The endocrine system acts with nervous system to coordinate the body's activities. Both systems enable cells to communicate with others by using chemical messengers. The endocrine system uses chemical messengers called hormones that are transported by the circulatory system (blood). They act on target cells that may be anywhere in the body. The endocrine system is slower than the nervous system because hormones must travel through the circulatory system to reach their target. Target cells have receptors that are specific to the signaling molecules. The binding of hormones to the receptors on or within the target cell produces a response by the target cell.
The chemical messengers used by the nervous system are neurotransmitters. Neurotransmitters travel across a narrow space (the synaptic cleft) and bind to receptors on the target cell. The nervous system conducts signals much quicker than the endocrine system. Endocrine Vs Exocrine glands
Endocrine glands do not have ducts. Exocrine glands have ducts that carry their secretions to specific locations. Two Kinds of Hormones
Peptide hormones are composed of amino acids.
A peptide hormone binds to a cell-surface receptor, it does not enter the cell. The resulting complex activates an enzyme that catalyzes the synthesis of cyclic AMP from ATP. Cyclic AMP activates other enzymes that are inactive.
Cyclic AMP is a second messenger; the hormone is the first messenger. Other second messengers have been discovered. Steroid Hormones
Steroid hormones enter the cell and bind to receptors in the cytoplasm. The hormone-receptor complex enters the nucleus where it binds with chromatin and activates specific genes. Genes (DNA) contain information to produce protein as diagrammed below. When genes are active, protein is produced.
Steroid hormones act more slowly than peptide hormones because of the time required to produce new proteins as opposed to activating...