Chapter 17 Digestive System

1
Chapter 17Digestive System

• Functions of Digestive System
• ingestion-take in food
• mechanical digestion
• chemical digestion
• propulsion-move food
• absorption
• defecation-elimination of waste

17-2
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Major Organs
17-3
3
Alimentary Canal Wall
17-5
4
Movements of the Tube

• mixing movements-segmentation
• peristalsis-propelling movements like kneading
• dough

17-6
5
Mouth

• ingestion
• mechanical digestion (mastication)
• prepares food for chemical digestion
• Organ of speech
• Cheek cells can be removed for DNA testing
• Labial frenulum attaches lips

17-8
6
Tongue
-Lingual frenulum attaches tongue -short frenulum
may cause a person to be tongue-tied -lingual
tonsils are at the root of the tongue
17-9
7
Palate

• roof of oral cavity
• Pharyngeal tonsils or adenoids are above border
  of soft palate
• Palatine tonsils are common sites of infection

17-10
8
Primary Teeth

• 8 incisors
• 4 cuspids
• 8 molars
• Also called baby
• teeth

17-11
9
Secondary Teeth
32 of these Incisors bite Cuspids tear Bicuspids
and molars grind
17-12
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Section of a Tooth
Enamel is hardest substance in body
17-13
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Salivary Glands
17-14
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Secretions of Salivary Glands

• Parotid glands
• clear
• water, serous fluid
• rich in amylase (starch dig.)
• Stensons ducts

• Sublingual glands
• primarily mucus
• most viscous
• Rivinuss ducts
• Thick and stringy

• Submandibular glands
• primarily serous fluid
• some mucus (thick secretions)
• Whartons ducts

17-15
13
Pharynx
Nasopharynx-air only-auditory tubes open
here Oropharynx-food and air Laryngopharynx-passag
e to esophagus
17-16
14
Swallowing Mechanism

• Chew food, mix with saliva to form bolus
• soft palate and uvula raise

• hyoid bone and larynx elevate

• epiglottis closes off top of trachea

• longitudinal muscles of pharynx contract

• inferior constrictor muscles relax and esophagus
  opens

• peristaltic waves push food through pharynx

17-17
15
Esophagus
Tube from mouth to stomach, esophageal hiatus is
the opening in the diaphragm, esophageal
sphincter (cardiac sphincter) prevents back up
of food
17-19
16
Stomach-J shaped pouch
Know these parts!
17-20
17
Lining of Stomach
17-22
18
Gastric glands

• Gastric pits are at the end of gastric glands
• Gastric glands contain 3 types of cells1.
  mucous or goblet cells-secrete mucous
• 2. chief cells secrete digestive enzymes
• 3. parietal cells secrete solution
  containing HCL
• Products of all 3 make up the gastric juice

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Gastric Secretions

• mucus
• from goblet cells and mucous glands
• protective to stomach wall

• pepsinogen
• from chief cells
• inactive form of pepsin

• pepsin
• from pepsinogen in presence of HCl
• protein splitting enzyme

• intrinsic factor
• from parietal cells
• required for vitamin B12 absorption

• hydrochloric acid
• from parietal cells
• needed to convert pepsinogen to pepsin

17-23
20
Phases of Gastric Secretion

• Cephalic phase-30-50 of secretory response
• triggered by smell, taste, sight, or thought of
  food
• parasympathetic impulses trigger gastric juice
  secretion

• Gastric phase-40-50 of response
• triggered by presence of food in stomach
• gastrin released-increases secretory activity of
  gastric glands
• gastric juice secreted (pH rises and enhances
  gastrin secretion
• Eventually pH falls to 3.0 and gastrin secretion
  is inhibited

• Intestinal phase 5 of response
• triggered by movement of food into small
  intestine
• intestinal cells release intestinal gastrin
• secretion of gastric juice is inhibited as more
  food enters intestine
• Cholecystokinin released in response to protein
  and fat in intestine which decreases gastric
  motility

17-24
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Gastric Absorption

• Stomach wall is not well adapted for absorption
• absorbs some water
• certain salts
• certain lipid-soluble drugs
• alcohol

17-26
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Mixing and Emptying Actions
Chyme is semi-fluid paste of food and gastric
juice
17-27
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Enterogastric Reflex

• Rate at which stomach empties depends on type of
  food
• Liquids pass through quickly
• Fatty food-3 to 6 hours
• Protein moves more quickly than fatty foods
• Carbohydrate is quicker than protein and fats
• enterogastric reflex
• -regulates the rate at which chyme leaves
  the stomach
• Vomiting empties the stomach in reverse, caused
  by
• irritation or distension, toxins, motion
  sickness, etc

17-28
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Pancreas
17-29
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Pancreatic Juice-formed in pancreatic acinar cells

• pancreatic amylase splits glycogen (starch)
  into disaccharides
• pancreatic lipase breaks down triglycerides
• trypsin, chymotrypsin, and carboxypeptidase
  digest proteins
• Trypsinogen is activated to trypsin in presence
  of enterokinase from mucosa of small intestine
• Trypsin activates chymotrypsin and
  carboxypeptidase
• nucleases digest nucleic acids
• bicarbonate ions make pancreatic juice alkaline

