Human Respiratory System

Breathing is a process of moving air into and out of the lungs for gaseous exchange with the internal body by bringing in oxygen and flushing out carbon dioxide. Breathing is a part of a process called respiration, wherein, oxygen gas is utilized by the cells to produce energy, and carbon dioxide gas is released as waste.  

Hence, the process of respiration can be broken down into three basic steps:

1. Inhaling oxygen from the surroundings.
2. Utilizing oxygen to get energy from food.
3. Exhaling carbon dioxide released during energy production.

Functions:

1. Nasal Cavity

The nasal cavity is the uppermost part of the respiratory system and provides the passage for the inhaled air from the nostrils to the rest of the respiratory tract. It is present above and behind the nose. Its function is to warm and moisturize the air entering the lungs. Hairs and mucus lining the nasal cavity help to prevent environmental contaminants like dust, mold, and pollens from entering the body. 

2. Pharynx

The pharynx is a hollow tube that is about 5 inches long. It is the common passageway leading from the mouth to the esophagus and nose to the larynx, making it a part of both the digestive system and the respiratory system in humans. Its function is to regulate the passage of air from the nasal cavity into the lungs during respiration. It is divided into three sections, the nasopharynx (adjoining the nasal cavity), oropharynx (adjoining the oral cavity), and laryngopharynx (adjoining the larynx).

5. Bronchi

 Trachea further divides into two smaller tubes called bronchi, one bronchus for each lung. They are the airways that connect the trachea to the lungs.  The air that we breathe in reaches the lungs via the nasal cavity, pharynx, larynx, trachea, and bronchi. The bronchi also expel air from the lungs back to the upper respiratory tract. They are the highways for gas exchange, with oxygen going to the lungs and carbon dioxide leaving the lungs through them. The bronchi are made up of smooth muscles with walls of cartilage. Each bronchus enters a lung and branches out as thousands of tiny bronchioles, and further into air sacs called alveoli.

6. Lungs

 Lungs are a pair of organs present on either side of the chest cavity. The right lung is bigger than the left, which shares space with the heart. Gas exchange takes place between the millions of alveoli in the lungs and the blood vessels (capillaries) that surround them. The inhaled oxygen moves from the alveoli to the blood in the capillaries and carbon dioxide from blood moves into the alveoli. It is then expelled through the respiratory tract.

The normal breathing rate for a person at rest is 12-20 times per minute which amounts to 2,900 gallons of air per day.

 Relationship between the Respiratory System and Digestive System

Once the oxygen reaches the blood, it is circulated to all the cells. Small food particles (glucose) from the digestive system are also transported to the cells. Oxygen reacts with glucose to gives us energy and carbon dioxide in the cells. The carbon dioxide is transported in the blood back to the lungs from where it is given out through our respiratory tract.

Check Point

Fill in the blanks:

1. Hairs and ___________in the nasal cavity help to prevent dust and pollens from entering the body.
2. ___________is the common passageway which is a part of both the digestive system and respiratory system in humans.
3. The trachea is also known as the
4. The normal breathing rate is ________ breaths per minute in a human being.
5. Each bronchus ends in tiny air sacs inside the lungs known as __________.
6. The respiratory tract sequentially includes the nasal cavity, _______, ________, _______, _______ and lungs.