Fluids are an essential component of diet comprising of milk, aqueous humor, CSF, amniotic fluid and water. The specialized fluids are secreted by specialized cells in the human body.

Milk:

Milk is the only food for the growth of young ones of all manners. It is secreted by the mammary glands. Milk holds a unique place as an almost complete natural food from the point of view in nutrition. Water, proteins, lipids, carbohydrates and calcium are present in milk. It however, lacks, iron, cooper and Vitamin C. Synthesis of lactose in the mammary gland is catalyzed by lacto synthase. Other Enzymes present in milk are lactoperoxidase, xanthine oxidase, lipase, lysozyme and other proteases. Human milk has higher carbohydrate content than cow’s milk while protein content is less. Protein is diluted and carbohydrate is added to make cow’s milk drinkable for humans.

Lipids in Milk: The white color of milk is due to the emulsified fat and the calcium caseinate. The lipids of milk are dispersed as small globules. The fatty acids are mainly saturated but 50% of them are medium chain fatty acids. Medium chain fatty acids are easily digested, absorbed and metabolized. The fatty acids found in milk are butyric acid (10%), lauric acid (20%), myristic acid (20%), palmatic acid (20%), stearic acid (15%) and oleic acid (15%). The yellow color of butter is due to the presence of beta carotene.

Proteins in milk: The protein content is proportional to the requirement for growth. 80% protein of cow milk is casein. It is a phospho protein. In human milk casein forms only about 40% of milk proteins and the rest 60% is present in whey.

Minerals in Milk: Milk has a high content of calcium, phosphorus, sodium and potassium but is poor in iron and cooper. Hence, young infants fed exclusively on milk may develop iron deficiency anemia.

Aqueous Humor:

The anterior chamber of the eye is field with a fluid called aqueous humor, which maintains the intraocular tension. The volume of the fluid is only 0.25 ml in the human eye. Normally, the protein content is low but the A/G ratio is frequently the same as that of plasma. The concentration of ascorbic acid is about 20 times than that of plasma. Aqueous Humor is secreted by the ciliary body and enters the anterior chamber by flow from the posterior chamber. It is drained from the anterior chamber through Schelmm’s Canal.

Cerebrospinal fluid (CSF): CSF was described by Domenico Cotugno in 1774. It is found within the subarachnoid space and ventricles of the brain, as well as around the spinal cord. The fluid originates in the choroid plexus and returns to the blood in the vessels of the lumbar region. The total volume of the fluid is 125 ml. It is a transudate or ultra filtrate of plasma. The protein concentration in the fluid is usually 10-30 mg/dl, out of which about 20 mg/dl.

Amniotic Fluid: Amniocentesis is the process by which by amniotic fluid is collected for analysis. Amniotic Fluid is essential for the detection of the health of the mother or the fetus in pregnancy. Lung maturity is also assessed by measuring the content of surfactant in the amniotic fluid. During pregnancy, the cells lining the fetal alveoli start synthesizing dipalmitoyl-lecithin so that the concentration of lecithin increases, whereas that of sphingomyelin remains constant. If the pregnancy is terminated before the fetal lung achieves maturity, chances of respiratory, distress syndrome are high.

Water: This is the most important component of diet. This fluid keeps the body hydrated and helps flush out the harmful toxins from the body.  It enhances metabolism and absorption of all the vital nutrients. 8 to 10 glasses of water are sufficient for adults in normal condition. For those undergoing strenuous physical activity where water is lost through sweat or urination, more water intake is recommended. Heavy sweating, diarrhea and vomiting also increase water losses. When renal function is normal and solute intakes are adequate, the kidneys can adjust to increased water intake by excreting up to 18 l/d of excess water. However, obligatory urine outputs can compromise hydration status when there is inadequate intake or when losses increase in disease or kidney damage. Infants have high requirements for water because of their large ratio of surface area to volume, the limited capacity of the immature kidney to handle high renal solute loads, and their inability to communicate their thirst.