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We have been breathing in and out since we were born. Respiration occurs in every living thing, from a single-celled amoeba to a multi-celled animal. Lungs are a part of the human respiratory system, which works and continues to work until the very last minute of our lives. Lungs, like the brain, heart, and other organs, play an important function in humans and animals such as whales, dolphins, frogs, birds, reptiles, and all other species. Humans have specialised lungs in comparison to all other animals including birds.
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Key takeaways: lungs, breathing, respiration, respiratory system, bronchioles, alveoli, branching, gases
Structure of Lungs
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Structure of lungs is divided into External as well as Internal Structure:
External structure of lungs
The lungs are pinkish-colored organs that are soft, spongy, and elastic. The apex and base of each lung are the upper and lower portions of the lung, respectively. The coastal surfaces of the lungs get their name from the fact that they are located adjacent to the ribs. The lungs' median surfaces are located near to the mediastinum.
The left lung is smaller than the right and has a concavity where the heart is located, known as the cardiac notch. The superior lobe and inferior lobe of the left lung are separated by the oblique fissure. The right lung is divided into three lobes: superior, middle, and inferior, which are separated by the horizontal and oblique fissures.
Internal structure of lungs
Bronchi
The primary bronchus separates into secondary bronchi as soon as it enters each lung. A tertiary bronchus is formed when a secondary bronchus divides. The cartilaginous rings of the secondary and tertiary bronchi are also present.
Bronchioles
The bronchioles, which lack cartilaginous rings, separate the tertiary bronchi into smaller branches. As the bronchioles travel further into the lungs, their diameter decreases and their epithelium thins. One of the smaller bronchioles enters a lung lobule called lobular bronchiole after repeated branching. The latter produces terminal bronchioles, which divide further into respiratory bronchioles.
Alveolar ducts, atria, alveolar sacs, and alveoli
The respiratory bronchioles open into the alveolar ducts, which lead to the atria (single, atrium), which then lead to the alveolar sacs or air sacs. The latter are the ones that open into the alveoli (also called acini). In two lungs, there are 300 million alveoli. Squamous epithelium makes up the alveoli's relatively thin wall. A large network of blood capillaries is interlaced with elastic and reticular connective tissue fibres on the alveolar wall. The exchange of gases is simple due to the close contact of blood capillaries with the alveoli. As a result, each alveolus can be thought of as a little lung where gases are exchanged. The alveoli of the lungs are generally lined by a film of lecithin that lowers the surface tension and maintains the alveoli open. However, the film of lecithin may not be present in all infants. Due to the baby's lungs collapsing, this could be fatal.
Significance of Lungs
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- Warms the air to the temperature of your body and moisturises it to the humidity level your body requires.
- Delivers oxygen to your body's cells.
- When you exhale, it removes waste gases from your body, including carbon dioxide.
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Steps involved in Lungs
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- The inflow (inspiration) and outflow (expiration) of air between the atmosphere and the alveoli of the lungs is referred to as breathing.
- Gases (O2 and CO2) diffuse over the alveolar membrane.
- Gases are transported by the bloodstream.
- O2 and CO2 diffusion between the blood and the tissues.
- The use of O2 by cells for catabolic activities and the emission of CO2 as a result (cellular respiration).
Blood supply in lungs
The primary function of lungs is to exchange the gases, which makes the use of blood from the pulmonary circulation. This blood supply carries deoxygenated blood to the lungs, where erythrocytes also known as red blood cells, pick up oxygen and move it to the tissues throughout the body. The pulmonary artery is a branch of the pulmonary trunk that carries deoxygenated arterial blood to the alveoli. As it travels the bronchi, the pulmonary artery branches many times, with each branch becoming smaller in diameter. One lung lobule is supplied and drained by a single arteriole and its connected venule. When the pulmonary arteries reach the alveoli, they become the pulmonary capillary network.
Small capillaries with very thin walls and no smooth muscle fibres make up the lungs' capillary network. The capillaries branch out and follow the anatomy of the bronchioles and alveoli.
The respiratory membrane is formed when the capillary wall joins the alveolar wall at this point.After being oxygenated, blood drains from the alveoli through several pulmonary veins, which exit the lungs through the hilum.
Nervous innervation of the lungs
The parasympathetic and sympathetic nervous systems work together to govern the airway's dilation and constriction. Bronchoconstriction is caused by the parasympathetic nervous system, whereas bronchodilation is stimulated by the sympathetic nervous system. Coughing reflexes and the ability of the lungs to regulate oxygen and carbon dioxide levels are similarly controlled by the autonomic nervous system. The vagus nerve and the second through fifth thoracic ganglia produce sensory nerve fibres. The pulmonary plexus is an area on the lung root produced by the nerves' hilum entry. The nerves then branch out to innervate muscle fibres, glands, and blood vessels as they follow the bronchi in the lungs.
