Function of the Respiratory System

Supply the body with oxygen and dispose of carbon dioxide

Pulmonary Ventilation

(breathing) movement of air into and out of the lungs so that the gases there are continuously changed and refreshed

External Respiration

movement of oxygen from the lungs to the blood and of carbon dioxide from the blood to the lungs.

Transport of Respiratory Gases

Transport of oxygen from the lungs to the tissue cells of the body, and of carbon dioxide from the tissue cells to the lungs. This transport is accomplished by the cardiovascular system using blood as the transporting fluid.

Internal Respiration

movement of oxygen from blood to the tissue cells and of carbon dioxide from tissue cells to blood.

Respiratory System includes

nose, nasal cavity, and paranasal sinuses; the pharynx; the larynx; the trachea; the bronchi and their smaller branches; and the lungs, which contain the terminal air sacs, or alveoli

Conducting Zone

all other respiratory passageways, which provide fairly rigid conduits for air to reach the gas exchange sites.

Respiratory Zone

the actual site of gas exchange, is composed of the respiratory bronchioles, alveolar ducts, and alveoli, all microscopic structures.

Philtrum

a shallow vertical groove just inferior to the apex of the nose

Nares

nostrils

Nasal Septum

formed anteriorly by the septal cartilage and posteriorly by the vomer bone and perpendicular plate of the ethmoid bone

Hard Palate

where the palate is supported by the palatine bones and processes of the maxillary bones

Nasal Vestibule

The part of the nasal cavity just superior to the nostrils, lined with skin containing sebaceous and sweat glands and numerous hair follicles.

Vibrissae

Nose hairs that filter coarse particles (dust, pollen) from inspired air.

Nose

Jutting external portion is supported by bone and cartilage. Internal nasal cavity is divided by midline nasal septum and lined with mucosa. Produces mucus; filters, warms, and moistens incoming air; resonance chamber for speech

Paranasal Sinuses

Mucosa-lined, air-filled cavities in cranial bones surrounding nasal cavity. Same as for nasal cavity; also lighten skull

Pharynx

Passageway connecting nasal cavity to larynx and oral cavity to esophagus. Three subdivisions: nasopharynx, oropharynx, and laryngopharynx. Passageway for air and food Houses tonsils (lymphoid tissue masses involved in protection against pathogens). Facilitates exposure of immune system to inhaled antigens

Bronchial Tree

Consists of right and left main bronchi, which subdivide within the lungs to form lobar and segmental bronchi and bronchioles. Bronchiolar walls lack cartilage but contain complete layer of smooth muscle. Constriction of this muscle impedes expiration. Air passageways connecting trachea with alveoli; cleans, warms, and moistens incoming air

Alveoli

Microscopic chambers at termini of bronchial tree. Walls of simple squamous epithelium are underlain by thin basement membrane. External surfaces are intimately associated with pulmonary capillaries. Main sites of gas exchange Special alveolar cells produce surfactant. Reduces surface tension; helps prevent lung collapse

Lungs

Paired composite organs that flank mediastinum in thorax. Composed primarily of alveoli and respiratory passageways. Stroma is fibrous elastic connective tissue, allowing lungs to recoil passively during expiration. House respiratory passages smaller than the main bronchi

Pleurae

Serous membranes. Parietal pleura lines thoracic cavity; visceral pleura covers external lung surfaces. Produce lubricating fluid and compartmentalize lungs

Respiratory Mucosa

is a pseudostratified ciliated columnar epithelium, containing scattered goblet cells, that rests on a lamina propria richly supplied with mucous and serous glands. (Mucous cells secrete mucus, and serous cells secrete a watery fluid containing enzymes.

Lysozyme

antibacterial enzyme.

Rhinitis

inflammation of the nasal mucosa accompanied by excessive mucus production, nasal congestion, and postnasal drip, caused by Cold viruses, streptococcal bacteria, and various allergens

Sinusitis

inflamed sinuses

Nasopharynx

subdivision of the pharynx, lies above the point where food enters the body, it serves only as an air passageway.

Uvula

(“little grape”)during swallowing (along with the soft palate) moves superiorly, an action that closes off the nasopharynx and prevents food from entering the nasal cavity.

Pharyngeal Tonsil

(or adenoids) traps and destroys pathogens entering the nasopharynx in air.

