Pulmonary Blood Flow Flashcards
Pulmonary circulation begins when mixed venous blood from the _____ ventricle enters the main pulmonary artery.
The main pulmonary artery then branches off like the airway as far as the ______ bronchioles. Those branches then break off to supply capillary beds in the walls of the ______, which is a highly efficient arrangement for gas exchange
Oxygenated blood is then collected from capillary beds by small pulmonary vessels that run between lobules and eventually unite to form 4 large veins that drain into the _____ _____ of the heart
Right
Terminal; alveoli
Left atrium
What are the basics of the anatomy of the heart according to Dr. Rogers?
4 chambers
4 valves
4 large vessels
4 small vessels
Right heart cycle:
Blood returns from systemic circulation and flows through the right atrium into the ventricle.
Contraction of this atrium tops off the ventricle, which then contracts –> ________ valve closes and ______ valve opens
Ejection of blood into _______ ______ at _____ pressure
Tricuspid; pulmonary
Pulmonary trunk; low
Left heart cycle:
Blood returns from lung and flows through left atrium straight into the ventricle.
Contraction of this atrium tops off the ventricle. The left ventricle contracts, the _____ valve closes and ______ valve opens.
Ejection of blood into the _____ at _____ pressure
Mitral; aortic
Aorta; high
Describe pressure and flow in the bronchial vessels of pulmonary circulation
High pressure, low flow
Circulation in bronchial vessels is high pressure, low flow. Systemic arterial blood goes where? Is this oxygenated or deoxygenated at the start?
Systemic arterial blood goes to the trachea, bronchial tree, support tissues of the lung, and adventitia of pulmonary arteries and veins
It is oxygenated at the start
Describe pressure and flow in pulmonary vessels of pulmonary circulation
Low pressure; high flow
Pulmonary vessels have low pressure, high flow circulation. ________ blood goes to the alveolar capillaries for gas exchange. Pulmonary vessels are branches of _______ artery. Blood is _______ at the start
Venous; pulmonary; deoxygenated
Overall, which circulation is under lower resistance: pulmonary or systemic?
Pulmonary has significantly lower resistance
Compare the walls of vessels in pulmonary circulation vs. systemic
Vessels in pulmonary circulation are very thin with little smooth muscle, which is opposite systemic which has thick walls and abundant smooth muscle
[this makes sense because the lung accepts 100% of cardiac output at all times]
What type of capillaries are associated with the right ventricle, function in gas exchange, and form sheets around millions of alveoli?
Alveolar capillaries
Alveolar capillaries are exposed to alveolar pressure. What happens to these capillaries if alveolar pressure increases?
They are compressed
What type of capillaries may be associated with the left ventricle, function in gas delivery to lung tissue, and return to the heart in pulmonary veins as venous admixture?
Extra-alveolar capillaries
Extra-alveolar capillaries include all arteries and veins that run through the lung _________. Their caliber is greatly affected by lung volume and very large vessels near the hilum are outside the lung substance and are exposed to ________ pressure, which is less than alveolar pressure and they are pulled open by the radial traction of surrounding parenchyma
Parenchyma
Intrapleural
Extra-alveolar capillaries return to the heart in pulmonary veins as ______ ______
This slightly ______ PaO2 and slightly _______ PaCO2
Venous admixture
Reduces; increases
What is the mean pressure in a pulmonary artery vs. a systemic artery?
Pulmonary artery = 15 mm Hg
Systemic artery = 100 mm Hg
How is vascular resistance calculated?
(Input pressure - output pressure) / blood flow
Why is the resistance so much lower in pulmonary vessels as compared to systemic?
The extensive capillary network in the lungs
How would you calculate BP and PBP?
BP = CO x TPR
PBP = CO x PVR
What are normal values for the following?
Pulmonary BP
Systemic BP
Cardiac output
Pulmonary BP = 25/15
Systemic BP = 120/80
Cardiac output = 5 L/min
What occurs with pulmonary vascular resistance during exercise?
Decreases; because of recruitment and distension of capillaries
Pulmonary vascular resistance ______ at high and low lung volumes, as well as with alveolar hypoxia
Increases
What factors determine pulmonary vascular resistance?
High capillary content, less sympathetic tone, and smooth muscle at arteriole level
Number of alveoli open and lung volume
An increase in either pulmonary arterial or venous pressure causes pulmonary vascular resistance to decrease. What are the 2 mechanisms for this?
Recruitment - as pressure rises, capillaries begin to conduct blood, lowering resistance
Distension - at higher vascular pressures, widening of individual capillary segments occurs, going from flat to more circular shape
What are the 3 zones of regional blood flow in the lungs, and which one receives the most in an upright human?
Zone 1 - low blood flow = apex
Zone 2
Zone 3 - high blood flow = base
In zone 1 of regional lung blood flow:
Alveoli are ______ and the BP is _____. Blood flow is low.
