Homeostasis Lecture Notes PDF

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester: 1 Module: Human Body Function (HBF) 102  Physiology of Homeostasis By: Dr. Mohamed abo el hassan Dr. Ramadan Saad Department: Physiology 11/19/2024 2  Objectives oDefine...

Faculty of Medicine Academic Year: 2024-2025 Year: 1 Semester: 1 Module: Human Body Function (HBF) 102  Physiology of Homeostasis By: Dr. Mohamed abo el hassan Dr. Ramadan Saad Department: Physiology 11/19/2024 2  Objectives oDefine and discuss the concept of homeostasis and its importance to the living organism. oDiscuss the physiologic control mechanisms that enable maintenance of the normal steady state of the body. oDefine a feedback mechanism and describe its components. oDifferentiate between positive and negative feedback mechanisms and give examples for each in the body. 3  Homeostasis is the ability of the body's systems to maintain a stable, relatively constant internal What is environment within the body despite fluctuations in either the external environment. Homeostasis? Homeostasis is the tendency to resist change in order to maintain a stable, relatively constant internal environment.​ Homeostasis refers to the maintenance of relatively constant internal conditions. For example, your body shivers to maintain a relatively constant body temperature when the external environment gets colder. 11/19/2024 4  Pathophysiology Disruption of Homeostasis Failure of homeostasis Disease Death 11/19/2024 5  Control system 1. Nervous system 2. Endocrine system Controls the body Regulates the activities activities that requires that requires duration. rapid responses (speed) Endocrine gland , Detects and initiates reactions to changes Pancreas, thyroid in external environment (sensory input e.g. parathyroid ,central nervous hormone regulating system ,motor out put) calcium levels, insulin e.g. regulation of control glucose level. blood pressure upon rising 6  Control centers in the brain play roles in regulating physiological parameters and keeping them within the normal range. Feedback As the body works to maintain loops homeostasis, any significant deviation from the normal range will be resisted and homeostasis restored through a process called a feedback loop. 11/19/2024 7 Feedback mechanisms Feedback mechanisms mean : Loop system in which the system responds to changes Positive feedback Negative feedback original stimulus reversed (resulting action in the opposite direction of Resulting action on the stimulus) same direction of the most feedback system in stimulus the body are negative If stimulus increases, If stimulus increases homeostatic control ,homeostasis control system activated to cause system activated to cause a decrease in the stimulus increase in the stimulus and vice versa. 8 Type of feedback mechanisms Feedback Negative Positive feedback feedback The effector response The effector response of the system is in the of the system is in the opposite direction to same direction to stimulus that initiated stimulus that initiated the response. the response. Most of the control Only few systems systems of the body display positive act by negative feedback. feedback. High Make temperature LOWER Make temperature HIGHER temperature 9  feedback loops A feedback loop has three basic components: 1. Sensors / Receptors - Monitors the internal physiological parameter and reports changes to the Control Center 2. The Control Center - Receives sensory input and compares the reported physiological parameter's value to the set point. 3. Effectors - If the Control Center finds that the value of the physiological parameter is too far away from the set point, the control center will send a command to effectors. 1. The effector will function to bring the physiological parameter closer to the set point. is the component in a feedback system that causes a change to reverse the situation and return the value to the normal range. 2. Effectors are muscles and glands. 11/19/2024 10  HOMEOSTASIS The maintenance of a constant internal environment Principles of Homeostasis Stimulus Receptors Self-corrective Mechanism Negative Feedback Change in internal Detect the To rectify the The reverse effect environment change change of the change Examples Regulation of blood Regulation of blood Regulation of body glucose water potential temperature concentration Copyright ©11/19/2024 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 19 November 2024 11 11  Negative Feedback Loop Schematic Negative feedback loops are the body’s most common mechanisms used to maintain homeostasis. A negative feedback system is one that tries to keep the body constant. Negative feedback is a mechanism in which the effect of the response to the stimulus is to shut off the original stimulus or reduce its intensity. In a negative feedback loop, when a mismatch is sensed by the control center, this deviation from the set point is resisted (counter-acted) through a physiological process that returns the body to homeostasis. 