Introduction to the Endocrine System

1. Introduction to the Endocrine System 7

2. 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 • Hormone evolution

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

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

5. Anatomy Summary: Hormones Figure 7-2 (3 of 4)

6. Anatomy Summary: Hormones PLAY Animation: Endocrine System: Endocrine System Review Figure 7-2 (4 of 4)

7. 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

8. 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

9. Hormones: Classification • Peptide or protein hormones • Steroid hormones • Amine hormones PLAY Animation: Endocrine System: Biochemistry, Secretion, and Transport of Hormones

10. Hormones: Peptides or Proteins • Preprohormone • Large, inactive • Prohormone • Post-translational modification • Peptide hormone-receptor complex • Signal transduction system

11. Peptide Hormone Synthesis, Packaging, and Release 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. 5 6 1 2 3 4 Golgi complex Endoplasmic reticulum (ER) To target Ribosome Active hormone Peptide fragment Transport vesicle 3 4 6 Secretory vesicle 5 Release signal Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3

12. Peptide Hormone Synthesis, Packaging, and Release 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. 1 Endoplasmic reticulum (ER) Ribosome Capillary endothelium 1 Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3, step 1

13. Peptide Hormone Synthesis, Packaging, and Release Enzymes in the ER chop off the signal sequence, creating an inactive prohormone. 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. 1 2 Endoplasmic reticulum (ER) Ribosome Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3, steps 1–2

14. Peptide Hormone Synthesis, Packaging, and Release Enzymes in the ER chop off the signal sequence, creating an inactive prohormone. 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. 1 2 3 Golgi complex Endoplasmic reticulum (ER) Ribosome Transport vesicle 3 Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3, steps 1–3

15. Peptide Hormone Synthesis, Packaging, and Release Enzymes in the ER chop off the signal sequence, creating an inactive prohormone. 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. 1 2 3 4 Golgi complex Endoplasmic reticulum (ER) Ribosome Active hormone Peptide fragment Transport vesicle 3 4 Secretory vesicle Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3, steps 1–4

16. Peptide Hormone Synthesis, Packaging, and Release Enzymes in the ER chop off the signal sequence, creating an inactive prohormone. 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. 5 1 2 3 4 Golgi complex Endoplasmic reticulum (ER) Ribosome Active hormone Peptide fragment Transport vesicle 3 4 Secretory vesicle 5 Release signal Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3, steps 1–5

17. Peptide Hormone Synthesis, Packaging, and Release 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. 5 6 1 2 3 4 Golgi complex Endoplasmic reticulum (ER) To target Ribosome Active hormone Peptide fragment Transport vesicle 3 4 6 Secretory vesicle 5 Release signal Prohormone Capillary endothelium 2 1 Signal sequence Cytoplasm ECF Plasma Preprohormone mRNA Figure 7-3, steps 1–6

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

19. Peptide Hormone-Receptor Complex Membrane receptors and signal transduction for peptide hormones Figure 7-5

20. 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

21. Steroid Hormones: Structure Steroid hormones are derived from cholesterol Figure 7-6

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

23. Steroid Hormones: Action Blood vessel 1 Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell. 1 Protein carrier Nucleus Interstitial fluid Cell membrane Figure 7-7, step 1

24. Steroid Hormones: Action Blood vessel Steroid hormone 1 Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell. 1 2 Protein carrier Nucleus 2 Steroid hormone receptors are typically in the cytoplasm or nucleus. Cytoplasmic receptor Nuclear receptor Interstitial fluid Cell membrane Figure 7-7, steps 1–2

25. Steroid Hormones: Action Blood vessel Steroid hormone 1 Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell. Cell surface receptor 2a Rapid responses 1 2 Protein carrier Nucleus 2 Steroid hormone receptors are typically in the cytoplasm or nucleus. Cytoplasmic receptor Nuclear receptor Some steroid hormones also bind to mem- brane receptors that use second messenger systems to create rapid cellular responses. 2a Interstitial fluid Cell membrane Figure 7-7, steps 1–2a

26. Steroid Hormones: Action Blood vessel Steroid hormone 1 Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell. Cell surface receptor 2a Rapid responses 1 2 Protein carrier Nucleus 2 Steroid hormone receptors are typically in the cytoplasm or nucleus. Cytoplasmic receptor Nuclear receptor DNA Some steroid hormones also bind to mem- brane receptors that use second messenger systems to create rapid cellular responses. 2a Interstitial fluid 3 Cell membrane The receptor- hormone complex binds to DNA and activates or represses one or more genes. 3 Figure 7-7, steps 1–3

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

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

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

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

31. Amine Hormones: Structure Tyrosine-derived amine hormones Figure 7-8

32. Endocrine Reflex Pathways • Stimulus • Afferent signal • Integration • Efferent signal (the hormone) • Physiological action • Negative feedback PLAY Animation: Endocrine System: The Actions of Hormones on Target Cells

33. Endocrine Reflex Pathways Hormones may have multiple stimuli for their release Figure 7-9