Gas Exchange

  • Gas exchange is the primary function of the lungs.
  • Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.

Oxygen cascade

  • The oxygen cascade describes the process of declining oxygen tension from atmosphere to mitochondria.

Alveolar PO2

  • PO2 in alveoli is 104 mmHg vs. 40 mmHg for the deoxygenated blood of the pulmonary arteries. So after .25 seconds, equilibrium is reached. That means that PO2 in the pulmonary capillary blood = 104 mmHg. 2) PCO2 in alveoli is at 40 mmHg vs. 45 mmHg in blood returning from tissues.

Alveolar gas equation

  • The partial pressure of oxygen in the pulmonary alveoli is required to calculate both the alveolar-arterial gradient of oxygen and the amount of right-to-left cardiac shunt, which are both clinically useful quantities.
  • The alveolar gas equation is a formula used to approximate the partial pressure of oxygen in the alveolus (PAO2):PAO2=(PB−PH2O)FiO2−(PaCO2÷R)where PB is the barometric pressure, PH2O is the water vapor pressure (usually 47mmHg), FiO2 is the fractional concentration of inspired oxygen, and R is the gas exchange ratio.

Pulmonary circulation

  • The pulmonary circulation is the portion of the circulatory system which carries deoxygenated blood away from the right ventricle, to the lungs, and returns oxygenated blood to the left atrium and ventricle of the heart. The term pulmonary circulation is readily paired and contrasted with the systemic circulation.

Tidal Volume

  • Tidal volume (symbol VT or TV) is the lung volume representing the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied. In a healthy, young human adult, tidal volume is approximately 500 mL per inspiration or 7 mL/kg of body mass.


  • Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, often respiratory disorders, and can cause tissue hypoxia as the blood is not supplying enough oxygen to the body.


  • Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (hypo meaning “below”) to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapnia) and respiratory acidosis.

Causes of Hypoventilation

  • Chronic obstructive pulmonary disease
  • Obesity
  • Trauma
  • Neuromuscular Disorder
  • Chest wall deformities
  • Myxedema
  • Central respiratory drive depression
  • Interference with the nerve tracts coming down through the spinal cord

Anterior Horn Cell

  • Anterior horn cells (α-motor neurons), located in the anterior gray matter of the spinal cord, are found at every segment and are concentrated in the cervical and lumbosacral enlargements.

Barre Syndrome

  • It is a rare disorder in which your body’s immune system attacks your nerves. Weakness and tingling in your extremities are usually the first symptoms. These sensations can quickly spread, eventually paralyzing your whole body.

Blood-Air barrier

  • Exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood, and from blood entering the alveoli. It is formed by the type 1 pneumocytes of the alveolar wall, the endothelial cells of the capillaries and the basement membrane between the two cells. The barrier is permeable to molecular oxygen, carbon dioxide, carbon monoxide and many other gases.

Shunted Blood

  • venous blood enters the bloodstream without passing through functioning lung tissue. Shunting of blood may result from abnormal vascular (blood vessel) communications or from blood flowing through unventilated portions of the lung

Intercostal Artery

  • The intercostal arteries are a group of arteries that supply the area between the ribs called the intercostal space.

Coronary Circulation

  • These include the great cardiac vein, the middle cardiac vein, the small cardiac vein, the smallest cardiac veins, and the anterior cardiac veins. Cardiac veins carry blood with a poor level of oxygen, from the myocardium to the right atrium. Most of the blood of the coronary veins returns through the coronary sinus.


  • anastomosis results from trauma or disease and may involve veins, arteries, or intestines. These are usually referred to as fistulas. In the cases of veins or arteries, traumatic fistulas usually occur between artery and vein.

Shunt equation

  • The Shunt equation quantifies the extent that venous blood bypasses oxygenation in the capillaries of the lung. Shunt and dead space are terms used to describe conditions where either blood flow or ventilation does not meet the other in the lung as it should for gas exchange to take place.

Bronchial circulation

  • The bronchial circulation is the part of the circulatory system that supplies nutrients and oxygen to the cells that constitute the lungs, as well as carrying waste products away from them.