Wednesday, Oct. 15 - The Human Body - Homeostasis and Disease

Homeostasis

Human bodies work to maintain a balanced state even in changes to the environment.

If you go outside in the cold without a coat, you shiver. That’s your body working to maintain a constant temperature. Changes in the temperature are detected by the nervous system, including receptors in the skin, and they send a signal to the brain. The brain sends a signal to have the muscles contract and relax, creating shivering in an attempt to produce body heat. Some muscles contract to constrict blood vessels to retain body heat and you instinctively try to curl up to expose as little of your body to cold as possible.

This balance is called homeostasis – the regulation of an internal environment to maintain conditions necessary to life – so some things about us that need to maintain homeostasis:

• Body temperature
• Heart rate
• Breathing rate
• Blood glucose levels
• Blood pH

Generally, your body reacts to a stimulus – sweating because it’s hot. Hungry because stomach is empty and eating.

A stimulus can be internal or external. Internal is hunger, thirst, tiredness. External is from the outside – being cold, not having enough air.

Feedback

Generally, you are in homeostasis as long as everything is healthy. Your body works to keep variables such as body temperature, blood sugar, blood pressure, etc. in a normal range.

The negative feedback system restores your body to normal. For example, if you get a fever, your body sends a signal to your brain – which will then tell capillaries to dilate and increase sweating to cool body down. Returning body to normal. Blood sugar and insulin are another example of this.

The positive feedback mechanism accelerates change to maintain homeostatis. A fever or blood clotting when you cut yourself is an example of this.

Immune System

Diseases can be infectious or noninfectious, meaning it can be caused by a virus that you breath in, contaminated food (like E.coli), blood borne illnesses or by improper nutrition, genetics, lack of exercise, etc. Think flu (infectious) vs. cancer (noninfectious).

The immune system is the body’s defense against pathogens.

Nonspecific defenses include things like the skin, mucus membranes and inflammation. For example, the mucus in your nose traps germs and dust. Inflammation happens, for example, when you get a cut. The injury causes cells near the injury to release chemicals and cause blood vessels to expand and sends platelets to seal the cut.

Specific defenses are used when a pathogen gets through the initial defense and infects the body. The body’s immune system begins to work against the pathogen. First, antigens (proteins on the cell walls of pathogens) trigger the immune response. White blood cells that target the specific invader are produced – B cells (produce antibodies which attach to the antigen) and T cells (seeks infected cells and looks for the antibodies stuck to the pathogen to identify and kill pathogen).

The immune system can respond to millions of different threats, and immune cells are inactive until activated by an antigen. The immune system can distinguish between body cells and cells from other organisms, and responds to cancerous cells, transplanted tissues, insect venom. It can also remember pathogens and develop immunity to a specific disease.