Pulmonary Vessels Flashcards
Name the three layers of the pulmonary vessels.
Tunica intima (inner) - endothelial cells
Tunica media (middle) - smooth muscle cells
Tunica adventitia (outer) - fibroblasts and ECM
Name the three layers of the pulmonary vessels and the layer in between these layers.
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
Describe the constituents of the bronchovascular bundle
Pulmonary arteriole
Bronchus
Pulmonary venule
Continuous adventitia
The pulmonary arterial tree has _____ generations and can be categorised into three types:
- ______: Thin walls compared to diameter. Tunica ______ contains ______ to allow stretch and withstand high pressures. Have few _______ cells and have their own blood supply - ________.
- _______ (<1mm): Less elastin and more______ cells in the _______ layer. Reroutes blood flow via _______.
- _______ (<100-300um): controls _______ blood flow. It is the main ______ to blood flow and therefore determines the overall _______.
The pulmonary arterial tree has 17 generations and can be categorised into three types:
- 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.
- Muscular arteries (<1mm): Less elastin and more smooth muscle cells in the media layer. Reroutes blood flow via contraction.
- Arterioles (<100-300um): controls capillary blood flow. It is the main resistance to blood flow and therefore determines the overall pressure.
Describe the structure of the alveolar capillary membrane ad how its adapted or its function
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
Describe the difference in structure between pulmonary and systemic vessels and therefore describe the blood pressures in each vessel
Systemic arteries are about 5x thicker than pulmonary arteries.
Therefore pressure in pulmonary circulation is 1/5h of that in systemic circulation
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.
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.
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)
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)
Name the 5 stages of lung development
- Embryonic (1-7 wks)
- Pseudoglandular (5-17 wks)
- Canalicular (16-26 wks)
- Saccular (24-38 wks)
- Alveolar (36+ wks)
Which vessel type is found to have the most pressure drop in the pulmonary circuit?
How is Pulmonary Vascular Resistance calculated?
Most pressure drop in the arterioles of the pulmonary circuit.
Units mmHg/Lmin-1
Describe how you would measure the Pulmonary Arterial Wedge Pressure
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.
Describe the pressures involved causing fluid movement in the capillaries.
How can the capillaries get overwhelmed and what will this lead to?
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
Capillary Wall tension is determined by Laplace Relationsip. What is this equation and how is it relevant?
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
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.
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.
Blockade of the pulmonary artery by an embolism can lead to haemoptysis. How does this occur?
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
Vascular tone is controlled by vasodilators (3) and vasoconstrictors (5). Name them
Vasodilators
- O2
- NO (from endothelium)
- Prostacyclins (from endothelium)
Vascoconstrictors
- ET-1 (from endothelium)
- ↑CO2
- ↓O2 (hypoxic pulmonary vasoconstriction)
- Cytokines
- Thromboxane
Describe the role of hypoxic vasoconstriction in the pulmonary system
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)
Describe the effects of gravity on the West Zones in terms of blood flow, capillary distension/patency, alveolar pressure (PA), arteriolar pressure (Pa), venular pressure(Pv).
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, PA>>Pa>Pv. 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>>>PA>Pv.
In the lower zone, P<span>a</span>>>Pv>PA.
Describe the changes in pulmonary vessels during exercise, with regards to Pulmonary artery pressure (PAP) and PVR
↑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:
- Recruitment of de-recruited vessels
- Distension of vessels
What is the pulmonary circulation innervated by? Name the neurotransmission involved and which is the main innervation route and its function?
Autonomic Nervous System
- Adrenergic
- Cholinergic
- Non-adrenergic, non-choinergic
Main neurotransission by adrenergic and this causes:
- Vasoconstriction
- Modlation of proximal compliance
Where is the nerve plexus found for the pulmonary circulation?
Tunica adventitia
The lung has other functions including:
- _____ function (mainly _____ cells): conversion of angiotensin I into II by _____. Also the degradation/uptake of ______/serotonin
- _____ unwanted material from circulation
- Immune function: production and secretion of _____
- Synthetic function: _____ (from surfactant), collagen and _____ protein synthesis
- Acts as a _____ for blood
The lung has other functions including:
- Metabolic function (mainly endothelial cells): conversion of angiotensin I into II by ACE. Also the degradation/uptake of bradykinin/serotonin
- Filters unwanted material from circulation
- Immune function: production and secretion of IgA
- Synthetic function: phospholipids (from surfactant), collagen and elastin protein synthesis
- Acts as a reservoir for blood
The pulmonary circulation in humans has a _____ pressure and _____ flow system with a very thin ACM.
The pulmonary circulation in humans has a low pressure and high flow system with a very thin ACM.
Describe three differences between the pulmonary and systemic circulation
- Lower pressures in pulmonary circulation
- Vessels are correspondingly thinner in pulmonary circulation
- HPV in pulmonary circlation whilst dilation in hypoxia of systemix vessels)
