1. Chemical signals in animals

2. Endocrine system All hormone-secreting cells
Hormones – chemical signals secreted into body fluids, only eliciting responses in selected target cells
Functions along with the NS in maintaining homeostasis
Effects tend to be slower and longer-lasting

3. 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

4. Invertebrate Endocrine Systems
Hydra – hormones control method of reproduction
Mollusk – hormone 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

5. 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

6. 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

7. 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

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

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

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

11. Hormones control the reproductive cycle of human females