Digestive System Functions

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Digestive System Functions

• MAJOR FUNCTIONS OF THE DIGESTIVE SYSTEM
• 1. Digestion
• Absorption
• SIX PROCESSES/ACTIVITIES OF THE DIGESTIVE SYSTEM
• INGESTION Placing food into the mouth
• PROPULSION 2 Types
• A. Peristalsis
• B. Segmentation
• THREE FOOD GROUPS Their BUILDING BLOCKS p. 447
• Carbohydrates BB Monosaccharide ie Glucose
  (Blood Sugar)
• B. Proteins BB Amino Acids ie Polypeptides
  Peptides
• C. Fats BB Fatty Acids Glycerol

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Digestive System Functions

• MECHANICAL DIGESTION PHYSICALLY breaking down
  food
• for digestion.
• PROPULSION Moving food from one organ to
  another.
• PERISTALSIS Alternating waves of contraction
  and relaxation of the muscles in the organ wall
  involuntary
• SEGMENTATION Food only moves back and forth
  across the internal wall of the organ mixing it
  with digestive juices
• ie Small Intestines
• ABSORPTION Major Absorption Site SMALL
  INTESTINE
• Define Transportation of digested end products
  from the lumen of the GI Tract to the Blood or
  Lymph.
• 5. DEFACATION Elimination of undigestable
  substances from the body via the anus in the form
  of FECES.
• 6. CHEMICAL DIGESTION Breaking down foods into
  their building blocks by using ENZYMES.

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Digestive System Functions

• NOTE Digestive Activity is mostly controlled by
  reflexes via the Parasympathetic division of the
  Autonomic Nervous System (Involuntary part of our
  Nervous System.)
• FOOD DIGESTION (Activities in the Mouth, Pharynx
  Esophagus)
• Both MECHANICAL and CHEMICAL digestion occur in
  the MOUTH.
• PHYSICAL Digestion occurs in the mouth by CHEWING
  (Mastication)
• CHEMICAL Digestion occurs in the mouth when the
  enzyme Salivary Amylase begins to digest
  STARCHES.
• When FOOD enters the Mouth, LARGE amounts of
  SALIVA pour out. EMOTIONAL stimuli can cause
  salivation also.
• ABSORPTION of FOOD in the MOUTH NO Food
  absorption occurs in the MOUTH.

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Digestive System Functions

• The PHARYNX and ESOPHAGUS have NO Digestive
  Function they simply provide passageways to
  carry food to the Stomach
• Food Movement in the MOUTH, PHARYNX ESOPHAGUS
• DEGLUTITION or swallowing involves the
  cooridinated activities of the TONGUE, SOFT
  PALATE, PHARYNX, AND ESOPHAGUS.
• After swallowing Food is moved through the
  PHARYNX and ESOPHAGUS by wavelike contractions of
  muscles called PERISTALSIS.

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Digestive System Functions

• ACTIVITIES IN THE STOMACH
• The breakdown of PROTEINS begins in the stomach.
  The sight, smell, and taste of food stimulate
  Parasympathetic Nervous System reflexes, which
  increases the secretion of GASTRIC JUICE.
• GASTRIN is the hormone that stimulates the
  following protein digesting enzymes, mucus and
  hydrochloric acid.
• CHEMICAL DIGESTION OF PROTEINS IN THE STOMACH
• A. PEPSINOGEN The Active Protein Digesting
  Enzyme
• B. MUCUS Production of this keeps the stomach
  safe from the
• stomach acids.
• C. HYDROCHLORIC ACID Makes stomach contents
  very acidic.
• D. RENNIN Second protein-digesting enzyme that
  works primarily on Milk Protein and converts it
  to a substance that looks like sour milk.
  Infants
• ABSORPTION in STOMACH Virtually NO absorption
  (exceptions to
• aspirin and alcohol.

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Digestive System Functions

• PHYSICAL DIGESTION in the STOMACH
• Process 3 muscle layers of the stomach compress
  and pummel the food, breaking it apart physically
  while continually mixing it with enzymes to make
  chyme.
• FOOD MOVEMENT in the STOMACH
• The PYLORUS of the stomach acts like a meter
  that allows only liquids and very small particles
  to pass through the PYLORIC sphincter.
• Because the PYLORIC sphincter is barely opened,
  each peristaltic contraction of the stomach
  muscle spits or squirts 3 ml or less of CHYME
  into the small intestines. The rest is propelled
  backwards into the STOMACH for more mixing.
• FOOD BREAKDOWN ABSORPTION in the SMALL
  INTESTINE
• The process of CHEMICAL FOOD digestion is
  accelerated in the SMALL INTESTINE.

