The Digestive System

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The Digestive System

• Tri-State Business Institute
• Micheal H. McCabe

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Introduction

• The digestive system is also called the
  alimentary canal and the gastrointestinal tract.
• The organs of the digestive system have four
  primary functions
• Ingestion
• Digestion
• Absorbtion
• Elimination

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Ingestion

• Ingestion involves all behaviors associated with
  the acquisition and consumption of food and
  beverage.
• Ingestion involves not only the organs and
  structures of the alimentary tract, but the
  entire organism body and mind.
• Ingestion is often governed as much by social
  convention as by hunger.

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Digestion

• Food is broken down mechanically in the mouth by
  chewing this increases the surface area of the
  food and speeds dissolution.
• Chemical action serves to break down food into
  its component parts. Complex materials are
  broken down into simpler compounds.
• Solvents, including water and strong acids,
  dissolve nutrients and allow for absorbtion.

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Chemical Digestion

• Enzymes are chemicals that speed-up chemical
  reactions and help in the breakdown of complex
  nutrients.
• Stomach Acids primarily hydrochloric acid
  dissolve minerals, and break down complex
  materials (like cellulose).
• Bile emulsifies fat to allow absorbtion.

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Absorbtion

• Digested food must by absorbed into the
  bloodstream by passing through the walls of the
  small intestine.
• Carbohydrates (sugars) and amino acids are
  distributed by the bloodstream throughout the
  body where they provide energy and raw materials
  to the individual cells.

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Absorbtion, Continued

• Amino acids are used as raw materials to build
  new protein structures within the cells.
• Excess carbohydrates are stored within the liver
  as starch (glycogen.)
• Fats are broken down into fatty acids and
  glycerol. Fatty acids are then stored in adipose
  tissue as an energy reserve.

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Elimination

• Many materials that are ingested cannot be
  absorbed.
• These materials are considered solid waste.
• The large intestine (colon) collects and
  concentrates this waste (called feces).
• Wastes ultimately pass from the body via the anus
  (defecation.)

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Anatomy of the Digestive System
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The Oral Cavity

• The oral cavity (mouth) is the first part of the
  digestive system.
• Food is ingested (eaten) and the digestive
  process begins within the mouth.
• Mastication (chewing) is the first step in the
  mechanical breakdown of nutrients.

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Anatomy of the Oral Cavity

• Cheeks form the lateral walls of the mouth.
• Lips surround the opening of the mouth.
• Hard Palate forms the anterior portion of the
  roof of the mouth.
• Soft Palate muscular structure forming the
  posterior portion of the roof of the mouth.
• Rugae are irregular ridges in the mucous
  membrane covering the anterior portion of the
  hard palate.
• Uvula small appendage of the soft palate.
  Serves as an accessory organ for speech and acts
  as a sense organ in swallowing.

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Anatomy of the Oral Cavity, Continued

• Tongue large muscular organ located on the
  floor of the oral cavity and attached to the
  mandible by muscles. Moves food around during
  mastication and swallowing.
• Mastication is the act of chewing.
• Deglutition is the act of swallowing.
• Papilla are small raised areas on the tongue
  that contain taste buds specialized sense organs
  that respond to the chemical composition of food.
• Tonsils are masses of lymphatic tissue located
  on both sides of the oropharynx.

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Anatomy of the Oral Cavity, Continued

• Gums are made of fleshy tissue and surround the
  sockets of the teeth.
• Teeth are specialized structures of several
  types that are used to cut, pierce, and grind
  food during mastication.
• A complete set of adult dentition includes 32
  permanent teeth. Milk Teeth sometimes
  present in newborns are not true teeth these
  are specialized structures of cartilage. Baby
  Teeth are called deciduous teeth and are
  replaced by larger adult teeth between the ages
  of 5-10 years.

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Diagram of the Oral Cavity
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The Dental Arch (Upper)
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Tooth Classification

• Central Incisors are designed to cut food the
  have a sharp chisel-shaped edge that allows you
  to sever a portion of food from a larger mass.
• Lateral Incisors also serve to cut food, the
  arch-shaped arrangement of the central and
  lateral incisors allows a discrete bite of food
  to be taken from a larger mass.
• Canines are pointed and provide the ability to
  pierce through tough membranes present in food.
  Sometimes called Fangs or cuspids they serve
  as a killing instrument in carnivorous animals.
• Bicuspids Also called pre-molars these teeth
  serve to crush food and break fibers up.

