Which Of The Following Statements About The Pleurae Is Not True?
The pleura are two membranes that cover the lungs. One membrane called visceral pleura covers the lungs while the other called parietal pleura covers the chest wall. Both these membranes have their own functions. For instance, the visceral pleura is thick with tiny pores through which oxygen enters into the pulmonary circulation. On the other hand, the parietal pleura is thin and smooth; it creates space between the chest wall and the lung. This membrane also prevents air from entering into the chest cavity.
Both these membranes play important roles in maintaining normal breathing. However, there are several myths about them. Let’s look at some of the most common ones.
1. Parietal and visceral pleuras are connected together by ligaments.
This myth is not true because both the pleural membranes are separated by intercostal muscles. Therefore, they cannot be joined together as ligaments do.
2. There are no holes or fissures on either membrane.
As mentioned earlier, the pleura has small pores through which oxygen enters into the pulmonary circulation. These pores exist only on the visceral membrane. Thus, this myth is not correct. But what does happen when someone lies down on his/her back for long time? If you observe closely then you will notice small dots all over your body especially on the abdomen. These dots are due to increased pressure. When we lie down flat on our backs, the diaphragm gets pushed against the chest wall, compressing the lungs. And this causes the fluid inside the chest cavity to accumulate around the lungs. This accumulation increases the intrathoracic pressure, causing the veins in the lower lobe of the left side of the lung to collapse. As a result, the veins swell up and form saccular dilations called bullae. These dilated veins cause problems like shortness of breath, cough, chest pain, and impaired ability to exercise. In addition, during sleep, a person may develop infections within the chest cavity.
3. It is possible to feel the beating heart under the rib cage.
A lot of people think that if you can feel the heartbeat under the ribs then you must be able to hear it too. But this is false. Underneath each rib there exists a pleura. A pleura acts as an insulator separating the internal organs from the bones. So, feeling any part of the body underneath the ribcage means you are touching the bone above it. But you cannot feel the beating heart underneath the ribcage because its location is just beneath the sternum – the very top part of the breastbone.
4. You should never try to clear mucus from your chest cavity.
Mucus plays an important role in keeping your respiratory system clean. But sometimes, excessive amounts of mucus build up in the chest cavity and make it difficult to breathe properly. Mucus helps protect us from bacteria and viruses. Its main function is to trap pathogens so that they don’t enter into the bloodstream and affect the rest of the body. However, if the chest cavity becomes filled with excess amount of mucus, it obstructs proper movement of the airways and leads to infection. Also, you shouldn’t expectorate mucus as it may spread disease.
5. People who suffer from emphysema have lost their capacity to produce more mucus.
Excess production of mucus is one of the symptoms of chronic bronchitis. Chronic bronchitis occurs when the cilia lining your airway become damaged with cigarette smoking or inhaling environmental pollutants such as dust particles. Cilia help remove foreign substances from the airway and move them towards throat where they get swallowed. Damage to cilia results in reduced effectiveness of mucociliary clearance. As a result, the mucus builds up in the trachea and traps pathogens making it impossible to breath.
6. Lung cancer develops in the outer layers of the lung.
Lung cancers generally develop within the cells of the innermost layer of the lungs known as alveoli. Cells in the alveolar walls can divide uncontrollably and grow rapidly forming malignant tumors. Most cases of lung cancer occur in the parts of the lung covered by the parietal pleura and therefore termed as thoracic cancers.
7. Cancer patients should avoid sleeping flat on their backs.
Sleeping flat on your back puts extra strain on the diaphragm. During deep sleep, the diaphragm contracts forcefully moving downwards. Since the bottom portion of the diaphragm is attached to the base of the liver, it pulls upwards. As a result, the liver moves upward thus putting additional stress on the stomach acid-secreting organ. Sleep apnea or snoring often occur in people with weak sphincters controlling the flow of saliva and gastric juices. Patients with poor control of these sphincters tend to regurgitate food into their mouths while sleeping. Regurgitated food mixes with gastric fluids creating highly acidic environment. Acidic environment damages the tissues surrounding the esophagus and stomach thereby increasing risk of developing precancerous lesions and ulcers.
