- Describe how the act of breathing is controlled
- Explain the body's response to high altitudes
- Describe how environmental hazards can affect respiration
Altitude sickness or hypoxia can occur at high altitudes. Symptoms include lack of energy and shortness of breath, headaches, nausea. Remaining at that altitude for two weeks or more allows the body to adapt somewhat.
At high elvevations air pressure is lower and the air is "thinner" than at sea level, which means that although oxygen and other gases are present in the air in the same proportions as at lower elevations there is less air in total, therefore there is less oxygen available for respiration. When an individual accustomed to living at lower elevations first arrives at a higher altitude the body cannot extract enough oxygen from the air to meet its metabolic needs and the result is altitude sickness. The body responds to the new environment with adjustments to the respiratory and circulatory systems. The first response to hypoxia is an increased breathing rate which helps to bring more oxygen in contact with the alveoli. For a period of about two weeks the body also produces more and more red blood cells. Eventually the body is able to take up enough oxygen from the air to carry on normal respiration. After a return to a lower altitude these extra blood cells can allow for exceptional physical endurance. Within a few weeks the red blood count drops back to its normal level. While these adaptations are temporary populations that live at higher altitudes tend to have more alveoli and lung capillaries than people at lower altitudes.
The Control of BreathingEdit
Since muscles need oxygen an increase in activity will lead to increased breathing rate. However a person breathes at the same rate from a tank of oxygen as they do from normal air, so it is the presence of carbon dioxide and not the amount of oxygen that triggers this increase. After the exchange of gases has taken place any carbon dioxide still present in the blood is carried to the heart and up to the lower portion of the brain called the medulla oblongata. When the concentration in the blood exceeds a certain level the medulla oblongata sends nerve impulses to initiate faster movement of the muscles of the rib cage and diaphragm. Under normal conditions the nerve impulses from the medulla oblongata fire regularly resulting in rythmic breathing. The concentration of oxygen does play a small role in control of breathing rate; some of the blood vessels including the aorta and carotid contain chemoreceptors that respond to oxygen pressure in the blood. When the oxygen content in blood drops below a certain level these chemoreceptors send signals to the medulla oblongata causing it to increase the breathing rate. The volume of air breathed in also plays a role in controlling breathing rate; inhaling more deeply than usual causes the lungs and alveoli to stretch causing stretch receptors in the walls of the alveoli to fire impulses that travel to the medulla oblongata which sends a signal to the respiratory muscles to stop the inhalation.
In up to 10% of drowning cases the victim suffers a laryngospasm, or reflex closing of the larynx. In these cases death actually occurs from asphyxiation rather than water entering the lungs. In other cases it depends whether drowning occurs in fresh or salt water. Fresh water washes away the lipoprotein lubricating film that coats the alveoli causing the alveoli to collapse and ending gas exchange. In salt water the concentration gradient means that fluid is drawn out of the capillaries and into the lungs which prevents oxygen from reaching the walls of the alveoli.
Carbon Monoxide PoisoningEdit
Carbon monoxide is an invisible, colourless, odourless, tasteless gas released during the combustion of organic materials. Carbon monoxide is toxic because it binds to the oxygen receptors in red blood cells about 200 times more tightly than oxygen does. Once inhaled, carbon monoxide is quickly absorbed into the bloodstream and prevents the blood from transporting oxygen to the cells of the body. Early symptoms of carbon monoxide poisoning are similar to those of hypoxia: headaches, weakness, dizziness, and nausea. If the victim is not treated promptly permanent damage to the internal organs and the nervous system is likely, followed by coma and death. Treatment usually involves administering pure oxygen but recorvery can be slow because the blood only gradually relinquishes carbon monoxide. Victims of carbon monoxide poisoning can suffocate even though they can breathe because the carbon monoxide blocks oxygen from binding to the receptors in blood. A concentration of as little as 0.002% of CO can be harmful if exposure is maintained for a few hours.
As smoke is drawn into the trachea it temporarily paralyses the cilia and prevents them from sweeping foreign particles out of the passages of the respiratory system. A single drag on a cigarette will slow the action of the cilia while more regular exposure can completely destroy them. Even light smokers have a greater tendency to cough and snore partly as a result of the damage to cilia in the trachea and nasal passages. Since the cigarette contains burning organic matter it releases carbon monoxide. The concentration in cigarette smoke is about 50 000 ppm (over 1000 times greater than the amount known to be harmful). A steady smoker constantly suffers from a mild level of carbon monoxide poisoning. More than 40 of the over 4000 chemicals in cigarette smoke cause cancer. The particles in cigarette smoke become lodged in the fine passageways of the respiratory system interfering with the passage of air and oxygen exchange. People who smoke a pack of cigarettes a day will absorb about 250 mL of tar into their lungs a year. This tar coats the lungs with a sticky , sooty material and is a key cause of lung cancer. Tar can also cause the alveoli to become brittle, leading to a respiratory disorder known as emphysema, where the lungs lose their elasticity, making inhalation and exhalation very difficult.
Indoors may result from use of chemical cleaners and particular construction materials; outdoors the emissions from cars and industrial processes are a key contributor. Airborne pollutants include molecules such as carbon monoxide, nitrogen oxides, chlorine, and methane, as well as small particles of dust and other compounds. These materials can contribute to a number of respiratory problems including asthma (bronchial tubes suddenly constrict making breathing difficult). Children have a higher respiratory rate than adults due to developing lungs and are more susceptible to problems. In urban area the combination of pollutants, heat, and sunlight often produces smog, a characteristic brownish haze. The chemicals in smog have effects similar to cigarette smoke, making the lungs less elastic and more vulnerable to disease. Smog tends to be worse on hot summer days and its concentration will be highest late in the day. For this reason even people with no history of respiratory problems should avoid strenuous outdoor activity during the late afternoon and those who already suffer from asthma of other respiratory problems may have to avoid going outdoors altogether.