CHAPTER 8: THE ENDOCRINE SYSTEM
Overview of The Endocrine System & Homeostasis
The endocrine system contributes to homeostasis by regulating the activity, metabolism and growth of target cells and also regulate reproduction. During ‘puberty’, fillies & colts begin to show the effects of the endocrine system. In fillies, estrogens promote the accumulation of adipose tissue in mammary glands. Increasing levels of testosterone in colts help to build muscle mass. In addition, the multitudes of hormones help regulate the activity of smooth muscle, cardiac muscle, and some glands; alter metabolism; spur growth and development; influence reproductive processes; and participate in circadian rhythms (daily). The nervous system and endocrine systems work together to coordinate the functions of all the body systems. Recall that the nervous system acts through nerve impulses (action potentials) conducted along axons of neurons. At synapses, nerve impulses trigger the release of a mediator (messenger) molecule called a Neurotransmitter (NT). Similarly, the endocrine system also controls body activities by releasing mediators called Hormones but the means of control for the two systems are very different. Both hormones and neurotransmitters exert their effects by binding to receptors on the target cell. Several mediators act as both a NT and hormone.
Example:
Responses from the endocrine system are generally SLOWER than responses of the nervous system however, they generally have a longer effect whereas the actions of the nervous system are more brief. The effects of the nervous system are specific (specific muscles or glands) whereas the endocrine effects are more global and broader. In summary, the nervous system and the endocrine system act in an interlocking fashion to produce a “Super System” for control bodily functions.
Endocrine versus Exocrine Glands
The body contains 2 types of gland: endocrine and exocrine.
1) Exocrine Gland : secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body.
Examples:
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