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Tooth Classification

• Molars serve to pulverize and grind the
  broken-up food particles into a fine mash.
• Dentists use special terms to describe the
  surfaces of teeth
• Labial is used to describe the surface of
  incisors and canine teeth adjacent to the lips.
• Buccal describes the surface of bicuspid and
  molar teeth nearest the cheek.
• Some dentists use the term facial to describe
  both the labial and buccal surfaces.
• Opposite the facial side, all teeth have a
  lingual surface near the tongue.

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Tooth Classification

• The mesial surface of a tooth is the face nearest
  the midline of the body.
• The distal surface of a tooth is the face
  farthest from the medial line.
• Bicuspids and Molars have an additional surface
  called the occlusal surface. This is where the
  teeth come together when chewing food.
• Incisors and Cuspids both have a sharp incisal
  edge. That serves as the cutting edge.

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Inner Anatomy of a Tooth
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Inner Anatomy of a Tooth

• Crown the portion of the tooth visible above
  the gum line.
• Root the portion of the tooth below the gum
  line.
• Enamel is the dense, hard, white substance that
  forms the outermost protective layer of the
  crown. Enamel is the hardest substance in the
  human body.

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Inner Anatomy of a Tooth

• Dentin forms the main substance of the tooth.
  Dentin is a yellow substance, similar to bone,
  that lies beneath the enamel and extends
  throughout the crown.
• Pulp lies beneath the dentin. Pulp is a soft
  and delicate tissue that forms the center of the
  tooth. Blood vessels, nerve endings, connective
  tissue, and lymph tissue are all found in the
  pulp canal (also called the root canal.)

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Salivary Glands

• Three pairs of salivary glands surround the oral
  cavity.
• These glands produce Saliva that contains
  important digestive enzymes such as salivary
  amylase that begin chemical digestion of food
  while still in the mouth.

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Salivary Glands
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The Gastrointestinal Tract
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Pharynx

• The pharynx (throat) is a muscular tube appx. 5
  inches long, lined with mucous membrane.
• The pharynx serves as a common passageway for
  both air traveling from the nose to the trachea,
  and food traveling from the oral cavity to the
  esophagus.
• When swallowing (deglutition) occurs, a flap of
  tissue, the epiglottis, covers the trachea so
  that food cant enter.

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Esophagus

• The esophagus is a muscular tube extending from
  the pharynx to the stomach.
• Rhythmic contractions of muscles in the wall of
  the esophagus propel food towards the stomach.
• Peristalsis is the name given to this
  progressive, involuntary, rhythmic contraction of
  smooth muscle observed in most of the organs in
  the digestive system.

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Stomach

• Food passes from the esophagus into the stomach
  through the cardiac (esophageal) sphincter.
• The cardiac sphincter normally closes after
  passing a bolus of food into the stomach this
  prevents gastric reflux (heartburn.)
• Abnormalities with the cardiac sphincter may
  result in GERD (gastroesophageal reflux
  disease.)

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Stomach, continued

• Within the stomach, gastric acid (primary
  hydrochloric acid) and enzymes breakdown food
  particles into simpler substances that can later
  be absorbed by the intestines.
• The stomach churns rhythmically contracts to
  thoroughly mix food with stomach acids and
  enzymes.

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Anatomy of the Stomach
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Yet More About the Stomach

• The stomach is a hollow, muscular organ that
  serves as a staging area where digesting food
  is held prior to passage into the small
  intestine.
• Rugae is a specialized tissue present in the
  stomach, urinary bladder, and similar hollow
  organs that allows the stomach to expand in size
  without causing injury.
• Specialized cells in the stomach wall produce
  hydrochloric acid and digestive enzymes.

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The Duodenum

• After food has been thoroughly mixed with stomach
  acid, the mixture (now called chyme) passes
  through the pyloric sphincter into the duodenum.
• Within the duodenum, bile and pancreatic juice
  are added to the chyme to emulsify fats and break
  proteins up into the 29 basic amino acids.
• The duodenum is the shortest segment of the small
  intestine normally about a foot in length.

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Accessory organs of Digestion

• The liver is a multi-purpose organ that produces
  bile as one of its principal functions.
• Bile is a salt made from acid and alkali
  compounds that serves to emulsify fats to allow
  absorbtion.
• The pancreas is also a multi-function organ that
  produces digestive enzymes needed to break down
  complex proteins into component amino acids.

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The Gallbladder and Bile Ducts

• Bile is manufactured by specialized cells in the
  liver.
• It moves through the hepetic duct to the cystic
  duct and is stored in the gallbladder until
  needed.
• When fatty foods are ingested, the gallbladder
  contracts, forcing bile into the duodenum via the
  cystic duct and common bile duct.