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Digestive System Functions

• Food reaching the SMALL INTESTINE is only
  partially digested. Carbohydrates PROTEIN
  digestion have been started, but virtually NO
  FATS have been digested before it reaches the
  SMALL INTESTINE.
• By the time the food reaches the END of the SMALL
  INTESTINE, Digestion is completed and nearly all
  food ABSORPTION has occurred.
• FOOD BREAKDOWN in the SMALL INTESTINE
• Small Intestine ENZYMES that aid in food
  breakdown
• BRUSH BORDER ENZYMES Break down double sugars
  into simple sugars and complete protein
  digestion.
• PANCREATIC ENZYMES Functions
• 1. Complete Starch Digestion
• 2. Carry out about half of Protein Digestion
• 3. Totally responsible for FAT Digestion
• 4. Digest Nucleic Acids

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Digestive System Functions

• Other functions of PANCREATIC JUICE Neutralize
  the acidic chyme coming from the stomach.
• BILE is SECRETED by the GALLBLADDER
• Function To breakdown large Fat globules into
  thousands of tiny one
• FOOD PROPULSION in the SMALL INTESTINES
• Peristalsis Alternating waves of contraction
  and relaxation of the muscular walls
• Segmentation Rhythmic segmental movements
  producing local constrictions of the intestine.
• FOOD BREAKDOWN ABSORPTION in the LARGE
  INTESTINE
• The COLON produces NO Digestive Enzymes
• Purpose of BACTERIA in the LARGE INTESTINES
• Metabolize some of the remaining nutrients
• Release gases that contribute to the odor of
  feces (500ml/day)
• Make some vitamins

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Digestive System Functions

• ABSORPTION by the LARGE INTESTINES (Colon)
• Absorption is limited to Vitamins K and B, some
  ions, and most of the remaining water.
• Solid product delivered to the RECTUM is called
  FECES.
• FECES makeup Undigested food residues, mucus,
  millions of bacteria, and just enough water to
  allow their smooth passage
• MOVEMENT of the RESIDUE DEFACATION
• 2 Major Types of Movements in the LARGE
  INTESTINES
• PERISTALSIS Alternating waves of contraction
  relaxation of muscular walls.
• MASS MOVEMENT Long, slow moving, powerful
  contractions that move over large areas of the
  colon 3-4 times daily forcing the contents toward
  the rectum. Usually occur just after eating.
  Fiber in the diet increases the strength of
  contractions and softens the stool.
• DEFACATION REFLEX Spinal reflex that causes the
  walls of the sigmoid colon and the rectum to
  contract and the anal sphincters to relax.

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Digestive System Disorders

• Gallstones Caused by bile being stored in the
  gallbladder TOO LONG or too much water is
  absorbed. The cholesterol it contains may
  crystallize, forming gallstones. Causes sharp
  agonizing pain.
• Hepatitis Inflammation of the Liver Most often
  due to a VIRAL INFECTION resulting from drinking
  contaminated water or transmitted in the blood
  via transfusion or contaminated needles.
• Cirrhosis Chronic inflammatory condition in
  which the liver is severely damaged and becomes
  hard and fibrous caused by excessive alcohol
  abuse for many years.
• Heartburn Cardioesophageal sphincter fails to
  close tightly and gastric juice backs up into the
  esophagus, which has little mucus protection.
  Can lead to inflammation of the esophagus
  (esophagitis)
• Hiatal Hernia Common cause of Heartburn The
  superior part of the stomach protrudes slightly
  above the diaphragm. Allows gastric juice to
  flow into the unprotected esophagus.

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Digestive System Disorders

• Pancreatitis Rare but extremely serious
  inflammation of the Pancreas that results from
  activation of pancreatic enzymes in the
  pancreatic duct. Since pancreatic enzymes break
  down all categories of molecules, the pancreatic
  tissue and ducts are digested. This painful
  condition can lead to nutritional deficiencies,
  because pancreatic enzymes are essential to
  digestion in the small intestine.
• Diverticulitis Narrowing of the colon due to its
  circular muscles contracting more powerfully
  (When the diet lacks bulk fiber)
• Leads to the formation of DIVERTICULA, in which
  the mucosa protrudes through the colon walls.
  Can be life threatening if ruptures occur.

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Digestive System Disorders

• Diarrhea Watery stools resulting from any
  condition that rushes food residue through the
  large intestine before water can be absorbed.
  Prolonged diarrhea can lead to dehydration and
  electrolyte imbalance.
• Constipation When food residue remains in the
  large intestine for extended periods, too much
  water is absorbed and the stool becomes hard to
  pass.
• Ulcers Craterlike erosion in the mucosa of any
  part of the alimentary canal that is exposed to
  the secretions of the stomach. Gastric Acid and
  Pepsin cause this damage.