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ESA 2 > CVS 8 - Special Circulations > Flashcards

CVS 8 - Special Circulations Flashcards

1
Q

Describe the systemic circulation pathway

A
  • Oxygenated blood is carried away from the heart and to the body
  • Deoxygenated blood is carried from the tissues back to the heart
  • A parallel system
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2
Q

Where is the output of the systemic circulation?

A

Left ventricle

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3
Q

Describe the pulmonary circulation pathway

A
  • Deoxygenated blood is carried away from the heart and to the lungs
  • Oxygenated blood is carried from the lungs and back to the heart
  • A system in series
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4
Q

Where is the output of the pulmonary circulation?

A

Right ventricle

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5
Q

Describe the pressure and resistance of the pulmonary circulation. Why is it this way?

A
  • Low pressure
  • Low resistance
  • Vessels are short and wide
  • Lots of capillaries
  • Low amount of smooth muscle in arterioles
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6
Q

What is the pressure in the pulmonary artery?

A
  • 15-30mmHg (systolic)

- 4-12mmHg (diastolic)

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7
Q

What is the pressure in the pulmonary capillaries?

A

9-12mmHg

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8
Q

What is the pressure in the pulmonary veins?

A

5mmHg

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9
Q

What is the pressure range of the right atrium?

A

0-8mmHg

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10
Q

What is the pressure range of the right ventricle?

A
  • 15-30mmHg (systolic)

- 0-8mmHg (diastolic)

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11
Q

What is the pressure range of the left atrium?

A
  • 1-10mmHg
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12
Q

What is the pressure range of the left ventricle?

A
  • 100-140mmHg (systolic)

- 1-10mmHg (diastolic)

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13
Q

What is the ventilation-perfusion ratio? What is its optimal value?

A
  • The matching of alveolar ventilation and alveolar perfusion with blood to give efficient oxygenation
  • 0.8 (no units)
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14
Q

What is the equation for ventilation-perfusion ratio? What is v? What is q?

A
  • v/q
  • v = ventilation (amount of air in and out of the lung)
  • q = perfusion (cardiac output)
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15
Q

What does a high VQ ratio signify? What does a low VQ ratio signify?

A
  • High = high ventilation, low perfusion

- Low = high ventilation, high perfusion (can’t saturate O2 to match perfusion)

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16
Q

What is VQ mismatch? What can it result in?

A
  • Areas of both high VQ and low VQ

- Leads to different levels of saturation which can lead to a lower overall oxygen saturation

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17
Q

How can VQ mismatch lead to a lower overall oxygen saturation?

A
  • Areas of high perfusion and decreased saturation outweigh other areas due to a higher number of red blood cells
  • Can lead to hypoxia
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18
Q

What can cause VQ mismatch?

A
  • Pulmonary embolism (leads to areas of no perfusion = high VQ)
  • Pneumonia
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19
Q

What is hypoxic pulmonary vasoconstriction

A
  • Adaptive response to hypoxia
  • Causes a decreased perfusion rate (Q) if the ventilation of alveoli is decreased
  • Optimises gas exchange
20
Q

How does the response of the pulmonary circulation to hypoxia differ to that of the systemic circulation?

A

Response of systemic circulation is to increase perfusion rate due to metabolite build up

21
Q

What can happen if hypoxic pulmonary vasoconstriction becomes chronic?

A
  • Can increase vascular resistance = chronic pulmonary hypertension
  • Increases pressure of right ventricle = failure
22
Q

What is tissue fluid?

A

Extracellular fluid that contains neither RBCs nor plasma proteins

23
Q

What are the starling forces?

A
  • Hydrostatic pressure = pressure exerted by the blood in the capillary (pushes water out)
  • Colloid oncotic pressure = pressure exerted by the proteins in the plasma (pulls water in)
24
Q

What can happen due to an increase in hydrostatic pressure in the pulmonary system? How can this be treated?

A
  • Movement of fluid out into the tissues due to an increase in capillary pressure = oedema
  • Impairment of gas exchange
  • Treated by diuretics/ underlying problem is treated
25
Q

What influences capillary pressure in the pulmonary circulation?

