Lungs are the essential respiratory organs found in humans and most animals. The respiratory framework is comprised of airway and lung parenchyma. The airway is made of the bronchus, which bifurcates into a windpipe and further partitions into bronchioles and alveoli.
Humans have two lungs – a right lung and a left lung. It is located in the thoracic cavity of the chest and is found near the backbone on either side of the heart. The structure of lungs is such that it functions to draw oxygen from the air and transport it into the bloodstream, and remove carbon dioxide from the blood. This whole process is known as gas exchange. Lungs also supply the airflow with the help of which human speech is possible.
The diaphragm is the muscle which is liable for driving gaseous exchange in the lungs. Both the lungs together weigh around 1.3 kg, the right one being heavier than the left. The lungs are encased in a pleural cavity called pleurae that is filled up with pleural liquid. The pleural liquid between the external and internal layers smoothes the course of breathing and prevents friction.
Lung – Anatomy
The lungs are cone-like in shape with a rounded, narrow apex at the top. At the base is an expansive concave base that lies on the convex surface of the diaphragm. Anatomically, lungs have an apex, three surfaces and three borders.
Borders of Lungs
The three borders of the lungs are anterior, posterior and inferior borders. The anterior border coincides with the pleural reflection and is known to form a cardiac notch in the left lung. The cardiac notch is a concavity that accommodates the heart. The posterior border extends from C7 to T10 and is a thicker structure. The inferior border is thin in nature and separates the base of the lung from the costal surface.
Surfaces of Lungs
The three surfaces are medial, costal and diaphragmatic surfaces. The costal surface is layered by the costal pleura and is found along the lines of the sternum and ribs. It connects the medial surface at the anterior and posterior borders and also joins the diaphragmatic surface at the inferior border. The medial surface is related to the sternum anteriorly and to the vertebrae posteriorly. The diaphragmatic surface is convex on the upper side, forming the floor of the thoracic cavity, and concave on the lower side, forming the roof of the abdominal cavity.
The lungs have a central recession called hilum, from where the blood vessels and airway arrive into the lungs and make up the root of the lung. The pleural membranes that surround the lung are double serous membranes in between which the pleural fluid is present. Each of the lungs is divided into lobes and lobules.
Right and Left Lung
The right lung has three lobes – an upper, middle and lower one. The right lung usually weighs between 155g – 720g in males and 100g to 590g in females.
The left lung has two lobes – an upper lobe and a lower lobe. It does not have a middle lobe like the right lung. It weighs between 110g – 675g in men and 100g – 590g in women.
Microanatomy
The lungs are a part of the lower respiratory tract, and they house the bronchial tubes that branch from the trachea. The main bronchus tube divides multiple times after entering the lungs and forms bronchioles that eventually form the minute air sacs called alveoli. The alveoli are the location of gaseous exchange between the respiratory system and blood capillaries. From the hilum, the lymphatic vessels, nerves, bronchus, and pulmonary arteries and veins enter the lungs.
All portions of the respiratory tract, such as the trachea, bronchi and bronchioles, are lined with respiratory epithelium. The respiratory epithelium is ciliated and scattered with goblet cells that secrete mucus.
Why Do We Respire?
All organisms need energy. The food that we eat is released in the form of energy by the process of respiration. During respiration, we breathe in oxygen and breathe out carbon dioxide. The oxygen we breathe is transported to all the cells in our body, and ultimately, the oxygen helps in the breakdown of food. The process of release of energy by the breakdown of food in the cells is called cellular respiration. There are two ways by which the food breaks down in our cells, aerobic and anaerobic respiration. When the food breaks down in the presence of oxygen, it is referred to as aerobic respiration. On the contrary, when there is a breakdown of food in the absence of oxygen, it is referred to as anaerobic respiration. An example of anaerobic respiration can be seen in yeasts that break down food in the absence of oxygen to form alcohol and carbon dioxide.
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