Human Nutrition: Cells, Digestion, and Energy
Cells: The Foundation of Life
Cells are essential to living beings. They are living structures that perform various vital processes.
- Prokaryotes are very simple, unicellular cells. The cell is limited to the plasma membrane, within which is the cytoplasm.
- Eukaryotic cells are multicellular and surrounded by a plasma membrane.
Essential Body Systems
- The digestive system incorporates the nutrients contained in food.
- The respiratory system incorporates oxygen into the body and performs gas exchange.
- The circulatory system carries nutrients to every cell in the body.
- The excretory system eliminates the waste generated in each cell.
Ingestion and Digestion of Nutrients
The digestive system consists of a long canal, the tract, composed of the following parts: mouth, esophagus, stomach, small intestine, large intestine, and anus. The glands include the liver, pancreas, and salivary glands.
Ingestion
Ingestion is the incorporation of food into the digestive system. This process involves the mouth.
Digestion
Digestion is the process in which food is broken down to extract its nutrients.
- Oral digestion: Food is crushed and mixed with saliva, which contains an enzyme called salivary amylase.
- Gastric digestion: The bolus crosses the esophagus, driven by contractions of the tract.
- Intestinal digestion: Chyme passes from the stomach slowly to the first installment of the small intestine, the duodenum, through another sphincter called the pyloric sphincter.
Absorption of Nutrients
The passage of nutrients occurs primarily in the small intestine through the absorption process.
Egestion of Waste
The remains of undigested food continue on their way through sections of the large intestine through the process of egestion, the last function of the digestive system.
Transport of Nutrients
This happens through the process of blood circulation and allows the distribution of oxygen and nutrients, among other substances, throughout the body. The circulatory system is responsible for transporting nutrients and gases absorbed in the digestive and respiratory systems.
Nutrients and Oxygen: Energy Sources
Every time we breathe, oxygen enters the cells, needed to use the energy gained from the nutrients.
Urine Formation
Urine is a yellowish liquid consisting of water and waste substances.
- Glomerular filtration rate: The flow of water and various substances dissolved in blood plasma from the glomerular capillaries into Bowman’s capsule.
- Tubular filtration: The filter located in Bowman’s capsule advances through the tubules of the nephron.
- Tubular secretion: This process is carried out along the renal tubules and is similar to resorption.
Nutrition in Humans
- Carbohydrates provide energy quickly to the cells. Examples include sugar, pasta, rice, and bread.
- Lipids are a source of energy for the cells. They are found in vegetable oils and animal fats.
- Protein is part of cellular structures. Sources include animal products (meat, fish, eggs) and plants (vegetables and cereals).