Name: how air moves in and out of lungs
Uploaded: 2019-03-11T09:21:32.000Z
Duration: 1 min 5 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Human Anatomy and Physiology

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From Molecules to Organisms: Structures and Processes

9-12.HA.1.9

Breathing

In humans, the process of breathing, the inhalation and exhalation of air requires coordination between the lungs, the chest wall, and the diaphragm, a skeletal muscle that makes up the floor of the thoracic cavity.

During inhalation the diaphragm and the intercostal muscles connected to the ribcage contract, increasing the volume of the thoracic cavity, thereby inversely decreasing the pressure relative to the outside.

As a result of the drop in pressure, air, now moving from high to low pressure is pulled into the respiratory passageways and into the alveoli of the lungs.

When the diaphragm and rib muscles relax, the volume decreases which increases the pressure pushing air out of the lungs and body.

Thus, breathing is a rapid process of inflating and deflating the lungs with every breath.

breathing

The process of breathing, inhaling and exhaling, involves the coordinated movement of the chest wall, the lungs, and the muscles that move them. Two muscle groups with important roles in breathing are the diaphragm, located directly below the lungs, and the intercostal muscles, which lie between the ribs. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and creating more room for the lungs to expand. When the intercostal muscles contract, the ribs move upward and the rib cage expands, similarly expanding the thoracic cavity.

Each lung is surrounded by two membranes called plurae, which are separated by fluid. This fluid creates an adhesive force that causes the lungs to stretch as the thoracic cavity expands. The increased volume in the lungs reduces the pressure. When the pressure drops below atmospheric pressure, this produces a pressure gradient that moves air from the higher-pressure atmosphere into the lower-pressure lungs.

When the diaphragm and intercostal muscles relax, the volume of the lungs decreases, increasing the pressure in the lungs. As pressure increases beyond atmospheric pressure, the resulting pressure gradient pushes air out of the body. In this way, the cycle of inhaling and exhaling is maintained.

<h4>Pressure-Volume Relationship</h4>

Boyle&rsquo;s law states that, at a given temperature in a closed space, the pressure of a gas increases as the volume of its container decreases. Stated differently, pressure is inversely proportional to the volume. This law, combined with the movement of gas from higher-pressure to lower-pressure areas, explains why air is brought into the lungs when the diaphragm contracts.

<h4>How Do Lungs Increase in Volume?</h4>

The diaphragm contracts, moving downward and increasing the thoracic volume, but how does this increase the volume of the lungs? While bronchi and bronchioles are stiff and do not expand (although they can become blocked or inflamed), alveoli, tiny air sacs in the lungs, allow the lungs to increase in volume.

<h4>Restrictive vs. Obstructive Diseases</h4>

Pulmonary diseases decrease the flow of gas to and from the lungs and can be divided into two categories: restrictive and obstructive. Restrictive diseases, such as pulmonary fibrosis (scarring of the lung), restrict the expansion of the lungs. Obstructive diseases, like asthma, emphysema, and chronic bronchitis, obstruct the airway, limiting gas exchange.

<h4>Surfactant</h4>

The inner surfaces of alveoli are lined with fluid that contains surfactant, a mixture of phospholipids and lipoproteins. Surfactant reduces the surface tension of the alveolar fluid, preventing alveoli from collapsing and making it easier for alveoli to inflate with air.

Premature babies sometimes do not produce enough surfactant in their lungs, causing respiratory distress syndrome (RDS). Without sufficient surfactant, it takes a lot of energy to keep the alveoli open and filling repeatedly with air, making it difficult for babies with RDS to breath.

The process of breathing, inhaling and exhaling, involves the coordinated movement of the chest wall, the lungs, and the muscles that move them. Two ...

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KEY TERMS AND CONCEPTS

how air moves in and out of lungs

Breathing depends on pressure changes in the chest, the lungs, and the muscles that move them. The diaphragm, which sits below the lungs, and the intercostal muscles, which are between the ribs, work together to change the size of the thoracic cavity.

When the diaphragm contracts, it moves downward. When the intercostal muscles contract, the ribs move upward and the rib cage expands. Both actions increase thoracic volume and give the lungs more room to expand.

Each lung is surrounded by two membranes called pleurae, and fluid lies between them. This fluid creates an adhesive force that helps the lungs stretch as the thoracic cavity expands. As lung volume increases, pressure inside the lungs drops below atmospheric pressure. That pressure gradient pulls air from the higher-pressure atmosphere into the lower-pressure lungs.

When the diaphragm and intercostal muscles relax, the thoracic cavity gets smaller. Lung volume decreases, and the pressure inside the lungs rises. When lung pressure becomes higher than atmospheric pressure, air moves out of the body, and the cycle of inhaling and exhaling continues.

Boyle’s law helps explain this pressure-volume relationship. At a given temperature in a closed space, gas pressure increases as volume decreases. In other words, pressure is inversely proportional to volume. Together with movement from higher pressure to lower pressure, this law explains why air enters the lungs when the diaphragm contracts.

