Most signal receptors are plasma membrane proteins Antigen- binding sites Antibody A Antigen Antibody B Antibody C Epitopes (antigenic determinants) Comparison of Endocrine to Nervous system EndocrineNervous Work together to maintain homeostasis Involves the binding of chemical signaling molecule to receptor on target cell Consists of endocrine cells and tissues Consists of brain, spinal cord, nerves and sense organs Use hormones as chemical signalsUse neurotransmitters as chemical signals Hormones travel through the bloodstream Neurotransmitters released at synapse with the effector Have a lag period of seconds or even days Effectors respond within milliseconds Effects may be prolongedResponse only prolonged if stimulus continues to be applied A hormonal stimulus typically produces one or more of the following changes: 1.Alters membrane permeability or membrane potential,or both, by opening or closing ion channels 2. Stimulates synthesis of proteins or regulatory molecules such as enzymes within the cell 3. Activates or deactivates enzymes 4. Induces secretory activity 5. Stimulates mitosis Types of Hormones Polypeptide Steroid Amine The chemical class will influence the location of the receptor on the target cell Two mechanisms of hormone action Tropic hormones Tropic hormones act on other endocrine glands; sometimes the name tells you which endocrine gland it acts on Thyroid stimulating hormone (TSH) is produced by the anterior pituitary stimulates the thyroid Follicle stimulating hormones (FSH) is produced by the anterior pituitary and stimulates the ovary to produce ova and the testes to produced sperm Luteinizing hormone (LH) and adrenocorticotropic hormone (ACTH) are also tropic hormones Negative feedback Homeostasis is maintained primarily by negative feedback Negative feedback returns things to normal The stimulus and the response are in opposite directions You need to know several examples, not just in the endocrine system Positive Feedback In positive feedback, the stimulus and response is in the same direction It may lead to disease or a metabolic imbalance, but in some cases, such as the action of oxytocin, it is normal I wish it worked this way with the hormones! In mammals, a decrease in body temperature results in which of the following responses? a. Release of thyroxine decreases the rate of metabolism. b. Blood vessels close to the surface of the skin constrict. c. Increased secretion of epinephrine restricts the amount of sugar released into the circulatory system. d.The adrenal glands increase the release of acetylcholine into the circulatory system. When a person exercises strenuously, all of the following occur EXCEPT: A)Glucose decreases. B)ADP increases. C)Lactic acid increases. D)Glycogen increases. Which of the following is LEAST likely to be associated with diabetes mellitus? A)Insulin receptors are insensitive to insulin. B)Urinalysis indicates a high concentration of sugar in urine. C)Pancreatic islet cells are destroyed. D)Liver cells absorb sugar from the blood at a rate that is greater than normal. Uptake and conversion of glucose molecules to glycogen, or the breakdown of glycogen to glucose molecules is controlled by hormones that target liver cells. Which best describes this antagonistic hormonal interaction? a. Insulin promotes glucose uptake by liver cells and glucagon promotes glycogen breakdown. b. Glucagon promotes glucose uptake by liver cells and insulin promotes glycogen breakdown. c. Insulin promotes glycogen uptake by liver cells and glucagon promotes glucose breakdown. d. Glucagon promotes glycogen uptake by liver ells and insulin promotes glucose breakdown. The secretion of hormone A causes an increase in activity X within an organism. If this mechanism works by positive feedback, which of the following statements represents that fact? a. An increase in activity X produces an increase in hormone A. An increase in hormone A produces an increase in activity X. b. An increase in activity X produces an increase in hormone A. An increase in hormone A produces a decrease in activity X. c. A decrease in activity X produces an increase in hormone A. A decrease in hormone A produces an increase in activity X. d. A increase in hormone A produces a increase in activity X. Activity X has no effect on production of hormone A. The endocrine system and nervous system work together to maintain homeostasis. This is accomplished primarily by negative feedback. Which of the following is an example of negative feedback in the endocrine system? a. At the onset of labor, stretch on the uterine wall stimulates the posterior pituitary to release oxytocin, which stimulates further contraction of the smooth muscle of the uterus b. As body temperature decreases in mammals, hormones of the hypothalamus exert an inhibitory effect on sweat glands, reducing the amount of heat lost by evaporation c. As blood glucose levels rise after a meal, alpha cells of the pancreas release insulin, which promotes the breakdown of glycogen in liver cells d. A decrease in blood calcium levels triggers the production of PTH; PTH targets osteoclasts in the bone which break down bone, releasing calcium and phosphates into the blood stream