Physiology Lecture Notes PDF

The body uses so much energy, even during sleep, because it must maintain a constant internal environment. This process of keeping things the same is called homeostasis. A series of automatic control systems ensures that the body maintains a constant temperature, and steady levels of water, ions a...

The body uses so much energy, even during sleep, because it must maintain a constant internal environment. This process of keeping things the same is called homeostasis. A series of automatic control systems ensures that the body maintains a constant temperature, and steady levels of water, ions and blood sugar. Homeostasis allows the body’s cells to work at their optimum. 1 of 40 © Boardworks Ltd 2007 Homeostasis: The term ‘homeostasis’ is derived from two Greek words; Homeo which means ‘unchanging’ and Stasis which means ‘standing’  Homeostasis is the process by which a stable internal environment is maintained despite changes in the external environment.  Homeostasis is The process that involves keeping the internal environment within set ranges 28.1 Levels of Organization Control systems in the body. – Sensors -gather data and detect changes – Control center - receives data, sends messages, usually the brain -Communication system - delivers messages in form of nerve impulses and hormones to target organs, tissues – Targets – organ, tissue or cell that responds to change 28.1 Levels of Organization Each organ system affects other organ systems. Organ systems must also work together to keep the organism healthy. There is no specific organ which controls homeostasis. The skin, kidneys, liver, endocrine system, nervous system and sensory system all play a part in maintaining the internal environment within narrow limits. The hypothalamus is involved to a degree in each of these regulations 28.1 Levels of Organization Body cells work best if they have the correct Temperature Glucose concentration, (sugar) Water levels 28.1 Levels of Organization Organs and involved: Water - kidneys : skin regulate water & mineral salts concentration tissue cells Thermoregulation –skin and muscles : regulate body temperature kidney Glucose - liver & pancreas : regulate blood glucose level liver blood + pancreas How is temperature controlled? Body temperature is monitored and controlled by temperature receptors in the skin and brain. hypothalamus These receptors detect changes in the temperature of blood flowing through those areas. The thermoregulatory centre in the brain is called the hypothalamus. If body temperature deviates from 37 °C, the hypothalamus and skin receptors send out electrical signals that trigger actions or behaviours that increase or decrease heat loss. 7 of 40 © Boardworks Ltd 2007 28.1 Levels of Organization Thermoregulation – process of maintaining a steady body temperature Sweating When your body is hot, sweat glands are stimulated to release sweat. The liquid sweat turns into a gas (it evaporates) To do this, it needs heat. As your skin loses heat, it cools down. 28.1 Levels of Organization Thermoregulation – process of maintaining a steady body temperature Shivering Hypothalamus signals skin , muscular, respiratory, and circulatory systems Blood vessels constrict to reduce blood flow to prevent loss of heat Muscles contract around pores Muscles contract causing shivering Thyroid releases hormones that increase metabolism Vasoconstriction and warming up Why do people go pale when they are cold? When core body temperature falls, blood vessels in the skin get narrower. This is called vasoconstriction. Vasoconstriction is caused by contraction of the muscular wall of the blood vessels. This reduces the volume of blood flowing near the skin surface, and reduces the amount of heat lost from the body. 10 of 40 © Boardworks Ltd 2007 Vasodilation and cooling down Why do people turn red when they are hot? When core body temperature rises, blood vessels in the skin get wider. This is called vasodilation. Vasodilation allows a larger volume of blood to flow near the skin surface, transferring heat to the environment. This cools the body down. Additional cooling occurs with the production of sweat from sweat glands. 11 of 40 © Boardworks Ltd 2007 What is blood glucose? Glucose is a type of sugar used by the body to provide energy. Sometimes there is too much glucose in the blood, and sometimes there is not enough. What affects the level of blood glucose?  Eating causes blood glucose levels to rise.  Vigorous exercise causes blood glucose levels to fall. How does the body regulate blood glucose levels? 