Why do we expel co2

As every cell in our body needs energy, every one of them needs oxygen. The energy released is stored in a chemical compound called adenosine triphosphate ATP , which contains three phosphate groups. When we need energy to carry out an activity, ATP is broken down into adenosine diphosphate ADP , containing only two phosphate groups. Breaking the chemical bond between the third phosphate group and ATP releases a high amount of energy. Our lungs supply oxygen from the outside air to the cells via the blood and cardiovascular system to enable us to obtain energy.

As we breathe in, oxygen enters the lungs and diffuses into the blood. It is taken to the heart and pumped into the cells. At the same time, the carbon dioxide waste from the breakdown of sugars in the cells of the body diffuses into the blood and then diffuses from the blood into the lungs and is expelled as we breathe out.

One gas oxygen is exchanged for another carbon dioxide. This exchange of gases takes places both in the lungs external respiration and in the cells internal respiration. Fig 1 summarises gas exchange in humans. Our respiratory system comprises a conduction zone and a respiratory zone.

The conduction zone brings air from the external environment to the lungs via a series of tubes through which the air travels. These are the:. The nasal cavity has a large number of tiny capillaries that bring warm blood to the cold nose. The warmth from the blood diffuses into the cold air entering the nose and warms it. The lining of the pharynx and larynx which form the upper respiratory tract and the lining of the trachea lower respiratory tract have small cells with little hairs or cilia.

These hairs trap small airborne particles, such as dust, and prevent them from reaching the lungs. The lining of the nasal cavity, upper respiratory tract and lower respiratory tract contains goblet cells that secrete mucus. It also traps particles, which the cilia then sweep upwards and away from the lungs so they are swallowed into the stomach for digestion, rather than getting trapped in the lungs.

This mechanism of moving trapped particles in this way is known as the mucociliary escalator. The lungs are a little like balloons: they do not inflate by themselves, but only do so if air is blown into them. We can blow into the lungs and inflate them — which is one of the two techniques used for cardiopulmonary resuscitation — but that does not happen in the normal daily life of healthy people.

We have to inhale and exhale air by ourselves. How do we do that? We have two lungs right and left contained in the thoracic cavity chest. Surrounding the lungs are ribs, which not only protect them from damage but also serve as anchors for the intercostal muscles. Beneath the lungs is a very large dome-shaped muscle, the diaphragm. All these muscles are attached to the lungs by the parietal and visceral membranes also called parietal and visceral pleura.

The parietal membrane is attached to the muscles and the visceral membrane is attached to the lungs. The liquid between these two membranes, pleural fluid, sticks them together just as panes of glass become stuck together when wet. As the visceral membrane covers, and is part of, the lungs and is stuck by pleural fluid to the parietal membrane, when the muscles in the thorax move, the lungs move with them.

If air gets between the membranes, they become unstuck and, although the muscles can still contract and relax, they are no longer attached to the lung — as a result, the lung collapses. This abnormal collection of air in the pleural space is called a pneumothorax. If the pleural fluid liquid becomes infected, the person develops pleurisy. When the intercostal muscles contract, they move up and away from the thoracic cavity. When the diaphragm contracts, it moves down towards the abdomen. This movement of the muscles causes the lungs to expand and fill with air, like a bellows inhalation.

Conversely, when the muscles relax, the thoracic cavity gets smaller, the volume of the lungs decreases, and air is expelled exhalation. When the thoracic muscles contract, the volume of the lungs expands so there is suddenly less pressure inside them. The air already in the lungs has more space, so it is not pushing against the lung walls with the same pressure.

To equalise the pressure, air rushes in until the pressure is the same inside and outside. Conversely, when the muscles relax, the volume of the lungs decreases, the air in the lungs has less space and is now at high pressure, so the air is expelled until pressure is equalised.

In short:. The job of the conduction zone is to get air into the lungs while warming, moistening and filtering it on the way. Once the air is in the respiratory zone composed of the alveolar ducts and alveoli , external gas exchange can take place Fig 2.

The lungs contain thin layers of cells forming air sacs called alveoli, each of which is surrounded by pulmonary blood capillaries that are linked to the pulmonary arteries coming out of the heart. The alveoli are kept open by liquid secretions pulmonary surfactant so they do not stick together when air is expelled from the lungs. Premature babies do not have enough pulmonary surfactant, so they need some sprayed into their lungs. External gaseous exchange then takes place, using the principle of diffusion:.

In other words: we inhale, high concentrations of oxygen which then diffuses from the lungs into the blood, while high concentrations of carbon dioxide diffuses from the blood into the lungs, and we exhale.

Once in the blood, the oxygen is bound to haemoglobin in red blood cells, taken through the pulmonary vein to the heart, pumped into the systemic vascular system and, finally, taken to all the cells of the body. Inhaled oxygen enters the lungs and reaches the alveoli. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other.

Oxygen passes quickly through this air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled. Oxygenated blood travels from the lungs through the pulmonary veins and into the left side of the heart, which pumps the blood to the rest of the body see Function of the Heart Function of the Heart The heart and blood vessels constitute the cardiovascular circulatory system.

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. The function of the respiratory system is to add oxygen to the blood and remove carbon dioxide. The microscopically thin walls of the alveoli allow inhaled oxygen to move quickly and easily from the lungs to the red blood cells in the surrounding capillaries.

At the same time, carbon dioxide moves from the blood in the capillaries into the alveoli. 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. Of course, there are always plenty of new babies who start to respire as we expire.

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