• The primary function of the lungs is gas exchange
  • Filters unwanted materials from the blood
  • It has metabolic functions and it acts as a reservoir for blood

Blood gas barrier

  • Where the diffusive gas exchange occurs


  • It is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax.


  • A micron is a millionth of a meter or a thousandth of a millimeter

Type 1 alveolar epithelial cell

  •  Type I cells are thin and flat epithelial lining cells, that form the structure of the alveoli. They are squamous (giving more surface area to each cell) and their long cytoplasmic extensions line more than 95% of the alveolar surface.

Capillary Endothelium

  • Endothelial cells are thin wafer-like cells joined at their borders and form the inner lining of the entire blood vascular system. In capillaries, the outer tunics of smooth muscle cells are absent and only the endothelium is present.

Extracellular Matrix

  • It is made up of the fusion of the basement membranes of the alveolar epithelium and the capillary endothelium

Stress Failure

  • When the stresses in the capillary walls rise to high levels, ultrastructural changes occur in the barrier, a condition known as stress failure.

Collagen Fibrils

  • Collagen fibrils are semi-crystalline aggregates of collagen molecules. These are actually bundles of fibrils. Each of the tissues has a different arrangement of these fibrils to give it different structure, shape and tensile strength.


  • A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework (stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of connective tissue in animals.

Fick’s laws of diffusion

  • Fick’s laws of diffusion describe diffusion and were derived by Adolf Fick in 1855. They can be used to solve for the diffusion coefficient, D. Fick’s first law can be used to derive his second law which in turn is identical to the diffusion equation.


  • A ridge at the base of the trachea (windpipe) that separates the openings of the right and left main bronchi (the large air passages that lead from the trachea to the lungs). Also called tracheal carina.


  • The trachea, colloquially called the windpipe, is a cartilaginous tube that connects the pharynx and larynx to the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from the larynx and branches into the two primary bronchi.

Lung parenchyma

  • Lung parenchyma is the substance of the lung outside of the circulation system that is involved with gas exchange and includes the alveoli and respiratory bronchioles, though some authors only include the alveoli.


  • Alveoli are an important part of the respiratory system whose function it is to exchange oxygen and carbon dioxide molecules to and from the bloodstream. These tiny, balloon-shaped air sacs sit at the very end of the respiratory tree and are arranged in clusters throughout the lungs.


  • The mucociliary transport system provides the means for drainage of secretory products and particulate matter out of the sinuses. It is dependent on proper ciliary function and mucus viscosity

Goblet Cells

  • Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin MUC5AC. The goblet cells mainly use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secretions, when under stress.The term goblet refers to the cell’s goblet-like shape. The apical portion is shaped like a cup, as it is distended by abundant mucus laden granules; its basal portion lacks these granules and is shaped like a stem.


  • A cilium is an organelle found on eukaryotic cells and are slender protuberances that project from the much larger cell body. There are two types of cilia: motile and non-motile cilia. The non-motile cilia are called primary cilia which typically serve as sensory organelles.

Clara Cells

  • Clara cells are non-ciliated, non-mucous, secretory cells in respiratory epithelium. These epithelial cells secrete several distinctive proteins, including Clara cell 10-kDa secretory protein (CCSP).

Epithelial cells

  • Epithelial cells are cells that come from surfaces of your body, such as your skin, blood vessels, urinary tract, or organs. They serve as a barrier between the inside and outside of your body, and protect it from viruses.

Columnar Cells

  • Columnar epithelial cells are taller than they are wide: they resemble a stack of columns in an epithelial layer, and are most commonly found in a single-layer arrangement.

Cuboidal cells

  • These cuboidal cells have large, spherical and central nuclei. Simple cuboidal epithelia are found on the surface of ovaries, the lining of nephrons, the walls of the renal tubules, and parts of the eye and thyroid. On these surfaces, the cells perform secretion and absorption.

Squamous cells

  • Squamous cells are the thin, flat cells that make up the epidermis, or the outermost layer of the skin. SCC is caused by changes in the DNA of these cells, which cause them to multiply uncontrollably.

Alveolar macrophages

  • Alveolar macrophages are the primary phagocytes of the innate immune system, clearing the air spaces of infectious, toxic, or allergic particles that have evaded the mechanical defenses of the respiratory tract, such as the nasal passages, the glottis, and the mucociliary transport system.

Weibel model of airways

  • The Weibel “A” model, developed in 1963, treats the lung as a single unit with regular, symmetric bifurcations although it is known that in the right lung the first generation airway produces three second generation airways while the left lung only gives rise to two second generation airways.

Pulmonary artery

  • One of the two vessels which are formed as terminal branches of the pulmonary trunk and convey un-aerated blood to the lungs. The two pulmonary arteries differ in length and anatomy. The right pulmonary artery is the longer of the two. It passes transversely across the midline in the upper chest and passes below the aortic arch to enter the hilum of the right lung as part of its root. The left pulmonary artery is the shorter of the two terminal branches of the pulmonary trunk. It pierces the pericardium (the sac around the heart) and enters the hilum of the left lung.

Systemic Artery

  • Systemic arteries are the arteries (including the peripheral arteries), of the systemic circulation, which is the part of the cardiovascular system that carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart.

Capillary bed

  • Capillaries are grouped together in capillary beds, which are simply a network of capillaries. Capillary beds are too small to see, but if you could see them, they would look like endless alleyways leading to virtually every tissue in your body. The rate of blood flow within a capillary bed is slow because there are so many different alleyways through which blood can travel.

Bronchial artery

  • The bronchial arteries supply blood to the bronchi and connective tissue of the lungs. They travel with and branch with the bronchi, ending about at the level of the respiratory bronchioles.