Each lung is enclosed by a double-layered serous membrane, called the pleura. The visceral pleura are firmly attached to the surface of the lung. At the hilum, the visceral pleura is continuous with the parietal pleura that lines the wall of the thorax. The small space between the visceral and parietal pleurae is the pleural cavity. It contains a thin film of serous fluid that is produced by the pleura. The fluid acts as a lubricant to reduce friction as the two layers slide against each other, and it helps to hold the two layers together as the lungs inflate and deflate.

PATHOLOGICAL CONDITIONS
Croup: Acute respiratory syndrome in children and infants characterized by obstruction of the larynx barking cough and strider.

Diphtheria: Acute infection of throat and upper respiration tract caused by chorine bacterium diphtheriae. It forms a leathery opaque membrane in the pharynx or in the respiratory tract causing an obstruction in the airflow, which may lead to health.

Pertusis: A bacterial infection of pharynx, larynx and trachea caused by bardetella pertusis, a highly contagious bacterium with woofing cough.

Asthma: Spasm and narrowing of the bronchus leading to bronchial airway obstruction caused by an allergen, gives paroxysmal (sudden) dyspnea, wheezing, and cough.

Chronic bronchitis: inflammation of the bronchi persisting from a long time due to infection or cigarette smoking leading to accumulation of mucus in bronchioles and COPD.

Atelectiasis: an incomplete expansion of the alveoli causing collapsed airless functionless lungs.

Emphysema: Hyper inflation of air sacs with destruction of alveolar walls causing loss of elasticity and breakdown of alveolar walls result in loss of air movement in air sac.

Pneumonia: Acute inflammation & infection of alveoli filling with pus in the lungs.

Pulmonary edema: Swelling and fluid collection in the air sacs and in the bronchioles in cases of congestive heart failure.

Pulmonary embolism: It is a process of obstruction of blood vessel by emboli like fats, clots, air, a chemical, leading to death of the pulmonary tissue called as pulmonary infraction.

ALLERGIC RHINITIS
Allergic rhinitis may be defined as the inflammation of nasal mucosa brought about by airborne pollens that react to release histamine. In other words, when some people breathe pollens that are in the air, the pollens cause histamine to be released. The excess of histamine in the body causes nasal mucosa to become inflamed. Causes of allergic rhinitis, more common during the warmest months of the year, include hay fever and allergic disorders which are common during seasons when the pollen count is high. Allergic rhinitis is also caused by house dust, occupational dust, molds, and animal dander (feathers, wool in blankets). Certain foods and drugs cause allergic rhinitis symptoms; sometimes bacteria cause this problem. The symptoms include:

• Nasal congestion.
• Profuse watery discharge.
• Itching of nose and conjunctiva.
• Sneezing.

PARANASAL SINUSITIS
Paranasal sinusitis is an infection of the mucous membranes that line the paranasal sinuses. Since the membrane that lines these sinuses is continuous with that of the of the nose and throat, paranasal sinusitis is a common complication of any upper respiratory infection. Causes of paranasal sinusitis include viruses, streptococci, and pneumococci.

Signs and symptoms of acute paranasal sinusitis are like those of acute rhinitis but are more severe. Included are headache, worse during the day; facial and tooth pain; tenderness over the sinuses; and fever and chills. There may be chronic recurrences of these signs and symptoms along with postnasal drip.

COMMON COLD
The common cold is a contagious, viral infection of the upper respiratory tract. The cold is usually caused by a strain of rhinovirus. Over ninety distinct strains of rhinovirus are known to cause the common cold. Although not everyone is susceptible to infection from a cold virus, this respiratory infection occurs more often than all other diseases combined. Whether or not a person develops a cold after being exposed to a cold virus is determined to some extent by the person’s general health. Fatigue, chilling of the body, wearing wet clothes and shoes, and the presence of irritating substances in the air make it more likely that the person will develop a cold.

These are signs and symptoms of the common cold:

• Malaise (general feeling of being unwell).
• Fever/chills.
• Headache.
• Nasal discomfort.
• Dry, sore throat.
• Cough (either productive or nonproductive).
• Mild leukocytosis (temporary increase in number of leukocytes in the blood).

