What is the composition of urine?
Of the forty-seven gallons of fluid filtered and processed by the nephrons daily, less than 1 percent actually becomes urine. Our urine is generally comprised of things our body has no need for, such as some by-products of cell metabolism, and also excessive quantities of things we normally need such as water and electrolytes. About 95 percent of urine is water, while the remaining 5 percent is substances dissolved within that water.
Do our kidneys do anything else?
Beyond regulating the composition of our blood, the kidneys engage in other operations involved in homeostasis. For instance, our kidneys are very sensitive to the amount of oxygenbeing transported in the blood. If they detect that the level of oxygen in our blood is too low, they will release a substance (hormone) into the blood that tells bones to make more red blood cells. If there are more red blood cells, then logically more oxygen can be transported in the blood. Furthermore, the kidneys are vital in the normal metabolism of vitamin D, which will be discussed later.
DIGESTION MAKES NUTRIENTS AVAILABLE TO OUR BODY
What does “digestion” mean and what is it all about?
The term digest means to break down or disintegrate. Therefore, digestion serves to break down the food we eat into smaller substances that are suitable for absorption into our body. All of the activities of digestion take place in our digestive or gastrointestinal tract. The digestive tract is a tube 22 to 28 feet long that actually passes through our body. As food moves through the length of the digestive tract, it is really on the outside of the body. Only when a substance crosses the cell lining of the digestive tract and enters into our circulation is it actually inside our body, which is called absorption.
Digestion requires both physical and chemical operations. The teeth, along with the musculature of the mouth, stomach, and small intestine, work to physically grind, knead, and mix food with digestive juices. At the same time, the muscular lining of our digestive tract serves to propel the digestive mixture forward. Meanwhile, chemical digestion involves the activities of digestive enzymes that will break down large complex food molecules into smaller substances appropriate for absorption. Proteins, carbohydrates, and lipids must be split into simpler molecules for absorption. Also, the vitamins and minerals found in foods must be liberated from other food molecules and complexes in order to be absorbed as well. Bile is also involved in chemical digestion; however, it functions not as an enzyme but more as a detergent. Bile is pivotal in the digestion and absorption of lipid substances.
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