Understanding Respiratory Systems

Oxygen-Carbon Dioxide Transit System

An understanding of respiratory systems helps you to understand what keeps you breathing. In the human sciences, breathing is known as “respiration, which is defined as the transport of oxygen from the outside air to cells within tissues, and the transport of carbon dioxide in the opposite direction, specifically by breathing through lungs.

There is also a biochemical class of respiration, cellular respiration, the basis for cell changes by which a living body obtains its energy. This process of reacting oxygen with glucose to yield water, carbon dioxide and a substance known as ATP (abbreviation for Adenosine Triphosphate) carries chemical energy to within the cells, enabling molecular changes necessary for survival. 

To put both another way, body breathing (in and out) sustains cellular-level gas exchanges in animals. What occurs inside individual cells, and the respirations that regulate exchanges between the organism as a whole and the environment around it, sustains life.


Respiratory Systems Structures Vary

Inhalation supplies the body with oxygen through the lungs, and exhalation expels carbon dioxide from the lungs. This process is called breathing or ventilation.

Blow out a candle sometime. Carbon dioxide blew out the flame, not oxygen. Oxygen is one of the primary ingredients that permit fire.

Human respiratory systems include trachea, bronchi, bronchioles, lungs, and a diaphragm, with a supportive cast of muscles and related body parts.

Molecules of oxygen and carbon dioxide pass between the gaseous external environment and the blood in an exchange process that occurs in air sacs (alveoli) within human lungs. In contrast, fish and many invertebrates, ventilate through gills.

Insects have even more simple respiratory systems; amphibian skin plays a vital role in the life-giving exchange of the gases; and holes on the undersides of leaves enable an opposite exchange to that of animals: carbon dioxide in and oxygen out. 


Human Respiratory System Function

Brain stem parts — the autonomic nervous system’s respiration regulatory center — coordinate respiratory movement. Breathing rate increases when carbon dioxide is more present in the blood. Exercise stimulates motor impulses originating from the brain and can increase the rate with increased inflation in the lungs.



Diaphragm contraction, supported by external muscles, initiates inhalation. 10 to 18 breaths per minute, with a time period of two seconds, are normal resting respirations. 

Under normal conditions, the diaphragm is the primary driver of inhalation. The diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward, resulting in a larger air-volume capacity and a negative pressure (compared to outside air). The pressure fall in the chest moves air into a conducting zone where it is filtered, warmed, and humidified on its way to the lungs.

Accessory neck muscles support vigorous inhalations exceeding 35 breaths per minute, or when approaching respiratory failure. During forced inhalation, such as a deep breath, these muscles further expand the air cavity, and further contract the diaphragm.



Exhalation is generally passive, but certain internal and abdominal muscles can impel active (forced) air exhalations, as when blowing out a candle on a birthday cake.

Natural lung elasticity, recoiling from the stretch of inhalation, flows air outward until chest and atmospheric pressures balance.


Gas Exchange Function

A respiratory system regulates the ongoing gas exchange between the external environment and an organism’s circulatory system. In humans and other mammals, blood oxygen increases as carbon dioxide and other gaseous wastes leave the circulation.

This whole mechanism of gas exchange is carried by the simple phenomenon of pressure difference. When air pressure is high inside the lungs, air from the lungs flows out. When the air pressure is low inside, air flows into the lungs.


Other Functions

As with other human systems, this one provides cells which secrete a variety of molecules that can come to the defense of the lungs. The cells also contain mucous membranes which produce disease-fighting white blood cells.

Beyond gas exchange, lungs manufacture substances for local use, and to break down clots in the pulmonary vessels. They release materials which enter parts of the arterial bloodstream via the pulmonary artery and remove waste substances from the veins. 

Gas moving through the larynx, pharynx and mouth allows humans to speak. Vibrations of air flow across the human larynx (vocal cords) results in sound. Because of this, gas movement (respiration) is vital for vocal communication purposes.


Coughs and Sneezes

Cough reflexes and sneezes are by-products of nerve irritation within the nasal passage airways, which expel air forcefully from the trachea or nose, respectively. In this manner, irritants caught in mucus lining the respiratory tract are expelled or moved to the mouth where they can be swallowed.

These violent reactions are, at times, comforting: Not many people have sneezed and not felt better afterward! After all, it’s only natural and that’s a good thing.


For a greater understanding oh respiratory systems , and the other human body systems, please read the other blogs in the current series, of which this one is a part brought to you by the makers of Instant CalMag-C.


© 2014 by Ronald Joseph Kule and Desiree Lotz. Reserved.

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