8. Excessive exposure to tobacco smoke could lead to emphysema.
Smoking cigarettes actually reduces the volume of oxygen passing across the lungs. Smoking is responsible for damage to the elastic fibers in the lungs causing loss of elasticity. Reduced elasticity of the lungs leads to increase in the size of the residual spaces in the lungs. These enlarged spaces allow carbon dioxide to mix with oxygen resulting in formation of toxic free radicals. Free radicals contribute to the development of emphysema.
9. Emphysema affects mostly smokers.
Emphysema is caused by aging process rather than smoking habit. Smoking doesn’t directly contribute to the development of emphysema but simply accelerates the natural degenerative changes occurring in the lungs with age. Aging process itself contributes to progressive loss of elastic tissue in the lungs leading to emphysema.
10. Chest pain is always cardiac related.
Chest pain could be due to many different reasons. Some of the major causes are coronary artery diseases, angina pectoris, arrhythmia, asthma attacks, pneumonia, tuberculosis etc. Chest pain associated with coronary artery diseases usually radiates to the shoulders, neck and jaw. Pain associated with angina pectoris usually starts below the breasts and radiates to the neck, upper arm, shoulder and back. Arrhythmias are often accompanied by severe tightness in the chest. Other conditions such as asthma attack and pneumonia typically cause sharp stabbing pain in the chest. Tuberculosis commonly presents with dull ache in the middle of the chest and spreading towards the back.
11. Pneumonia is a condition affecting the entire lung.
Pneumonia is characterized by inflammation of the lung tissues. Inflammation of the lung tissues makes it easier for bacteria, virus, fungi, and parasites to multiply and invade the air sacs. Bacteria and fungus release toxins which irritate neighboring tissues and create inflammatory reaction. Infection spreads throughout the lungs and causes fever, chills, coughing, and difficulty in breathing.
12. Pneumothorax is a rare medical emergency.
It happens when air leaks out of the lung into the chest cavity creating a vacuum effect within the chest cavity. As a result, the patient feels sudden tightness in the chest followed by suffocating sensation. Pneumothorax is treated by inserting needle through the chest wall into the underlying lung and sucking the air trapped in the chest cavity. Sometimes, the air leak might go unnoticed until it progresses to pneumoperitoneum i.e., air leakage into peritoneal cavity causing bloating and discomfort.
13. Pneumomediastinum is another medical emergency.
Air collects in the mediastinal region between the two layers of the airway, namely, the parietal and visceral pleura. Air collecting in the mediastinal region blocks the passage of airwaves along the windpipe causing obstruction of airway. Eventually, airways are blocked completely and suddenly rupture causing life threatening condition known as tension pneumothorax. Tension pneumothorax requires immediate treatment with insertion of a tube through the mouth and nose and placing it outside the airway to relieve airway pressure.
14. Nausea and vomiting are signs of severe illness.
Nausea and vomiting are symptoms which indicate presence of serious illnesses. They are rarely seen in healthy individuals. Vomiting is caused by irritation of gastrointestinal tract. Gastrointestinal tract contains millions of specialized nerve endings that detect chemical signals produced by various chemicals present in the gastrointestinal tract. Any change in the concentration level of these chemicals stimulates vomiting reflex. Nausea is caused by malfunctioning of the same mechanism that triggers nausea. Severe nausea is treated with antiemetics, drugs used to prevent nausea.
15. Fever is a sign of infection.
Fever is caused by immune response to bacterial infection. Fever protects body from invading organisms. Fever is measured using thermometer. Normal temperature is considered 99 degrees Fahrenheit. Temperature higher than 100 degrees F is called hyperthermia. Hyperthermia is treatable with antipyretics, drugs designed to reduce fever.
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