chapter 13 the respiratory system: movement of air copyright © 2013 by john wiley & sons, inc....

Chapter 13

The Respiratory System: Movement of Air

Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved.

The Respiratory System

• Human life depends on the integrated functioning of the cardiovascular and respiratory systems because neither system, by itself, can supply what we need to survive

• The respiratory system – Delivers oxygen– Expels carbon dioxide– Filters incoming air– Maintains blood pH– Helps control fluid and thermal homeostasis– Produces sound

© 2013 by John Wiley & Sons, Inc. All rights reserved.

The Respiratory System

• The respiratory system has two anatomical divisions

• Upper respiratory tract– Organs include the nose,

pharynx, and larynx– Warms, moistens, and filters

air as it enters the body

• Lower respiratory tract– Organs include the trachea,

bronchial tree (bronchi, bronchioles), and lungs

– Allows oxygen to enter the blood, and waste gases to leave it


The Upper Respiratory Tract – “Nose”

• Filtering– Coarse hairs in the nostrils filter

out larger particles– Mucus of the nasal passages

filters incoming air by trapping small particles

• The epithelium in the upper respiratory tract is pseudostratified ciliated columnar epithelium– Cilia move mucus (containing

trapped debris) away from lungs– The nasal epithelium has

chemosensory neurons which provide the sense of smell


The Upper Respiratory Tract – “Pharynx”

• The pharynx has three parts – Nasopharynx – upper throat

• Normally open for breathing, but it must close when we swallow• The uvula, a fleshy tab of tissue that hangs down in the back of the throat,

contracts when touched by solids, moving upward and closing the internal nares (that lead to the nasopharynx)

• The Eustachian (auditory) tubes link the nasopharynx and the middle ear– When your ears “pop,” these tubes open to equalize air pressure

between the middle and outer ear– Oropharynx - directly behind the tongue

• Covered by the uvula when it hangs down – all activities of the mouth• The palatine and lingual tonsils are found here

– Laryngopharynx – the end of the laryngopharynx has two openings • The anterior opening leads to the larynx and the rest of the respiratory

system • The posterior opening leads to the esophagus and the digestive system


The Upper Respiratory Tract – “Pharynx”


The Upper Respiratory Tract – “Larynx”

• The larynx divides the upper and lower respiratory tracts– Composed entirely of cartilage– Holds the respiratory tract open– Guards the lower tract against particulate matter– Produces the sounds of speech


The Upper Respiratory Tract – “Larynx”

• The larynx is attached to the tongue muscles– When the tongue pushes against the roof of the mouth in preparation for

swallowing, the larynx moves up toward the epiglottis• The larynx is called the “voice box” because it is the location of the vocal

cords• The larynx is composed of hyaline cartilage and consist of three parts

– Thyroid cartilage – in the front of the larynx• Usually larger in men - testosterone stimulates its growth - thickening the

vocal folds; “Adam's apple” refers to the larger laryngeal cartilages in men– Epiglottis - a leaflike flap of cartilage on the superior part of the larynx

• Covers the opening to the lower respiratory tract • Prevents food from entering the lungs

– Cricoid cartilage – a complete ring of cartilage• Holds the respiratory system open


• The main function of the lower tract is to move inhaled air to the respiratory membrane– Structures include the trachea, bronchial tree, lungs

• Conducting zone– Physiologically, the upper tract and the first portion of the lower tract– Conducts air from the atmosphere to the respiratory zone deeper in the body– Includes all the structures of the upper respiratory tract, as well as the

trachea, bronchi, bronchioles, and terminal bronchioles

• Respiratory zone– Lies deep within the lungs - where the actual exchange of gases takes place– Includes only the respiratory bronchioles and alveoli

The Lower Respiratory Tract


The Lower Respiratory Tract


The Lower Respiratory Tract – “Trachea”

• The trachea connects the larynx to the bronchi

• Approximately 2.5 centimeters in diameter– Composed of muscular walls

embedded with 16 to 20 “C”-shaped pieces of hyaline cartilage

– The “C” rings support the trachea so it does not collapse during breathing

– While also allowing the esophagus to expand during swallowing

• At its lower base is the carina – The mucous membrane of the

carina is more sensitive to touch than any other area of the larynx or trachea

– This spot triggers a dramatic cough reflex when any solid object touches it


The Lower Respiratory Tract – “Bronchial Tree”


• The lower portion of the conducting zone and the respiratory zone are collectively referred to as the bronchial tree

• The trachea splits into two tubes called the primary bronchi– At the level of the fifth thoracic vertebra – each leading to one lung

