INNOVATIVE WORK ON BLOOD GROUP IN THE FORM OF DRAMA

The Human Respiratory System

INTRODUCTION

Every tissue within the body requires oxygen to function. The respiratory system, which includes air passages, pulmonary vessels, the lungs, and breathing muscles, provides oxygenated blood to the body tissues and removes waste gases. 

The respiratory system, which includes air passages, pulmonary vessels, the lungs, and breathing muscles, aids the body in the exchange of gases between the air and blood, and between the blood and the body’s billions of cells. Most of the organs of the respiratory system help to distribute air, but only the tiny, grape-like alveoli and the alveolar ducts are responsible for actual gas exchange.

In addition to air distribution and gas exchange, the respiratory system filters, warms, and humidifies the air you breathe. Organs in the respiratory system also play a role in speech and the sense of smell.

The respiratory system also helps the body maintain homeostasis, or balance among the many elements of the body’s internal environment.

The respiratory system is divided into two main components:

Upper respiratory tract: Composed of the nose, the pharynx, and the larynx, the organs of the upper respiratory tract are located outside the chest cavity.

• Nasal cavity: Inside the nose, the sticky mucous membrane lining the nasal cavity traps dust particles, and tiny hairs called cilia help move them to the nose to be sneezed or blown out.
• Sinuses: These air-filled spaces along side the nose help make the skull lighter.
• Pharynx: Both food and air pass through the pharynx before reaching their appropriate destinations. The pharynx also plays a role in speech.
• Larynx: The larynx is essential to human speech.

Lower respiratory tract: Composed of the trachea, the lungs, and all segments of the bronchial tree (including the alveoli), the organs of the lower respiratory tract are located inside the chest cavity.

• Trachea: Located just below the larynx, the trachea is the main airway to the lungs.
• Lungs: Together the lungs form one of the body’s largest organs. They’re responsible for providing oxygen to capillaries and exhaling carbon dioxide.
• Bronchi: The bronchi branch from the trachea into each lung and create the network of intricate passages that supply the lungs with air.
• Diaphragm: The diaphragm is the main respiratory muscle that contracts and relaxes to allow air into the lungs.

The cells of the human body require a constant stream of oxygen to stay alive. The respiratory system provides oxygen to the body’s cells while removing carbon dioxide, a waste product that can be lethal if allowed to accumulate. There are 3 major parts of the respiratory system: the airway, the lungs, and the muscles of respiration. The airway, which includes the nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles, carries air between the lungs and the body’s exterior. The lungs...

The cells of the human body require a constant stream of oxygen to stay alive. The respiratory system provides oxygen to the body’s cells while removing carbon dioxide, a waste product that can be lethal if allowed to accumulate. There are 3 major parts of the respiratory system: the airway, the lungs, and the muscles of respiration. The airway, which includes the nose, mouth, pharynx, larynx, trachea, bronchi, and bronchioles, carries air between the lungs and the body’s exterior. The lungs

act as the functional units of the respiratory system by passing oxygen into the body and carbon dioxide out of the body. Finally, the muscles of respiration, including the diaphragm and intercostals muscles, work together to act as a pump, pushing air into and out of the lungs during breathing.

Nose  and Nasal Cavity

The nose and nasal cavity form the main external opening for the respiratory system and are the first section of the body’s airway—the respiratory tract through which air moves. The nose is a structure of the face made of cartilage, bone, muscle, and skin that supports and protects the anterior portion of the nasal cavity. The nasal cavity is a hollow space within the nose and skull that is lined with hairs and mucus membrane. The function of the nasal cavity is to warm, moisturize, and filter air entering the body before it reaches the lungs. Hairs and mucus lining the nasal cavity help to trap dust, mold, pollen and other environmental contaminants before they can reach the inner portions of the body. Air exiting the body through the nose returns moisture and heat to the nasal cavity before being exhaled into the environment.

Mouth
The mouth, also known as the oral cavity, is the secondary external opening for the respiratory tract. Most normal breathing takes place through the nasal cavity, but the oral cavity can be used to supplement or replace the nasal cavity’s functions when needed. Because the pathway of air entering the body from the mouth is shorter than the pathway for air entering from the nose, the mouth does not warm and moisturize the air entering the lungs as well as the nose performs this function. The mouth also lacks the hairs and sticky mucus that filter air passing through the nasal cavity. The one advantage of breathing through the mouth is that its shorter distance and larger diameter allows more air to quickly enter the body.

