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BIOLOGY UNIT 3

BIOLOGY UNIT 3. PRINCIPLES OF COMMUNICATION. Production of a signal Detection of the signal Transfer or transduction of the signal Response to the signal Control of the signal by switching it off. SIGNALS FROM THE ENVIRONMENT. External receptors (exteroceptors).

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BIOLOGY UNIT 3

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  1. BIOLOGY UNIT 3

  2. PRINCIPLES OF COMMUNICATION • Production of a signal • Detection of the signal • Transfer or transduction of the signal • Response to the signal • Control of the signal by switching it off. 12 BIOLOGY, CH 4

  3. SIGNALS FROM THE ENVIRONMENT External receptors(exteroceptors) 12 BIOLOGY, CH 4

  4. SIGNALS FROM THE ENVIRONMENT Internal and external environment 12 BIOLOGY, CH 4

  5. SIGNALS FROM THE ENVIRONMENT Internal receptors (interoceptors) Most cells in a multicellular organism are surrounded by tiny spaces filled with interstitial fluid. The interstitial fluid makes up the internal environment and needs to be maintained within narrow limits of pH, solute concentrations and temperature, for cells to operate at maximum efficiency. 12 BIOLOGY, CH 4

  6. SIGNALS FROM THE ENVIRONMENT (cont.) Chemoreceptors in the aorta and carotid arteries detect carbon dioxide levels. Thermoreceptors in the hypothalamus detect body temperature. 12 BIOLOGY, CH 4

  7. Cells and organisms need to respond: • Growth and reproduction • Cells divide and differentiate in response to internal and external signals. • Cancer and malformations result from incorrect signals. • Homeostasis • “The maintenance of a relatively stable internal environment within a small range of tolerance, despite changes in the external environment.” • Concentrations of O2, CO2, glucose, H+ ions (pH), etc all impact on the way cells function. • Surviving challenges in the external environment • Avoiding injury or death requires organisms to detect and respond to dangers in the environment. 12 BIOLOGY, CH 4

  8. Review questions – set 1 12 BIOLOGY, CH 4

  9. THE STIMULUS-RESPONSE MODEL eg. pin prick pain receptor (nerve) central nervous system muscle cell finger moves away from pain 12 BIOLOGY, CH 4

  10. NEGATIVE FEEDBACK high blood glucose level receptor in pancreas pancreas cancels the original stimulus release of insulin by α-cells lower blood glucose level 12 BIOLOGY, CH 4

  11. POSITIVE FEEDBACK The response actually reinforces the original stimulus eg. tadpoles metamorphose into frogs as a result of positive feedback on the production of the hormone thyroxine (which is usually under negative feedback control) Positive feedback is rare and is usually harmful 12 BIOLOGY, CH 4

  12. Positive Feedback in Childbirth Oxytocin produced by the posterior pituitary gland stimulates contraction of the uterus and also stimulates the pituitary gland to produce even more of the hormone. Note the positive feedback nature of the inputs. From Jacaranda Biology 3&4 12 BIOLOGY, CH 4

  13. PRINCIPLES OF CELL COMMUNICATION Production of an extracellular signalling molecule by a cell. Detection of this signal by a receptor protein in the target cell. Transduction of this signal through the cell. The response of the cell itself. Control or regulation of the signal or response. 12 BIOLOGY, CH 4

  14. ANIMATION 12 BIOLOGY, CH 4

  15. Review questions – set 2 12 BIOLOGY, CH 4

  16. CHEMICAL COMMUNICATION IN ANIMALS • Most chemical communication in animals is carried out by hormones: • They travel in the bloodstream • Only specific target cells respond • Need very small amounts of hormone • Involved in homeostasis, growth, reproduction, energy and behaviour 12 BIOLOGY, CH 4

  17. CHEMICAL COMMUNICATION IN ANIMALS • There are two main types of hormones: • Steroid hormones – mostly the sex hormones eg. testosterone and oestrogen • Polypeptide or protein hormones – eg. insulin, glucagon, growth hormone, thyroxine, adrenaline. 12 BIOLOGY, CH 4

  18. DETECTING THE SIGNAL Receptor proteins in target cells have a complementary shape to the hormone, similar to the active site on an enzyme. Receptor proteins are found either on the surface of the cell or in the cytoplasm. 12 BIOLOGY, CH 4

  19. DETECTING THE SIGNAL >> do SRAM 62 12 BIOLOGY, CH 4

  20. SECOND MESSENGER SYSTEMS(used by protein hormones) Receptor proteins stimulate the production of a small molecule (eg. cyclic AMP) which acts as a second messenger in the cell and produces a response. One hormone molecule can stimulate the production of many second messengers. 12 BIOLOGY, CH 4

  21. DIRECT SYSTEMS(used by steroid hormones) Steroid hormones are fat-soluble and can move through the plasma membrane. They bind with a receptor protein in the cytoplasm. They then move into the nucleus where they turn genes on or off and this affects the types of enzymes that are produced. 12 BIOLOGY, CH 4

  22. Review questions – set 3 Signal Transduction Video on YouTube See also Heineman Text CD: Interactive Tutorials Hormone Action >> do SRAM 63 12 BIOLOGY, CH 4

  23. Control of Blood Glucose Levels (BGL) Glucose is necessary for the effective functioning of cells and therefore the whole organism. It is used for energy production and is also involved in creating osmotic differences across cell membranes which affect the movement of substances across the membranes. 12 BIOLOGY, CH 4

