Hormones and the Endocrine system

1. Chapter 45 Hormones and the Endocrine system

2. Overview: The Body’s Long-Distance Regulators • Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body. • Hormones reach all parts of the body, but only target cells are equipped to respond. • Insect metamorphosis and many other processes are regulated by hormones. • P.S. – Plants have hormones too

3. Overview: continued… • Two systems coordinate communication throughout the body: the endocrine system and the nervous system. • The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior. • The nervous system conveys high-speed electrical signals along specialized cells called neurons.

4. Hormones trigger specific responses • Chemical signals bind to receptor proteins on target cells. • Only target cells respond to the signal.

5. Types of Secreted Signaling Molecules • Secreted chemical signals include: • Hormones • Local regulators • Neurotransmitters • Neurohormones • Pheromones

6. What is a Hormone? • Endocrine chemicals secreted into extracellular fluids and travel in the bloodstream. • Endocrine glands are ductless and secrete hormones directly into surrounding fluid. • Hormones mediate responses to environmental stimuli and regulate growth, development, and reproduction.

7. Fig. 45-2a • Blood • vessel • Response • (a) Endocrine signaling • Response • (b)Paracrine signaling • Response • (c) Autocrine signaling

8. Not all Glands are Endocrine. • Exocrine glands have ducts and secrete substances onto body surfaces or into body cavities (for example, tear ducts).

9. Local Regulators • Local regulators are chemical signals that travel over short distances by diffusion. • Local regulators help regulate blood pressure, nervous system function, and reproduction. • Local regulators are divided into two types: • Paracrine signals act on cells near the secreting cell • Autocrine signals act on the secreting cell itself

10. Fig. 45-2a • Blood • vessel • Response • (a) Endocrine signaling • Response • (b)Paracrine signaling • Response • (c) Autocrine signaling

11. Neurotransmitters and Neurohormones • Neurons (nerve cells) contact target cells at synapses. • Neurons secrete chemical signals called neurotransmitters that diffuse a short distance across the synapse to bind to receptors on the target cell.

12. Fig. 45-2b • Synapse • Neuron • Response • (d) Synaptic signaling • Neurosecretory • cell • Blood • vessel • Response • (e) Neuroendocrine signaling

13. Neurohormones: • Are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream. • Endorphins are an example.

14. Fig. 45-2b • Synapse • Neuron • Response • (d) Synaptic signaling • Neurosecretory • cell • Blood • vessel • Response • (e) Neuroendocrine signaling

15. Pheromones • Pheromones - chemical signals that are released from the body and used to communicate with other individuals in the species. • Pheromones are “outside” the body. • Pheromones - mark trails to food sources, warn of predators, and attract potential mates.

16. Chemical Classes of Hormones • Three major classes of molecules function as hormones in vertebrates: • Polypeptides (proteins and peptides) • Amines derived from amino acids • Steroid hormones

17. Classes and properties of hormones • The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells. • Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not.

18. Fig. 45-3 • Water-soluble • Lipid-soluble • 0.8 nm • Polypeptide: • Insulin • Steroid: • Cortisol • Amine: • Epinephrine • Amine: • Thyroxine

19. Cellular Response Pathways • Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors. • Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells.

20. Cell Signaling: • Signaling by any of these hormones involves three key events: • Reception • Signal transduction • Response

21. Fig. 45-5-1 • Fat-soluble • hormone • Water- • soluble • hormone • Transport • protein • Signal receptor • TARGET • CELL • Signal • receptor • NUCLEUS • (a) • (b)

22. Fig. 45-5-2 • Fat-soluble • hormone • Water- • soluble • hormone • Transport • protein • Signal receptor • TARGET • CELL • OR • Signal • receptor • Cytoplasmic • response • Gene • regulation • Cytoplasmic • response • Gene • regulation • NUCLEUS • (a) • (b)

23. Water soluble example: • The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress. • Epinephrine binds to receptors on the plasma membrane of liver cells. • This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream.

24. Fig. 45-6-1 • Epinephrine • Adenylyl • cyclase • G protein • GTP • G protein-coupled • receptor • ATP • Second • messenger • cAMP

25. Fig. 45-6-2 • Epinephrine • Adenylyl • cyclase • G protein • GTP • G protein-coupled • receptor • ATP • Second • messenger • cAMP • Protein • kinase A • Inhibition of • glycogen synthesis • Promotion of • glycogen breakdown

26. Pathway for Lipid-Soluble Hormones • The response to a lipid-soluble hormone is usually a change in gene expression. • Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus. • Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes.

27. Fig. 45-7-1 • Hormone • (estradiol) • Estradiol • (estrogen) • receptor • Plasma • membrane • Hormone-receptor • complex

28. Fig. 45-7-2 • Hormone • (estradiol) • Estradiol • (estrogen) • receptor • Plasma • membrane • Hormone-receptor • complex • DNA • Vitellogenin • mRNA • for vitellogenin

29. Multiple Effects of Hormones • The same hormone may have different effects on target cells that have: • Different receptors for the hormone • Different signal transduction pathways • Different proteins for carrying out the response • A hormone can also have different effects in different species.

30. Negative feedback and antagonistic hormone pairs are common features of the endocrine system • Hormones are assembled into regulatory pathways. • Feedback loops are commonly used. • Hormones are often arranged in pairs that work against each other. • Blood sugar regulation and calcium deposition in bones are common test examples.