The Respiratory System.

Transcription

1 1 The Respiratory System. All living organisms respire and exchange gases with their environment. Although, not all organisms have to breath. If an organism is aerobic, it will require oxygen to survive. That organism may be unicellular or multicellular. The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood. Overview : Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale. The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs. Basic Functions of Respiratory System: It ensures that oxygen can enter a cell in an organism and that carbon dioxide can leave a cell. This entering and leaving of oxygen and carbon dioxide is often referred to as gas exchange. Requirements of a Respiratory System : There must be a large enough surface area for gas exchange to occur so that it can accommodate the organism s metabolic needs. Respiration must also take place in a moist environment (so as to allow for the dissolving of oxygen and carbon dioxide). The lungs provide an internal respiratory surface connected to the air by means of internal passageways. This may vary from species to species in terms of structures and their efficiency Three basic elements of the lungs are : i) one or two lungs with a moist respiratory surface ; ii) a means of bringing air in contact with the surface of the lungs ; iii) a circulatory system to carry gases between lungs and the other cells of the body. In mammals, respiration can be subdivided into the following processes: A) Breathing includes inspiration (the act of taking air into the lungs) and expiration (the act of breathing out).

2 2 B) External Respiration is the exchange of oxygen and carbon dioxide between air and the blood. C) Internal Respiration is the exchange of oxygen and carbon dioxide between blood and cells of the surrounding tissues. D) Cellular Respiration is the complex series of chemical reactions that take place in the mitochondria of cells. Parts of the Respiratory Tract and their functions : 1. Nasal Cavity (nose/nostrils) : The air first enters into the respiratory system. Capillaries are located here which warms incoming air in order to protect the lining of the lungs. They contain thin bones called turbinates that increase the surface area of the nasal chambers and secrete a mucus which moistens the air. 2. Pharynx (throat) : The pharynx is a section of the alimentary canal that connects the mouth and nasal cavity the larynx and esophagus. Air enters from the nasal passages (through the nasal cavity) and from the mouth into the pharynx which then leads to the larynx and the esophagus. 3. Glottis : The glottis is the opening of the trachea (the passageway that conducts air to the lungs). 4. Epiglottis : The epiglottis is the flap-like structure that protects the glottis by preventing the entry of food into the trachea. 5. Larynx (vocal cords) : The larynx is where air enters after leaving the pharynx and passing through the glottis. 6. Trachea (windpipe) : This is where air enters from the larynx. Support is given by semicircular cartilage rings which prevents the trachea from collapsing. NOTE: All structures listed so far are lined with ciliated cells that secrete mucus that trap particles and dust. 7. Bronchi (bronchus) : These are the two branches of the trachea; (found level with the armpit). One bronchus enters each lung. 8. Bronchioles : These are the finer tubes that the bronchi branch into; (located in each lung). 9. Alveoli (alveolus) : They are the grape-like clusters of moist tiny sacs found at the ends of bronchioles. They are the sites where gas exchange occurs.

3 3 10. Pleura : It is a double membrane which surrounds each lung. 11. Diaphragm : It is a muscle layer which assists in ventilation of the lungs; (ie.) inhalation and exhalation. Structures that aid in Human Respiration : 1. Cilia are hair-like structures that can trap bacteria, dust and other particles. It helps to remove mucus and trapped foreign material. 2. Mucus membranes secrete mucus which traps bacteria, dust and other particles. It also moistens the air. 3. Large surface area of alveoli helps to increase gas exchange. Mechanics of Breathing : Ventilation relies on the principle that air will flow from a region of higher pressure to a region of lower pressure. When we breathe, we use two muscular structures to control the air pressure inside our lungs: the intercostal muscles and the diaphragm. The intercostal muscles are those muscles associated with the ventral surface of the rib cage. The diaphragm is a muscular layer that separates the region of the lungs (thoracic cavity) from the region of the stomach and liver (abdominal cavity). INHALATION : During inhalation, air moves into the lungs; (the active phase of breathing).the external intercostal muscles and the diaphragm both contract. The intercostal muscles expand the rib cage. The diaphragm moves downward. The chest cavity becomes larger which decreases the air pressure and results in the expansion of the lungs. As a result of this expansion, air flows into the lungs due to a decrease in air pressure within the lungs. EXHALATION : During exhalation, air is forced out of the lungs; (the passive phase of breathing). The diaphragm relaxes and the external intercostal muscles relax. The internal intercostal muscles contract to help pull rib cage back to its original position. The chest cavity becomes smaller thus increasing the pressure. The lungs shrink and pressure increases within the lungs and air then flows out. Lung Capacity : Tidal volume is the volume of air inhaled and exhaled in a normal breathing movement. Inspiratory reserve volume is the additional volume of air that can be taken in beyond a regular (tidal) inhalation. Expiratory reserve volume is the additional volume of air that can be forced out of the lungs beyond the regular (tidal) exhalation.

4 4 Vital capacity is the total volume of gas that can be moved into or out of the lungs. Residual volume is the amount of gas that remains in the lungs and the passageways of the respiratory system even after a full exhalation. vital capacity = inspiratory + expiratory + tidal volume reserve volume reserve volume See the diagram in your text on p Disorders of the Respiratory System : 1. Lung cancer is the uncontrolled and invasive growth of abnormal cells in the lungs. The carcinoma, or malignant tumor grows and abnormal cells continue to multiply taking over normal tissue. death is not usually caused by difficulty in breathing but when the cancer moves out of the lungs. Most cases are a result of smoking due to carcinogens (cancer causing agents) found in tobacco. It can also be caused by exposure to radon, a radioactive element. The symptoms include the following : chronic cough, coughing up blood, weight loss and loss of appetite, shortness of breath, chest pain, and fever without known cause. Treatments may include surgery, chemotherapy, and radiation therapy. 2. Pneumonia is a disease of the lungs that causes the alveoli in the lungs in inflame and fill with liquids. It impairs their ability to take in oxygen so body cells become oxygen starved. There are two main types : lobar pneumonia and bronchial pneumonia. Pneumonia may be caused by bacteria, viruses, fungi, and some chemicals. 3. Asthma is a chronic obstructive lung disease that can develop at any age. It is characterized by extreme sensitivity of the lungs to certain triggers that cause the airways to become obstructed. The effects can vary from mild to very severe. It usually occurs in episodes or attacks that cause these three changes to the lungs to occur: the airway swells, the bronchial muscles tighten, and there is an increase in the amount of mucus secreted into the airways. This condition can be managed with the use of anti-inflammatory medications or bronchodilators. 4. Chronic bronchitis is an obstructive respiratory disorder in which the airways are inflamed and become filled with mucus. It is very common for a cough to bring up the mucus which can lead to infection occurring. It is most commonly found in smokers.

5 5 5. Emphysema is a chronic and incurable disease in which the alveoli become distended and their walls become damaged. This reduces the surface area for gas exchange to occur, and less oxygen is available for the brain and tissues. The elasticity of the lungs is also reduced thereby decreasing the force behind exhaling. The best treatment is to reduce or eliminate smoking, to exercise, use of oxygen supplements, and some drugs. Impact of Environmental Factors on Asthma : Besides the gases we need to survive, the air we breathe contains many different particles. For people with asthma, these particles can cause and allergic reaction that triggers an asthma attack. Common particles found in air: i) spores from mildew or mould.; dust and pets; ii) many types of food can also trigger asthma attacks; iii) ozone, nitrogen dioxide, sulfur dioxide, and vehicle emissions; iv) odours from perfumes, room deodorizers, paints, petrochemical fumes, and baby talcum powders contain many airborne particles