  24. 12 BIOLOGY, CH 4

  25. Insulin and Glucagon Blood glucose levels are maintained within narrow tolerance limits by the action of two antagonistic hormones: insulin and glucagon. Antagonistic hormones have opposing actions in a given situation. Both of these hormones are produced in the pancreas. Insulin is produced in the beta(β) cells of the islets of Langerhans, and glucagon is produced in the alpha(α) cells. 12 BIOLOGY, CH 4

  26. Islets of Langerhans Section through pancreas tissue showing islet of Langerhans (the pale circle at lower left). The islets are clumps of secretory cells that form part of the hormone system. The islets also contain nerve cells that influence insulin and glucagon secretion. From Jacaranda Biology 3&4 12 BIOLOGY, CH 4

  27. Islets of Langerhans Islet of Langerhans (yellow) surrounded by acini cells (pink). Beta cells (yellow) secrete insulin. Alpha cells (red) secrete glucagon. Delta cells (blue) secrete somatostatin and gastrin. The circle of acini cells (pink) produces the pancreatic digestive enzymes. From Jacaranda Biology 3&4 12 BIOLOGY, CH 4

  28. Insulin • Insulin lowers the blood glucose levels by: • Increasing uptake of glucose by cells • Increasing conversion of glucose to glycogen and fat • Reducing the conversion of glycogen to glucose 12 BIOLOGY, CH 4

  29. Insulin 12 BIOLOGY, CH 4

  30. Glucagon • Glucagon raises the blood glucose levels by: • Inhibiting the production of insulin • Increasing conversion of glycogen to glucose • Formation of glucose from non-carbohydrate sources (eg. Fats and proteins) 12 BIOLOGY, CH 4

  31. 12 BIOLOGY, CH 4 From Jacaranda Biology 3&4

  32. Hyperglycaemia • Hyperglycaemia occurs when BGL is high: • glucose is excreted in the urine • person produces large amounts of urine • person drinks large amounts of water 12 BIOLOGY, CH 4

  33. Hypoglycaemia • Hypoglycaemia occurs when BGL is low. • person feels tired and lacking energy • Glucagon is secreted and the BGL is raised to optimal levels 12 BIOLOGY, CH 4

  34. Diabetes • Diabetes occurs in two main forms: • Type 1: insulin-dependent diabetes (Diabetes mellitus) where the pancreas is unable to secrete enough insulin • Type 2: adult-onset diabetes is caused by the adoption of a Western diet high in fats, sugars and processed foods, and a lack of exercise. >> do SRAM 74 12 BIOLOGY, CH 4

  35. Review questions – set 4 12 BIOLOGY, CH 4

  36. Thyroid Hormones • Thyroid hormones, often called thyroxines, are secreted by the thyroid gland, situated in the neck close to the larynx, or voice box. • Thyroxine is derived from the amino acid tyrosine and the element iodine. • It affects three main physiological processes: • cellular differentiation, • growth and • metabolism. • There are very few cells that are not affected by these hormones. 12 BIOLOGY, CH 4

  37. Control of Thyroid Hormones Thyroxine production is controlled through two negative feedback loops. Thyroxine inhibits the secretion of thyroid-stimulating hormone (TSH) from the pituitary gland and also the secretion of thyrotrophin-releasing hormone (TRH) from the hypothalamus. 12 BIOLOGY, CH 4

  38. Hypothyroidism People suffering from too little thyroxine (hypothyroidism) often show puffiness around the eyes and coarsening of the skin. 12 BIOLOGY, CH 4

  39. Hyperthyroidism Protrusion of the eyeballs (exophthalmia) is a symptom of hyperthyroidism, when the thyroid gland produces too much thyroxine. 12 BIOLOGY, CH 4

  40. Goitre Reduced or impaired production of thyroxine by the thyroid gland can cause it to enlarge to form a goitre. 12 BIOLOGY, CH 4

  41. Review questions – set 5 12 BIOLOGY, CH 4

  42. Hormones vary in the distance they travel Hormones can be classified by the distance over which they travel to their target cells. Endocrine hormones are distributed widely to target cells throughout the body. 12 BIOLOGY, CH 4

  43. Hormones vary in the distance they travel Paracrine hormones act locally on neighbourhood cells. 12 BIOLOGY, CH 4

  44. Hormones vary in the distance they travel Autocrine hormones act on the cell that secreted them or cells of the same type. 12 BIOLOGY, CH 4

  45. Hormones vary in the distance they travel Contact-dependent signalling requires cells to be in direct contact. 12 BIOLOGY, CH 4

  46. Review questions – set 6 (see next slide) 12 BIOLOGY, CH 4

  47. Question 19 • fatty acid hormone • not secreted by glands • produced and secreted by cell membranes • quickly destroyed by enzymes in the intersticial fluid • can act as a paracrine and autocrine hormone • (first isolated from the prostate gland) • more than 16 prostaglandins have been isolated • involved in: • digestion • blood clotting • smooth muscle contraction eg. uterus during childbirth • initiate inflammatory response in injured or infected tissue • vasodilation of arterioles to increase blood-flow • aspirin and hydrocortisone suppress the production of prostaglandins 12 BIOLOGY, CH 4

  48. Nervous System An excellent site on many aspects of the nervous system. A site about the Neuron Label the Neuron (Students produce a summary of the nervous system as outlined in this file >>) The file is also on Studywiz. 12 BIOLOGY, CH 4

  49. Nerve Impulse Animation Show Animation (http://www.biology4all.com/resources_library/source/63.swf) A domino model of a nerve impulse 12 BIOLOGY, CH 4

  50. Nerve Impulse 12 BIOLOGY, CH 4

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