4ZSS0167 Human Anatomy And Physiology

Table of Contents


Discuss how the lower respiratory system facilitates gas exchange, and the physical principles that regulate it.


The tract or lower respiratory system is made up of the trachea and bronchus, bronchioles and bronchioles. There are also alveoli, which include the lungs.

This system draws air from the upper respiratory systems to absorb oxygen and release carbon dioxide.

Additional structures such as rib and thoracic cage, diaphragm support and protect these structures.

The function of the upper respiratory tract is to draw in air and then pass it down to the lower respiratory tract, towards the trachea.

The anatomy of the alveolar and the bronchial structures, as well as the drawing in and processing of the air by the structures of the lower respiratory tract, facilitate gas exchange.

The following essay will discuss the structure and function that lower respiratory systems facilitate gaseous exchange, as well as the physical principles that govern this process.

Gaseous exchange is governed by physical principles. These include diffusion of oxygen through the respiratory membrane, ventilation and exchange of gases.

Gaseous exchange is made possible by the lower respiratory tract, which follows the physical principles of gas exchange.

First, the diameter of the trachea is one inch and it is tubeless.

It runs from the bottom of the larynx to just below and behind your sternum, where it branches into smaller tubes known as bronchi.

Inhalation occurs when air is warm. It is filtered by the upper respiratory tract, which passes from the pharynx to the larynx and down to the trachea to reach the bronchi and lung.


These rings have a C-shaped gap on the posterior side. They help to bend the trachea when the oesophagus presses against food.

During exhalation, the deoxygenated air in the lungs returns to the trachea.

Bronchi are the next structure. They are the passageways that carry air into and out of the lungs.

From the bottom of the trachea, the tubes of primary bronchus split into secondary and tertiary lung bronchi. Finally, bronchioles are formed.

These tiny airways are responsible for delivering oxygen-rich air from the trachea to the lungs.

Inhalation is when deoxygenated blood rich in carbon dioxide escapes the lungs via the reverse route. (Ionescu 2013,

Bronchioles also have a similar mechanism. Smooth muscle relaxation in the bronchioles results in dilation, which allows for greater ventilation. This causes bronchoconstriction to occur.

The main and most important organ for gas exchange in the respiratory system is the lungs.

This organ is responsible for the exchange of oxygen and carbon dioxide.

It is enclosed within the thoracic cavity, which is divided into right and left lung.

Left lung has two lobes, and is slightly smaller than right lung.

The accommodating heart is found at the curve of the cardiac notch.

The right lung is composed of three lobes, with the diaphragm muscles sitting higher than the liver.

The oxygen taken from the air is absorbed in the bloodstream, which then passes through microscopic sacs called Alveoli into nearby capillaries (Albertine 2016,).

Deoxygenated or carbon dioxide waste is diffused in the opposite direction from alveoli to capillaries.

The deoxygenated oxygen is then expelled by the lungs during exhalation.

This organ is where the physical principle of gaseous exchanging takes place. It’s called diffusion.

The process of diffusion occurs when the blood in the pulmonary capillaries absorbs oxygen and releases carbon dioxide.

This is where carbon dioxide and oxygen are exchanged between blood and alveoli in the lungs (Protti and al.

Alveoli are where oxygen diffuses into bloodstreams and oxygen from the blood enters the alveoli.

This happens through diffusion, which requires a concentration gradient. Alveoli oxygen should have a higher partial pressure than blood. Also, alveoli carbon dioxide should be lower in concentration than blood.

This would allow for gaseous exchange via diffusion in the alveoli of the lungs and bloodstream (Mercer & Crapo 2015).

Alveoli also play a role in external respiration. The tiny air sacs that serve as bronchioles within the lungs allow for gaseous exchange.

Alveoli, the terminal end of the respiratory tract where external respiration occurs, are filled with oxygen by inhalation from bronchioles.

The oxygen is pumped into the bloodstream by passing through the alveoli and surrounding pulmonary networks.

