Explain the structure and function of the respiratory membrane.

The primary function of the basement membrane is to anchor down the epithelium to its loose connective tissue underneath. This is achieved by cell-matrix adhesions through substrate adhesion molecules (SAMs).

The basement membrane acts as a mechanical barrier, preventing malignant cells from invading the deeper tissues. Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called carcinoma in situ.

The basement membrane is also essential for angiogenesis (development of new blood vessels). Basement membrane proteins have been found to accelerate differentiation of endothelial cells.

The most notable examples of basement membranes is in the glomerular filtration of the kidney, by the fusion of the basal lamina from the endothelium of glomerular capillaries and the basal lamina of the epithelium of the Bowman's capsule, and between lungalveoli and pulmonary capillaries, by the fusion of the basal lamina of the lung alveoli and of the basal lamina of the lung capillaries, which is where oxygen and CO2 diffusion happens. Basement membrane is non cellular.

The respiratory membrane, also known as the air-blood barrier, is comprised of the fused basement membranes of the alveolar and capillary walls. It has gas flowing past on one side and blood flowing past on the other. Gas exchanges occur by simple diffusion through the respiratory membrane. Oxygen passes from the alveolar air into the capillary blood and carbon dioxide leaves the blood to enter the gas-filled alveoli.