The first stage of constitutive secretion sees proteins from the rough endoplasmic reticulum (ER) travel through the Golgi apparatus. Clicking on each of the
thumbnail images will bring up a larger, labeled version of the
see the Flash movie for the following sequence of images,
Some unpolarized cells, such as certain white blood cells, only secrete one type of protein. These proteins are packaged into secretory vesicles and sent to the cell membrane.
Proteins destined for the constitutive secretion pathway must first leave the endoplasmic reticulum and pass through the Golgi apparatus. All eukaryotic cells use constitutive secretion to maintain their plasma membranes.
If no modifications are made to the protein while inside the Golgi, it will enter the default secretory pathway, and the secretory vesicle it is packaged into will be sent directly to the cell membrane for immediate secretion.