All of these must pass through the cell membrane. Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vescicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis.ll of these must pass through the cell membrane. Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vescicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis.
Many enzymes that occur in certain tissues are found in blood plasma at higher levels when the cancer involves that tissue. Enzymes are usually measured by determining the rate at which they convert a substrate to an end product, while most tumor markers of other types are measured by a test called an immunoassay.
More in Heart Disease. Cardiac enzymes (the old name), or cardiac biomarkers (the new name), are blood tests that are used to detect damage to heart muscle cells. Cardiac biomarkers are proteins from heart muscle cells that have leaked out into the bloodstream after an injury to the cardiac muscle. Creatine kinase and troponin are the two proteins currently measured in biomarker tests.