THE ENDOCRINE SYSTEM   The Endocrine System consists of glands that transmit chemical messengers throughout the body.  These chemical messengers, called hormones circulate in the bloodstream and affect many types of body cells.   OBJECTIVES:  Compare exocrine glands with endocrine glands.  Contrast amino acid-based hormones with steroid hormones.  Describe two ways that hormones affect their target cells.  Distinguish hormones from prostaglandins.   HORMONES: Chemical Signals   1. A GLAND is an Organ that consists of Cells that Secrete materials into other regions of the Body.   2. The body contains TWO TYPES of GLANDS:       A. EXOCRINE GLANDS: Secrete NONHORMONAL Chemicals into DUCTS, which transport the Chemicals to a Specific Location inside and outside the Body.  Sweat Glands, Mucous Glands, Salivary Glands, and other Digestive Glands are Examples of Exocrine Glands.       B. ENDOCRINE GLANDS - are DUCTLESS Glands that are located throughout the body.  Endocrine Glands Secrete Hormones into the Bloodstream through the fluid that surrounds their Cells.   3. A HORMONE is a Chemical Signal, made in one place and delivered to another, that regulates the body's activities.  Hormones are compounds that are secreted in small amounts into the bloodstream and that influence the activity of distant cells.   4. Various organs throughout the body are sources of Hormones.   5. Organs that produce Hormones are called  ENDOCRINE GLANDS and form the ENDOCRINE SYSTEM .   6. Some other Organs NOT considered Glands produce Hormones. The Brain and Kidney are two other organs that also produce Hormones.   7.  Endocrine Glands Secret Hormones Directly into the Bloodstream - DUCTLESS GLANDS.   8. The Hormones travel to a Specific Tissue or Organ called TARGET CELLS.   9. At the Target Cells, Hormones elicit a Specific Response.   10.  Hormones are essential to maintaining Homeostasis.   11.  The Endocrine system works Hand - in - Hand with the Nervous System to:       A.  Maintain the body's internal steady state - HOMEOSTASIS (nutrition, metabolism, excretion, water and salt balances).       B.  React to stimuli from outside the body.       C.  Regulate growth, development and reproduction.       D.  Produce, use and store energy   12.  The Endocrine and Nervous Systems are so closely linked that they are often are considered a single system – The Neuroendocrine System.   13.  Both Nerve Impulses and Hormones elicit a response  BUT:       A.  Nerve Impulses prompt a nearly instantaneous response to a change in the environment.       B.  Hormones on the other hand are Released More Slowly than nerve impulses, but their effects usually Last Longer.  Effects of some Hormones can last 10 to 20 minutes.  Some Hormones can last for several hours.   HOW HORMONES WORK   1. A Hormone DOES NOT seek out a particular organ; to the contrary, the Organ is AWAITING the Arrival of the Hormone.   2. Cells that can react to a Hormone have Specific Receptor Proteins on their Plasma Membrane or in their Cytoplasm that combine with the Hormone In a "LOCK-AND-KEY" manner. The Specific Shape of the Hormone must MATCH the Specific Shape of the Receptor Protein.   3. RECEPTORS are Proteins that are located BOTH Inside the Cytoplasm and on the Surface of a Target Cell.   4. Therefore, Certain Cells respond to one Hormone and not another, depending on their Receptor Proteins.   5. Hormones are Chemical Messengers that influence the Metabolism of the Recipient Cell.   6. Fitting the Hormone Molecule into the Receptor CHANGES the Receptor's Shape, which causes the Cell's Activities to Change.   7. The MAIN Effect of a Hormone on a Cell is to Change the Activity or Amounts of Enzymes (Speed up chemical reactions) present in that Cell.   TWO TYPES OF HORMONES   1. Hormones are substances that fall into TWO General Categories:       A. STEROID HORMONES – Hormones the Body Synthesizes from Cholesterol (A Lipid).       B. AMINO ACID-BASED HORMONES (PEPTIDE HORMONES) – Hormones made of Amino Acids.    2. STEROID HORMONES:        A. Steroid Hormones are produced by the Adrenal Cortex, the Ovaries, and the Testes.  ALL OTHER GLANDS PRODUCE AMINO ACID-BASED HORMONES OR PEPTIDE HORMONES!       B. Steroid Hormones DO NOT Bind with the Plasma Membrane (A Lipid Bilayer) Receptors of the Target Cells; they can ENTER the Cell and the Cell Nucleus FREELY.       C. Within the Cytoplasm, a Steroid Hormone can Bind with a Receptor Protein, then enter the Cell Nucleus AND BIND TO DNA, where it will Trigger changes in the Chromosomes.       D. The Hormone –Receptor Unit attaches to the DNA, This attachment activates certain Genes in that Cell, causing particular Proteins, including New Protein Enzymes, to be produced.       