Chapter 41 Lecture 14 Animal Hormones Dr. Alan McElligott

Animal Hormones Aims: To appreciate the variety and roles of hormones in the body To understand the basic types of hormones To understand how hormones work To introduce the study of mechanisms of hormone action To examine the roles of hormones in maintaining blood glucose levels

Aims: To appreciate the variety and roles of hormones in the body To understand the basic types of hormones To understand how hormones work To introduce the study of mechanisms of hormone action To examine the roles of hormones in maintaining blood glucose levels These lecture aims form part of the knowledge required for learning outcome 4: Appreciate how the physiology of an organism fits it for its environment (LOC4). Animal Hormones

Essential reading Pages Pages Page 883 Page 887 Pages All of the chapter is worth reading. Animal Hormones

41 Animal Hormones 41.1 What Are Hormones and How Do They Work? 41.2 How Do the Nervous and Endocrine Systems Interact? 41.3 What Are the Major Mammalian Endocrine Glands and Hormones? 41.4 How Do We Study Mechanisms of Hormone Action?

41.1 What Are Hormones and How Do They Work? Hormones are chemical signals secreted by cells of the endocrine system. Endocrine cells: cells that secrete hormones Target cells: cells that have receptors for the hormones

41.1 What Are Hormones and How Do They Work? Circulating hormones diffuse into the blood and can activate target cells far from the site of release. Paracrine hormones: affect only target cells near the site of release. Autocrine hormones: affect the cells that released the hormones.

Figure 41.1 Chemical Signaling Systems

41.1 What Are Hormones and How Do They Work? Some endocrine cells are single cells (e.g., in the digestive tract.) Endocrine glands: aggregations of secretory cells. Hormones are secreted to the extracellular space. Exocrine glands: ducts carry products to the outside of the body.

41.1 What Are Hormones and How Do They Work? Chemical communication arose early in evolution. Plants, sponges, protists all use chemical signals. In arthropods, hormones control molting and metamorphosis.

41.1 What Are Hormones and How Do They Work? Three types of hormones: Peptides or polypeptides: water-soluble, transported in blood but not across membranes. Steroid hormones: lipid-soluble; must be bound to carrier proteins to be carried in blood. Amine hormones: derivatives of tyrosine

41.1 What Are Hormones and How Do They Work? Hormone receptors: Lipid soluble hormones: receptors are inside the cell Water-soluble hormones cannot readily pass cell membrane—receptors are on the outside

41.1 What Are Hormones and How Do They Work? Receptors are glycoproteins with three domains: Binding domain: projects outside plasma membrane Transmembrane domain Cytoplasmic domain: extends into cytoplasm—initiates target cell response

41.1 What Are Hormones and How Do They Work? One hormone can trigger different responses in different types of cells. Example: epinephrine (amine), fight-or- flight response

Figure 41.4 Epinephrine Stimulates “Fight or Flight” Responses

Epinephrine Stimulates “Fight or Flight” Responses Human physiological response to adrenaline

Figure 41.5 The Endocrine System of Humans

41.2 How Do the Nervous and Endocrine Systems Interact? The pituitary gland is attached to the hypothalamus of the brain. Posterior pituitary secretes neurohormones (synthesized by neurons in the hypothalmus): oxytocin and ADH.

Figure 41.6 The Posterior Pituitary Releases Neurohormones

41.2 How Do the Nervous and Endocrine Systems Interact? The anterior pituitary secretes: Tropic hormones: control other endocrine glands Growth hormone: promotes growth Prolactin: breast development and milk production Enkephalins and endorphins: natural opiates

Figure 41.7 The Anterior Pituitary Produces Many Hormones

41.3 What Are the Major Mammalian Endocrine Glands and Hormones? Thyroxine regulates cell metabolism. Anterior pituitary secretes thyrotropin (TSH), which activates the follicles to produce thyroxine.

41.3 What Are the Major Mammalian Endocrine Glands and Hormones? The thyroid gland produces thyroxine (T 4 ) and triiodothyronine (T 3 )

Figure 41.9 The Thyroid Gland Consists of Many Follicles (A) Thyroxine is produced by the follicles

41.3 What Are the Major Mammalian Endocrine Glands and Hormones? Adrenal gland: two glands Adrenal medulla: epinephrine and norepinephrine On target cells:  -adrenergic and  - adrenergic receptors.  -blockers block  -adrenergic receptors.

Figure The Adrenal Gland Has an Outer and an Inner Portion

41.3 What Are the Major Mammalian Endocrine Glands and Hormones? Adrenal cortex produces corticosteroids from cholesterol: Glucocorticoids: cortisol Mineralocorticoids: aldosterone Sex steroids

Figure The Corticosteroid Hormones are Built from Cholesterol

41.4 How Do We Study Mechanisms of Hormone Action? To study hormone action: Identify and measure the hormone Identify the receptors Determine the signal transduction pathways in different tissues.

41.4 How Do We Study Mechanisms of Hormone Action? Hormones occur in extremely small concentrations. Immunoassay techniques are used to measure concentration in the blood. Half-life: time required for one half of the hormone molecules to be depleted.

Figure An Immunoassay Measures Hormone Concentration

41.4 How Do We Study Mechanisms of Hormone Action? One hormone may bind to different receptors. Drugs can be created to block specific responses. Receptors can be identified by affinity chromatography. Receptors can also be identified by genomic analyses.

41.4 How Do We Study Mechanisms of Hormone Action? Abundance of hormone receptors can be regulated by negative feedback. Downregulation: continuous high levels of hormone decreases number of receptors. Upregulation: when hormone secretion is suppressed, receptors increase.

41.4 How Do We Study Mechanisms of Hormone Action? Type II diabetes mellitus results from downregulation of insulin receptors. Possibly due to overstimulation of pancreatic release of insulin by excessive carbohydrate intake. Beta blockers can result in upregulation—if beta receptors are blocked over time, more receptors are produced.

41.4 How Do We Study Mechanisms of Hormone Action? Receptors can be linked to different signal transduction pathways. Example: epinephrine and norepinephrine connect with different pathways—can have different effects even in the same cell.

Figure Some Hormones Can Activate a Variety of Signal Transduction Pathways

41.4 How Do We Study Mechanisms of Hormone Action? Signal transduction pathways can be “cascades,” in which each step amplifies the response. One hormone molecule binding to a receptor might result in millions of molecules of final product. Example: response of liver cells to epinephrine.

Check out 41.1 RECAP, page 879, questions 2 and CHAPTER SUMMARY, page 893, see Web/CD activity RECAP, page 890, question 3 only 41.4 RECAP, page CHAPTER SUMMARY, page 894, See WEB/CD Activity 41.2 Self Quiz page 894: Chapter 41, questions 5, 9 and 10 For Discussion page 895: Chapter 41, question 4 Animal Hormones

Key terms: affinity chromatography, amine hormone, autocrine, chemical messenger, diabetes, downregulation, endocrine, epinephrine, exocrine, feedback, glucagon, hormone, hypothalamus, immunoassay, insulin, neurohormone, pancreas, paracrine, peptide hormone, pituitary gland, receptor, signal transduction pathway, steroid hormone, stomatostatin, target cell, upregulation Animal Hormones