Homeostasis Lab

Introduction: 

The body can store many of the things it needs to function such as vitamins and food in the form of fat.  Oxygen is one item that cannot be stored in sufficient quantities for more than a few minutes.  At rest, the blood holds about a quart of dissolved oxygen, but it is continually being used by the cells to produce energy.  The lungs need to be constantly working to furnish a sufficient supply for various activities. 

Human respiration rate is controlled by a part of the brain called the medulla.  The autonomic motor portion of the medulla sends signals to the body to adjust the breathing speed to provide enough oxygen for every activity such as sleeping, eating, exercising, etc.  The level of carbon dioxide, not oxygen, in the blood is measured by the brain which in turn makes needed adjustments in the respiration rate.  During exercise, the cells burn oxygen faster to produce more energy for the body, which creates more carbon dioxide as a waste product.  Carbon dioxide will quickly combine with water to cause increased carbonic acid in the blood.  This increased carbonic acid level in detected by the sensory portion of the medulla, which signals for a higher respiration rate to lower the carbon dioxide in the blood and increase the amount of oxygen for the cells. 

Breathing is an involuntary action controlled by the brain, but it can also be controlled voluntarily.  Holding your breath is one example.  This can be done only for a few minutes before we become faint and the involuntary control takes over and restores breathing to a normal rate. 

Hyperventilating is abnormally rapid, deep breathing and usually occurs when anxiety or emotional stress stimulates the part of the brain that regulates breathing (the medulla).  Kidney failure and diabetes may also cause hyperventilation.  Too much carbon dioxide is exhaled, leaving less in the blood.  This causes the vessels to constrict, decreasing the flow of blood.  With too like blood reaching the brain, the person may become dizzy and faint.  Hyperventilation attacks many last a half hour.  They can be controlled by trying to slow the breathing rate.  Exhaling into a paper bag and re-breathing the air can increase the carbon dioxide content in the blood and shorten the attack. 

The lungs have two ways to increase oxygen intake in response to a changing demand during exercise.  One is to breathe faster (respiratory rate) and the other is to breathe deeper (volume).  The heart also has two ways to increase blood to muscles.  The heart can beat faster (pulse rate) or pump more blood with each beat (increased stroke volume).