Oropharynx

subdivision of the pharynx, lies posterior to the oral cavity and is continuous with it through an archway called the isthmus of the fauces

Palatine Tonsils

lie embedded in the oropharyngeal mucosa of the lateral walls of the fauces.

Laryngopharynx

subdivision of the pharynx, serves as a passageway for food and air and is lined with a stratified squamous epithelium. It lies directly posterior to the upright epiglottis and extends to the larynx, where the respiratory and digestive pathways diverge.

Larynx

Connects pharynx to trachea. Has framework of cartilage and dense connective tissue. Opening (glottis) can be closed by epiglottis or vocal folds. Air passageway; prevents food from entering lower respiratory tract Houses vocal folds (true vocal cords). Voice production

Thyroid Cartilage

large, shield-shaped, covers the front of the larynx

Laryngeal Prominence

the midline of the thyroid cartilage (adams apple)

Cricoid Cartilage

Inferior to the thyroid cartilage, ring-shaped, perched atop and anchored to the trachea inferiorly.

Arytenoid, Cuneiform, and Corniculate cartilages

form part of the lateral and posterior walls of the larynx

Epiglottis

(“above the glottis”), is composed of elastic cartilage and is almost entirely covered by a taste bud–containing mucosa.

Vocal Ligaments

attach the arytenoid cartilages to the thyroid cartilage. These ligaments, composed largely of elastic fibers, form the core of mucosal folds called the vocal folds, or true vocal cords, which appear pearly white because they lack blood vessels

Vocal Folds

vibrate, producing sounds as air rushes up from the lungs.

Glottis

vocal folds and the medial opening between them through which air passes

Vestibular Folds

or false vocal cords. These play no direct part in sound production but help to close the glottis when we swallow.

Valsalva’s Maneuver

Under certain conditions, the vocal folds act as a sphincter that prevents air passage. During abdominal straining associated with defecation, the glottis closes to prevent exhalation and the abdominal muscles contract, causing the intra-abdominal pressure to rise. Help empty the rectum and can also splint (stabilize) the body trunk when one lifts a heavy load.

Trachea

Flexible tube running from larynx and dividing inferiorly into two main bronchi. Walls contain C-shaped cartilages that are incomplete posteriorly where connected by trachealis muscle. Air passageway; cleans, warms, and moistens incoming air

Layers of trachea

mucosa, submucosa, and adventitia—plus a layer of hyaline cartilage

Carina

The last tracheal cartilage is expanded, and a spar of cartilage, projects posteriorly from its inner face, marking the point where the trachea into the two main bronchi.

Heimlich Maneuver

a procedure in which air in the victim’s lungs is used to “pop out,”or expel, an obstructing piece of food, has saved many people from becoming victims of “café coronaries.”

Bronchial Tree

Consists of right and left main bronchi, which subdivide within the lungs to form lobar and segmental bronchi and bronchioles. Bronchiolar walls lack cartilage but contain complete layer of smooth muscle. Constriction of this muscle impedes expiration. Air passageways connecting trachea with alveoli; cleans, warms, and moistens incoming air

Main (primary) Bronchi

The trachea divides into left and right subdivisions.

Lobar (secondary) Bronchi

the subdivision of the main bronchi, three on the right and two on the left—each supplying one lung lobe.

Segmental (tertiary) Bronchi

third-order bronchi

Bronchioles

(“little bronchi”) Passages smaller than 1 mm in diameter

Terminal bronchioles

the smallest of bronchioles less than 0.5 mm in diameter.

Alveoli

thin-walled air sacs in the lungs

Alveolar Ducts

walls consist of diffusely arranged rings of smooth muscle cells, connective tissue fibers, and outpocketing alveoli.

Alveolar Sacs

terminal clusters of alveoli

Respiratory Membrane

The walls of the alveoli are composed primarily of a single layer of squamous epithelial cells, called type I cells.

Type II Cells

secrete a fluid containing a detergent-like substance called surfactant that coats the gas exposed alveolar surfaces. Prevents the aveoli from collapsing during expiration.

Alveolar Pores

connecting adjacent alveoli allow air pressure throughout the lung to be equalized and provide alternate air routes to any alveoli whose bronchi have collapsed due to disease

Alveolar Macrophages

crawl freely along the internal alveolar surfaces, keeps the alveolar surface clean.

