The Digestive System

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The Digestive System

• alimentary canal

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Overall Function

• Digestion is the chemical and physical breakdown
  of food into a form usable by cells.

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Organs of Digestive System

• MAJOR ORGANS
• Mouth
• Oropharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Rectum

• ACCESSORY ORGANS
• salivary glands
• Tongue
• Teeth
• Liver
• Gallbladder
• Pancreas
• Vermiform appendix

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Digestive Tract

• Also known as alimentary canal or
  gastrointestinal (GI) tract.
• It forms a tube that separates from digesting
  food from the bodys internal cavity.

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Layers of GI tract

• Mucosa
• Inner layer of the lumen (open space)
• Submucosa
• Made of connective tissue, glands, blood vessels
  and nerves

• Muscularis
• Surrounds submucosa, smooth muscle that contains
  nerves that form part of the intramural plexus
• Serosa
• Outermost layer made of connective tissue

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The Mouth

• Lips
• When closed form the oral fissure
• Cheeks
• Formed by muscle and adipose tissue
• Hard soft palate
• Uvula suspends from soft palate
• Tongue
• Muscle movements aid in mastication

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The Mouth
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Salivary Glands

• Pairs include parotids, submandibular, and
  sublingual
• Secrete 1L of saliva per day
• Buccal glands in the mucosa lining produces a
  small amount of saliva

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The Teeth

• Three main parts
• Crown
• Neck
• Root
• Deciduous teeth(20) are baby teeth
• Permanent teeth(32) show up from 6-13 yrs

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The Pharynx

• Deglutition is the act of swallowing a bolus,
  rounded mass of food and saliva from the mouth to
  the stomach.

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The Esophagus

• 10 inches longs
• Sits posterior to trachea and heart
• It is normally flatted in resting state
• Each end is guarded be a sphincter
• Upper esophageal (UES)
• Lower (cardiac) esophageal (LES)
• Esophageal hiatus is opening in diaphragm where
  esophagus passes
• When enlarged can lead to hiatal hernia
• GERD- gastro esophageal reflux disorder, severe
  acid reflux and indigestion caused by weakened
  LES.

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The Stomach

• Located directly below the diaphragm
• Normally holds 1-1.5 L
• 3 parts
• Fundus (upper left)
• Body (central)
• Pyloris (lower)
• 2 sphincter
• LES(cardiac)
• Pyloric

Esophageal hiatis
fundus
body
pyloris
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The Stomach

• Gastric Mucosa, lining of the stomach contain
  many folds called rugae and depression called
  gastric pits
• Cells in the stomach produce HCL and intrinsic
  factor
• Intrinsic factor binds to B12 molecules keeping
  them from being broken down so they can be
  absorbed in the sm. Intestines

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The Stomach

• Gastric muscles, muscularis, is made of
  longitudinal, circular and oblique layers. This
  gives it strong grinding power.

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The Stomach

• Overall Functions
• Secrete gastric juices and intrinsic factor
• Store partially digested food
• Churn food with digestive juices and move it into
  duodenun
• Limited absorption, alcohol, some H2O and some
  fats
• Release hormones that regulate digestive
  functions
• Destroy pathogenic bacteria

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The Small Intestine

• 6m in length
• 3 parts
• Duodenum- first section, shaped like a C
• Jejunum- 2.5m, begins with abrupt turn
• Ileium- last 3.5m
• Small projections called villi line the sm.
  Intestine.
• Each contain an arteriole, venuole and lacteal
• Microvilli present on the villi increase the
  surface area of intestinal wall

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The Small Intestine

• Secretion of digestive enzymes and absorption
  occur in small intestine
• Small pockets at the base of the villi, called
  crypts, contain cells that reproduce rapidly
• These cells push up and constantly replace older
  cells that are shed

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Large Intestine

• 1.5-1.8m
• 3 parts
• Cecum- first 5-8cm
• Colon
• Ascending
• Transverse
• Descending
• Sigmoid (s-shaped)
• Rectum17-20cm
• Anal canal has folds with a vein and artery
• Hemorrhoids are enlargement of those veins
• Anus is made up of two sphincters

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The Large Intestines
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Accessory Structures

• Vermiform appendix- thought to hold beneficial
  flora
• Peritoneum- serous membrane that lines abdominal
  cavity
• Mesentery- fan shaped part of peritoneum which
  attaches to small intestine
• Omentum- attached to greater curvature of the
  stomach and is laced with fat deposits

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The Liver

• Weighs 1.5kg
• Made of two lobes
• Left lobe is smaller
• Right lobe has 4 parts
• Liver is made of small units called hepatic
  lobules

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The Liver

• Blood enters the lobules from the hepatic portal
  system to be cleaned
• The liver
• Destroys old RBCS, bacteria
• Vitamins and nutrients are metabolized
• Toxins are absorbed and detoxified
• Bile formed collects in small bile ducts

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Bile Ducts

• The right and left bile ducts emerge from under
  the liver to form the common hepatic duct
• The common hepatic duct joins with the cystic
  duct (gallbladder) to form the common bile duct
• Common bile duct empties into the duodenum

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Function of the Liver

• Detoxify substance-alcohol, medicines
• Bile production
• Metabolize fats, proteins and carbohydrates
• Store substances- Fe, vitamins A, B12, D
• Bile salt released by liver aid in absorption of
  fats

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Gall Bladder

• Main function is to store and concentrate bile
• Contain tiny folds of rugae that contract to
  secrete bile during digestion
• Jaudice is caused by a buildup of bile in the
  blood
• Cholelithiasis is the formation of gallstones

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Pancreas

• Fish shaped textured organ that is exocrine and
  endocrine gland
• Rests below stomach on top of duodenum
• Exocrine portion secrete digestive enzymes that
  collect in the pancreatic duct, that joins the
  common bile duct
• Endocrine islets cells secrete insulin and
  glucagon directly into the blood