12 of 40 © Boardworks Ltd 2007 28.1 Levels of Organization Controlling Glucose levels Excess glucose gets turned into glycogen in the liver This is regulated by 2 hormones (chemicals) from the pancreas called Insulin and Glucagon In this way, the concentration of glucose in the blood is kept within narrow limits The pancreas and blood glucose Blood glucose levels are pancreas monitored and controlled by the pancreas. The pancreas produces and releases different hormones depending on the blood glucose level.  Insulin is released when blood glucose levels are high – the liver stores excess glucose as glycogen.  Glucagon is released when blood glucose levels are low – the liver converts stored glycogen into glucose and releases it into the blood. 14 of 40 © Boardworks Ltd 2007 Why is water important? The human body is about 60-70% water. Water molecules and ions constantly move in and out of cells, and are essential for all life processes. Dehydration (loss of too much water from the body) damages cells. How is water gained and lost?  Water is absorbed from food and drink.  Water is lost from the body in, sweat, urine and faeces. 15 of 40 © Boardworks Ltd 2007 28.1 Levels of Organization Water Regulation The amount of water in the blood must be kept more or less the same all the time to avoid cell damage as a result of osmosis. There has to be a balance between the amount of water gained (from your diet though drinks and food and the water produced by cellular respiration) and the amount of water lost by the body (in sweating, evaporation, feces and urine). This is achieved by the action of the hormone ADH (anti-diuretic hormone). 28.1 Levels of Organization Water Regulation Part of the brain, the hypothalamus, detects that there is not enough water in the blood. The hypothalamus sends a message to the pituitary gland which releases ADH. This travels in the blood to your kidneys and as a result you make a smaller volume of more concentrated urine. The level of water in your blood increases until it is back to normal. If the level of water in your blood goes up the hypothalamus detects the change and sends a message to the pituitary. The release of ADH into the blood is slowed down or even stopped. Without ADH the kidneys will not save as much water and you produce large volumes of dilute urine. This is an example of negative feedback.  Feedback systems  Negative feedback  Positive feedback Negative feedback  Negative feedback: Response triggered by changed conditions serves to reverse the change  E.g., Body temperature increases  Skin blood vessels dilate  Body temperature decreases  Body temperature increases Normal Hypothalamus body sends a message temperature to blood vessels Body temperature Skin blood vessels decreases dilate Positive feedback  Positive feedback: The response triggered by changing conditions serves to move the variable even further away from its steady state  E.g., uterine contractions are stimulated by oxytocin  baby moves towards cervix  more oxytocin is released  Glossary (1/3)  ADH – The hormone released from the pituitary gland that acts on kidneys and blood vessels to maintain the body’s water balance.  dehydration – The loss of too much water from the body.  homeostasis – The constant regulation of the body's internal environment.  hyperthermia – Dangerously high body temperature.  hypothalamus – The part of the brain that helps to regulate the body's internal environment.  hypothermia – Dangerously low body temperature.  glucose – The main source of energy for the body. 23 of 40 © Boardworks Ltd 2007  Glossary (2/3)  glucoregulation – The homeostatic control of the body’s blood sugar level.  glycogen – A storage form of glucose, found in the liver and muscles.  insulin – A hormone involved in the control of blood sugar, and which is reduced or absent in people with diabetes.  kidney – The bean-shaped organ that filters the blood and produces urine.  negative feedback – A stabilizing mechanism that slows down or reverses a stimulus. 24 of 40 © Boardworks Ltd 2007  Glossary (3/3)  osmoregulation – The homeostatic control of the body’s water and ion balance.  pancreas – The organ that secretes the hormone insulin.  thermoregulation – The homeostatic control of the body’s temperature.  vasoconstriction – The narrowing of the blood vessels in the skin in order to reduce heat loss.  vasodilation – The widening of the blood vessels in the skin in order to increase heat loss. 25 of 40 © Boardworks Ltd 2007