Biology Revision - Chapter 9 Homeostasis PDF

Biology Revision Chapter 9: Homeostasis and Hormonal Control 1 Define homeostasis. Homeostasis is the maintenance of a constant internal environment. It is the process which ensures that the composition of the body fluids is kept with...

Biology Revision Chapter 9: Homeostasis and Hormonal Control 1 Define homeostasis. Homeostasis is the maintenance of a constant internal environment. It is the process which ensures that the composition of the body fluids is kept within narrow limits. Note: The external environment is the environment in which an organism lives. The internal environment includes the blood and tissue fluids that surround the cells in the body. Homeostasis helps an organism be independent of changes in the external environment. 2 Explain the principle of homeostasis (use these terms: stimulus, corrective mechanism, negative feedback) Normal / set point Stimulus – a change in the internal environment Receptor – an organ or a structure which detects the stimulus Corrective mechanism – which brings about the reverse effect of the stimulus Negative feedback – a feedback to the receptor when the normal condition is reached, and this causes the corrective mechanism to stop. 3 What do you understand by negative feedback? Negative feedback is a regulatory mechanism in which a stimulus causes the body to oppose the change, so as to restore the body to the normal level. OR Refers to the process where the body reacts to give the reverse effect of a stimulus (a change from the norm). It restores the normal conditions of the internal environment. 4 Identify parts of the human skin. Pg 1 of 6 5 (a) How does your body produce and gain heat? 1. Heat is released as a result of metabolic activities such as cellular respiration. High level of cellular respiration takes place in the muscles and liver. 2. Vigorous muscular exercise 3. Consumption of hot food 4. Being in a warm environment. (b) How does your body lose heat? Heat is lost 1. through the skin by radiation, convection, and conduction. 2. by evaporation of water in sweat from the skin surface 3. in faeces and urine 4. in expired air. 6 Describe how the body maintains a constant body temperature (to include role of hypothalamus, receptors and insulation) (a) Role of hypothalamus The hypothalamus monitors and regulates body temperature. Hypothalamus receives information about temperature changes from two sources: 1. thermoreceptors in the skin detect temperature change from the environment; nerve impulses are generated and sent to the hypothalamus 2. thermoreceptors in the hypothalamus detect temperature change in the blood Hypothalamus sends nerve impulses to relevant body parts to regulate body temperature. (b) What happens when the human body temperature begins to rise? On a hot day, increase in external temperature is detected by the thermoreceptors in the skin. OR During vigorous exercise, a large amount of heat is released and blood temperature increases. This is detected by the hypothalamus. Hypothalamus sends nerve impulses to the relevant body parts to bring about changes to restore the body temperature to the normal condition. Arterioles in the skin dilate and shunt vessels constrict allowing more blood to flow to the blood capillaries near the skin surface. Heat is lost through the skin by radiation, convection, and conduction. Sweat glands become more active, resulting in increased production of sweat. Sweat flows through the sweat duct to the sweat pore which opens at the skin surface. As more water in the sweat evaporates from the surface of the skin, more latent heat is lost from the body. Metabolic rate decreases to reduce to the amount of heat released within the body. Hair erector muscles in skin relax. (not effective in humans). (c) What happens when the human body temperature begins to drop? On a cold day, decrease in external temperature is detected by the thermoreceptors in the skin. OR The hypothalamus detects a drop in blood temperature. Hypothalamus sends nerve impulses to the relevant body parts to bring about changes to restore the body temperature to the normal condition. Pg 2 of 6  Arterioles in the skin constrict and shunt vessels dilate so that less blood flows to the blood capillaries near the skin surface. This reduces heat lost through the skin by radiation, convection, and conduction. Sweat glands become less active, resulting in decreased production of sweat. As less water in the sweat evaporates from the surface of the skin, less latent heat is lost from the body. Metabolic rate increases to reduce to the amount of heat released within the body. When the above reactions are insufficient to prevent a drop in body temperature, shivering occurs. This is a reflex contraction of body muscles to increase the amount of heat released and this helps to raise the body temperature to normal. Hair erector muscles in skin contract to trap a layer of still air. Air is a poor conductor of heat, and this provides insulation against heat loss. (not effective in humans) 7 What are hormones? A hormone is a chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organ(s) where it exerts its effect(s). After hormones have performed their functions, they are eventually destroyed by the liver. 8 What is meant by endocrine gland? An endocrine gland is a ductless gland that secretes the hormone directly into the bloodstream e.g., islets of Langerhans in the pancreas. 