Homeostasis and Control Systems

1. Homeostasis and Control Systems

2. Homeostasis The term homeostasis refers to the body’s attempt to adjust to a fluctuating external environment The body maintains a constant balance or steady state, through a series of monitored adjustments The system requires constant monitoring and feedback about body coniditions

3. Control Systems The control system has three functional components: A monitor A coordinating centre A regulator

4. Negative Feedback System An adjustment that brings the body back within an acceptable range is called a Negative Feedback System – designed to resist change Your house thermostat is an example of a negative feedback system Called Negative because the control mechanism counteracts any further change in the same direction

5. Negative Feedback System – Con’t Thermometer = the monitor Thermostat = the control centre Furnace (air conditioner) = the regulator Temperature falls below 20°,thermostat turns on the furnace Temperature goes higher than 25°,thermostat turns on the air conditioner Most homeostatic mechanisms are negative feedback

6. Positive Feedback System Positive feedback reinforce the change, moves the controlled variable even further away from the steady state The reason to have a positive feedback system is to allow a physiological event to take place rapidly. Once it is accomplished the feedback system stops. Positive feedback systems are less common in the body

7. Positive Feedback – Con’t Example: During lactation (milk production) the suckling of a baby stimulates the production of oxytocin Oxytocin causes contraction of the smooth muscle surrounding the milk duct in the breast causing the milk to flow As long as the baby is nursing, oxytocin is produced and milk flows – when baby stops suckling, oxytocin is no longer produced and milk stops flowing

8. Positive Feedback – Con’t Example 2 During the later stages of pregnancy there is a decrease in progesterone which causes small contractions of the uterus These contractions causes oxytocin to be released which causes stronger contractions The baby moves down the cervix which cause more oxytocin to be released When baby is expelled the contractions stop and so does the release of oxytocin

9. Thermoregulation

10. Thermoregulation The maintenance of body temperature within an optimal temperature range In humans, normal body temperature is normally stated to be 37 degrees but there is variation within the population

11. Heat Stress Sensors in the brain (monitor) detect a rise in temperature and a signal is sent to the hypothalamus (coordinating centre) Which sends: A signal to sweat glands to initiate sweating (causing cooling of skin by evaporation) A signal to the blood vessels in the skin, causing them to dilate, allowing more blood to flow to the skin, which is being cooled and so the blood loses heat and cools the core of the body

12. Cold Stress Sensors send message to hypothalamus which sends: A signal to arterioles to constrict, limiting blood flow to skin and preventing heat loss A signal to smooth muscles that surround hair follicles in the skin causing the hair to stand on end – goose bumps. The erect hair traps warm still air near skin and helps reduce heat loss. A signal to skeletal muscles causing shivering, this generates heat production.

13. Evaporation of water helps regulate body temp Hypothalamus regulates temperature and changes in osmotic pressure Pancreas regulates blood sugar Skeletal muscles contract and release heat Blood distributes heat throughout the body Kidney’s maintain water balance