Human Respiratory System: Definition, Diagram and Examples

What is Respiration?

Breathing is a fundamental life-sustaining mechanism by which people and all other living things metabolise oxygen and release carbon dioxide, a by-product into the environment. Lungs, the trachea, and the diaphragm are used to help facilitate the exchange of gases. Being one of the main regulatory and metabolic functions that are associated with every cell, the respiratory system is a vital component of human physiology. In respiration, air is directly taken into the lungs then the oxygen in it is transported to the various cells for metabolic purposes. At the same time, the carbon dioxide resulting from metabolism is transported back to the lungs to be expelled through exhalation maintaining the health of all tissues/organs in the body.

Anatomy of the Human Respiratory System

The human respiratory tract has the following parts:

Nose and Nasal Cavity

• Structure and function: The principal pathways for air are the following: the external opening made of the nostrils, internal concha, and nasal septum.

• Role in filtering and humidifying air: This structure prevents the entry of dust and pathogens by using nasal hair and mucous membranes. They also heat and moisten the incoming air to increase protection for the highly sensitive structures of the respiratory tract.

Pharynx and Larynx

Structure and function: The Pharynx is a muscular passage that forms a common wall of the nasal and oral cavities and it also connects to the larynx. The larynx, also known as the voice box is located below the pharynx and is found to contain the vocal cords.

Role in directing air to the lungs: The pharynx helps guide the air from the nose and mouth to the larynx and then to the trachea so that a proper distribution to the lungs is facilitated.

Trachea and Bronchi

Structure and function: The Trachea is a tubular structure made of cartilage that begins at the larynx and moves down to the chest where it branches off to the main bronchi.

The division into bronchi and bronchioles: The trachea branches into two parts of the bronchus the left and right which continue into the lungs branching out into smaller bronchial tubes which enable the distribution of the air within the lungs.

Lungs

Structure of the lungs: Lungs are two large spoke air-containing organs located in the thoracic cavity which is sheltered by ribs.

Lobes of the lungs: The right lung has three lobes; the right upper lobe, the right middle and the right lower lobe while the left lung has only two lobes; the left upper lobe and the left lower lobe because of the presence of the heart.

Alveoli

Structure and function: Alveoli are enormously small, these are the terminal branches of bronchial tubes which are again covered by a web of capillaries.

Gas exchange process: This is of significance in regards to the process of respiration as well as oxygenation of the alveoli tissues, they facilitate the exchange of oxygen and carbon monoxide in the air to the bloodstream or vice versa where needed most of the time.

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Gas Exchange and Transport

This involves the following process:

Gas Exchange in the Alveoli

Diffusion of oxygen and carbon dioxide: This process of gas exchange in alveoli is conducted through the process of diffusion in which the oxygen content has a freedom of movement from the alveolar surface to blood at the capillary walls while, on the other hand, the carbon dioxide from blood has the freedom of movement and get accumulated at the alveolar surfaces.

Partial pressures of gases: The diffusion process is stated through the partial pressure for oxygen and carbon dioxide; oxygen has a higher partial pressure in the alveoli than in the blood while carbon dioxide has a higher partial pressure in the blood than in the alveoli.

Transport of Oxygen

Binding to hemoglobin in red blood cells: When oxygen gets in the blood it combines with the hemoglobin of the red blood cells to form what is known as oxyhemoglobin, which is then distributed to various tissues of the body.

Transport of Carbon Dioxide

Conversion to bicarbonate ions: Carbon dioxide generated by the cells moves out of the cells into the plasma; the major portion of it is changed to bicarbonate owing to the enzyme carbonic anhydrase present in the red blood cells.

Transport in plasma and red blood cells: The CO2 is transported in 3 forms in blood; First dissolved in blood plasma, secondly, bound to the haemoglobin forming carbaminohemoglobin, and finally as bicarbonate ions in the blood which is the most common form of CO2 that is transported back to the lungs for exhalation.

Respiratory System Functions

The functions of the respiratory system are:

Inhalation and Exhalation

The respiratory system helps in inhalation whereby the diaphragm muscle and the muscles between the ribs expand to take in air during breathing and exhalation whereby the diaphragm muscle and the muscles between the ribs contract and force out air from the lungs during the process of breathing.

Exchange of Gases between Lungs and Bloodstream

Oxygen penetrates alveolar walls to access the capillaries on the same note, carbon dioxide that is within the blood gets to pass through the alveoli to get eliminated through respiration thus in the process helping regulate the concentration of these gases in the body.

Exchange of Gases between Bloodstream and Body Tissues

Blood containing oxygen gets transported to the several tissues of the body where oxygen is utilised in several activities and the carbon dioxide which is the end product of any metabolism is transported back to the lungs.

The Vibration of the Vocal Cords

It is a part of the respiratory system and also contains vocal cords, which vibrate and create sound as the air is breathed out. This function can allow for talking and phonic communication in one way or another.

Olfaction or Smelling

The nasal cavity has olfactory receptors that can detect chemicals floating in the air which gives the sense of smell. These receptors transport some impulses to the brain and they help in the feeling of scent.

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