Pharynx
The pharynx, also known as the throat, is a muscular funnel that extends from the posterior end of the nasal cavity to the superior end of the esophagus and larynx. The pharynx is divided into 3 regions: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is the superior region of the pharynx found in the posterior of the nasal cavity. Inhaled air from the nasal cavity passes into the nasopharynx and descends through the oropharynx, located in the posterior of the oral cavity. Air inhaled through the oral cavity enters the pharynx at the oropharynx. The inhaled air then descends into the laryngopharynx, where it is diverted into the opening of the larynx by the epiglottis. The epiglottis is a flap of elastic cartilage that acts as a switch between the trachea and the esophagus. Because the pharynx is also used to swallow food, the epiglottis ensures that air passes into the trachea by covering the opening to the esophagus. During the process of swallowing, the epiglottis moves to cover the trachea to ensure that food enters the esophagus and to prevent choking.

Larynx

The larynx, also known as the voice box, is a short section of the airway that connects the laryngopharynx and the trachea. The larynx is located in the anterior portion of the neck, just inferior to the hyoid bone and superior to the trachea. Several cartilage structures make up the larynx and give it its structure. The epiglottis is one of the cartilage pieces of the larynx and serves as the cover of the larynx during swallowing. Inferior to the epiglottis is the thyroid cartilage, which is often referred to as the Adam’s apple as it is most commonly enlarged and visible in adult males. The thyroidholds open the anterior end of the larynx and protects the vocal folds. Inferior to the thyroid cartilage is the ring-shaped cricoid cartilage which holds the larynx open and supports its posterior end. In addition to cartilage, the larynx contains special structures known as vocal folds, which allow the body to produce the sounds of speech and singing. The vocal folds are folds of mucous membrane that vibrate to produce vocal sounds. The tension and vibration speed of the vocal folds can be changed to change the pitch that they produce.

Trachea
The trachea, or windpipe, is a 5-inch long tube made of C-shaped hyaline cartilage rings lined with pseudostratified ciliated columnar epithelium. The trachea connects the larynx to the bronchi and allows air to pass through the neck and into the thorax. The rings of cartilage making up the trachea allow it to remain open to air at all times. The open end of the cartilage rings faces posteriorly toward the esophagus, allowing the esophagus to expand into the space occupied by the trachea to accommodate masses of food moving through the esophagus.

The main function of the trachea is to provide a clear airway for air to enter and exit the lungs. In addition, the epithelium lining the trachea produces mucus that traps dust and other contaminants and prevents it from reaching the lungs. Cilia on the surface of the epithelial cells move the mucus superiorly toward the pharynx where it can be swallowed and digested in the gastrointestinal tract.

Bronchi and Bronchioles

At the inferior end of the trachea, the airway splits into left and right branches known as the primary bronchi. The left and right bronchi run into each lung before branching off into smaller secondary bronchi. The secondary bronchi carry air into the lobes of the lungs—2 in the left lung and 3 in the right lung. The secondary bronchi in turn split into many smaller tertiary bronchi within each lobe. The tertiary bronchi split into many smaller bronchioles that spread throughout the lungs. Each bronchiole further splits into many smaller branches less than a millimeter in diameter called terminal bronchioles. Finally, the millions of tiny terminal bronchioles conduct air to the alveoli of the lungs.

As the airway splits into the tree-like branches of the bronchi and bronchioles, the structure of the walls of the airway begins to change. The primary bronchi contain many C-shaped cartilage rings that firmly hold the airway open and give the bronchi a cross-sectional shape like a flattened circle or a letter D. As the bronchi branch into secondary and tertiary bronchi, the cartilage becomes more widely spaced and more smooth muscle and elastin protein is found in the walls. The bronchioles differ from the structure of the bronchi in that they do not contain any cartilage at all. The presence of smooth muscles and elastin allow the smaller bronchi and bronchioles to be more flexible and contractile.

The main function of the bronchi and bronchioles is to carry air from the trachea into the lungs. Smooth muscle tissue in their walls helps to regulate airflow into the lungs. When greater volumes of air are required by the body, such as during exercise, the smooth muscle relaxes to dilate the bronchi and bronchioles. The dilated airway provides less resistance to airflow and allows more air to pass into and out of the lungs. The smooth muscle fibers are able to contract during rest to prevent hyperventilation. The bronchi and bronchioles also use the mucus and cilia of their epithelial lining to trap and move dust and other contaminants away from the lungs.

