Human Breathing System – Human Respiratory System – and Why Do We Breathe?

Why do we breathe? We breathe so that we can live. To live, we constantly need a supply of energy to our body cells. To have energy, we need to eat food with carbohydrates. To have energy, we need to digest carbohydrates to glucose (sugar). To have energy, we need to convert glucose to energy. To convert glucose to energy, we need to burn glucose with oxygen in our bodies to release the energy to the cells. To have oxygen, we need to inhale oxygen when we breathe in. The equation for this process is as follows:

Glucose + Oxygen → Energy + Carbon dioxide + Water

This equation is called aerobic respiration equation. This process of aerobic respiration takes place in a section of a cell called mitochondria.

From the aerobic respiration equation, when glucose is burned using oxygen to release energy there are two waste products produced. These two wastes are carbon dioxide and water. These two wastes are called metabolic wastes. These wastes will diffuse out of the cells and into the blood before diffusing out of the blood to be exhaled. These wastes of carbon dioxide and water are exhaled as carbon dioxide gas and water vapour when we breathe out.

So, why do we breathe? We breathe in to inhale oxygen which is used to burn food into energy for our body cells. We breathe out to exhale out carbon dioxide gas and water vapour which are waste products when food is converted into energy for our body cells. Without energy for our body cells we can not live.

The five principle parts of a human respiratory system are:
1. Nose
2. Trachea, also known as wind-pipe
3. Bronchi
4. Lungs
5. Diaphragm

The Nose is that part on the face in humans that contains two nostrils. The nose contains the organs of smell and functions as the usual passageway for air in the breathing process. In the Human Respiratory process, air from the atmosphere will enter the nose. In the nose, air is cleaned, warmed and moistened. The nose has tiny hairs and mucus for trapping germs and dust contained in the air.

Nasal Cavity is therefore defined as a system of chambers with mucus membrane through which air passes from the nostrils to the pharynx. During the breathing in process, air is filtered, warmed, moistened, and smelled. Pharynx is a hollow tube about 10 cm long that starts behind the nose and ends at the top of the trachea (windpipe). If you were to breathe through the mouth, air would enter the pharynx.

Another name for trachea is the windpipe. The trachea is a wide pipe which is kept open by C-shaped rings of tough tissue. It’s the passageway through which air passes. The trachea has mucus membrane for trapping dust and germs and moving them towards pharynx.

We can define larynx as the voice box. In humans, it’s that hollow muscular organ with vocal cords for air passage. When air passes over larynx, it vibrates.

And we define epiglottis as an elastic flap that covers the trachea during swallowing, at the root of the tongue, so that food does not enter the windpipe.

As the trachea approaches the lungs it subdivides into two branches. Each branch is called a bronchus. Plural of bronchus is bronchi. Each bronchus joins a separate lung. The bronchi are lined with mucus membranes for trapping dust and microscopic particles such as germs. The bronchi are also kept open by C-shaped rings of tough tissue.

As the bronchi extend further into the lungs they subdivide into many smaller tubes called bronchioles. The bronchioles are to be found inside the lungs. Bronchioles do not have the C-shaped rings of tough tissue, but they are just tubes. The bronchioles are also lined with mucus membranes for trapping off dust and germs from the air.

Human have a pair of lungs situated within the rib cage called a chest. There is a lung on each side of the chest, left and right. The bronchioles inside the lungs divides into millions of fine tubes that lead to air sacs called Alveoli. The air sacs have capillaries that allow gas exchange. During the exchange of gas in the air sacs, oxygen is absorbed by the blood whilst at the same time the blood gives out carbon dioxide. This is called Diffusion of gases between the air surrounding the alveoli.

The diaphragm is a dome-shaped, muscular partition separating the chest (thorax) from the abdomen. Contraction and retraction of the diaphragm will increase or decrease the volume of the chest thus inflating and deflating the lungs as follows:

a) When the diaphragm moves downwards, the volume of the chest will increase and the lungs will expand sucking in air. This is called breathing in - inhalation.

b) When the diaphragm moves upwards, the volume of the chest will decrease and the lungs will contract expelling out air. This is called breathing out - exhalation.

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