The Digestive System

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Chapter 15

• The Digestive System

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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.

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Alimentary Canal

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small Intestine
• Large Intestine
• Rectum
• Anus

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• 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.

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• 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.

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• 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.

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• 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.

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15.2 General Characteristics

• 3 parts of the small intestine
• Duodenum
• Jejunum
• Ileum

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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. Lumenpassageway.
• Submucosa contains loose connective tissue,
  glands, blood vessels, lymphatic vessels, and
  nerves. Carry away absorbed materials.

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

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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.

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• 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.

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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.

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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.

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• 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.

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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.

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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.

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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.

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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.

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

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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.

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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.

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Gastric Secretions

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

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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.

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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.

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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.

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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.

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• 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.

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• 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.

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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.

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• 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.

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• 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.

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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.

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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.

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• 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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.