Chapter 45 Chemical Signals in Animals; Hormones and the Endocrine System

1. Chapter 45Chemical Signals in Animals;Hormones and the Endocrine System Michael Kosofsky and Emily Pipilas

2. Comparison Endocrine System • Hormones travel in blood to target cells • Controls tissues • Regulates metabolism • Feedback in seconds to months Nervous System • Electrical signals • Release neurotransmitters to synapse • Controls muscles and glands • Quick feedback

3. Feedback Mechanisms • Negative Feedback • Primary mechanism of homeostasis • Change in physiological variable triggers response that counteracts initial ‘away from normal’ fluctuation • Positive Feedback • Physiological control mechanism • Change in variable triggers mechanisms to amplify that change

4. Steroid Model vs. Protein Model Steroid Model Protein Model • Diffuse through cell membrane • Receptors in nucleus • Response has slow onset • Long-lasting • Typically derived from cholesterol • Examples: Androgens, Estrogens, Progesterone • Don’t diffuse through cell membrane • Receptors on surface of cell • Response has quick onset • Short-lasting • Typically derived from amino acids • Examples: GH, Insulin, Glucagon

5. Paracrine Signaling: local signaling between nearby cells within organ (don’t travel in blood) • Endothelial cells of blood vessels release nitric oxide to help relax the smooth muscle in blood vessels, thus dilating blood vessels • Smooth muscle cells also produce prostoglandins, which aid in smooth muscle contraction • Examples: uterine wall contractions

6. 3 Stages of Cell Signaling • Reception: occurs when signal molecule binds to specific receptor protein • Receptor proteins are built into the plasma membrane of the target cell or located inside the target cell • Target cell: Cell that responds to a regulatory signal such as a hormone • Signal Transduction: events within the target cell that are triggered from the binding of a signal molecule to a receptor protein • Response: change in the cell’s behavior

7. Ligand • Ligand: molecule that binds specifically to the receptor site of another molecule • 3 Models for Ligand/Receptor Interactions • G-Protein Linked Receptors • Tyrosine-Kinase Receptors • Ion-Channel Receptors • Intracellular Receptors

8. Ligand-Gated Channel • Protein pores in the plasma membrane that open or close in response to a chemical signal, allowing the blocking or flow of specific ions such as sodium or calcium ions. • Bind to signal molecule as a ligand at a specific sight on their extracellular side. • The shape change produced in the channel protein immediately leads to a flow of particular ions along their concentration gradient through the channel.

9. Steroid Hormones • Derived from cholesterol • Lipid soluble (able to diffuse through cell membrane) • Sex hormones • Progesterone • Estrogen • Testosterone • Adrenal Cortex Hormones • Actions • Hormone crosses membrane • Hormone combines with receptor in nucleus • Attaches to section of DNA • Transcription (synthesis of mRNA) activated • mRNA enters cytoplasm to ribosome to create protein

10. Second Messenger • Chemicals that transfer and amplify the signal from the receptor to proteins • Cause a specific response

11. Calcium Ions and InositolTriphosphate IP3 in Signaling (Secondary Messengers) • Signal molecule (first messenger) binds to G-protein-linked receptor, leads to activation of phospholipase C • Phospholipase C cleaves a plasma membrane phospholipid called PIP2 into DAG and IP3 • DAG functions as a second messenger in other pathways • IP3 diffuses through cytosol, binds to a ligand-gated calcium channel in the ER membrane, causing it to open. • Calcium ions flow out of ER (down concentration gradient) raising calcium ion level in cytosol • Calcium ions activate the next protein in more signaling pathways, often acting via calmodulin, a calcium ion-binding protein

12. Cellular Response to Cell-Signaling Pathway • Response of liver cells to signaling by the hormone epinephrine • Helps regulate cellular energy metabolism • Activates the enzyme that catalyzes the breakdown of glycogen

13. Duct vs. Ductless Glands Duct Glands Ductless Glands • Exocrine • Secrete their products into ducts • Lead directly to external environment • Examples: sweat glands, salivary glands, mammary glands • Endocrine • Do not possess any ducts by which secretions are discharged • Secrete hormones directly into bloodstream • Examples: thyroid, parathyroid, thymus, pituitary body, pineal body

