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Transcript
The Endocrine System I. General Characteristics • Endocrine glands are ductless • Exocrine glands have ducts 1 Endocrine Glands Paracrine secretions Endocrine glands • act locally • release hormones • affect only neighboring cells • hormones travel through blood to target cells Autocrine secretions • affect only the secreting cell 2 Comparison of Nervous System and Endocrine System • Neurons release neurotransmitters into a synapse, affecting postsynaptic cells • Glands release hormones into the bloodstream • Only target cells of hormone responds 3 Comparison of Nervous System and Endocrine System 4 Major Endocrine Glands 5 II. Hormone Action General Characteristics: Needed in small amounts (potent) Produces long-lasting effects Regulate metabolic processes (homeostasis) Regulated by negative feedback Chemistry of Hormones Steroid or Steroid-Like Hormones sex hormones adrenal cortex hormones Nonsteroid Hormones (most hormones) amines proteins peptides glycoproteins 6 Prostaglandins paracrine substances act locally very potent in small amounts regulate cellular responses to hormones can activate or inhibit adenylate cyclase controls cAMP production alters cell’s response to hormones wide variety of functions 7 III. Control of Hormonal Secretions Controlled by negative feedback mechanism Control Sources: Hypothalamus, ANS, and by Regulating Blood Levels 8 Hormone Secretion is Under Negative Feedback Control 9 Pituitary Gland Two portions anterior pituitary (adenohypophysis) posterior pituitary (neurohypophysis) The pituitary gland is attached to the hypothalamus and lies in the sella turcica of the sphenoid bone. 10 Pituitary Gland Control Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release hormones 11 Hypothalamic Hormones, Hormones from the Anterior Pituitary and their Target Organs 12 The overall scheme for the release of most hormones is in the above chart (pg 501). First, the Hypothalamus secretes “releasing hormones” that target 13 the anterior pituitary gland. Posterior Pituitary Gland Located behind anterior pituitary gland Is continuous with nerve fibers of the hypothalamus Does not produce hormones (they are produced by the hypothalamus), but stores them until stimulated Secretes 2 hormones: Antidiuretic Hormone (video: Hormone Communication) Oxytocin 14 Thyroid Gland Involved in Iodine uptake (to produce T4 and T3). See table 13.7 Thyroid gland consists of two lobes connected bya an isthmus Follicular cells secrete thyroid hormones 15 Parathyroid Glands 4 small glands embedded in the posterior surface of the thyroid gland 16 Parathyroid Hormone • PTH and calcitonin to maintain homeostasis of Ca+2 • PTH stimulates bone to release Ca+2 and the kidneys to conserve calcium. It indirectly stimulates the intestine to absorb calcium. The increase in blood Ca+2 inhibits secretion of PTH. 1. 2.a. 3. 2.b. 2.c. 17 Parathyroid Hormone Mechanism by which PTH promotes calcium absorption in the intestine • Vit. D is synthesized from dietary cholesterol and intestinal enzymes convert it into provitamin D. • Sun exposure changes it into Vit. D (some also comes from foods) •The liver changes, stores it, and with PTH, the kidneys can control absorbtion of Ca+2 ions from the intestine. 18 Adrenal Glands • The adrenal glands consist of an outer cortex and inner medulla. •The cortex has 3 layers, or zones of cells. 19 Hormones of the Adrenal Cortex • Aldosterone increases blood volume and pressure by promoting conservation of Na+1 and water (steps 1-4). Laser Disc Slide 9 – 36490 Intro to 39145 20 Hormones of the Adrenal Cortex • Negative feedback regulates cortisol secretion, similar to the regulation of thyroid hormone. 21 Pancreas • The hormone-secreting cells of the pancreas are grouped in clusters, or islets, that are closely associated with blood vessels. •Islets of Langerhans (pancreatic cells) secrete glucagon, insulin and somatostatin (digestive enzymes). 22 Insulin and Glucagon • Insulin and glucagon together stabilize [blood glucose] • Negative feedback responding to [blood glucose] controls the levels of both hormones • Glucagon stimulates liver (breaks down glycagon to glucose) • Insulin forms glycogen from glucose 23 Other Endocrine Glands Pineal Gland • secretes melatonin • regulates circadian rhythms Thymus Gland • secretes thymosins • promotes development of certain lymphocytes • important in role of immunity 24 Other Endocrine Glands Reproductive • ovaries produce estrogens and progesterone • testes produce testosterone • placenta produces estrogens, progesterone, and gonadotropins 25 Stress Types of Stress • physical stress • psychological stress Physical stress • threatens tissues • extreme hot/cold, decreased [02], infections, injuries, etc. Psychological stress • varies from person to person • thoughts from dangers, grief, fear, anxiety, etc. 26 Responses to Stress • • • • • • • • • • • 27 Life-Span Changes • endocrine glands decrease in size • muscular strength decreases as GH levels decrease • ADH levels increase due to slower break down in liver and kidneys • calcitonin levels decrease; increase risk of osteoporosis • PTH level changes contribute to risk of osteoporosis • insulin resistance may develop • changes in melatonin secretion affect the body clock • thymosin production declines increasing risk of infections 28 Negative Feedback Model hormone 1 lowers body condition gland high specific body condition low raises body condition gland hormone 2 2005-2006 Endocrine System Control Feedback Blood Sugar insulin body cells take up sugar from blood pancreas high liver stores sugar reduces appetite liver blood sugar level low triggers hunger liver releases sugar liver pancreas glucagon 2005-2006 Endocrine System Control Blood Osmolarity Feedback ADH increased water reabsorption pituitary increase thirst nephron high blood osmolarity blood pressure adrenal gland low increased water & salt reabsorption nephron renin aldosterone angiotensin angiotensinogen 2005-2006