Pulmonary Vessels

Question 1

Name the three layers of the pulmonary vessels.

Answer 1

Tunica intima (inner) - endothelial cells

Tunica media (middle) - smooth muscle cells

Tunica adventitia (outer) - fibroblasts and ECM

Question 2

Name the three layers of the pulmonary vessels and the layer in between these layers.

Answer 2

Tunica intima (inner) - endothelial cells

Tunica media (middle) - smooth muscle cells

Tunica adventitia (outer) - fibroblasts and ECM

Elastic laminum is found in between the layers - minimses pressure stresses

Question 3

Describe the constituents of the bronchovascular bundle

Answer 3

Pulmonary arteriole

Bronchus

Pulmonary venule

Continuous adventitia

Question 4

The pulmonary arterial tree has _____ generations and can be categorised into three types:

1. ______: Thin walls compared to diameter. Tunica ______ contains ______ to allow stretch and withstand high pressures. Have few _______ cells and have their own blood supply - ________.
2. _______ (<1mm): Less elastin and more______ cells in the _______ layer. Reroutes blood flow via _______.
3. _______ (<100-300um): controls _______ blood flow. It is the main ______ to blood flow and therefore determines the overall _______.

Answer 4

The pulmonary arterial tree has 17 generations and can be categorised into three types:

1. Elastic arteries: Thin walls compared to diameter. Tunica media** contains **elastin to allow stretch and withstand high pressures. Have few smooth muscle cells and have their own blood supply - vaso vasorum.
2. Muscular arteries (<1mm): Less elastin and more smooth muscle cells in the media layer. Reroutes blood flow via contraction.
3. Arterioles (<100-300um): controls capillary blood flow. It is the main resistance to blood flow and therefore determines the overall pressure.

Question 5

Describe the structure of the alveolar capillary membrane ad how its adapted or its function

Answer 5

ACM: alveolar epithelial cell

interstitial layer (type IV collagen - has high tensile strengths against pressure changes)

vascular endothelial cell

One cell thin each layer leading to efficient as exchange

Question 6

Describe the difference in structure between pulmonary and systemic vessels and therefore describe the blood pressures in each vessel

Answer 6

Systemic arteries are about 5x thicker than pulmonary arteries.

Therefore pressure in pulmonary circulation is 1/5h of that in systemic circulation

Question 7

Evolution of the pulmonary circulation: As the ______ demands of a species increased, there was a need for a pulmonary circulation with ______ walls and higher _____ _____ for efficient gas exchange.

Answer 7

Evolution of the pulmonary circulation: As the metabolic demands of a species increased, there was a need for a pulmonary circulation with thinner walls and higher surface area for efficient gas exchange.

Question 8

Embryology of the pulmonary circulation: The heart develops separately to the microvasculature. The _____ and the _____ _____ join by mid ______ stage of lung development (therefore, there is a joint between arterial and venous system)

Answer 8

Embryology of the pulmonary circulation: The heart develops separately to the microvasculature. The capillaries and the pulmonary artery join by mid pseudoglandular stage of lung development (therefore, there is a joint between arterial and venous system)

Question 9

Name the 5 stages of lung development

Answer 9

1. Embryonic (1-7 wks)
2. Pseudoglandular (5-17 wks)
3. Canalicular (16-26 wks)
4. Saccular (24-38 wks)
5. Alveolar (36+ wks)

Question 10

Which vessel type is found to have the most pressure drop in the pulmonary circuit?

How is Pulmonary Vascular Resistance calculated?

Answer 10

Most pressure drop in the arterioles of the pulmonary circuit.

Units mmHg/Lmin^-1

Question 11

Describe how you would measure the Pulmonary Arterial Wedge Pressure

Answer 11

Multi-lumen catheter (Swan-Ganz catheter) into a peripheral vein, then advancing the catheter into the right atrium, right ventricle, pulmonary artery, and then into a branch of the pulmonary artery.

The balloon is then inflated, which occludes the branch of the pulmonary artery. When this occurs, the pressure in the distal port rapidly falls, and after several seconds, reaches a stable lower value that is very similar to left atrial pressure (mean pressure normally 8-10 mmHg).

The pressure recorded during balloon inflation is similar to left atrial pressure because the occluded vessel and its distal branches that eventually form the pulmonary veins act as a long catheter that measures the blood pressures within the pulmonary veins and left atrium.

Question 12

Describe the pressures involved causing fluid movement in the capillaries.

How can the capillaries get overwhelmed and what will this lead to?

Answer 12

Hydrostatic, oncotic and osmotic pressures are involved in fluid movement. There is a net leakage into the lymphatics.

When overwhelmed (i.e. ↑hydrostatic pressure or ↓osmotic pressure in capillaries) it leads to interstitial (Kerley B lines) and pulmonary oedema

Question 13

Capillary Wall tension is determined by Laplace Relationsip. What is this equation and how is it relevant?

