Research paper regarding Lungs

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ANATOMY & PHYSIOLOGY

Chapter 22 THE RESPIRATORY SYSTEM

Part 2

The Lungs

Pulmonary ventilation

College Physics

Chapter # Chapter Title

PowerPoint Image Slideshow

Hi and welcome to the second part of the chapter corresponding to the respiratory system. In this section we will address the lungs.

learning objectives

Outline the anatomy of the lungs

Describe the blood supply and pleura of the lungs

Explain the mechanics of breathing and the factors affecting pulmonary ventilation

the learning objectives are the following:

Outline the anatomy of the lungs

Describe the blood supply and pleura of the lungs

Explain the mechanics of breathing and the factors affecting pulmonary ventilation

the lungs

Large superficial area

Lobes: 3 right, 2 left

Cardiac notch: space for the heart

Inferior border: diaphragm (muscle)

A major organ of the respiratory system, each lung houses structures of both the conducting and respiratory zones. The main function of the lungs is to perform the exchange of oxygen and carbon dioxide with air from the atmosphere. The lungs are pyramid-shaped, paired organs that are connected to the trachea by the right and left bronchi; on the inferior surface, the lungs are bordered by the diaphragm, a flat, dome-shaped muscle. The lungs are enclosed by the pleurae, which are attached to the mediastinum. The right lung is shorter and wider than the left lung, and the left lung occupies a smaller volume than the right. The cardiac notch is an indentation on the surface of the left lung, and it allows space for the heart.

blood supply of the lungs

Pulmonary circulation:

Blood that needs to be oxygenated: right ventricle => pulmonary arteries=> pulmonary capillaries

Oxygenated blood leaves the lung in the pulmonary veins

Cardiac output is the same- as much flow through the lungs as the rest of the body

High flow but low pressure, b/c of low resistance: shorter vessels, large cross-sectional area of pulmonary arterioles

Bronchial circulation

oxygenated blood coming from the aorta supplying all the lungs but the alveoli

Deoxygenated blood from the pulmonary circulation enters the lungs through pulmonary arteries, which branch till becoming the pulmonary capillaries where gas exchange takes place. The oxygenated blood leaves via pulmonary veins. You may recall from the circulatory chapter that the cardiac output is the same for the systemic and pulmonary circulations. While the latter is high flow, its pressure is lower due to the large cross-sectional area of all pulmonary arterioles together. The short bronchial circulation provides oxygenated blood to all structures of the lungs except the alveoli.

pleura of the lungs

Parietal: covers the thoracic walls and the upper side of the diaphragm

Visceral: covers the lungs

Between them: pleural cavity, filled with pleural liquid (reduces tension)

Each lung is enclosed within a cavity that is surrounded by the pleura. The pleura (plural = pleurae) is a serous membrane that surrounds the lung. The pleurae consist of two layers. The visceral pleura is the layer that is superficial to the lungs, and extends into and lines the lung fissures. In contrast, the parietal pleura is the outer layer that connects to the thoracic wall, the mediastinum, and the diaphragm. The visceral and parietal pleurae connect to each other at the hilum. The pleural cavity is the space between the visceral and parietal layers. Pleural fluid is secreted by mesothelial cells from both pleural layers and acts to lubricate their surfaces. This lubrication reduces friction between the two layers to prevent trauma during breathing, and creates surface tension that helps maintain the position of the lungs against the thoracic wall

breathing: pulmonary ventilation

Pulmonary ventilation consists of two phases

Inspiration: gases flow into the lungs

Expiration: gases exit the lungs

Depends on pressure relationships:

atmospheric pressure patm

intra-alveolar pressure Palv

intrapleural pressure pip

Pulmonary ventilation is the act of breathing, which can be described as the movement of air into and out of the lungs. It consists of 2 phases: inspiration (or inhalation) and expiration (or exhalation). The major mechanisms that drive pulmonary ventilation are atmospheric pressure (Patm); the air pressure within the alveoli, called intra-alveolar pressure (Palv); and the pressure within the pleural cavity, called intrapleural pressure (Pip).

boyle’s law

Boyle’s law – the relationship between the pressure and volume of gases

P1V1 = P2V2

Gases will flow from higher pressure to lower pressure

Before we start analyzing the different types of pressures governing pulmonary ventilation, let’s recap a basic law of physics called Boyle’s law. This law basically states that the same number of gas molecules compressed in a smaller volume will have a higher pressure, and vice versa. If the containers in the figure were somehow connected, the gas would be moving from higher to lower pressure, in this case form right to left. As we will see, this is exactly how air moves in and out the lungs: following pressure gradients due to changes in lung volumes.

atmospheric & intra-alveolar pressure

Atmospheric pressure (Patm)

