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Hormones (part 1): Endocrine glands and insulin

Students should be able to: <br>- define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver <br>- explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas<br>- explain how the blood glucose concentration is regulated by insulin and glucagon as a homeostatic mechanism <br>- describe the signs, such as an increased blood glucose level and glucose in urine, and the treatment of diabetes mellitus using insulin

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Hormones (part 1): Endocrine glands and insulin

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  1. Hormones and endocrine glands Chapter 15

  2. Hormones Definition Chemical substances produced in minute quantities by an endocrine gland that is transported in the bloodstream to target organ(s) where it exerts its effects ⚫ Assist nervous system in coordination (synergy) ⚫ Have powerful effects on the body (must balance production) 2 functions: 1. Exercise control over other glands/muscles 2. Control/coordinate body activities (growth & development)

  3. 2 methods of testing hormonal levels in our bodies 1. 2.

  4. Endocrine vs exocrine glands Exocrine glands = glands that have ducts to carry away their secretions out of the body Endocrine glands = ductless glands = does not have ducts/tubes to carry away its secretion (hormones pass directly into bloodstream for distribution around the body)

  5. Examples Exocrine sweat gland (sweat) Endocrine thyroid gland (thyroxine) Both gonads (testosterone) pancreas (pancreatic juice) Islets of Langerhans (insulin & glucagon)

  6. Location of endocrine glands

  7. Location of the adrenal gland

  8. Control of endocrine glands By nervous system Chemical substances Hormones from other endocrine glands 1. 2. 3.

  9. Important pointers: Pituitary gland = “master gland”/”controller” → secretes a number of hormones → each controls particular gland activity Some glands do not function until a certain age → reproductive organs (gonads) Long-term vs short-term hormones → thyroxine (long-term, permanent effects) → adrenaline (short-lived effects) 1. 2. 3.

  10. Important pointers: Production of hormones must be adequate and balanced → excessive production of certain hormones may be harmful Hormones are destroyed by the liver and excreted by the kidneys after performing their functions 4. 5.

  11. Insulin

  12. Islet of Langerhans (in pancreas) ▪ produce insulin ▪ during increase in blood glucose concentration Effects of insulin: [overall increase in cell glucose utilization] 1. Increased cell membrane permeability to glucose → increasing rate of glucose uptake by cells 2. Cause increased oxidation of glucose during tissue respiration 3. Causes conversion of EXCESS glucose to glycogen for storage in liver and muscles

  13. Effects of lack of secretion Blood glucose conc. rises → not utilized by cells → diabetes mellitus Body weakness → no glycogen reserves → continuous loss of weight Fat oxidation preferred → formation of ketones (poisonous) → excreted in urine (ketonuria) → death may occur 1. 2. 3.

  14. Effects of oversecretion Abnormal decrease in blood glucose conc. Shock results Coma and death ensues 1. 2. 3.

  15. Diabetes mellitus Body unable to control its blood glucose conc. within safe limits Kidney unable to reabsorb all the glucose Glucose not reabsorbed is excreted in the urine 2 main types: Type 1 Type 2 ▪ ▪ ▪ 1. 2.

  16. Type 1 diabetes ▪ Juvenile/early-onset diabetes (occurs early in life) ▪ Due to inability of pancreas to produce sufficient insulin

  17. Type 2 diabetes ▪ Late-onset diabetes (occurs later in life) ▪ Overweight people more prone ▪ Due to failure of target cells (e.g. muscle cells) to respond to insulin

  18. Treatment Measure blood glucose conc. Test urine regularly Watch diet carefully (not too much carbohydrate intake) Type 1: Inject insulin into veins daily Ensure supply of sugary foods → too low (due to too much insulin, exercise too much or eat too little → coma Type 2: Watch carbohydrate content in diet Seldom need for insulin jabs 1. 2. 3. ▪ ▪ ▪ ▪

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