The Digestive System

The Digestive System and Body Metabolism Slide 14.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Digestion  Breakdown of ingested food  Absorption  Passage of nutrients into the blood  Metabolism  Production of cellular energy (ATP)

Organs of the Digestive System Slide 14.2a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Two main groups  Alimentary canal – continuous coiled hollow tube  Accessory digestive organs

How is food digested? Digestion involves: Breaking down of food into smaller pieces Breaking down of food into smaller pieces The mixing of food The mixing of food Movement through the digestive tract Movement through the digestive tract Chemical breakdown of the large molecules of food into smaller molecules. Chemical breakdown of the large molecules of food into smaller molecules.

Digestive System The digestive tract is a series of hollow organs joined in a tube from the mouth to the anus. Food passes through the digestive tract. The digestive tract is a series of hollow organs joined in a tube from the mouth to the anus. Food passes through the digestive tract. Accessory organs include the liver, gall bladder, and pancreas. Food does not pass through these organs. Accessory organs include the liver, gall bladder, and pancreas. Food does not pass through these organs.

Organs of the Digestive System Slide 14.2b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 14.1

Organs of the Alimentary Canal Slide 14.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Mouth  Pharynx  Esophagus  Stomach  Small intestine  Large intestine  Anus

Mouth  Teeth bite off and chew food into a soft pulp that is easy to swallow.  Chewing mixes the food with saliva, from salivary glands around the mouth and face, to make it moist and easy to swallow.  Enzymes in the saliva begin digestion of carbohydrates.

Pharynx Slide 14.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Serves as a passageway for air and food  Food is propelled to the esophagus by two muscle layers  Longitudinal inner layer  Circular outer layer  Food movement is by alternating contractions of the muscle layers (peristalsis)

Esophagus  The esophagus is a muscular tube. It takes food from the throat and pushes it down through the neck, and into the stomach.  It moves food by waves of muscle contraction called peristalsis.

Esophagus Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Runs from pharynx to stomach through the diaphragm  Conducts food by peristalsis (slow rhythmic squeezing)  Passageway for food only (respiratory system branches off after the pharynx)

Stomach Functions Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Acts as a storage tank for food  Site of food breakdown  Chemical breakdown of protein begins  Delivers chyme (processed food) to the small intestine

Stomach Anatomy Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 14.4a

Small Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  The body’s major digestive organ  Site of nutrient absorption into the blood  Muscular tube extending form the pyloric sphincter to the ileocecal valve  Suspended from the posterior abdominal wall by the mesentery

Subdivisions of the Small Intestine “Dogs Just Itch! Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Duodenum  Attached to the stomach  Curves around the head of the pancreas  Jejunum  Attaches anteriorly to the duodenum  Ileum  Extends from jejunum to large intestine

Chemical Digestion in the Small Intestine Slide 14.23a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Source of enzymes that are mixed with chyme  Intestinal cells  Pancreas  Bile enters from the gall bladder

Villi of the Small Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Fingerlike structures formed by the mucosa  Give the small intestine more surface area Figure 14.7a

Microvilli of the Small Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Small projections of the plasma membrane  Found on absorptive cells Figure 14.7c

Structures Involved in Absorption of Nutrients Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Absorptive cells  Blood capillaries  Lacteals (specialized lymphatic capillaries) Figure 14.7b

Digestion in the Small Intestine Slide 14.57a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Enzymes from the brush border  Break double sugars into simple sugars  Complete some protein digestion  Pancreatic enzymes play the major digestive function  Help complete digestion of starch (pancreatic amylase)  Carry out about half of all protein digestion (trypsin, etc.)

Digestion in the Small Intestine Slide 14.57b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Pancreatic enzymes play the major digestive function (continued)  Responsible for fat digestion (lipase)  Digest nucleic acids (nucleases)  Alkaline content neutralizes acidic chyme

Absorption in the Small Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Water is absorbed along the length of the small intestine  End products of digestion  Most substances are absorbed by active transport through cell membranes  Lipids are absorbed by diffusion  Substances are transported to the liver by the hepatic portal vein or lymph

Small Intenstine  This part of the digestive tract is narrow, but very long - about 20 feet.  Enzymes continue the chemical reactions on the food.  The nutrients are broken down small enough to pass through the lining of the small intestine, and into the blood (diffusion).  Nutrients are carried away to the liver and other body parts to be processed, stored and distributed.