Answer 13

An increase in tension (i.e. HTN) needs to be reduced. The body decreases tension by increasing wall thickness (remodelling) and therefore there is LVH

There is distension of the capillaries however due to the increased pressures so there needs to be more compensation of wall thickness

Question 14

Bronchial Vessels: The bronchial arteries arise from the _____ and therefore are under the _____ pressure. It supplies the _____ and the _____ tissue of the lung.

Blood flows from the bronchial artery into the bronchial vein into the _____ vein and to the right atrium.

Blood can also flow from the bronchial artery into the _____ vein, via the _____ vein and to the left atrium.

Blood can also flow from the bronchial artery into the ______ artery.

Answer 14

Bronchial Vessels: The bronchial arteries arise from the aorta and therefore are under the systemic pressure. It supplies the bronchi and the connective tissue of the lung.

Blood flows from the bronchial artery into the bronchial vein into the azygous vein and to the right atrium.

Blood can also flow from the bronchial artery into the pulmonary vein, via the bronchopulmonary vein and to the left atrium.

Blood can also flow from the bronchial artery into the pulmonary artery.

Question 15

Blockade of the pulmonary artery by an embolism can lead to haemoptysis. How does this occur?

Answer 15

The blockade will lead to more reliance on the bronchial system to deliver blood. This requires hypertrophy and the bigger bronchial arteries are more fragile, therefore leading to haemoptysis

Question 16

Vascular tone is controlled by vasodilators (3) and vasoconstrictors (5). Name them

Answer 16

Vasodilators

1. O₂
2. NO (from endothelium)
3. Prostacyclins (from endothelium)

Vascoconstrictors

1. ET-1 (from endothelium)
2. ↑CO₂
3. ↓O₂ (hypoxic pulmonary vasoconstriction)
4. Cytokines
5. Thromboxane

Question 17

Describe the role of hypoxic vasoconstriction in the pulmonary system

Answer 17

Diversion of blood flow allows for ventilation/perfusion matching (i.e. high blood flow to a low oxygen demand area will be inefficient, so vasoconstriction of this route will divert blood to better match other tissue)

Question 18

Describe the effects of gravity on the West Zones in terms of blood flow, capillary distension/patency, alveolar pressure (P_A), arteriolar pressure (P_a), venular pressure(P_v).

Answer 18

The effects of gravity on the distribution of blood flow in the lung are attributed to the hydrostatic pressure difference between the top and bottom of the pulmonary arterial system.

At the uppermost parts of the lung, P_A>>P_a>P_v. Therefore, these vessels collapse and the alveoli that these vessels traverse will receive little blood flow. This accounts for some ‘wasted ventilation’ or physiological dead space.

In the gravitational middle zone, P_{<span>a</span>}>>P_A>P_v.

In the lower zone, P_{<span>a</span>}>>P_v>P_A.

Question 19

Describe the changes in pulmonary vessels during exercise, with regards to Pulmonary artery pressure (PAP) and PVR

Answer 19

↑O₂ demand ↑CO₂ output in exercise (~20x above rest)

CO increased up to 6 times

There is an increase in PAP but PVR may remain normal or become lower due to:

1. Recruitment of de-recruited vessels
2. Distension of vessels

Question 20

What is the pulmonary circulation innervated by? Name the neurotransmission involved and which is the main innervation route and its function?

Answer 20

Autonomic Nervous System

1. Adrenergic
2. Cholinergic
3. Non-adrenergic, non-choinergic

Main neurotransission by adrenergic and this causes:

1. Vasoconstriction
2. Modlation of proximal compliance

Question 21

Where is the nerve plexus found for the pulmonary circulation?

Answer 21

Tunica adventitia

Question 22

The lung has other functions including:

1. _____ function (mainly _____ cells): conversion of angiotensin I into II by _____. Also the degradation/uptake of ______/serotonin
2. _____ unwanted material from circulation
3. Immune function: production and secretion of _____
4. Synthetic function: _____ (from surfactant), collagen and _____ protein synthesis
5. Acts as a _____ for blood

Answer 22

The lung has other functions including:

1. Metabolic function (mainly endothelial cells): conversion of angiotensin I into II by ACE. Also the degradation/uptake of bradykinin/serotonin
2. Filters unwanted material from circulation
3. Immune function: production and secretion of IgA
4. Synthetic function: phospholipids (from surfactant), collagen and elastin protein synthesis
5. Acts as a reservoir for blood

Question 23

The pulmonary circulation in humans has a _____ pressure and _____ flow system with a very thin ACM.

Answer 23

The pulmonary circulation in humans has a low pressure and high flow system with a very thin ACM.

Question 24

Describe three differences between the pulmonary and systemic circulation

Answer 24

1. Lower pressures in pulmonary circulation
2. Vessels are correspondingly thinner in pulmonary circulation
3. HPV in pulmonary circlation whilst dilation in hypoxia of systemix vessels)