11/19/2024 12  TEMPERATURE REGULATION (Thermoregulation) The body regulates its temperature through a process called thermoregulation. Thermoregulation is the ability of the body to maintain its temperature between ~36.5–37.5 °C (or 97.7–99.5 °F). Thermoregulation is an example of negative feedback. The negative feedback loop that regulates temperature can function to ultimately turn the internal temperature up or down (as needed) to get closer to the body's necessary set point.  TEMPERATURE REGULATION (Thermoregulation) The hypothalamus in the brain is the master switch that works as a thermostat to regulate the body’s core temperature. The living organisms can normally survive only within a certain range of temperature of about 0-45° C. A. Above 45°C: the enzymes are destroyed, proteins get denatured, plasma membrane breaks down, and cells suffer lack of oxygen. B. Below 0°C. At temperatures below freezing point, the cells may burst by the formation of needle-like ice crystals inside and between the cells. The enzymes are inactive. If the temperature goes above the set core temperature: Blood Flow Redirection Blood vessels in the skin begin to dilate allowing more blood from the body core to flow to the extremities and the surface of the skin. This allows for heat loos through the skin which cools the internal temperature. Sweat glands are activated to increase their secretion of sweat. As the sweat evaporates from the skin surface into the surrounding air, it dissipates heat and cools the skin. 11/19/2024 15 11/19/2024 16  If the temperature falls below the set core temperature: Blood Flow Redirection - Blood vessels in the skin begin to restrict the blood flow away from the body's extremities and away from the skin's surface, thereby conserving heat. The blood flow is diverted to the body's core to ensure that the vital organ continue normal function. Shivering If heat loss is severe, the brain triggers muscle contraction known as shivering. The act of shivering releases heat while using up ATP. 11/19/2024 17  Negative Feedback Example: Insulin in Blood Glucose Regulation 11/19/2024 18  Glucose and Insulin Pancreas Glucose intake occurs during digestion of food that is needed for energy expenditure to perform routine physical activities. The pancreas is the key organ that regulates the glucose levels in body by secreting two Liver hormones, insulin and glucagon. The liver also helps to store the excess glucose in form of glycogen to be utilized later. 11/19/2024 19  Glucose and Insulin Negative Feedback Loop Boy eating cake Increases Glucose Levels (-) Stimulates β cells of CYCLE 1 Lowers Blood pancreas to secrete insulin Glucose levels Insulin stimulates the cells to take up glucose from the blood. 11/19/2024 20  CYCLE 2 Low Blood Glucose Levels (-) Stimulated Alpha Cells in High blood glucose levels Pancreas and Cycle 1 continues Glucagon is released Glucagon stimulates liver cells to release glucose into the blood 11/19/2024 21  Glycogen If there is too much glucose in the blood, Insulin converts some of it to glycogen Glucose in the blood 11/19/2024 22  Glycogen If there is not enough glucose in the blood, Glucagon converts some glycogen into glucose. Glucose in the blood 11/19/2024 23 Diabetes Some people do not produce enough insulin. When they eat food, the glucose levels in their blood cannot be reduced. This condition is known as DIABETES. Diabetics sometimes have to inject insulin into their blood. They have to be careful of their diet. 11/19/2024 24  Glycogen The glucose But there in the is no Glucose blood insulinincreases. to convert concentration rises it into glycogen. to dangerous levels. Glucose in the blood 11/19/2024 25 BP regulation Calcium regulation Effects of Parathyroid Hormone Effects of Calcitonin Attenuates absorptive ability of osteoclasts Inhibits formation of new osteoclasts Osteoclast decrease causes osteoblast decrease Effect to decrease calcium is transitory Causes reduced bone turnover Has weak effect in kidney and intestines  Kidney and Water Regulation The nephron is the most important functional part of the kidney. It filters nutrients like salts and amino acids in the Bowman’s capsule into ascending loop and filters the urine. 