Human Anatomy:The Lungs

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Your lungs are a pair of pyramid-shaped organs inside your chest that allow your body to take in oxygen from the air. They have a spongy texture and are pinkish-gray in color. The lungs bring oxygen into the body when breathing in and send carbon dioxide out of the body when breathing out. Carbon dioxide is a waste gas produced by the cells of the body.

The process of breathing in is called inhalation. The process of breathing out is called exhalation. Breathing is a vital function of life. The lungs add oxygen to the blood and remove carbon dioxide in a process called gas exchange.

In addition to the lungs, your respiratory system includes airways, muscles, blood vessels, and tissues that help make breathing possible. Your brain controls your breathing based on your body’s need for oxygen.

Your lungs lie on each side of your breastbone and fill the inside of your chest cavity. The right lung is divided into three main sections called lobes, and the left lung has two lobes to allow space for the heart. Your left lung is slightly smaller than your right lung.

The airways are pipes that carry oxygen-rich air to your lungs. They also carry carbon dioxide, a waste gas, out of your lungs. The airways include your:

  • Mouth
  • Nose and linked air passages called the nasal cavity and sinuses
  • Larynx, or voice box
  • Trachea, or windpipe
  • Tubes called bronchial tubes, or bronchi, and their branches
  • Small tubes called bronchioles that branch off of the bronchial tubes

Air first enters your body through your nose or mouth, which wets and warms the air. Cold, dry air can irritate your lungs. The air then travels past your voice box and down your windpipe. The windpipe splits into two bronchial tubes that enter your lungs. A tough tissue called cartilage helps the bronchial tubes stay open.

Within the lungs, your bronchial tubes branch into thousands of smaller, thinner tubes called bronchioles. The muscular walls of the bronchioles are different from the bronchial tubes. The bronchioles do not have cartilage to help them stay open, so the walls can widen or narrow to allow more or less airflow through the tubes.

The thousands of bronchioles end in clusters of tiny round air sacs called alveoli. Your lungs have about 150 million alveoli. Normally, your alveoli are elastic, meaning that their size and shape can change easily. Surfactant coats the inside of the sacs or alveoli and helps the air sacs stay open.

Each of these alveoli is covered in a mesh of tiny blood vessels called capillaries. The space where the alveoli come into contact with the capillaries is called the lung interstitium. The capillaries connect to a network of arteries and veins that move blood through your body.

The pulmonary artery and its branches deliver blood rich in carbon dioxide and lacking in oxygen to the capillaries that surround the air sacs. Carbon dioxide moves from the blood into the air inside the alveoli. At the same time, oxygen moves from the air into the blood in the capillaries.

The Respiratory System. The image shows an enlarged view of the airways and lungs as well as the trachea; bronchial tubes, or bronchi; and bronchioles. The image also shows a close-up view of gas exchange at the alveoli. The blue arrows show the oxygen in the air you inhale passing into the bloodstream, and the green arrows show the carbon dioxide from your body passing out of the bloodstream. 

The pleura and the muscles used for breathing

The lungs are enclosed by the pleura, a membrane that has two layers. The space between these two layers is called the pleural cavity. The membrane’s cells create pleural fluid, which acts as a lubricant to reduce friction during breathing.

The lungs are like sponges; they cannot move on their own. Muscles in your chest and abdomen contract, or tighten, to create space in your lungs for air to flow in. The muscles then relax, causing the space in the chest to get smaller and squeeze the air back out.

These muscles include the:

  • Diaphragm, which is a dome-shaped muscle below your lungs. It separates the chest cavity from the abdominal cavity. The diaphragm is the main muscle used for breathing.
  • Intercostal muscles, which are located between your ribs. They also play a major role in helping you breathe.
  • Abdominal muscles. They help you breathe out when you are breathing fast, such as during physical activity.
  • Muscles of the face, mouth, and pharynx. The pharynx is the part of the throat right behind the mouth. These muscles control the lips, tongue, soft palate, and other structures to help with breathing. Problems with these muscles can cause sleep apnea.
  • Muscles in the neck and collarbone area. These muscles help you breathe in when other muscles involved in breathing are not working well or when lung disease impairs your breathing.

Damage to the nerves in the upper spinal cord can interfere with the movement of your diaphragm and other muscles in your chest, neck, and abdomen. This can happen due to a spinal cord injury, a stroke, or a degenerative disease such as muscular dystrophy. The damage can cause respiratory failure. Ventilator support or oxygen therapy may be necessary to maintain oxygen levels in the body and protect the organs from damage.

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