The Digestive System and Biomolecules: A Comprehensive Guide

Posted on Nov 1, 2024 in Biology

Biomolecules

Lipids

Lipids are a group of biomolecules insoluble in water and tend to float on it due to their low density. They consist of:

  • Fats
  • Waxes
  • Phospholipids
  • Steroids

Fats

Fats serve as energy reserves and protect internal organs from the cold. For example, polar bears have a thick layer of fat covering their bodies.

Waxes

Wax molecules have a protective function and are stable. Waterfowl have their feathers coated with wax, which allows them to maintain body heat and repel water.

Phospholipids

Phospholipids are membrane lipids, forming the basis of biological membranes. They permit the separation of two aqueous halves.

Steroids

Steroids have vitamin and hormonal activity and give rise to other molecules.

Proteins

Proteins are biomolecules characterized by their specificity. Each person has their own unique proteins, made by cells according to DNA instructions. Meat, mushrooms, eggs, milk, and fish are excellent sources of high-quality protein because they contain all 20 different amino acids.

Protein Structure

Proteins have a concrete form that depends on the type of amino acids at the molecular level. If they lose this form due to heat, alcohol, or acids, they become denatured irreversibly.

Proteins perform various functions, and many have familiar names:

  1. Hemoglobin: A red protein specialized in transporting respiratory gases (O2 and CO2). It’s a vital part of red blood cells.
  2. Collagen: A tensile protein that gives resistance to bone tissue, cartilage, and connective tissue. Wrinkles are partly due to a lack of collagen.
  3. Enzymes: Proteins that catalyze metabolic reactions.
  4. Actin-Myosin: Two proteins that act together to cause muscle contraction.

Nucleic Acids: DNA and RNA

Nucleic acids are large, complex, informative molecules. They are considered the core of cells, and chromosomes are composed of DNA and protein.

DNA Biological Functions

  1. Self-replication: The basis of cell reproduction, where one DNA molecule forms two identical copies. The two strands separate, and each acts as a template to form its complementary strand. This process can also occur in vitro and has many applications, such as DNA testing in criminal investigations.
  2. Transcription:

Vitamins

Vitamins are biomolecules with regulatory functions, necessary for metabolism, growth, and maintenance of the organism. They are typically of plant origin and are needed in small quantities. A varied diet ensures sufficient intake of all vitamins.

  • Scurvy: Lack of vitamin C (found in fruits).
  • Beri-beri: Characterized by a lack of vitamin B, leading to nerve and muscle degeneration.
  • Rickets: Lack of vitamin D, needed for bone development. Sunlight favors vitamin D absorption.
  • Xerophthalmia: Lack of vitamin A, affecting sight.
  • Anemia: Results from a lack of vitamin B9, necessary for hemoglobin formation.

The Digestive System

The digestive system’s purpose is to process food and provide energy. A varied diet ensures all necessary amino acids and vitamins. The digestive system consists of:

  • Ingestion
  • Digestion
  • Absorption
  • Egestion

Digestion

Digestion speed depends on the type of food. Carbohydrates are digested faster than other nutrients.

Key Organs and Components

Tongue

A muscular organ capable of a wide range of movements that aids in chewing. It’s covered in taste buds (papillae) that detect sweet, sour, salty, and acidic tastes.

Dentition

Formed by different types of teeth: 8 incisors, 4 canines, 8 premolars, and 12 molars. Their function is to cut and grind food. Enamel is a thin, hard, crystalline layer that can fracture if biting hard objects, allowing bacteria to enter.

Pharynx

Funnel-shaped with distinct connections: esophagus, nasal passages, larynx, and ears. The airway closes reflexively upon swallowing.

Esophagus

A tube connecting the pharynx to the stomach through a valve called the cardia.

Stomach

A dilatation of the digestive tract with a volume of about 1.5 liters. The stomach wall has muscle layers in different directions. Gastric juice contains hydrochloric acid (HCl), pepsin, and mucus. Mucus protects the stomach lining, preventing ulcers. HCl is required for pepsin formation. Pepsin is an enzyme that breaks down proteins. Gastric juice is produced by the stomach’s mucosal glands.

Small Intestine

About 8 meters long, divided into the duodenum, jejunum, and ileum. Its function is digestion and nutrient absorption.

  • Duodenum: The shortest section (24cm) where the hepatic and pancreatic ducts empty.

Liver

The largest gland, weighing 1kg and protected by the ribs. It’s a vital organ with over 200 functions, acting as the body’s central chemical processing unit. Its “archenemy” is alcohol.

Pancreas

An elongated gland located below the stomach. It’s a vital, mixed endocrine gland that produces hormones like insulin and glucagon, which control glucose metabolism.

Large Intestine

1.5 meters long, divided into the cecum, colon, and rectum.

  • Cecum: Contains the appendix.
  • Colon: Ascending, transverse, descending, and sigmoid sections. Its main function is water absorption, forming feces. Bacteria in the large intestine, unlike the small intestine, produce vitamin K.