E. The Male Sex Hormone TESTOSTERONE and the Female Sex Hormones ESTROGEN and PROGESTERONE are examples of Steroid Hormones.     3. AMINO ACID-BASED HORMONES (Peptide Hormones):        A. Hormones made from Amino Acids.       B. Because Peptide Hormones are Polar Molecules (posses both positive and negative ends) they CANNOT PASS (DIFFUSE) through the Plasma Membrane of their Target Cells.       C. Peptide Hormones must send their Message from OUTSIDE the Target Cell, a TWO-Messenger System is commonly required for the action of most of these Hormones.       D. Peptide Hormones attaches to Receptors on the Plasma Membrane, THE FIRST MESSENGER, carrying the message from the Endocrine Gland to the Cell Surface, and pass the message to another Molecule Inside the Cytoplasm – THE SECOND MESSENGER.       E. In Many cases, the Hormone-Receptor complex indirectly activates an enzyme that converts Molecules of ATP to Cyclic AMP (c-AMP) inside the Target Cell.       F. Cyclic Amp acts as a Second Messenger by indirectly Activating other Enzymes and Proteins in the Target Cell.  Thus, c-AMP initiates a chain of Biochemical Events that leads to functional changes within the Target Cell.       G.  A single Hormone molecule binding to a receptor in the plasma membrane can result in the formation of many Second Messengers.   PROSTAGLANDINS   1. PROSTAGLANDINS are a group of Hormone-Like Lipids, that also Regulate Cell Activities.   2. Unlike Hormones, Prostaglandins are NOT Produced by Specific Endocrine Glands.   3. Prostaglandins are produced in small quantities by many cells throughout the body.  Rather than being transported through the blood to distant regions of the body, prostaglandins ACT LOCALLY.   4. Their effects include relaxation of Smooth Muscles that line the air passageways and blood vessels, regulation of blood pressure, contraction of the intestinal walls and the uterus, and stimulation of the Body's Inflammatory Response to infection.   FEEDBACK MECHANISMS   The endocrine system uses feedback mechanisms to respond and adjust to changes that occur in and outside the body.  In a Feedback Mechanism, the last step in a series of events controls the first step.   OBJECTIVES:  Define the terms feedback mechanism and antagonistic hormones.  Distinguish positive feedback from negative feedback.  Explain the role of negative feedback mechanisms in maintaining homeostasis.  Give examples of a negative feedback in the endocrine system.   HOMEOSTASIS   1. HOMEOSTASIS is Defined as a STABLE Internal Environment.   2. The Endocrine System plays an important role in the Maintenance of Homeostasis because it Affects the Activities of Cells; Tissues, and Organs Throughout the body.   3. ANTAGONISTIC HORMONES are Hormones that have an Opposite Effect on the body.    4. To maintain homeostasis, hormone Secretions must be Tightly Regulated.   5. Most hormones are controlled by a FEEDBACK MECHANISM.    6. MOST Hormone Systems use NEGATIVE FEEDBACK, in which release of an Initial Hormone Stimulates Release or production of other hormones or substances that subsequently INHIBITS Further Release of the Initial Hormone.   7. In POSITIVE FEEDBACK, Release of an Initial Hormone Stimulates Release or Production of other Hormones or Substances, which STIMULATES Further Release of the Initial Hormone.   NEGATIVE FEEDBACK MECHANISMS -Regulating Hormone Release   1. Because the body produces more than 30 Hormones, it must be able to regulate the release of these Hormones.   2. Negative Feedback Mechanisms in the Body involve interactions of the Nervous, Endocrine, and Circulatory Systems.   3. In Negative Feedback, the FINAL STEP in a Series of events INHIBITS the INITIAL SIGNAL in the Series.   4. The Hypothalamus, the Anterior Pituitary, and the other Endocrine controlled by the Anterior Pituitary are all involved in a Self-Regulating Negative Feedback Mechanism.   5. Negative Feedback is a process by which a change in an Environment causes a Response that returns conditions to their Original State.   6. A Good Example is the way a Thermostat that controls the Room Temperature:        A. If the thermostat is set at 72 F.     B. If the Room stays at 72 F nothing happens.       C. But if the Temp Drops to say 68 F.       D. The thermostat turns on the heater, Returning the Room to 72 F.       E. Once the Room Reaches the proper Temp 72 F, the thermostat turns the heater back off.   2. The way the Thermostat maintains the temperature in a room is similar to the way Most Endocrine Glands help the Body to Maintain Homeostasis.     3. Negative Feedback Mechanisms help maintain Hormone Concentration at a Certain Level.