Wednesday January 22

Chapter 17 The Endocrine System

endocrinology : the study of hormone signaling and the various endocrine organs that secrete hormones

hormones : chemical messengers secreted by cells and extrecellular fluids (ex. blood, lymph), Regulate metabolic function of other cells

hormone targets : most cells of the body, reproduction, growth and development, stressor defense, electrolyte and water balance

endocrine glands : ductless glands that release hormones into surrounding fluid

1. Amino Acid Based : majority of hormones, couple with cell surface receptors
2. Lipid Based : derivatives of cholesterol, STEROIDS, couple with intracellular receptors

Target Cell Specificity :
specific protein receptors
on the plasma membrane (PM), or could be inside the cell

Target Cell Activation
depends on
1. blood level of the hormone
2. receptor levels
3. the affinity of the bond between hormone and receptor

Amino Acid Based Hormone Mechanism of Action
cell surface receptors : second messenger systems
1. cAMP (cyclic AMP)
2. PIP-calcium signaling

phosphatidyl inositel biphosphate (PIP2)
--> diaglycerol (DAG)
--> inositel triphosphate (IP3)

Steroid Hormone Mechanism of Action
intracellular receptors
nuclear receptors
1. hormone diffuses through PM
2. binds to its protein receptor
3. the hormone/receptor complex binds to specific sites on the DNA and regulate transcription
4. the DNA is transcribed into mRNA, which is translated into new protein

Cellular Responses to Hormones
1. alter the permeability of the PM
2. stimulate the synthesis of proteins or other regulatory modules
3. activate or deactivate enzymes
4. activate secretion of substances
5. stimulate mitosis

Duration of Hormone Activity
depends on concentration :
1. rate of release
2. rate of inactivation or removal
- mostly takes place in kidney and liver