Chapter #15 The Digestive System

Chapter 15.1 Digestion is the mechanical and chemical breakdown of foods and the absorption of the resulting nutrients by cells. The digestive system consists of the alimentary canal, which extends about 9 meters (27 feet or 900 cm) from the mouth to the anus.

Alimentary Canal Mouth Pharynx Esophagus Stomach Small Intestine Large Intestine Rectum Anus

Mouth Mechanical breakdown of food; begins chemical digestion of carbohydrates (bread). Salivary glands secrete saliva, which contains enzymes that initiate breakdown of carbohydrates. Pharynx connects mouth with esophagus.

Esophagus peristalsis pushes food to stomach. Peristalsis wavelike motion that propels food. Stomach secretes acid and enzymes. Mixes food with secretions to begin enzymatic digestion of proteins.

Small Intestine mixes food with bile and pancreatic juice Small Intestine mixes food with bile and pancreatic juice. Final enzymatic breakdown of food molecules: main site of nutrient absorption. Liver produces bile, which emulsifies fat. Gallbladder stores bile and introduces it into small intestine. Pancreas produces and secretes pancreatic juice, containing digestive enzymes and bicarbonate ions, into sm. Intestine. Accessory organs are organs that are not a direct route of the digestive system.

Large intestine absorbs water and electrolytes to form feces. Rectum regulates elimination of feces. Anus eliminates feces. The digestive system is a tube, open at both ends, that has a surface area of 186 square meters. The main function is to supply body with nutrients.

15.2 General Characteristics 3 parts of the small intestine Duodenum Jejunum Ileum

Alimentary Canal Mucosa or mucous membrane the inner most layer. Contains glands that secrete mucus and digestive enzymes. Carries on secretion and absorption. Also, has projections that increase the surface area. Lumen=passageway. Submucosa contains loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves. Carry away absorbed materials.

Muscular layer produces the movements. Serosa or serous layer the outer covering of the digestive tube. Secretes fluid that lubricates the tube’s outer surface so organs slide freely against one another.

15.3 The Mouth The mouth receives food and begins digestion by mechanically reducing the size of food and mixes them with saliva. Oral cavity includes the chamber between the palate and tongue. Palate forms the roof of the oral cavity and is made of a hard palate (front) and Soft palate (rear). Tongues function is to move food toward the palate. Made out of skeletal muscle.

During swallowing, muscles draw the soft palate and uvula upward to separate the oral and nasal cavities. Salvia cleanse the mouth and teeth, dissolve chemicals necessary to tasting food, and help in the formation of food bolus.

Tonsils Palatine are lymphatic tissue in the back of the mouth, on either side of the tongue and closely associated with the palate. Help to fight infection. Pharyngeal or adenoids are on the posterior wall of the pharynx. They can be removed. Tonsillectomy tonsil are surgically removed.

Teeth Humans have 2 sets of teeth. Primary teeth or deciduous usually erupt at 6months-4 years of age. 20 primary teeth. 10 upper and 10 lower. Secondary teeth or permanent consist of 32 teeth.

Good dental hygiene is essential because once damaged, enamel cannot be replaced. Enamel cover the crown. White and shiny. Dentin is found beneath the enamel. Dentin is a substance similar to bone. Pulp cavity contains blood vessels, nerves, and connective tissue. Root canals contains the root.

Teeth 4 types of teeth Incisors (Front 4 teeth) bite off pieces of food. Cuspid grasp and tear food. Bicuspids or premolars grind food. Molars grind food.

15.4 Salivary Glands The salivary glands secret saliva. Saliva moistens food particles, helps them bind, and begins the chemical digestions of carbohydrates. Saliva dissolves food so that they can be tasted. 2 types of secretions from the salivary glands. Amylase digestive enzyme in mouth, stomach, pancreas. Mucus which binds with food particles to lubricate for swallowing.

Types of Salivary Glands Parotid glands the largest. Submandibular glands located in the floor of the mouth. Sublingual glands the smallest of the salivary glands, are on the floor of the mouth.

15.5 Pharynx and Esophagus Pharynx connects the nasal and oral cavities with the larynx and esophagus. 3 parts Nasopharynx communicates with the nasal cavity and provides a passageway for air during breathing. Oropharynx is posterior to the soft palate and inferior to the nasopharynx. It is the passageway for food moving downward from the mouth and for air moving to and from the nasal cavity. Laryngopharynx just inferior to the oropharynx, is a passageway to the esophagus.

Epiglottis closes off the top of the trachea (windpipe) so food is less likely to enter.

15.6 Stomach The stomach is a J-shaped , pouchlike organ that hangs inferior to the diaphragm in the upper left portion of the abdominal cavity and has a capacity of about 1 liter. The stomach has thick folds of mucosal and submucosal layers and disappear when the stomach wall is distended.

Stomach The stomach is divided into four regions. Cardiac Fundic is the area that acts as a temporary storage area for ingested food. Body Pyloric Fatty food stay in the stomach the longest.

Gastric Secretions Gastric juice Hydrochloric acid Pepsin begins to digest protein Chyme is a semifluid paste of food particles and gastric juice.

