HUMAN RESPIRATORY SYSTEM

The respiratory system is a biological system that allows organisms to take in oxygen and expel carbon dioxide. It includes the organs and structures involved in breathing, which are responsible for exchanging gases between the body and the environment.

The human respiratory system is responsible for facilitating the exchange of gases between the body and the environment. Its main function is to take in oxygen and expel carbon dioxide, which is a waste product of cellular respiration.

Features of the Human Respiratory System

The respiratory system in humans has the following important features:

• The energy is generated by the breakdown of glucose molecules in all living cells of the human body.

• Oxygen is inhaled and is transported to various parts and are used in the process of burning food particles (breaking down glucose molecules) at the cellular level in a series of chemical reactions.

• The obtained glucose molecules are used for discharging energy in the form of ATP- (adenosine triphosphate)

Respiratory System Parts and Functions

Let us have a detailed look at the different parts of the respiratory system and their functions.

• Nose

The nose is the primary organ of the respiratory system responsible for detecting and processing inhaled air. It is located centrally on the face and serves as the entry point for air that is inhaled into the respiratory system.

The nose is made up of several parts, including the nostrils (also known as nares), nasal passages, nasal cavity, sinuses, and the olfactory epithelium. Air enters the nose through the nostrils and passes through the nasal passages, which are lined with mucus and tiny hairs called cilia. The mucus and cilia work together to filter, humidify, and warm the air, and to trap any foreign particles, such as dust or bacteria, that may be present in the air.

The nasal cavity is a hollow space inside the nose that contains the nasal conchae, which are bony protrusions that increase the surface area of the nasal passages. The sinuses are air-filled spaces located above and behind the nose that help to lighten the weight of the skull and provide resonance to the voice.

The olfactory epithelium is located at the top of the nasal cavity and is responsible for detecting smells. It contains specialized cells called olfactory receptor neurons that are capable of detecting and responding to different odor molecules.

Overall, the nose plays an important role in the respiratory system by filtering, warming, and humidifying inhaled air, as well as detecting and processing smells.

• Larynx

The larynx, also known as the voice box, is a structure located in the neck that plays a crucial role in the respiratory system. It is made up of cartilage, muscles, and other tissues, and serves as the entry point for air that is inhaled into the respiratory system.

larynx

The larynx also contains the vocal cords, which vibrate to produce sound and enable speech. Additionally, the larynx helps to protect the trachea and lungs from foreign objects by producing a cough reflex. Disorders of the larynx, such as laryngitis or vocal cord paralysis, can impact speech and breathing.

• Pharynx

The pharynx is a muscular tube-shaped structure located at the back of the mouth and nasal cavity that plays a critical role in both the respiratory and digestive systems. It is commonly known as the throat, and it extends from the base of the skull to the esophagus and trachea.

In the respiratory system, the pharynx serves as a passageway for air to travel from the nasal and oral cavities to the larynx and trachea. In the digestive system, the pharynx is a pathway for food and liquids to travel from the mouth to the esophagus.

The pharynx is divided into three regions: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx connects the nose to the rest of the pharynx, while the oropharynx and laryngopharynx are involved in both respiration and digestion.

• Trachea

The trachea, also known as the windpipe, is a tube-shaped structure that connects the larynx to the bronchi in the lungs. It is a vital part of the respiratory system and plays a key role in the process of breathing.

The trachea is made up of C-shaped rings of cartilage that help to keep the airway open, as well as smooth muscle and other tissues. The trachea is lined with a thin layer of cells that produce mucus, which helps to trap foreign particles and microorganisms in the air, and cilia, which move in a coordinated manner to push the mucus out of the airway.

As air travels down the trachea, it is warmed, moistened, and filtered before it enters the lungs. The trachea also contains sensory nerves that trigger the cough reflex in response to irritants or foreign objects in the airway.

• Bronchi

The bronchi are the two main branches of the trachea that extend into the lungs. They are large air passages that divide into smaller and smaller tubes known as bronchioles, which eventually lead to the tiny air sacs called alveoli where gas exchange occurs.

The right and left bronchi branch off at the bottom of the trachea, and each enters a lung. The right bronchus is wider and more vertical than the left bronchus, making it more susceptible to foreign object inhalation and subsequent blockages.

