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The Respiratory System

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When you think of respiration you probably think of breathing.  The two processes are not the same.  Breathing involves getting air in and out of your body---inhalation and exhalation.  Respiration involves getting the oxygen that you breathe in along with the other gases present in our atmosphere to the cells of your body and getting the carbon dioxide (a waste product of cellular metabolism) out of your body.

The body parts of the respiratory are few compared to other systems.  The nose, the breathing tubes, and the lungs are the only organs that you use to respire. Once the oxygen is taken up by the blood, it travels via the circulatory system to get to your cells.

Nose and nasal cavity

Two nostrils supported by bone and cartilage allow air to enter and leave the body. The nostrils lead to the nasal cavity, a hollow space divided into right and left portions and separated by the nasal septum.  Internal hairs filter some pollutants from the air as it passes.  Membranes secrete mucous which traps dust and small particles. Blood vessels heat the air which adjusts the air’s temperature to that of the body. 

As the mucus and trapped particles move on toward the pharynx, the mucous is swallowed and acids in stomach fluids kill bacteria that may have been in the air.

Paranasal sinuses

These air-filled spaces are housed in the maxillary, frontal, ethmoid and sphenoid bones of the skull and open into the nasal cavity.  These sinuses affect the sound of the voice.

Pharynx

The pharynx or throat is the passageway for food traveling from the mouth to the esophagus and for air passing to the larynx.

Larynx

The larynx contains the vocal cords and conducts air in and out of the trachea (windpipe). As air is forced through and between the vocal cords, they vibrate which generates sounds waves. Contracting or relaxing the muscles that change the tension of the elastic cords changes the pitch, or tone, of the sound produced. The more tension, the higher the pitch; the less tension, the lower the pitch. Pitch is also affected by the thickness of the cords. Loudness (intensity) of the sounds is produced by the force of air that passes over the cords.

An opening between the cords called the glottis leads to the trachea.  Swallowing causes the muscles within the cords close off the glottis and a flaplike structure called the epiglottis presses downward to cover the opening.  In this way, food and liquids are prevented from entering the trachea.

Trachea

The trachea (windpipe) is a tube approximately 2.3 cm in diameter and 12.5 cm in length.  It extends downward in front of the esophagus and splits into the right and left bronchii.

Bronchii

The right and left bronchi lead to the right and left lungs, respectively.  The primary bronchii continue to branch into smaller and smaller tubes until they end in groups of microscopic air sacs called alveoli.

When you think of respiration you probably think of breathing.  The two processes are not the same.  Breathing involves getting air in and out of your body---inhalation and exhalation.  Respiration involves getting the oxygen that you breathe in along with the other gases present in our atmosphere to the cells of your body and getting the carbon dioxide (a waste product of cellular metabolism) out of your body.

Lungs

Healthy lung tissue is soft and spongy.  The right and left lungs are located in the thoracic cavity and are enclosed by the rib cage and the diaphragm.  The right lung is larger than the left lung; the right lung is divided into three lobes and the left is divided into two.  A major branch of the bronchial tubes supplies each lobe with air. Lobes also have connective, lymph, and nerve tissue and an ample blood supply. 

Alveoli

In the alveoli inhaled oxygen diffuses through the capillary walls and into the blood.  Carbon dioxide diffuses from the blood and enters the alveoli to complete the breathing process and be exhaled.

An adult lung has approximately 300 million alveoli providing a tremendous amount of surface area.

How We Breathe

If you ask most students how we breathe, most would probably say we breathe with our lungs.  Our lungs, however, have little to do with the breathing process.  Respiration involves the delivery of oxygen to our cells and the removal of carbon dioxide from the cells.  Breathing is getting the air into (inhalation) and out of (exhalation) the body. Differences in air pressure allow us to breathe. 

When the diaphragm contracts and moves downward, air pressure inside the lungs decreases and air from outside the body is forced inside.  At the same time, intercostal muscles between the ribs contact, the ribs move up and the thoracic cavity enlarges.  This decreases the pressure inside the lungs even more and more air is forced inside the airways.

If a person has to take an even deeper breath, additional muscles, such as the pectoralis minors and the sternocleidomastoids, further enlarge the thoracic cavity and further decrease internal air pressure.

The diaphragm and muscles relax after contraction and the lungs and abdominal organs spring back into their original positions.  Air is forced out through the passageways and out of the body.  Normal exhalation is a passive process. 

If a person needs to exhale more air than normal, internal intercostal muscles are stimulated to pull the ribs and sternum downward.  This increases the pressure in the lungs.  Additionally, muscles of the abdominal wall, such as the external and internal obliques, the transversus abdominus, and the rectus abdominus, squeeze even more air out out of the lungs. 

One inspiration and one expiration is called a respiratory cycle. The volume of air that enters or leaves during a respiratory cycle is called a tidal volume.

Even after the most forceful exhalation, about 1,200 ml of air remain in the lungs.  This is called the residual volume.  Residual air remains in the lungs at all times.

Note:  Groups of neurons in the pons and medulla oblongata in the brain control respiratory function.

Check for understanding

1. What is respiration?

 

 

 

 

2. What are the functions of the mucous membranes that line the nasal cavity?

 

 

 

 

3. How do the vocal cords produce sounds?

 

 

 

 

 

4. Explain how gases are exchanged in the alveoli.

 

 

 

 

 

5. Describe how we breathe.

 

 

 

 

 

 

 

6. Residual air remains in the lungs at all times and therefore, newly inhaled air mixes with air already in the lungs.  How is this beneficial?

 

 

 

 

 

7. Why doesn’t it hurt your little brother if he tries to hold his breath during a temper tantrum?

 

 

 

 

8.  Label the diagram of the respiratory system.







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