17-30
26
Regulation of PancreaticSecretions

• acidic chyme stimulates release of secretin
• secretin stimulate release of pancreatic juice
  with few digestive enzymes but lots of
  bicarbonate ions
• Also proteins and fats in chyme stimulate
  cholecystokinin which causes pancreatic juice
  high in digestive enzymes to be secreted

17-31
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Liver
17-32
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Hepatic Lobule-functional units
17-33
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Liver Functions

• produces glycogen from glucose
• breaks down glycogen into glucose
• converts noncarbohydrates to glucose
• oxidizes fatty acids
• synthesizes lipoproteins, phospholipids, and
  cholesterol
• converts carbohydrates and proteins into fats
• deaminates amino acids
• forms urea
• synthesizes plasma proteins
• converts some amino acids to other amino acids
• stores glycogen, vitamins A,D, B12, iron, and
  blood
• phagocytosis of worn out RBCs and foreign
  substances
• removes toxins from blood
• produces and secretes bile

17-35
30
Composition of Bile

• water
• bile salts
• emulsification of fats
• absorption of fatty acids, cholesterol, and
  fat-soluble vitamins
• bile pigments-bilirubin and biliverdin come from
  the break down hemoglobin
• cholesterol
• electrolytes

17-36
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Gallbladder
17-37
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Regulation of Bile Release

• Common bile duct is formed by the union of common
  hepatic duct and cystic duct
• fatty chyme entering duodenum stimulate
  gallbladder to release bile
• Gall stones are caused by crystals of cholesterol
• Bile salts are important in emulsification of
  fats which enhances adsorption of fatty acids and
  cholesterol

17-38
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Three Parts of Small Intestine
17-39
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Mesentery

• suspends portions of the small intestine from
  the posterior abdominal wall

17-40
35
Intestinal Villus
17-41
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Wall of Small Intestine
17-43
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Secretions of Small Intestine

• peptidase breaks down peptides into amino
  acids
• sucrase, maltase, lactase break down
  disaccharides into monosaccharides
• lipase breaks down fats into fatty acids and
  glycerol
• enterokinase converts trypsinogen to trypsin
• somatostatin hormone that inhibits acid
  secretion by stomach
• cholecystokinin hormone that inhibits gastric
  glands, stimulates pancreas to release enzymes in
  pancreatic juice, stimulates gallbladder to
  release bile
• secretin stimulates pancreas to release
  bicarbonate ions in pancreatic juice
• See table 17.9

17-44
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Regulation of SmallIntestinal Secretions

• mucus secretion stimulated by presence of chyme
  in small intestine
• distension of intestinal wall activates nerve
  plexuses in wall of small intestine
• parasympathetics trigger release of intestinal
  enzymes

17-45
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Absorption in the Small Intestine

• monosaccharides and amino acids through
  facilitated diffusion and active transport and
  enter blood
• Protein digestion begins in stomach and ends in
  small intestine

• electrolytes and water are absorbed through
  diffusion, osmosis, and active transport and into
  blood
• Fat molecules are absorbed almost entirely by
  enzymes from intestinal mucosa and pancreatic
  juice

17-46
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Movements of the Small Intestine

• mixing movements
• peristalsis pushing movements
• segmentation ringlike contractions
• overdistended wall triggers peristaltic rush
  resulting in diarrhea

17-48
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Large Intestine
Know these parts
17-49
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Large Intestinal Wall
Remember these layers?
17-50
43
Functions of Large Intestine

• little or no digestive function
• absorbs water and electrolytes
• secretes mucus
• houses intestinal flora
• forms feces
• carries out defecation

17-51
44
Movements of Large Intestine

• slower and less frequent than those of small
  intestine
• mixing movements
• peristalsis
• mass movements usually follow meals
• Defecation reflex pushes food into rectum

17-52
45
Feces

• water-90 reabsorbed
• electrolytes
• mucus
• bacteria-these help synthesize vitamins like B12
  and K
• bile pigments altered by bacteria provide color
• smell produced by bacterial compounds
• Gas (flatulence) is a product of bacterial
  metabolism

17-53
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Life-Span Changes

• teeth become sensitive
• gums recede
• teeth may loosen or fall out
• heartburn more frequent
• constipation more frequent
• nutrient absorption decreases
• accessory organs age but the effects are less
  noticeable

17-54
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Clinical Application
Hepatitis

• inflammation of the liver
• most commonly caused by viral infection
• can be caused by reactions to drug, alcoholism
  or autoimmunity

• Signs and Symptoms
• headache
• low fever
• fatigue
• vomiting
• rash
• foamy urine
• pale feces
• jaundice
• pain

Hepatitis A not washing hands or eating raw
shellfish Hepatitis B chronic serum Hepatitis
C serum Hepatitis D very severe only
produces symptoms if infected with B
serum Hepatitis E, F, G more rare
17-55