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Respiratory System

Why can't humans breathe underwater? Why can′t humans breathe underwater? It is a known fact that water is made up of oxygen and hydrogen. But, when we go underwater, why do we require an oxygen cylinder and why are we unable to breathe under water? Have you thought about this mystery? – Humans cannot breathe underwater because our lungs do not have enough surface area to absorb enough oxygen from water, and the lining in our lungs is adapted to handle air rather than water. Read on the human respiratory system in detail to resolve the mysteries of breathing.

Learning Objectives

After completing the topic, the student will be able to:

  • Delineate the structures of respiratory system and their functions.
  • Describe the basic structure and function of human lungs.
  • Define "respiratory cycle" and distinguish between inspiration and expiration.
  • Understand and explore the mechanism of breathing control in lungs.
  • Explore how gases are exchanged during breathing.
  • Systematize the path of a molecule of oxygen as it passes from the human nose to an alveolus.
  • List some of the diseases/conditions that badly influence the mechanism of breathing.
  • Classify several common respiratory disorders according to their causative agents.
Inhale and Exhale The two lungs are located near the backbone on either side of the heart Their principal function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. This exchange of gases is accomplished in the mosaic of specialized cells that form millions of tiny, exceptionally thin–walled air sacs called alveoli.
Respiratory System

Lungs are located within our chest cavity inside the rib cage and are made of spongy, elastic tissue that stretches and constricts as we breathe. The airways that bring air into the lungs (the trachea and bronchi) are made of smooth muscle and cartilage, allowing the airways to constrict and expand. The lungs and airways bring in fresh, oxygen – enriched air and get rid of waste carbon dioxide made by your cells. They also help in regulating the concentration of hydrogen ion (pH) in blood.

Parts of lungs:

  • nasal cavity: chamber in from the nose where air is moistened and warmed.
  • epiglottis: a flap of tissue that closes over the trachea when you swallow so that food does not enter your airway.
  • larynx: voice box where the vocal cords are located.
  • trachea :rigid tube that connects the mouth with the bronchi (windpipe).
  • bronchus: a branch of the trachea that goes from the trachea into the lung (plural – bronchi).
  • bronchioles: numerous small tubes that branch from each bronchus into the lungs. They get smaller and smaller.
  • alveolus: tiny, thin – walled air sac at the end of the bronchiole branches where gas exchange occurs (plural – alveoli).
  • diaphragm: muscle at the base of the chest cavity that contracts and relaxes during breathing.
  • intercostal muscles: muscles along the rib cage that assist in breathing.
  • pleural membranes: thin, membranes that cover the lungs, separate them from other organs and form a fluid – filled chest cavity.
  • pulmonary capillaries: small blood vessels that surround each alveolus.
alveoli Closer look of alveoli Alveoli are the tiny air sacs in the lungs at the end of the smallest airways, where the exchange of oxygen and carbon dioxide takes place
Anatomy of a human lung

At the bottom of the trachea, or windpipe, there are two large tubes. These tubes are called the main stem bronchi, and one heads left into the left lung, while the other heads right into the right lung. Each main stem bronchus – the name for just one of the bronchi – then branches off into tubes or bronchi that get smaller and even smaller still, like branches on a big tree. The tiniest tubes are called bronchioles and there are about 30,000 of them in each lung. Each bronchiole is about the same thickness as a hair.

At the end of each bronchiole is a special area that leads into clumps of teeny tiny air sacs called alveoli. There are about 600 million alveoli in your lungs and if you stretched them out, they would cover an entire tennis court. Each alveolus – what we call just one of the alveoli – has a mesh – like covering of very small blood vessels called capillaries. These capillaries are so tiny that the cells in your blood need to line up single file just to march through them.

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