The body must be able to monitor its internal conditions at all times. These internal conditions are controlled by set points, which are values for various physiological conditions that the body tries to maintain. For example, body temperature has a set point of 98.6°F with a normal range of 97°F to 99°F.
Homeostasis
Homeostasis is the state of relatively stable internal conditions. Organisms detect and respond to a stimulus in order to maintain homeostasis. The body achieves this through feedback loops.
Normal Ranges
| Lab | Normal Range |
|--------|---------------|
| Na+ | 136-145 |
| K+ | 3.5-5.0 |
| Cl+ | 98-106 |
| Ca+ | |
| Albumin| |
| Crea | 0.7-1.3 |
| BUN | 10-20 |
| Glucose| 70-110 |
| WBC | 5000-10000 |
| RBC | (M)4.7-6.1 |
| Hgb | (M)14-18 |
| Hct | (M)42-52 |
| PLTS | 150,000-400,000 |
| PT | 11-12.5 |
| PTT | 60-70 |
| INR | 0.9-1.2 |
| ALT | (M)10-40 |
| AST | (M)12-31 |
The pH scale is used to measure the acidity or alkalinity of a substance. A pH of 7 is considered neutral, values below 7 are acidic, and values above 7 are alkaline.
Feedback Loops
There are two types of feedback loops: negative and positive. A stimulus is a variable that will cause a response, while receptors or sensors are sensory organs that detect a stimulus and send this information to the control center in the brain. The control center then sends commands to effectors, which are muscles or glands, to respond to the stimulus.
Negative Feedback
Negative feedback is the most common feedback mechanism. It reduces the effect of the stimulus with examples such as sweat, blood sugar, and breathing rate.
Example: Negative Feedback
Body temperature regulation is a classic example of negative feedback. When the room temperature rises, the control center sends commands to the air conditioner to turn on, causing the room temperature to drop and restoring it to the normal condition. In response to heat, the body will sweat to maintain a normal body temperature.
Positive Feedback
Positive feedback increases the effect of a stimulus. Examples include childbirth, blood clotting, and fruit ripening.
Example: Positive Feedback
In the case of blood clotting, when there is a break or tear in a blood vessel wall, the body initiates a positive feedback cycle which leads to the rapid formation of a platelet plug to seal the break and prevent excessive blood loss.
Homeostatic Imbalances
There are many reasons why the body may not be able to regulate homeostasis. Some examples include genetic disorders, drug or alcohol abuse, and exposure to intolerable conditions such as extreme heat or cold.
Inhibition
Stimulation
