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Respiratory > 18. Pulmonary circulation > Flashcards

18. Pulmonary circulation Flashcards

1
Q

Pulmonary circulation

A

Blood going to gas exchange surface

not blood supplying pulmonary tissue to keep it alive

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2
Q

How does the pressure in the pulmonary circulation differ from the systemic circulation?

A

Pressure in the pulmonary circulation is much LOWER than the systemic circulation

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3
Q

State a key difference in the structure of the pulmonary arteries compared to the systemic arteries.

A

Pulmonary arteries have a greater lumen: wall thickness ratio meaning that they are more compliant

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4
Q

Why is the right ventricular wall thinner?

A

Pumping to pulmonary circuit

Needs to be low pressure (vs left ventricle)

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5
Q

How does pressure change with distance from the heart?

A

Pressure gradually decreases with distance from the heart

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6
Q

How does the mean arterial blood pressure vary between the systemic and pulmonary circulation?

A

MAP in the pulmonary circulation is 15% that of the systemic circulation

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7
Q

How does the pressure gradient differ between the systemic and pulmonary circulation?

A

10% of systemic

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8
Q

How does the resistance differ between the systemic and pulmonary circulation?

A

10% of systemic

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9
Q

What volume is carried by the systemic and pulmonary circulations?

A

Systemic: 4.5L
Pulmonary: 0.5L

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10
Q

List 3 primary functions of the pulmonary circulation

A

Gas exchange (O2 delivery, CO2 removal)
Metabolism of vasoactive substances
Filtration of blood

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11
Q

Describe the metabolism of vasoactive substances that occurs in the pulmonary circulation

A

Special endothelial cells expressing ACE for converting Ang I to Ang II
Breaks down Bradykinin (which is a vasodilator)
Specific substrates it binds and converts only expressed in endothelium of lung and kidney

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12
Q

Where is ACE expressed?

A

In the lung endothelium and in the kidneys

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13
Q

What does ACE do?

A

Converts Angiotensin I to Angiotensin II

Breaks down bradykinin

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14
Q

Embolus

A

a ‘mass’ within the circulation capable of causing obstruction

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15
Q

Embolism

A

an ‘event’ characterised by obstruction of a major artery

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16
Q

Describe the protective role of the pulmonary circulation.

A

It filters the blood before it reaches the systemic circulation.
Small emboli are eliminated
Large emboli are trapped (causing occlusion to blood flow)

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17
Q

Pulmonary shunts

A

circumstances associated with bypassing the respiratory exchange surface

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18
Q

State 3 pulmonary shunts.

A

Bronchial Circulation
Foetal circulation
Congenital defect

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19
Q

Describe the pulmonary shunts in Foetal circulation

A 
Lungs not being ventilated, so beneficial to bypass:
Foramen Ovale (links atria) and Ductus Arteriosus (allows bifurcation of pulmonary arteries of pulmonary trunk to connect to aortic arch)
20
Q

Describe the pulmonary shunt in Bronchial Circulation

A

Blood goes through left side of heart to bronchial circulation, some drains back into pulmonary vein and returns back to left side of heart.

21
Q

Describe the pulmonary shunts in a congenital defects

A

If foramen ovale does not close= Atrial septal defect (ASD)
Ventricular septal defect (VSD) allows mixing of blood across septum, causes right side becomes stronger ventricle.
Many people have an ASD, even a small opening comprises the filtration function of the pulmonary circulation, potential for plaque to bypass filter and enter systemic circulation

22
Q

How does the pulmonary circulation respond to an increase in cardiac output?

A

Pulmonary arteries are more compliant
Can distend to prevent significant increase in pressure
Increased recruitment of hypo-perfused beds (apex) also prevents increase in pressure
Allow increase in CO without increasing fluid leakage and compromising pulmonary function

23
Q

Describe perfusion at rest

A

Preferential perfusion down path of least resistance at base of lung (not against gravity)

24
Q

Describe perfusion during increased CO

A

Increased vascular recruitment
Increase in flow through apex of lung
Huge capacity for increasing throughput without increasing pressure

25
Q

Which vessels in the lungs are affected during inspiration and expiration?

A

Inspiration: Compresses alveolar vessels
Expiration: Compresses extra-alveolar vessels

26
Q

When is resistance lowest?

A

At functional residual capacity (default mechanical equilibrium)

27
Q

When is resistance highest?

