How Breathing In And Out Works Biology Essay

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"I bet you aren't breathing automatically now," is a common and effective joke that people play on each other. The person who hears this begins to think about the way they breathe and the statement becomes true. Breathing comes naturally to us; we don't normally have to think about it. The respiratory system is a vital part of our body that provides our cells with the oxygen required to live.

Simply put, the respiratory system consists of the organs and tissues that help us breathe. It includes the airways, lungs, blood vessels, and muscles. Airways consist of the nose, mouth, and the passages that lead into the lungs. The lungs consist of alveoli, which are important to the respiratory system. The blood vessels carry the oxygen to the different tissues that need it. Muscles in the respiratory system enable us to breathe.

A person breathes through both their nose and their mouth, although the nose serves as the respiratory opening. There is lots of blood flow to and from the nose, which keeps the air we inspire warm. The inner lining of the nose is made of nasal mucosa. The mucous produced at the back of the nose helps keep the air moist and prevents the nose from drying out.

The sinuses, which are pockets in the skull that contain air, are located behind and slightly above the nasal cavity. They serve two purposes: to lighten our heads and to affect the sound of speech. If you plug your nose and try to talk, the air is forced to flow straight into your mouth; the sinuses then don't affect the sound of your speech and the voice sounds funny and plugged up.

Cilia, the tiny hairs that line all the airways except for the mouth, are very important to the respiratory system. Moving constantly, they are coated with a mucous


that traps dirt and dust particles and sweeps them up and away from the lungs. This process helps clean the air that is inhaled.

Diagram 1As can be seen in Diagram 1, the pharynx is divided into three sections: the nasopharynx, oropharynx, and laryngopharynx. Both the nasopharynx and the oropharynx are part of the respiratory system. The nasopharynx is directly behind the nasal cavity, while the oropharynx is directly behind the mouth.

Untitled diagram of the pharynxThe oropharynx has a smooth, hard surface and is part of both the respiratory and the digestive systems. It is commonly thought of as the back of the throat. Like the nasopharynx and the nasal cavity, the surface of the oropharynx is moist.

The laryngopharynx isn't really considered part of the respiratory system; it assists with speech because it contains the larynx, or voice box. The larynx is made up of two thin rows of skin-like material, referred to as vocal cords. Held apart for breathing, the cords stretch and come nearly closed for speaking. When the opening is smaller, the sound is higher-pitched, and when it's bigger the sound is lower. The vocal cords are longer and thicker in males, which is why men have deeper voices than women.

The next part of the respiratory system is the trachea, or windpipe. In adults the trachea is about 4 inches long and 0.5 to 0.75 inches wide (Parker, 1997, p. 16). This tube connects the larynx to the primary bronchi, which leads to the lungs. It lies in front


of the esophagus and is held open by C-shaped rings of cartilage. Cilia line the epithelium and sweep debris out of the lungs as air passes through.

The trachea splits into the two primary bronchi, with the right primary bronchus leading into the right lung and the left into the left lung. This paper will be following the path into the right lung, although it would be the same information for the left. Bronchi have the same structure as the trachea, but they are fully rounded. As they become smaller, their walls thin and the rings of cartilage disappear.

The right primary bronchus enters the right lung, where it branches into the secondary bronchi, and then into bronchioles. Bronchioles terminate in tiny air sacs called alveoli, which are covered with capillaries that connect to the pulmonary circuit of the cardiovascular system.

The lungs are cone-shaped and take up most of the thoracic cavity. They have a broad, concave bottom that fits with the convex diaphragm. All the other sides of the lungs follow the shape of the thoracic cavity. The purpose of the lungs is to deliver oxygen to the body, while removing carbon dioxide.

Untitled diagram of the pharynxThe right lung has three lobes, while the left has only two lobes. Scientists believe that this is to make room for the heart which is situated slightly to the left of the thoracic area. The lobes of the lung further divide into lobules. Every lobule has hundreds of bronchioles ending in hundreds of alveoli.