11/19/2024 30  Kidney and Water Regulation Anti-Diuretic Hormone, ADH (also called vasopressin), is secreted by the pituitary gland and acts on the nephron to conserve water and regulate the tonicity of body fluids. Anti- Diuretic Hormone ADH acts on Nephron to reabsorb water and decrease blood osmolality (saltiness) 11/19/2024 31  ADH regulated water conservation in kidneys Less water in the Excess water blood in the blood Stimulates osmoreceptors in Stimulates osmoreceptors in hypothalamus to send signals to hypothalamus to send signals to the pituitary gland the pituitary gland Pituitary glands secretes Pituitary glands secretes high levels of ADH low levels of ADH Less ADH makes the tubules less ADH makes the tubules more permeable permeable and less water is reabsorbed and more water is reabsorbed back into the back into the bloodstream (urine is bloodstream (urine is concentrated). 11/19/2024 dilute). 32  Positive feedback intensifies a change in the body’s physiological condition rather than reversing it. Positive A deviation from the normal range results in more change, Feedback and the system moves farther away from the normal range. Loops Positive feedback in the body is normal only when there is a definite end point. 11/19/2024 33  Positive Feedback In most cases, once the purpose of the feedback loop is completed, counter-signals are released that suppress or break the loop. Childbirth contractions stop when the baby is out of the mother's body. Chemicals break down the blood clot. Lactation stops when the baby no longer nurses. 11/19/2024 34  Positive Feedback Loops Normal childbirth is driven by a positive feedback loop. A positive feedback loop results in a change in the body’s status, rather than a return to homeostasis. The first contractions of labor (the stimulus) push the baby toward the cervix (the lowest part of the uterus). The cervix contains stretch-sensitive nerve cells that monitor the degree of stretching (the sensors). These nerve cells send messages to the brain, which in turn causes the pituitary gland at the base of the brain to release the hormone oxytocin into the bloodstream. Oxytocin causes stronger contractions of the smooth muscles in of the uterus (the effectors), pushing the baby further down the birth canal. This causes even greater stretching of the cervix. The cycle of stretching, oxytocin release, and increasingly more forceful contractions stops only when the baby is born. At this point, the stretching of the cervix halts, stopping the release of oxytocin. 11/19/2024 35  Positive Feedback A positive feedback loop occurs when the output of a system acts to enhance the changes to the input of the system. One example of a biological positive feedback loop is the onset of contractions in childbirth. When a contraction occurs, the hormone oxytocin is released into the body, which stimulates further contractions. This results in contractions increasing in amplitude and frequency. 11/19/2024 36  Positive Feedback Another example is blood clotting. The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot. Lactation involves positive feedback so that the more the baby suckles, the more milk is produced. 11/19/2024 37 Which is an example of negative feedback? 1. Lowering of blood glucose after meal. 2. Blood clotting after injury 3. Lactation during nursing 4. Uterine contraction during nursing The body’s thermostat is located in the ___. 1. Cerebral cortex 2. Hypothalamus 3. Spinal cord 4. Cerebellum 11/19/2024 38 This mechanism is in play when the original state is restored due to a response that opposes that change. a) Positive feedback loop b) Negative feedback loop c) Effector loop d) Control center loop e) Receptor feedback loop 11/19/2024 39  summary “Homeostasis” is the ability of the body to maintain a constant internal environment by making small internal adjustments to compensate for large external disturbances. Injuries, illness, disease and death can disrupt homeostasis. Diabetes causes disruption of glucose homeostasis. It is only one example of the potentially severe problems caused by disrupting homeostasis. Science is actively pursuing a broader, more detailed understanding of homeostatic mechanisms and the consequences of their disruptions. 11/19/2024 40  Carry Home Message Negative Feedback: Example 1. Regulation of blood glucose 2. Regulation of blood pressure 3. Regulation of body temperature Positive Feedback: Example 1. Clotting 2. Protein digestion 3. A temperature of 100.2 0F causes further increase 11/19/2024 41 11/19/2024 42