The lungs increase in volume because of the alveoli, which are tiny air sacs. The bronchi and bronchioles are stiff and do not expand, although they can become blocked or inflamed. Alveoli allow the lung tissue to expand during breathing.

Pulmonary diseases can reduce gas flow to and from the lungs. Restrictive diseases, such as pulmonary fibrosis, limit lung expansion because of scarring. Obstructive diseases, such as asthma, emphysema, and chronic bronchitis, block the airway and limit gas exchange.

The inner surfaces of the alveoli contain fluid with surfactant, a mix of phospholipids and lipoproteins. Surfactant lowers surface tension, so the alveoli do not collapse as easily and can inflate more easily. Premature babies may not make enough surfactant, which can cause respiratory distress syndrome, or RDS. Without enough surfactant, keeping the alveoli open and refilling them takes much more energy, making breathing difficult.

How Air Moves In and Out of Lungs

the respiratory system

Lungs, Airways, and Gas Exchange

The respiratory system moves air through the airways and into the lungs. Air enters through the nostrils and mouth, then passes the pharynx, or throat, and the larynx, or voice box. From there, it travels into the trachea, also called the windpipe. Inside the thoracic cavity, the trachea splits into two bronchi. These tubes carry air into the lungs. The bronchi divide into smaller bronchioles, which end in tiny air sacs called alveoli. Gas exchange happens in the alveoli. The respiratory...

Breathing depends on pressure changes in the chest, the lungs, and the muscles that move them. The diaphragm, which sits below the lungs, and the intercostal muscles, which are between the ribs, work together to change the size of the thoracic cavity. When the diaphragm contracts, it moves downward. When the intercostal muscles contract, the ribs move upward and the rib cage expands. Both actions increase thoracic volume and give the lungs more room to expand. Each lung is surrounded by two...

lung capacity

Lung Volume and Capacity Measures

Lung volume and lung capacity describe how air moves through the lungs and how much air stays inside them. Lung volume measures the amount of air taken in, released, or left over after a lung action, such as one breath. Lung capacity is a sum of two or more lung volume measures. There are four lung volumes. Tidal volume is the amount of air inhaled and exhaled in a normal breath. Inspiratory reserve volume is the extra air that can be inhaled after a regular breath in. Expiratory reserve...

gas exchange and transport

Alveoli and Capillaries in Gas Exchange

Gas exchange depends on the movement of oxygen and carbon dioxide between the lungs and the blood. During respiration, gases move along pressure gradients, which means they travel from higher partial pressure to lower partial pressure. In mammals, this exchange takes place in the alveoli of the lungs, where air and blood come very close together. When the lungs expand, pressure inside the lungs drops below atmospheric pressure. That drop draws oxygen-rich air into the lungs. The air in the...

anatomy of the circulatory system

Circulatory Pathways of the Heart and Blood

The human circulatory system moves blood through the heart, blood vessels, and the body. The heart works as a central pump. Blood vessels carry blood away from the heart, around the body, and back again. Humans have a double circulatory system. Blood travels through the heart twice as it moves through the pulmonary circuit and the systemic circuit. The pulmonary circuit sends blood between the heart and lungs. In the pulmonary capillaries, oxygen enters the blood and carbon dioxide leaves it. <br...

anatomy of the heart

Heart Chambers, Valves, and Blood Flow

The human heart has three tissue layers and is surrounded by the pericardium, a membrane that protects and confines it. The outermost layer, closest to the pericardium, is the epicardium. A pericardial cavity separates the pericardium from the epicardium. Beneath the epicardium is the myocardium, which is the middle layer. The innermost layer is the endocardium. The heart also has four chambers: the right atrium, right ventricle, left atrium, and left ventricle. These chambers contain two...

the cardiac cycle

How the Heart’s Beat Is Controlled

The heart’s beat is controlled by a repeating electrical pattern called the cardiac cycle. It combines contraction, or systole, with relaxation, or diastole. This rhythm keeps blood moving through the heart in a steady sequence. The cycle begins when electrical signals leave the sinoatrial, or SA, node in the wall of the right atrium. The signal spreads to the atrioventricular, or AV, node between the right atrium and right ventricle. This causes both atria to contract at the same time. When...

blood flow

Blood Flow Through Vessels

Blood flow moves from the heart into the aorta, the largest artery in the body, and then into smaller arteries, arterioles, and capillaries. As the vessels get smaller, the speed of blood flow decreases. When blood returns to the heart through venules and veins, its velocity increases again. This change in speed is linked to total cross-sectional area, which is the combined area of all the vessels in a group. Blood does not move from one vessel into just one smaller vessel. It spreads into...

key terms and concepts

Learn how the diaphragm, intercostal muscles, pleurae, Boyle’s law, alveoli, and surfactant work together to power inhaling and exhaling.

How Air Moves In and Out of Lungs | JoVE K12

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How Air Moves In and Out of Lungs

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