• The primary bronchi divide into the secondary bronchi – inside the lungs– The right bronchus divides into three secondary bronchi– The left bronchus splits into two secondary bronchi

• This branching pattern continues getting smaller and smaller as the tubes extend farther from the primary bronchus– The sequentially smaller tubes are called tertiary bronchi, bronchioles,

terminal bronchioles, and respiratory bronchioles



• The bronchial tree undergoes two major changes as it reaches deeper into the body1. The cells of the mucous membrane get smaller

• Pseudostratified ciliated columnar epithelium• Significant mucus secretion – which cilia sweep upward• Terminal bronchioles have no cilia – are lined with simple columnar

epithelium– If dust reaches this area – only macrophages can remove it

2. The composition of the walls of the bronchi and bronchioles changes• Amount of cartilage decreases as the size of the bronchi and bronchioles

decreases• Simultaneously, amount of smooth muscle increases• Without cartilage – these smaller tubes can be completely shut by

contraction of the smooth muscle

The Lower Respiratory Tract – “Lungs”


• The lungs are the key organs of respiration• These lightweight organs extend from just above the clavicle to the

twelfth thoracic vertebra and fill the rib cage– The base of the lungs is the broad portion sitting on the diaphragm– The apex of the lungs is the small point extending above the clavicles

• The lungs are paired, but they are not identical– The right lung is shorter and fatter, and has three lobes– The left lung is thinner and has two lobes

• It also has a depression for the heart, called the cardiac notch, on the medial side

The Lower Respiratory Tract – “Lungs”


• The lungs are covered in a serous membrane called the pleura– Allows that allows the lungs to expand and contract without tearing the

delicate respiratory tissues• The visceral pleura is snug against the lung tissue• The parietal pleura lines the walls of the thoracic cavity• The pleural cavity between the two pleural membranes contains serous

fluid

• The lobes of each lung are separate sections of the lung that can be lifted away from the other lobes– Air enters each lobe through one secondary bronchus

The Anatomy of the Lungs


Gas Exchange – “Bronchopulmonary Segment”

• Each lung has a different number of secondary bronchi

• Each lung has ten terminal bronchioles– Each supplying one

bronchopulmonary segment

• A bronchopulmonary segment– Looks like a bunch of

grapes


Gas Exchange – “Alveoli”


• Gases diffuse in the alveoli– Oxygen enters the bloodstream and carbon dioxide exits– Alveoli have a cup-shaped membrane at the end of the terminal bronchiole– Alveoli are clustered into an alveolar sac at the end of terminal bronchiole

• The walls of the alveolar sacs are two squamous epithelial cells “thin”– One cell from the alveolar wall, one cell from the capillary wall– Allowing for efficient diffusion of gases

• Septal cells, scattered through the lung, produce surfactant– A detergent-like fluid that moistens the alveoli but prevents their walls from

sticking together during exhalation– Provides a moist membrane for efficient diffusion of gases– Also solubilizing oxygen gas to promote uptake

• Alveolar macrophages patrol the alveoli– These immune cells remove inhaled particles that escaped the mucus and cilia

within the conducting zone– No cilia in alveoli

Gas Exchange


Gas Exchange – The Anatomy of an Alveolar Sac


• The respiratory membrane– At the end of the

respiratory tree

• Consists of– Alveolar cells– Epithelial basement

membrane– Capillary basement

membrane– Endothelium of the

capillary

Gas Movement Across the Respiratory Membrane


• Oxygen diffuses from the alveoli to the blood in the capillary• Carbon dioxide diffuses from the capillary to the alveoli• Remember - The alveoli lumen (interior) is “space” that fills with air

Respiration


• Respiration involves the interplay between the respiratory and cardiovascular systems– The respiratory system moves the gases in and out of the body– The cardiovascular system transports the gases within the body

• The pulmonary capillaries exchange gases in the lungs• The systemic capillaries exchange gases in the body• Pulmonary ventilation

– Is governed by Boyle's law– Which states that the volume of a gas varies inversely with its pressure

Inhalation / Exhalation

• During inhalation, the diaphragm contracts, the chest expands, and the lungs are pulled outward

• All of these decrease pressure within the lungs, allowing air to rush in

– The diaphragm contracts and flattens out – causing the bottom of the thoracic cavity to drop and expand its size

– The intercostal muscles contract – raising the ribs and expanding the size of the ribcage

