Delete Content. A plasma membrane is permeable to specific molecules that a cell needs. Transport proteins in the cell membrane allow for selective passage of specific molecules from the external environment. Each transport protein is specific to a certian molecule (indicated by matching colors).
The pancreas contains cells which release both insulin and glucagon. The endocrine system consists of a number of different glands which secrete hormones that dictate how cells and organs behave.
Thus the working muscle can take in glucose even though little insulin is present. Another hormone from the pancreas, glucagon, stimulates the liver to release glucose to provide fuel for the muscles. The pancreas secretes two hormones, insulin and glucagon, to help maintain blood glucose levels.