Animals ingest their food by:
    • Omnivores - eat both plants and animals; ex. humans, cockroaches, raccoons 
    • Herbivores - eat only plants; ex. deer, cattle, gorillas
    • Carnivores - eat only other animals; ex. snakes, lions, sharks

    • Suspension feeders - extract food particles suspended in surrounding water; ex. baleen whales
    • Substrate feeders - live on/in their food source and eat their way through; ex. earthworms
    • Fluid feeders - suck nutrient-rich food fluid from a living host; ex. mosquitoe, aphid
    • Bulk feeders - eat large pieces at a time; ex. humans, tigers

Food processing occurs in 4 stages:
    • Ingestion - getting food into the body; eating
    • Digestion - breaking food down into molecules small enough for the body to absorb
    • Absorbtion - food molecules enter the bloodstream to be taken to the body cells
    • Elimination - undigested food leaves the organism

Digestion occurs in specialized compartments.
    • Simple animals may have a single opening leading to a gastro vascular cavity.
    • More complex animals (ie. humans) have an alimentary canal where food enters one orifice, is digested and absorbed, and the remaining material is eliminated via another orifice.
    • Some organisms have a crop to store and soften food.
    • Some organisms have a gizzard containing "teeth" or grit to help grind food.

The Digestive System includes:

1) organs of the alimentary canal (gastrointestinal tract, or GI tract)
     a) mouth
     b) pharynx
     c) esophagus
     d) stomach
     e) small intestines
     f) large intestines
2) accessory organs
     a) teeth
     b) tongue
     c) salivary glands
     d) liver
     e) gallbladder
     f) pancreas

I. The Mouth

A. Food is mechanically ground up in the mouth. It is the job of the teeth to masticate (chew) the food. They are assisted by the tongue and cheek muscles that move the food around.
B. Teeth
     1) The 20 deciduous (baby) teeth are replaced by 32 permanent teeth.
     2) The outer surface is covered with enamel.
     3) Most of the interior of the tooth is made of dentin.
     4) The central pulp cavity contains blood vessels and nerves.
C. Tongue
     1) The tongue is a mucosa-covered skeletal muscle.
     2) It contains different muscles to change shape and position.
D. Salivary Glands
     1) The salivary glands secrete saliva into the mouth.
     2) Saliva moistens and cleanses the mouth.  It moistens food and allows chemical digestion to occur.
     3) Saliva contains water, salivary amylase, ions, proteins, lysozyme, mucin, metabolic wastes, IgA.
     4) The salivary amylase starts digesting the starches in food.

A. The tongue helps to send the bolus of food into the pharynx.
B. This starts the swallowing (deglutition) process.
C. The muscles in the pharynx move food down to the esophagus

A. It extends from the bottom of the laryngopharynx to the stomach (about 10")
B. A wave-like muscle action (peristalsis) pushes the bolus down to the stomach (in about 1-2 seconds for fluids and 4-8 seconds for food)
C. It adjoined the stomach at the cardiac orifice, which is surrounded by the gastroesophageal sphincter
D. when gastric juice backs up into the esophagus, heartburn results

A. It can stretch to hold as much as one gallon of material.
B. There are several features.
     1) rugae - the folds lining the inside of the stomach; contain glands that secrete gastric juices
     2) cardiac sphincter - holds the upper opening (to the esophagus) closed
     3) pyloric sphincter - hols the lower opening (to the small intestines) closed
C. The gastric juices released in the stomach include:
     1) hydrochloric acid (kills bacteria, helps chemical reactions to occur)
     2) pepsin (dissolves protein)
D. The dissolved food/enzyme mixture is known as chyme.
E. Vomiting (emesis) is caused by stretching of the stomach or by irritants (bacteria, certain foods, etc.)
F. Gastric ulcers can be caused by H. pylori bacteria.

A. Small Intestines
     1) This is the body's major digestive organ, where digestion is completed and absorption occurs.
     2) It is composed of three sections.
          a) duodenum
              i) about 10" long
              ii) where bile (from the gall bladder) and pancreatic juice (from the pancreas) is added to the chyme
          b) jejunum
              i) about 8' long
              ii) the middle section of small intestine
          c) ileum
              i) about 12' long
              ii) connects to the large intestines (in the lower right abdomen) at the cecum
     3) It is lined with small finger-like extensions (villi) that contain lymph and blood vessels.
     4) Food particles are absorbed into the blood through the walls of the villi
     5) Intestinal juice is also secreted in the intestines to help food move through.

B. Liver
     1) It is the largest gland in the body (3 pounds)
     2) It performs a variety of functions in the body. In the digestive system, it produces bile.
     3) Bile is a yellow-green substance made of bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes.
          a) Bile salts - their job is to emulsify fats
          b) Bilirubin - a pigment that comes from the hemoglobin in destroyed erythrocytes; it is converted into a brown substance called urobilinogen that pigments the feces
     4) There are 3 types (A, B, C) of hepatitis, all of which are caused by a viral infection

C. Gall Bladder
     1) It is located at the bottom of the liver.
     2) It is about 4" long.
     3) It stores bile produced by the liver until it is needed.
     4) When needed, the bile is secreted into the duodenum of the small intestine.
     5) Gallstones are crystallized cholesterol that block the flow of bile through the cystic or bile ducts.

D. Pancreas
     1) It produces pancreatic juice, which is secreted into the duodenum of the small intestine.
     2) Pancreatic juice includes trypsinogen, amylase, lipases, and nucleases to aid in completion of digestion in the small intestines.

A. It is about 4.5' long, with a larger diameter than the small intestines.
B. It's main job is to absorb water back into the body.
C. The first section is called the cecum.  The appendix is attached to the cecum.
D. Solid waste (feces) moves through the rectum and exits the body.
E. It contains bacteria that ferment some of the indigestable carbohydrates, while producing irritating acids and gases.
F. The process of emptying the large intestines of feces is called defecation.

You need to be able to take information from a food label (see p. 447)

Behavior factors that may increase cancer and/or cardiovascular disease.
    • Your choice of diet may reduce the risk of cardiovascular disease and cancer.
    • Saturated fats may lead to high blood cholesteral levels
    • Saturated fats come from animals and from hydrogenated vegetable oils.
    • Trans-fats created by hydrogenation have been linked to heart disease.
    • High levels of low-density lipoproteins (LDLs) in the blood may increase chances of blocked blood vessels.
    • Eating more saturated fats increases LDL levels.
    • High levels of high-density lipoproteins (HDLs) in the blood may decrease the chances of blocked blood vessels.
    • Exercise increases HDL levels.  Eating unsaurated fats may raise HDLs and lower LDLs.

To Reduce Cancer Risks:
    • Fat makes up less than 30% of diet
    • Eat high-fiber foods
    • Avoid cured, smoked, charred food
    • Eat foods rich in vitamins A and C