Time Spent in organs Mouth a few minutes Esophagus a few minutes Stomach 4 hours Small Intestine 12 hours Large Intestine 5 hours Total time in digestive system 21 hours.

15.7 Pancreas The pancreas make three different enzymes. One enzyme break down fats (pancreatic lipase), one enzyme break down protein (proteolytic), and the third enzymes break down carbohydrates.

15.8 Liver The liver is the largest organ in the body it is the heaviest organ in the body at around 3 pounds. It makes the chemical bile. Bile is a green liquid that breaks large fat droplets into small fat droplets. Gallbladder is a small, baglike part located under the liver. It stores bile until it is needed by the small intestine.

Hepatitis Hepatitis is an inflammation of the liver. Types of Hepatitis Hepatitis A spreads by contact with food or objects contaminated with virus-containing feces. Hepatitis B spreads by contact with virus-containing body fluids, such as blood, saliva, or semen.

Hepatitis C is believed to be responsible for about ½ the cases of hepatitis. Transmitted in blood-by sharing razors or needles, from pregnant woman to fetus, or in blood transfusions. Hepatitis D occurs in people already infected with hepatitis B. It is blood borne and associated with blood transfusions and intravenous drug use.

Hepatitis E virus is usually transmitted in the water contaminated with feces. Hepatitis F passes from feces and can infect other primates. Hepatitis G accounts for many cases of fulminant hepatitis.

15.9 Small Intestine Small Intestine is a tubular organ that extends from the pyloric sphincter to the beginning of the large intestine. This is where most of the nutrients are absorbed. Receives secretions from the pancreas and liver. Completes digestion, absorbs the products of digestion, and transports the residues to the large intestines.

The small intestines constits of three portions. Duodenum Jejunum Ileum Mesentery suspense the small intestine. Intestinal villi is the inner wall of the small intestine appears velvety. ¼ of feces is dead epithelial cells from the sm. Intestine.

The small intestine compared to the large intestine is narrower and longer. Heartburn is caused by acid moving from the stomach into the esophagus. Animals that do not have a digestive system absorb nutrients through their body covering. Example Tapeworm. Plant eating animals have longer digestive systems because of the intake of cellulose which is not absorbed by the intestine. Digestion is the breaking down of food into small, usable molecules usually glucose.

Digestive enzymes Salivary glands make chemicals that digest only carbohydrates. Pancreas makes chemicals that digest fat, protein, and carbohydrates. Liver makes chemicals that digest only fat. Stomach makes chemicals that digest only protein. Small intestine makes chemicals that digest protein and carbohydrates. Large intestine makes no chemicals to digest food.

15.10 Large Intestine Large intestine is so named because its diameter is greater than that of the small intestine. Large intestine are about 1.5 meters long, and begins in the lower right side of the abdominal cavity. The large intestine absorbs water and electrolytes.

The 4 parts of the large intestine: Cecum is the beginning Colon is divided into 4 portions the ascending, transverse, descending, and sigmoid colons. The colon is home to 100 trillion bacteria. Rectum extends about 5 cm below the tip of the coccyx (tailbone). Anal canal the last 2.5 to 4 cm of the large intestine. Feces include materials that were not digested or absorbed, water, electrolytes, mucus, intestinal cells, and bacteria. Feces is about 75% water. Feces pungent odor results from a variety of compounds that bacteria produce.

15.11 Nutrition and Nutrients Nutrition is the study of nutrients and how the body utilizes. Nutrients all the chemicals that food is made up of which in include carbohydrates, lipids, proteins, vitamins, minerals, and water. Nutrients that human cells cannot synthesize, such as certain amino acids, are called essential nutrients.

Carbohydrates Are organic compounds used primarily to supply energy for cellular processes. Found in foods such as starch and sugar Not stored in large amounts in the body Needed in greatest amount each day. Cellulose is a complex carbohydrate that is abundant in food- it gives celery its crunch. Humans cannot digest so cellulose provides bulk (fiber or roughage) which facilitates food movement through the digestive system.

Lipids Lipids are organic compounds that include fats, oils, and fatlike substances. Found in foods such as butter and oil The food that is often stored and used later as an energy source. The nutrient stored under the skin and around body organs.

Protein Proteins are polymers of amino acids with a wide variety of functions. Used to form muscle, bone, and skin Food rich in protein include meats, fish, poultry, cheese, nuts, milk, eggs, and cereals.

Vitamins Are organic compounds that are required in very small amounts for normal metabolic processes. Not an energy source. Riboflavin and niacin are examples Vitamins allows cells to use carbohydrates and proteins. Vitamins are needed for growth and tissue repair. Amount given as % RDA. Recommended Daily Allowance.

Minerals Are elements other than carbon that are essential in human metabolism. Found on the Periodic Table. Calcium, iron, potassium, sodium, zinc, and magnesium are examples. Need in very small amounts May cause anemia or muscle twitching if missing from diet. Amount Given as % RDA. Not an energy source.

Water Water is needed to cool the body, to chemical reactions in the body, and to carry away body waste. 50% to 60% of the human body is water. The average adult needs about 2 liters of water a day.

Diets Balanced diet is a diet with the right amount of each nutrient. Malnutrition if a persons diet lacks essential nutrients or a person fails to use available foods.