Nutrition Digestion System

Why We Need Nutrients Daily

1. Energy

2. Growth

3. Maintenance & Repair

4. Regulation

Energy

Nutrients (especially carbohydrates and fats) provide energy for cellular and bodily processes

Growth

Nutrients support the creation of new cells, tissues, and organs

Maintenance & Repair

Cells constantly break down and must be repaired or replaced

Regulation

Nutrients regulate metabolism, temperature, fluid balance, nerve signaling, and hormones

Organization of the Human Body

1. Cells

2. Tissues

3. Organs

4. Organ Systems

5. Organism

Cells

• Smallest living unit

• All nutrients ultimately support cell health and function

Tissues

Groups of similar cells working together

Organs

Structures made of multiple tissues with specific jobs

Organ Systems

Groups of organs working together (digestive system)

Organism

The entire human body

How Cells Use Nutrients Daily

• Energy production

• Building cell structures

• Making enzymes, hormones, and signaling molecules

• Repair and replacement of damaged components

Nutrient Deficiency

Occurs when the body does not receive enough of a nutrient to maintain normal cellular function

Nutrient Deficiency Consequences

• Cell malfunction

• Tissues weaken

• Organs lose function

• Organ system can fail overtime

Digestion

• The process of breaking food down into its smallest forms, so nutrients can be absorbed

  • includes mechanical digestion (chewing)

  • included chemical digestion (enzymes breaking bonds)

Absorption

The transport of digested nutrients from the GI tract to the blood or lymph

Size Matters

• Large molecules cannot cross the intestinal wall

• Food must be broken into smallest units before absorption

Too Large to Absorb

• Starch

• Fiber

• Proteins (polypeptides)

• Triglycerides & diglycerides

Small Enough to Absorb

• Monosaccharides

• Amino acids

• Fatty acids

• Monoglycerides

• Cholesterol

• Vitamins

• Minerals

• Water

Mucosa Cells

• Line the small intestine

• Absorb all nutrients

→ increase surface area

Mouth Digestion & Absorption

• Chewing (mechanical digestion of all nutrients)

• Some chemical digestion

• Very little absorption

Esophagus Digestion & Absorption

• Transport only, food moves through peristalsis

• No digestion or absorption

Stomach - Gastric Pits

• Indentations in the stomach lining

• Contain cells that produce stomach secretions

Stomach Functions

• Muscular Contractions

• Gastric Juice

Stomach Muscular Contractions

• Mix food with gastric juice

• Create chyme (partially digested food)

• Mechanical digestion continues

Stomach Gastric Juice

• Hydrochloric Acid (HCL)

• Gastric Lipase

• Proteases

• Mucus

• Intrinsic Factor

Gastric Juice - Hydrochloric Acid (HCL)

• Protein digestion

• Kills salivary amylase

Gastric Juice - Gastric Lipase

• Can live in acidic environment

• Begins fat digestion

Gastric Juice - Proteases

• Begin protein digestion

• Break proteins into polypeptides

Gastric Juice - Mucus

Protects stomach lining from HCL and enzymes

Gastric Juice - Intrinsic Factor

Required for vitamin B12 absorption later in the small intestine

Small Intestine - Muscle Contractions

• Peristalsis

→ moves chyme along GI tract

Small Intestine - Mucus

Protects intestinal lining

Small Intestine - Bicarbonate

• Neutralizes acidic chyme from the stomach

• Creates optimal pH for enzymes

Bile

• Made in the liver

• Stored in the gallbladder

Bile Role

• Breaks large fat (triglycerides) droplets into smaller droplets

• Increases surface area for lipase

NOT an enzyme

Bile Recycling

• Bile is reused

• Reabsorbed and returned to the liver

Pancreatic Juice

Produced by the pancreas and released into the small intestine

Contains:

• Pancreatic fat enzyme (lipase)

• Pancreatic carbohydrate enzyme (amylase)

• Pancreatic protein enzyme (proteases)

• Bicarbonate - neutralizes HCL acid

Villi

Finger-like projections lining the small intestine

Microvilli

Tiny projections on villi

Water-Soluble Nutrient Absorption

• Monosaccharides

• Amino acids

• Minerals

• Water-soluble vitamins

• Absorbed directly into the blood

• Travel first to the liver

Fat-Soluble Nutrient Absorption

• Fatty acids

• Monglycerides

• Cholesterol

• Fat-soluble vitamins

• Absorbed into the lymph

• Enter bloodstream later

Microbiota

• Trillions of microorganisms living in the large intestine

• Support digestion and gut health

Cephalic

Digestion begins before food enters mouth

Bioavailability

Amount of a nutrient actually absorbed and used

Epiglottis

Flap that prevents food entering airway

Cecum

First part of the large intestine

Enzymes in the Mouth

Salivary amylase

Salivary amylase

• Breaks down: starch

• Breaks starch into: smaller carbohydrates

• Location: mouth

Begins carbohydrate digestion

Enzymes in the Stomach

Pepsin

Pepsin

• Breaks down: proteins

• Breaks proteins into: polypeptides

• Location: stomach

• Works in acidic conditions (HCL)

Enzymes in the small intestine

• Pancreatic amylase

• Maltase

• Sucrase

• Lactase

• Proteases

• Lipase

Pancreatic amylase

• Breaks down: starch

• Breaks starch into: disaccharides

• Continues carbohydrate digestion

Maltase

• Breaks down: maltose

• Breaks maltose into: 2 glucose

Sucrase

• Breaks down: sucrose

• Breaks sucrose into: glucose + fructose

Lactase

• Breaks down: lactose

• Break proteins into: glucose + galactose

Proteases

• Break down: proteins

• Break proteins into: amino acids

Lipase

• Breaks down: triglycerides

• Breaks triglycerides: fatty acids and glycerol

Lactose Intolerance

The inability to digest lactose due to insufficient lactase enzyme

• Problem nutrient: Lactose (disaccharide)

• Foods with lactose: Milk, yogurt, cheese, ice cream

• Unavailable monosaccharides: Glucose + galactose

Undigested lactose causes gas, bloating, and diarrhea

GI Tract Absorption - Stomach

• Alcohol (20% of total)

• Water (minor amount)

GI Tract Absorption - Small Intestine

• Calcium, magnesium, iron (& other minerals)

• Glucose

• Amino acids

• Fats

• Vitamins

• Water (70-90% of total)

• Alcohol (80% of total)

• Bile acids

GI Tract Absorption - Large Intestine

• Sodium

• Potassium

• Some fatty acids

• Gases

• Water (10-30% of total)

Accessory Organs of the GI Tract

Assist digestion but food does not pass though them

• Salivary glands: Produce saliva & enzymes

• Liver: Produces bile to emulsify fats

• Gallbladder: Stores and released bile

• Pancreas: Produces digestive enzymes and bicarbonate

All release substances into the small intestine to aid digestion and absorption

Nutrients we can Absorb

• Monosaccharides

• Amino acids

• Fatty acids

• Monoglycerides

• Vitamins

• Minerals

• Water

Microbiota

The community of microorganisms living in the GI tract

Prebiotics

• Non-digestible fibers

• Feed beneficial bacteria

Ex: soluble fiber & resistant starch

Probiotics

• Live beneficial bacteria

• Help maintain gut health and balance

Ex:

• Yogurt

• Kefir

• Kombucha

• Fermented veggies

Poop (feces)

• Undigested food

• Fiber

• Dead bacteria

Pee (Urine)

• Absorbed nutrients that are in excess

• Water-soluble waste products

• Absorbed first, then excreted