UNIT 10: DIGESTIVE SYSTEM

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UNIT 10 DIGESTIVE SYSTEM
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Intro

• The digestive system prepares food molecules for
  use in the body.
• Digestion the process by which food is changed
  into a form that can be absorbed through the cell
  membranes of the alimentary canal
• It accomplishes this through and

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Digestion 2 types

1. Mechanical digestion physical digestion ( food
   is broken into smaller particles)
2. Chemical digestion series of catabolic reactions
   that change the chemical makeup of the food
   molecules

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The digestive organs are broken into 2 groups

• 1 Gastrointestinal Tract (GI tract) essentially
  a tube running from mouth to anus
• 2. Accessory digestive organs structures which
  contribute to digestion, but are not a part of
  the tube ( teeth, tongue, liver, pancreas, gall
  bladder)

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Mucosa inner most lining of lumen, has 3 layers

1. Epithelium innermost sublayer generally
   composed of simple columnar epithelium and goblet
   cells. Functions in protection, secretion and
   absorption
2. Lamina propria areolor connective tissue that
   holds the epithelium tissue to underlying layers,
   it is rich in blood and lymph
3. Muscularis mucosa smooth muscle, keeps mucosa
   folded and increases surface area

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Histology

• The wall of the GI tract is composed of 4 layers
  or tunics ( from inside hollow tube called lumen
  to outside
• Mucosa inner most lining of lumen, has 3 layers

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Histology

1. Submucosa thick layer of areolar C.T. It is
   highly vascularized and has nerve endings
2. Muscularis composed of 2 layers of muscle an
   inner layer running in circular rings and an
   outer layer running longitudinally ( lengthwise)
3. Serosa outer most layer composed of connective
   tissue and epithelium

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Some terms

• Peritoneum double layered serous membrane that
  lines the body cavity
• Parietal peritoneum lines the wall of abdominal
  cavity
• Visceral peritoneum covers digestive organs
• The space between the two is the peritoneal
  cavity
• Mesentery binds small intestines to posterior
  body wall
• Peritonitis inflammation of peritoneum, is
  dangerous since it can easily spread to all
  abdominal organs

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Mouth (BUCCAL CAVITY)

• Is formed by cheeks, lips, tongue and hard and
  soft palates
• Tongue is necessary for speech and housing
  taste buds, also mixes food when chewing and
  shapes it into a rounded mass called a bolus
• It aso initiates swallowing

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Salivary glands

• Are buccal glands in the mouth which secrete some
  saliva
• Most come from 3 pairs of glands located outside
  the buccal cavity
• Paratid under front of ears
• Submandibular near base of tongue in back
  of mouth
• Sublingual beneath tongue
• Mumps a viral infection in one of these glands,
  usually the paratid

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Saliva

• Produced at a rate of 1 to 1 ½ liters per day
• Is 99.5 water and some amylase ( enzymes that
  break down starch)
• Functions to lubricate food allowing for tasting
  and swallowing
• Is under involuntary neural control
• Mastication chewing

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Teeth (dentes)

• A set of teeth is called dentition
• Humans have 2 sets of teeth
• Deciduous teeth the 20 baby teeth or milk teeth
• Permanent teeth 32

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Tooth Parts

• Crown exposed portion of tooth
• is covered with enamel
• Gingiva gum
• Root protein embedded in jaw
• Dentin bone-like tissue comprising bulk of tooth
• Cementum connective tissue which cements tooth
  to periodontal ligament which anchors teeth to
  jaw and acts as a shock absorber

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Deglutition ( swallowing)

• Involves coordinating the esophagus, tongue, soft
  palate, pharynx and 22 plus muscles
• Composed of 2 Phases
• Buccal ( voluntary) tongue pushes bolus into
  oropharynx
• Pharyngeal ( involuntary) all routes except
  desired one are closed

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• Pharyngeal continued actions include
• Soft palate rises blocking nasopharynx
• Tongue blocks mouth
• Larynx rises contracting epiglottis which closes
  glottis
• Pharyngeal muscles propel bolus into esophagus

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1. Esophageal ( involuntary) wave-like contractions
   called peristalysis alternate between the
   longitudinal and circular layers of the esophagus
   moving the bolus to the stomach

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Stomach

• Has 4 regions cardiac, pyloric, body and fundic
  ( see diagram)
• Folds within stomach that increase surface area
  for digestion are called rugae
• The stomach serves primarily as a mixing and
  holding chamber with both digestion and
  absorption being very limited
• The stomach emptying and inhibition of gastric
  secretions are controlled by the small intestines
  via the release of hormones

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The stomach wall has the same 4 layers with 2
modifications

