Where is gas exchanged in the body

The heart pumps the blood to the lungs so it can pick up oxygen and then pumps oxygen-rich blood to the body Oxygen-deficient, carbon dioxide-rich blood returns to the right side of the heart through two large veins, the superior vena cava and the inferior vena cava.

Then the blood is pumped through the pulmonary artery to the lungs, where it picks up oxygen and releases carbon dioxide. To support the absorption of oxygen and release of carbon dioxide, about 5 to 8 liters about 1. At the same time, a similar volume of carbon dioxide moves from the blood to the alveoli and is exhaled. During exercise, it is possible to breathe in and out more than liters about 26 gallons of air per minute and extract 3 liters a little less than 1 gallon of oxygen from this air per minute.

The rate at which oxygen is used by the body is one measure of the rate of energy expended by the body. Breathing in and out is accomplished by respiratory muscles Control of Breathing Breathing is usually automatic, controlled subconsciously by the respiratory center at the base of the brain.

Breathing continues during sleep and usually even when a person is unconscious The function of the respiratory system is to move two gases: oxygen and carbon dioxide. Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.

Three processes are essential for the transfer of oxygen from the outside air to the blood flowing through the lungs: ventilation, diffusion, and perfusion. Diffusion is the spontaneous movement of gases, without the use of any energy or effort by the body, between the alveoli and the capillaries in the lungs. Air enters the lungs and travels through progressively narrowing passages to the alveolus, where gas exchange between the body and the atmosphere takes place.

With an average thickness of 0. Alveoli are hollow spherical shaped structures that are clustered in bundles resembling grapes on the vine. Their shape provides a greater surface area for atmospheric air to come into contact with pulmonary capillaries and facilitate gas exchange. The amount of air that enters and leaves the lungs in one breath is referred to as tidal volume Vt , which includes air that is unusable by alveoli air in the dead space because it remains in the areas of the lung that do not contain alveoli dead space and is therefore not useable for gas exchange.

Over the course of one minute, the volume of air entering and leaving the lungs is referred to minute volume Mv , and the volume of air that reaches the alveoli is referred to as alveolar ventilation VA. The physiology of breathing happens in two phases: 1 mechanical ventilations , and 2 cellular respirations. The process of mechanical ventilation is regulated by the brain to physically move air in and out of the lungs so that oxygen and carbon dioxide can be exchanged with atmospheric air.

During inhalation, the diaphragm contracts in a downward motion and the intercostal muscles contract pulling the ribs outward which causes the cavity containing the lungs to expand and enlarge. The inhalation process is considered an active process because it requires muscle contraction to move the diaphragm and ribs to create negative thoracic pressures.

Exhalation, on the other hand, is generally a passive process. In healthy persons when active contraction of the diaphragm and intercostal muscles ceases, the diaphragm and ribs move back to their relaxed positions.

The positive pressure that is created pushes air out of the lungs. This process is typically passive but can be active by recruiting accessory respiratory muscles when necessary, for instance when coughing, blowing out candles, or blowing up a balloon.

During the citric acid cycle, a series of reactions consume glucose, oxygen, and several other metabolic components to create 30 adenosine triphosphate ATP molecules. Only cells containing mitochondria are capable of creating ATP because the citric acid cycle occurs exclusively within cellular mitochondria.

Although the citric acid cycle produces essential ATP, it also produces carbon dioxide, a potentially harmful byproduct. The process of converting one glucose molecule into 30 ATP molecules also produces six carbon dioxide molecules. Red blood cells are durable unbound cells designed to carry oxygen and, to a lesser degree, carbon dioxide to and from body tissues while withstanding the forces of bouncing off the walls of the vascular system, collisions with other cells and the high pressure forces of the capillary networks.

Externally, their round shape combined with a relatively thick edge and a thinner center increases their surface area while still allowing for them to move freely through the vascular network. Internally, they are predominantly comprised of antioxidant enzymes and structural proteins that protect and support the cell.

However, they lack a nucleus and contain only a few organelles, which prevents them from dividing or repairing themselves. The average adult has about 25 trillion circulating red blood cells.

Each red blood cell contains about million hemoglobin molecules and each hemoglobin molecule can carry up to four oxygen molecules. This massive oxygen-carrying ability of red blood cells helps maintain some reserve oxygen capacity for the body.

The cardiovascular system is specially designed to move blood throughout the body. This system consists of two primary components, the heart pump and the vessels arteries, veins and capillaries.

The heart, which weighs — grams, is a relatively small organ with a large and unending job. The amount of blood pumped out of the heart in one beat is called stroke volume SV , which is on average 60— mL. The amount of blood pumped by the heart in one minute is called cardiac output CO. The transport system for blood throughout the body is the vascular system, which is divided into two circuits: the pulmonary and systemic circuits.

The systemic circuit circulates blood to the entire body via the left side of the heart. The right side of the heart right atrium and right ventricle receives oxygen-depleted, carbon-dioxide rich blood from the body via the superior and inferior venae cavae.

From there, blood passes through the right atrium into the right ventricle, where it is then pumped into the pulmonary circuit via the pulmonary artery. Once the blood is in the pulmonary arteries, it is pushed through the capillaries surrounding the alveoli of the lungs and collected in the pulmonary veins.