Lungs

The lungs are a pair of large, spongy organs found in the thorax lateral to the heart and superior to the diaphragm. Each lung is surrounded by a pleural membrane that provides the lung with space to expand as well as a negative pressure space relative to the body’s exterior. The negative pressure allows the lungs to passively fill with air as they relax. The left and right lungs are slightly different in size and shape due to the heart pointing to the left side of the body. The left lung is therefore slightly smaller than the right lung and is made up of 2 lobes while the right lung has 3 lobes.

The interior of the lungs is made up of spongy tissues containing many capillaries and around 30 million tiny sacs known as alveoli. The alveoli are cup-shaped structures found at the end of the terminal bronchioles and surrounded by capillaries. The alveoli are lined with thin simple squamous epithelium that allows air entering the alveoli to exchange its gases with the blood passing through the capillaries.

Muscles of Respiration
Surrounding the lungs are sets of muscles that are able to cause air to be inhaled or exhaled from the lungs. The principal muscle of respiration in the human body is the diaphragm, a thin sheet of skeletal muscle that forms the floor of the thorax. When the diaphragm contracts, it moves inferiorly a few inches into the abdominal cavity, expanding the space within the thoracic cavity and pulling air into the lungs. Relaxation of the diaphragm allows air to flow back out the lungs during exhalation.

Between the ribs are many small intercostal muscles that assist the diaphragm with expanding and compressing the lungs. These muscles are divided into 2 groups: the internal intercostal muscles and the external intercostal muscles. The internal intercostal muscles are the deeper set of muscles and depress the ribs to compress the thoracic cavity and force air to be exhaled from the lungs. The external intercostals are found superficial to the internal intercostals and function to elevate the ribs, expanding the volume of the thoracic cavity and causing air to be inhaled into the lungs.

Pulmonary Ventilation

Pulmonary ventilation is the process of moving air into and out of the lungs to facilitate gas exchange. The respiratory system uses both a negative pressure system and the contraction of muscles to achieve pulmonary ventilation. The negative pressure system of the respiratory system involves the establishment of a negative pressure gradient between the alveoli and the external atmosphere. The pleural membrane seals the lungs and maintains the lungs at a pressure slightly below that of the atmosphere when the lungs are at rest. This results in air following the pressure gradient and passively filling the lungs at rest. As the lungs fill with air, the pressure within the lungs rises until it matches the atmospheric pressure. At this point, more air can be inhaled by the contraction of the diaphragm and the external intercostal muscles, increasing the volume of the thorax and reducing the pressure of the lungs below that of the atmosphere again.

To exhale air, the diaphragm and external intercostal muscles relax while the internal intercostal muscles contract to reduce the volume of the thorax and increase the pressure within the thoracic cavity. The pressure gradient is now reversed, resulting in the exhalation of air until the pressures inside the lungs and outside of the body are equal. At this point, the elastic nature of the lungs causes them to recoil back to their resting volume, restoring the negative pressure gradient present during inhalation.

External Respiration

External respiration is the exchange of gases between the air filling the alveoli and the blood in the capillaries surrounding the walls of the alveoli. Air entering the lungs from the atmosphere has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than does the blood in the capillaries. The difference in partial pressures causes the gases to diffuse passively along their pressure gradients from high to low pressure through the simple squamous epithelium lining of the alveoli. The net result of external respiration is the movement of oxygen from the air into the blood and the movement of carbon dioxide from the blood into the air. The oxygen can then be transported to the body’s tissues while carbon dioxide is released into the atmosphere during exhalation.

Internal Respiration

Internal respiration is the exchange of gases between the blood in capillaries and the tissues of the body. Capillary blood has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than the tissues through which it passes. The difference in partial pressures leads to the diffusion of gases along their pressure gradients from high to low pressure through the endothelium lining of the capillaries. The net result of internal respiration is the diffusion of oxygen into the tissues and the diffusion of carbon dioxide into the blood.

Transportation of Gases
The 2 major respiratory gases, oxygen and carbon dioxide, are transported through the body in the blood. Blood plasma has the ability to transport some dissolved oxygen and carbon dioxide, but most of the gases transported in the blood are bonded to transport molecules. Hemoglobin is an important transport molecule found in red blood cells that carries almost 99% of the oxygen in the blood. Hemoglobin can also carry a small amount of carbon dioxide from the tissues back to the lungs. However, the vast majority of carbon dioxide is carried in the plasma as bicarbonate ion. When the partial pressure of carbon dioxide is high in the tissues, the enzyme carbonic anhydrase catalyzes a reaction between carbon dioxide and water to form carbonic acid. Carbonic acid then dissociates into hydrogen ion and bicarbonate ion. When the partial pressure of carbon dioxide is low in the lungs, the reactions reverse and carbon dioxide is liberated into the lungs to be exhaled.

