The Endocrine System Chapter 45

Types of chemical messengers: Hormone Paracrine regulators pheromones

Types of Chemical Messengers Hormone Regulatory chemical that is secreted into extracellular fluid and carried by the blood Can act at a distance from source Endocrine system Organs and tissues that produce hormones Only targets having the appropriate receptor can respond http://www.personal.kent.edu/~cearley/ChemWrld/drugs/drugs.htm

Types of Chemical Messengers Paracrine regulators do not travel in blood Allow cells of an organ to regulate each other Can be neurotransmitters Pheromones are chemicals released into the environment to communicate among individuals of a single species Not involved in normal metabolic regulation within an animal

Types of Chemical Messengers Neurohormones Some neurotransmitters are distributed by the blood and act as a hormone Norepinephrine coordinates the activity of heart, liver, and blood vessels during stress

Endocrine System The endocrine system includes all the organs that secrete hormones Endocrine – product secreted into extracellular fluid and carried in blood Exocrine – secrete product into a duct

2 basic hormone characteristics Must be sufficiently complex to convey regulatory information to their target cells Must be adequately stable to resist destruction before reaching their target cells (having to survive in extracellular environments) What’s with the beret & eye patch? I have to be both Tough and complex! HORMONE

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamus Hypothalamus Pineal gland Pineal gland Neurohypophysis Pituitary gland Adenohypophysis Thyroid gland Thymus Parathyroid glands (behind thyroid) Adrenal glands Pancreas Testes (in males) Ovaries (in females)

1. Human Chorionic Gondadotrophin 3 Classes of Hormones Peptides and proteins Glycoproteins Amino acid derivatives Catecholamines Thyroid hormones Melatonin Steroids Sex steroids Corticosteroids 1. Human Chorionic Gondadotrophin ( a glycoprotein) 2. Catecholamines 2. themedicalbiochemistrypage.org 3. Steroids 1. www.dreamstime.com 3. www.vanderbilt.edu

Hormones may be categorized as: Lipophilic (nonpolar) – fat-soluble Steroid hormones and thyroid hormones Travel on transport proteins in blood Bind to intracellular receptors Tend to act over brief time period Hydrophilic (polar) – water-soluble All other hormones Freely soluble in blood Bind to extracellular receptors Tend to have much longer active period

Lipophilic hormones Transported by proteins Cross cellular membrane Bind to receptor in nucleus, activating transcription factors Notice where the hormone ended up in this picture

Hydrophilic hormones Bind to receptors on cell surface Initiates signal transduction through activation of protein kinases Regulatory enzymes that activate intracellular proteins through phosphorylation

Paracrine Regulation occurs in most organs www.labbookpages.co.uk

Hydrophilic Hormones Second-messenger systems Many hydrophilic hormones work through second messenger systems Two have been described One involving cyclic adenosine monophosphate (cAMP) One that generates 2 lipid messengers: inositol triphosphate (IP3) and diacyl glycerol (DAG)

The Pituitary Gland Also known as the hypophysis Hangs by a stalk from the hypothalamus Consists of two parts Anterior pituitary (adenohypophysis) Appears glandular Posterior pituitary (neurohypophysis) Appears fibrous Different embryonic origins Different hormones

The Posterior Pituitary Appears fibrous because it contains axons that originate in cell bodies within the hypothalamus and that extend along the stalk of the pituitary as a tract of fibers Develops from outgrowth of the brain

The Posterior Pituitary Releases 2 hormones: ADH Oxytocin

The Anterior Pituitary Develops from a pouch of epithelial tissue of the embryo’s mouth Not part of the nervous system Produces at least 7 essential hormones Tropic hormones or tropins Act on other endocrine glands Can be categorized into three families

3 families of anterior pituitary hormones: Peptide Corticotropin – stimulates adrenal to make cortisol Melanocyte-stimulating hormone – stimulates dispersion of pigment Protein Growth hormone Prolactin – stimulate mammary glands Glycoprotein Thyroid-stimulating hormone – acts on thyroid Luteinizing hormone – acts on ovaries, testes Follicle-stimulating hormone – development of ovarian follicles, development of sperm

Anterior pituitary controlled by hormones from hypothalamus Hypothalamus secretes neurohormones into anterior pituitary causing anterior pituitary to release hormones www.austincc.edu

The hypothalamus and the anterior pituitary are partially controlled by the very hormones whose secretion they stimulate (FEEDBACK) Negative feedback (most) Positive feedback (few) Causes deviations from homeostasis Control of ovulation and labor contractions

The Thyroid Gland In humans, the thyroid gland is shaped like a bow tie, and lies just below the Adam’s apple in the front of the neck Secretes Thyroid hormones Thyroxine Triiodothyronine Calcitonin

More Glands: Parathyroid Glands 4 small glands attached to the thyroid Produce parathyroid hormone (PTH) Raises blood Ca2+ levels by… Pulling It out of bone (via osteoclasts) Stimulating the kidneys to reabsorb Ca2+ from the urine Vitamin D activated by a PTH controlled enzyme Stimulates the intestinal absorption of Ca2+

The Adrenal Glands Medulla (inner portion) Cortex (outer portion) Stimulated by the sympathetic division of the autonomic nervous system Secretes the catecholamines epinephrine and norepinephrine (adrenalin and noradrenalin) Cortex (outer portion) Stimulated by anterior pituitary hormone ACTH Corticosteroids Glucocorticoids: maintain glucose homeostasis (e.g., cortisol) Aldosterone: helps regulate mineral balance Mayoclinic.com

The Pancreas Exocrine and endocrine glands Connected to the duodenum of the small intestine by the pancreatic duct Islets of Langerhans are scattered clusters of cells throughout the pancreas These govern blood glucose levels through two hormones with antagonistic functions

The Pancreas Insulin Glucagon Secreted by beta (b) cells of the islets Stimulates cellular uptake of blood glucose and its storage as glycogen in the liver and muscle cells, or as fat in fat cells Glucagon Secreted by alpha (a) cells of the islets Promotes the hydrolysis of glycogen in the liver and fat in adipose tissue

The Gonads Ovaries and testes in vertebrates Produce sex steroids that regulate reproductive development Estrogen and progesterone “Female” hormones Androgens “Male” hormones Testosterone and its derivatives

The Pineal Gland Located in the roof of the third ventricle of the brain Secretes melatonin Functions of melatonin Reduces dispersal of melanin granules Synchronizes various body processes to a circadian rhythm Secretion of melatonin activated in the dark