Chapter 39

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What circulations does lung have?

High-pressure lowflow circulation, and a low-pressure high flow circulation

What does high pressure low flow circulation supply?

It supplies systemic arterial blood to trachea, bronchial tree, supporting tissues of lung and outer coats (adventitia) of pulmonary arteries and veins

Low pressure high flow-circulation supplies what?

Venous blood from all parts of body to alveolar capillaries hwere oxygen is added and carbon dioxide is removed

What does the pulmonary artery receive its blood from?

From right ventricle (arterial branches carry blood to alveolar capillaries for gas exchange and pulmonary veins return blood to left atrium to be pumped by left ventricle through systemic circulation)

What does the pulmonary artery divide into?

Right and left main branches that supply blood to the two respective lungs

Tell more about the pulmonary vessels?

Pulmonary artery has a wall thickness one third that of aorta, pulmonary arterial branches are short and all pulmonary arteries have larger diameters than their counterpart systemic arteries

What does pulmonary arterial tree have?

A large compliance, averaging almost 7 ml/mm Hg, which is similar to that of entire systemic arterial tree

What does the large compliance of pulmonary arterial tree allow?

It allows the pulmonary arteries to accommodate the stroke volume output of right ventricle

What about the pulmonary veins?

They are like pulmonary arteries short, and empty their effluent blood into left atrium

How does blood also flow to the lungs?

Through small bronchial arteries that originate from systemic circulation (this bronchial arterial blood is oxygenaatd blood, in contract to partially deoxygenated blood in pulmonary arteries)

Bronchial arterial blood supplies what?

It supplies the supporting tissues of the lungs, including connective tissue, septa and large and small bronchi, and after it passes through supporting tissues, it empties into pulmonary veins and enter left atrium

Where are lymph vessels present?

In all supporitve tissues of the lung, beginning in the connective tissue spaces that surround the terminal bronchioles, coursing to the hilum of the lung, and then mainly into right thoracic lymph duct

What is the systolic pressure in right ventricle of normal human?

25 mm Hg

What is the diastolic pressure averaging in normal human in right ventricle?

About 0 to 1 mm Hg

Whaat happens during systole?

The pressure in the pulmonary artery is equal to pressure inr right ventricle (25 mm Hg)

What happens after the pulmonary valve closes at end of systole?

The ventricular pressure falls precipitously, whereas the pulmonary arterial pressure falls more slowly as blood flows through capillaries of lungs

What does systolic pulmonary arterial rpessure normally average?

About 25 mm Hg in human being, and idastolic pulmonary arteiral pressure is about 8 mm Hg, and mean pulmoonary arterial pressure is 15 mm Hg

What is the mean pulmonary capillary pressure?

It is about 7 mm Hg

What is the mean pressure in left atrium and major pulmonary veins?

About 2 mm Hgi n recumbent human being, varying from as low as 1 mm Hg to as high as 5 mm Hg

How can the left atrial pressure be sstimated?

By pulmonary wedge pressure (inserting a catheter through peripheral vein to right atrium, into one of small branches of pulmonar yartery, pushing catheter until it wedges tightly in the small branch)

What is the wedge pressure about?

5 mm Hg (this wedge pressure is usually only 2 to 3 mm Hg greater than elft atrial pressure) when left atrial pressure rises to higih values, the pulmonary wedge pressure also rises

In what ways can wedge pressure be used?

To study changes in pulmonary capillary pressure and left atrial pressure in patients with congestive heart failure

What is the blood volume of lungs about?

About 450 milliliters, about 9% of total blood volume of entire circulatory system, approximately 70 milliliters of this is in pulmonary capilaries and remainder is divided between pulmonary arteries and veins

Quantity of blood in lungs can vary, but what happens when blowing a trumpet?

As muchas 250 milliliters of blood can be expelled from pulmonary circulatory system into systemic circulation, (also loss of blood from systemic circulation by hemorrhage can be partly compensated for by the automatic shift of blood from lungs into systemic vessels)

What happens due to failure of left side of heart or increased resistance to blood flow through mitral valve due to mitral stenosis or mitral regurgitation?

It causes blood to dam up in the pulmonary circulation, sometimes increasing the pulmonary blood volume as much as 100 percent % and causing large increases in pulmonary vascular pressures

What is blood flow through the lungs?

It is equal to cardiac output (therefore factors that control cardiac output such as peripheral factors also control pulmonary blood flow)

What happens when concentration of O2 in air of alveoli decreases below normal?

Adjacent blood vessels constrict, with vascular resistance increasing more than fivefold at extremely low O2 levels

What about the standing position at rest?

There is little flow in the top of lung, but about five times as much flow in the bottom, the lung is divided into three zones, and in each zone the patterns of blood flow are quite different

What happens in zone 1 (no blood flow during all portions of cardiac cycle)?

Because local alveolar capillary pressure in that area of lung never rises higher than the alveolar air pressure during any part of cardiac cycle

What happens in zone 2 (intermittent blood flow)?

Only during peaks of pulmonar yarterial rpessure because systolic pressure is then greater than alveolar air pressure, but diastolic pressure is less than alveolar air pressure

What happens in zone 3 (continous blood flow)?

