• What Is The Respiratory System?
|What Is The Respiratory System?
It is the body's breathing equipment. The respiratory system consists of the nose, lungs, diaphragm and the air passages, such as the trachea, which connect them. Similar to the digestive system, it takes substances from outside the body (gases, particularly oxygen), circulates them through the body to cells and tissues, then dumps (excretes) the excess and waste. Oxygen is the respiratory system's 'food' and carbon dioxide is its 'waste'. Breathing is probably the most important and fundamental action of the human body: if we stop breathing for more than a couple of minutes we die.
|HOW OXYGEN ENTERS THE BODY
The Passage of Air From Nose To Lungs
|What Is Breathing?
Breathing is the inhalation and exhalation of air and the gases it contains.
How Do We Breathe?
We breathe through the nose and the system of passageways and organs with which it connects. The nose is the only organ of respiration that we can see. The following section explains the structure and function of the organs of the respiratory system.
What Is The Nose?
The nose is an organ on the face. It acts as the first passageway for air entering the body.
Once air has been filtered, moistened and warmed in the nose it travels to the pharynx, a tube which leads from the back of the nose and mouth and divides into the esophagus (posteriorly) and larynx (anteriorly). It works as part of both the digestive and respiratory systems.
From the pharynx, air travels down to the larynx (also known as the voice box).
From the larynx, air travels to the trachea.
The bronchi are the branches of the respiratory tube which transport air in and out of each lung.
Structure: Bronchi (singular: bronchus) connect the trachea to the lungs. There are 2 of them, one on the left and one on the right which enter the lungs at the hilum, where they subdivide into different branches for different lobes of the lungs. Like the trachea, they are made of hyaline cartilage, involuntary muscle and connective tissue and are lined with ciliated (hairy) epithelium.
Function: To pass air from the trachea into the bronchioles, and thus to the lungs.
The two lungs are the centre of the respiratory system. It is in these two spongy organs that gases enter and exit the blood.
Structure: The lungs are positioned on either side of the heart. The left lung is divided into 2 lobes, the superior and inferior lobes, whereas the right lung is divided into 3, the superior, middle and inferior. Lobes are subdivided into lobules. The tissue of the lungs is made of bronchioles, alveoli, blood vessels, nerves, connective tissue and elastic tissue. They are covered with the pleura, a special membrane.
Function: Lungs allow the exchange of gases into and out of the blood.
|HOW BREATHING WORKS
Internal and External Respiration
|Mechanism Of Respiration
Although all of these separate tubes and passageways have individual functions, it is their function as a whole that is important i.e. to allow us, and every cell in our body, to breathe. The entrance and exit of air in and out of the body is a process known as breathing, whereas the entrance and exit of oxygen and carbon dioxide in and out of cells is known as gaseous exchange.
What Is External Respiration?
External respiration is the breathing in and out of air, and the diffusion of oxygen from the alveoli into the blood and carbon dioxide from the blood to the alveoli. In order to understand how the gases pass from one tissue to the next it is important to know the following physical law:
Diffusion occurs when a strong concentration of a gas comes into contact with a weak concentration of the same gas. The dissolved gas molecules will move from the strong concentration to the weak concentration until the concentration is equal on both sides. In the case of oxygen and carbon dioxide this occurs through the capillary and alveoli walls. The oxygen in the alveoli is under more pressure than the venous, deoxygenated blood in the capillaries so the oxygen passes from the alveoli (high pressure) into the capillaries (low pressure). Once the pressure in both is the same, the exchange stops. The carbon dioxide in the blood is under more pressure than the carbon dioxide in the alveoli so it diffuses through the capillary walls to the alveoli. The blood is thus oxygenated and its waste removed and it now travels back to the heart ready to be pumped round the body. The lungs then expel the carbon dioxide through the process of exhalation.
What Is Internal Respiration?
Internal respiration is the diffusion of oxygen from the blood to the body cells, and of carbon dioxide from the body cells to the blood. Once blood has been oxygenated in the lungs it travels back to the heart and is then pumped round the body. When blood reaches the various cells of the body, oxygen is again transferred by diffusion: the pressure of the oxygen in the blood is high whereas the pressure of the oxygen in the cells is low, so the oxygen passes into the cells. The amount of oxygen delivered depends on how busy the cell is. For example, more oxygen will be delivered to a muscle cell when it is exercising than when it is resting. The blood delivers its oxygen and collects the carbon dioxide (pressure in the blood is lower than in the cells so the carbon dioxide passes into the blood), carrying it back to the lungs where it will be delivered to the alveoli and then exhaled.
How Does Blood Travel To And From The Lungs?
It travels via the pulmonary circulation system, which is the movement of blood from the heart to the lungs and back again.
How Does Air Get Into The Body In The First Place?
Through the same gaseous pressure principle. Air enters the respiratory system (this is known as inspiration or inhalation) when the pressure is lower inside the lungs and leaves the lungs when the pressure in the atmosphere around the body is lower (known as expiration or exhalation). But it is the action of the muscles involved in respiration that make these changes in pressure, and the movement of air, happen. The main muscle involved in the mechanics of respiration is the diaphragm which is helped by the intercostal muscles (positioned between the ribs).
|What Is The Diaphragm?
The diaphragm is a large muscle. It is positioned between the chest and abdomen and separates them from each other.
What Are The Intercostal Muscles?
They are the muscles between the ribs. These muscles aid the diaphragm in respiration. During inspiration the external intercostal muscles contract at the same time as the diaphragm, lifting the rib cage up and outwards. The flattened and lowered diaphragm and the raised ribs cause an increase in the size of the chest cavity. During expiration, the external intercostals relax allowing the ribs to fall down and inwards, helping to decrease the size of the chest cavity. Nerve impulses delivered by the intercostal nerves tell the muscles when to contract and relax.
|How Does The Body Know When To Breathe?
Nerve cells called chemoreceptors, found in the aorta and carotid arteries (the arteries close to the heart) send impulses to the respiratory centre in the medulla oblongata of the brain with messages about the low levels of oxygen and high levels of carbon dioxide. When the level of carbon dioxide is too high and the level of oxygen too low a nerve impulse is sent to the diaphragm telling it to contract, thus causing inhalation. This is especially important during exercise and illness.
The Brain's Role In Breathing
Two centers of the brain are involved -the respiratory centre in the medulla oblongata and the pons Varolii:
Note: It is important to remember that breathing is not an intermittent process! The body does not stop breathing when the correct levels of oxygen and carbon dioxide are established, although breathing slows down and speeds up depending on our level of activity and health. Cells and tissues need to breathe all the time because every bodily function and movement requires oxygen and produces carbon dioxide. Breathing is a necessary and (in a healthy person) automatic function which continues throughout life.
Air that comes into the body contains approximately 21 percent oxygen and 0.04 percent carbon dioxide whereas air that leaves the body contains approximately 15 percent oxygen and 4 percent carbon dioxide. Thus, the air we exhale contains 100 times more carbon dioxide and 6 percent less oxygen than the air we inhale.
|Diseases And Disorders Of The Respiratory System
Chronic Obstructive Airways Disease (COPD)
Severe Acute Respiratory Syndrome (SARS)
The respiratory system links to:
Diagrams and Other Systems
Female Body: Diagrams of the different organs.
| Other Useful Guides
Recommended health screenings for women: Tests for all ages.
Back To Homepage: Womens Health Advice