Contents
Molecular biology, one of the Biology Topics, focuses on the study of biological molecules.
What is the Structure and Function of the Respiratory System?
We have already studied that the process of digestion in human beings produces energy-rich simple compounds like glucose. The digested food (glucose) is carried to all the cells of our body by the blood circulatory system. The human beings obtain energy from the digested food (glucose) by the process of respiration which takes place in every cell. In human beings, many organs take part in the process of respiration. We call them organs of respiratory system. The main organs of human respiratory system are: Nose, Nasal passages (Passages in the nose), Trachea, Bronchi, Lungs and Diaphragm. The human respiratory system is shown in Figure.
Our nose has two holes which are called nostrils (see Figure). There is a passage in the nose behind the nostrils. This is called nasal passage (or nasal cavity). The nasal passage joins the nostrils to the trachea (see Figure). The trachea is a tube which is also called windpipe. The upper end of trachea has a voice box called larynx. The trachea (or windpipe) branches into two smaller tubes called ‘bronchi’ at its lower end (see Figure) (The singular of bronchi is bronchus). The two bronchi are connected to the two lungs—one to the left lung and other to the right lung (see Figure).
Each bronchus divides in the lungs to form a large number of still smaller tubes called ‘bronchioles’. The smallest bronchioles have tiny air-sacs at their ends (see Figure 13). The pouch-like air-sacs at the ends of the smallest bronchioles are called ‘alveoli’. The walls of alveoli are very thin and they are surrounded by very thin blood capillaries. The exchange of gases between the air and blood takes place across the walls of the alveoli.
The diaphragm is a curved sheet of muscle below the lungs. The breathing organs of human beings are lungs. Our lungs lie in the chest cavity, which is bound by the rib cage and diaphragm. The muscles of rib cage and diaphragm help in ‘breathing in and ‘breathing out’.
When we breathe in and out, our chest goes up and down (or heaves). This happens as follows: When we ‘breathe in’ air, our chest cavity expands. This expansion movement of the chest cavity helps in sucking in air (containing oxygen in it). On the other hand, when we ‘breathe out’ air, then the chest cavity contracts. This contraction movement of the chest cavity helps in squeezing out carbon dioxide from the walls of the lungs and expelling it from the body. We will now describe the working of respiratory system in human beings.
We normally breathe in air (containing oxygen) through the nose. The air enters the nostrils, passes through the nasal passage, larynx, trachea, bronchi, and finally reaches the lungs (see Figure). In the lungs, air passes through a large number of small tubes called bronchioles and then reaches the tiny air-sacs called alveoli. The alveoli are surrounded by very thin blood vessels called capillaries which carry blood in them. The oxygen of air diffuses out from the alveoli into the blood in the capillaries. The blood carries oxygen to all the parts of the body. This oxygen is carried by a red pigment called ‘haemoglobin’ present in the red blood cells.
As blood passes through the tissues of the body, the oxygen present in it diffuses into the cells. This oxygen combines with the digested food (glucose) present in cells to release energy. The materials like fatty acids and glycerol (produced by the digestion of fats) are also oxidised during respiration to produce energy. Carbon dioxide and water are produced by the oxidation of food during respiration. The waste products of respiration, carbon dioxide and water, enter into blood. Blood carries the carbon dioxide and water to the alevoli in the lungs. From the lungs, carbon dioxide and water vapour are removed with the air we breathe out. In this way, the process of gaseous exchange is completed in the human respiratory system.
Sneezing
The sudden expulsion of air from the nose (without our control over it) due to the irritation of nasal passage, is called sneezing (see Figure). We often sneeze when we inhale air containing dust, smoke or pollen, etc. This happens as follows : The air around us sometimes contains various types of small, unwanted particles such as dust, smoke, pollens, etc. Now, there are some very fine hair inside our nose in the nasal passage (or nasal cavity). When we inhale air, the unwanted particles present in air usually get trapped in the hair present in our nasal passage.
Sometimes, however, the particles of dust, smoke and pollens, etc., present in inhaled air get past the hair in the nasal passage and irritate the lining of nasal passage, as a result of which we sneeze. Sneezing expels all the unwanted particles from the inhaled air so that a dust free, clean air enters into our lungs (see Figure). Please note that whenever we sneeze, we should cover our nose properly with a handkerchief so that the unwanted particles which we expel during sneezing are not inhaled by other persons nearby us.
Yawning
The action of opening one’s mouth wide while taking a long and deep breath of air (without any control over it) is called yawning (see Figure). Yawning is called ‘jambhai or ‘ubasi’ in Flindi. A person yawns when he is tired, bored, stressed, over-worked, feeling sleepy or drowsy. There are many theories about why people yawn. According to one theory, yawning is caused by insufficient oxygen in the body.
This is said to happen as follows : When we are tired, bored, stressed, over-worked, feel sleepy or drowsy, we do not breathe as deeply as we normally do and hence our breathing rate slows down. Due to slower breathing rate, less oxygen (of air) goes into our body which is insufficient for respiration (production of energy). Yawning helps in bringing more oxygen into our blood because during yawning our mouth opens wide and we take a long and deep breath of air.
Smoking
The lungs are very delicate organs which are essential for breathing and keeping of our lungs is the habit of smoking. Smoking tobacco in the form of beedi, cigarette or cigar damages our lungs gradually and causes ill health. Smoking sends tobacco smoke inside the body. The chemicals present in tobacco smoke damage the lungs in many ways. Some of the harmful effects of smoking are as follows:
- Smoking destroys the lung tissue gradually due to which breathing becomes very difficult.
- Smoking causes lung cancer (see Figure).
- Smoking causes heart diseases.
- Smoking also damages the health of non-smokers who inhale the air containing tobacco smoke.
Smoking kills. Many people die every year from diseases caused by smoking. The bad habit of smoking must be avoided to lead a healthy life.