 ACUTE PHARYNGITIS
 Acute pharyngitis is an inflammation of the pharynx. This disease, inflammation of the mucosa of the pharynx, usually occurs as part of an upper respiratory tract disorder. The nose, sinuses, larynx, and trachea may also be affected. The most common causes are bacterial or viral infection. Very rarely, acute pharyngitis is caused by inhalation of irritant gases or ingestion of irritant liquids. Sometimes, acute pharyngitis is one symptom of a specific disease such as measles, chickenpox, scarlet fever, or whooping cough.

Common signs and symptoms are listed below. A complication may be a secondary infection.

• Dry and sore throat.
• Fever.
• Malaise.
• Strep infection may be present with white pus pocket formation.
• Cough.

 ACUTE TONSILLITIS/STREP THROAT

 Tonsillitis: Tonsillitis is a painful disease caused by bacteria or viruses that infect one or both of the palatine tonsils. People between the ages of ten and forty have the majority of tonsillitis attacks.

 Strep throat: Strep throat is an infectious disease that affects the membranes of the throat and tonsils. This disease is also called septic sore throat, acute streptococcal pharyngitis, and acute streptococcal tonsillitis. The disease is caused by group A beta-hemolytic streptococci bacteria. It spreads from person to person through droplets of moisture sprayed from the nose and mouth. Some people only carry the bacteria. These carriers exhibit no symptoms themselves but spread the disease.

 Signs/Symptoms include:

• Sore throat.
• Strong breath odor.
• Pain in swallowing.
• Fever/chills.
• Posterior cervical lymphadenopathy (disease of the lymph nodes).
• Headache.
• Malaise.
• Red or swollen tonsils or pharynx (with or without fluid, cells, or cellular debris from blood vessels (exudates)).
• Increased white blood cells with bacterial pharyngitis.
• With bacterial pharyngitis (strep throat), the throat culture is positive.

ACUTE BRONCHITIS
Acute bronchitis is inflammation of the bronchial mucous membrane of the bronchial tree. Infection, dust, chemical agents, and/or allergies can cause bronchitis. When the bronchi are infected, the mucous membranes (linings) of the bronchi secrete mucus and pus cells (white blood cells that can attack infectious agents). The large outpouring of mucus partially obstructs the airways. Additionally, the irritated membranes may swell, further obstructing the airways.

Signs/Symptoms include:

• Chilliness.
• Malaise.
• Soreness and constriction behind the sternum-worse when patient coughs.
• Slight fever.
• Cough, at first dry and painful; later, green or yellowish sputum with pus cells.

PLEURITIS
Pleuritis is an inflammation of the pleural lining, a lining that covers the lungs and the chest cavity. The two surfaces of this lining are moist and allow the lungs to move smoothly over the chest wall when a person breathes. The surfaces of the lining become dry and rough and rub together when the pleura lining is inflamed. This condition, called pleurisy or pleuritis, is very painful and becomes more painful when the person breathes deeply or coughs. Most cases of pleuritis occur as complications of some other respiratory condition such as pneumonia, tuberculosis, or another infectious disease. The underlying disease must be treated in order to cure the pleuritis.

Signs/Symptoms: Pleuritis signs and symptoms include the following:

• Pain–varies from vague discomfort to sharp severe stabbing in the chest. The pain becomes worse when the person coughs or breathes deeply.
• Respirations–short, shallow, and rapid. Motion–limited on the affected side.
• Breath–diminished sound.
• Fever.
• Chills.
• Friction rub–usually heard only after 24 to 48 hours.

PNEUMONIA
Pneumonia is an acute infection of the alveoli spaces of the lungs. Causes of pneumonia include injury to the respiratory mucosa with pneumonia as a secondary infection, influenza, common colds, and bronchitis.

There are three types of pneumonia: bacterial; mycoplasmal (bacteria having no cell wall and bounded by a triple-layered membrane); viral. Bacterial pneumonia is further subdivided into these types: pneumococcal; staphylococcal; klebsiella (Friedlander’s bacillus); streptococcal; and influenza bacillus.

