Homeostasis is the way that the human body (and other organisms) keep a stable internal environment by sensing changes in the body, and reacting to them in an appropriate way. The term (homeostasis) comes from the Greek words homeo which means “same” and stasis which means “stable.” The first person to use this term was Walter Cannon in his book, “The Wisdom of the Body.” It talks about how the body maintains its levels, as well as the earth.  The body reacts to different things in its environment and needs to constantly be changing itself in order to keep stable. Some things that need to be maintained are temperature, glucose levels, and pH. When these things are disrupted it can cause problems like diabetes.
Negative Feedback Loops
Maintenance of homeostasis involves negative and positive feedback loops. Negative feedback loops when the body detects a change and does something to counter that change. Negative feedback loops involves three components: the sensor, the control, and the effector. 
The sensor is what detects the change in the body’s environment and sends the message to the control center. The two control centers are the brain and the endocrine system (which controls things like hormones),they tell a certain part of the body to react to the shift in environment. A major control center in the brain is the hypothalamus which controls things like temperature and blood pressure. The effector is an organ or tissue that gets the message from the control center and takes action to follow that command. Kidneys are an example of an effector. 
Temperature: You can see negative feedback loops in the way the body responds to temperature. When the body's temperature rises too high, the hypothalamus in the brain senses it and sends signals to other nerve cells. These nerve cells send signals to the blood vessels in the skin and they dilate so that more blood can go to the skin's surface and extra heat can be produced. If that process is not enough to cool the body down, then the brain will produce sweat which helps cool the body.  When sweat is produced it evaporates and takes the heat from that particle with it, which cools the surface of the skin.  On the other hand, when the body's temperature gets too low the hypothalamus sends signals to the cutaneous arteries to constrict instead of dilate. Constricting the blood vessels allows for warm blood to stay deeper in the body and for the surface of the skin to lose less heat. If that does not work then the body will begin to shiver. Shivering helps keep the body warm because each tremor of the muscle lets out heat energy into the body. 
Blood Sugar: Negative feedback loops are also present in the body's maintaining blood sugar. The main two things that change the levels of blood sugar in the body are insulin and glucagon. Insulin lowers the concentration of glucose in the blood and glucagon increases it. After eating, the body’s glucose levels rise so the pancreas produces insulin to lower these levels. On the other hand, when somebody hasn’t eaten, it lowers the glucose levels so glucagon gets released which increases the glucose levels. The body also maintains homeostasis using negative feedback loops with pH, sugar levels, water balance, and other things.
Positive Feedback Loops
A positive feedback loop is the opposite of a negative feedback loop. It actually increases the stimulus instead of inhibiting it.
Childbirth: Positive feedback loops are present in childbirth. When the mother is in labor a hormone called oxytocin is released from the pituitary gland in her body which speeds up contractions. That causes more oxytocin to be let out in the body until the baby is born. 
Blood Clotting: Another way that a positive feedback loops is used in the body is in blood clotting. When the body receives a cut and starts bleeding it is in danger of losing too much blood. This releases a chemical that causes platelets to be sent to the area that is being affected. After that, those platelets release a chemical which tells more platelets to go the cut. This continues until the cut is clotted.
Diseases and Other Problems
Diabetes: The full name of diabetes is Insulin Dependent Diabetes Mellitus (IDDM). It is an auto-immune disease in which cells that produce insulin in the pancreas are killed, so the body stops receiving insulin. Insulin is crucial to the body because it helps bring blood sugar to the cells.  What happens with diabetes is that the blood sugar stays in the bloodstream instead of going to the cells. If that continues without treatment it can lead to a diabetic coma which can kill a person. It can also put too much stress on the liver and the kidneys.
- Symptoms: Some common symptoms of diabetes are: hunger and fatigue, peeing constantly and being thirstier, dry mouth and itchy skin, and blurred vision. 
- Treatments: Some treatments for diabetes include: Exercise, diet, medication, insulin injections, and vitamins. 
Hypoglycemia: Hypoglycemia is another word for low blood glucose. Instead of there being too much glucose in the blood, there is not enough. People who have type 1 diabetes are more likely to get hypoglycemia. 
- Symptoms: Some symptoms of hypoglycemia are: shakiness, irritability, hunger, disorientation, paleness, dizziness, and having trouble concentrating, among others. 
- Treatments: Hypoglycemia can be treated by constantly checking glucose levels and taking something with glucose in it, or getting injections. 
Toxins: Just as diseases can disrupt the body, so can toxins. An example of a toxin that disrupts the body is tobacco. When a person consumes tobacco it damages the blood vessels, and forces the heart to work harder than it would normally which also increases the potential for a heart attack or a stroke. When somebody smokes tobacco it paralyzes the cilia in the lungs that clear the lungs of dirt or bacteria, and can make breathing more difficult as well as increases the risk for infections or lung disorders.
Pathogens: A huge contributing factor to the imbalance of homeostasis are pathogens. Some examples of pathogens are viruses and bacteria. They cause infections in the body and the reason a person gets things like fevers, runny nose, and headaches is because the body is trying to fight these pathogens. When a virus attacks the body it can respond with: a fever to try and kill the virus, sending a lot of antibodies to attack the virus, or releasing a chemical called an interferon to stop the virus from reproducing.
Psychological Homeostasis: Homeostasis occurs not only in the body, but also in the mind. A normal state of mind would be happy, and at peace. If a person becomes sad, stressed, nervous, or angry it disrupts the person’s homeostatic state and it even affects their body. For example, if somebody is nervous their body may react with sweat, faster heart rate, and even stomach problems. 
Here is a short video that helps explain homeostasis a bit more.
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