Homeostatic Control of Respiration

Under normal resting conditions, the body maintains a quiet breathing rate and depth called eupnea. Eupnea is maintained until the body’s demand for oxygen and production of carbon dioxide rises due to greater exertion. Autonomic chemoreceptors in the body monitor the partial pressures of oxygen and carbon dioxide in the blood and send signals to the respiratory center of the brain stem. The respiratory center then adjusts the rate and depth of breathing to return the blood to its normal levels of gas partial pressures.

The Human Respiratory System

The Pathway

• Air enters the nostrils
• passes through the nasopharynx,
• the oral pharynx
• through the glottis
• into the trachea
• into the right and left bronchi, which branches and rebranches into
• bronchioles, each of which terminates in a cluster of
• alveoli

Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80 times the area of our skin!).

Breathing

In mammals, the diaphragm divides the body cavity into the

• abdominal cavity, which contains the viscera (e.g., stomach and intestines) and the
• thoracic cavity, which contains the heart and lungs.

The inner surface of the thoracic cavity and the outer surface of the lungs are lined with pleural membranes which adhere to each other. If air is introduced between them, the adhesion is broken and the natural elasticity of the lung causes it to collapse. This can occur from trauma. And it is sometimes induced deliberately to allow the lung to rest. In either case, reinflation occurs as the air is gradually absorbed by the tissues.

Because of this adhesion, any action that increases the volume of the thoracic cavity causes the lungs to expand, drawing air into them.

• During inspiration (inhaling),
• The external intercostal muscles contract, lifting the ribs up and out.
• The diaphragm contracts, drawing it down .
• During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breath 15–18 times a minute exchanging about 500 ml of air.
• In more vigorous expiration,
• The internal intercostal muscles draw the ribs down and inward
• The wall of the abdomen contracts pushing the stomach and liver upward.

Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each breath. This is called the vital capacity. Even with maximum expiration, about 1200 ml of residual air remain.

The table shows what happens to the composition of air when it reaches the alveoli. Some of the oxygen dissolves in the film of moisture covering the epithelium of the alveoli. From here it diffuses into the blood in a nearby capillary. It enters a red blood cell and combines with the hemoglobin therein.

At the same time, some of the carbon dioxide in the blood diffuses into the alveoli from which it can be exhaled.

Composition of atmospheric air and expired air in a typical subject. Note that only a fraction of the oxygen inhaled is taken up by the lungs.
Component	Atmospheric Air (%)	Expired Air (%)
N2 (plus inert gases)	78.62	74.9
O2	20.85	15.3
CO2	0.03	3.6
H2O	0.5	6.2
	100.0%	100.0%

The ease with which oxygen and carbon dioxide can pass between air and blood is clear from this electron micrograph of two alveoli (Air) and an adjacent capillary from the lung of a laboratory mouse. Note the thinness of the epithelial cells (EP) that line the alveoli and capillary (except where the nucleus is located). At the closest point, the surface of the red blood cell is only 0.7 µm away from the air in the alveolus. (Reproduced with permission from Keith R. Porter and Mary A. Bonneville, An Introduction to the Fine Structure of Cells and Tissues, 4th. ed., Lea & Febiger, 1973.) 

Central Control of Breathing

The rate of cellular respiration (and hence oxygen consumption and carbon dioxide production) varies with level of activity. Vigorous exercise can increase by 20–25 times the demand of the tissues for oxygen. This is met by increasing the rate and depth of breathing.

It is a rising concentration of carbon dioxide — not a declining concentration of oxygen — that plays the major role in regulating the ventilation of the lungs. Certain cells in the medulla oblongata are very sensitive to a drop in pH. As the CO2 content of the blood rises above normal levels, the pH drops
[CO2 + H2O → HCO3− + H+],
and the medulla oblongata responds by increasing the number and rate of nerve impulses that control the action of the intercostal muscles and diaphragm. This produces an increase in the rate of lung ventilation, which quickly brings the CO2 concentration of the alveolar air, and then of the blood, back to normal levels.

However, the carotid body in the carotid arteries does have receptors that respond to a drop in oxygen. Their activation is important in situations (e.g., at high altitude in the unpressurized cabin of an aircraft) where oxygen supply is inadequate but there has been no increase in the production of CO2. People who live at high altitudes, e.g., in the Andes, have enlarged carotid bodies.