Because the alveeolar capillary pressure remains greater than alveolar air pressure during entire cardiac cycle

When does zone 1 blood flow occur?

Only under abnormal conditions (when either pulmonary systolci arterial pressure is too low or alveolar pressure is too high to allow flow) , severe blood loss can be one cause

What happens during exercise?

Blood flow through all parts of lungs increases (because pulmonary vascular pressures rise enough during exercise to convert lung apices from a zone 2 pattern into a zone 3 pattern of flow)

During heavy exercise, blood flow through lungs may increase fourfold to sevenfold, this extra flow is accommodated in lungs in what three ways?

1) increasing number of open capillaries 2) distending all capillaries and increasing rate of flow through each capillary more than twofold 3) increasing pulmonary arterial rpessure

Left atrial pressure in healthy person never rises what?

About +6 mm Hg

When can the left atrial rpessure rise from 1 to 5 mm Hg all the way up to 40 to 50 mm Hg?

When the left side of heart fails, blood begins to dam up in left atrium, the rise in atrial pressure up to 7 mm Hg has little effect on pulmonary circulatory function, but greater than 7 or 8 mm Hg can cause increased load on right heart

Any increase in left atrial pressure above 7 or 8 mm Hg increases what?

Increases capillary pressure almost equally as much and above 30 mm Hg causing increases in capillaruy pressure and pulmonary edema will develop

What are alveolar walls lined with?

With many capillaries, so that many capillaries almost touch one another side by side, therefore it is often said that the capillary blood flows in the alveolar walls as a sheet of flow, rather than in individual capillaries

What can measure pulmonary capillary pressure?

Isogravimetric measurement of pulmonary capillary pressure, giving a value of 7 mm Hg (this value is probably correct because mean left atrial pressure is about 2 mm Hg and mean pulmonary arteril pressure is only 15 mm Hg, so that is the mean value)

What happens when cardiac output is normal?

Blood passes through pulmonary capillaries in about 0,8 second, when cardiac output increases this time can shorten to as little as 0,3 second

What are the differences between lung capillary membranes and peripheral tissues quantitatively (because qualitatively they are the same)?

Pilmonary capillary pressure is low (7 mm Hg), capillary pressure in peripheral tissues is about (17 mm Hg)

What are the differences between lung capillary membranes and peripheral tissues quantitatively (because qualitatively they are the same)?2

Interstitial fluid rpessure in lung is slightly more negative than that in peripheral subcutaneous tissue

What are the differences between lung capillary membranes and peripheral tissues quantitatively (because qualitatively they are the same)?3

Colloid osmotic pressure of pulmonary interstitial flud is about 14 mm Hg, in comparison with less than half this value in peripheral tissues

What are the differences between lung capillary membranes and peripheral tissues quantitatively (because qualitatively they are the same)?

Alveolar walls are extremely thin, and alveolar epithelium covering alveolar surfaces is weak that it can be ruptured by positvie pressure in intertitial spaces grater than alveolar air pressure

What does the mean filtration rpessure +1 mm Hg tell us?

This filtration pressure causes a slight continual flow of fluid from pulmonary capillaries into interstitial spaces and, except for a small amount that evaporates in alveoli, this fluid is pumped back to circulation through pulmonary lymphatic system

What keeps the alveoli from filling with fluid under normal conditions?

Whenever extra fluid appears in alveoli, it will simply be sucked into the lung interstitum through small openings between alveolar epithelial cells, the excess fluid is then carried away through pulmonary lympahtics keeping the alveoli dry

What is causing pulmonary edema?

Left sided heart failure or mitral valve disease OR 2) damage to pulmonary blood capillary membranes by infectiosn such as pneumonia or noxious substances causing leakage of plasma proteins and fluid out of capillaries and into both lung interstitial spaces and alveoli

Pulmonary capillary pressure must do what in order to cause pulmonary edema?

Pulmonary capillary pressure must rise from normal level of 7 mm Hg to more than 28 mm Hg to cause pulmonary edema, giving an acute safety factor agianst pulmonary edema of 21 mm Hg

Total amount of fluid in each pleural cavity is what?

ONLY a few milliliters, and when the quantity becomes more than barely enough to begin flowing in the pleural cavity, the excess fluid is pumped away by lymphatiec vessels opening from pleural cavity to 1) mediastinum 2) superior surface of diaphragm 3) lateral surfaces of parietal pleura

What about the pleural space?

It is the space between parietal and visceral pleurae and is called a potential space because it normally is so narrow that it is not obviously a physical space

What is keeping the lungs expanded?

A negative force on outside of lungs

What is pleural effusion?

It is analogous to edema fluid in the tissues and can be called edema of pleural cavity

Which are the causes of pleural effusion?

They are the same as the causes of edema in other tissues including 1) blockage of lymphatic rainage from pleural cavity 2) cardiac failure 3) greatly reduced plasma colloid osmotic pressure 4) infection or any other cause of inflammation of the surfaces of pleural cavity, which increases permeability of capillary membranes and allows rapid dumping of both plasma proteins and fluid into the cavity

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