Expanded; low
Describe the relationship of alveolar, arterial, and capillary/venous pressure in zone 1 of regional lung blood flow
Alveolar pressure is greater than both arterial and capillary/venous pressures
In zone 2 of regional lung blood flow:
Alveoli are average size, blood pressure is a little ____ than zone 1, and is at roughly the same height in the body as the _______
Higher; heart
Describe the relationship of alveolar, arterial, and capillary/venous pressure in zone 2 of regional lung blood flow
Arterial pressure is greater than alveolar pressure
Alveolar pressure is greater than capillary/venous pressure
[Pa > PA > Pv]
In zone 3 of regional lung blood flow:
The alveoli are ____ and BP is ______
Small; high
Describe the relationship of alveolar, arterial, and capillary/venous pressure in zone 3 of regional lung blood flow
Arterial pressure is greater than capillary/venous pressure
Capillary/venous pressure is greater than alveolar pressure
[Pa > Pv > PA]
The concept of regional blood flow is due to the fact that ____ has a large influence of blood flow in the lung
Pressures like pulmonary artery pressure, pulmonary vein pressure, and alveolar pressure are key. _______ pressure is constant.
Zones are __________, not anatomical
Gravity
Alveolar
Physiological
What biological molecule is secreted by endothelium with L-arginine as its precursor (made by eNOS)?
Nitric Oxide (NO)
What effect does Nitric Oxide have on blood flow?
Vasodilation
What effect does endothelin-1 (ET-1) have on blood flow?
Vasoconstriction
What effect does thromboxane A2 (TXA2) have on blood flow?
Vasoconstriction
A decreased level of NO would result in what effect on blood flow?
Vasoconstriction
Endothelin-1 (ET-1) is a vasoconstrictor. Inhibitors of ET-1 receptors are used to treat what condition?
Pulmonary hypertension
Alveolar hypoxia is a condition that constricts the small pulmonary arteries, this is probably a direct effect of the low PO2 on vascular smooth muscle.
This occurs during fetal life; when must it be released?
At birth to transition from placental to air breathing
With alveolar pulmonary vasoconstriction:
A PAO2 decreases, constriction increases and blood flow decreases. What occurs in the smooth muscle of small arterioles in the hypoxic region?
Contraction!
The small thickness of tissue that separates the capillary blood from air in the lung produces the problem of keeping the alveoli free from fluid.
What are the 2 basic forces driving fluid movement between alveoli and capillaries?
Hydrostatic pressure
Osmotic pressure
[these are known as STARLING forces!]
Osmotic pressures include capillary pressure and tissue pressure. Which direction do each of these forces operate?
Capillary pressure pulls water into capillary, out of alveolus
Tissue pressure pulls water out of capillary into alveolus
Hydrostatic pressures include capillary pressure and tissue pressure. Which direction do each of these forces operate?
Capillary pressure drives fluid out of the capillary and into the alveolus
Tissue pressure drives fluid into the capillary and out of the alveolus
The starling forces in the lungs consist of 2 basic forces: hydrostatic pressure and osmotic pressure. What is the result of the net pressure?
Net pressure actually drives fluid from capillary into alveolus because the tissue pressure is NEGATIVE - this is bad
Net pressure actually drives fluid from capillary into alveolus because the tissue pressure is NEGATIVE - this is bad. Where does this excess fluid go?
Lymphatics run in perivascular spaces and help to transport excess fluid into hilar lymph nodes
[the rate of lymph flow increases with increases in capillary pressure]
What enzyme exists in the lungs and is responsible for converting angiotensin I to angiotensin II?
Angiotensin converting enzyme (ACE)
Where does the angiotensin I come from that the lung then converts to angiotensin II using ACE?
Angiotensinogen is converted to angiotensin I by renin in the kidney
Up to 80% of _______ is inactivated by ACE in the lungs
Bradykinin
Why do patients on ACE-inhibitors for blood pressure often develop a cough?
Cough develops due to inactivation of bradykinin
What substance, formed through the action of phospholipase A2 acting on membrane-bound phospholipids, is metabolized in the lung?
Arachidonic acid
What are the 2 major breakdown pathways of arachidonic acid?
When acted on by lipoxygenase –> leukotrienes
When acted on by cyclooxygenase –> prostaglandins, thromboxane A2
When arachidonic acid is metabolized by lipooxygenase it forms leukotrienes. What are leukotrienes and what effect do they have on the airway?
Slow reacting substance of anaphylaxis
They cause airway constriction, asthma, and inflammation
When arachidonic acid is broken down by cyclooxygenase, it forms prostaglandins and thromboxane A2. What effects do prostaglandins have on blood flow?
Vasoconstriction or vasodilation; can also affect platelet aggregation and clotting cascade
What is the one general, major example of the lung serving metabolic function?
Blood pressure regulation
Blood flow is greatest through which portion of the lungs in a seated individual?
A. Zone 1
B. Zone 2
C. Zone 3
D. Zone 4
C. Zone 3
Infusion of a solution containing high levels of thromboxane A2 would result in which of the following changes in lung blood flow?
A. Pulmonary vasoconstriction
B. Pulmonary vasodilation
C. Pulmonary embolism
D. Decreased pulmonary resistance
A. Pulmonary vasoconstriction
