Chapter 7a Introduction to the Endocrine System

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

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

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

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

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

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

Hormones: Classification Be able to give types and example. Compare synthesis, half-life and location of receptor 1.Peptide or protein hormones Insulin from amino acids 2.Steroid hormones  Sex steroids; estrogen, lipophilic 3.Amine hormones epinephrine

Table 7-1 Hormones: Classification

Figure 7-3 Peptide Hormone Synthesis, Packaging, and Release 1 mRNA Ribosome To target Prohormone Signal sequence Transport vesicle Active hormone Endoplasmic reticulum (ER) Golgi complex Secretory vesicle ECFCytoplasmPlasma Peptide fragment Release signal Capillary endothelium Preprohormone 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 secretory vesicle releases its contents by exocytosis into the extracellular space. The hormone moves into the circulation for transport to its target. Enzymes in the ER chop off the signal sequence, creating an inactive prohormone. 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

Peptide Hormone Synthesis, Packaging, and Release Figure 7-4 PreprohormoneHormoneOther peptides Signal sequence processes to PreproTRH (242 amino acids) 6 TRH (3 amino acids each) (a) (c) TRH (b) Pro-opiomelanocortin ProhormoneActive hormone(s) Other peptide fragments processes to ACTH lipotropinendorphinFragment + + Proinsulin Insulin C-peptide

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

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

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

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

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

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

Amine Hormones: Examples Thyroid hormones Catecholamines Epinephrine Norepinephrine Dopamine

Amine Hormones: Structure Figure 7-8 Tyrosine Catecholamines Dopamine Norepinephrine Epinephrine Thyroid hormones Thyroxine (Tetraiodothyronine, T 4 ) Triiodothyronine (T 3 )

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

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