1. Chapter 18a The Endocrine System
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2. Functional Organization of
Chapter 18a
Functional Organization of
Endocrine System

3. Endocrine System Characteristics
Produce hormones
In minute amounts secreted into interstitial spaces
Enters circulatory system
Acts on target tissues at another site
Regulate activities of body structures
Amplitude modulated signals
Frequency-modulated signals
Response slower and longer duration than nervous system

4. Chemical Signals
Intercellular: Allow one cell to communicate with other cells as hormones
Autocrine
Released by cells and have a local effect on same cell type from which chemical signals released as prostaglandin
Paracrine
Released by cells and affect other cell types locally without being transported in blood as somatostatin
Pheromones
Secreted into environment that modify behavior and physiology as sex pheromones

5. Chemical Structure of Hormones

6. Control of Secretion Rate
Most hormones are not secreted at constant rate
Patterns of regulation
Involves action of substance other than hormone on an endocrine gland
Involves neural control of endocrine gland
Involves control of secretory activity of one endocrine gland by hormone or neurohormone secreted by another endocrine gland

7. Nervous System Regulation

8. Hormonal Regulation

9. Positive and Negative Feedback

10. Control of Secretion Rate
Negative-feedback
Mechanisms that function to maintain homeostasis control most of hormone secretion
Mechanisms of hormone secretion from endocrine tissue
Nonhormone substance
Stimulation by nervous system
Hormone from another endocrine tissue

11. Transport and Distribution
Hormones dissolve in blood plasma and are transported in free form or bound to plasma proteins
As concentration of free hormone molecules increase, more hormones molecules diffuse from capillaries into interstitial spaces to bind to target cells

12. Transport and Distribution
A large decrease in plasma protein concentration can result in loss of a hormone from the blood because free hormones are rapidly eliminated from circulation through kidney or liver
Hormones are distributed quickly because they circulate in the blood

13. Metabolism and Excretion
Half-life: The length of time it takes for half a dose of substance to be eliminated from circulatory system
Long half-life
Regulate activities that remain at a constant rate through time
Short half-life
Water-soluble hormones as proteins, epinephrine, norepinephrine
These hormones have a rapid onset and short duration
Hormones also eliminated by blood by excretion by
Kidneys and liver
Enzymatic degradation
Conjugation
Active transport

14. Hormone Interaction with Target Tissues
Hormones
Ligands or chemical signals
Binding site
Receptor site
Specificity

15. Target Cell Response to Hormones
Target tissues have receptor molecules specific for particular hormone

16. Down and Up-Regulation
Down-regulation
Number of receptors decreases within target cells
Up-regulation
Some stimulus causes number of receptors for a hormone to increase within target cell

17. Classes of Hormone Receptors
Membrane-bound receptors bind to water-soluble or large-molecular-weight hormones
Intracellular receptors bind to lipid-soluble hormones

18. Membrane-Bound Hormone Receptors
Proteins or glycoproteins that have polypeptide chains folded to cross cell several times
Results of ligand binding
Changes permeability of plasma membrane
Alters activity of G proteins
Alters activity of intracellular enzymes

19. Activation of G Proteins

20. G Proteins and Ca2+ Channels

21. G Proteins and Synthesis of cAMP

22. Membrane-Bound Receptors

23. Cascade Effect

24. Intracellular Receptors
Are proteins in cytoplasm or nucleus
Hormones bind with intracellular receptor and receptor-hormone complex activates genes, DNA activated to produce mRNA, mRNA initiates production of certain proteins (enzymes) that produce response of target cell to hormone
Slow-acting because time is required to produce mRNA and protein
Processes limited by breakdown of receptor-hormone complex

25. Intracellular Receptor Model
Positive and Negative Feedback