Carbon dioxide is expelled by exhalation from the deoxygenated blood and diffuses into the alveoli.

The organ responsible for providing muscle for breathing and forming the floor of the thoracic cavity, the diaphragm.

This organ is responsible for the physical process of inhalation and exhalation.

Inhalation is characterized by contraction of the diaphragm and movement towards the abdominal cavity.

This allows the volume of the lungs and thoracic cavity to grow when it occurs during deep breathing (Weibel 2015).

Normal exhalation involves relaxation of the diaphragm, external intercostals muscles, and lungs. Thoracic cavity shrinkage occurs as air is expelled.

All the organs mentioned above have physical properties that allow for gaseous exchange.

The exchange of gases is the primary function of the respiratory system.

The exchange of gases is governed by three main principles. These are ventilation, perfusion, and diffusion.

The air flows inside and out of the lungs through the ventilation mechanism.

Diffusion is another mechanism. It is the spontaneous movement of gas without effort between the blood in the lungs’ capillaries and the gas in the alveoli. (Morrell 2015.

The gaseous exchange is also facilitated by perfusion, where oxygenated blood is circulated throughout the lungs.

For the exchange of oxygen and carbon dioxide between cells and their environment, partial pressure is crucial.

Alveoli and capillaries have thin walls that provide a surface area of 75 square meters.

In internal respiration, intracellular oxygen is used to produce ATP. It can also be produced by simple diffusion along partial pressure gradients.

Actual blood flow occurs through pulmonary circulation.

Because of its large surface area and thinness, the exchange of gases occurs at the air-blood interface.

Right ventricle blood is pumped into the lungs via pulmonary arterial.

This artery can be divided into right or left branches, which supply blood to both lungs.

The divided parts of the artery branch out and supply each lung with 2% blood. This is pumped from the right ventricle, which does not penetrate into the alveolar veins.

This is known as shunted blood, which drains into the left side of the heart without any alveolar gaseous exchange. (Gilbert Barness, Spicer, and Steffensen 2014).

The above discussion shows that the lower respiratory system structure facilitates efficient gas exchange.

This regular mechanism is responsible for the gaseous exchange in lower respiratory tract.

Due to diffusion towards the concentration gradient, diffusion takes place in alveoli.

The air is heated by the trachea and filtered down through the pharynx, larynx, and trachea to reach the lungs.

Bronchi are passageways that transport oxygen rich air from the trachea into the lungs.

The essential organs of alveoli, the lungs, are responsible for gaseous exchange. Oxygen diffuses into the alveoli and the surrounding pulmonary capillaries. This oxygen then reaches the bloodstream.

Deoxygenated blood also releases carbon dioxide through diffusion into the alveoli and is expelled via exhalation.

This is how the lower respiratory tract facilitates gaseous interchange efficiently, aligning with the physical principles.

Refer to

Anatomy and function of the lungs.

Murray and Nadel’s Textbook of Respiratory Medicine, Sixth Edition (pp.

2014, and Dashe, J.

Williams Obstetrics 24e.

Respiratory system.

Handbook of Pediatric Autopsy Pathology (pp.

The human respiratory system.

The Human Respiratory System (pp.

Leong, F.J.W.M.

Anatomy and Histology for the Human Lung.

A Color Atlas of Comparative Pathology of Pulmonary Tuberculosis, p.31.

Crapo, J.D.

The gas exchange area of the lungs.

Comparative Biology of the Normal lung (Second edition), pp.

Marie Krogh, One hundred years of pulmonary functions testing: A perspective on “The diffusion of gases through man’s lungs”.

The Journal of physiology 593(2) pp. 351-352.

Protti, A. and Andreis, D.T. Milesi. M.; Iapichino. G.E. Monti. M. Comini. B., Pugni. P. Melis. V. Santini. A., Dondossola. D. and Gatti. S. 2015.

Lung anatomy, energy load and ventilator-induced lung injuries.

The tricks that alveolar epithelial cells use to build a healthy lung.

American journal of critical and respiratory medicine, 191(5): pp. 504-513.

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