Question

Please give a brief yet thorough explanation of the physiology of the lungs broken down short enough and in bullets for a powerpoint.

Answer 1

The lungs, or rather, the respiratory system, can be “broken down” into five main parts: the upper airways, the trachea, the bronchi and bronchioles, and the alveoli.
The Upper Airways
The upper airways include the nasal cavity and mouth, the pharynx and the larynx. The reason these parts of the respiratory tract are all grouped under one name is that the purpose they all serve is to simply direct air into the lungs. As we breathe in, the upper airway warms the air and adds moisture to it so that it is more comfortable for our lungs
The Trachea
Once air moves down through the upper airways, it reaches the trachea, or “windpipe.” The trachea is basically a tube with an upside-down Y shape. It can be thought of as the first part of the lungs reached by air when inhaling. The trachea serves to direct air into the two lungs. The trachea has a protective coating of special cells that helps defend against inhaled dust and particles.
The Bronchi and Bronchioles
After the air passes through trachea, it moves into arms of the upside-down “Y,” the large airways called the left bronchus and the right bronchus. A series of tubes, known as the bronchi (large tubes) and bronchioles (small tubes) are referred to as the bronchial tree because they resemble the branches of a tree that get smaller and smaller as they get closer to the leaves. These structures, similar to the trachea, carry air further into the lung and attach finally at the alveoli, which are like the leaves.

The Alveoli
The alveoli, also known as air sacs, are responsible for the most important work done in the lung: the transfer of gases. The alveoli are very, very small sacs of air attached to the ends of the smallest airways, the bronchioles. The air sac is made of a very thin membrane (tissue). When we breathe air in, oxygen moves across that membrane and into the small blood vessels that go through the lung. Carbon dioxide and other gases from the blood cross the membrane and are then exhaled through the same structures that oxygen-rich air came in. Then, the process is repeated over and over again.

The pulmonary system exists on the most basic level to facilitate gas exchange from environmental air into the circulatory system. We breathe in oxygen, which diffuses into the blood for systemic circulation and ultimately produces ATP for use as energy on a cellular level, and we breathe out Carbon dioxide along with other metabolic byproducts from the body. This process is facilitated by the respiratory tract organs, which include the nose, throat, larynx, trachea, bronchi, and lungs. The lungs are further divided into five separate lobes, two on the left and three on the right. Each lobe is made up of small sacks of air called alveoli. There are approximately 300 million alveoli in healthy lungs
The overarching mechanism of breathing to ventilate alveoli breaks down into four aspects: lung compliance, chest wall compliance, airway resistance, and rate of ventilation. These components work to facilitate the principle that as the lung expands, the air pressure in the alveoli drops, causing air to move into the lungs. As lung volume decreases, pressure increases, forcing air out of the lungs.

Lung compliance is based on the elastic properties of the supporting tissues surrounding the alveoli and the surface tension of the alveoli. The mathematical equation is:

Lung compliance = 1/elastance or change in lung volume/change in lung pressure
Elasticity is controlled by the content of elastin (stretchy fibers) and collagen (stiff structural fibers) within lung tissue. The surface tension of the alveoli describes the ease at which the alveoli are allowed to expand. A high surface tension tends to cause alveoli to collapse and not expand with aeration. Surface tension is reduced by type II pneumocyte cells within the lung which produce a liquid secretion composed of approximately 40% dipalmitoylphosphatidylcholine, 40 % other phospholipids, and 20 % other lipids.

Chest wall compliance is similarly based on elastic properties. However, this is more of a balance of chest wall elastic recoil, which tries to increase lung volume, and the lung’s elastic properties, which are trying to decrease lung volume.
Airway resistance is based on the physics principle of Ohm’s law where:
Flow rate = change in pressure/resistance of the airway
Resistance = 8(viscosity of air)(length of the tube)/(3.14)(radius of the tube)^4
it is important to make some basic assumptions. The viscosity of air does not change, and the length of the airway does not change. This leaves the only variable in the equation that physiologically adjusts to be the diameter of the airway. The resistance of breathing, therefore is primarily controlled by the airway diameter. Diameter change has three primary etiologies: intraluminal, such as secretions blocking the airway; intramural, such as edema or the interstitial space; or extraluminal, such as loss of interstitial collagen and elastic traction tissues.

1. Finally, the rate of ventilation increases the exchange rate of oxygen from the environmental air into the lung and removes carbon dioxide out of the lung to maintain favorable concentrations of these gasses to facilitate diffusion.