Circulation Lecture

Question 1

High-pressure, low-flow circulation

Answer 1

Supplies systemic arterial blood to: trachea, bronchial tree, supporting tissues of the lung, outer coats of pulmonary arteries and veins

Question 2

Low pressure, high-flow circulation

Answer 2

Supplies systemic venous blood to: all parts of the body to the alveolar capillaries where oxygen is added and CO2 removed

Question 3

What carries blood to the alveolar capillaries for gas exchange?

Answer 3

The pulmonary artery (which receives blood from the right ventricle) and its arterial branches

Question 4

What returns the blood for systemic circulation?

Answer 4

The pulmonary veins to the left atrium to be pumped out through the left ventricle

Question 5

What are the pulmonary vessels?

Answer 5

Pulmonary trunk (artery) extends only 5 cm beyond the apex of the right ventricle; dividing into right and left pulmonary artery
- Pulmonary arteries have larger diameters than systemic artieries as well as thin walls making them quite distensible and largely compliant

Question 6

What are bronchial vessels?

Answer 6

Oxygenated blood that supplies supporting tissues of lungs
Empties into left atrium
Flow of left ventricular output is about 1-2% > than that of the right ventricular output

Question 7

What are lymphatics?

Answer 7

Present in all supportive tissue of lungs

Function: removal of particulate matter, removal of plasma protein leaking from lung capillaries

Question 8

Blood flow and distribution?

Answer 8

Cardiac output –> factors that control CO also control pulmonary blood flow

• Under normal conditions pulmonary vessels are passive distensible tubes
• • Blood must be distributed to areas of the lung where the alveoli are best oxygenated

Question 9

Mechanisms of aeration?

Answer 9

Diminished alveolar oxygen signals constriction of the adjacent blood vessels
Increase alveolar oxygen signals dilation of the adjacent blood vessels
– Possibly a vasoconstricting substance secreted by alveolar epithelial cells when they become hypoxic allowing for blood flow to go to areas that are better aerated

Question 10

What are pulmonary capillary dynamics?

Answer 10

Alveolar wall are lined with several capillaries –> Capillaries touch one another side by side –> Capillary blood flows in alveolar as a “sheet of flow” rather than individual capillaries

Question 11

What is mean filtration pressure?

Answer 11

Capillary pressure = +7
Interstitial fluid colloid osmotic pressure = 14
Negative intersitital fluid pressure = 8
Total outward force 7+14 +8 = 29
Total inward force = 28
Net mean filtration pressure =+1
A slight continual flow occurs forcing fluid from the pulmonary capillary into the interstitial spaces

Question 12

What happens to extra fluid?

Answer 12

Carried away by pulmonary lymphatics or absorbed into the pulmonary capillaries

Question 13

Fluid in the pleural cavity?

Answer 13

When the lungs expand and contract during normal breathing, they slide back and forth within the pleural cavity

• This is facilitated by a thin layer of mucoid fluid that lies between the parietal and visceral pleurae
• • Each of these two pleurae is a very porous membrane through which small amounts of interstitial fluid permeates continually into the pleural spaces

Question 14

What happens when there is continual fluid permeating into the pleural spaces?

Answer 14

These fluids carry with them tissue proteins that give the pleural fluid a mucoid characteristics which allows for easy movement of lungs within the spaces

Question 15

What causes the lungs to try to collapse and what prevents this?

Answer 15

The recoil tendency of the lungs
A negative force is required on the outside of the lungs to keep them expanding –> provided by negative pressure in the normal pleural space

Question 16

What is the cause of negative pressure?

Answer 16

The pumping of fluids from the space of the lumphatics

Question 17

Pleural fluid pressure?

Answer 17

Always at least 4 mm Hg to keep the lungs expanded (actual measurement is about 7 mmHg

Question 18

What is pulmonary edema?

Answer 18

Anything that causes the pulmonary interstitial fluid pressure to rise from the negative range will cause sudden filling of the pulmonary interstitial spaces and alveoli with large amounts of free fluid

Question 19

What results in impaired gas transfer?

Answer 19

the Capillary endothelium is much more permeable to water and solutes than the alveolar epithelium, edema fluid accumulates first in the interstitium and later in the alveoli

Question 20

Common causes of pulmonary edema?

Answer 20

Left-sided heart failure or mitral valve disease

Damage to the pulmonary blood capillary membranes

Question 21

Left-sided heart failure or mitral valve disease

Answer 21

Great increase in pulmonary venous pressure and pulmonary capillary pressure and flooding of the interstitial spaces and alveoli

Question 22

Damage to the pulmonary blood capillary membranes caused by?

Answer 22

Infection (pneumonia) or breathing noxious substance such as Cl gas or SO2 gas (rapid leakage of both plasma proteins and fluid out of the capillaries and into both the lung interstitial spaces and the alveoli)

Question 23

In order for pulmonary edema to occur?

Answer 23

Pulmonary capillary pressure normally must rise to a value at least equal to the colloid osmotic pressure of the plasma inside the capillaries