Role of Alveoli

Alveoli (plural: alveoli, from Latin alveolus, “small cavity”) are hollow, distensible cup-shaped spaces in the lungs where oxygen and carbon dioxide are exchanged. The lung parenchyma, which comprises 90% of the total lung capacity, is made up of alveoli, which constitute the lung’s functioning tissue. The respiratory bronchioles, which indicate the start of the respiratory zone, contain the first alveoli. The alveolar duct walls are lined with them, and the blind-ended alveolar sacs, where they are more frequent, are where they may be found in greater numbers. There are four fundamental units of respiration: the acini, with gas exchange occurring in all of the alveoli present. You’ll see capillaries around the airway’s alveolar membrane. Oxygen diffuses into the capillaries via the membrane, while carbon dioxide is discharged into the alveoli, where it is exhaled. Alveoli are unique to the lungs of mammals. Other vertebrates’ gas exchange mechanisms use a variety of structures.

Structure

Scattered from their lumens, the alveoli initially appear in the respiratory bronchioles as out pockets. Breathing bronchioles are quite long and have many side branches of alveolar ducts, which are thickly coated with alveoli, increasing their alveolation. Each bronchiole has between two and eleven ducts.  There are five or six alveolar sacs in each duct, and each alveolar cluster opens into one of these sacs.

The respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli make up each acinus, the terminal respiratory unit. There are new alveoli forming to age eight.  Sacs and capillaries in the alveoli. Roughly 70 to 80 square metres of surface area is available for gas exchange in a normal human pair of lungs, which contain about 300 million alveoli. About 70% of the surface area of each alveolus is covered by a thin mesh of capillaries. Typically, alveoli are between 200 and 500 nm in diameter.

Microanatomy 

Simple squamous epithelium (thin, flattened cells) and an extracellular matrix surrounded by capillaries make up an alveolus.  As part of the alveolar membrane, or respiratory membrane, the epithelial lining permits gases to be exchanged. There are multiple layers to the membrane – a narrow interstitial gap between the epithelial lining and the capillary membrane; a capillary basement membrane that frequently unites with the alveolar basement membrane; and the capillary endothelial membrane. Even at its thickest point, the membrane’s thinnest component is barely 0.2 m thick. The pores of Kohn are air channels that link alveoli in the alveolar walls. Collagen and elastic fibres are found in the alveolar septa, which divide the alveoli in the alveolar sac. Additionally, the septa contain the alveolar capillary network. When the alveoli fill with air during inhalation, the elastic fibres enable them to stretch. The carbon dioxide-rich air is expelled by springing them back into action during exhale. A human alveolar sac histological slide Alveolar cells come in three main varieties. In the alveolar wall, there are two kinds of pneumocytes or pneumonocytes known as type I and type II pneumocytes, and an enormous phagocytic cell known as an alveolar macrophage. When it comes to the shape of alveoli in the lungs are squamous and flat type I cells known as type I pneumocytes or alveolar cells It’s thought that the pulmonary surfactant released by these cells helps to reduce the surface tension of the air, and they can also differentiate to replace injured type I cells. 

 Role of alveoli

When a breath is taken during inhalation, the alveolus receives more oxygen than the red blood cells. As a result, oxygen will pass through the alveolus and into the red blood cells.

The reverse happens during exhale. Because the alveolus contains less carbon dioxide than the red blood cells, carbon dioxide exits the red blood cell, enters the alveolus, and is exhaled.

Due to the fact that gases are continually needed physiologically and created as by-products of cellular and metabolic activities in the body, an effective mechanism for their exchange is essential. As a result, respiration plays a critical regulating function in gas exchange.

For instance, in individuals with diabetic ketoacidosis (DKA), metabolic alterations eventually result in abnormalities in respiratory patterns. This is because DKA causes metabolic acidosis, which the body first buffers with its bicarbonate buffering mechanism. However, after the body is overloaded and no longer able to adapt for the acidosis, one compensatory mechanism is hyperventilation, which reduces blood carbon dioxide levels by exhalation (extreme forms of this hyperventilation are known as Kussmaul respiration).

Function of alveoli

• Alveoli are the respiratory system’s terminus. The respiratory process begins with the inhalation of air via the mouth or nose.
• The trachea, often known as the windpipe, is where the air travels. The air then enters the lungs through airways called bronchi.
• The air is then guided via a series of increasingly narrow channels called bronchioles. The air then enters a particular alveolus via a small duct called the alveolar duct. Surfactant is the fluid that lines the alveoli.
• This fluid helps maintain the form of the air sac and keeps it open, allowing oxygen and CO2 to flow through.
• At this stage, the oxygen molecules reach the circulation through a single layer of lung cells in the alveolus and subsequently by a single cell layer in a capillary. CO2 is produced as a by-product of the process in which cells consume oxygen to generate energy. CO2 molecules enter the alveolus as oxygen leaves. 
• They are then exhaled via the nose or mouth.

Conclusion 

Alveoli are a critical component of the respiratory system. They are responsible for oxygenating and deoxygenating the circulation. Alveolar diseases may result in major health complications. This category includes chronic lung diseases such as emphysema and TB. Additionally, several malignancies may arise in the alveoli. Other infections, such as pneumonia, are more transient yet nonetheless dangerous. Certain disorders affecting the alveoli may result in respiratory failure.