The Digestive System Chapter 14

1. Digestion- Breakdown of ingested food 2. Absorption- Passage of nutrients into the blood 3. Metabolism- Production of cellular energy (ATP) The Digestive System & Body Metabolism

Organs are divided into two main groups: 1.Alimentary canal – continuous coiled hollow tube 2.Accessory digestive organs Organs of the Digestive System

Figure 14.1

1. Mouth 2. Pharynx 3. Esophagus 4. Stomach 5. Small intestine 6. Large intestine 7. Anus Organs of the Alimentary Canal

1. Mastication- (chewing) of food 2. Mixing masticated food with saliva 3. Initiation of swallowing by the tongue 4. Allowing for the sense of taste Processes of the Mouth

1. Serves as a passageway for air and food 2. Food is propelled to the esophagus by two muscle layers  Longitudinal inner layer  Circular outer layer 3. Food movement is by alternating contractions of the muscle layers (peristalsis) Pharynx

1. Runs from pharynx to stomach through the diaphragm 2. Conducts food by peristalsis (slow rhythmic squeezing) 3. Passageway for food only (respiratory system branches off after the pharynx) Esophagus

1.Located on the left side of the abdominal cavity 2.Food enters at the cardioesophageal sphincter. It exits the pyloric sphincter (into the small intestine. 3.Regions of the stomach  Cardiac region – near the heart  Fundus  Body  Phylorus – funnel-shaped terminal end Stomach

Stomach Anatomy

1.Acts as a storage tank for food 2.Site of food breakdown 3.Chemical breakdown of protein begins 4.Delivers chyme (processed food) to the small intestine Stomach Functions

1.The body’s major digestive organ 2.Site of nutrient absorption into the blood 3.Muscular tube extending form the pyloric sphincter to the ileocecal valve 4.Suspended from the posterior abdominal wall by the mesentery Small Intestine

1. Source of enzymes that are mixed with chyme  Intestinal cells  Pancreas 2. Bile enters from the gall bladder 3. Pancreatic enzymes play the major role in digestive functioning Chemical Digestion in the Small Intestine

Figure 14.6

Villi of the Small Intestine Fingerlike structures formed by the mucosa Give the small intestine more surface area

Gastrointestinal Tract

1. Water is absorbed along the length of the small intestine 2. End products of digestion a) Most substances are absorbed by active transport through cell membranes b) Lipids are absorbed by diffusion 3. Substances are transported to the liver by the hepatic portal vein or lymph Absorption in the Small Intestine

1. Larger in diameter, but shorter in length than the small intestine 2. Frames the internal abdomen Large Intestine

Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 14.8

1. Absorption of water 2. Eliminates indigestible food from the body as feces 3. Does not participate in the digestion of food 4. Goblet cells produce mucus to act as a lubricant Functions of the Large Intestine

1. No digestive enzymes are produced 2. Resident bacteria digest remaining nutrients a) Produce some vitamin K and B b) Release gases 3. Water and vitamins K and B are absorbed 4. Remaining materials are eliminated via feces Food Breakdown & Absorption in the Large Intestine

1.Salivary glands 2.Teeth 3.Pancreas 4.Liver 5.Gall bladder Accessory Digestive Organs

 Mixture of mucus and serous fluid helps to form a food bolus  Contains salivary amylase to begin starch digestion  Dissolves chemicals so they can be tasted The Importance of Saliva

1. Produces a wide spectrum of digestive enzymes that break down all categories of food 2. Enzymes are secreted into the duodenum 3. Alkaline fluid introduced with enzymes neutralizes acidic chyme 4. Endocrine products of pancreas: a) Insulin b) Glucagons Pancreas

1. Largest gland in the body 2. Located on the right side of the body under the diaphragm 3. Consists of four lobes suspended from the diaphragm and abdominal wall 4. Connected to the gall bladder via the common hepatic duct Liver

1. Several roles in digestion 2. Detoxifies drugs and alcohol 3. Degrades hormones 4. Produce cholesterol, blood proteins (albumin and clotting proteins) 5. Plays a central role in metabolism Role of the Liver in Metabolism

Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 1. Sac found in hollow fossa of liver 2. Stores bile from the liver by way of the cystic duct 3. Bile is introduced into the duodenum in the presence of fatty food 4. Gallstones can cause blockages Gall Bladder

Mechanical digestion 1. Mixing of food in the mouth by the tongue 2. Churning of food in the stomach 3. Segmentation in the small intestine Processes of the Digestive System

Absorption 1. End products of digestion are absorbed in the blood or lymph 2. Food must enter mucosal cells and then into blood or lymph capillaries Defecation- Elimination of indigestible substances as feces

Chemical Digestion 1. Enzymes break down food molecules into their building blocks 2. Each major food group uses different enzymes a) Carbohydrates are broken to simple sugars b) Proteins are broken to amino acids c) Fats are broken to fatty acids and alcohols

Processes of the Digestive System

1. Mostly controlled by reflexes via the parasympathetic division 2. Chemical and mechanical receptors are located in organ walls that trigger reflexes Control of Digestive Activity