Lungs

Paired composite organs that flank mediastinum in thorax. Composed primarily of alveoli and respiratory passageways. Stroma is fibrous elastic connective tissue, allowing lungs to recoil passively during expiration. House respiratory passages smaller than the main bronchi

Costal Surface

anterior, lateral, and posterior lung surfaces lie in close contact with the ribs and form the continuously curving

Apex

Top point of the lungs

Hilum

an indentation on the mediastinal surface of each lung

Lobes of the Lungs

The left lung is subdivided into superior and inferior lobes by the oblique fissure, whereas the right lung is partitioned into superior, middle, and inferior lobes by the oblique and horizontal fissures.

Cardiac Notch

aconcavity in the medial aspect of the left lung

Bronchopulmonary Segments

separated from one another by connective tissue septa. Each segment is served by its own artery and vein and receives air from an individual segmental (tertiary) bronchus. Initially each lung contains ten bronchopulmonary segments arranged in similar (but not identical) patterns

Pulmonary Arteries

delivers systemic venous blood that is to be oxygenated in the lungs

Pulmonary Capillary Networks

surrounding the alveoli

Pulmonary Veins

delivers freshly oxygenated blood from the lungs to the heart

Bronchial Arteries

provide oxygenated systemic blood to lung tissue

Pulmonary Plexus

The lungs are innervated by parasympathetic and sympathetic motor fibers, and visceral sensory fibers. These nerve fibers enter each lung through the pulmonary plexus on the lung root and run along the bronchial tubes and blood vessels in the lungs. Parasympathetic fibers constrict the air tubes, whereas the sympathetic nervous system dilates them.

Pleurisy

inflammation of the pleurae, often results from pneumonia. Inflamed pleurae become rough, resulting in friction and stabbing pain with each breath. As the disease progresses, the pleurae may produce an excessive amount of fluid. This increased fluid relieves the pain caused by pleural surfaces rubbing together, but may exert pressure on the lungs and hinder breathing movements.

Atmospheric Pressure

Patm, which is the pressure exerted by the air (gases) surrounding the body.

Intrapulmonary Pressure

intra-alveolar Ppul is the pressure in the alveoli. Intrapulmonary pressure rises and falls with the phases of breathing, but it always eventually equalizes with the atmospheric pressure

The Intrapleural Pressure

Pip The pressure in the pleural cavity

The lungs’ natural tendency to recoil

Because of their elasticity, lungs always assume the smallest size possible.

The surface tension of the alveolar fluid

The molecules of the fluid lining the alveoli attract each other and this produces surface tension that constantly acts to draw the alveoli to their smallest possible dimension.

Transpulmonary Pressure

the difference between the intrapulmonary and intrapleural pressures (Ppul – Pip) that keeps the air spaces of the lungs open or keeps the lungs from collapsing.

Atelectasis

lung collapse

Pneumothorax

The presence of air in the pleural cavity

Inspiration

taking air into the lungs

Action of the diaphragm

When the dome-shaped diaphragm contracts, it moves inferiorly and flattens out. As a result, the superior-inferior dimension (height) of the thoracic cavity increases.

Action of the Intercostal Muscles

Contraction of the external intercostal muscles lifts the rib cage and pulls the sternum superiorly. Because the ribs curve downward as well as forward around the chest wall, the broadest lateral and anteroposterior dimensions of the rib cage are normally directed obliquely downward. But when the ribs are raised and drawn together, they swing outward, expanding the diameter of the thorax both laterally and in the anteroposterior plane.

Expiration

air leaving the lungs

Forced Expiration

an active process produced by contraction of abdominal wall muscles, primarily the oblique and transversus muscles.

Airway Resistance

The major nonelastic source of resistance to gas flow is friction, or drag, encountered in the respiratory passageways.

Acute Asthma Attack

histamine and other inflammatory chemicals can cause such strong bronchoconstriction that pulmonary ventilation almost completely stops, regardless of the pressure gradient.

Surface Tension

the unequal attraction produces a state of tension at the liquid surface.

Surfactant

a detergent-like complex of lipids and proteins produced by the type II alveolar cells. Surfactant decreases the cohesiveness of water molecules,much the way a laundry detergent reduces the attraction of water for water, allowing water to interact with and pass through fabric. As a result, the surface tension of alveolar fluid is reduced, and less energy is needed to overcome those forces to expand the lungs and discourage alveolar collapse.