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Points to Remember
- Various muscle systems in different species carry out respiration.
- The lungs provide airflow that allows vocal sounds, such as human speech, to be produced.
- The lungs are the most important organs in the human respiratory system.
- The heart shares some of the space designated to the left lung, which has an indentation in its border called as the cardiac notch of the left lung.
- The walls of the respiratory bronchioles and alveolar ducts contain alveoli. The lungs have about 2,400 kilometres of airways and 300 to 500 million alveoli.
Sample Questions
Ques: What is yawning? (2 Marks)
Ans: We can breathe more oxygen into our lungs by yawning. It is an uncontrollable activity that is accompanied with a protracted intake (or exhalation). When the brain cells detect a lack of oxygen, they send a message to our sensory system, which causes us to take a long, deep breath or yawn.
Ques: What is the respiratory quotient? (2 Marks)
Ans: The respiratory quotient is the ratio between the volume of oxygen ingested and the volume of carbon dioxide exhaled during cellular respiration. It's also known as the respiratory ratio and is abbreviated as RQ. Between 0.7 and 1.0 is the usual respiratory quotient.
Ques: Which is stronger among inhalation and exhalation? (2 Marks)
Ans: Inhalation is generally more powerful than exhalation throughout the breathing process. The air is filtered as we breathe in by the nasal chambers, which are then followed by the nose. As a result, inhaling and exhaling through the nose is preferable to doing so through the mouth.
Ques: What are lungs? (3 Marks)
Ans: In the respiratory system, the lungs perform a critical role. A pair of lungs in humans are structured in such a way that they are separated by thin membranes and smaller tubes known as bronchioles. It also contains a balloon-like structure known as alveoli, as well as a network of blood capillaries that enhances the surface area of the lungs for gas exchange. Humans have two lungs, which are located in the chest cavity called the thoracic cavity. The pleura is a thin membrane sac that contains soft, spongy, and elastic organs. Lungs are separated into bronchi, which are further divided into bronchioles and alveoli, providing a wider surface area and maximising gas exchange inside the lungs.
Ques: What are the risks to lungs? (3 Marks)
Ans: Infections and damage to the lungs are very common. Some illnesses can render a lung worthless by destroying large portions of it. Toxic substances such as tobacco smoke, asbestos, and environmental dust can cause lung inflammation and cause considerable harm. Healed lung tissue transforms into a fibrous scar that can no longer perform breathing functions. There is no indication that lung tissue can be rebuilt once it has been destroyed.
Ques: What are the steps involved in respiration? (5 Marks)
Ans: The steps involved in respiration are:
- The inflow (inspiration) and outflow (expiration) of air between the atmosphere and the alveoli of the lungs is referred to as breathing.
- Gases (O2 and CO2) diffuse over the alveolar membrane.
- Gases are transported by the bloodstream.
- O2 and CO2 diffusion between the blood and the tissues.
- The use of O2 by cells for catabolic activities and the emission of CO2 as a result (cellular respiration).
Ques: Write about the blood supply in the lungs. (5 Marks)
Ans: The lungs' primary function is gas exchange, which necessitates the use of blood from the pulmonary circulation. This blood supply carries deoxygenated blood to the lungs, where erythrocytes also known as red blood cells, pick up oxygen and move it to the tissues throughout the body. The pulmonary artery is a branch of the pulmonary trunk that carries deoxygenated arterial blood to the alveoli. As it travels the bronchi, the pulmonary artery branches many times, with each branch becoming smaller in diameter. One lung lobule is supplied and drained by a single arteriole and its connected venule. When the pulmonary arteries reach the alveoli, they become the pulmonary capillary network. Small capillaries with very thin walls and no smooth muscle fibres make up the lungs' capillary network. The capillaries branch out and follow the anatomy of the bronchioles and alveoli. The respiratory membrane is formed when the capillary wall joins the alveolar wall at this point.After being oxygenated, blood drains from the alveoli through several pulmonary veins, which exit the lungs through the hilum.
Ques: Write about the nervous innervation in lungs. (4 Marks)
Ans: The parasympathetic and sympathetic nervous systems work together to govern the airway's dilation and constriction. Bronchoconstriction is caused by the parasympathetic nervous system, whereas bronchodilation is stimulated by the sympathetic nervous system. Coughing reflexes and the ability of the lungs to regulate oxygen and carbon dioxide levels are similarly controlled by the autonomic nervous system. The vagus nerve and the second through fifth thoracic ganglia produce sensory nerve fibres. The pulmonary plexus is an area on the lung root produced by the nerves' hilum entry. The nerves then branch out to innervate muscle fibres, glands, and blood vessels as they follow the bronchi in the lungs.
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