A
  • Arterial pressure
  • Venous pressure

(increase of either/both = increase of cap. pressure)

26
Q

What influences capillary pressure in the systemic circulation?

A

Venous pressure

27
Q

What is the cerebral circulation? Describe its demand

A
  • The blood supply to the brain in a given period of time

- Very high demand (15% of cardiac output)

28
Q

How is the cerebral circulation adapted to meet its high demand?

A
  • High capillary density (large SA, short diffusion pathway)
  • High basal flow rate
  • High oxygen extraction
29
Q

What are the consequences of ischaemia in the cerebral circulation?

A
  • Loss of consciousness (if for a few seconds)

- Irreversible neuronal damage (if over ~4 minutes)

30
Q

How is blood supply in the cerebral circulation functionally ensured?

A
  • Myogenic autoregulation = maintenance of perfusion when pressure decreases (increase bp = vasoconstriction, decrease bp = vasodilation)
  • Controlled by metabolic factors e.g. more CO2 = More perfusion
  • Brain can prioritise e.g. Cushing’s Reflex
31
Q

What is Cushing’s Reflex?

A

Increasing of the sympathetic vasomotor activity due to impaired blood flow to the vasomotor control centre of the brain stem

e.g. increased cerebral bp = peripheral vasoconstriction = higher flow to brain

32
Q

Describe the oxygen demand of coronary circulation. Why is this significant?

A
  • High basal rate for oxygen (high demand)

- Needed for the heart to keep beating

33
Q

How does cardiac muscle ensure efficient oxygen delivery?

A
  • High capillary density (1 per fibre)
  • Smaller fibre diameter
  • Continuous production of NO by coronary endothelium

= Constant perfusion at a high basal flow

34
Q

Describe the filling of the coronary arteries

A
  • Left and right coronary arteries come from left and right aortic sinuses - Fill during diastole
  • Systole = contraction means increased pressure so is too high to fill coronary arteries
35
Q

Describe the relationship between mechanical work and oxygen demand of the myocardium

A
  • High blood flow as high demand

- Nearly linear - very high demand = small increase in o2 extracted due to lower pH and higher metabolites

36
Q

Why does partial occlusion of the coronary arteries happen? What can it result in?

A
  • Coronary arteries are prone to atheroma (functional end arteries)
  • Leads to angina
  • Disruption of atheroma can result in a thrombus (MI in coronary artery)
37
Q

What can also cause angina?

A
  • Stress and cold

- Causes sympathetic vasoconstriction

38
Q

When does angina occur? Why?

A
  • During exercise (chest pain)
  • Increased oxygen demand but decreased duration of diastole due to higher heart rate
  • Decreased filling time and blood flow
39
Q

When does the oxygen and blood supply demand of skeletal muscle increase? Why?

A
  • During exercise
  • Increase oxygen and nutrient delivery
  • Increase metabolite removal
40
Q

How are increases in blood flow in skeletal muscle brought about?

A
  • Opening of more capillaries due to vasodilator nervous activity and local metabolites
  • Reduces sympathetic vasoconstrictor tone
41
Q

How is efficient blood flow ensured in skeletal muscle?

A
  • Capillary density is dependent on muscle type
  • High vascular tone - lots of vasoconstriction = lots of vasodilation which increases blood pressure
  • At rest, only 50% of capillaries are perfused. During exercise, recruitment means that the diffusion distance decreases
  • Metabolic hyperaemia - increased perfusion and vasodilation due to an increase in metabolites
42
Q

Describe the function of the blood flow through the skin

A

Mostly not nutritive but instead for temperature regulation

43
Q

How is temperature in the skin regulated? Why is this significant?

A
  • Through the regulation of blood flow via artereo-venous anastamoses (AVAs)
  • Leads to rapid bypassing when heat needs to be lost quickly
44
Q

How is temperature in the skin regulated?

A

Sympathetically rather than by metabolites

45
Q

How does a decrease in temperature affect blood flow?

A
  • Increases sympathetic activity which causes vasoconstriction and a decrease in blood flow
46
Q

How does an increase in temperature affect blood flow?

A
  • Decreases sympathetic activity which causes vasodilation and an increase in blood flow

ESA 2 (63 decks)

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