Homeostasis in human

Homeostasis
Homeostasis refers to the ability of an organism or environment to maintain stability in spite of changes. The human body is full of examples of homeostasis.

Homeostasis refers to stability, balance, or equilibrium within a cell or the body. It is an organism’s ability to keep a constant internal environment. Homeostasis is an important characteristic of living things. Keeping a stable internal environment requires constant adjustments as conditions change inside and outside the cell. The adjusting of systems within a cell is called homeostatic regulation. Because the internal and external environments of a cell are constantly changing, adjustments must be made continuously to stay at or near the set point (the normal level or range). Homeostasis can be thought of as a dynamic equilibrium rather than a constant, unchanging state.

Common Homeostasis Examples

1. Humans’ internal body temperature is a great example of homeostasis. When an individual is healthy, his or her body temperature retains a temperature 98.6 degrees Fahrenheit. The body can control temperature by making or releasing heat. 
2. Glucose is a type of sugar that is found in the bloodstream, but the body must maintain proper glucose levels to ensure that a person remains healthy. When glucose levels get too high, the pancreas releases a hormone known as insulin. If blood glucose levels happen to drop too low, the liver converts glycogen in the blood to glucose again, raising the levels.
3. When bacteria or viruses that can make you ill get into your body, your lymphatic system kicks in to help maintain homeostasis. It works to fight the infection before it has the opportunity to make you sick, ensuring that you remain healthy.
4. The maintenance of healthy blood pressure is an example of homeostasis. The heart can sense changes in the blood pressure, causing it to send signals to the brain, which then sends back signals telling the heart how to respond. If blood pressure is too high, naturally the heart should slow down; while if it is too low, the heart wants to speed up.
5. A human’s body contains chemicals known as acids and bases, and a proper balance of these is required for the body to function optimally. Lungs and kidneys are two of the organ systems that regulate acids and bases within the body. 
6. More than half of a human’s body weight percentage is water, and maintaining the correct balance of water is an example of homeostasis. Cells that have too much water in them bloat and can even blow up. Cells with too little water can end up shrinking. Your body maintains a proper water balance so that neither of these situations occurs.
7. Calcium levels in the blood must be maintained at proper levels. The body regulates those levels in an example of homeostasis. When levels decrease, the parathyroid releases hormones. If calcium levels become too high, the thyroid helps out by fixing calcium in the bones and lowering blood calcium levels.
8. Exercising causes the body to maintain homeostasis by sending lactate to the muscles to give them energy. Over time, this also signals to the brain that it is time to stop exercising, so that the muscles can get the oxygen they need.
9. The nervous system helps keep homeostasis in breathing patterns. Because breathing is involuntary, the nervous system ensures that the body is getting much needed oxygen through breathing the appropriate amount of oxygen.
10. When toxins get into your blood, they disrupt your body’s homeostasis. The human body, however, responds by getting rid of these toxins by use of the urinary system. An individual simply urinates the toxins and other nasty things from the blood, restoring homeostasis to the human body.  

Feedback Regulation Loops

The endocrine system plays an important role in homeostasis because hormones regulate the activity of body cells. The release of hormones into the blood is controlled by a stimulus. For example, the stimulus either causes an increase or a decrease in the amount of hormone secreted. Then, the response to a stimulus changes the internal conditions and may itself become a new stimulus. This self-adjusting mechanism is called feedback regulation.

Feedback regulation occurs when the response to a stimulus has an effect of some kind on the original stimulus. The type of response determines what the feedback is called. Negative feedback occurs when the response to a stimulus reduces the original stimulus. Positive feedback occurs when the response to a stimulus increases the original stimulus.

Thermoregulation: A Negative Feedback Loop

Negative feedback is the most common feedback loop in biological systems. The system acts to reverse the direction of change. Since this tends to keep things constant, it allows the maintenance of homeostatic balance. For instance, when the concentration of carbon dioxide in the human body increases, the lungs are signaled to increase their activity and exhale more carbon dioxide, (your breathing rate increases). Thermoregulation is another example of negative feedback. When body temperature rises, receptors in the skin and the hypothalamus sense the temperature change. The temperature change (stimulus) triggers a command from the brain. This command, causes a response (the skin makes sweat and blood vessels near the skin surface dilate), which helps decrease body temperature. Figure 1 shows how the response to a stimulus reduces the original stimulus in another of the body’s negative feedback mechanisms.

Positive feedback is less common in biological systems. Positive feedback acts to speed up the direction of change. An example of positive feedback is lactation (milk production). As the baby suckles, nerve messages from the mammary glands cause the hormone prolactin, to be secreted by the pituitary gland. The more the baby suckles, the more prolactin is released, which stimulates further milk production.

Not many feedback mechanisms in the body are based on positive feedback. Positive feedback speeds up the direction of change, which leads to increasing hormone concentration, a state that moves further away from homeostasis.

System Interactions
• The removal of metabolic waste. This is known as excretion. This is done by the excretory organs such as the kidneys and lungs.
• The regulation of body temperature. This is mainly done by the skin.
• The regulation of blood glucose level. This is mainly done by the liver and the insulin and glucagon secreted by the pancreas in the body.

Each body system contributes to the homeostasis of other systems and of the entire organism. No system of the body works in isolation and the well-being of the person depends upon the well-being of all the interacting body systems. A disruption within one system generally has consequences for several additional body systems. Most of these organ systems are controlled by hormones secreted from the pituitary gland, a part of the endocrine system. Table 1 summarizes how various body systems work together to maintain homeostasis.

Main examples of homeostasis in mammals are as follows:

• The regulation of the amounts of water and minerals in the body. This is known as osmoregulation. This happens primarily in the kidneys.

Urinary SystemToxic wastes build up in the blood as proteins and nucleic acids are broken down and used by the body. The urinary system rids the body of these wastes. The urinary system is also directly involved in maintaining proper blood volume. The kidneys also play an important role in maintaining the correct salt and water content of the body. External changes, such as a warm weather, that lead to excess fluid loss trigger feedback mechanisms that act to maintain the body’s fluid content by inhibiting fluid loss. The kidneys also produce a hormone called erythropoietin, also known as EPO, which stimulates red blood cell production.

Reproductive System

The reproductive system does little for the homeostasis of the organism. The reproductive system relates instead to the maintenance of the species. However, sex hormones do have an effect on other body systems, and an imbalance in sex hormones can lead to various disorders. For example, a woman whose ovaries are removed early in life is at higher risk of developing osteoporosis, a disorder in which bones are thin and break easily. The hormone estrogen, produced by the ovaries, is important for bone growth. Therefore, a woman who does not produce estrogen will have impaired bone development.

Disruption of Homeostasis

Many homeostatic mechanisms keep the internal environment within certain limits (or set points). When the cells in your body do not work correctly, homeostatic balance is disrupted. Homeostatic imbalance may lead to a state of disease. Disease and cellular malfunction can be caused in two basic ways: by deficiency (cells not getting all they need) or toxicity (cells being poisoned by things they do not need). When homeostasis is interrupted, your body can correct or worsen the problem, based on certain influences. In addition to inherited (genetic) influences, there are external influences that are based on lifestyle choices and environmental exposure. These factors together influence the body’s ability to maintain homeostatic balance. The endocrine system of a person with diabetes has difficulty maintaining the correct blood glucose level. A diabetic needs to check their blood glucose levels many times during the day and monitor daily sugar intake.