Chapter Eight

Chapter Eight
Digestive System and Nutrition
Overview of Digestion
The organs of the digestive system are located within a tube called the gastrointestinal tract (GI tract).
• Ingestion- when food goes into the mouth.
• Digestion- can be mechanical or chemical. Divides food into pieces and hydrolyzes food to molecular nutrient. It occurs in the mouth and stomach.
• Movement- food is passed along from one organ to the next and indigestible remains are expelled.
• Absorption- unit molecules produced by digestion cross the wall of the GI tract and enter the blood for delivery to cells.
• Elimination- removal of indigestible wastes through the anus


Wall of the Digestive Tract
• The walls of the digestive tract has four layers
• Lumen- is the central space that contains water
• Mucosa- Inner mucous membrane layer that is modified according to the digestive organ

• Diverticulitis-when the pouches become infected or inflamed

• Submocosa- broadband of loose connective tissue that contains nerves, blood, and lymphatic vessels.

• Inflammatory bowel disease

• Muscularis- two layers of smooth muscle

• Irritable bowel syndrome

• Serosa- thin, outermost tissue that is the visceral peritoneum.

• Appendicitis

Layers of the GI Tract










First Part of the Digestive Tract
The Mouth
The mouth receives food and begins the process of digestion.
• The roof of the mouth has two parts:

• The anterior (up front) hard palate

• Posterior (in the back) soft palate

• Three pairs of salivary glands sends juices by way of ducts to the mouth.
• Saliva is a solution of mucus and water, which contains bicarbonate and an enzyme called salivary amylase.
• The mechanical digestion-teeth chews food into pieces convenient for swallowing and the tongue moves food around the mouth.
• Chemical digestion- salivary amylase begins the process of digesting starch
The Pharynx and Esophagus
The mouth and nasal passages lead to a cavity called the pharynx. The food passage and air passage cross in the pharynx because the trachea is anterior to the esophagus, a long, narrow tube that takes food to the stomach.
-Swallowing
• Has a voluntary phase
• Swallowing becomes a reflex action preformed automatically.
• We do not breathe when we swallow.
• The soft palate moves back to close off the nasal passages, and the trachea moves up under the epiglottis to cover the glottis which prevents food from entering the nose or entering the trachea when we swallow.









Process of Swallowing









The Stomach and Small Intestine
The Stomach
• Is a thick-walled, j-shaped organ that lies on the left side of the body beneath the diaphragm.
• Stores food
• Initiates the digestion of protein and controls movement of chyme into the small intestine.
• The stomach expands
• The mucosa of the stomach has deep folds, the rugae, which disappear as the stomach fills.
• The mucosa of the stomach had millions of gastric pits, which lead into gastric glands, which produces gastric juice.
• Gastric juice contains an enzyme called pepsin.







The stomach and Layers





The Small Intestine
• Digestion is completed in the small intestine
• Complete digestion using enzymes, which digest all types of food and absorb the products of the digestive process
• The walls of the small intestine contain villi that have an outer layer of columnar epithelial cells, each containing thousands of microvilli.
• Nutrients are absorbed in the small intestine
Lactose Intolerance
• Lactose is the primary sugar in the milk.
• People who can not digest lactose are lactose intolerance.
Obesity: Diabetes Type 2 and Cardiovascular Disease
• The intake of too much sugar and fat can result to obesity.
• Being obese can result to have diabetes and cardiovascular disease.
Three Accessory Organs and Regulation of Secretions
Three Accessory Organs
• Pancreas
• Liver
• Gallbladder

• Pancreas-produces pancreatic juice, which contains digestive enzymes for carbs, protein and fat.

• Liver- Produces bile, destroys old blood cells, detoxifies blood, stores iron, makes plasma proteins, stores glucose as glycogen, breaks down glycogen to glucose, produces urea, and helps regulate blood cholesterol levels.

• Gallbladder- stores bile, which is produced by the liver.

Regulation of Digestive Secretions
• The secretions of digestive juices are controlled by the nervous system and by digestive hormones.
The Large Intestine and Defecation
• Includes the cecum, the colon, the rectum and the anal canal.
Functions of the Large Intestine
• The large intestine absorbs water, which is an important function that prevents dehydration of the body.
• Absorbs vitamins produced by bacteria called the intestinal flora.
• Forms feces.



The large intestine and an image of the large of intestine

Disorders of the Colon and Rectum
• Diarrhea- caused by infection of the lower intestinal tract and nervous stimulation.
• Constipation- when the feces are dry and hard.

• Chronic constipation is associated with hemorrhoids.

• Diverticulosis- is the occurrence of little pouches of mucosa that have pushed out through weak spots in the muscularis.
• Irritable bowel syndrome (IBS)- is the condition in which the muscularis contracts powerfully but without its normal coordination.
• Inflammatory bowel disease (IBD)- is a collective term for a number of inflammatory disorders.
• Polyps and Cancer- polyps (small growths arising from the epithelial lining.) whether benign or cancerous.
Nutrition and Weight Control
Obesity had doubled in the US in 20 years!! Nearly one-third of adults are now obese.
How Obesity is defined
• Is defined as a body mass index (BMI).



Classes of Nutrients
• Nutrient can be defined as a component of food that performs a physiological function in the body.

• Carbohydrates

• Proteins

• Lipids

Minerals
• Are divided into major mineral and trace minerals

• Calcium

• Sodium

Vitamins
• Are organic compounds that the body uses for metabolic purposes but is unable to produce in adequate quantity.

• Antioxidants

• Vitamin D

How to Plan Nutritious Meals
• Eat a variety of food.
• Eat more fruit, vegetables, whole grains and low fat products.
• Eat less of food in high fat (fast food places, alcohol)
• Be physically active everyday.




Eating Disorders
• Anorexia nervosa- is a severe psychological disorder characterized by an irrational fear of getting fat that results in the refusal to eat enough food to maintain a healthy body weight. About 90% young women suffer from this disorder.
• Bulimia nervosa- binge eating and then purges to avoid gaining weight. A average of 4% young women suffer from this disorder.
• Binge-eating disorder- some obese people suffer from this disorder, it is overeating.
• Muscle dysmorphia- thinking his or her body is underdeveloped. A person can hours exercising and obsession with a diet.



http://www2.potsdam.edu/french85/digestion.html
http://mednote.co.kr/11CYTOHISTO.htm
http://www.answers.com/topic/swallowing?cat=health
http://www.acm.uiuc.edu/sigbio/project/digestive/late/lg_intestine.html
http://www.pta.org/documents/foodpyramid.jpg