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The Pancreas and Pancreatic Duct

• Digestive enzymes are made by specialized cells
  in the pancreas and secreted via the pancreatic
  duct into the duodenum.
• The pancreatic duct communicates with the common
  bile duct and duodenum infection or
  inflammation within any of these organs is
  readily transmitted to the other two.
• Example pancreatitis resulting from infection
  can present clinically with jaundice as the
  gallbladder and liver become involved.
• Likewise, gallstones or inflammation of the
  gallbladder can result in inflammation of the
  pancreas.

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Absorbtion of Nutrients in the Small Intestine.

• Absorbtion of nutrients begins in the duodenum as
  chyme moves past millions of microscopic villi.
• The villi resemble small fingers extending from
  the intestinal wall.
• Each villi contains a rich bed of capillaries
  that serve to absorb nutrients and carry it into
  the bloodstream.
• Each villi also contains a specialized lymph
  vessel called a lacteal that serves to absorb
  emulsified fat and conduct it into the lymphatic
  circulation.

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The Jenunum

• The second segment of the small intestine is
  called the jejunum.
• The jejunum is appx. 8 feet long and continues
  the process of digestion and absorbtion.
• Chyme is passed from the jenunum into the third
  section of the small intestine.

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The Ileum

• The ileum is the third section of the small
  intestine and is the last section of the
  gastrointestinal tract to be concerned with the
  absorbtion of nutrients.
• The ileum is also the longest section of the
  small intestine and is approximately 11 feet
  long.
• By the time that chyme leaves the small intestine
  via the ileocecal valve, most water-soluble and
  emulsified nutrients including carbohydrates,
  protein, and fat have been absorbed.
• The remaining matter consists largely of waste
  and is called feces, or stool, once it enters the
  large intestine.

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The Large Intestine

• The large intestine is divided anatomically into
  seven parts
• The cecum
• The appendix
• The ascending colon
• The transverse colon
• The descending colon
• The sigmoid colon
• The rectum

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The Cecum

• The cecum is a pouch on the lower end of the
  ascending colon.
• Fecal matter enters the cecum through the
  ileocecal valve where the cecum communicates with
  the ileum.
• The principal function of the large intestine is
  recovery of water, minerals, bile, and enzymes
  from the waste stream.
• Recover, Recycle, and Reuse.

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The Appendix

• The appendix has no clear function in humans.
• If clogged or blocked by fecal matter, the
  appendix can become infected and inflamed
  appendicitis.
• Rupture of an inflamed appendix can result in
  peritonitis, sepsis, and death.

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The Ascending Colon

• The ascending colon extends upward from the cecum
  (lower right side) to the undersurface of the
  liver.
• Below the liver, a 90 degree bend in the colon
  (called the hepatic fixture) occurs and fecal
  matter passes into the transverse colon.

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Transverse Colon

• The transverse colon passes across the abdominal
  cavity towards the spleen.
• A second 90 degree bend in the colon occurs near
  the spleen (splenic fixture) and fecal matter
  progresses into the descending colon.

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Descending Colon

• From the splenic fixture, fecal matter moves
  downward through the descending colon toward the
  pelvic crest.
• At the pelvic crest, the descending colon makes
  an S turn and becomes known as the sigmoid
  colon.

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Sigmoid Colon

• The S shaped section of the colon serves to
  carry fecal matter from the abdominal cavity into
  the pelvic cavity.
• The lower (distal) end of the sigmoid colon
  connects with the rectum.

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The Rectum

• The rectum is an expansive, muscular organ that
  serves to store fecal matter until it can be
  expelled from the body.
• The opening of the rectum is called the Anus and
  is equipped with two sphincters the inner
  sphincter is involuntary and controlled by the
  autonomic nervous system.
• The outer sphincter is under voluntary control
  to a point.

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Elimination

• The elimination reflex is triggered by a sense of
  pressure in the rectum.
• When the sensation of pressure in the rectum
  becomes apparent, the inner (involuntary)
  sphincter relaxes and the need to pass stool
  becomes urgent.
• Voluntary control of the external sphincter
  allows reasonable selectivity regarding the time
  and place of elimination.

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Elimination, Continued

• The extent of voluntary control is limited in
  scope and duration.
• If voluntary defecation isnt undertaken, stool
  continues to collect in the rectum and pressure
  increases.
• Beyond a certain point, voluntary control of the
  external sphincter is lost and defecation occurs
  automatically.

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Diagram of the Gastrointestinal Tract
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