Signs/Symptoms include:

• Mild nasopharyngitis (inflammation of the nasopharynx)– several days before onset of the disease.
• Sudden onset of illness.
• Vomiting.
• Severe chest pain–in 70 percent of the cases.
• Productive cough–rusty sputum.
• Fever (103 – 106oF)/chills.
• Often acutely ill.
• Dyspnea (labored breathing) and cyanosis. Cyanosis in light-skinned individuals gives a bluish cast to skin, lips, and nail beds. In dark-skinned individuals or blacks, the discoloration is grey or grayish. The cause is not enough oxygen in the blood.
• Decreased movement on one side of the chest.
• Severe, shaking chill.
• Signs of consolidation (inflammatory solidification of the lung); dull to percussion; bronchial breath sounds; fine rales.

 Hyperventilation:
 Hyperventilation, a common response to phsychological stress, is a condition that develops as a result of an individual breathing too deeply and too rapidly. Blood pH (hydrogen ion) is raised above normal, and the body experiences alkalosis (a condition in which the blood pH is between 7.45 and 8.00). By breathing as rapidly as possible for three to five minutes, a person can bring on the signs and symptoms of hyperventilation deliberately.

 Hyperventilation Syndrome:
 Patients who are anxious and often feel fatigue, nervousness, and dizziness may suffer from hyperventilation syndrome. The individual may breathe rapidly, breathing out so much carbon dioxide that he becomes unconscious. Unconscious, he begins to breath normally again, the carbon dioxide level becomes normal, and he regains consciousness. When the patient becomes nervous and anxious again, he is likely to experience hyperventilation syndrome again.
The following signs/symptoms are characteristic of a hyperventilation syndrome attack:

• Nervousness.
• Tachypnea–rate of breathing is excessively high (for adults over 25 respirations/per minute).
• “Unable to catch breath.”
• Dizziness.
• Tingling or numbness around mouth or in hands and feet.
• Carpopedal spasm–spasm of muscles in the carpus (the joint between the hand and the wrist and/or spasm of muscles in the foot).

Tuberculosis
Tuberculosis is a chronic disease caused by the bacteria Mycobacterium tuberculosis. The initial disease may not be noticed, but eventually the infection may spread to various parts of the body–tuberculosis of the bones and joints; intestinal tuberculosis; urinary tract tuberculosis. The incidence of tuberculosis is less today than in the past. In the United States Army in World War II, the number of tuberculosis cases was 1 per 1,000 soldiers. By 1982, only 250,000 cases were reported in the United States. The decline in the number of cases can be attributed to three factors: education about causes of tuberculosis; better diet and nutritional information; and early diagnosis and treatment of tuberculosis cases.

Chronic Obstructive Pulmonary Disease
COPD is a term that refers to a group of lung diseases that can interfere with normal breathing. It is estimated that more than 16 million Americans suffer from COPD. It is the fourth leading cause of death in the US.

What are the different types of COPD?
The two most common conditions of COPD are chronic bronchitis and emphysema. Some physicians agree that asthma should be classified as a chronic obstructive pulmonary disease, while others do not.

Lung Cancer
Lung cancer is cancer that usually starts in the lining of the bronchi, but can also begin in other areas of the respiratory system, including the trachea, bronchioles, or alveoli. It is the leading cause of cancer death in both men and women. In 2007, 213,380 new cases of lung cancer are expected, according to the American Cancer Society.

Lung cancers are believed to develop over a period of many years.

Nearly all lung cancers are carcinomas, a cancer that begins in the lining or covering tissues of an organ. The tumor cells of each type of lung cancer grow and spread differently, and each type requires different treatment. More than 95 percent of lung cancers belong to the group called bronchogenic carcinoma.

Lung cancers are generally divided into two types:

1. Nonsmall cell lung cancer is more common than small cell lung cancer. The three main kinds of nonsmall cell lung cancer are named for the type of cells in the tumor:

• Squamous cell carcinoma also called epidermoid carcinoma, is the most common type of lung cancer in men. It often begins in the bronchi and usually does not spread as quickly as other types of lung cancer.

• Adenocarcinoma usually begins along the outer edges of the lungs and under the lining of the bronchi. It is the most common type of lung cancer in women and in people who have never smoked.

• Large cell carcinomas are a group of cancers with large, abnormal-looking cells. These tumors usually begin along the outer edges of the lungs.
• Small cell lung cancer sometimes called oat cell cancer because the cancer cells may look like oats when viewed under a microscope, grows rapidly and quickly spreads to other organs.