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FEEDBACK MECHANISMS M AINTAINING E QUILIBRIUM Living versus non-living Living organisms have the ability to sense and respond to changes in environment The cells of living organisms function best in a constant, balanced internal environment Organisms must maintain a “steady state” called homeostasis to survive M AINTAINING E QUILIBRIUM Cells, tissues, organs, and organ systems must work together to adjust to changing conditions Cold temperatures: humans respond by shivering to increase body temperature by muscle movement Hot temperatures: humans may respond by sweating to cool off W HAT IS F EEDBACK ? Feedback is the process in which part of the output of a system is returned to its input in order to regulate its further output. N EGATIVE F EEDBACK Have you ever been scolded for not cleaning your room? Cleaning your room is how you respond to being scolded. A negative feedback system involves the detection of an undesirable condition and the response to make that condition ideal. Negative Feedback + _ N EGATIVE F EEDBACK Basic structure: INPUT DETECTION RESPONSE OUTPUT SHUT OFF N EGATIVE F EEDBACK Negative feedback occurs when the output of a system acts to oppose changes to the input of the system A thermostat is an example of a negative feedback system Room temp Set point increases is reached Room temp is Room temp is below the THERMOSTAT above the setpoint setpoint Set point Room temp is reached decreases A thermostat is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. N EGATIVE F EEDBACK IN B IOLOGY Negative feedback also regulates many systems in organisms The endocrine system is one example This diagram shows a negative feedback loop for stress hormones Areas of negative feedback are indicated with a minus sign, (-) KEEPING THE BODY IN BALANCE! E NDOCRINE SYSTEM The endocrine system is composed of glands that produces chemical messengers called hormones Hormones are produced in one part of the body and travel to target organs through the bloodstream E NDOCRINE S YSTEM The brain continuously sends signals to the endocrine glands to secrete and release hormones The glands, in turn, send feedback to the nervous system The hypothalamus in the brain is the master switch that sends signals to the pituitary gland which can release up to eight hormones into the bloodstream The hormone travels to its target organ and usually results in the release of another hormone into the bloodstream E NDOCRINE S YSTEM The hypothalamus then detects the rising hormone levels from the target organ and decreases the release of hormones from the pituitary which results in a decrease in hormone release from the target organ The process of maintaining normal body function through negative feedback mechanisms is called homeostasis G LUCOSE AND I NSULIN 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 Liver levels in body by secreting two hormones, insulin and glucagon. The liver also helps to store the excess glucose in form of glycogen to be utilized later. G LUCOSE AND I NSULIN N EGATIVE F EEDBACK L OOP Increases Glucose Levels Eating cake Stimulates β cells of (-) pancreas to secrete insulin Lowers Blood CYCLE 1 Glucose levels Insulin stimulates the cells to take up glucose from the blood Low Blood Glucose Levels Stimulated Alpha Cells in Pancreas (-) High blood glucose levels CYCLE 2 and Cycle 1 continues Glucagon is released Glucagon stimulates liver cells to release glucose into the blood G LUCOSE AND I NSULIN N EGATIVE F EEDBACK L OOP Two primary Hormones Insulin Glucagon Lowers Blood Glucose Raises Blood Glucose Levels Levels The opposite actions of these two hormones helps to maintain normal blood sugar levels in the body hence maintain homeostasis of the body. TAKE A B REAK AND C HAT W ITH YOUR N EIGHBOR ! Turn to the person behind or in front of you and discuss the following topics: What is a feedback and an example of a negative AND positive system? What is the endocrine system and why is it important? Define homeostasis and how normal body function is maintained with feedback mechanisms. K IDNEYS AND WATER R EGULATION The kidneys play a key role in maintaining water regulation. K IDNEY AND WATER R EGULATION 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. K IDNEY AND WATER R EGULATION 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) ADH REGULATED WATER CONSERVATION IN KIDNEYS Less water in the Excess water in blood 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 ADH makes the tubules more permeable Less ADH makes the tubules less and more water is reabsorbed back into the permeable and less water is reabsorbed bloodstream (urine is concentrated). back into the bloodstream (urine is dilute). ADH REGULATED WATER CONSERVATION IN KIDNEYS Osmoregulators send negative feedback to the hypothalamus about the concentration of water in the bloodstream. The hypothalamus then stimulates the pituitary glands to secrete high or low concentrations of anti-diuretic hormone. ADH then makes the tubules more or less permeable and hence, maintains water and electrolyte homeostasis. TEMPERATURE REGULATION OF BODY Animals that are capable of maintaining their body temperature within a given range are called homeotherms. Temperature is regulated by negative feedback control. Thermoreceptors located in hypothalamus detect temperature fluctuations in the body. T EMPERATURE R EGULATION OF THE B ODY Increased temperature causes vasodilatation (blood vessels near the surface of the skin dilate). The large surface area allows heat to be lost from the blood and lowers the body temperature. Sweating also helps lower the temperature. Decreased temperature causes vasoconstriction (blood vessels constrict) and minimal heat loss occurs which helps maintain body temperature. Hair on the body provides insulation and helps maintain body temperature. P OSITIVE F EEDBACK 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. P OSITIVE F EEDBACK 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. P OSITIVE F EEDBACK 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. O THER K INDS OF F EEDBACK Feed-forward Not technically feedback, but similar. The system responds in anticipation of a change Hunger is an example of feed-forward. If you typically eat lunch at noon, your body will begin to make digestive enzymes in anticipation.
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