Human Respiratory System: Diagram, Design and Functions

Human Respiratory System is composed of the airways (upper and lower), the lungs, and the blood vessels. The nose, paranasal sinus, and pharynx are the parts of the upper airways system while the lower airways system consists of the larynx, trachea, and stem bronchi.

• The lungs are soft spongy organs that function as the main site for the gaseous exchange.
• The major respiratory muscle, the diaphragm, and the intercostal muscles of the chest wall work together to push air into the lungs.
• The thorax's interior space is expanded and contracted by the muscles; the ribs and thoracic vertebrae make up its bony skeleton.

Read Also: Aerobic Anaerobic Respiration

Key Terms: Respiratory System, Nasal Cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveoli, lungs, vocal cord, olfaction.

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Human Respiratory System 

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Human Respiratory System is a complex biological system of organs and tissues that helps in gaseous exchange.

• The system comprises airways, lungs, and blood vessels.
• Its primary function is to introduce oxygen and expel carbon dioxide from the body.
• The atmospheric air is regularly pumped in and out through a system of pipes which are also known as the conducting airways.
• There are a vast number of muscles and blood vessels involved in the whole process of respiration.

Also Read: Oviparous and Viviparous

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Features of Human Respiratory System 

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The Human Respiratory System has the following important features-

• The respiratory system is crucial for inhalation of oxygen and transport of the same to the different parts of the body where it is used for cellular respiration.
• The design of the lungs is created in such a way that it helps in gaseous exchange in an efficient manner.
• The other parts of the respiratory system such as the nose, larynx, pharynx, trachea, bronchi help in the process of bringing in oxygen to the lungs and taking carbon dioxide out of it.
• There is an array of muscles such as the diaphragm and intercostal muscles that help in the process of human respiration.

Also Read: Muscle Contraction

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Design of the Human Respiratory System 

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The main gas-exchange organ, the lung, is located in the thorax region where it is protected by the strong and bony thoracic cage. The soft tissue of the lung provides the tissue of the human body with a regular flow of oxygen and carbon dioxide.

• The atmospheric air is pumped in and pumped out regularly into conducting airways.
• They join the gas-exchange region lung with the outside of the body.
• The whole system can be divided into upper and lower airway systems.
• The transition between these systems is located near the place where pathways of the respiratory and digestive systems cross, at the top of the larynx.

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Upper Airways System 

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The upper airway system in the human respiratory system comprises the nose and the sinus, the pharynx, and partly the oral cavity as sometimes it is used in the breathing process. Here, the morphology of the upper airways system has been stated below-

Nose

The nose is the external protuberance of the inner nasal cavity.

• It is divided into two parts- the right and the left canal separated by a cartilaginous septum called the nasal septum.
• Each canal opens to the pharynx by the choana and the outside by the nostrils.
• The interior lining of the nasal cavity is full of hair follicles that act as the first line of defense against pathogens.
• They also provide humidity to the inhaled air.

Paranasal Sinus

These are the sets of paired single or multiple cavities of different sizes.

• They are located in four different skull bones- the maxilla, the frontal, the ethmoid, and the sphenoid bones.
• The main functions of the paranasal sinuses are to keep the weight of the skull within a reasonable limit.
• They serve as the resonance chamber for the human voice.

The Pharynx

The nasal chamber opens up in a wide hollow chamber called the pharynx.

• It is used as the common passage for air and food particles in the windpipe.
• Elastic cartilage called epiglottis serves as a switch for the entry of air into the respiratory tract and food particles into the esophagus.
• It also connects the tympanic cavity of the middle ear.
• Anatomically the pharynx can be divided into three floors- the nasopharynx-primarily the passageway for air, the middle floor- the oropharynx and the lower floor hypopharynx.

Also Check: Lung Diseases

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Lower Airways System 

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The lower airway system comprises the larynx, the trachea, the stem bronchi and all the air tracts within the lungs.

The Larynx

The larynx is a complex structure that serves two important dual functions: i. air canal to the lungs and controller of its access and ii. as the organ of phonation.

• It is a triangle-shaped structure composed of about a dozen of cartilages that are attached to the surrounding structure by muscles or fibrous and elastic tissue components.
• The cavity of the larynx extends from its triangle-shaped opening to the epiglottis.
• The mucous membrane lining of the larynx forms two pairs of lateral folds – the upper vestibular fold, also known as the false vocal cord, and the lower folds, which are known as the vocal cords.
• The vocal cords produce the sounds for the speech and other vocalizations.

The Trachea and the Stem Bronchi

The trachea lies below the larynx and it’s a long tubular structure with characteristic horseshoe-shaped incomplete cartilage rings opened towards the back.

• The cartilaginous rings are crucial to maintaining the structure of the trachea during expansion.
• At its lower end, the trachea divides into two stems or main bronchi.
• The structures of the stem bronchi are similar to that of the trachea.

Lungs

The lungs are the most important organ of respiration in humans. Located in the chest cavity, they are responsible for adding oxygen to the blood and removing carbon dioxide from the blood. Lungs are the soft spongy, light, elastic organs connected with the trachea by its main bronchi and to the heart by pulmonary arteries.

• The human lungs are encased by a thin membranous layer called the pleura.
• The point at which the bronchi, pulmonary arteries and veins, nerves, and lymphatic vessels enter the lungs is called the hilum.
• The main bronchus subdivides numerous times inside the lung, giving rise to a system that looks like an inverted tree.
• The branches 3mm or less in diameter are called bronchioles.
• These are attached to the minute air sacs called alveoli, where the actual exchange of gas molecules takes place.

Read More: Central Nervous System

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Functions of Human Respiratory System 

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The functions of the Human Respiratory System are given below-

• Inhalation and Exhalation: The main function of the respiratory system is breathing or pulmonary ventilation. The air inhaled through the nostrils moves through the parts of the respiratory tract into the lungs where the gaseous exchange takes place. The carbon dioxide comes out of the system by following the same pathway. The changes in the pressure and the volume aid pulmonary ventilation.
• Exchange of Oxygen between Lungs and Bloodstream: Inside the spongy tissue of the lungs the oxygen and carbon dioxide enter and exit through millions of sac-like alveoli. The oxygen diffuses into the pulmonary capillaries. The oxygen diffuses out of the capillaries to bind with the haemoglobin in the blood for further transportation to the cells. The carbon dioxide from the blood diffuses into the blood and is ultimately carried out to the lungs for release.
• The vibration of the vocal cords: While we speak, the muscles in the larynx help to move the arytenoid cartilage and these cartilages push the vocal cords together. During exhalation, while air passes through the vocal cords it makes them vibrate to create sound.
• Olfaction or Smelling: When the air is inhaled it directly goes to the nasal cavity. On the roof of the nasal cavity, the sensory epithelium assesses the quality of the air while a dozen olfactory nerves send the sensation of smell to the central nervous system.

Also Read: Human Body: anatomy and physiology

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Things To Remember

• Human Respiratory System is the system that is solely responsible for the gaseous exchange.
• The respiratory system works for the inhalation of oxygen and transport of the same to the different parts of the body.
• It also helps in removing carbon dioxide from the body.
• The Human Respiratory System can be divided into two airways systems- the upper airways system and the lower airways system.
• The upper airways system comprises the nose, paranasal sinus, and pharynx.
• The lower airways system consists of the larynx, trachea and stem bronchi.
• The main function of the Human Respiratory System, as mentioned before, is to bring oxygen to the body and remove carbon dioxide as an excretory gas.

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