Local Control of Breathing

The smooth muscle in the walls of the bronchioles is very sensitive to the concentration of carbon dioxide. A rising level of CO2 causes the bronchioles to dilate. This lowers the resistance in the airways and thus increases the flow of air in and out.

Diseases of the Lungs

Pneumonia

Pneumonia is an infection of the alveoli. It can be caused by many kinds of both bacteria (e.g., Streptococcus pneumoniae) and viruses. Tissue fluids accumulate in the alveoli reducing the surface area exposed to air. If enough alveoli are affected, the patient may need supplemental oxygen.

Asthma

In asthma, periodic constriction of the bronchi and bronchioles makes it more difficult to breathe in and, especially, out. Attacks of asthma can be

• triggered by airborne irritants such as chemical fumes and cigarette smoke
• airborne particles to which the patient is allergic.

Emphysema

In this disorder, the delicate walls of the alveoli break down, reducing the gas-exchange area of the lungs. The condition develops slowly and is seldom a direct cause of death. However, the gradual loss of gas-exchange area forces the heart to pump ever-larger volumes of blood to the lungs in order to satisfy the body's needs. The added strain can lead to heart failure.

The immediate cause of emphysema seems to be the release of proteolytic enzymes as part of the inflammatory process that follows irritation of the lungs. Most people avoid this kind of damage during infections, etc. by producing an enzyme inhibitor (a serpin) called alpha-1 antitrypsin. Those rare people who inherit two defective genes for alpha-1 antitrypsin are particularly susceptible to developing emphysema.

Chronic Bronchitis

Any irritant reaching the bronchi and bronchioles will stimulate an increased secretion of mucus. In chronic bronchitis the air passages become clogged with mucus, and this leads to a persistent cough. Chronic bronchitis is usually associated with cigarette smoking.

Chronic Obstructive Pulmonary Disease (COPD)

Irritation of the lungs can lead to asthma, emphysema, and chronic bronchitis. And, in fact, many people develop two or three of these together. This constellation is known as chronic obstructive pulmonary disease(COPD).

Among the causes of COPD are

• cigarette smoke (often)
• cystic fibrosis (rare)

Cystic fibrosis is a genetic disorder caused by inheriting two defective genes for the cystic fibrosis transmembrane conductance regulator (CFTR), a transmembrane protein needed for the transport of Cl− and HCO3−ions through the plasma membrane of epithelial cells. In healthy lungs, secretion of Cl− (along with Na+ through a different channel) draws water by osmosis into the fluid bathing the cells. In cystic fibrosis, inadequate secretion of Cl− and the resulting lack of water produces a thick, sticky mucus covering the epithelia and hampering the ability of ciliated cells to move it up out of the lungs. In addition, diminished secretion of HCO3−lowers the pH of this liquid making it more hospitable to colonization by inhaled bacteria. The resulting inflammation increases the accumulation of mucus which plugs the airways interfering with breathing and causing a persistent cough. Cystic fibrosis is the most common inherited disease in the U.S. white population.

Lung Cancer

Lung cancer is the most common cancer and the most common cause of cancer deaths in U.S. males. Although more women develop breast cancer than lung cancer, since 1987 U.S. women have been dying in larger numbers from lung cancer than from breast cancer.

Lung cancer, like all cancer, is an uncontrolled proliferation of cells. There are several forms of lung cancer, but the most common (and most rapidly increasing) types are those involving the epithelial cells lining the bronchi and bronchioles.

Ordinarily, the lining of these airways consists of two layers of cells. Chronic exposure to irritants

• causes the number of layers to increase. This is especially apt to happen at forks where the bronchioles branch.
• The ciliated and mucus-secreting cells disappear and are replaced by a disorganized mass of cells with abnormal nuclei.
• If the process continues, the growing mass penetrates the underlying basement

• At this point, malignant cells can break away and be carried in lymph and blood to other parts of the body where they may lodge and continue to proliferate.
• It is this metastasis of the primary tumor that eventually kills the patient.

Reference

http://www.livescience.com/22616-respiratory-system.html

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Pulmonary.html

http://hes.ucfsd.org/gclaypo/repiratorysys.html

http://www.innerbody.com/anatomy/respiratory

https://en.wikipedia.org/wiki/Respiratory_system#Humans_and_mammals

Jango-Cohen, J. (2005). The respiratory system. Minneapolis: Lerner Publications Co.

Subramanian, S., Berry, S., & Hasan, S. (2004). The respiratory system. Pittsburgh, PA: Dorrance Pub. Co.