Introduction:

The cells of the human body require a constant stream of oxygen to stay alive. The respiratory system provides oxygen to the body’s cells while removing carbon dioxide, a waste product that can be lethal if allowed to accumulate. There are 3 major parts of the respiratory system: the airway, the lungs, and the muscles of respiration:

The airway

  • Nose
  • Mouth
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles

The lungs

act as the functional units of the respiratory system bypassing oxygen into the body and carbon dioxide out of the body.

The muscles of respiration:

  • Diaphragm
  • Intercostal muscles

Nasal cavity/ nose

  • The nose is the external protuberance of an internal space, the nasal cavity. It is subdivided into a left and right canal by a thin medial cartilaginous and bony wall, the nasal septum.
  • Each canal opens to the face by a nostril and into the pharynx by the choana.
  • The floor of the nasal cavity is formed by the palate, which also forms the roof of the oral cavity.

Pharynx:the pharynx can be divided into three floors:

  • Nasopharynges
  • Oropharynx
  • Laryngopharynx

Larynx:

The larynx is the short tube that connects the pharynx (throat) to the trachea (windpipe).

It runs at the front of the throat at the level of c3 to c6 vertebrae and lies anterior to the esophagus.

The function of the larynx:

  • It allows air to be directed into the respiratory organs for gas exchange.
  • The larynx is also the organ that is responsible for producing vocal sounds (phonation) and therefore it is commonly known as the voice box.
  • In addition, the larynx also plays a role in preventing food and drink from entering the respiratory system.

Cartilages of the larynx:

  • Single laryngeal cartilages:

–       Cricoid

–       Epiglottic

–       Thyroid

  • Paired laryngeal cartilages:

–       Arytenoid

–       Corniculate

–       Cuneiform

Trachea: below the larynx lies the trachea, a tube about 10 to 12 cm (3.9 to 4.7 inches) long and 2 cm (0.8 inches) wide. Its wall is stiffened by 16 to 20 characteristic horseshoe-shaped. Trachea (windpipe) the trachea (or windpipe) is a wide, hollow tube that connects the larynx (or voice box) to the bronchi of the lungs. It is an integral part of the body's airway and has the vital function of providing airflow to and from the lungs for respiration.

Lungs:

The inside of the thoracic cavities and the lung surface are covered with:

  • Serous membranes respectively
  • The parietal pleura
  • Visceral pleura
  • The parietal pleura can be subdivided into three portions:

–       The mediastinal costal

–       Diaphragmatic pleurae

Bronchi:a bronchus, is a passage of airway in the respiratory system that conducts air into the lungs. The first bronchi to branch from the trachea are the right main bronchus and the left main bronchus. Bronchiole any of the minute branches into which bronchus divides alveoli.

Blood supply, lymphatic drainage, and nerve supply:

  • The pulmonary arteries
  • Bronchial arteries.
  • The pulmonary vein
  • The bronchial veins drain the larger bronchi.
  • The principal function of the sympathetic (t2-4) supply to the lung is bronchodilatation, while the vagus fibers act as stretch receptors.

Respiration:the act of inhaling and exhaling air to exchange oxygen for carbon dioxide.

Exchange of gases:

  • Pulmonary ventilation (movement of air into and out of the lungs)
  • External respiration (in the lungs)
  • Internal respiration (in the tissue)

External respiration:

External respiration is the exchange of gases between the air filling the alveoli and the blood in the capillaries surrounding the walls of the alveoli. Air entering the lungs from the atmosphere has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than does the blood in the capillaries. The difference in partial pressures causes the gases to diffuse passively along their pressure gradients from high to low pressure through the simple squamous epithelium lining of the alveoli. The net result of external respiration is the movement of oxygen from the air into the blood and the movement of carbon dioxide from the blood into the air. The oxygen can then be transported to the body’s tissues while carbon dioxide is released into the atmosphere during exhalation.

Internal respiration:

Internal respiration is the exchange of gases between the blood in capillaries and the tissues of the body. Capillary blood has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than the tissues through which it passes. The difference in partial pressures leads to the diffusion of gases along their pressure gradients from high to low pressure through the endothelium lining of the capillaries. The net result of internal respiration is the diffusion of oxygen into the tissues and the diffusion of carbon dioxide into the blood.

Transportation of gases: The 2 major respiratory gases, oxygen and carbon dioxide, are transported through the body in the blood. Blood plasma can transport some dissolved oxygen and carbon dioxide, but most of the gases transported in the blood are bonded to transport molecules. Hemoglobin is an important transport molecule found in red blood cells that carries almost 99% of the oxygen in the blood. Hemoglobin can also carry a small amount of carbon dioxide from the tissues back to the lungs. However, the clear majority of carbon dioxide is carried in the plasma as bicarbonate ion. When the partial pressure of carbon dioxide is high in the tissues, the enzyme carbonic anhydrase catalyzes a reaction between carbon dioxide and water to form carbonic acid. Carbonic acid then dissociates into hydrogen ion and bicarbonate ion. When the partial pressure of carbon dioxide is low in the lungs, the reactions reverse, and carbon dioxide is liberated into the lungs to be exhaled.

Accessory muscles:

Diaphragm

origin: xiphoid process (posterior surface), lower six ribs and their costal cartilage (inner surface) and upper three lumbar vertebrae as right crus and upper two lumbar vertebrae as left crus. Insertion: central tendon nerve supply: motor nerve supply by the phrenic nerve (c3 c4 c5) and sensory supply by the phrenic nerve to central tendon and lower 6 or 7 intercostal nerve to peripheral parts.

Intercostal muscles:

  • they are three types:

–        external intercostal muscles.

–        internal intercostal muscles.

–       innermost intercostal muscles.