1. Chemical signals in animals

2. Key concepts
Hormones are compounds produced in one part of the body and transported to another location to produce specific responses; small amount s can induce substantial responses.
Chemical signals produced by the body are mostly produced by glands.
Hormones either affect a target effector organ directly or via the signal transduction pathway.
Effects of hormones vary depending on whether they bind to a receptor in the plasma membrane or within the nucleus of a cell.
Action of hormones is controlled by feedback mechanisms.
Hormones are classified by mode of transport or through chemical composition.
Diseases in the endocrine system occur when levels of hormones released are at an abnormal level or when receptors of that particular hormone are damaged.

3. Endocrine system Hormone-secreting cells
Chemical signals secreted into body fluids, eliciting responses in target cells
Functions with NS in maintaining homeostasis
Effects are slower and longer-lasting

4. Maintenance of Homeostasis by the ES and NS
Neurosecretory cells – nerve cells that secrete hormones into bloodstream (eg. epinephrine)
Feedback regulation
Positive feedback
Suckling  release of oxytocin  milk secretion
Negative feedback
Control of blood calcium and glucose levels

5. Invertebrate Endocrine Systems
Hydra –control method of reproduction
Mollusks –controls egg-laying
Arthropods – extensive endocrine systems for molting and maturity
Ecdysone  molting and promotion of adult features
Brain hormone (BH)  regulates production of ecdysone
Juvenile hormone (JH)  retention of larval characteristics

6. Chemical signals and their modes of action
Hormones bind to specific receptor proteins on/within target cells
Signal transduction pathway is initiated
Target cell changes its behavior to produce a response
most peptides, proteins and glycoproteins
steroids and thyroid hormones

7. Importance of signal transduction pathways
1) Different pathways in different cells  different responses to the same signal
2) Amplification of the single signal allows small amounts of hormones to have a large effect

8. Vertebrate endocrine systems
Hypothalamus integrates endocrine and nervous functions
Neurosecretory cells of the hypothalamus produce hormones
Stored and secreted by posterior pituitary
Affect anterior pituitary’s release of own hormones

9. Copyright © 2002 Pearson Education, Inc
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

10. Table 45.1 (continued)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

11. Feedback control loops: a closer look
Regulation of thyroid hormones
Regulation of glucose in the blood

12. Hormones control the reproductive cycle of human females