The Digestive System Human Digestion Digestion n Process

The Digestive System Human Digestion

Digestion n Process by which food molecules are broken down into simpler molecules that can be absorbed and used by the cells of the body – Nutrients are passed through cell membrane (absorption) but large particles must be broken down first.

Mechanical Breakdown n Chewing and cutting (teeth)

Chemical Breakdown n Digestive enzymes (saliva)

The Human Digestive System n n n Food passes n through the digestive n tube in the following n order n n n Oral cavity (mouth) Pharynx (throat) Esophagus (gullet) Stomach Small intestine Large intestine Rectum Anus

The Human Digestive System

The Mouth and Pharynx n Mechanical breakdown of food

The Mouth and Pharynx n Mechanical breakdown of food Teeth

The Mouth and Pharynx n Food mixed with saliva – 3 pair of salivary glands in mouth

The Mouth and Pharynx n Saliva wets food and causes it to stick together – Bolus – food mass

The Mouth and Pharynx n Chemical digestion in mouth with saliva – Salivary amylase – enzyme in saliva that breaks starch into maltose and glucose

The Mouth and Pharynx n Food pushes into pharynx n Epiglottis – flap of tissue covering trachea or pharynx so food/air goes down the right tube

Esophagus n Tube through which food passes from pharynx to stomach

Esophagus n Sphincter Muscle – ring of muscle where esophagus tube meets stomach

Esophagus n Peristalsis – rhythmic muscular movement of organs that “pushes” food through digestive tract

Stomach n Food broken down! – Mechanically: stomach contractions – Chemically: gastric juices secreted by glands in stomach walls

Stomach Glands Pyloric Gland – secretes mucus to cover stomach lining and protect it 2. Gastric Gland – secretes gastric juices 1. a. p. H of 1. 5 – 2. 5 (acidic) b. Contains HCl (hydrochloric acid) and pepsin (digestive enzyme that breaks down protein and curdles milk)

Stomach 3 mechanisms that stimulate the flow of gastric juices: 1. Thought, smell, sight, or taste of food sends message from brain to gastric gland 2. Food touching the stomach lining

Stomach 3. When food mass stretches stomach walls Stretching stimulates lining to secrete gastrin (hormone) into blood stream Gastrin signals gastric glands to produce large amounts of gastric juices

Stomach n Liquids pass through stomach in

Stomach n Liquids pass through stomach in 20 minutes or less

Stomach n Solids

Stomach Solids take longer n Reduced to thin soupy liquid – Chyme – that passes through Pyloric Sphincter (muscle controlling passage of chyme from stomach to small intestine) n

Stomach n ULCER – mucus layer of stomach breaks down and part of stomach wall is digested

Small Intestine n Fluids are alkaline n Chyme is mixed with bile from liver, pancreatic juice from pancreas, and intestine juice from small intestine

Small Intestine n Peristalsis * squeezes chyme through intestine * mixes chyme with digestive enzymes * breaks down chyme mechanically * speeds absorption by bringing contents into contact with intestinal walls

Small Intestine n Pancreatic Enzymes a. Amylase – breaks starch into maltose

Small Intestine n Pancreatic Enzymes a. Amylase – breaks starch into maltose b. Protease – breaks proteins trypsin chymotrypsin

Small Intestine n Pancreatic Enzymes a. Amylase – breaks starch into maltose b. Protease – breaks proteins trypsin chymotrypsin c. Lipase – breaks lipids

Small Intestine n Bile – from cells of liver and is stored in gallbladder n Aids in digestion of fats and oils by breaking them into tiny droplets – emulsification – and increases surface area for enzyme action

Small Intestine n Intestinal Juices – walls of small intestine contains millions of intestinal glands that secrete intestinal juices

Small Intestine n Absorption – small intestine is site of absorption of substances into blood vessels of circulatory system

Small Intestine n Small intestine contains folds and lining is covered with projections called villi

Large Intestine n Undigested and unabsorbed materials pass from small intestine to large intestine n NO digestion occurs here

Large Intestine n Lower right side of body where small intestine and large intestine meet is a pouch - appendix

Large Intestine n Main function of large intestine is reabsorption of water from food mass

Large Intestine n Main function of large intestine is reabsorption of water from food mass n Second function is to absorb vitamins produced by bacteria normally living in large intestine – Bacteria live on undigested food material and in turn produce vitamin K which is essential for blood clotting

Large Intestine n Third function is to eliminate undigested or indigestible material (feces)

Rectum n Stores feces

Anus n Feces eliminated from body here THE END!