14. Anterior Pituitary Hormones • Growth Hormone (GF) • Endorphins • Prolactin (PRL) • Follicle-Stimulating Hormone (FSH) • Luteinizing Hormone (LH) • Thyroid Stimulating Hormone (TSH) • Adrenocorticotropic Hormone (ACTH) • Melanocyte-Stimulating Hormone (MSH)

15. Hypothalamus-region of lower brain that recieves information from nerves throughout the body and from other parts of the brain then initiates endocrine signals appropriate to environmental conditions -secretes hormoones of the posterior pituitary and releasing factors, which regulate the anterior pituitary • Neurosecretory cells • Influence the pituitary gland which integrate endocrine and neural function • Posterior Pituitary: extension of hypothalamus that stores and release two hormones (oxytocin and antidiuretic hormone) • Anterior Pituitary: Releases and inhibits hormones conveyed by portal vessels in the hypthalamus. Hormones include: TSH, FSH, LH, GH, PRL, ACTH, MSH, endorphins

16. Antidiuretic Hormone • Release of ADH from the anterior pituitary is inhibited by drinking alcochol • How would this affect urination?

17. Thyroid Gland • Releases Calcitonin when blood calcium levels are too high, lowering calcium levels in the blood • Osteoblasts build bone • Produces T3 and T4 (iodine-containing hormones) • Stimulate metabolism • Influence development and maturation Parathyroid Gland • Secretes Parathyroid Hormone (PTH) • Raises calcium levels in blood plasma when they are below normal • Works with calcitonin to maintain blood calcium homeostasis • Stimulates kidneys to activate Vitamin D, which causes intestines to increase uptake of calcium from food

18. Iodine Deficiency in Diet • Results in goiter • Enlargement of thyroid • In the absence of sufficient iodine, thyroid gland cannot synthesize adequate amounts of T3 and T4 • Leads to continuous secretions of TSH, which then leads to an enlarged thyroid

19. Thymus Gland • Active in establishing the immune system • Secretes thymosins • Promotes the development of white blood cells (lymphocytes) • Stimulate T cells (immunity)

20. Pancreatic Hormones & the Regulation of Blood Sugar (Negative Feedback) Insulin Glucagon • Released when blood sugar levels are high • Stimulates cells to • Perform cellular respiration • Turn glucose into glycogen (where it is stored) • Turn excess glucose into fat • Take in amino acids for protein synthesis • Convert fatty acids into lipids • Released when blood sugar is low • Liver- change glycogen into glucos • Adipose (fat) tissue- breakdown of fats and proteins to form glucose

21. Stimulation of the Adrenal Gland • Hypothalamus • Neural Signals • Sympathetic Impulses • Adrenal Medulla (medial) • Epinephrine and Norepinephrine Released • Short term “fight or flight” or alarm stage • Hypothalamus • CHR Released • Anterior Pituitary • Releases ACTH • Adrenal Cortex (lateral) • Releases Cortisol • Long term Adjustment or Resistance Stage

22. Epinephrine • Causes short term “fight or flight” or alarm stage • Blood glucose increases • Blood glycerol and fatty acids increase • Heart rate increases • Blood pressure rises • Breathing rate increases • Air passages dilate • Pupils dilate • Blood flow redistributes, leading to increased alertness and decreased digestive and kidney activity

23. Gonadotropic Hormones FSH LH • Stimulates gamete formation • Female: follicle, egg-maturation in ovary, release of estrogen • Male: sperm production in tubes of testes, release of testosterone • Negative Feedback: Release of Gonadotropin Releasing Hormone (GnRH) from the hypothalamus-decreased when levels of progesterone and testosterone rise • Stimulates ovulation in the ovary (female) • Ovulation causes release of progesterone • Causes production of testosterone in testes (male) • Negative Feedback: Hypothalamus decreases its release of GnRH when levels of progesterone and testosterone rise

24. Secondary Sex Traits Secreted by Ovaries (Female) Secreted by Testes (Male) • Estrogen • Support egg maturation • Controls period • Testosterone • Sperm production • Protein synthesis in muscle