Human Respiratory System – Class 11 | Chapter – 17 | Biology Short Notes Series PDF

Human Respiratory System: Human Respiratory System is a network of organs and tissues that helps us breathe. The primary function of this system is to introduce oxygen into the body and expel carbon dioxide from the body.

Features of the Human Respiratory System

The Human Respiratory System 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)

Human Respiratory System

Parts of Human Respiratory System

  • Nose

We inhale air through our nose which is the first step in the process of respiration. The nose and nasal cavity are the initial segment of the body’s airway—the respiratory tract through which air moves—and are the principal external opening for the respiratory system. The nose is a cartilage, bone, muscle, and skin structure on the face that supports and protects the nasal cavity’s anterior section. Before being expelled into the environment, air leaving the body through the nose returns moisture and heat to the nasal cavity.

  • Larynx

These are two cartilaginous chords, situated at the joining pointof the pharynx and trachea. They are also called the voice box. The laryngopharynx and the trachea are connected by a brief piece of the airway. The larynx is found in the anterior part of the neck, slightly below the hyoid bone and above the trachea. The form of the larynx is determined by various cartilage components. The larynx has specific structures termed vocal folds, which allow the body to produce speaking and singing sounds in addition to cartilage. Vocal folds are mucous membrane folds that vibrate to make vocal sounds. The pitch produced by the vocal folds can be altered by altering the tension and vibration speed of the vocal folds.

  • Pharynx

The pharynx is a common path for the passage of both air and food, to their respective organ systems. The pharynx, often known as the throat, is a muscular funnel that runs from the nasal cavity’s posterior end to the esophagus and larynx’s superior end. The nasopharynx, oropharynx, and laryngopharynx are the three parts of the pharynx. The nasopharynx is the upper part of the pharynx that is located in the back of the nasal cavity. The nasopharynx receives inhaled air from the nasal cavity and transports it to the oropharynx, which is positioned in the back of the oral cavity. At the oropharynx, air inhaled through the mouth cavity enters the pharynx. The epiglottis is a flap of elastic cartilage between the trachea and the esophagus that serves as a switch between the two.

  • Trachea

The trachea or the windpipe is like a long tube that takes the inhaled air into the further process. It is divided into left and right bronchi. The trachea, or windpipe, is a 5-inch long tube coated with pseudostratified ciliated columnar epithelium and formed up of C-shaped hyaline cartilage rings. The trachea’s primary role is to maintain a free airway for air to enter and exit the lungs. Furthermore, the mucus produced by the epithelium lining the trachea collects dust and other impurities, preventing them from reaching the lungs. Mucus is moved superiorly toward the throat by cilia on the surface of epithelial cells, where it can be eaten and processed in the gastrointestinal system.

  • Bronchi

Bronchi are further subdivided into small, finer channels called bronchioles. These bronchioles have balloon or bag-like structures at their ends that are known as alveoli. The airway splits into left and right branches at the inferior end of the trachea, known as the main bronchi. Before branching off into smaller secondary bronchi, the left and right bronchi enter each lung. The secondary bronchi—two in the left lung and three in the right lung—carry air into the lobes of the lungs. Within each lobe, the secondary bronchi branches into several smaller tertiary bronchi. The tertiary bronchi are divided into several smaller bronchioles that travel throughout the lungs. Each bronchiole then differentiates into multiple smaller branches, known as terminal bronchioles, with a diameter of less than a millimeter. Finally, the air is carried to the lungs’ alveoli by millions of small terminal bronchioles.

  • Lungs

Then there are lungs. The inhaled air is purified, and the oxygen necessary for all the body functioning is passed to various organs through the blood vessels. The exchange of oxygen and carbon dioxide takes place in small bags, alveoli. And the impure air of the carbon dioxide is exhaled out of the body through the same tract. The lungs are a pair of big, spongy organs located in the thorax, above the diaphragm, and lateral to the heart. A pleural membrane surrounds each lung, providing space for it to expand as well as a negative pressure area relative to the rest of the body. As the lungs relax, they passively fill with air thanks to the negative pressure.

  • Respiratory Tract

The respiratory tract of the Human Respiratory System is a series of organs, starting from the external organs and going up to the internal ones. Each of these organs performs a distinct role in the respiratory system function.

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.

Functions of Human Respiratory System

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 to haemoglobin 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.

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By Team Learning Mantras