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Regulating Mechanisms

Regulating Mechanisms. Homeostasis. Homeostasis. This is the regulation of the body’s internal environment within tolerable limits despite changes in the external environment. Negative Feedback Control. Control of Heart Rate. The pacemaker initiates each heart beat.

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Regulating Mechanisms

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  1. Regulating Mechanisms Homeostasis

  2. Homeostasis • This is the regulation of the body’s internal environment within tolerable limits despite changes in the external environment.

  3. Negative Feedback Control

  4. Control of Heart Rate • The pacemaker initiates each heart beat. • The rate at which the heart beats can be altered by nervous and hormonal activity.

  5. Autonomic Nervous Control • Two branches of the autonomic nervous system supply the heart. • Control centres in the medulla regulate heart rate. • The cardio-accelerator centre sends impulses via sympathetic nerves resulting in an increase in heart rate. • The cardio-inhibitor centre sends impulses via the parasympathetic nerves resulting in a decrease in heart rate. • The pathways are antagonistic.

  6. Autonomic Nervous Control

  7. Hormonal Control • The hormone adrenaline increases heart rate. • During times of stress or exercise the sympathetic nervous system acts on the adrenal gland making adrenaline which acts on the pacemaker.

  8. Effects of Exercise on the Respiratory System • Rate and depth of breathing increases. • Resulting in increased ventilation promoting uptake of oxygen and removal of carbon dioxide. • The rate and depth of breathing is stimulated by high levels of carbon dioxide (but eventually low levels of oxygen will act as a stimulus)

  9. Effect of Exercise on CVS • Stroke Volume (vol blood pumped by each ventricle) and heart rate increase with exercise. • Cardiac Output (vol blood pumped by each ventricle per minute) • CO = HR x SV • Cardiac output therefore also increases with exercise.

  10. Redistribution of Blood • Blood flow to the muscles, heart and skin is increased by widening of the arterioles – VASODILATION • Blood flow to the kidneys, gut, liver etc… is decreased by narrowing of the arterioles - VASOCONSTRICTION

  11. Redistribution of Blood Flow during Exercise During exercise, blood flow to the heart, skin and muscles increases.

  12. Homeostatic Control of Respiratory System • Chemoreceptors are in the carotid arteries and the aorta. • They are sensitive to carbon dioxide conc in the blood. • They send out an impulse to the medulla if the conc of carbon dioxide increases. • It responds by sending impulses to the intercostal muscles and diaphragm increasing their activity resulting in an increase in rate and depth of breathing.

  13. Control of Breathing

  14. Medulla Oblongata Many motor impulses Many sensory impulses Diaphragm and intercostal muscles Chemoreceptors in carotid arteries Increase in carbon dioxide conc Increase in rate and depth of breathing Normal situation no deviation from set point Normal carbon dioxide conc Normal carbon dioxide conc Deacrease in carbon dioxide conc Descrease in rate and depth of breathing Chemoreceptors in carotid arteries Diaphragm and intercostal muscles Few sensory impulses Few motor impulses Medulla Oblongata

  15. Control of Blood Sugar Level • This is by homeostatic control. • Insulin released by the pancreas stimulates an enzyme to convert glucose to glycogen where it is stored in the liver. • Glucagon released by the pancreas stimulates an enzyme to convert glycogen to glucose

  16. Role of Hormones

  17. Adrenaline • In an emergency when the body needs additional glucose supplies, adrenaline is released which overrides the homeostatic control and promotes the breakdown of glycogen to glucose. • ‘Fight or Flight’ situation.

  18. Adrenal Glands • The adrenal glands are located above the kidneys and they secrete the hormone adrenaline.

  19. Diabetes Mellitus • Insulin secreting pancreas cells are not functioning properly. • Subsequently they have high levels of glucose in their blood. • This results in less being reabsorbed by the kidneys so glucose is found in the urine. • It is treated by regular injections of insulin.

  20. Glucose Tolerance Curve

  21. Control of Body Temperature • Under homeostatic control • Hypothalamus is the body’s temperature-monitoring centre. • It acts as a thermostat keeping the body at a constant temp. • Changes in temp are detected by thermoreceptors in the hypothalamus.

  22. Vasodilation More blood flows close to the skin so heat is lost

  23. Vasoconstriction Blood flows away from the skin so only little heat is lost.

  24. Hair in Cold Temperatures

  25. Hair in Hot Temperatures

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