1. A GUIDE

2. Homeostasis refers to the maintenance of a constant internal environment 3. Internal environment: This refers to the conditions within the body of the organism. In humans, this includes the blood and tissue fluids. Therefore, homeostasis is the process which ensures that the composition of bodily fluids is kept within narrow limits. 4. By ensuring a relatively stable internal environment, homeostasis allows organisms to be independent from changes in the external environment (the surroundings) This external environment is the environment in which an organism lives. 5. Homeostasis also involves a process called negative feedback: In homeostasis control, your body reacts to bring about changes that are opposite to the changes that are being detected. If the system (you body) is disturbed, the disturbance sets in motion, a sequence of events that restores the body to its original state. This is called the negative feedback process. 6. In a negative feedback control loop, there must be: A normal condition or set-point to be maintained A stimulus; which is a change in the internal environment A receptor that can detect the stimulus and sends signals to the control centre A corrective mechanism, which brings about an opposite effect of the stimulus A feedback to the receptor when the set-point is reached, causing the corrective mechanism to stop. 7. Temperature homeostasis (Thermoregulation) basically refers to the regulation of body temperature, which in turn means the process of maintaining the temperature of the human body at a constant, acceptable rate. 8. The body regulates temperature by balancing the amount of heat lost and heat produced from and by the body. Animals that maintain a constant body temperature are called endotherms. Animals that have a variable body temperature are called ectotherms. 9. Endotherms: Normally maintains their body temperature at 35-40 degrees, and hence known as warm-blooded creatures (e.g. Birds and mammals) Ectotherms: Known as cold-blooded creatures these animals can also warm themselves in the day by basking in the sun, etc. (E.g. bumblebees and tuna) We humans use both mechanisms! Difference Endotherms Ectotherms Uses internal corrective mechanism to regulate temperature (the maintenance of temperature occurs inside the body) Uses behavioural mechanism to regulate temperature (E.g. lying in the sun when cold, moving into the shade when hot) 10. In Humans, Heat is produced in the body when processes such as cellular respiration (when cells respire) occurs. High levels of cellular respiration occurs in the liver and muscles. As a result, large amounts of heat is released in these organs, and then distributed evenly throughout the body via the bloodstream. 11. The body can gain extra heat through: Vigorous muscular exercise The consumption of hot food Being in warm environments (e.g. being outdoors on a very hot day. 12. The body can lose heat through: The skin by radiation the transfer of heat in the form of waves without the use of a medium, convection the transfer of heat through a medium in the for of currents, and to a limited extent, conduction-the transfer of heat from one object/medium to another. By evaporation of water in sweat at the surface of our skin In the faeces and urine, including the air that we exhale. 13. How does you body regulate temperature? The hypothalamus (a portion of your brain that contains a small number of nuclei, that performs a variety of functions) in your brain monitors and regulates your body temperature. The hypothalamus receives information about temperature changes from two sources: 1) the thermo receptors in your skin which detect temperature from the environment, and 2) the thermo receptors of the hypothalamus which detect the temperature of the blood 14. What happens when human body temperature begins to rise? When one performs rigorous exercise, a large amount of heat is produced. This heat accumulates in the body, causing a rise in blood temperature. This change is detected by the hypothalamus, causing it to send out nerve impulses to the relevant body parts to bring about changes such as: Dilation of tiny arteries called arterioles in our skin, and the constriction of vessels called shunt vessels which connects the skin arterioles to the skin venules-tiny veins. This allows more heat to be lost through radiation, convection and conduction. Sweat glands become more active, resulting in more sweat being produced. As more water evaporates from the sweat on the skin surface, more heat is lost. There is also a decreased metabolic rate, thus reducing the amount of heat produced in the body. 15. What happens when human body temperature begins to fall? On a cold day, the rate of heat loss increases, especially at the skin surface. This drop in temperature stimulates the temperature receptors to rapidly send nerve impulses to the hypothalamus. The hypothalamus with then send nerve impulses to the relevant body parts to bring about these changes: Constriction of skin arterioles and dilation of shunt vessels so that less blood flows through the blood capillaries in the skin, thus reducing heat loss by conduction, convection and radiation. Sweat glands become less active, resulting in decreased production of sweat. Less water evaporates from the body, and thus less heat is lost. Increased metabolic rate, to increase the amount of heat released within the body. When the above are insufficient, shivering, a reflex action occurs. This contraction of the 16. Blood Glucose concentration 17. It is the balance of the hormones insulin & glucagon to maintain the concentration of glucose