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Body Systems > Capillary Exchange > Flashcards

Capillary Exchange Flashcards

1
Q

What is the primary function of capillary exchange?

A

To obtain nutrients and oxygen, and to remove metabolic wastes like CO2

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2
Q

What is required to exchange substances across capillary networks?

A

A minimum pressure, known as capillary hydrostatic pressure

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3
Q

Why are capillaries good sites for substance exchange?

A
  • Short distance for diffusion
  • Thin walls (1µm)
  • Small diameter (8µm)
  • Close proximity to cells
  • Blood flows slowly
  • Large cross-sectional area of capillary network
  • Large surface area for exchange (600m²)
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4
Q

What are the three types of capillaries?

A
  • Continuous (most capillaries)
  • Fenestrated - water-filled pores = rapid exchange in solutes (endocrine organs, intestines, kidneys)
  • Sinusoid - large cleft between endothelial cells and incomplete BM = free exchange of water and larger solutes e.g. plasma proteins (endocrine organs, liver, bone marrow, spleen)
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5
Q

What is the main mechanism of substance exchange in capillaries?

A

Diffusion (down a conc gradient)
Bulk flow (down pressure gradient)
Transcytosis (by vasicular transport through endothelial cells)

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6
Q

What types of molecules pass through capillary walls by diffusion?

A
  • Lipid-soluble gases (e.g., O2, CO2)
  • Ions (e.g., Na+, K+, Ca2+, Cl-)
  • Small water-soluble molecules (e.g., water, glucose, urea, amino acids)
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7
Q

What influences fluid and solute movement across capillary walls?

A

Net Filtration Pressure (NFP)

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8
Q

What are the four forces that influence fluid movement in capillaries?

A
  • Blood Colloid Osmotic Pressure (BCOP)
  • Interstitial Fluid Colloid Osmotic Pressure (ICOP)
  • Capillary Hydrostatic Pressure (CHP)
  • Interstitial Fluid Hydrostatic Pressure (IHP)
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9
Q

What happens to net filtration pressure (NFP) during hypertension?

A

Increased filtration and fluid collects in extremities, leading to systemic oedema

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10
Q

What is the typical NFP value at normal conditions?

A

10 mmHg

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11
Q

How does dehydration affect net filtration pressure?

A

Increases reabsorption, recalling fluid from tissues into the bloodstream

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12
Q

What is a significant characteristic of pulmonary circulation?

A

Pulmonary vascular resistance is very low

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13
Q

What occurs if pulmonary capillary hydrostatic pressure exceeds 25 mmHg?

A

Fluid leaks into alveoli, causing pulmonary oedema

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14
Q

How does coronary circulation respond to increased cardiac output?

A

Coronary artery vasodilation is promoted by SNS/adrenaline

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15
Q

What is the flow rate of blood to the brain?

A

750 ml/min

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16
Q

Fill in the blank: The process by which substances move down concentration gradients in capillaries is called _______.

A

Diffusion

17
Q

True or False: Capillary exchange occurs at the site of capillary networks only.

A

True

18
Q

What happens to coronary blood flow during systole?

A

Coronary flow is restricted due to compression of the left coronary artery

19
Q

What is the typical capillary hydrostatic pressure (CHP) at the arterial end?

A

35 mmHg

20
Q

What type of capillary has large clefts between endothelial cells for free exchange?

A

Sinusoid capillaries

21
Q

What is the effect of tissue damage on net filtration pressure?

A

Increased filtration due to plasma proteins leaking into interstitial fluid

22
Q

Describe the structure of a capillary

A

Designed for two-way process of exchange
- short distance for diffusion = thin walls (1 um), small diameter (8 um) and close proximity to cells
- blood flows slowly = large cross-sectional area of capillary network (lots of exchange)
- large surface area for exchange = 10+ billion capillaries (so greater diffusion)

23
Q

What is net filtration pressure?

A

Bulk flow between capillaries and interstitial fluid is determined by the net pressure difference across capillary walls

  1. Capillary hydrostatic pressure = Pushes fluid OUT
  2. Interstitial fluid hydrostatic pressure = pushes fluid IN
  3. Blood colloid osmotic pressure = pulls fluid IN (from interstitial fluid)
  4. Interstitial fluid colloid osmotic pressure = pulls fluid OUT
24
Q

How is net filtration pressure calculated?

A

Net hydrostatic pressure - net osmotic pressure

25
Q

How is net hydrostatic pressure calculated?

A

Favours “pushing” fluid from capillary to IF = filtration

Capillary hydrostatic pressure (CHP) - Interstitial fluid hydrostatic pressure (IHP)

CHP decreases along capillary
IHP is generally negligible (0mmHg)

26
Q

How is net osmotic pressure calculated?

A

Favours “pulling” fluid into capillary from IF = reabsorption

Blood colloid osmotic pressure (BCOP) - Interstitial fluid colloid osmotic pressure (ICOP)

BCOP is affected by blood volume
ICOP is generally negligible

27
Q

What are the special circumstances in pulmonary circulation?

A
  • In lungs, arterioles constrict in regions of low O2 to shunt blood flow to O2-rich areas
  • Enhances O2 absorption
  • In other organs, vessels dilate when O2 falls
  • Enhances O2 delivery

Pulmonary circulation supplies >300 million alveoli

SO

  • Pulmonary vascular resistance is very low = arterioles are shorter, wider and have thinner walls
  • CHP is lower than in systemic circulation = 10 mmHg rather than 35 mmHg
  • Arteries are more distensible = can accommodate increased CO with little increase in pressure
28
Q

What are the special circumstances in coronary circulation?

A

A wide range of molecules regulate myocardial perfusion

  • SNS/Adrenaline promotes coronary artery vasodilation
  • Coronary flow increases when vasoconstriction dominates elsewhere
  • Coronary flow is restricted during systole due to compression of left coronary artery
  • Coronary flow is highest during diastole enabled by arterial elastic recoil

TO COMPENSATE

  • Cardiomyocytes have high O2 reserves
  • The myocardium has high capillary density = increases O2 extraction
29
Q

What are the special circumstances in cerebral circulation?

A
  • Blood flow to the brain must be preserved at all times
  • In emergencies, there is vasodilation of cerebral vessels while there is vasoconstriction in the periphery

THE BRAIN
- consumes 12% CO for 2% body mass
- flow rate = 750 ml/min
- neurons have poor metabolic reserves
- 4 arteries used to supply the brain which anatosome inside cranium
- flow can be maintained if there is distruption

Body Systems (19 decks)

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