Extracellular fluid and Intracellular fluid
Water represents 60% of body weight in males and 50% in females. However, this water contains a lot of soluble substances. The total body water in the body is divided into intracellular and extracellular.
Intracellular fluid is the liquid contained inside the cell membrane. It comprises of approximately 25-40 litres of fluid.
Extracellular fluid (ECF) includes all the fluid present outside the cells. The total amount of ECF is approximately 14 litres in a 70 kg person. Depending upon the location in the body, ECF is divided into the interstitial fluid, plasma, cerebrospinal fluid, intraocular fluid, lymph, gastrointestinal fluid and fluid in potential space. The fluid present in the space between the cells is known as the interstitial fluid. Plasma is a colourless, protein-rich liquid with mature red blood cells, white blood cells, and platelets. The interstitial fluid that enters and circulates throughout the lymphatic system is called lymph. It is rich in white blood cells and helps in fighting against infection. Cerebrospinal fluid (CSF) is found in the brain and the subarachnoid spaces surrounding the brain. It is also found in the spinal cord. The intraocular fluid or the aqueous humor is the transparent fluid present in the front part of the eye. Potential spaces are the spaces between the two adjacent structures. They contain a large amount of fluid. For example, the space between the visceral and the parietal pleura, peritoneal cavity, pericardial cavity, joint cavities and bursae. The fluid in the gastrointestinal tract is the gastrointestinal fluid. Milk, secreted by the milk-producing glands located in the breasts of female mammals is another example of extracellular fluid.
Characteristic ions of ECF and ICF
The intracellular fluid mainly contains K+ and P- with the protein anions. The ICF contains small amount of sodium and chloride ions and almost no calcium ions. Na+ is the main cation and Cl- is the main anion of the ECF. ECF also contains large quantities of bicarbonate ions and small quantities of potassium, magnesium, sulfate, phosphate and organic acid ions. The amount of proteins in the ECF is less as compared to the ICF (Sapakova & Maasova, n.d.).
Maintaining electrolyte balance
Sodium and potassium play a major role in maintaining electrolyte balance in the body. This is done by maintaining the exchange of fluids and the electrolytes.
Role of sodium to maintain electrolyte balance
Sodium functions mainly in controlling and regulating water balance. A decrease in ECF results in reduced vascular volume, blood pressure, and cardiac output. This is known as volume contraction. Conversely, volume expansion is the increase in vascular volume, blood pressure and cardiac output that occur when the ECF in the body is increased. If the Na+ balance in the body is decreased, ECF volume decreases. This results in the decrease in the renal NaCl excretion. On the other hand, when the Na+ balance is positive, ECF volume increases. This enhances the renal NaCl excretion and is known as natriuresis (Koeppen & Stanton, 2013).
Role of potassium to maintain electrolyte balance
According to the American certification agency for healthcare professionals (2011), potassium is an important electrolyte to maintain skeletal, cardiac and smooth muscle activity. The sodium-potassium pump regulates extracellular potassium levels by pumping sodium out of the cells and allowing potassium flow back into the cells. Acting on the distal tubules in the kidneys, aldosterone triggers excretion of potassium and reabsorption of sodium. Thus, maintaining the electrolyte balance in the body.
Homeostasis
Homeostasis is the body’s attempt to maintain a constant internal environment. This requires constant monitoring and adjustments as the conditions change. All the cells in the body are sensitive to changes in the H+ ion concentration. If the pH of the body is not maintained, the cells may become denatured and get destroyed. This disrupts the homeostasis of the body. If the electrolyte level in the body is not maintained, it may lead to dehydration or hyperhydration. Dehydration is the decreased body fluid volume while, hyperhydration is the increase in the body fluid volume.
The kidneys regulate the acid base balance in the body along with blood, proteins and acids which act as buffers. When there is a rise in the pH, the excess H+ ions are released to neutralize the base. If there is a drop in the pH (acidosis), H+ ions bind to raise pH to normal. The ECF contains the phosphate buffer system in low concentration to maintain the pH. The human body also has carbonate buffer system. The lungs take in oxygen and give off carbon dioxide. This regulates pH in the blood. The glucose level in the blood is regulated and maintained by the liver. The hormones insulin and glucagon secreted by the pancreas also play an important role in regulating the blood glucose level in the body. To maintain homeostasis, the kidneys remove urea. This adjusts the concentration of the urea and different ions (Blay, 2002).
References
Sapakova,H., & Maasova,D. Fluids and electrolytes.
American Certification Agency for Healthcare Professionals. (2011). Blood electrolytes (3rd ed.).Osceola, IN.
Koeppen,M.B., & Stanton,A.B. (2013). Renal physiology.Elsevier