– The lungs connect to the walls of the thoracic cavity through the pleura• So the lungs also expand in size – allowing for air to enter from the

environment outside

• During exhalation, the diaphragm and intercostal muscles relax, and the volume of the thoracic cavity and lungs decrease

• All of these increase the pressure within the lungs, thus forcing the air back out


Muscles of Inhalation


Pressure Changes in Pulmonary Ventilation


Respiratory Rate

• Respiratory rate is governed by the medulla oblongata and the pons in the brain stem

– The respiratory center in the medulla oblongata causes rhythmic contractions of the diaphragm, stimulating contraction for two seconds and allowing three seconds of rest

– This cycle repeats continuously unless overridden by higher brain function

• The body senses the levels of carbon dioxide and oxygen in the blood through chemoreceptors in the carotid artery and aorta

– High carbon dioxide levels immediately trigger an increase in the depth and rate of respiration


Respiratory Volume

• Different respiratory volumes describe different types of breath

• During “normal breathing”– The volume of air inhaled per minute reflects the respiratory rate and the

volume of each normal breath, called the tidal volume (TV)

• Tidal volume, approximately 500 ml

• During a “forced inhalation”– The average adult male can inhale approximately 3,300 ml of additional air,

and the average adult female can force in approximately 1,900 ml

– This volume is called inspiratory reserve volume (IRV)


Respiratory Volume

• We can exhale much more than the 500 ml tidal volume after a normal tidal inhalation, up to about 1,000 ml for males and 700 ml for females, in the expiratory reserve volume (ERV)– This volume is lower than IRV because exhalation is largely passive

• Vital capacity (VC) – Measures the total volume of air the lungs can inhale and exhale in one huge

breath, which is essentially the maximum amount of air the lungs can move in one respiratory cycle

– VC is the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume

– VC is between 3,100 and 4,800 ml; males generally have the larger volume

• The amount of air that remains in the lungs after forced expiration is called residual volume (RV)– The residual volume holds the alveoli open and fills the “anatomical dead

spaces” – RV is usually between 1,100 and 1,200 ml


“External Respiration”


• External respiration is the exchange of gases between the air in the alveoli and the blood in the respiratory capillaries

• Oxygen enters the alveoli, and carbon dioxide leaves the alveoli

• The exchanges during external and internal respiration are driven by the partial pressures of oxygen and carbon dioxide

– In external respiration, the driving force is the difference in the partial pressures in the alveolar air and the capillary blood

– In internal respiration, the driving force is the partial pressure difference in the capillary blood and the tissue fluid

Dalton’s Law• Gases move independently

down their pressure gradients– From higher to lower

pressure

• Oxygen will diffuse– From the air in the alveoli

into the blood

• Carbon dioxide will diffuse– From blood into the alveoli

• Each gas independently moves toward an area of lower pressure without affecting any other gas


“Internal Respiration”


• Internal respiration is the exchange of gases between body cells and blood in the systemic capillaries

• Oxygen enters the tissues, and carbon dioxide diffuses out of the tissues, again based on partial pressure– The partial pressure of oxygen in the capillary beds of the systemic circuit is

approximately 95 mmHg, whereas the partial pressure of oxygen in most tissues is about 40 mmHg

– This gradient allows oxygen to leave the blood and enter the respiring cells without requiring energy from the body

• Cellular respiration produces carbon dioxide, and the partial pressure of carbon dioxide in the tissues is about 45 mmHg– Blood in the capillary beds has a carbon dioxide partial pressure of 40 mmHg– This small gradient is still enough to cause carbon dioxide to diffuse from the

cells to the blood, which carries it off to the lungs for release into the alveolar air

External/Internal Respiration


Hemoglobin

• Hemoglobin molecules in red blood cells carry oxygen as the blood circulates – Picks up oxygen through a bond between the oxygen molecule and the iron

atom of the hemoglobin’s heme complex

• Hemoglobin has a high affinity for oxygen under some conditions but will release it under other conditions

• Hemoglobin is best known for carrying oxygen, but it also conveys about 23 percent of total carbon dioxide through the bloodstream


Hemoglobin


The Transport of Carbon Dioxide

• Carbon dioxide binds to the protein portion of hemoglobin, forming carbaminohemoglobin (Hb–CO2)– 7 percent of the blood-borne carbon dioxide is carried as dissolved CO2 gas

– The major share of blood-borne carbon dioxide (about 70 percent of total carbon dioxide) moves as bicarbonate ions in plasma

• The bicarbonate ion in the plasma then serves as a buffer, helping to maintain blood pH – Without this buffering, we could not control our internal pH, and we would

perish


The Transport of Carbon Dioxide


Diseases of the Upper Respiratory Tract

• The upper respiratory tract is susceptible to infection and inflammation of the nasal passages, sinuses, and larynx