in the blood at a constant level. This is controlled to provide the cells with a constant supply of energy. The cells in our bodies require glucose (a sugar) for respiration. What is it? 18. Insulin is a hormone which plays a key role in the regulation of blood glucose levels. It is secreted by the beta cells of the pancreas in response to high blood glucose levels. Glucagon is a hormone which also plays a major role in maintaining normal concentrations of glucose in the blood. It is secreted by the alpha cells of the pancreas when the blood glucose levels are low. Insulin & Glucagon 19. Insulin is released from pancreatic beta cells in the Islets of Langerhans. The uptake of glucose is stimulated, the cells absorb glucose more quickly Excess glucose is converted into glycogen in the liver, this is caused by the hormone insulin. The excess glucose which was converted to glycogen is then stored for a later date in the liver. Hence, the concentration of glucose in the blood is decreased. When Glucose Levels Are Too High 20. The hormone glucagon is secreted by the alpha cells in the Islets of Langerhans in the pancreas. During starvation or after intense exercise, glucagon promotes the conversion of the stored glycogen in the liver to glucose. The glycogen which has been converted to glucose enters the bloodstream. Thus, the concentration of glucose in the blood increases. When Glucose Levels Are Too Low 21. What is blood Pressure? the pressure of the blood against the inner walls of the blood vessels, varying in different parts of the body during different phases of contraction of the heart and under different conditions of health It is also the pressure of the blood in the circulatory system, often measured for diagnosis since it is closely related to the force and rate of the heartbeat and the diameter and elasticity of the arterial walls: 22. Regulation of blood pressure The circulatory system plays a major role in the regulation of temperature, body fluids, glucose and gases. The blood transports hormones , gases and nutrients and allows for heat gain or loss. The pressure at which the blood is pumped and distributed is also controlled by a homeostatic mechanism. 23. Whats the purpose of regulating blood pressure ? Changes in blood pressure are routinely made in order to direct appropriate amounts of oxygen and nutrients to specific parts of the body. So if we are exercising, then more blood is sent to the muscles. Having eaten, more is sent to the gut to aid absorption. 24. How is Blood Pressure Controlled by Homeostasis? Blood Pressure is controlled by homeostasis through the use of sensory receptors and hormonal secretions. A barorecetor reflex is a homeostasis mechanism which uses sensory receptors in the heart to send messages to the brain to regulate blood pressure. Homeostasis also works via adrenal secretions to control blood pressure. 25. A diagram on Blood Pressure Homeostasis It shows the contribution of vasopressin and vasopressin receptor type V1a and V2 in the regulation of blood pressure homeostasis. 26. A HOMEOSTATIC IMBALANCE IS THE DISTURBANCE OF THE HOMEOSTASIS IN THE HUMAN BODY. THIS RESULTS IN AN UNSTABLE INTERNAL ENVIRONMENT THAT INCREASES THE RISK OF ILLNESS. IT IS RESPONSIBLE FOR MANY DISEASES AND PHYSICAL CHANGES IN OLD AGE. 27. DIABETES MELLITUS Insulin is a hormone responsible for regulating carbohydrates and fats in the body. It causes the cells in the body to absorb glucose from the blood. Diabetes mellitus can be caused by the bodys failure to produce insulin or when cells fail to use insulin properly. Due to the bodys failure to regulate the carbohydrate and fat metabolism in the body, this results to homeostatic imbalance, Diabetes Mellitus. Diabetes mellitus is the failure to keep blood glucose concentration within the normal level. 28. DEHYDRATION Dehydration is the excessive loss of body water. Fluid balance is maintained through a process called water homeostasis. When a person is dehydrated, the amount of water in the circulation is low and this is detected by the brain. A hormone is then released by the pituitary gland to ensure that the amount of water being released, in the form of urine, is reduced. 29. HYPOGLYCaEMIA / HYPERGLYCAEMIA Hypoglycaemia is the condition in which a person has low blood glucose level. Hyperglycaemia is the condition in which a person has high blood glucose level. The causes of hypoglycaemia are the excessive insulin produced in the body, hormone deficiencies and organ failures. While, the cause of hyperglycaemia is the inadequate insulin production. When too much insulin is produced, the release of glucagon is inhibited. Glucagon is a hormone that converts glycogen to glucose. When glucagon is not released, needed glucose is also not released, therefore resulting in hypoglycaemia. When too much glucagon is released, too much glucose is released resulting in hyperglycaemia. 30. GOUT Gout is caused by the high levels of uric acid in the blood. * Uric acid is a metabolic product that causes a person to get sick when contained in high levels. Gout causes painful inflammation in muscle joints. When there is a high level of uric acid, crystals of uric acid may form and typically collect in a joint, causing the joints to be irritated and hence the person experience a gout attack. 31. Medical conditions: An inability to maintain homeostasis may lead to death or a disease condition known as homeostatic imbalance. For example: Heart failure Diabetes Dehydration Hypoglycemia Hyperglycemia Gout; etc. Medical intervention can help restore homeostasis and possibly prevent permanent damage to organs.