Chapter 7a

1. Chapter 7a Introduction to the Endocrine System

2. Endocrinology • Study of hormones • Specialized chemical messengers • Secreted by select cells • Action at distant sites via blood • Effects • Enzymatic reactions • Membrane transport • Gene expression

3. About this Chapter • Function and purpose of hormones • Classification, structure, and synthesis of hormones • Pathways of nervous to endocrine regulation • Effects of hormone interactions • Pathologies of the endocrine system

4. Anatomy Summary: Hormones Figure 7-2 (1 of 2)

5. Anatomy Summary: Hormones Figure 7-2 (2 of 2)

6. Chemical Regulating Systems • Hormones: cell–to–cell communication molecules • Made in gland(s) or cells • Transported by blood • Distant target tissue receptors • Activates physiological response • Pheromones: organism to organism communication

7. Hormones: Function • Control of • Rates of enzymatic reactions • Transport of ions or molecules across cell membranes • Gene expression and protein synthesis • Exert effects at very low concentrations • Bind to target cell receptors • Half-life indicates length of activity

8. Hormones: Classification Be able to give types and example. Compare synthesis, half-life and location of receptor • Peptide or protein hormones • Insulin from amino acids • Steroid hormones • Sex steroids; estrogen, lipophilic • Amine hormones • epinephrine

9. Hormones: Classification Table 7-1

10. Peptide Hormone Synthesis, Packaging, and Release 2 3 4 1 5 6 Enzymes in the ER chop off the signal sequence, creating an inactive prohormone. The hormone moves into the circulation for transport to its target. Messenger RNA on the ribosomes binds amino acids into a peptide chain called a preprohormone The chain is directed into the ER lumen by a signal sequence of amino acids. The prohormone passes from the ER through the Golgi complex. Secretory vesicles containing enzymes and prohormone bud off the Golgi. The enzymes chop the prohormone into one or more active peptides plus additional peptide fragments. The secretory vesicle releases its contents by exocytosis into the extracellular space. Golgi complex Endoplasmic reticulum (ER) To target Ribosome Active hormone Peptide fragment Transport vesicle 3 6 4 Secretory vesicle 5 Release signal Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3

11. Peptide Hormone Synthesis, Packaging, and Release (a) Signal sequence processes to + + Preprohormone Hormone Other peptides TRH + + 6 TRH (3 amino acids each) PreproTRH (242 amino acids) (b) Other peptide fragments processes to + Prohormone Active hormone(s) + Pro-opiomelanocortin ACTH lipotropin endorphin Fragment (c) C-peptide Proinsulin Insulin Figure 7-4

12. Peptide Hormone-Receptor Complex • Surface receptor • Hormone binds • Enzyme activation • Open channels • Second messenger systems • Cellular response

13. Peptide Hormone-Receptor Complex • Membrane receptors and signal transduction for peptide hormones Opens ion channel Second messenger system phosphorylate Proteins KEY TK = Tyrosine kinase Cellular response AE = Amplifier enzyme G = G protein Figure 7-5

14. Steroid Hormones: Features • Cholesterol-derived • Lipophilic and can enter target cell • Cytoplasmic or nuclear receptors (mostly) • Activate DNA for protein synthesis • Slower acting, longer half-life • Examples • Cortisol, estrogen, and testosterone

15. Steroid Hormones: Structure Cholesterol is the parent compound for all steroid hormones. modified by enzymes to make steroid hormones such as In adrenal cortex In ovary Ovary Adrenal cortex Aldosterone Cortisol Estradiol (an estrogen) Figure 7-6

16. Steroid Hormones: Action 1 Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell. Blood vessel Steroid hormone Cell surface receptor 2a Rapid responses 1 2 Steroid hormone receptors are in the cytoplasm or nucleus. 2 Protein carrier Nucleus 2a Some steroid hormones also bind to membrane receptors that use second messenger systems to create rapid cellular responses. Cytoplasmic receptor Nuclear receptor DNA Interstitial fluid 3 The receptor-hormone complex binds to DNA and activates or represses one or more genes. 3 Endoplasmic reticulum Transcription produces mRNA Cell membrane 4 Activated genes create new mRNA that moves back to the cytoplasm. 5 4 New proteins Translation 5 Translation produces new proteins for cell processes. Figure 7-7

17. Amine Hormones: Features • Derived from one of two amino acids • Tryptophan • Tyrosine • Ring structure

18. Amine Hormones: Examples • Thyroid hormones • Catecholamines • Epinephrine • Norepinephrine • Dopamine

19. Amine Hormones: Structure Tyrosine Catecholamines Thyroid hormones Dopamine Thyroxine (Tetraiodothyronine, T4) Norepinephrine Epinephrine Triiodothyronine (T3) Figure 7-8

20. Endocrine Reflex Pathways • Stimulus • Afferent signal • Integration • Efferent signal (the hormone) • Physiological action • Negative feedback

21. Endocrine Reflex Pathways: Insulin release KEY Blood glucose Eat a meal Stimulus Receptor Stretch receptor in digestive tract Efferent path Effector Tissue response Afferent neuron Sensory neuron CNS Efferent neuron Integrating center Negative feedback Efferent neuron Systemic response Pancreas Insulin Blood glucose Target tissues Glucose uptake and utilization Figure 7-9