Animal Form and Function & Hormones and the Endocrine System Chapters 40 & 45

YOU MUST KNOW The importance of homeostasis & examples How feedback systems control homeostasis One example of positive feedback and one example of negative feedback How hormones bind to target receptors and trigger specific pathways The secretion, target, action, and regulation of at least two hormones An illustration of both positive and negative feedback in the regulation of homeostasis by hormones

I. Control & Coordination A I. Control & Coordination A. Endocrine system – produces hormones (chemical signals), releases them into blood, act at target tissues that contain receptors B. Nervous system – transmit information between locations by nerve impulses

II. Homeostasis Maintaining a relatively stable internal environment Must stay within a range of tolerance 1. Sensors detect stimulus above or below and trigger response Hypothermia <95.0 ° F Normal 97.7 – 99.5 °F Fever >100 °F

Negative Feedback 1. Keep body within range of tolerance (maintains homeostasis)

III. Positive Feedback 1. Used to amplify a signal Another example is blood clotting

IV. Thermoregulation Endotherms – warmed by heat generated by metabolism (mammals, birds) Ectotherms – gain heat from external sources (reptiles)

C. Countercurrent exchange – heat transfer involves antiparallel arrangement of blood vessels so that heat in vessels on the way to extremities transfers heat to blood returning from extremities

IV. Energy Requirements Metabolic rate – energy used per time 1. Generally higher for endotherms 2. Standard (ectotherms) v Basal (endotherms) Metabolic rates (both at rest) 3. Inversely related to body size

V. Secretion & Response Endocrine system is all hormone-secreting cells and tissues 1. Endocrine glands – no ducts, secrete hormones directly into body fluids 2. Hormones – chemical signals that cause a response in target cells

Target cell receptors 1. Cell-surface receptors – at the cell membrane, binding of hormone causes signal transduction pathway Ex. epinephrine binding to liver cell causes conversion of glycogen to glucose https://www.youtube.com/watch?v=FXMgd-aAFMA

2. Intracellular receptors – found within the cell (require lipid-soluble hormones), receptor-hormone complex acts as a transcription factor affecting gene expression Ex. Testosterone stimulates expression of specific genes https://www.youtube.com/watch?v=wJk7nRccLbc

Receptors can be on one tissue, multiple tissues, most tissues, or other endocrine glands (tropic hormones) a. Hypothalamus – coordination between nervous & endocrine systems

b. Posterior pituitary – stores and releases hormones made by the hypothalamus -Oxytocin – causes uterine contractions during childbirth and ejection of milk during nursing -Antidiuretic hormone (ADH) – target cells are collecting ducts of kidneys, makes them more permeable to water so that more water is reabsorbed back to the body instead of exiting in urine

Anterior pituitary – synthesizes & secretes hormones, many tropic, -Follicle-Stimulating Hormone (FSH) – stimulates gametogenesis (formation of eggs & sperm) -Luteinizing Hormone (LH) – triggers ovulation and production of testosterone