A

At residual volume (empty)

At total lung capacity (full)

28
Q

Describe and explain the effects of increasing ventilation on pulmonary resistance.

A

Ventilation increases pulmonary resistance at the extremities (round alveoli)
Near residual volume (forced expiration), intrathoracic pressure presses on the extra-alveolar arteries thus increasing resistance.
Near TLC, expansion of the alveolus presses on the alveolar arteries thus increasing resistance.

29
Q

Systemic and pulmonary responses to hypoxaemia

A

Systemic: Vasodilation
Pulmonary: Vasoconstriction

30
Q

Why does the pulmonary vasculature vasoconstrict in response to hypoxaemia?

A

To achieve better ventilation-perfusion matching

So it is not sending blood to parts of the lung that are inadequately ventilated

31
Q

Describe the mechanism causing vasoconstriction of pulmonary vessels in response to hypoxia

A 
Closure of O2 sensitive K+ channels
Decrease in K+ efflux
Increase in membrane potential
Membrane depolarisation: Opening of VGCC
Vascular smooth muscle contraction
32
Q

Describe Hypoxic pulmonary vasoconstriction that may occur at High altitude/ COPD

A

Breathing hypoxic air
Causes global constriction all over lungs
Significant impact on pressure
Right ventricle working harder against resistance
Gets stronger
Concentric hypertrophy, septum begins to change
Effects EDV on left side of heart
Comprises stroke volume

33
Q

Give an example of a situation in which the response of the pulmonary circulation to hypoxia is beneficial

A

During foetal development
Blood follows the path of least resistance
High-resistance pulmonary circuit means increased flow through shunts
1st breath increases alveolar PO2 and dilates pulmonary vessels

34
Q

Give an example of a situation in which the response of the pulmonary circulation to hypoxia is DETRIMENTAL.

A

COPD
Reduced alveolar ventilation and air trapping
Increased resistance in pulmonary circuit
Leads to pulmonary hypertension and right ventricular hypertrophy
Leads to congestive heart failure.

35
Q

Where does greater perfusion of the lungs occur?

A 
Base 
Higher intravascular pressure (due to the effects of gravity)
More recruitment 
Less resistance 
Higher flow rate
36
Q

Where does greater ventilation of the lungs occur?

A

Base
Smaller transmural pressure gradient
Alveoli smaller and more compliant
More ventilation

37
Q

What 2 key pressures are important in pulmonary fluid balance?

A 
Hydrostatic pressure (in capillary and interstitium)
Oncotic pressure (in capillary and interstitium)
38
Q

Describe the hydrostatic pressure through a capillary (plasma hydrostatic pressure)

A

Highest at arterial end (as blood flows down pressure gradient), gradually decreases

39
Q

Describe interstitial hydrostatic pressure

A

Tiny, barely noticeable

40
Q

Describe the plasma oncotic force and what this causes

A

High osmolarity in plasma
Low osmolarity in interstitial fluid
Causes more fluid to be drawn into vessel than out

41
Q

What is the net net movement of fluid between plasma and interstitial fluid? How is this dealt with?

A

1 mmHg out into interstitial fluid

“Mopped up” by lymphatic system, steady fluid accumulation is kept under control

42
Q

What occurs if too much fluid accumulates, exceeding the maximum rate of clearance of the lymphatic system?

A

Pulmonary Oedema

43
Q

Mitral stenosis

A

Hardening of the valve between the LA and LV

44
Q

How is the pulmonary fluid balance affected in mitral stenosis?

A 
Pressures back up from left heart through pulmonary circulation
Increased plasma hydrostatic pressure
More fluid forced into interstitium
Max. lymph clearance rate exceeded
= OEDEMA develops
45
Q

How is the pulmonary fluid balance affected in liver failure?

A

Liver synthesises plasma proteins, failure results in Hypoproteinaemia
Plasma oncotic pressure reduced
Less fluid drawn into capillary “reduced sucking force”
Fluid accumulates in interstitium
Lymph clearance exceeded
= OEDEMA develops

46
Q

How is the pulmonary fluid balance affected in metastatic breast cancer?

A

Cancerous cells spread to nearby thoracic lymph nodes/ducts
Tumours obstruct lymphatic drainage
Lymph clearance compromised
= OEDEMA develops

Respiratory (21 decks)

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