Homeostasis: Introduction to Homeostasis and Internal Environment

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 so because some processes are constantly ongoing inside your body and they are necessary for your survival.

Please read on the basic characteristics of life here.

Now, let's imagine that someone has a fever. His or her temperature will be abnormally high as a result of the fever. 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.

Please read on vectors of diseases here.

Medically speaking, for a person to be physiologically healthy, the conditions and processes within 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 comprises of everything that surrounds you; for instance air, water, your phone, shoes and anything around you right now. 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 environmental sanitation, 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 child's body systems and invariably, the environment inside their body (internal environment).

Please read on microorganisms causing food, water and air borne diseases 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 above diagram illustrates the various fluids seen within and around the cell

The fluid filled space present outside all the cells of any multi-cellular organism is termed the Extracellular fluid (or ECF).

Note: Blood plasma present inside the blood vessels (that is, arteries, veins and capillaries) is a component of the ECF because it is present outside the body cells. The same is true for the interstitial fluid which is also another component of the ECF.

Please read on various disorders of the artery here.

The ECF accounts for about 35% (one-third) of the Total Body Water (TBW) in healthy adults.

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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 TBW is ICF. For this reason, the volume of ICF is greater than that of ECF with regards to the Total Body Water.

The TBW accounts for about 65% of the body weight of an average man although this value will vary with age. For instance, children will have a higher percentage of TBW value while that of the aged will be lower.

The above explanations on TBW affirms that humans are composed more of water (liquid) than solids.

You can read on some amazing facts in biology here.

The two compartments accounting for the TBW are the ICF and ECF respectively; and both make up the internal environment. It is these internal environments that are regulated via homeostasis.

You can read on the red blood cells and hemoglobin here.

Understand that 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 function by restoring the internal environment to it's normal composition and pH.

You can read on types and functions of drugs here.

Systems Coordinating Homeostasis

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

1. Nervous System: It comprises of the brain and spinal cord.
   Please read an introduction to the human brain Man here.

2. Endocrine System: It has every thing to do with hormones. The pituitary gland is serves as the master endocrine gland. This implies that it regulates the homeostatic functions of other endocrine glands (or glands that produces hormones).

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

These two systems (nervous and endocrine systems) coordinates all homeostatic processes by regulating the respective homeostatic organs in the body.

Homeostatic Organs

Below are some homeostatic organs alongside a summary of their homeostatic functions:

• Hypothalamus: It regulates the body temperature, sleep, appetite and thirst.

• Kidneys: It regulates water, salts and electrolytes through the formation and elimination of urine.

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

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

• Pancreas: It regulates blood glucose and glycogen.

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

The diagram below shows the various homeostatic organs and their locations.

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

Please read more on negative feedback mechanism in homeostasis here.

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