Infant Respiratory Distress Syndrome

(IRDS), a condition peculiar to premature babies. When too little surfactant is present, surface tension forces can collapse the alveoli. Once this happens, the alveoli must be completely reinflated during each inspiration, an effort that uses tremendous amounts of energy.

Lung Compliance

Healthy lungs are unbelievably stretchy

Tidal volume (TV)

During normal quiet breathing, about 500 ml of air moves into and then out of the lungs with each breath

Inspiratory Reserve Volume

(IRV) The amount of air that can be inspired forcibly beyond the tidal volume (2100 to 3200 ml)

Expiratory Reserve Volume

(ERV) is the amount of air—normally 1000 to 1200 ml—that can be evacuated from the lungs after a tidal expiration.

Residual Volume

(RV) after the most strenuous expiration, about 1200 ml of air remains in the lungs; which helps to keep the alveoli patent (open) and to prevent lung collapse.

Inspiratory Capacity

(IC) is the total amount of air that can be inspired after a tidal expiration, so it is the sum of TV and IRV.

Functional Residual Capacity

(FRC) represents the amount of air remaining in the lungs after a tidal expiration and is the combined RV and ERV.

Vital Capacity

(VC) is the total amount of exchangeable air. It is the sum of TV, IRV, and ERV. In healthy young males,VC is approximately 4800 ml.

Total Lung Capacity

(TLC) is the sum of all lung volumes and is normally around 6000 ml.

Anatomical Dead Space

Some of the inspired air fills the conducting respiratory passageways and never contributes to gas exchange in the alveoli, typically amounts to about 150 ml (The rule of thumb is that the anatomical dead space volume in a healthy young adult is equal to 1 ml per pound of ideal body weight.) This means that if TV is 500 ml, only 350 ml of it is involved in alveolar ventilation. The remaining 150 ml of the tidal breath is in the anatomical dead space.

Alveolar Dead Space

If some alveoli cease to act in gas exchange (due to alveolar collapse or obstruction by mucus, for example)

Total Dead Space

Anatomical Dead Space + Alveolar Dead Space

Spirometry

most useful for evaluating losses in respiratory function and for following the course of certain respiratory diseases. It cannot provide a specific diagnosis, but it can distinguish between obstructive pulmonary disease involving increased airway resistance (such as chronic bronchitis) and restrictive disorders involving a reduction in total lung capacity resulting from structural or functional changes in the lungs

Minute Ventilation

the total amount of gas that flows into or out of the respiratory tract in 1 minute. During normal quiet breathing, the minute ventilation in healthy people is about 6 L/min (500 ml per breath multiplied by 12 breaths per minute). During vigorous exercise, the minute ventilation may reach 200 L/min.

FVC

forced vital capacity, measures the amount of gas expelled when a subject takes a deep breath and then forcefully exhales maximally and as rapidly as possible.

FEV

or forced expiratory volume, determines the amount of air expelled during specific time intervals of the FVC test.

AVR

Alveolar Ventilation Rate takes into account the volume of air wasted in the dead space and measures the flow of fresh gases in and out of the alveoli during a particular time interval.

Cough

Taking a deep breath, closing glottis, and forcing air superiorly from lungs against glottis; glottis opens suddenly and a blast of air rushes upward. Can dislodge foreign particles or mucus from lower respiratory tract and propel such substances superiorly.

Sneeze

Similar to a cough, except that expelled air is directed through nasal cavities as well as through oral cavity; depressed uvula routes air upward through nasal cavities. Sneezes clear upper respiratory passages.

Crying

Inspiration followed by release of air in a number of short expirations. Primarily an emotionally induced mechanism.

Laughing

Essentially same as crying in terms of air movements produced. Also an emotionally induced response.

Hiccups

Sudden inspirations resulting from spasms of diaphragm; believed to be initiated by irritation of diaphragm or phrenic nerves, which serve diaphragm. Sound occurs when inspired air hits vocal folds of closing glottis.

Yawn

Very deep inspiration, taken with jaws wide open; not believed to be triggered by levels of oxygen or carbon dioxide in blood. Ventilates all alveoli (not the case in normal quiet breathing).

Dalton’s Law of Partial Pressures

states that the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture.

