The Endocrine System In fluctuating environments, animals manage a steady state within their bodies by regulating or conforming o Regulators – animals using internal mechanisms to control internal change relative to external variability o Conformers – allow internal change in relation to external environmental changes (exotherms = cold blooded) Endotherm vs. Exotherm o Some organisms regulate some internal conditions while conforming to others Example: snake conforms to outside temperature; but regulates concentration of solutes in blood o Homeostasis – the steady state of the physiological condition of the body; maintenance of internal balance Animals can achieve homeostasis even when there are extreme changes in the environment Can be achieved for a variety of physical and chemical properties of the body Temperature (36 to 42 C in homeotherms, approx. 37 C in humans) pH: 7.4±0.1 in humans Sugar (Glucose): 70-110 mg per 100 ml of blood in humans o Maintain homeostasis by keeping variable (temp, pH, glu-, etc) at a near set point Changes in variable above/below set point act as a stimulus Stimulus detected by some form of sensor Sensor then triggers response by some control center o Homeostasis is a dynamic equilibrium Homeostasis in animals relies on negative feedback mechanism that reduces the stimulus Positive feedback amplifies stimulus but doesn’t play a big role in homeostasis Example: Blood Clotting o Break in blood vessel o Clotting by platelets o Chemical releases more platelets o Clot is filled Animal endocrine system helps regulate homeostasis, development, behavior through hormones and other signaling molecules o Human endocrine tissues and organs
Major endocrine glands, other organs containing endocrine cells
Chemical stimulus are used by cells to communicate with each other Classify communication of type of sensory cell and route signal takes to reach target cell o Endocrine signals Hormones are secreted into extracellular fluids by endocrine fluids by endocrine cells; reach target cells via bloodstream ( hemolymph – fluid filling spaces between cells) Functions to maintain homeostasis Blood pressure and blood volume Energy/metabolism and energy allocation Solutes concentrations in body fluids Also… Helps maintain responses to environmental stimuli (hot/cold) Regulate growth/development Physical and behavioral change during sexual reproduction o Paracrine and Autocrine signaling Occurs over short distances and reach target cells via diffusion Signaling molecules produced and secreted by cells are local regulators Many types of cells produce and secrete local regulators (immune cells, prostrate gland cells, cells of placenta) Paracrine signals – occurs when target cells lie near secretory cells Autocrine signals – occurs when secreting cells are the target cells Example of local regulators include prostaglandins,
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- Spring '12
- Endocrine System, cells