عملية الهضم والألياف الغذائية

Introduction to Nutrition and Digestion

• Human biology focuses on the processes of nutrition and digestion.
• A pyramid diagram illustrates different food groups and their proportions in a balanced diet.
• Nutrients are essential molecules in food needed by every cell in the body.
• Food nutrients are building blocks, provide energy, and nourish the body.
• Digestion breaks down tightly bound food molecules into individual nutrients, absorbed by body cells.

Nutrients Types

• Our body needs two types of nutrients:
  • Macronutrients: Needed in large amounts.
  • Micronutrients: Needed in small amounts.

Macronutrients: Carbohydrates

• Carbohydrates are sugars found in foods like bread, cereals, rice, pasta, fruits, and vegetables.
• Carbohydrates provide 40% of the body's energy.
• Types of sugars:
  • Intrinsic sugars: Naturally found in fruits, vegetables, milk, and cereals. These are complex carbohydrates.
  • Extrinsic sugars: Extracted, refined, and concentrated sugars (e.g., beet, cane, sucrose, table sugar). These are simple carbohydrates.
• Dieticians recommend complex carbohydrates over simple carbohydrates.

Fibers in Carbohydrates

• Fibers are mainly complex carbohydrates that cannot be digested.
• Water-soluble fibers: Found in fruits, vegetables (apples, bananas, carrots), and some cereals. They are crucial for maintaining good health and lowering blood cholesterol.
• Water-insoluble fibers: Found in wheat, brown rice, and green beans. They increase the water content in feces, relieving constipation and potentially reducing colon cancer risk. Fibers can also bind to environmental toxins (e.g., pesticides) and eliminate them.

The Importance of Water

• Water is essential for numerous bodily functions.
• It's a part of most enzymatic reactions in the body.
• Water maintains body temperature homeostasis.
• Water regulates the concentration of body fluids like blood and urine.

Macronutrients: Fats (Lipids)

• Fats (lipids) are a major source of energy found in meat, milk, cheese, vegetable oils, and nuts.
• Essential fats: Polyunsaturated fatty acids (omega-6 and omega-3) are vital for health and are primarily found in nuts, seeds, and fish.
• Non-essential fats: Saturated fats are found in meat.
• Deficiency in essential fats can affect the immune system, potentially causing hardened arteries and skin problems.

Macronutrients: Proteins

• Proteins provide amino acids, essential for body cell function.
• Protein-rich foods include beef, poultry, fish, beans, eggs, nuts, and dairy products (milk, yogurt, cheese).
• High-quality proteins: Rich in most essential amino acids. Found in Milk and eggs.
• Low-quality proteins: Deficient in one or more essential amino acids. Found in meat, poultry, cheese and soya peas.
• Proteins serve as structural components in cells and as functional components like hormones and enzymes.

Micronutrients: Minerals and Vitamins

• Minerals: Vital for fluid balance, muscle contractions, nerve impulse transmission, and bone/tooth formation.
• Magnesium: Crucial for bone health, energy production, and activates more than 300 cellular enzymes. Deficiency can lead to muscle problems, weakness, irritability, restlessness, depression, and weak bones. Magnesium is found in whole-grain bread and cereals.
• Vitamins: Often act as coenzymes and assist in various body functions.
  • Vitamin C: Improves iron absorption, may protect against cancer/heart disease, and potentially slows aging.
  • Vitamin B12: Found attached to proteins; requires protein breakdown and an intrinsic factor for absorption in the small intestine.

Digestion: The Digestive System Overview

• Digestion breaks down food via mechanical and chemical processes.
• Digestion begins in the mouth, using teeth for mechanical breakdown and salivary amylase for chemical breakdown. Starch converts to maltose.
• Swallowing moves food from the mouth, through the pharynx, and into the esophagus. The soft palate and trachea will adjust during this process.
• The esophagus transports food to the stomach via peristalsis.
• The stomach further digests food using churning (mechanic) and hydrochloric acid, enzymes, and mucus. Proteins are digested by pepsin into short chains of peptides. Fats are broken down by HCl.
• The small intestine completes digestion using pancreatic enzymes, bile, and brush border enzymes absorbing the nutrients.
• The large intestine absorbs water and electrolytes, and eliminates waste.

Summary of Absorption

• The small intestine absorbs monosaccharides, amino acids, and fatty acids (absorbed via chylomicrons)
• The large intestines absorbs water and electrolytes