The bronchi are lined with mucus-producing cells and cilia, which work together to trap foreign particles and move them out of the airway. The bronchi also contain smooth muscle that can contract and relax, allowing the airways to adjust their diameter to control air flow to different parts of the lungs.

• Lungs

The lungs are a pair of large, spongy organs located in the chest that play a crucial role in the respiratory system. Their primary function is to exchange gases between the air we breathe and the bloodstream, delivering oxygen to the body and removing carbon dioxide.

The lungs are made up of several different structures, including bronchi, bronchioles, and alveoli. The lungs are also surrounded by a thin, protective layer known as the pleura, which helps to protect and cushion them.

The lungs are highly adaptable organs, and their size and capacity can change in response to various factors, such as exercise or disease.

Respiratory Tract

The respiratory tract in humans is made up of the following parts:

• External nostrils – For the intake of air.
• Nasal chamber – which is lined with hair and mucus to filter the air from dust and dirt.
• Pharynx – It is a passage behind the nasal chamber and serves as the common passageway for both air and food.
• Larynx – Known as the soundbox as it houses the vocal chords, which are paramount in the generation of sound.
• Epiglottis – It is a flap-like structure that covers the glottis and prevents the entry of food into the windpipe.
• Trachea – It is a long tube passing through the mid-thoracic cavity.
• Bronchi – The trachea divides into left and right bronchi.
• Bronchioles – Each bronchus is further divided into finer channels known as bronchioles.
• Alveoli – The bronchioles terminate in balloon-like structures known as the alveoli.
• Lungs – Humans have a pair of lungs, which are sac-like structures and covered by a double-layered membrane known as pleura.

Air is inhaled with the help of nostrils, and in the nasal cavity, the air is cleansed by the fine hair follicles present within them. The cavity also has a group of blood vessels that warm the air. This air then passes to the pharynx, then to the larynx and into the trachea.

The trachea and the bronchi are coated with ciliated epithelial cells and goblet cells (secretory cells) which discharge mucus to moisten the air as it passes through the respiratory tract. It also traps the fine bits of dust or pathogen that escaped the hair in the nasal openings. The motile cilia beat in an ascending motion, such that the mucus and other foreign particles are carried back to the buccal cavity where it may either be coughed out (or swallowed.)

Respiratory System Functions

The functions of the human respiratory system are as follows:

Inhalation and Exhalation

The respiratory system helps in breathing (also known as pulmonary ventilation.) The air inhaled through the nose moves through the pharynx, larynx, trachea and into the lungs. The air is exhaled back through the same pathway. Changes in the volume and pressure in the lungs aid in pulmonary ventilation.

Exchange of Gases between Lungs and Bloodstream

Inside the lungs, the oxygen and carbon dioxide enter and exit respectively through millions of microscopic sacs called alveoli. The inhaled oxygen diffuses into the pulmonary capillaries, binds Hb to and is pumped through the bloodstream. The carbon dioxide from the blood diffuses into the alveoli and is expelled through exhalation.

Exchange of Gases between Bloodstream and Body Tissues

The blood carries the oxygen from the lungs around the body and releases the oxygen when it reaches the capillaries. 

The oxygen is diffused through the capillary walls into the body tissues. The carbon dioxide also diffuses into the blood and is carried back to the lungs for release.

The Vibration of the Vocal Cords

While speaking, the muscles in the larynx move the arytenoid cartilage. These cartilages push the vocal cords together. During exhalation, when the air passes through the vocal cords, it makes them vibrate and creates sound.

Olfaction or Smelling

During inhalation, when the air enters the nasal cavities, some chemicals present in the air bind to it and activate the receptors of the nervous system on the cilia. The signals are sent to the olfactory bulbs via the brain.

Respiration is one of the metabolic processes which plays an essential role in all living organisms. However, lower organisms like the unicellular do not “breathe” like humans – instead, they utilize the process of diffusion. Annelids like earthworms have a moist cuticle which helps them in gaseous exchange. Respiration in fish occurs through special organs called gills. Most of the higher organisms possess a pair of lungs for breathing.