arterial supply, CNS will be unaffected
Coronary Blood Flow

23
Q

What happens with coronary blood flow?

A

• Coronary blood flow varies throughout the cardiac cycle influenced by heart rate
• Blood flow through the coronary artery is interrupted curing cardiac contraction as a result of compression
• In order to compensate
- High capillary density leading to a high capacity (70%) for O2 extraction
- Capillaries have few arterial collateral interconnections
• Adrenaline promotes vasodilation of coronary vessels, increases heart rate and the strength of contractions of the myocardia
- Elsewhere in the body adrenaline is a vasoconstrictor
- Coronary blood flow increases where elsewhere in the body vasoconstriction predominates

24
Q

What does blood flowing through the capillaries slowly allow time for?

A

diffusion or active transport of materials across the capillary walls

25
Q

How can water, ions and small organic molecules (e.g. glucose) usually enter or leave the bloodstream?

A

by diffusion between adjacent endothelial cells or through the pores of the fenestrated capillaries

26
Q

When are large water-soluble compounds able to leave the bloodstream?

A

at fenestrated capillaries such as those of the hypothalamus, the kidneys, many endocrine organs, and the intestinal tract

27
Q

How can lipids and lipid-soluble materials cross the capillary walls?

A

by diffusion through the endothelial plasma membranes

28
Q

Where is the only place plasma proteins can cross the endothelial lining?

A

the sinusoids

29
Q

What happens in capillary filtration?

A

water and small solutes are forced across a capillary wall leaving larger solutes and suspended proteins in the bloodstream

30
Q

What does the osmotic pressure of a solution represent?

A

the pressure that must be applied to prevent osmotic movement across a membrane. The higher the solute concentration of a solution the greater the solution’s osmotic pressure

31
Q

What do suspended proteins that cannot cross capillary walls create?

A

an osmotic pressure called blood colloid osmotic pressure (BCOP) otherwise known as oncotic pressure

32
Q

What is bulk flow and what does it do?

A

the continuous net movement of water out of the capillaries, through peripheral tissues and then back to the bloodstream by way of the lymphatic system:

  • it ensures that plasma and interstitial fluid communicate and exchange material constantly
  • It accelerates the distribution of nutrients, hormones and dissolved gases throughout tissues
  • It assists in the transport of insoluble lipids and tissue proteins that cannot cross the capillary walls and enter the bloodstream
  • It flushes out bacteria toxins and other chemicals carrying them to the lymphatic tissues
33
Q

What is the net hydrostatic pressure the difference between?

A

the hydrostatic pressure inside the capillary and outside the capillary

34
Q

What are the conditions that limit the heart’s ability to increase it’s output?

A
  • Permanent restrictions or blockage of coronary vessels

- Tissue damage

35
Q

What happens with oxygen content and the alveoli?

A

When an alveolus contains plenty of oxygen its blood vessels dilate. Blood flow then increases, promoting the absorption of oxygen from air inside the alveolus. When the oxygen content of air is very low the vessels constrict. They shunt the blood to alveoli that contains more oxygen. This mechanism is the opposite from other tissues where a decline in the O2 level causes local vasodilation rather than vasoconstriction

36
Q

What happens as you begin light exercise?

A
  • Extensive vasodilation occurs as skeletal muscles consume oxygen more quickly. Peripheral resistance decreases, blood flow through the capillaries increases and blood enters the venous system at a faster rate
  • The venous return increases as skeletal muscle contractions squeeze blood along the peripheral veins and faster breathing pulls blood into the vena cavae by the respiratory pump
  • Cardiac output rises in response to increased venous return and atrial stretching
37
Q

What happens during heavy exercise?

A

• When doing heavy exercise the cardiac and vasomotor centres activate the sympathetic nervous system increasing cardiac output

  • Also severely restricts blood flow to nonessential organs (e.g. the digestive system)
  • Only blood supply to the brain remains unaffected
38
Q

How does regular exercise lower the risk of cardiovascular disease?

A

lowers cholesterol by stimulating enzyme that help move low density lipoproteins from the blood to the liver. In the liver cholesterol is converted to bile and excreted from the body

Body Systems (20 decks)

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