Homeostasis and Human Body Systems Miss Richardson SBI4U

How would you feel if you were here?

How would you feel if you were here?

How would you feel? South Pole, <41°C

Homeostasis … is the tendency of the body to maintain a constant internal environment This is done through regulating various systems Human body: body temp: 37⁰C blood pH: 7.3 – 7.4 Blood sugar: 5mmol/L blood

Feedback Systems The body maintains homeostasis through feedback systems Feedback systems consist of three components: Receptor/sensor – detect the stimuli/change in internal environment and send signal to control centre Integrator/Control Centre – receives information and takes appropriate action Effector – cause change and make a response to change conditions

Negative Feedback Systems Most homeostatic mechanisms in animals use negative feedback systems to operate Negative Feedback Systems: brings the system back to its original state If a level increases, the body works to decrease it If a level decreases, the body works to increase it Example: When you exercise, your muscles produce heat, raising your body temperature Signals are sent to control centre to induce sweating and dilation of blood vessels Results in heat loss through radiation and conduction

Why does the body need to regulate temperature? Human enzymes work best at 37°C. The hypothalamus is a part of the brain that detects change in internal body temperature. Thermoregulation is the process of regulating body temperatures When we are hot: Erector muscles in skin relax, allowing hairs to lie flat so the body is less insulated Vasodilation – blood capillaries near the skin’s surface get wider, and more blood flows near skin surface allows for more heat loss due to radiation Sweat glands secrete – allows for cooling due to evaporation

Thermoregulation When we are cold: Shivering – muscles contract and relax quickly to release heat Rate of cellular respiration increases to release heat and energy Vasoconstriction – blood capillaries near skin surface narrow to keep blood near the core of the body and conserve heat Hairs on skin stand up – erector muscles contract, allowing more air to be trapped between hairs to act as insulating layer Sweat secretion is reduced

Thermoregulation

Positive Feedback Systems moves system further from the steady state Example: In labour, a woman’s uterine muscles contract, triggering production of oxytocin Oxytocin increases strength of contractions

Feedback Systems Other examples of positive feedback systems include: Platelets – when platelets clump to form blood clots that signals more platelets are activated Lactation – when breastfeeding, the more the baby suckles the more milk is produced Estrogen – during follicular phase it causes the thickening of the uterine lining Nerve signals – Na+ channels open when stimulated, this causes more Na+ channels to open resulting in an action potential