Biological Foundations: Nucleic Acids and Human Digestion
Nucleic Acids: DNA and RNA Fundamentals
Deoxyribonucleic Acid (DNA)
DNA, or Deoxyribonucleic Acid, is a fundamental type of nucleic acid.
- Sugar: Deoxyribose
- Nitrogenous Bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
- Other Component: Phosphoric acid
Function: DNA contains the genetic information of a living being, which is essential for all protein synthesis and the overall functioning of an organism.
Ribonucleic Acid (RNA)
RNA, or Ribonucleic Acid, is another crucial type of nucleic acid.
- Sugar: Ribose
- Nucleobases: Adenine (A), Guanine (G), Cytosine (C), Uracil (U)
Function: RNA is primarily responsible for reading the information contained in DNA and translating it into proteins, playing a vital role in gene expression.
Human Nutrition and Digestion
Stages of Nutrition
The nutrition process is divided into three main stages:
- Uptake: The digestive system is responsible for the digestion and ingestion of food to extract nutrients.
- Distribution: The circulatory system transports oxygen and nutrients from the organs where they are absorbed to every cell in our body.
- Elimination: The excretory system is responsible for eliminating waste products generated by cells.
Digestive Processes
The digestive system performs several key processes:
- Ingestion: The act of taking food into the body.
- Digestion: The mechanical and chemical breakdown of food into simpler substances.
- Absorption: The passage of nutrients from the digestive tract into the blood or lymph.
- Egestion: The elimination of unabsorbed substances (feces) from the body.
The Digestive Tube
The digestive tube is a continuous conduit that begins in the mouth and ends at the anus, typically ranging from 8 to 11 meters in length. It consists of several concentric layers of tissue. The innermost layer, called the mucosa, is made up of epithelial cells covered with a protective and lubricating substance called mucus.
Attached glands are complex organs that discharge their secretions inside the digestive tract. These secretions contain substances involved in the decomposition of food.
Key Digestive Organs
Stomach
The stomach is a J-shaped organ that connects the esophagus to the small intestine via the pylorus. It has three layers of muscle, allowing it to perform complex movements for proper mixing of food with gastric juice.
Liver
The liver is a vital organ whose main functions include metabolic processes, storing substances, and facilitating numerous chemical reactions. It also aids in digestion by secreting bile.
Pancreas
The pancreas is a leaf-shaped, mixed gland. It secretes hormones into the bloodstream (endocrine function) and pancreatic juice (exocrine function). Pancreatic juice is an aqueous solution of sodium bicarbonate and digestive enzymes, crucial for breaking down food.
Small Intestine
The small intestine is a tube approximately 6 to 7 meters long, beginning at the pylorus and ending at the ileocecal valve, which connects it to the large intestine. Its inner surface has folds called villi, which increase the surface area for absorption. It is divided into three parts:
- Duodenum: The first and shortest section of the small intestine, where secretions from the liver and pancreas are poured. The first inch of its lining is smooth.
- Jejunum and Ileum: These make up the rest of the small intestine, although the boundary between them is not always appreciable. They also have villi and are primarily responsible for the absorption of nutrients.
Large Intestine
The large intestine begins at the ileocecal valve and is a tube about 1.5 meters (five feet) long. It has a larger diameter than the small intestine and lacks the folds and villi found in the small intestine. Its walls contain glands that secrete mucus for lubrication. It ends at a sphincter that regulates the output of stool.
Its main functions are to absorb water and compact waste material. It also produces gases responsible for the odor of feces.