Nervous and Endocrine System Year 12 WACE Curriculum

8 Pages • Topic Notes • Year: Pre-2021

All nervous and endocrine system notes, year 12 2017: sample: Endocrine System: Glands that secrete their contents (hormones) directly into the blood and have no ducts or tubes Exocrine: Glands that release their secretions into ducts or tubes that deliver their contents into a cavity or surface Human body functions need to be controlled and regulated. The endocrine system consists of ductless glands that release hormones (this controls either the release of other hormones or acts directly on the cells activities). Hormones: Characteristics: 1. derived from proteins or steroid compounds 2. secreted directly into blood where they circulate around whole body but only affect the targeted tissue 3. work slower than nerves but with a more prolonged action 4. synthesised by an anabolic process by specialised cells 5. are the main regulators of metabolism, growth/development, reproduction, stress response and homeostasis of the body Mechanisms of Hormone Action: hormones bring about characteristic effects on cells by altering cell activity 1. changes in plasma membrane permeability or electrical state by opening or closing ion channels 2. synthesis of proteins or enzymes within the cell 3. enzyme activation or deactivation 4. induction of secretory activity 5. stimulation of mitosis Principles of Hormone Activity: • specificity of action depends on the target cells which have receptor molecules (made of protein) • each target cell is regulated by the hormone it has receptor molecules for • different cells may respond differently to the same hormone (e.g adrenaline) • some hormones, such as ones that maintain solute concentration in body fluids (e.g. insulin) are present much of the time while some are only secreted when needed • blood hormone levels are usually governed by negative feedback control • once hormones bind to receptor molecules they usually degrade rapidly. Rapid recovery system means target cells can be sensitive to changing levels of hormones that regulate their activities • Hormones can be removed from the blood by the kidney and liver enzyme systems Lipid soluble vs Water soluble Lipid soluble: They can pass right through target cells membrane, they bind to receptors inside the cell which activates a hormone which then binds to part of the DNA. Binding causes genes to turn enzyme activity on or off (alters the activity of the cell) - steroid derived hormones are lipid soluble, which means they act directly on the cell

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