Nutrition and Digestion: Biomolecules, Vitamins, Minerals, and Digestive Systems

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Biomolecules and Nutrition

Monomers of Major Biomolecules

Biomolecules are essential for life and are broken down into their basic building blocks, or monomers, during digestion.

Carbohydrates: Monosaccharides (simple sugars such as glucose)
Proteins: Amino acids
Lipids: Glycerol and fatty acids

Saturated vs. Unsaturated Fats

Fats are classified based on the presence of single or double bonds in their fatty acid chains.

Saturated fats: Contain only single bonds; usually solid at room temperature (e.g., butter).
Unsaturated fats: Contain one or more double bonds; usually liquid at room temperature (e.g., oils). Considered the "good fat" due to health benefits.

Water in the Body

Water is vital for numerous physiological processes and constitutes 55–60% of the human body.

Functions include: chemical reactions in cytoplasm, digestion, waste elimination, blood volume maintenance, temperature regulation, and skin moisture.
Recommended intake: 8 cups per day to replace water lost through urine, sweat, and respiration.

Vitamins

Vitamins are organic molecules required in small amounts for essential metabolic functions, growth, and development. They are classified as fat-soluble or water-soluble.

Fat-soluble vitamins: A, D, E, K. Stored in fat tissue, not easily eliminated, risk of toxicity in high doses.
Water-soluble vitamins: B, C. Not stored in the body, excess excreted in urine.

Vitamin	Key Function	Example Source
Vitamin A	Vision, healthy skin and bones	Fruit
Vitamin B1	Carbohydrate metabolism, muscle tone	Beans
Vitamin C	Bones, teeth, gums, blood vessels, immune system	Fruit
Vitamin D	Calcium absorption, bone formation	Fish
Vitamin E	Strengthens red blood cell membranes	Fruit

Minerals

Minerals are inorganic elements required for metabolic processes and tissue formation or repair.

Calcium, phosphorus: Bone formation (dairy products)
Sodium: Nerve impulse transmission, muscle contraction (salt)
Iron: Component of hemoglobin for oxygen transport (red meat)
Magnesium: Found in dark, leafy greens
Potassium: Found in grains

Healthy Eating and Energy Balance

Maintaining a healthy body mass requires balancing energy intake with energy output. Canada’s Food Guide provides recommendations for servings, sizes, and types of food.

Variables affecting balance: physical activity, amount of food, types of food.

Body Mass Index (BMI)

BMI is an estimate of body fat based on height and weight.

Formula:
Not always reliable for all individuals (e.g., athletes).

Eating Disorders

Eating disorders are psychological conditions that can have serious physical health consequences.

Obesity: Excessive body fat, risk factors include genetics, diet, inactivity.
Anorexia: Severe dieting, excessive exercise, distorted body image, risk of starvation.
Bulimia: Binge-purge behavior, awareness of abnormality, risk of electrolyte imbalance.
Treatment involves behavioral and nutritional therapy, and continuous support.

Potential signs of an eating disorder, including excessive exercise, preoccupation with feeling fat, abnormal electrolyte levels, intense fear of gaining weight, unusually large intake of food, and anxiety around or avoidance of eating.

Digestive Systems and Digestion

Introduction to Digestion

Digestion is the process of breaking down food into small particles and absorbing nutrients into the bloodstream for cellular use.

Main Steps in Digestion

Ingestion: Taking in nutrients.
Digestion: Physical and chemical breakdown of food into smaller molecules.
Absorption: Transfer of digested nutrients from the digestive system to the bloodstream.
Egestion: Removal of undigested waste from the body.

Specialized Digestive Systems in Simple Animals

Simple animals, such as jellyfish and flatworms, possess a gastrovascular cavity—a single opening for both ingestion and egestion.

Food is taken directly into the cavity and broken down by chemicals.
Nutrients are absorbed through the cavity walls.
Examples: Jellyfish, flatworms.

Diagram of a jellyfish showing the gastrovascular cavity, mouth/anus, and tentacle. The gastrovascular cavity serves as the site for both digestion and nutrient absorption. Photograph of flatworms, which also possess a gastrovascular cavity with a single opening for food intake and waste expulsion.

A Complete Digestive System

More complex animals have a complete digestive tract with two openings (mouth and anus), allowing for unidirectional movement of food and specialized regions for digestion and absorption.

Example: Earthworm digestive tract includes mouth, pharynx, esophagus, crop, gizzard, intestine, and anus.

Human Digestive System

The human digestive system is a complete gastrointestinal (GI) tract, approximately 7–9 meters long, where digestion and absorption occur.

Major organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus.
Accessory organs: salivary glands, liver, gall bladder, pancreas.

Diagram of the human digestive system showing the mouth, salivary glands, pharynx, esophagus, liver, gall bladder, stomach, pancreas, small intestine, large intestine, rectum, and anus.

Integration with Other Body Systems

The digestive system interacts with other organ systems for optimal function:

Muscular and skeletal systems: Enable food capture and ingestion.
Circulatory system: Transports oxygen and nutrients to and from digestive organs.
Nervous and endocrine systems: Regulate digestive processes.
Respiratory system: Provides oxygen for cellular metabolism.