Human Respiratory System: Definition, Diagram and Examples
The human respiratory system enables breathing and sustains life by delivering oxygen to tissues and removing carbon dioxide. Its organs—from the nose to the alveoli—work together to filter, warm, conduct, and exchange gases efficiently. Mastering its structure and mechanisms is essential for NEET and Class 11–12 Biology.
This Story also Contains
- What Is the Human Respiratory System?
- What is Respiration?
- Anatomy of the Human Respiratory System
- Gas Exchange and Transport
- Mechanism Of Breathing (Ventilation)
- Functions of the Respiratory System
- Human Respiratory System NEET MCQs (With Answers & Explanations)
What Is the Human Respiratory System?
The human respiratory system facilitates the exchange of gases, providing oxygen to the body and removing carbon dioxide. It includes organs such as the nose, pharynx, larynx, trachea, bronchi, and lungs. This system plays a vital role in maintaining cellular respiration and energy production.
What is Respiration?
Breathing is a fundamental life-sustaining mechanism by which people and all other living things metabolise oxygen and release carbon dioxide, a by-product into the environment. Lungs, trachea, and diaphragm are used to help facilitate the exchange of gases. Being one of the main regulatory and metabolic functions that are associated with every cell, the respiratory system is a vital component of human physiology. In respiration, air is directly taken into the lungs then the oxygen in it is transported to the various cells for metabolic purposes. At the same time, the carbon dioxide resulting from metabolism is transported back to the lungs to be expelled through exhalation maintaining the health of all tissues/organs in the body.
Anatomy of the Human Respiratory System
The human respiratory tract has the following parts:
Nose and Nasal Cavity
Structure and function: The principal pathways for air are the following: the external opening made of the nostrils, internal concha, and nasal septum.
Role in filtering and humidifying air: This structure prevents the entry of dust and pathogens by using nasal hair and mucous membranes. They also heat and moisten the incoming air to increase protection for the highly sensitive structures of the respiratory tract.
Pharynx and Larynx
Structure and function: The Pharynx is a muscular passage that forms a common wall of the nasal and oral cavities and it also connects to the larynx. The larynx, also known as the voice box is located below the pharynx and is found to contain the vocal cords.
Role in directing air to the lungs: The pharynx helps guide the air from the nose and mouth to the larynx and then to the trachea so that a proper distribution to the lungs is facilitated.
Trachea and Bronchi
Structure and function: Trachea is a tubular structure made of cartilage that begins at the larynx and moves down to the chest where it branches off to the main bronchi.
Division into bronchi and bronchioles: The trachea branches into two parts of the bronchus, the left and right which continue into the lungs branching out into smaller bronchial tubes which enable the distribution of the air within the lungs.
Lungs
Structure: Lungs are two large spoke air-containing organs located in the thoracic cavity which is sheltered by ribs.
Lobes of the lungs: The right lung has three lobes; the right upper lobe, the right middle and the right lower lobe. The left lung has only two lobes; the left upper lobe and the left lower lobe because of the presence of the heart.
Alveoli
Structure and function: Alveoli are enormously small, these are the terminal branches of bronchial tubes which are again covered by a web of capillaries.
Gas exchange process: This is of significance in regards to the process of respiration as well as oxygenation of the alveoli tissues, they facilitate the exchange of oxygen and carbon monoxide in the air to the bloodstream or vice versa where needed most of the time.
Gas Exchange and Transport
This involves the following process:
Gas Exchange in the Alveoli
This process of gas exchange in alveoli is conducted through the process of diffusion in which the oxygen content has a freedom of movement from the alveolar surface to blood at the capillary walls while, on the other hand, the carbon dioxide from blood has the freedom of movement and get accumulated at the alveolar surfaces.
The diffusion process is stated through the partial pressure for oxygen and carbon dioxide; oxygen has a higher partial pressure in the alveoli than in the blood while carbon dioxide has a higher partial pressure in the blood than in the alveoli.
Transport of Oxygen
When oxygen gets in the blood it combines with the hemoglobin of the red blood cells to form what is known as oxyhemoglobin, which is then distributed to various tissues of the body.
Transport of Carbon Dioxide
Carbon dioxide generated by the cells moves out of the cells into the plasma; the major portion of it is changed to bicarbonate owing to the enzyme carbonic anhydrase present in the red blood cells.
The CO2 is transported in 3 forms in blood; dissolved in blood plasma, bound to the haemoglobin forming carbaminohemoglobin, and finally as bicarbonate ions in the blood which is the most common form of CO2 that is transported back to the lungs for exhalation.
Mechanism Of Breathing (Ventilation)
The mechanism of breathing takes place via:
Inhalation
When the diaphragm contracts, it becomes flat, and it moves down into the chest cavity space below, creating more space in the chest cavity and air rushes into the lung.