Alveoli are really what make up the lungs. They, along with the interstitial muscle, are the reason for the spongy texture of the lungs. In the alveoli, gas exchange occurs between the air in the lungs and the blood in the capillaries of the pulmonary circuit. The pulmonary circuit is the path of blood from the heart to the lungs and back.


Hemoglobin, a red blood cell pigment, picks up oxygen from the alveoli and becomes oxyhemoglobin. The reaction to form oxyhemoglobin is: Hb + O2 ƒ  HbO2 where Hb is deoxyhemoglobin (or hemoglobin), O2 is oxygen and HbO2 is oxyhemoglobin. This reaction is sped up by the carbonic amylase enzyme that is in red blood cells.

While the blood is picking up oxygen it is also depositing carbon dioxide. Carbon dioxide is carried by bicarbonate ions after leaving the tissues. As the carbon dioxide enters the lungs, the bicarbonate ions give up the carbon dioxide and become water. The reaction to separate carbon dioxide from the bicarbonate ions is: H+ + HCO3- ƒ  H2CO3 ƒ  H2O + CO2 where H+ is a hydrogen ion, HCO3- is a bicarbonate ion, H2O is water, and CO2 is carbon dioxide. This process is sped up by carbonic anhydrase, also found in the red blood cells.

Both these reactions are possible because carbon dioxide and oxygen are gasses, so both have pressure. As a rule, gas molecules move towards areas with less pressure. Because the blood coming to the lungs has lots of carbon dioxide, and the lungs have little carbon dioxide, the carbon dioxide in the blood wants to go to the lungs. This is why it naturally diffuses out of the blood into the alveoli sacs.

The lungs have lots of oxygen however. This means that, as with all gasses, the oxygen wants to leave. Blood arriving at the lungs has little or no oxygen. So, as with carbon dioxide, oxygen naturally diffuses out of the alveoli sacs and into the bloodstream. External respiratory is this gas exchange between the air in the lungs and the blood in the capillaries.

The ability of the hemoglobin to pick up oxygen is called the binding capacity. This is affected by several things, the first of which is the partial pressure, the amount of


pressure that can be exerted by each gas. Temperature is the second factor of the binding capacity. The lungs have a temperature of about 37° C, the tissues that the oxygen is carried to have a temperature of 38° C. PH is last factor. The lungs have a pH of 7.4, while the tissues have a pH of 7.38. These temperatures and pHs are ideal for the maximum binding capacity.

The blood carries the oxyhemoglobin to all the tissues that need it. Once it reaches the tissue, the oxygen diffuses into them. The reaction to break up oxyhemoglobin is: HbO2 ƒ  Hb + O2 where HbO2 is oxyhemoglobin, Hb is deoxyhemoglobin, and O2 is oxygen. As this is happening, the carbon dioxide is expelled from the cells and enters the bloodstream.

Bicarbonate ions are made according to this reaction: CO2 + H2O ƒ  H2CO3 ƒ  H+ + HCO3- where CO2 is carbon dioxide, H2O is water, H2CO3 is carbonic acid, H+ is a hydrogen ion, and HCO3- is a bicarbonate ion. The enzyme carbonic anhydrase makes this reaction possible. Carbaminohemoglobin is carried back to the heart by the blood. Blood is pumped out of the right ventricle and into the pulmonary circuit by the heart.

Various muscles make breathing possible. When a person breathes in, they mostly feel the muscles in their chest and diaphragm. In reality, it's the intercostal muscles (muscles between your ribs) and your diaphragm that do most of the work. Abdominal muscles and a few muscles around the collarbone are also used.

Breathing is controlled by four parts of the brain. Two of these parts are in the medulla oblongata, the control center of the brain, and two are in the Pons. The two in the medulla oblongata tell your body to inhale and exhale through the inspiratory and expiratory areas. They work together, with one fading out as the other becomes active.


As its name would suggest, the inspiratory center controls inhalation. It sends signals to the respiratory muscles to contract and also signals the expiratory center to be inactive. It lasts about two to three seconds and during those seconds several things happen. First of all, the diaphragm becomes shorter and flatter. This makes more room for the lungs to expand downward. Secondly, the intercostal muscles tighten. This brings the rib cage and sternum up and out. As these muscles work, the lungs expand and air rushes in.

