Homeostasis

Homeostasis is like your home’s thermostat Thermostat’s set point is 75ºF heat Inside temperature = 75ºF 74ºF 73ºF 72ºF

Defined: Process where the body maintains a constant internal environment Importance: Internal reactions & enzymes work best in specific conditions Control systems adjust to internal/external changes Changes controlled: pH, temp, fluids

Control Systems Sensors (aka: receptors) !*%!?%&# Sensors (aka: receptors) Gather information about the body and external environment Ex: skin senses pressure Communication Center Messages sent throughout the body to respond Ex: Impulse travel through your nerves Control Center Receives information from the sensors Ex: Brain interprets the impulse Targets Body part that changes its activity Ex: Muscles in foot stretch/contract abruptly

Negative Feedback Loops Regulates most of the body Reverses any change that moves conditions from a set point Ex: if your temp drops…you will shiver to generate heat 97.5 97.7 98.4 98.6 97.2 98.1 97.2 98.4 98.6 98.1 97.7 97.5 96.8

Negative Feedback Loops Regulates most of the body Reverses any change that moves conditions from a set point Ex: if your temp drops…you will shiver to generate heat Ex: If your temp rises…you will sweat to cool down 99.5 99.2 98.8 98.6 99.7 99.7 98.6 98.8 99.2 99.5 100.1

Negative Feedback Loop: Cold Response

Negative Feedback Loop: Breathing

Positive Feedback Loop Increases the changes away from set points Important when rapid change is needed Ex: Pregnancy contractions Uterus contractions begin slowly Oxytocin released to speed up the contractions Negative feedback would reverse and stop the contractions. But if the contractions stopped, would the baby be delivered? Ask yourself… If this was negative feedback, what would happen next? So how will the body respond to the contractions if it’s positive feedback?

Positive Feedback Loop More examples… Growth hormones stimulate cell division Torn vessel stimulates release of clotting factors platelets fibrin white blood cell red blood cell blood vessel clot

Working Together Thermoregulation: Maintenance of body temperature Skin (sensors): sensors detect cold Nervous system (communication system): electrical impulse sent to brain Hypothalamus (endocrine system) in brain (control center): releases hormones into blood stream Muscles (target) : Hormones cause shivering

Homeostasis disruption Beck Weathers, thought to be dead, survived a night exposed to Mt. Everest cold. Some disruptions are temporary Infections, fever, sore throats, muscle soreness Some disruptions are too great for your body to control Frost bite: Sensors are destroyed Paralysis: Messages from brain can’t reach target Can lead to death

Diabetes Defined: Inability to control blood sugar Normally Glucose in blood rises after meals Pancreas releases insulin Cells remove the glucose Type 1 Immune system destroys pancreas cells Pancreas unable to make insulin Blood pH decreases as glucose builds up Type 2 Pancreas does not make enough insulin glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose glucose insulin insulin insulin insulin insulin insulin insulin glucose glucose glucose glucose

Review Define homeostasis. Name and describe the four parts of the “control system.” What is negative feedback? What is positive feedback? Is the following example positive or negative feedback? During heavy exercise your body loses water when you sweat. As a result of water loss, your body redirects the remaining water inside your body to vital parts of your body to replenish these vital organs. What is diabetes? Which organ releases insulin? How does Type I and Type II diabetes differ? What happens when blood glucose levels are too high ?