The pulmonary veins return the oxygen-rich blood, which has been depleted of carbon dioxide, to the left side of the heart. The left side of the heart left atrium and left ventricle receives the freshly oxygenated blood from the pulmonary circuit.

The blood passes through the left atrium into the left ventricle, where it is pumped to the body via the ascending and descending aorta.

Blood is pushed through the arterial network and into the capillaries at the tissue level and collected in the veins. The venous system collects the oxygen-depleted, carbon-dioxide rich blood from the body via the superior and inferior venae cavae, and the cycle repeats. Under normal conditions, blood pressure in the pulmonary circuit is much lower than the blood pressure in the systemic circuit. The cardiovascular system and the lungs play equally vital roles in the gas-exchange process.

An inefficiency of one system will compromise both. A ventilation-perfusion ratio of 0. The purpose of mechanical ventilation is to bring oxygen molecules into contact with alveolar capillaries of the lungs. The functionality of the lungs completely depends on the number of oxygen molecules that not only reach the alveolus but are able to pass through the alveolar membrane and reach the hemoglobin of the red blood cells.

Conversely, atmospheric air contains only 0. However, carbon dioxide will readily leave the tissues because the atmospheric concentrations are so low. Changing the atmospheric concentrations of either oxygen or carbon dioxide will affect their partial pressures and thus their absorption and elimination ratios. If oxygen levels are low, the partial pressure of oxygen will be low and less oxygen will diffuse into the lung tissues. If carbon dioxide levels are high, the partial pressure of carbon dioxide will be high, causing less carbon dioxide to diffuse out of the lung tissues.

As the blood plasma becomes saturated with oxygen the hemoglobin of the red blood cells will begin to bind with the excess oxygen molecules.

Once the partial pressure of oxygen drops below this level, oxygen molecules will begin to offload from the hemoglobin. This is what is known as the oxyhemoglobin dissociation curve. So when the red blood cells reach the capillaries of the body tissues, which contain a lower partial pressure of oxygen and higher partial pressure of carbon dioxide, the oxygen will leave the plasma and enter the tissues through the capillary walls.

This decreases the oxygen plasma concentrations and the partial pressure of oxygen, causing oxygen to unbind from the hemoglobin of the red blood cells and enter the plasma.

As carbon dioxide is released by the cells metabolizing oxygen, much of it is quickly bound to either a water molecule as carbonic acid or a hydrogen molecule and an oxygen molecule as bicarbonate.

Some carbon dioxide molecules, however, stay unbound. This creates a higher partial pressure of carbon dioxide in the tissues, which diffuses into the blood plasma and then binds to the hemoglobin of red blood cells.

When the red blood cells return to the capillaries of the lungs, the partial pressure of carbon dioxide in the blood plasma is higher than that of the capillaries and surrounding tissues. This pressure gradient causes carbon dioxide to diffuse out of the plasma, off the hemoglobin, through the capillary and alveolar walls and into the air space of the lungs to be exhaled. Additionally, some of the carbonic acid and bicarbonate will disassociate, freeing carbon dioxide molecules into the plasma and then the tissues of the lungs to be exhaled as well.

At the same time, the high partial pressure of oxygen in the alveolar tissues causes oxygen to diffuse back on to the hemoglobin of the red blood cells, and the cycle repeats. However, attempting to increase the pressure of oxygen by forcing a higher volume of air into the lungs will not necessarily increase the net movement of oxygen if the concentration of the forced air stays the same.

Pressure changes because of altitude can dramatically affect oxygen diffusion rates. At sea level, the partial pressure of oxygen is a little more than 3 PSI mmHg [ However, at 10, feet elevation, partial oxygen pressure drops to 2. This drop in pressure will reduce the oxygen molecule content of the air and reduce the oxygen diffusion rate.

The left lung is divided into two lobes: upper and lower. The right lung is divided into three lobes: superior, middle, and inferior. Within each lung is a respiratory tree, comprised of the bronchi and its branching subdivisions—the primary bronchi, which branches into the secondary bronchi, which branches into the tertiary bronchi , which branches into the bronchioles.

The bronchi deliver oxygen-rich air to the lungs, where gas exchange occurs in tiny air sacs called alveoli. Exhaled air oxygen-poor and carbon dioxide—rich go the reverse way—from the ends of the bronchioles and back up.

Alveoli are tiny air sacs in the lungs—1. Oxygen diffuses from the alveoli into the capillaries, which carry it out of the lungs and to the rest of the body; carbon dioxide diffuses into the alveoli and is then exhaled out of the body.

The respiratory membrane is the barrier through which oxygen and carbon dioxide are exchanged. In pulmonary circulation—circulation between the heart and lungs—the vasculature are flipped. While normally arteries bring oxygenated blood away from the heart to the rest of the body, the pulmonary arteries take deoxygenated blood away from the heart to the lungs for replenishment. The pulmonary veins, likewise, return oxygenated blood to the heart from the lungs.

Image captured from Human Anatomy Atlas. Be sure to subscribe to the Visible Body Blog for more anatomy awesomeness!