Homeostasis and Negative Feedback Mechanism

What is Homeostasis?

Have you ever wondered why on a sunny day you drink a lot of water and tend to produce lesser urine? On the contrary, think about how likely you will produce more urine on a cold day and drink less water too. This is because some processes are constantly ongoing inside your body and they are necessary for your survival.

Now, let's imagine that someone has a fever; his or her temperature will be abnormally high. The person may sweat abnormally or even urinate abnormally. On your part, you will suspect that some processes are not working right inside the person. Medically speaking, for a person to be physiologically healthy, the conditions and processes in his or her body must be carefully and properly controlled. This internal control is what homeostasis entails.

Homeostasis can be defined as the regulation and maintenance of a constant (or nearly constant) internal environment.

Understanding Internal Environment:

Recall that your environment is everything that surrounds you; for instance air, water, phone, shoes and so on. This concept of environment is your external environment. In physiology, we have another concept of environment called the internal environment; and it is this environment that the bodily homeostatic organs constantly regulate to it's best optimum conditions.

Now let's think of it this way; if for instance; the external environment is very dirty and unhealthy (from lack of regulation, cleanliness and healthy living), children will suffer from illnesses and diseases like cholera, typhoid and dysentery. This is true because the respective causative organisms (of such diseases) will find their way into the children's body systems and invariably, the environment inside their body (internal environment). You can read on diseases and their causative agents here.

As living organisms, human beings are composed of trillions of cells. These cells aren't just stacked upon one another (like a pack of cards); instead, they are separated by a fluid filled space. The fluid filled space present outside all the cells of any multi-cellular organism is termed as the Extracellular fluid or ECF. It accounts for about 35% (one-third) of the Total Body Water (TBW) in healthy adults. Please read on basic introduction to biology here.

Similarly, inside each of the cells is another kind of fluid called the Intracellular Fluid or ICF. The ICF comprises of the cytoplasm of each cell's organelle which contains water, proteins and electrolytes. About 65% (two-third) of the Total Body Water is ICF. For this reason, the volume of ICF is greater than that of ECF with regards to the Total Body Water (TBW).

The Total Body Water (TBW) accounts for about 65% of the body weight of an average man. (This value will vary with age, for instance children will have a higher percentage value while that of the aged will be lesser).  This is generally why physiologist affirm that "humans are composed more of water (liquid) than solids".

You can read on some amazing facts in Biology here.

The two compartment accounting for the Total Body Water are the ICF and ECF; and these presents the internal environment.

It is this internal environment that is regulated via homeostasis.

Note: The concentration of substances within the internal environment must be at a very narrow range, else, the organism becomes sick and may eventually die. Most of the medical drugs work simply by restoring the internal environment to it's normal composition. You can read on types and functions of drugs here.

 

Systems Coordinating Homeostasis

In humans, homeostasis is achieved by two systems; these are:

1. Nervous System: It comprises of the brain and spinal cord.

2. Endocrine System: It has every thing to do with hormones. The pituitary gland is often referred to as the master endocrine gland; that is, it regulates the homeostatic functions of other endocrine glands.

For now, think of endocrine glands as the producers of hormones.

These two systems coordinates all homeostatic processes by regulating the respective homeostatic organs in the body.

Below are some homeostatic organs alongside a summary their homeostatic functions;

• Hypothalamus: Regulates body temperature, sleep, appetite and thirst.

• Kidney: Regulates water, salts and electrolyte via urine formation.

• Skin: Regulates water, salts and electrolyte via sweat formation.

• Liver: Regulates the storage of glucose, storage of blood, production of bile, breakdown of proteins, cleansing of the body and much more.

• Pancreas: Regulates blood glucose and glycogen.

• Lungs: Regulates oxygen and carbon(IV)oxide intake through breathing.

Image Credit: Phagcse Science

Note: The nervous and endocrine systems regulate the above homeostatic organs through a mechanism called the negative feedback mechanism.

 

Negative feedback Mechanism

To explain what a negative feedback mechanism is, take a moment to imagine yourself walking down the road on a sunny day. You are most likely to sweat. Your sweating is good for you because this is how the homeostatic process regulates (attempts to cool) your body from the sun's hot rays. Again, sweating helps lowers your body temperature and this is a good thing because when an increased bodily temperature isn't checked, controlled or regulated, it becomes dangerous to the health.

Still using the above instance, you will notice that the amounts of urine produced by your kidneys will be lesser on this sunny day. This is because you are already losing water and salt (through sweating), thus less urine is produced in an attempt to make up for your water loss (that is; conserve water).

Again, you are very likely be drink a lot of water on this sunny day because of a higher tendency to feel thirsty. This thirstiness is brought about by the hypothalamus and it's aim is to compensate for the water loss which resulted from sweating.

All of these homeostatic processes in the above paragraphs will continue on and on. If not checked,  it might become detrimental to the your health. For instance, from our above instance (walking down the road on a sunny day), you can't continue to sweat forever because that will not be good for you. Now, what seems to be a solution at the beginning of our example (sweating) can now potentially cause excessive water loss; and this is where the negative feedback mechanism comes into play. To this end, the kidneys produce less urine and the hypothalamus stimulates thirst (so that you can drink more water).

Note: When you leave the sunny environment into a cold environment, your homeostatic organs will begin to revert their initial actions; for instance:

• The skin starts producing less sweats
• The kidneys produces more urine
• The hypothalamus inhibits thirst

  The above homeostatic organs are able to revert their actions (from negative feedback) as a result of coordination from the nervous and endocrine systems

Negative feedback mechanism therefore allows the increasing product of a process or pathway to be controlled, decreased or put into check.

It generally causes a decrease in the function of a process.

We will discuss more on each of the homeostatic organs in a further article.

Thanks for reading.

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