The expiratory center does the opposite of the inspiratory center. It signals the respiratory muscles to relax. It also signals the inspiratory center to become inactive. It lasts about two to three seconds as well. During these seconds, the diaphragm widens and puffs up slightly. Both the ribs and sternum are brought down and into the chest by the intercostals muscles relaxing. All this makes the lungs shrink and the air is pushed out.

Respiratory rate is the amount of times a person breathes a complete breath, in and out, during one minute. According to Steve Parker, this varies slightly with the age of a person.

An adult at rest breathes in and out about 12 to 16 times each minute. This is called

respiratory rate.

A newborn at rest breathes in and out about 40 to 50 times each minute.

A ten-year-old child at rest breathes in and out about 20 times each minute (1997, p.


Resting respiratory rate is the respiratory rate when a person is relaxed and not doing anything. Respiratory rate also changes during exercise; this is controlled by the part of the brain called the Pons.


The Pons has two different areas that control breathing. The first of these is the apneustic area. Nerves located in the muscles and joints send signals to this part of the brain. When the nerves signal that there is lots of body movement, the apneustic area sends out signals to make inspiration stronger and expiration weaker. This is why we breathe harder during exercise. The pneumotaxic area of the Pons terminates the effects of the apneustic area. It slows the inspiration and strengthens the expiration. Eventually this gets the respiratory system back to normal breathing.

Sensors in the brain and arteries also help control the speed of our breathing. They detect the oxygen and carbon dioxide levels in the blood and send signals to the brain. If the oxygen levels are low, and carbon dioxide levels are high, the brain sends commands to speed up breathing. This way, our body takes in more oxygen and raises the oxygen levels of the blood. If the oxygen levels are high, and carbon dioxide levels are low, then the brain tells our body to slow down our breathing.

There are also sensors in our airways. These sensors detect dust and other irritants that are reaching the lungs. They then cause sneezing and coughing, which brings up the irritants and dust out of the lungs. Sensors located in the alveoli detect fluid in the lungs. They send signals to change the breathing so that it's quick and shallow.

As with any body system, problems can occur with the respiratory system. According to an online encyclopedia, Chronic Obstructive Pulmonary Disease (COPD) is a serious respiratory problem:

Worldwide, COPD ranked as sixth leading cause of death in 1990. It is projected to be

the fourth leading cause of death worldwide by 2030 due to an increase in smoking

rates and demographic changes in many countries. COPD is the 4th leading cause of

death in the U.S., and the economic burden of COPD in the U.S. in 2007 was $42.6


billion in health care costs and lost productivity (Anonymous, 2010, pp. 1 & 2).

COPD has symptoms including but not limited to: cough and sputum production, dyspnea, rhonchi, airflow limitation on pulmonary function testing, wheezing, tight chest, rapid breath rate, crackles or wheezing in the lungs, enlargement of chest, more time to exhale than inhale, active use of neck muscles to breathe, breathing through pursed lips, and barrel chest. Dypsnea, or shortness of breath, is the most common sign. Very severe cases of COPD can develop cor pulmonale, an enlargement of the right ventricle of the heart because the blood pressure in the lungs has risen. Severe cases may result in respiratory failure, which can be fatal.

Lifelong smokers will get COPD if another disease or disorder doesn't get them first. Long, heavy exposure to dust and chemicals can also cause COPD. Jobs such as coal and gold mining and cotton textile production involve heavy exposure to dust. Cadium, isocyanates, and the fumes from welding are sources for the chemicals that cause COPD.

Air pollution is yet another cause for COPD. This means that it's generally more common among people who live in the city than those who live in the country. COPD is also believed to be partly genetic, but it very rarely occurs in people under the age of forty. Autoimmune disease and bronchial hyper-responsiveness can also lead to COPD.

