Secretion
Secreted by the adrenal cortex, which is a gland located on the top of the human kidney, the hormone cortisol plays an important role in preparing the body to respond to stressful situations. Part of a class of hormones known as corticosteroids, cortisol is derived from cholesterol molecules, making it hydrophobic and insoluble in water.
In times of stress, the brain's pituitary gland will secrete adrenocorticotropic hormone (ACTH) into the blood stream. When ACTH reaches the adrenal cortex's cells, it bonds to their special receptors to trigger the increased production of cortisol molecules. Once complete, the hydrophobic cortisol molecules easily pass through the cell membranes into the capillaries and blood stream.
Transcortin (lit. "Corticosteroid-Binding Globulin")
Transcortin or "CBG" is a protein found in blood plasma that binds to about 75 percent of cortisol in circulation. In binding to cortisol, CBG inactivates it---helping regulate the hormone's immediate effects on glucose, fat and protein metabolism in the body. CBG also helps cortisol dissolve better in the water-based blood as it is pumped throughout the vascular system.
Meanwhile, most of the remaining cortisol binds to albumin, a common protein in blood that also inactivates the hormone while helping it dissolve in water.
Free Fraction Cortisol
Comprising roughly 5 percent of all cortisol secreted, free fraction cortisol is undissolved, unbound and chemically active. It circulates in the blood freely. When it comes in contact with a special cortisol receptor on the cells of the intestines and liver (via capillaries), it triggers the re-absorption of sodium and potassium as well as the breakdown of glycogen into glucose, respectively.
Tags: adrenal cortex, blood stream, cortisol molecules, percent cortisol