DIGESTIVE SYSTEM

Thursday November 24th, 2011

WHY DO WE NEED TO DIGEST? Heterotrophic! Obtain nutrients by

consuming other organisms. Food that we consume is in the form of

large, complex molecules. We need nutrients to be small enough to

enter our cells. (pass through cell membrane)

Every major organ system requires nutrients to function.

THE 4 COMPONENTS OF THE DIGESTIVE SYSTEM

#1: Ingestion The taking in of nutrients

#2: Digestion The breakdown of complex organic molecules into small molecules. (By enzymes)

#3: Absorption The transport of digested nutrients to the tissues of the body.

#4: Egestion The removal of waste food materials from the body.

DIGESTIVE ENZYMES Catalyst: A compound that speeds up the rate

of a chemical reaction without being used up in the reaction.

Enzymes are biological catalysts, they speed up chemical reactions in the body.

Increases temp helps speed up chemical reactions, but we can’t do this inside our bodies.

Enzymes are required to break down nutrient molecules during digestion.

Without enzymes, digestion would take too long and we would die before the nutrients were ever absorbed.

IMPORTANT MACROMOLECULES Macromolecule – very large molecules

consumed in our diets. Molecules must be broken down into

smaller monomers in order to be absorbed by our cells.

Proteins amino acids Carbohydrates simple sugars Fats fatty acids, glycerol

DIGESTION IN SIMPLE ORGANISMS

INGESTION IN EARTHWORMS AND BIRDS Digestive systems that have a separate

opening for a mouth and an anus are called alimentary canals.

Mouth Pharynx Esophagus Crop Gizzard Pharynx: Muscular area past the mouth that

helps push food down the esophagus. Esophagus Carries food from the pharynx to

the stomach. Crop Stores undigested food. Gizzard Muscular chamber, usually

containing small stones that helps to physically break down food.

INGESTION IN HUMANS Mouth

Physical and chemical digestionPhysical = breakdown of food into smaller

pieces by teeth.

Incisors Cutting Canine Tearing Premolars Grinding Molars Crushing

Chemical breakdown in mouthSaliva Mix of water and enzymes produced by

the salivary glands in the mouth.Contains the enzyme Amylase, which breaksdown

complex carbohydrates into simple sugars.Saliva also helps lubricate the food to make it

easier to swallow.

THE ESOPHAGUS Connects the

pharynx to the stomach.

Very muscular Waves on muscle

contractions send food down to the stomach.

Called peristalsis Swallowed food =

bolus

THE STOMACH Function: Muscular sac that stores food

and performs chemical digestion. Can hold approx 1.5L The inner wall of the stomach contains

many folds called Rugae.

STOMACH CONTINUED Rugae allow the stomach to expand as

more food enters. The stomach contains many gastric cells

that secrete gastric juices. Gastric juice Hydrochloric acid (pH 2-

3), mucus, and enzymes. Mucus is secreted to protect the

stomach from digesting itself. Hydrochloric acid breaks down the food

into smaller pieces. Enzyme Pepsin: Digests proteins.

Cardiac Sphincter Circular muscle that controls the movement of food into the stomach.

Pyloric Sphincter Controls the movement of food from the stomach into the small intestine.

PEPSIN Different enzymes have different

conditions under which they function the most efficiently.

Pepsin digests proteins in the stomach, so it has an optimum pH of 2-3.

Trypsin is an enzyme that functions in the small intestine. It has an optimal pH of 7-8.

THE SMALL INTESTINE Site for the greatest amount of

digestion. Narrow diameter (2-2.5cm) but very

long (7-8m) 3 parts: duodenum, jejunum, and ileum. Most digestion occurs in the duodenum.

Partially digested food from the stomach enters the duodenum.

This sets off a chemical signalling process.

Acidity of food entering duodenum causes prosecretin to be converted into

secretin.

Secretin is absorbed into bloodstream and travels to pancreas.

Secretin stimulates pancreas to release a bicarbonate solution (basic)

Bicarbonate solution moves into the small intestine, neutralizing the gastric juices

from pH of 2.5 to 9.

Now the partially digested food will not harm the small intestine.

The change in pH deactivates the pepsin enzyme.

ABSORPTION IN THE SMALL INTESTINE Inner wall of the small

intestine is made up of finger-like projections called villi.

Villi increase the surface area of the small intestine, maximizes absorption of nutrients.

Villi contain capillary bed, allow digested nutrients to enter bloodstream.

Also contain a lacteal which is part of the lymphatic system

(absorb fatty acids).

THE PANCREAS Besides releases bicarbonate solution to

neutralize the acid from the stomach, the pancreas also releases digestive enzymes into the duodenum.

Trypsin Continues to digest proteins. Erepsin Complete the digestion of

proteins. Amylase Breaks down carbohydrates. Lipase Breaks down fats.

THE LIVER Produced bile. Bile is essential for the digestion of fats. Bile is stored in the gall bladder before

being released into the duodenum during digestion.

THE LARGE INTESTINE Main function is the absorption of water. Approx 90% of water is absorbed back

into bloodstream. Billions of bacteria are present, help

break down undigested materials. Many of these bacteria produce

important vitamins which are absorbed back into the bloodstream. (vitamin B, vitamin K)

HOMEWORK Biozone pg 63,69-70,78-81 Handout: The Human Digestive System IB only: read pg 151-156. 3U only: pg 238 # 1,3,4,10