Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings EMILY BRADSHAW, PH.D. SC 131 Unit 5 Digestive System

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Agenda  Anatomy of the digestive system  Process of digestion  Benefits of dietary fiber

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Digestive System and Body Metabolism  Digestion  Breakdown of ingested food  Absorption of nutrients into the blood  Metabolism  Production of cellular energy (ATP)  Constructive and degradative cellular activities

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Processes of the Digestive System  Ingestion  Mechanical Digestion  Chemical Digestion  Enzymes break down food  Carbohydrates are broken to simple sugars  Proteins are broken to amino acids  Fats are broken to fatty acids and alcohols  Absorption  Defecation

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mouth (Oral Cavity) Anatomy  Mastication (chewing) of food  Mixing masticated food with saliva  Initiation of swallowing by the tongue  Allowing for the sense of taste Figure 14.2a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Pharynx Function  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)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Esophagus  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)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stomach Functions  Acts as a storage tank for food  Site of food breakdown  Chemical breakdown of protein begins  Delivers chyme (processed food) to the small intestine

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Stomach Mucosa  Gastric pits formed by folded mucosa  Presence of food or falling pH causes the release of gastrin  Gastrin causes stomach glands to produce protein- digesting enzymes  Hydrocholoric acid makes the stomach contents very acidic  Activates pepsinogen to pepsin for protein digestion  Provides a hostile environment for microorganisms

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion in the Small Intestine  Source of enzymes that are mixed with chyme  Intestinal cells  Pancreas  Bile enters from the gall bladder

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Villi of the Small Intestine  Fingerlike structures formed by the mucosa  Give the small intestine more surface area  Absorptive cells  Blood capillaries  Lacteals – absorb fat Figure 14.7a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Stimulation of the Release of Pancreatic Juice  Vagus nerve  Local hormones  Secretin  Cholecystokinin  Pancreatic enzymes play the major digestive function  Lipase  Nucleases  Alkaline Figure 14.16

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Absorption in the Small Intestine  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

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Large Intestine  Larger in diameter, but shorter than the small intestine  Does NOT participate in digestion of food; ONLY absorption of water  Eliminates indigestible food from the body as feces  Goblet cells produce mucus to act as a lubricant  Resident bacteria digest remaining nutrients  Produce some vitamin K and B  Release gases

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Liver  Largest gland in the body  Consists of four lobes suspended from the diaphragm and abdominal wall  Connected to the gall bladder via the common hepatic duct  Bile - produced by cells in the liver  Composition: bile salts, bile pigment (mostly bilirubin from the breakdown of hemoglobin), cholesterol, phospholipids, electrolytes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Gall Bladder  Sac found in hollow fossa of liver  Stores bile from the liver by way of the cystic duct  Bile is introduced into the duodenum in the presence of fatty food  Gallstones can cause blockages

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Dietary Fiber  Includes all parts of plant foods that your body can't digest or absorb.  Fiber is commonly classified into two categories: those that don't dissolve in water (insoluble fiber) and those that do (soluble fiber).  Insoluble fiber: Promotes the movement of material through your digestive system and increases stool bulk.  Examples: Whole-wheat flour, wheat bran, nuts and many  Soluble fiber: Dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels.  Examples: Oats, peas, beans, apples, citrus fruits, carrots, and barley Image credit:

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Benefits of Dietary Fiber  Normalizes bowel movements. Dietary fiber increases the weight and size of your stool and softens it. A bulky stool is easier to pass, decreasing your chance of constipation.  Helps maintain bowel integrity and health. A high-fiber diet may lower your risk of developing hemorrhoids, and small pouches in your colon (diverticular disease).  Lowers blood cholesterol levels. Soluble fiber found in beans, oats, flaxseed and oat bran may help lower total blood cholesterol levels by lowering low-density lipoprotein, or "bad," cholesterol levels.  Helps control blood sugar levels. Fiber, particularly soluble fiber, can slow the absorption of sugar, which for people with diabetes can help improve blood sugar levels.  Aids in weight loss. High-fiber foods generally require more chewing time, which gives your body time to register when you're no longer hungry, so you're less likely to overeat. Also, a high-fiber diet tends to make a meal feel larger and linger longer, so you stay full for a greater amount of time. And high-fiber diets also tend to be less "energy dense," which means they have fewer calories for the same volume of food.  Uncertain effect on colorectal cancer. Evidence that dietary fiber reduces colorectal cancer is mixed — some studies show benefit, some show nothing and some suggest increased risk.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sources of dietary fiber  Grains and whole-grain products  Fruits  Vegetables  Beans, peas and other legumes  Nuts and seeds  Refined or processed foods — such as canned fruits and vegetables and pulp-free juice, white bread and pasta, and non-whole-grain cereals — are lower in fiber content. Whole foods rather than fiber supplements are generally better.  Fiber supplements — such as Metamucil, Citrucel and FiberCon — don't provide the vitamins, minerals and other beneficial nutrients that high-fiber foods do. Image credit:

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Questions???? Image Credit: Microsoft Clip Art