In order to diagnose COPD, a person first has to have their breathing tested through spirometry. A spirometer is a machine that measures the forced expiratory volume (FEV) in one second and the forced vital capacity (FVC) of one breath. Usually about 70% of the FVC exits the lungs during the FEV. If the FEV is lower than normal, that means the person has COPD; the lower the ration of FEV to FVC the more severe


the COPD. Severity also depends on the severity of dyspnea and the amount of exercise a person can endure.

In addition to a spirometer, a person with suspected COPD also has to undergo an X-ray to check for the classic signs of COPD. Signs that the doctor is looking for include hyperinflation of the lungs, a flattened diagram, larger airspace behind the sternum, and bullae (enlarged blood vessels). Blood samples may also be taken to check for high oxygen levels (hypoxemia) or high carbon dioxide levels (respiratory acidosis).

There is no cure for COPD - it gets worse over time and eventually leads to death. However it can be managed through healthy lifestyle choices. Quitting smoking is one of the first steps. Depending on whether there are chemical or dust causes, a change of work might be needed. Avoiding high pollution areas is also another good choice. Healthy nutrition choices can help; being overweight or underweight does affect COPD. If a person is thin, a high calorie diet can ease COPD.

There are also several medical options. In select cases surgery, such as a bullectomy, may be helpful for people suffering from COPD. The use of bronchodilators is another option. There are various medicines that, through an inhaler or nebulizer, can reduce the symptoms by relaxing the smooth muscle of the airways. Corticosteroids can also be helpful. Taken through a tablet or inhaler, they decrease the attacks that are associated with moderate or severe COPD. They work to reduce inflammation in the airways and lungs which, in theory at least, reduces the damage to the lungs and airways. However, corticosteroids are associated with pneumonia. Supplemental oxygen via a mask or nasal tubing can also improve the quality of life for people with COPD.

Asthma is another respiratory disease, and it affects the airways of the lungs. It is episodic so it can sometimes be mistaken for other respiratory ailments. Symptoms


include: wheezing, coughing, shortness of breath, the feeling of a tight chest, and just general resistance to breathing. These symptoms come in episodes called asthma attacks, which vary in severity and symptoms from person to person.

An asthma attack is generally brought on by a trigger. A trigger can be a number of things; again it depends on the person. I have asthma which is triggered by dust, scents, weather changes, exercise, and fire smoke. Other common triggers include food, pollen, allergies, dry air, humid air, and smoke. Sometimes asthma goes undiagnosed because the asthmatic believes they just have allergies.

During an asthma attack several things happen. First of all, the smooth muscle in the airways constricts. The opening is then narrowed even more by the airways swelling up. During the attack, the airways begin to secrete more mucous than usual and the already small opening narrows even further. As one might guess, this makes breathing difficult and in some cases impossible.

Picture 1Asthma is a chronic condition that normally develops between the ages of five and fifteen. The cause of asthma is not known, but environmental and genetic sources are thought to contribute to it. Diagnosing a person is usually done quickly. If there is a history of asthma in the family, the person has asthmatic symptoms, and they can't pass a peak flow meter test, then they have asthma. However, doctors may also use a spirometer to confirm the diagnosis.

Untitled picture of a diskusAfter diagnosis, the treatments are fairly simple. Usually the asthmatic is prescribed an inhaler, of which there are many different kinds. There is also the diskus, which can be seen in Picture two, which is generally used daily. Preventative pills that can be taken as well to


decrease the chance of an asthma attack occurring.

I have two inhalers between which I alternate. This is because I found that, after awhile, using just one type of inhaler makes it ineffective. I also have a diskus that I use in the mornings when my asthma seems to be very reactive that day. My asthma is actually the reason I chose to do my report on the respiratory system. I have never fully understood how it worked, and this paper gave me the chance to learn about it.

In conclusion, I think that learning about the respiratory system has helped me understand better what asthma is and appreciate more fully how my lungs work. The respiratory system is important, as is any other body system. Although people don't think about it, the way a person can breathe is amazing. The respiratory system is a vital part of the body and through it the cells receive the oxygen they need to live.