Respiratory System
Respiration is the entire process of taking air in, exchanging needed gases for unnecessary gases, using the needed gases, and releasing the waste form of gases. The Human respiratory system consists of the following parts, divided into the upper and lower respiratory tracts.
Upper Respiratory Tract
Mouth, nose & nasal cavity
The nostrils act as the air intake, bringing air into the nose, where it’s warmed and humidified. Tiny hairs called cilia protect the nasal passageways and other parts of the respiratory tract, filtering out dust and other particles.
Pharynx
Pharynx is part of the digestive system as well as the respiratory system because it carries both food and air.
Larynx
This is also known as the voice box as it is where sound is generated. It also helps protect the trachea by producing a strong cough reflex if any solid objects pass the epiglottis.
Lower Respiratory Tract
Trachea (Wind Pipe)
It carries air from the throat into the lungs. The inner membrane of the trachea is covered with cilia. The trachea is surrounded by 15-20 C-shaped rings of cartilage at the front and side which help protect the trachea and keep it open.
Bronchi
The trachea divides into two tubes called bronchi, one entering the left and one entering the right lung.
Bronchioles
Tertiary bronchi continue to divide and become bronchioles, very narrow tubes, less than 1 millimetre in diameter. There is no cartilage within the bronchioles and they lead to alveolar sacs.
Alveoli
Individual hollow cavities contained within alveolar sacs. Alveoli have very thin walls which permit the exchange of gases Oxygen and Carbon Dioxide. They are surrounded by a network of capillaries, into which the inspired gases pass.
Thorax or the chest cavity
It is the airtight box that houses the bronchial tree, lungs, heart, and other structures. The top and sides of the thorax are formed by the ribs and attached muscles, and the bottom is formed by a large muscle called the diaphragm.
Diaphragm
It is located below the lungs. It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily. Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges which pulls air into the lungs. Upon exhalation, the diaphragm relaxes and returns to its domelike shape, and air is forced out of the lungs.
Steps in Respiration
Respiration involves the following steps:
- Breathing or pulmonary ventilation by which atmospheric air is drawn in and CO2 rich alveolar air is released out.
- Diffusion of gases (O2 and CO2) across alveolar membrane.
- Transport of gases by the blood.
- Diffusion of O2 and CO2 between blood and tissues.
- Utilisation of O2 by the cells for catabolic reactions and resultant release of CO2.
The process of Respiration
In a process called diffusion, oxygen moves from the alveoli to the blood through the capillaries (tiny blood vessels) lining the alveolar walls. Blood has a massive capacity to dissolve oxygen – much more oxygen can dissolve in blood than could dissolve in the same amount of water. This is because blood contains Haemoglobin – a specialized protein that binds to oxygen in the lungs so that the oxygen can be transported to the rest of the body. This oxygen-rich blood then flows back to the heart, which pumps it through the arteries to oxygen-hungry tissues throughout the body.
In the tiny capillaries of the body tissues, oxygen is freed from the hemoglobin in the blood and moves into the cells. Carbon dioxide, which is produced during the process of diffusion, moves out of these cells into the capillaries, where most of it is dissolved in the plasma of the blood.
Blood rich in carbon dioxide then returns to the heart via the veins. From the heart, this blood is pumped to the lungs, where carbon dioxide passes into the alveoli to be exhaled.
