The Respiratory System

The Respiratory system consists of the organs that help to breathe. Respiration, also known as breathing, is the process which delivers oxygen from the external atmosphere to the body and removes the carbon dioxide from body and expels out.

The main parts of the respiratory system are:

  • The nostrils
    • Nostrils are involved in air intake, i.e. they bring air into the nose, where air is warmed and humidified. The tiny hairs called cilia filters out dust and other particles present in the air and protects the nasal passage and other regions of the respiratory tract.
  • Pharynx
    • Besides the nose, air can enter into the lungs through the mouth. The pharynx is a tubular structure, positioned behind the oral and nasal cavities, that allows air to pass from the mouth to the lungs.
  • Trachea
    • The trachea is also known as windpipe. The trachea filters the air we inhale and branches into the bronchi.
  • Bronchi
    • The bronchi are the two air tubes that branch off of from the trachea and carry atmospheric air directly into the lungs.
  • Lungs
    • The main organ of the respiratory system is lungs. The human lungs are a pair of large, spongy organs optimized for gas exchange between our blood and the air. Our bodies require oxygen in order to survive. The lungs provide us with that vital oxygen while also removing carbon dioxide before it can reach hazardous levels.
  • Alveolus
    • Alveolus is the tiny sac like structure present in the lungs which the gaseous exchange takes place
  • Diaphragm
    • Breathing begins with a dome-shaped muscle located at the bottom of the lungs which is known as diaphragm. When we breathe in the diaphragm contracts and flatten out and pull downward. Due to this movement the space in the lungs increases and pulls air into the lungs. When we breathe out, the diaphragm expands and reduces the amount of space for the lungs and forces air out

Breathing Cycle

Air is typically drawn in through the nose, where it is filtered of dust, pollens and other pollutants by the hairs and mucous layer of the nose and sinuses. It then travels down the trachea, and into the left and right bronchi. These bronchi then split into many smaller bronchioles. These continue to divide into smaller passages, until the air reaches the alveoli. This is there it reaches the capillary beds, and gaseous exchange takes place. The air then follows the same pathway, in reverse, to be expelled from the body, with one exception. Ordinarily, air is expired through the mouth.

When air is inspired through the mouth, it triggers a stress response in the body. Due to the larger amount of air which can be taken in, this pathway is usually used in instances where greater volumes of oxygen is required (fight or flight situations). So, when we voluntarily breathe through this pathway, the brain usually doesn’t differentiate between the breathing and the physiological need. And, because of this, it still stimulates the same set of chain reactions.

Breathing Mechanism

In order to cause the inspiration of air, a low pressure is created within the chest cavity. This then draws air in, to fill this low pressure. In correct breathing, this is caused by the diaphragm moving down (increasing space from below), and the chest wall expanding. Both of these are caused by muscular contraction. Then, when these contractions relax, the chest wall returns to normal position, as does the diaphragm. This causes an increase in pressure within the chest cavity, forcing air out. This expiration can also be done forcefully, through another set of muscular contractions, in order increase the rate of the air being expelled. This correct/preferred method of breathing is known chest breathing, or diaphragmatic breathing.

Another method of causing the decrease in pressure in the chest cavity is by what is termed “belly breathing”. Once again, this causes decreased pressure by increasing the space in the chest from below. What is seen as moving the belly out, the abdominal content (viscera) is moved out, resulting in the diaphragm moving down. When the belly moves back in, the diaphragm is then pushed back up. Since this method of breathing only increases the chest cavity through moving the diaphragm, it doesn’t cause as much air to be inspired. Rather, it leads to shorter, shallower breaths. Generally speaking, this method of breathing is used in hyperventilation.

Gaseous exchange

In the capillary beds of the alveoli, carbon dioxide is released from the red blood cells, and oxygen takes it place. This oxygen is then, as previously mentioned, carried back to the heart, and subsequently off to the rest of the body, and all its working tissues. Unfortunately for us, there is a chemical that the haemoglobin “prefers” to bind with, that we often breathe in. and, this chemical is carbon monoxide. This is one of the most common industrial pollutants, and can be easily found streaming out of the exhaust pipe of every car on the road. But, it is also voluntarily inspired in cigarette smoke. As a result of this preference, working tissues become starved of oxygen, when carbon monoxide is present.

One of the adaptations the body makes to exercise is an increased number of capillaries. This will happen in the alveoli, as well as other tissues. In the alveoli, this allows for a greater surface area over which gaseous exchange can take place. As the body requires more oxygen to meet the demands of exercise, and it produces more carbon dioxide as a byproduct, the need for more capillaries becomes apparent. And, this is why the body will be forced to increase the number of capillaries.