Nutrition, The Human Body Lecture #3

Course Information

• Course title: Introduction to Nutrition: Concepts & Controversies
• Course code: EPHE 155
• Institution: University of Victoria, School of Exercise Science, Physical and Health Education
• Instructor: Dr. Kimberly McQueen, BSc ND
• Email: [email protected]

The Human Body

• The human body is composed of trillions of cells
• Cells are self-contained living entities
• Cells need oxygen, energy sources (nutrients), and water to survive
• Cells die at varying rates
• The level of organization in the human body includes: cells → tissues → organs → body systems

Cells

• Cells have a membrane enclosing their contents
• Nucleus contains hereditary material (genes)
• Genes control characteristics and daily workings of the cell
• Genes are copied when the cell duplicates
• Instructions from genes translate into proteins performing functions
• Mitochondria take in nutrients and release energy

Genes

• Genes provide the blueprint for body functions
• Genes are short sections of DNA
• An estimated 30,000 genes are in the Human Genome
• Genes direct protein production, often enzymes
• Genes provide instruction for the structural components of cells
• Different genes are active in different cells
• Genes are also impacted by nutrient status

Enzymes

• Enzymes are working proteins speeding up chemical reactions
• Enzymes do not change during reactions

Genetics

• Individuals genetically differ
• We inherit genes from parents, but subtle/non-subtle mutations can occur
• Nutritional genomics studies how nutrients affect genes and vice versa
• Epigenetics is the study of how behavior and environment impact gene expression

Body Systems Supporting Digestion

• Cardiovascular: delivers oxygen, nutrients to tissues, removes waste, and works with the digestive system
• Endocrine: regulates digestion via hormones, such as insulin and glucagon
• Nervous: controls hunger and appetite, coordinates muscle movement in the digestive tract
• Excretory: removes waste materials via kidneys, lungs, liver, skin

Body Fluids

• Body fluids supply energy, oxygen, nutrients, and water
• Body fluids deliver fresh supplies and remove wastes
• Blood travels in arteries, veins, capillaries, and heart chambers
• Lymph travels in its own vessels, eventually draining back into the bloodstream

The Digestive System

• Digest: Breaks down food molecules into smaller components
• Absorb: Extracts nutrients and delivers them to the body
• Excrete: Removes waste material after digestion is complete
• The digestive tract is 8 meters long, flexible, and muscular
• The digestive tract has accessory organs (salivary glands, liver, gallbladder, pancreas) aiding digestion

Digestion

• Mechanical digestion: begins in the mouth (chewing), involves peristalsis (wave-like muscle movements) in the esophagus, stomach, and intestines, and sphincters regulating food flow
• Chemical digestion: enzymes break down carbohydrates, proteins, and lipids
• Chyme: fluid resulting from stomach's action
• Feces: waste material remaining after digestion and absorption

Transit Time

• Approximately 24 hours for food to travel through the digestive system
• Transit time varies depending on the type and amount of food consumed

Small Intestine

• Beginning section called duodenum
• Comprised of villi and microvilli
• Site for nutrient absorption
• Contains microbiota
• Some digestive enzymes on surface for last-minute nutrient breakdown

Large Intestine, Appendix, and Diverticula

• Diverticula are abnormal pockets in colon wall, potentially entrapping feces, causing infection, and requiring medical intervention.
• Appendix is a small sac protruding from large intestine, hosting beneficial microorganisms.

The Microbiota

• Diverse community of 100 trillion microbes in the digestive tract (mostly in large intestine)
• Includes beneficial bacteria, yeast, and other microorganisms
• Supports digestion by fermenting fibers into short-chain fatty acids (SCFAs)
• Produces essential vitamins like K2
• Strengthens immunity
• Influences hormone production

Absorption

• Stomach: absorbs alcohol (20% of total) and a minor amount of water
• Small intestine: absorbs calcium, magnesium, iron, other minerals, glucose, amino acids, fats, vitamins, water (70-90% of total), alcohol (80% of total), and bile acids
• Large intestine: absorbs sodium, potassium, some fatty acids, vitamin K and biotin, gases, water (10-30% of total)

Storage

• Body designed to eat at intervals
• Cells need a constant nutrient supply
• Major storage sites include liver (carbohydrates), muscles (carbohydrates), and fat cells (fats and related substances)

Undernutrition

• Digestive system sensitive to malnutrition
• Severe undernutrition shrinks absorptive surface of small intestine, causing impaired digestion, worsening malnutrition
• Undernutrition can lead to downregulation of specific enzymes, but these mechanisms can recover given adequate nutrition