Human digestive system

The Digestive System

Purpose of the Digestive system:• Breaks down food into substances that cells can absorb

and use.

How is food digested?– Breaking down of food into smaller piece– The mixing of food– Movement through the digestive tract– Chemical breakdown of the large molecules of food

into smaller molecules

Nutrition Process by which organisms obtain and utilize their food.

There are two parts to Nutrition:1. Ingestion- process of taking food into the digestive system so that it may be hydrolized or digested.2. Digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients

Types of Nutrients • Micronutrients- vitamins, minerals, & water

• Macronutrients- proteins, lipids, carbohydrates, etc…

Mouth• Mechanical digestion - teeth• Chemical digestion – saliva• Chewing mixes the food with

saliva, from salivary glands around the mouth and face, to make it moist and easy to swallow = BOLUS

• Enzymes in the saliva begin digestion of carbohydrates.

• Epiglottis – flap of cartilage that blocks trachea when swallowing

Esophagus

• Muscular tube• It moves food by waves

of muscle contraction called peristalsis.

• Physically moving the food along to the stomach.

• Mechanical Digestion

Stomach• The stomach lining

produces strong digestive juices (HCl, pepsin)– chemical digestion

• These create chemical reactions in the stomach, breaking down and dissolving its nutrients = CHYME

• Digests proteins and fats in the stomach

• Peristalsis = mechanical digestion

Small Intestine• Enzymes continue the

chemical reactions on the food – chemical digestion

• The nutrients are broken down small enough to pass through the lining of the small intestine, and into the blood (diffusion).

• Digests proteins, fats, and carbohydrates.

• Peristalsis = mechanical digestion

Absorption by Small Intestines• Absorption through villi & microvilli

– finger-like projections– increase surface area for absorption

VILLI

Pancreas

• Accessory organ• Food does not go

through the pancreas• Produces chemicals to

help break down macromolecules = chemical digestion

• Also produces insulin = helps control blood sugar levels

Liver

• Produces bile to help digest fat – Mechanical Digestion, fats are broken into smaller “fat globules”

• Bile is stored in the Gall Bladder and released into the small intestine

Large intestines (colon)

• Function– re-absorb water – (NO DIGESTION)

• use ~9 liters of water every day in digestive juices

• > 90% of water reabsorbed– not enough water absorbed

» diarrhea – too much water absorbed

» constipation

Large Intestine• Solid materials pass

through the large intestine.• These are undigestible

solids (fibers).• Water is absorbed.• Vitamins K and B are

reabsorbed with the water.• Rectum- solid wastes exit

the body.

You’ve got company!• Living in the large intestine is a community

of helpful bacteria– Escherichia coli (E. coli)

• produce vitamins – vitamin K; B vitamins

• generate gases– by-product of bacterial metabolism – methane, hydrogen sulfide