pulmonary circulation Flashcards
what are the 2 circulation systems in the lungs
- bronchial circulation
- pulmonary circulation
what does the bronchial circulation do
supplies O2 and nutrients to meet the metabolic requirements of the lungs
what does the pulmonary circulation do
carries deoxygenated blood away from the heart to the lungs’ alveoli to undergo gas exchange and returns oxygenated blood back to the heart
describe movement of deoxygenated blood
- leaves the right ventricle through the pulmonary valve
- enters the pulmonary trunk - this divides into the right and left pulmonary arteries
how does blood become oxygenated in the lungs
- arteries divide further into smaller capillaries at the alveoli
- allows gas exchange
- Oxygen diffuses from the alveoli into the pulmonary capillaries
- carbon dioxide diffuses from the capillaries into the alveoli
describe movement of oxygenated blood
- leaves lungs through the pulmonary veins to the heart’s left atrium, completing the pulmonary cycle.
- the blood is then distributed around the body via the systemic circulation.
why must the pulmonary circulation be able to accept the entire cardiac output
because the right heart can’t work without the left heart
both the right and left ventricle must have the same cardiac output to prevent blood from building up in either the systemic or pulmonary circulation
why does the pulmonary circulation need adaptations
to facilitate high volumes of blood flowing through it
what are the adaptations of pulmonary circulation
- low pressure
- low resistance
adaptations of pulmonary capillaries for gas exchange
- large SA
- short diffusion distance
- hypoxic pulmonary vasoconstriction
why is pulmonary circulation a lower pressure system
it is lower than systemic circulation
because the pulmonary arteries have thin vascular walls and high compliance, allowing them to carry more blood
why is pulmonary circulation a lower resistance system
- pulmonary vessels are shorter and wider compared to systemic vessels
- pulmonary capillaries run in parallel, rather than in series like the systemic circulation
- relatively little smooth muscle in the arterioles - helps to reduce arterial tone.
These properties allow the pulmonary circulatory system to operate at a lower resistance.
how do pulmonary capillaries achieve a large SA
due to the branching structure of the pulmonary tree.
how do pulmonary capillaries achieve a short diffusion distance
the very high density of capillaries also means that the alveolar wall is always close to a capillary
what is hypoxic pulmonary vasoconstriction
an important mechanism which responds to low alveolar oxygen levels to increase the efficiency of gas exchange
what is an optimal V/Q ratio
0.8-1.0
why is it important that the ventilation of the alveoli is matched by their perfusion
for efficient oxygenation of the blood
how is optimal V/Q ratio maintained
- blood must be diverted away from poorly ventilated alveoli and directed towards better-ventilated alveoli.
- ensured by hypoxic pulmonary vasoconstriction, whereby small pulmonary arteries constrict to redirect blood flow from poorly ventilated areas of the lung to better-ventilated lung areas.
what determines fluid formation in tissues
starling forces
The increased hydrostatic pressure of the blood in the capillaries pushes fluid out of the vessels at the arterial end. In contrast, oncotic pressure (exerted by large molecules such as plasma proteins) draws fluid back into the capillary at the venous end.
what minimises fluid formation in the lungs
the low capillary pressure of the pulmonary vessels - means that only a small amount of fluid leaves the capillaries, and nearly all of this is reabsorbed.
a protective mechanism against fluid formation in the lungs
role of bronchial arteries
- receive blood from the thoracic aorta and the upper intercostal arteries.
- they enter the lung at the hilum and branch at the main bronchus
what do one portion of bronchial arteries supply
the lower trachea, extrapulmonary airways, and supporting structures
drains into the superficial bronchial veins
These veins join the azygous (from the right lung), the accessory hemizygous or intercostal vein (from the left lung), before reaching the inferior vena cava to enter the right heart.
what do the other portion of bronchial arteries supply
the intrapulmonary airways up to the level of the terminal bronchioles, where they form extensive anastomoses with the pulmonary vasculature.
drains via deep bronchial veins within the lung and joins the pulmonary veins to travel to the left heart.
what is pulmonary vascular resistance
the resistance against blood flow from the pulmonary artery to the left atrium
what causes pulmonary hypertension
in chronic hypoxia, there is widespread vasoconstriction of the pulmonary vessels due to (the normally protective) hypoxic pulmonary vasoconstriction.
causes a chronic increase in vascular resistance, leading to pulmonary hypertrnsion