Henry’s Law

when a gas is in contact with a liquid, that gas will dissolve in the liquid in proportion to its partial pressure. Accordingly, the greater the concentration of a particular gas in the gas phase, the more and the faster that gas will go into solution in the liquid.

Oxygen Toxicity

develops rapidly when PO2 is greater than 2.5–3 atm. excessively high O2 concentrations generate huge amounts of harmful free radicals, resulting in profound CNS disturbances, coma, and death

Composition of Alveolar Gas

the gaseous makeup of the atmosphere is quite different from that in the alveoli. The atmosphere is almost entirely O2 and N2; the alveoli contain more CO2 and water vapor and much less O2.

These differences reflect the effects of
(1) gas exchanges occurring in the lungs (O2 diffuses from the alveoli into the pulmonary blood and CO2 diffuses in the opposite direction)
(2) humidification of air by conducting passages,
(3) the mixing of alveolar gas that occurs with each breath.

External Respiration

During external respiration (pulmonary gas exchange) dark red blood flowing through the pulmonary circuit is transformed into the scarlet river that is returned to the heart for distribution by systemic arteries to all body tissues.

The following three factors influence the movement of oxygen and carbon dioxide across the respiratory membrane:
1. Partial pressure gradients and gas solubilities
2. Matching of alveolar ventilation and pulmonary blood perfusion
3. Structural characteristics of the respiratory membrane

Ventilation-Perfusion Coupling

For gas exchange to be efficient, there must be a close match, or coupling, between the amount of gas reaching the alveoli, known as ventilation, and the blood flow in pulmonary capillaries, known as perfusion.

Partial Pressure Gradients and Gas Solubilities

Ventilation

Perfusion Coupling - For gas exchange to be efficient, there must be a close match, or coupling, between the amount of gas reaching the alveoli, known as ventilation, and the blood flow in pulmonary capillaries, known as perfusion.

Oxyhemoglobin

hemoglobin-oxygen combination

Deoxyhemoglobin

reduced hemoglobin

Oxygenhemoglobin Dissociation Curve

between the degree of hemoglobin saturation and the PO2 of blood is not linear, because the affinity of hemoglobin for O2 changes with O2 binding, as we just described.

Bohr Effect

oxygen unloading is enhanced where it is most needed.

Hypoxia

inadequate oxygen delivery to body tissues

Anemic hypoxia

reflects poor O2 delivery resulting from too few RBCs or from RBCs that contain abnormal or too little Hb.

Ischemic (stagnant) Hypoxia

results when blood circulation is impaired or blocked. Congestive heart failure may cause bodywide ischemic hypoxia, whereas emboli or thrombi block oxygen delivery only to tissues distal to the obstruction.

Histotoxic Hypoxia

occurs when body cells are unable to use O2 even though adequate amounts are delivered. This variety of hypoxia is the consequence of metabolic poisons, such as cyanide.

Hypoxemic Hypoxia

is indicated by reduced arterial PO2. Possible causes include disordered or abnormal ventilationperfusion coupling, pulmonary diseases that impair ventilation, and breathing air containing scant amounts of O2.

Carbon Monoxide Poisoning

is a unique type of hypoxemic hypoxia, and a leading cause of death from fire. Carbon monoxide (CO) is an odorless, colorless gas that competes vigorously with O2 for heme binding sites.Moreover, because Hb’s affinity for CO is more than 200 times greater than its affinity for oxygen, CO is a highly successful competitor. Even at minuscule partial pressures, carbon monoxide can displace oxygen.

Carbon Dioxide Transport

Normally active body cells produce about 200 ml of CO2 each minute—exactly the amount excreted by the lungs.

Blood transports CO2 from the tissue cells to the lungs in three forms
1. Dissolved in plasma (7–10%). The smallest amount of CO2 is transported simply dissolved in plasma.
2. Chemically bound to hemoglobin (just over 20%). In this form, dissolved CO2 is bound and carried in theRBCs as carbaminohemoglobin
3. As bicarbonate ion in plasma (about 70%). Most carbon dioxide molecules entering the plasma quickly enter the RBCs, where most of the reactions that prepare carbon dioxide for transport as bicarbonate ions

Carbonic Anhydrase

an enzyme that reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid

Chloride Shift

ion exchange process, occurs via facilitated diffusion through a RBC membrane protein.

