Maintaining dynamic equilibrium in living systems. Homeostasis: Maintaining dynamic equilibrium in living systems. [or keeping us alive]

So…what does it all mean? To keep the balance, an organism must sense changes in external and internal environment respond to those changes Examples: Cells in your brain are sensitive to changes (even small) in the levels of oxygen and sugar. low blood sugar triggers the liver to release stored sugar when you stand up quickly, blood pressure increases to keep oxygen flow to your brain. Homeostasis is a characteristic of all living things.

Homeostasis The body’s ability to maintain a relatively constant state. Temperature Water Balance Glucose Levels Oxygen & Carbon Dioxide Levels And many, many more…

Temperature Cold Sense: Neurons in our skin Response: change in blood flow increased heart rate constriction of blood vessels close to the surface keeps brain, liver, and heart constant (core) (37˚C) shivering

Temperature Hot Sense: Neurons in our skin Response: change in blood flow dilation of blood vessels close to the surface diverts blood flow away from internal organs sweating

Homeostasis & Water Balance The Urinary System: Disposing of Wastes

Waste Products The body produces many waste materials each day. Wastes become toxic if they build up Wastes and how they are disposed include:

The Urinary System Rids the body of urea Liver converts ammonia into urea Kidneys are the main organ Eliminate urea from the body (secretes) Adjusts fluid volumes and regulates blood pressure (restores and reabsorbs) Filters 125 mL of water is filtered each minute = 180 liters per day!

Or why we breath hard during exercise! CO2 and the Effect On pH Or why we breath hard during exercise!

As we exercise breathing and heart rate increase. CO2 builds up in blood because of muscles burning nutrients to make energy. Increased CO2 causes the blood to become more acidic. The human body doesn’t tolerate changes in pH.

Special receptors in nerve cells in the aorta, brain, and arteries that lead to the head monitor the pH. When the pH begins to drift out of normal range (7.35 - 7.45), these receptors are engaged. This causes the brain to send signals to begin breathing at a faster rate. By breathing faster, more CO2 is exhaled bringing the pH back to normal.

If too much CO2 is exhaled, like when one hyperventilates, the pH begins to drift the other way and becomes more alkaline. If this happens, the receptors register a lack of O2. The person will faint and the brain will slow breathing down to balance the amount of O2 in the body. One way to fix this is to have person inhale and exhale into a paper bag. The CO2 balance is regained and the breathing slows down.

So….what happens when something goes wrong?

What Works Together? To keep the balance! The hypothalamus: part of the nervous system Regulates water balance, body temperature, feeding, sleep, and works with the endocrine system. The endocrine system: release chemical Messengers into the blood (hormones). The nervous system, respiratory system, urinary system, circulatory system, digestive system, and so on… To keep the balance!

Feedback In response to a condition, the body responds by adjusting internal conditions. Negative feedback: changes that correct an abnormal situation i.e. dehydration (goes away from a situation) Positive feedback: critical process must completed quickly. I.e. blood clot. (goes toward a situation)