The Respiratory System

The respiratory system is responsible for breathing and inhaling vital oxygen. It also has the task of expelling CO2. After inhaling the air, the oxygen is bound with blood, which transports it and nutrients to the tissues. While the tissue is taking the oxygen from the blood, it's giving carbon dioxide in the blood. It is then taken to the lungs, and afterwards expelled from the body.

Nasal cavity

After the air enters our body, it passes through the nasal cavity. The nasal cavity is a large space filled with air, placed above and behind the nose. Its first task is to either cool down, or heat up the air to about the same temperature as our body. The second one is to humidify the air. The nasal hair and the mucosa inside the nasal cavity clean the dust particles and some bacteria and viruses. The mucosa is covered by mucus, which is responsible for filtering the air. The cilia (organelles in most of the cells) move the mucus and the particulate matter through the pharynx into the esophagus, which leads the mucus into the stomach, where it’s digested.

The nasal cavity is responsible for sensing different smells. It also contributes to the sensing of tastes and flavors.

Pharynx

The pharynx (Greek: “throat”) is a chamber that is placed below the nasal cavity and is connected to the larynx and the esophagus. It doesn’t only have respiratory functions but also digestive functions since the pharynx’s muscles, which are connected to the base of the skull, help push the food inside of the esophagus and prevent air from being swallowed.

The pharynx is subdivided into 3 parts: the nasal pharynx, the oral pharynx, and the laryngeal pharynx. The nasopharynx is basically the anterior region of the nasal cavity. The oral pharynx begins in the mouth and goes down the throat. There's a flap of tissue that covers the air passage to prevent food from entering the lungs. The isthmus connects the oral pharynx with the nasal pharynx. It allows us to breathe through the mouth and, if necessary, insert food through the nose, with the help of a nasogastric tube. The third region, the laryngeal pharynx, leads the food into the esophagus and the air into the larynx. Moreover, the pharynx has two tubes connected to the middle ears, that help regulate the air pressure on the eardrums.

Larynx

The larynx (also called the voice box) is a tube that leads the air from the pharynx to the trachea. It also produces vocal sounds and prevents food from entering the trachea. The larynx is made of cartilage, which prevents it from collapsing. These cartilaginous plates are held together by membrane and muscle fibers. They form Adam’s apple and tend to be replaced by bone cells.

The epiglottis is a flaplike projection into the throat. When food enters the mouth, the whole larynx rises to the epiglottis, and this way, it blocks the entrance to the respiratory tract. After the food enters the esophagus, the larynx relaxes.

The larynx has two openings on two sides. Both of them have large folds in the mucous membrane of the larynx. While the first pair is known as the 'false' vocal cords, the second is known as the true vocal cords, the glottis. Speech is produced when air comes from the lungs and vibrates the vocal cords. Sound exits the larynx, which after that is resonated in the upper cavities. If the larynx is removed, the human body can still produce sounds through the esophagus, but it doesn't work equally well.

Trachea

The trachea is a tube that leads the air from the larynx into the main bronchi, which ultimately leads the oxygen into the lungs. In most mammalian creatures, trachea is protected by a cartilage structure. It has the task of warming the air and preventing foreign particles from entering the lungs. It has a mucous-membrane layer full of cilia, which trap particles. There are also ducts that secrete mucus and water. There are also many lymphatic vessels that have the task of removing foreign particles.

The trachea is held together with a few cartilage rings. The trachea can lower and raise while breathing. Along the cartilage rings, there are muscle fibers. They narrow and shorten the trachea if needed. That happens when they have to, for example, reduce the amount of cold air and smoke entering the lungs, or while coughing.

Before entering the lungs, the air passes through the bronchi, a system of canals that lead the air to the air sacs, or alveoli, where oxygen is added to the blood and carbon dioxide is removed.

Lungs

The lungs are large breathing organs located in our chest. They are responsible for exchanging the carbon dioxide in our blood for oxygen, which is vital for the human body. Each of the two lungs is located in a membranous sac, the pleura. It's connected to the bronchi, which ultimately lead to the trachea, and the pulmonary arteries. The lungs are soft, light, spongy, elastic organs. When they are healthy, they float on water, if not, they sink.

The hilum is the point where the bronchi, the arteries, the lymphatic vessels, and the nerves enter the lung. It's about 2/3 of the actual length of the lung. After entering the lung, the primary bronchi split into many branches, which makes them look like a tree. All of these branches are connected to the alveoli. Each lung is divided into lobes. The right lung has three lobes, while the smaller left lung has two lobes. The lobes are divided from each other by tissue. Each lobe is subdivided into many lobules. Each lobule contains a bronchiole and branches, which lead to the alveoli on the walls of the lobule.

The alveoli, or pulmonary alveoli, are responsible for the exchange of gases. As already mentioned, they remove CO2 and take oxygen to distribute it into the body. The alveoli form some clusters, the alveolar sacs, which resemble grapes.