Carbonic Acid–Bicarbonate Buffer System

is very important in resisting shifts in blood pH, as shown in the equation in point 3 concerning CO2 transport. For example, if the hydrogen ion concentration in blood begins to rise, excess is removed by combining with HCO3 – to form carbonic acid (a weak acid). If H concentration drops below desirable levels in blood, carbonic acid dissociates, releasing hydrogen ions and lowering the pH again.

The Haldane Effect

The amount of carbon dioxide transported in blood is markedly affected by the degree of oxygenation of the blood. The lower the PO2 and the lower the extent of Hb saturation with oxygen, the more CO2 that can be carried in the blood.

Ventral Respiratory Group

(VRG) contains rhythm generators whose output drives respiration.

Dorsal Respiratory Group

(DRG) integrates peripheral sensory input and modifies the rhythms generated by the VRG.

Pontine Respiratory Centers

interact with the medullary respiratory centers to smooth the respiratory pattern.

phrenic and Intercostal nerves

excites the diaphragm and external intercostal muscles, respectively a result, the thorax expands and air rushes into the lungs.When the VRG’s expiratory neurons fire, the output stops, and expiration occurs passively as the inspiratory muscles relax and the lungs recoil

Eupnea

normal respiratory rate and rhythm

Chemoreceptors

Sensors responding to such chemical fluctuations

Central Chemoreceptors

are located throughout the brain stem, including the ventrolateral medulla.

Peripheral Chemoreceptors

found in the aortic arch and carotid arteries.

Hypercapnia

As PCO2 levels rise in the blood CO2 accumulates in the brain.

Hyperventilation

is an increase in the rate and depth of breathing that exceeds the body’s need to remove CO2.A person experiencing an anxiety attack may hyperventilate involuntarily to the point where he or she becomes dizzy or faints.

Apnea

breathing cessation

Inflation Reflex, or Hering

Breuer reflex - As the lungs recoil, the stretch receptors become quiet, and inspiration is initiated once again.

Acute Mountain Sickness (AMS)

headaches, shortness of breath, nausea, and dizziness. When you travel quickly from sea level to elevations above 8000 ft, where atmospheric pressure and PO2 are lower

Chronic Obstructive Pulmonary Diseases (COPD)

exemplified best by emphysema and chronic bronchitis, are a major cause of death and disability in North America. The key physiological feature of these diseases is an irreversible decrease in the ability to force air out of the lungs.

Emphysema

distinguished by permanent enlargement of the alveoli, accompanied by destruction of the alveolar walls. Invariably the lungs lose their elasticity. This has three important consequences

(1) Accessory muscles must be enlisted to breathe, and victims are perpetually exhausted because breathing requires 15–20% of their total body energy supply (as opposed to 5% in healthy individuals).
(2) For complex reasons, the bronchioles open during inspiration but collapse during expiration, trapping huge volumes of air in the alveoli. This hyperinflation leads to development of a permanently expanded “barrel chest” and flattens the diaphragm, thus reducing ventilation efficiency.
(3) Damage to the pulmonary capillaries as the alveolar walls disintegrate increases resistance in the pulmonary circuit, forcing the right ventricle to overwork and consequently become enlarged.

Chronic Bronchitis

inhaled irritants lead to chronic excessive mucus production by the mucosa of the lower respiratory passageways and to inflammation and fibrosis of that mucosa. These responses obstruct the airways and severely impair lung ventilation and gas exchange.

Asthma

characterized by episodes of coughing, dyspnea, wheezing, and chest tightness—alone or in combination

Tuberculosis (TB)

the infectious disease caused by the bacterium Mycobacterium tuberculosis, is spread by coughing and primarily enters the body in inhaled air. TB mostly affects the lungs but can spread through the lymphatics to affect other organs. a massive inflammatory and immune response usually contains the primary infection in fibrous, or calcified, nodules (tubercles) in the lungs.

Squamous Cell Carcinoma

(25–30% of cases), which arises in the epithelium of the bronchi or their larger subdivisions and tends to form masses that may cavitate (hollow out) and bleed

Adenocarcinoma

(about 40%), which originates in peripheral lung areas as solitary nodules that develop from bronchial glands and alveolar cells

Small Cell Carcinoma

(about 20%), which contains round lymphocyte-sized cells that originate in the main bronchi and grow aggressively in small grapelike clusters within the mediastinum