Secret of Body’s Survival: The Wonders of Extracellular Fluid and Homeostasis

Anurag Maskey

Our body consists of cells which are tiny living units capable of carrying out functions essential for life and also reproducing themselves. The food that we eat, everything diffuses into cells after breaking down by digestive processes, and eventually the cell utilizes the energy released in the cytoplasm, which is the intracellular fluid. The released energy is stored in  the mitochondria, a tiny organ of  the cell that store energy in usable packets called ATP. We have about 100 trillion cells in our body and they take up a lot of space. However, we also have fluid in between the cells; in fact all the fluid in our body found outside our cells is known as extracellular fluid. 

The extracellular fluid consists of three parts, the interstitial fluid, the blood plasma and the trans-cellular fluid. The interstitial fluid which surrounds our cells, maintains a constant environment in which the cell can function i.e. the cells gets its nutrients and oxygen, and dispose waste products in it. The blood plasma carries hemoglobin molecules in red blood cells which becomes rich in oxygen after passing through the lung. It is pumped by the heart to different parts of our body where cells are located, and the cells thus receive the oxygen. The blood is also responsible for transporting nutrients absorbed by our body to the interstitial fluid and facilitating its uptake by the cell. The rest of the fluid is called the trans-cellular fluid. It is found in the eye, ear, and the spine and surrounds the joints. 

The extracellular fluid also consists of a large number of sodium ions which is involved in nerve impulses throughout our body. It also consists of chloride and bicarbonate ions. Hence plays an extremely important role in acid base and electrolyte balance of the body. In severe form of diarrhea such a cholera in which the patient loose electrolytes in large scale because of loose motion and death may occur because of such dehydration. The extracellular fluid also consists of energy storing molecules such as glucose, fatty acids, and amino-acids. 

The extracellular fluid plays a major role in homeostasis, as we will discuss in detail now. Homeostasis is the maintenance of the cells’ internal environment, the mechanism which retains normality within the body amidst fluctuation.  The components of the extracellular fluid diffuse into the cells; likewise the materials within the cells can also diffuse outside the cells into the extracellular fluid. That is how the cells internal environment is preserved.

The way our body maintains a constant concentration of oxygen, carbon dioxide, glucose, as well as blood pressure, all attributes to homeostasis. When there is excess of carbon dioxide in the interstitial fluid, the molecule of hemoglobin carried in blood plasma releases the oxygen to be taken up by the cells. If there is too much oxygen and too little carbon dioxide in the interstitial fluid then the hemoglobin will not release the oxygen and thus will not be taken up by the cells.   

The heart rate and plasma volume in the blood is also maintained by a system called the baroreceptor system. These are the receptors which can measure the pressure changes. If the stretch on the artery is more because of increased blood flow, the baroreceptor will sense it , the thus will decrease the heart rate. Similarly if the stretch on the artery is less, the heart rate is increased, thus increasing the pressure on the arteries. 

This mechanism in which the excess or deficiency of substance is sensed and corrected to bring it to normal, is called negative feedback and is the most important component of homeostasis. 

Another process is called positive feedback, which accelerates the processes of our body and allows them to lead to combined quicker responses. The blood clotting, the forming of plugs to block the flow of blood and to preserve the blood in the body, is such a mechanism. When the blood clotting takes place, the blood clotting factors (enzymes which are protein molecules causing a reaction to take place), are activated and they activate other enzymes, i.e. other clotting factors, allowing the process to take place more effectively. 

Another way the positive feedback occurs is in the nerve fiber. The sodium enters the nerve fibre through sodium channels after stimulation of the nerve. Since sodium is positively charged, it changes the membrane potential, (the electric charge within the membrane), thus more sodium keeps on entering and causes more channels to open which is the positive feedback. Eventually the concentration of sodium become enough to bring about an action potential, a nerve signal of information which allows body to do various functions.

All of these positive feedback mechanisms lie within the bigger negative feedback framework, and allow the body to maintain homeostasis. For example the blood clots allow to preserve blood volume by ultimately stopping the bleeding, and the nerve signal generated allow the nervous system to operate optimally in keeping the balance of internal environment of the body.  

The homeostasis through extracellular fluid is so important that even a little bit of change without the protective intervention of homeostasis may cause drastic consequences. If the body temperature rises above 7 degree Centigrade then the cellular metabolism will increase causing cell death. If the ph drops 0.5 below normal that can cause death. An amount of glucose below 1/3 of the normal causes convulsions as the brain needs glucose to function. Another is potassium ions which when decreased 1/3 below the normal, then the person may suffer from paralysis, whereas when the person has 2-3 times the normal potassium level, the heart becomes depressed. It is the ECF and homeostasis that keep these fluctuations within the normal limit.

Therefore the secret of the body's survival lies in the functioning of the extracellular fluid and homeostasis , a wonder that a human body possesses with such precision and effectiveness.  

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