Human digestive system After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested. Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours. In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

The Digestive System How is food digested? 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