• 1. mucosa layer when not stretched lies in folds
  called rugae
• This layer is dotted with millions of gastric
  pits leading to gastric glands containing several
  types of secretory cells

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Types of secretory cells

• zymogenic ( chief) cells secrete pepsinogen to
  digest pepsin
• Parietal cells secrete HCL
• Mucous cells secrete a sticky mucous coat that
  counter-acts stomach acid ( its a base)
  preventing stomach from digesting itself
• Enteroendocrine cells secrete diff hormones
  which stimulate parietal and chief cells to
  secrete
• All above are known as Gastric juices

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• submucosa not modified
• Muscularis this is the mixing churning layer.
  The soupy liquid of food and gastric juices is
  now called chyme
• Serosa not modified
• Gastric secretions is under the control of the
  nervous system when food is seen, smelled,
  tasted and when stomach Is expanded

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Pancreas

• Is approximately 7 inches long and 2 inches wide
  and is located behind the stomach
• The pancreas has both endocrine and exocrine
  functions
• The clusters of Acini cells secrete the
  pancreatic juice into the duodenum (upper small
  intestines)
• The secretion is controlled by the presence of
  the chyme
• Pancreatic juice consist of water, pancreatic
  amylase ( digests carbohydrates) trypsin (
  protein digesting) and lipase ( lid or fat
  digesting) thus breaking down all categories of
  food

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Liver

• The largest glandular organ of the body, it
  weighs approximately 3 pounds
• It is divided into 4 loges right, left ,
  quadrate, and caudate lobes

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Liver Functions

• Carbohydrate metabolism
• Lipid metabolism
• Protein metabolism ex heparin
• Storage of vitamines A, D, E, K, iron and copper
• Filters blood
• Detoxification
• Secretes bile salts
• Production of RBCs

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Small intestines

• Portion of the GI tract between pyloric sphincter
  of stomach and ileocecal sphincter of small
  intestine
• Function of small intestines major site of
  digestion and absorption (90 absorption in small
  intestines)
• Absorption is the passage of nutrients from the
  alimentary canal to blood or lymph

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3 portions of small intestines

• Duodenum 1 foot long
• Jejunum 8 feet long
• Ilium 12 feet long

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Digestive modifications

• There are intestinal glands into the pits between
  villi which secrete intestinal juice (
  watery/alkaline fluid which is reabsorbed)
• Duodenal ( Brunners glands) in submucosa
  secrete protective alkaline mucus
• Goblet cells found between absorptive cells,
  secrete mucus

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Large Intestines (colon)

• The terminal portion of the alimentary canal
  which is approximately 5 feet in length and
  connects to the ileum of the small intestines
• Functions
• Manufacture, vitamins B K
• Formation of feces composed of 30 water, 30
  bacteria, the remainder is dead cells, cellulose
  and undigestive food
• Absorption of water

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Bile

• Contains bile salts and bile pigments waste
  from breaking down of RBCs
• The color of feces is due to these pigments
• Failure to get aid to rid them results in
  jaundice ( yellow skin)

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Regions of largen intestines
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Physiology of Digestive system

• After nutrients are broken down by digestion and
  absorbed, their components may be
• Converted into a storage for starch or adipose
• Used as building blocks to grow and repair
• Be catabolized ( burned) for energy

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• Digestion reduces carbohydrates down into various
  simple sugars which are then transported to the
  liver
• If not stored in the liver these sugars are
  converted into glucose
• All cellular respiration is centered on burning
  glucose
• The energy released in cellular respiration
  either escapes as heat or is trapped in the bonds
  of the ATP molecules
• The ATP is then shuttled around the cell
  providing the energy for all the various
  metabolic processes in life

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• It takes about 4 hr for GI tract to complete
  absorption
• This time period during and after a meal is
  called the absorptive state
• The post-absorptive state is that period when the
  GI tract is empty
• During the absorptive state glucose is the major
  fuel, where as in the post-absorptive state,
  bodily reserves of glycogen and fat are
  catabolized

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Metabolic Rate

• The energy used by the body per hour (kcal/m2/hr)
• Factor which influence metabolic rate include
• Exercise/activity
• Hormones
• Age
• Sex
• Body surface area compared to volume ( meaning
  thinner people have a higher rate)
• Body temperature
• food

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• Since many factors affect a persons metabolic
  rate, it is usually measured at a standard
  condition ( reclining 12 hr after eating,
  mentally and physically relaxed) this is called
  Basal Metabolic Rate

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Digestive System
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Duodenum
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• Cardiac region of the stomach
• Note the gastic pits, glands mucosa and submucosa