Pressure exerted by the air surrounding the body

760 mm Hg at sea level

respiratory pressures are described in relationship to patm, negative is lower, positive is higher

Intrapulmonary (intra-alveolar) pressure (Palv)

Pressure in the alveoli

Fluctuates with breathing

Always eventually equalizes with Patm

Atmospheric pressure is the amount of force that is exerted by gases in the air surrounding any given surface, such as the body. Atmospheric pressure can be expressed in terms of the unit atmosphere, abbreviated atm, or in millimeters of mercury (mm Hg). One atm is equal to 760 mm Hg, which is the atmospheric pressure at sea level. Typically, for respiration, other pressure values are discussed in relation to atmospheric pressure. Therefore, negative pressure is pressure lower than the atmospheric pressure, whereas positive pressure is pressure that it is greater than the atmospheric pressure. A pressure that is equal to the atmospheric pressure is expressed as zero. Intra-alveolar or intrapulmonary pressure is the pressure of the air within the alveoli, which changes during the different phases of breathing. Because the alveoli are connected to the atmosphere via the tubing of the airways, the intrapulmonary pressure of the alveoli always equalizes with the atmospheric pressure.

intrapleural pressure

Intrapleural pressure (Pip):

Pressure in the pleural cavity

Fluctuates with breathing

Always a negative pressure (less than Palv)

Why negative?

elasticity of lung walls (tend to recoil)

surface tension of alveolar tissue (tends to recoil)

surface tension within the pleural wall (pulls outward), slightly greater

Transpulmonary pressure: Palv – Pip

Intrapleural pressure is the pressure of the air within the pleural cavity, between the visceral and parietal pleurae. Similar to intra-alveolar pressure, intrapleural pressure also changes during the different phases of breathing. However, due to certain characteristics of the lungs, the intrapleural pressure is always lower than, or negative to, the intra-alveolar pressure (and therefore also to atmospheric pressure). Although it fluctuates during inspiration and expiration, intrapleural pressure remains approximately –4 mm Hg throughout the breathing cycle. The reason for this is due to the sum of opposing forces. The elasticity of the lungs and the surface tension of the alveolar tissue tends to pull the lungs inward. This pull is opposed by the surface tension within the pleural cavity, caused by the presence of pleural liquid. Ultimately, the outward pull is slightly greater than the inward pull, creating the –4 mm Hg intrapleural pressure relative to the intraalveolar pressure. Transpulmonary pressure is the difference between the intrapleural and intra-alveolar pressures, and it determines the size of the lungs. A higher transpulmonary pressure corresponds to a larger lung.

pressure relationships

Let’s look at the figure to understand better the pressure relationships. You can see how the intraalveolar and the atmospheric pressures are the same as they are connected with each other. Picture the lungs as a balloon, if not inflated they will recoil, due to its elasticity. What keeps them open is that the pleural fluid (think an adhesive) in the pleural cavity keeps the pleura together, which in turn follow the movements of the thoracic cage. This negative pressure keeps the lungs inflated. In case of pneumothorax, when air enters the pleural cavity, this difference disappears and the lung collapses.

physical factors affecting breathing

Breathing depends on contraction & relaxation of respiratory muscles:

diaphragm

intercostals

They will expand or recoil the thoracic wall, changing lung volumes (and pressures)

Thoracic wall must be compliant

Size of airways affect resistance: smaller diameter causes greater resistance

Surfactant reduces surface tension of alveoli keeping them open during expiration

In addition to the differences in pressures, breathing is also dependent upon the contraction and relaxation of muscle fibers of both the diaphragm and thorax. The lungs themselves are passive during breathing, meaning they are not involved in creating the movement that helps inspiration and expiration. Contraction and relaxation of the diaphragm and intercostals muscles (found between the ribs) cause most of the pressure changes that result in inspiration and expiration. These muscle movements and subsequent pressure changes cause air to either rush in or be forced out of the lungs. The expansion of the thoracic cavity directly influences the capacity of the lungs to expand. If the tissues of the thoracic wall are not very compliant, it will be difficult to expand the thorax to increase the size of the lungs. Resistance is a force that slows

motion, in this case, the flow of gases. The size of the airway is the primary factor affecting resistance. As noted earlier, there is surface tension within the alveoli caused by water present in the lining of the alveoli. Pulmonary surfactant secreted by type II alveolar cells mixes with that water and helps reduce this surface tension.

airway resistance

Highest in the medium bronchi

Susceptible to neural and chemical controls In asthma the bronchi are constricted, treated with beta-agonists (imitate sympathetic response) drugs bind to b2 receptors provoking bronchodilation

Recall that as the bronchi branch in the lungs, they will present less cartilage and more smooth muscle. This smooth muscle presents autonomous innervation, which controls the diameter of the airways (similarly as peripheral resistance works in blood circulation).