9 Endocrine glands and their hormonal secretions Pg 3 of 6 10 Regulation of blood sugar level – effects of insulin and glucagon Amount of insulin secreted Effect Normal decreases blood glucose concentration by o making cell membranes more permeable to glucose, allowing more glucose to diffuse into the liver and muscle cells o stimulating the liver and muscle cells to convert excess glucose to glycogen for storage o increasing the use of glucose for respiration Lack of secretion increases blood glucose level o glucose cannot be stored or utilized by tissue cells, some glucose lost in the urine. This gives rise to a disease called diabetes mellitus. muscle cells have no reserves of glycogen, the body grows weak and continuously loses weight. Oversecretion abnormal decrease in blood glucose concentration such that o low blood glucose concentration results in a condition called shock o seizures or fits. Collapsing or passing out may follow Pg 4 of 6  Pancreas increase the secretion of glucagon when the concentration of blood glucose decreases below normal levels. Main target of glucagon is the liver. Glucagon increases the blood glucose concentration by stimulating o the conversion of glycogen into glucose o the conversion of fats and amino acids into glucose. 11 (a) What happens when the blood sugar concentration rises beyond the normal level? After a meal rich in sugar or starch, glucose is absorbed into the bloodstream by the small intestine. Blood glucose concentration rises above normal. Pancreas is the receptor; it detects the increase in blood glucose level and secretes more insulin into the bloodstream. Blood transports insulin to the liver and muscles. Insulin increases the permeability of cell surface membrane to glucose. Glucose is absorbed more quickly by the cells. Insulin stimulates the liver and muscles to convert excess glucose to glycogen for storage. Glycogen is stored in the liver and muscles. Blood glucose level decreases. This provides a feedback to the receptor (pancreas) to reduce insulin production. Blood glucose level returns to normal. (b) What happens when the blood sugar concentration falls below the normal level? During vigorous muscular contraction or during starvation, blood glucose decreases below normal. Pancreas is the receptor; it detects the decrease in blood glucose level and secretes more glucagon into the bloodstream. Blood transports glucagon to the liver and muscles. Glucagon stimulates the liver and muscles to convert stored to glucose. From the liver, glucose enters the bloodstream. Blood glucose level decreases. This provides a feedback to the receptor (pancreas) to reduce glucagon production. Blood glucose level returns to normal. 12 (a) What is diabetes mellitus? A disease in which the body is unable to control the blood glucose concentration in order for it to remain within normal limits. As a result, the blood glucose concentration can rise to a level that exceeds the kidney’s ability to completely reabsorb all the glucose. The glucose that is not reabsorbed is excreted in the urine. (b) What are the signs of diabetes mellitus? Persistent high blood glucose level Presence of glucose in the urine after a meal Healing of wounds is slow or difficult Frequent urination Weight loss Thirst Pg 5 of 6  (c) How can diabetes mellitus be treated? Type 1 diabetes – pancreas unable to produce or secrete sufficient insulin. Inject insulin directly into their bloodstream. They have to ensure that they have a supply of sugary food e.g. glucose sweets as their blood glucose can drop too low if they use too much insulin, exercise too much or eat too little. In severe cases, low glucose may cause them to go into a coma. Type 2 diabetes – target cells e.g., muscle cells, do not respond well to insulin. Carefully regulate the carbohydrate content in their diet. Exercise. (d) What are the risk factors for type 2 diabetes Obsesity Age Family history Blood lipid levels Sedentary lifestyle (e) Healthy lifestyle can reduce the risk of getting type 2 diabetes Eating healthily: consume foods that are low in calories and high in fibre e.g., eat more fruit and vegetables. Engage in more active physical activities. Avoid being inactive for long periods of time. Maintain a healthy body weight, based on your age and height. 13 How do the kidneys help regulate water potential of blood? (refer to anti-diuretic hormone) (a) Loss of water through sweating Water potential in blood plasma decreases below normal. This stimulates the hypothalamus in the brain to produce more anti-diuretic hormone (ADH) and the pituitary gland to secrete more ADH into the bloodstream. ADH causes the cells in the walls of the collecting ducts to become more permeable to water. More water is reabsorbed from the collecting ducts into the blood capillaries. Smaller volume of urine is produced. Urine is more concentrated. Water potential of blood returns to normal. (b) Large intake of water through drinking Water potential in blood plasma increases above normal. This stimulates the hypothalamus in the brain to produce less anti-diuretic hormone (ADH) and the pituitary gland to secrete less ADH into the bloodstream. ADH causes the cells in the walls of the collecting ducts to become less permeable to water. Less water is reabsorbed from the collecting ducts into the blood capillaries. Larger volume of urine is produced. Urine is more diluted. Water potential of blood returns to normal. Pg 6 of 6