Name: alveoli and capillaries in gas exchange
Uploaded: 2019-03-11T09:21:33.000Z
Duration: 1 min 20 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Human Anatomy and Physiology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.HA.1.9

Gas Exchange and Transport

Oxygen supply and carbon dioxide removal are integral to cell performance and survival. This gas exchange is driven by diffusion of gas to areas of lower partial pressure. The pressure that is exerted by one gas in a mixture of gasses in different parts of the respiratory and circulatory systems.

When oxygen enters the lungs it mixes with residual air decreasing the alveolar partial pressure of oxygen and increasing the uptake of oxygen by the lungs. Oxygen then diffuses through the alveoli into the neighboring capillaries again moving into a lower partial pressure medium.

In the blood oxygen binds to the respiratory pigment hemoglobin found in red blood cells and travels to tissue where the partial pressure of oxygen is lower. So it dissociates from hemoglobin and is released.&nbsp;

In the same way carbon dioxide goes down its pressure gradient from tissue to blood and is transported back to the lungs where the pressure gradient drives carbon dioxide into the alveoli and oxygen into the blood, starting the cycle again.

gas exchange and transport

Gas exchange, the intake of molecular oxygen (O2) from the environment and the outflow of carbon dioxide (CO2) into the environment, is necessary for cellular function. Gas exchange during respiration occurs largely via the movement of gas molecules along pressure gradients. Gas travels from areas of higher partial pressure to areas of lower partial pressure. In mammals, gas exchange occurs in the alveoli of the lungs, which are adjacent to capillaries and share a membrane with them.

When the lungs expand, the resultant decrease in pressure relative to the atmosphere draws oxygen into the lungs. Air entering the lungs from the environment has a higher oxygen concentration and a lower carbon dioxide concentration than the oxygen-depleted blood that travels from the heart to the lungs. Thus, oxygen diffuses from the alveoli to the blood in the capillaries, where it can be delivered to tissue. Carbon dioxide, by contrast, diffuses from the capillaries to the alveoli, where it can be expelled through exhalation.

<h4>Partial Pressure</h4>

Gas flow is determined by the pressure gradient of each gas, with each gas moving down its gradient. The pressure exerted by an individual gas in a mixture of gases is its partial pressure, and each gas moves from a higher to a lower partial pressure. Thus, the movement of O2 and CO2 are not directly related.

<h4>The Big Picture</h4>

Oxygen is used by the human body to convert sugar and other organic molecules into the energy compound ATP during the process of cellular respiration. A byproduct of cellular respiration is CO2, which needs to be removed from cells or it will change the pH and damage the cells. Because oxygen is necessary to provide energy for crucial cellular functions, and CO2 cannot be allowed to build up, the human body needs a constant flow of blood to and from all tissue to enable gas exchange.

<h4>Alveoli</h4>

The respiratory and circulatory systems structurally and functionally meet at the alveoli. Alveoli and capillaries are intertwined and physically touch, and because both are typically one cell thick, gas exchange occurs easily between the two. Even though the lungs are not large, the amount of O2 and CO2 that is exchanged is huge because there are so many alveoli&mdash;hundreds of millions per lung&mdash;with a surface area of around 100 m2!

Gas exchange, the intake of molecular oxygen (O2) from the environment and the outflow of carbon dioxide (CO2) into the environment, is necessary for ...

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KEY TERMS AND CONCEPTS

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 lungs has more oxygen and less carbon dioxide than the oxygen-depleted blood arriving from the heart, so oxygen diffuses from the alveoli into the capillaries. Carbon dioxide moves in the opposite direction, from the capillaries into the alveoli, and is then removed during exhalation.

Partial pressure is the pressure exerted by one gas in a mixture of gases. Each gas follows its own gradient, so the movement of oxygen and carbon dioxide is not directly linked. This helps explain why oxygen enters the blood while carbon dioxide leaves it at the same time.

Oxygen is needed for cellular respiration, where cells use sugar and other organic molecules to make ATP, the body’s energy compound. Carbon dioxide is a byproduct of this process and must be removed from cells because it can change pH and damage cells if it builds up. For that reason, the body needs a steady flow of blood to and from tissues to keep gas exchange going.

The respiratory and circulatory systems meet at the alveoli. Alveoli and capillaries are intertwined and physically touch, and both are usually one cell thick, which makes diffusion easy. Even though the lungs are not large, gas exchange is very efficient because there are hundreds of millions of alveoli in each lung and the total surface area is about 100 m2.

Alveoli and Capillaries in Gas Exchange

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

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...

lung capacity

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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 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...

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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

Explore how alveoli and capillaries exchange oxygen and carbon dioxide using partial pressure, diffusion, and blood flow in the lungs.

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Alveoli and Capillaries in Gas Exchange

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