The parasympathetic system causes bronchoconstriction, whereas the sympathetic nervous system stimulates bronchodilation. Reflexes such as coughing, and the ability of the lungs to regulate oxygen and carbon dioxide levels, also result from this autonomic nervous system control. Some medications, such as the broncodilators used for asthma attacks act on autonomous receptors to modulate airway resistance.

summary of inspiration

Inspiration is the process that causes air to enter the lungs. In general, two muscle groups are used during normal inspiration: the diaphragm and the external intercostal muscles. Additional muscles can be used if a bigger breath is required. When the diaphragm contracts, it moves inferiorly toward the abdominal cavity, creating a larger thoracic cavity and more space for the lungs. Contraction of the external intercostal muscles moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity. Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure. As a result, a pressure gradient is created that drives air into the lungs.

summary of expiration

The process of normal expiration is passive, meaning that energy is not required to push air out of the lungs. Instead, the elasticity of the lung tissue causes the lung to recoil, as the diaphragm and intercostal muscles relax following inspiration. In turn, the thoracic cavity and lungs decrease in volume, causing an increase in intrapulmonary pressure. The intrapulmonary pressure rises above atmospheric pressure, creating a pressure gradient that causes air to leave the lungs. A respiratory cycle is one sequence of inspiration and expiration.

respiratory volumes and capacities

Quiet breathing: eupnea

Deep breath: Diaphragmatic, shallow breath: costal

Forced breathing: hyperpnea

Respiratory volume is the term used for various volumes of air moved by or associated with the lungs at a given point in the respiratory cycle. There are four major types of respiratory volumes: tidal, residual, inspiratory reserve, and expiratory reserve. Tidal volume (TV) is the amount of air that normally enters the lungs during quiet breathing, which is about 500 milliliters. Expiratory reserve volume (ERV) is the amount of air you can forcefully exhale past a normal tidal expiration, up to 1200 milliliters for men. Inspiratory reserve volume (IRV) is produced by a deep inhalation, past a tidal inspiration. This is the extra volume that can be brought into the lungs during a forced inspiration. Residual volume (RV) is the air left in the lungs if you exhale as much air as possible. The residual volume makes breathing easier by preventing the alveoli from collapsing. Respiratory volume is dependent on a variety of factors, and measuring the different types of respiratory volumes can provide important clues about a person’s respiratory health

Respiratory capacity is the combination of two or more selected volumes, which further describes the amount of air in the lungs during a given time. For example, total lung capacity (TLC) is the sum of all of the lung volumes (TV, ERV, IRV, and RV), which represents the total amount of air a person can hold in the lungs after a forceful inhalation. Vital capacity (VC) is the amount of air a person can move into or out of his or her lungs, and is the sum of all of the volumes except residual volume (TV, ERV, and IRV), which is between 4000 and 5000 milliliters. Inspiratory capacity (IC) is the maximum amount of air that can be inhaled past a normal tidal expiration, is the sum of the tidal volume and inspiratory reserve volume. On the other hand, the functional residual capacity (FRC) is the amount of air that remains in the lung after a normal tidal expiration; it is the sum of expiratory reserve volume and residual volume

pulmonary function tests

Minute ventilation: total amount of gas flow into or out of the respiratory tract in one minute

Forced vital capacity (FVC): gas forcibly expelled after taking a deep breath

Forced expiratory volume (FEV): the amount of gas expelled during specific time intervals of the FVC

Increases in TLC, FRC, and RV may occur as a result of obstructive disease

Reduction in VC, TLC, FRC, and RV result from restrictive disease

In pulmonary function tests, done with a spirometer, the subject will be asked to breath both normally and forcibly, to collect additional parameters, such as the forced vital capacity and expiratory volumes. Changes in these volumes can help the clinician to distinguish between obstructive and restrictive lung diseases.

obstructive and restrictive lung diseases

Less elastance: returning to its resting volume when stretching force is released => obstructive lung diseases (COPD: emphysema & chronic bronchitis, asthma)

Less compliance: ability to stretch +> restrictive lung diseases (sarcoidosis, chronic pulmonary fibrosis)

The term obstructive lung disease includes conditions that hinder a person’s ability to exhale all the air from their lungs, due to decreased elastance. Those with restrictive lung disease experience difficulty fully expanding their lungs due to decreased compliance. Obstructive and restrictive lung disease share one main symptom–shortness of breath with any sort of physical exertion. Obstructive conditions include COPD or chronic obstructive pulmonary disease, asthma, and cystic fibrosis. Restrictive examples are sarcoidosis, silicosis, and pulmonary fibrosis.

respiratory system

This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted.

And with this, we conclude part 2 of the lecture corresponding to the respiratory system. It is highly recommended that you review some of the video materials regarding this chapter for a better understanding. Thank you.