Nose and nasal cavity, sinuses, pharynx, larynx, trachea, lungs, bronchi,alevoli-3

The Bronchi

At the level of the fifth thoracic vertebra, the trachea splits into two bronchi, the right and left bronchi, which enter the lungs. The primary bronchi is another name for them. A depression or notch known as the hilus or hilum serves as each bronchus' entry point into the lung. In this area, the blood vessels and nerves also connect to the lung.

The right bronchus: Is much more vertically oriented, 2.5 cm shorter (and wider in diameter) than the left, and extends downward. Therefore, it is likely that a foreign object will enter the right lung if it is inhaled.

The left bronchus: Is 5 cm longer and 3 cm smaller than the right bronchus. It is separated into two branches further.

The Bronchioles

Each bronchus quickly divides into smaller bronchi known as the secondary bronchi after entering the lung at the hilus (3 from right and 2 from left). The tertiary bronchi are smaller branches that emerge from the secondary bronchi (10 on each). The bronchial tree is another name for the subdivision of the bronchi since it resembles a tree's branches. The bronchi repeatedly divide into smaller and smaller divisions, the smallest of which are referred to as bronchioles. The terminal bronchioles, which number 50 to 80 on each lung, are the smallest divisions of the bronchial tree and serve as the site of gas exchange. The lungs are divided into 10 broncho-pulmonary segments on the right and 10 on the left by the tertiary or segmental bronchioles. The smallest functionally independent region of a lung that can be isolated and removed during surgery without affecting neighboring regions is a broncho-pulmonary segment. They are segmentally supplied by the pulmonary artery, and pulmonary vein tributaries typically pass between and along the edges of segments.

Structure of the Bronchi and the Bronchioles

Small pieces of cartilage can be found in the bronchi, which help to keep the passages open and firm so that air can flow readily in and out. However, as the bronchi get smaller, less cartilage is produced. Pseudostratified ciliated columnar epithelium lines them. There is no cartilage at all in the bronchioles; what is left is primarily smooth muscle, which is regulated by the autonomic nervous system. The bronchioles have a diameter of less than 1 mm. The cuboidal epithelium that makes up their walls is ciliated.

Blood Supply

The bronchi receive arterial blood from the right and left bronchial arteries. The bronchial vein removes the venous blood.

Nerve Supply

The bronchus is supplied by both the sympathetic and parasympathetic nerve.

Functions of the Bronchi and Bronchioles

• Air from the outside environment can enter the lungs through the bronchi and bronchioles, where gaseous exchange can occur.
• They add to the incoming air's moisture.
• The bronchial cartilage maintains the airway open for simple airflow.
• The foreign particles cannot enter the alveoli because of the mucus in the bronchial wall.

Alveoli

There is a cluster of air sacs that resembles a bunch of grapes at the end of each of the terminal bronchioles. We refer to these sacs as alveoli. They have outpockets that resemble cups that surround the terminal bronchioles. In total, there are about 300 million alveoli in the human lungs.

Structure of the Alveoli

• Squamous (flat) epithelium is a single cell layer that makes up each alveolus.
• This incredibly thin wall makes it simple for gases to enter and exit the blood as it travels through the millions of minuscule capillaries in the alveoli.
• The actual surface for gas exchange is the alveolar membrane.
• Alveolar epithelial cells of two different types make up the walls of alveoli. Simple squamous epithelial cells known as type I cells make up the majority of the alveolar walls.
• Cuboidal epithelial cells known as type II cells secrete a fluid that contains surfactant and coats the alveolar surface.
• This fluid lowers the surface tension ("pull") of the fluids that border the alveoli, preventing them from collapsing.
• Alveolar macrophages, also known as dust cells, are found in the alveolar wall and are responsible for clearing the alveolar space of small dust particles and other detritus.
• Each kilogram of body weight corresponds to approximately one square meter of alveolar surface area. The capillary network covering this large surface area is dense, and the capillary and alveolar walls are both very thin.
• The respiratory membrane, which has gas on one side and blood flowing on the other, is made up of the alveolar and capillary walls working together. By diffusing across the respiratory membrane, gas exchange takes place.

Functions of the Alveoli

• Air and blood can exchange gases thanks to alveoli.
• Alveoli have a fluid that keeps them from collapsing.
• The alveolar macrophages clear the alveolar space of small dust and other debris.