Feedback Mechanisms- Biology PDF

**FEEDBACK MECHANISMS** **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. **Negative Feedback** - Occurs when the output of a system acts to oppose changes to the input of the system. - Regulates many sy...

**FEEDBACK MECHANISMS** **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. **Negative Feedback** - Occurs when the output of a system acts to oppose changes to the input of the system. - Regulates many systems in organisms - Endocrine system is an example  **Endocrine System** - 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. **Glands of the Endocrine System:** - Pituitary gland - Thyroid Gland - Parathyroid glands - Thymus - Adrenal glands - Pancreas - Ovary and Testis **Endocrine System** - The brain continuously sends signals to the endocrine glands to secrete and release hormones and 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. - 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**. **Glucose and Insulin** - 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 hormones, insulin and glucagon. - The liver also helps to store the excess glucose in form of glycogen to be utilized later.  **Glucose and Insulin Negative Feedback Loop** - The opposite actions of these two hormones, insulin and glucagon, helps to maintain normal blood sugar levels in the body hence maintain homeostasis of the body. **Kidneys and Water Regulation** - The kidneys play a key role in maintaining 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. - **Anti-Diureticn 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  **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. - 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. **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. - 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 chemical 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. - 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.