The endocrine system

THE ENDOCRINE SYSTEM
A. This system, along with the nervous system, aids in maintaining homeostasis in
the
human body.
B. The endocrine system is composed of collections of epithelial tissue known as
Glands.
C. Endocrine glands secrete their hormones into the bloodstream. These chemical
agents
then travel all over the body to stimulate specific cells or organs known as
Target Cells or Target Organs. Recall that exocrine glands release their
products through a
tube (duct) onto a body surface (skin or internal organ).
II. FUNCTIONS OF THE ENDOCRINE SYSTEM
A. Maintaining homeostasis
B. Regulating: metabolism, reproduction, growth and development
III. HORMONES-as noted earlier, these are chemical substances secreted by glands that
regulate
the metabolic functioning of cells and organs.
A. Hormones are classified based on their chemical structure. The major types of
hormones
include:
1. Amino acid-based hormones-these vary in size from small amino acids to
large
protein based hormones. Most human hormones are composed of amino
acids.
2. Steroid based hormones-are composed of compounds that are
synthesized from
cholesterol. The gonadal and adrenocortical hormones are steroid based.
3. Eicosanoids-these are typically released by cell membranes, and these
are often
involved in inflammation and allergic reactions. Examples of eicosanoids
include leukotrienes (regulate immune responses) and prostaglandins
(stimulate
inflammation and blood clotting).
B. Hormones are specific for certain target cells or target organs in the body.
C. Hormonal secretion is regulated by the nervous system. The Autonomic Nervous
System plays a key role in governing hormonal secretions. The release of most
hormones is regulated by a Negative Feedback System.
1. Hormone secretion is typically well regulated to prevent Hyposecretion
(deficient
production) and Hypersecretion (excessive production).
IV. MAJOR ENDOCRINE GLANDS
A. The Pituitary Gland (Hypophysis)-sits in the Sella Turcica of the sphenoid bone.
1. This gland secretes a number of important hormones.