• One of the most common upper respiratory diseases is sinusitis– An inflammation or swelling of the sinuses– Acute sinusitis - usually caused by a common cold and goes away on its own

within two to three weeks– Chronic sinusitis - is more severe and its causes are less clear

• Most people who suffer from chronic sinusitis also have allergies, asthma, or a compromised immune system


Diseases of the Lower Respiratory Tract

• Diseases of the lower respiratory tract are usually either– Obstructive

• Something is obstructing the normal flow of gases through the lungs– Constrictive

• The airways have been narrowed or constricted in some way

• Bronchitis is a constrictive respiratory disease – An inflammation of the mucous membrane lining the bronchi

• Acute bronchitis - caused by viruses and occasionally bacteria• Chronic bronchitis - caused by smoking – lasts from months to years


Asthma

• Asthma is a constrictive pulmonary disease that can be life-threatening• During an attack

– The smooth muscle of the bronchi contract– Mucus production increases in these tubes– The bronchi swell, interfering with the passage of air

• Asthma kills up to 5,000 people every year in the United States


Obstructive Pulmonary Diseases

• The most common obstructive pulmonary diseases are– Pneumonia, tuberculosis, emphysema, and lung cancer

• In all of these diseases– After exhalation the tubes of the airway do not spring back open because the

elastic tissue is destroyed– Pressure builds in the lungs as the patient tries to force air through the

collapsed tubes, damaging the delicate alveoli and reducing the respiratory surface area

• Pulmonary fibrosis– A destructive increase in collagen makes the lungs less elastic– Often a result from occupational exposure to silicon or other irritants


Chronic Obstructive Respiratory Disease


• Chronic obstructive pulmonary disease (COPD) is actually two diseases– Emphysema and chronic bronchitis– Both obstruct airflow

• In the United States, the death rate from COPD has doubled in the past 30 years– Globally, scientists predict that COPD will be the third-largest cause of death by

2020 • The major cause is cigarette smoking

– But other airborne toxins and pollutants are also to blame

Emphysema


• Emphysema begins when a pollutant or cigarette smoke damages the alveoli, forming holes that cannot be repaired– Delicate lung structures become fibrotic (filled with fibers) and stiff, reducing

their elasticity, making exhaling difficult– The disease starts gradually, with a shortness of breath, and gets worse with

age

• Smoking causes more than 80 percent of such cases – About 5 percent of Americans suffer from genetic emphysema caused by the

lack of a protein necessary for lung function

Pneumonia

• Bacteria living in the warm, moist, lung tissue – Cause two of the more common obstructive respiratory diseases

• Pneumonia and tuberculosis

• Pneumonia – A general term for a buildup of fluid in the lung

• Inflamed alveolar membranes secrete fluid in an attempt to rid the pathogen

• The fluid interferes with gas exchange across the alveolar membrane– Symptoms include

• A productive cough, lethargy, fever, chills, and shortness of breath


Tuberculosis

• Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis– It can pass from person to person in airborne droplets generated by a sneeze or

cough– The bacterium can enter the lymphatic system and infect just about any organ – The bacterium can also remain dormant for years and then reappear in the

lungs without warning

• Symptoms include – A productive (and often bloody) cough, fever, chills, weight loss, night sweats,

and shortness of breath

• Antibiotics have reduced the incidence of TB in industrialized nations – However, TB is on the rise again because antibiotic-resistant strains have

appeared


Lung Cancer

• Lung cancer causes one-third of all cancer deaths– It can affect the bronchi or the alveoli – It ultimately causes cells to proliferate, obstruct airflow, and prevent gas

exchange

• Lung cancer is primarily due to tobacco smoking– 90 percent of all lung cancer patients in the United States are current or

former smokers


Cystic Fibrosis

• Cystic fibrosis (CF) is a genetic disorder – Results from a defective gene that controls the consistency of mucus in the

lungs• The CF version of this gene causes thick, sticky mucus to be produced,

rather than thin, fluid mucus that is conducive to diffusion• This thick mucus traps bacteria and slows airflow through the bronchial

tree, and it may also block the pancreas and bile duct• Treatment

– Physical therapy to dislodge the mucus• Approximately 30,000 people in the United States are currently living

with cystic fibrosis– 1,000 are diagnosed yearly, usually before age 3


chapter 13 the respiratory system: movement of air copyright © 2013 by john wiley & sons, inc....

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