15.1 Homeostasis and the Endocrine System Homeostasis: Maintains body stability through receptors, coordinating centers, and effectors. Feedback Systems: Negative feedback: Restores balance by resisting changes. Positive feedback: Amplifies a response for rapid completion of an event. Hormones: Chemical regulators transported via the circulatory system, affecting target and non-target cells. Types of Hormones and Their Action Steroid Hormones: Lipid-based, soluble in fat; activate genes directly within cells. Protein Hormones: Water-soluble; bind to receptors on cell membranes, activating secondary messengers like cyclic AMP. 15.2 Hormones and Blood Sugar Regulation Pancreas: Functions as both endocrine (insulin and glucagon production) and exocrine gland. Diabetes Mellitus: Type 1: Insulin deficiency due to beta-cell destruction. Type 2: Decreased insulin effectiveness, often managed with lifestyle changes or drugs. Gestational Diabetes: Temporary during pregnancy, increasing the risk of Type 2 diabetes. Islet Cell Transplants: Potential treatment for Type 1 diabetes, facing challenges like immune rejection. 15.3 Hormones Affecting Metabolism Thyroid Gland: Produces thyroxine (T4) and triiodothyronine (T3) for metabolism regulation. Thyroid Disorders: Hypothyroidism: Low thyroid hormone levels, causing lethargy and weight gain. Hyperthyroidism: Excess hormone production, leading to high metabolism and nervousness. Parathyroid Glands: Regulate calcium levels using calcitonin (from thyroid) and parathyroid hormone (PTH). 15.4 Water and Ion Balance ADH: Regulates water balance, reducing urine output in response to dehydration. Aldosterone (RAAS system): Controls blood volume and pressure by retaining sodium and water. Diabetes Insipidus: Results from insufficient ADH or kidney response, leading to excessive urine output. 15.5 Stress Responses Hormones like epinephrine and cortisol help manage stress. Short-term stress: Activates the adrenal medulla (epinephrine). Long-term stress: Involves adrenal cortex hormones like cortisol. Hormonal Glands and Functions Pituitary Gland: Anterior lobe: Produces hormones like GH, TSH, ACTH, FSH, LH. Posterior lobe: Stores ADH and oxytocin. Pineal Gland: Produces melatonin, affecting sleep. Thymus: Secretes thymosin for immune cell development. Adrenal Glands: Medulla: Produces stress hormones (epinephrine, norepinephrine). Cortex: Produces cortisol, aldosterone, and sex hormones.