Large Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Larger in diameter, but shorter than the small intestine  Frames the internal abdomen

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

Functions of the Large Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Useful substances that were not absorbed in the small intestine, such as spare water and body minerals, are absorbed through the walls of the large intestine, back into the blood.  Eliminates indigestible food from the body as feces  Does not participate in digestion of food

Food Breakdown and Absorption in the Large Intestine Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  No digestive enzymes are produced  Resident bacteria digest remaining nutrients  Produce some vitamin K and B  Release gases  Water and vitamins K and B are absorbed

Identify and tell the function of each part of the digestive system

Rectum and Anus The end of the large intestine and the next part of the tract, the rectum, store the feces. The end of the large intestine and the next part of the tract, the rectum, store the feces. Feces are finally squeezed through a ring of muscle, the anus, and out of the body. Feces are finally squeezed through a ring of muscle, the anus, and out of the body.

Pancreas Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Produces a wide spectrum of digestive enzymes that break down all categories of food  Enzymes are secreted into the duodenum  Alkaline fluid introduced with enzymes neutralizes acidic chyme  Endocrine products of pancreas  Insulin  Glucagons

Gall Bladder  A small baglike part under the liver.  It stores a fluid called bile, which is made in the liver.  As food from a meal enters the small intestine, bile flows from the gall bladder along the bile duct into the intestine.  It helps to digest fatty foods and also contains wastes for removal.

Liver Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Largest gland in the body  Located on the right side of the body under the diaphragm  Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament

Liver  Blood from the intestines enters to the liver, carrying nutrients, vitamins and minerals, and other products from digestion.  The liver is like a food-processing factory with more than 200 different jobs. It stores some nutrients, changes them from one form to another, and releases them into the blood according to the activities and needs of the body.

Role of the Liver in Metabolism Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Several roles in digestion  Detoxifies drugs and alcohol  Degrades hormones  Produce cholesterol, blood proteins (albumin and clotting proteins)  Plays a central role in metabolism

Bile Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Produced by cells in the liver  Composition  Bile salts  Bile pigment (mostly bilirubin from the breakdown of hemoglobin)  Cholesterol  Phospholipids  Electrolytes

Processes of the Digestive System Slide 14.42a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Ingestion – getting food into the mouth  Propulsion – moving foods from one region of the digestive system to another

Processes of the Digestive System Slide 14.42b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Peristalsis – alternating waves of contraction  Segmentation – moving materials back and forth to aid in mixing Figure 14.12

Processes of the Digestive System Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Mechanical digestion  Mixing of food in the mouth by the tongue  Churning of food in the stomach  Segmentation in the small intestine

Processes of the Digestive System Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Chemical Digestion  Enzymes break down food molecules into their building blocks  Each major food group uses different enzymes  Carbohydrates are broken to simple sugars  Proteins are broken to amino acids  Fats are broken to fatty acids and alcohols

Processes of the Digestive System Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Absorption  End products of digestion are absorbed in the blood or lymph  Food must enter mucosal cells and then into blood or lymph capillaries  Defecation  Elimination of indigestible substances as feces

Processes of the Digestive System Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 14.11

Control of Digestive Activity Slide 14.47b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Stimuli include:  Stretch of the organ  pH of the contents  Presence of breakdown products  Reflexes include:  Activation or inhibition of glandular secretions  Smooth muscle activity

Nutrition Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Nutrient – substance used by the body for growth, maintenance, and repair  Categories of nutrients  Carbohydrates: simple sugars, starches, fiber  Lipids: triglycerides, phospholipids, fatty acids  Proteins: amino acids  Vitamins  Mineral  Water

Body Energy Balance Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Energy intake = total energy output (heat + work + energy storage)  Energy intake is liberated during food oxidation  Energy output  Heat is usually about 60%  Storage energy is in the form of fat or glycogen