Exhalation
The diaphragm relaxes and moves upward, reducing the chest cavity size and forcing air out of the lungs.
Diaphragm & Intercostal Muscles
Diaphragm is the main muscle of respiration. It is dome-shaped which flattens during inhalation. The intercostal muscles expand and contract the rib cage. They also assist in the inspiration & expiration.
Functions of the Respiratory System
The functions of the respiratory system are:
Inhalation and Exhalation
The respiratory system helps in inhalation whereby the diaphragm muscle and the muscles between the ribs expand to take in air during breathing and exhalation whereby the diaphragm muscle and the muscles between the ribs contract and force out air from the lungs during the process of breathing.
Gas Exchange between Lungs and Bloodstream
Oxygen penetrates alveolar walls to access the capillaries on the same note, carbon dioxide that is within the blood gets to pass through the alveoli to get eliminated through respiration thus in the process helping regulate the concentration of these gases in the body.
Removal of metabolic CO₂
Blood containing oxygen gets transported to the several tissues of the body where oxygen is utilised in several activities and the carbon dioxide which is the end product of any metabolism is transported back to the lungs.
Voice Production
It is a part of the respiratory system and also contains vocal cords, which vibrate and create sound as the air is breathed out. This function can allow for talking and phonic communication in one way or another.
Smell via olfactory receptors
The nasal cavity has olfactory receptors that can detect chemicals floating in the air which gives the sense of smell. These receptors transport some impulses to the brain and they help in the feeling of scent.
Human Respiratory System NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
Mechanism of breathing
Functions of the respiratory system
Practice Questions for NEET
Q1. Trachea divides into right and left bronchi at the level of
L5
C5
T5
L7
Correct answer: 3) T5
Explanation:
The trachea splits into the right and left bronchi at the level of the fifth thoracic vertebra, or T5, which is also referred to as the sternal angle. This is called the carina and signifies the start of the bronchial tree, from which each bronchus leads to its particular lung. The right main bronchus is generally more vertical and larger in diameter, while the left is smaller in diameter and horizontally oriented because it is located below other anatomical structures. Such branching of bronchi will provide proper air entry to the lungs to facilitate gas exchange.
Hence, the correct answer is option (3) T5.
Q2. Regarding the functions of our respiratory system, mark the wrong entry.
Humidifier the air
Warms up the air
Exchange of gases
Cleans up the air
Correct answer: 4) Cleans up the air
Explanation:
The respiratory system removes undesirable carbon dioxide from the air we breathe and absorbs oxygen from it. The lungs are the respiratory system's primary organ. The trachea, the nose, and the breathing muscles (the diaphragm and the intercostal muscles) are further respiratory organs.
Hence, the correct answer is option 4) Cleans up the air.
Q3. The respiratory process is regulated by certain specialised centres in the brain. One of the following listed centres can reduce the inspiratory duration upon stimulation
Medullary inspiratory centre
Pneumotaxic centre
Apneustic centre
Chemosensitive centre
Correct answer: 2) Pneumotaxic centre
Explanation:
Inspiration is the process of breathing in oxygen-rich air. The lungs' volume increases during inspiration as a result of the diaphragm being flat and the ribs being drawn higher and outward. To control inspiratory volume and respiratory rate, the pneumatic centre, which is situated in the upper pons, sends inhibitory impulses to the inspiratory centre, stopping inspiration. The fine-tuning of respiration most certainly involves this region.
Hence, the correct answer is option 2) Pneumotaxic centre.
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Frequently Asked Questions (FAQs)
The human respiratory system can be composed of the following; nasal cavity and nose, throat or pharynx, voice box or larynx, windpipe or trachea, bronchi, and lungs.
In the alveoli there are two processes, which take place and these involve diffusion. Oxygen present in the inhaled air moves to the alveolar walls and enters the capillaries, while carbon dioxide in the blood moves across the alveolar walls to be expelled.
The diaphragm is a muscle in the form of a dome fixed at the lower level in the area of the lungs’ position. During inspiration, the diaphragm relaxes but becomes thinner and this in turn expands the thoracic cavity to allow a low pressure to suck in the air into the lungs.
Other respiratory illnesses are asthma, COVID-19, pneumonia, bronchitis, and lung cancer. The symptoms are many but the common ones are difficulties in breathing, wheezing sound, cough that does not stop, pain in the chest and mucus. These are diseases that require early diagnosis and treatment since they are chronic.
The following measures are recommended to have a healthy respiratory tract; refrain from smoking and exposure to cigarette smoke, decrease exposure to pollutants, undertake regular exercises, practice cleanliness to minimise get infections, and regular check-ups.