The%20Digestive%20System

1
The Digestive System

• Chapter 14

2
I. Overview of Digestive System
3
(No Transcript)
4
(No Transcript)
5
A. Digestive System Organs

• alimentary canal
• also called gastrointestinal tract
• mouth, pharynx, esophagus, stomach, small
  intestine, and large intestine

6
(No Transcript)
7
B. Digestive Processes

• 1. Ingestion taking food in
• 2. Propulsion move food through alimentary
  canal
• swallowing
• peristalsis alternate waves of contraction
  relaxation of muscles, squeezes food

8
(No Transcript)
9

• 3. Mechanical digestion physically prepares
  food for chemical digestion
• mastication chewing, mix with saliva
• churning mixing food in stomach
• segmentation rhythmic local constrictions of
  intestine

10

• 4. Chemical digestion large food molecules are
  broken down to their monomers
• carbohydrates monosaccharides
• glucose, fructose, galactose
• proteins amino acids
• lipids fatty acids glycerol

11

• 5. Absorption transport of digested end
  products from lumen of GI tract to blood
• occurs in small intestine
• 6. Defecation elimination of indigestible
  substances from body via anus in form of feces

12
II. Anatomy of the Digestive System
13
A. Mouth Associated Organs
14
(No Transcript)
15
1. Tongue

• movements required for speech, mixes food with
  saliva to form bolus, swallowing
• papillae taste buds
• lingual tonsil

16
2. Salivary Glands

• Saliva
• cleanses teeth, moistens food
• dissolves food to release taste
• enzymes for chemical breakdown of starch -
  amylase
• parotid, submandibular, sublingual

17
3. Teeth

• deciduous 20
• permanent 32
• incisors cutting
• canines tearing
• premolars crushing
• molars crushing

18
B. Pharynx

• passageway for food, fluids, air

19
C. Esophagus

• muscular tube 25 cm long
• goes through diaphragm at esophageal hiatus
• joins stomach at gastroesophageal sphincter which
  is closed when food is not being swallowed

20
D. Stomach

• temporary storage tank for food site for
  mechanical chemical breakdown of proteins
• produces semifluid mass called chyme

21
(No Transcript)
22
1. Gross Anatomy

• large longitudinal folds - rugae
• pyloric sphincter controls stomach emptying

23
2. Microscopic Anatomy

• four layers of muscle all running in different
  directions that allows food to be churned mixed
• chief cells produce pepsinogen, inactive form
  of protein-digesting enzyme pepsin

24

• parietal cells secrete HCl
• HCl needed for activation of pepsin kills
  bacteria
• mucous neck cells produce sticky, alkaline
  mucus that protects stomach walls

25
E. Small Intestine

• 1. Gross Anatomy
• major digestive organ
• convoluted tube extending from pyloric sphincter
  to ileocecal valve
• 6 m
• most of water absorbed occurs here

26

• duodenum
• ducts delivering bile to break down fat
  pancreatic juice
• jejenum
• ileum

27
(No Transcript)
28
2. Microscopic Anatomy

• modifications for absorption
• increase surface area
• plicae circulares force chyme to move spirally
  to enhance mixing
• villi fingerlike projections
• microvilli tiny projection on villi increase
  surface area

29
Histology

• enteroendrocrine cells secrete hormones
• intestinal crypts secrete intestinal juice
• goblet cells secrete mucus to protect digestive
  organs

30

• blood capillaries absorption of nutrients
• absorptive cells
• lacteal absorbs lipids
• Peyers patches kill bacteria
• Brunners glands produce an alkaline mucus that
  neutralize acidic chyme

31
(No Transcript)
32
F. Liver Gallbladder

• store concentrates bile - gall bladder
• store vitamins
• important role in detoxification of blood
• produce bile

33
(No Transcript)
34
G. Pancreas

• Location
• Lies deep to the greater curvature of the stomach
• The head is encircled by the duodenum and the
  tail abuts the spleen
• Exocrine function
• Secretes pancreatic juice which breaks down all
  categories of foodstuff
• Acini (clusters of secretory cells) contain
  zymogen granules with digestive enzymes
• The pancreas also has an endocrine function
  release of insulin and glucagon

35
Pancreatic Activation
36
Composition and Function of Pancreatic Juices

• Water solution of enzymes and electrolytes
  (primarily HCO3)
• Neutralizes acid chyme
• Provides optimal environment for pancreatic
  enzymes
• Enzymes are released in inactive form and
  activated in the duodenum

37
Composition and Function of Pancreatic Juices

• Examples include
• Trypsinogen is activated to trypsin
• Procarboxypeptidase is activated to
  carboxypeptidase
• Active enzymes secreted
• Amylase, lipases, and nucleases
• These enzymes require ions or bile for optimal
  activity

38
Regulation of the Pancreas

• Secretin and CCK are released when fatty or
  acidic chyme enters the duodenum
• CCK and secretin enter the bloodstream
• Upon reaching the pancreas
• CCK induces the secretion of enzyme-rich
  pancreatic juice
• Secretin causes secretion of bicarbonate-rich
  pancreatic juice
• Vagal stimulation also causes release of
  pancreatic juice

39
(No Transcript)
40
H. Large Intestine

• ileocecal valve to anus
• dry out indigestible food residues by absorbing
  water
• eliminate residues as feces
• mass peristalsis
• absorption of vitamins some electrolytes

41
(No Transcript)
42
III. Physiology of Digestion
43
A. Mouth

• Ingestion food placed in oral cavity
• Mechanical mastication by teeth mixing
  movements by tongue

44

• Chemical breakdown of starch by salivary amylase
  produced by salivary glands
• Propulsion tongue propels food into pharynx

45
(No Transcript)
46
B. Pharynx Esophagus

• Propulsion peristaltic waves move food bolus to
  stomach

47
C. Stomach

• Mechanical Propulsion peristaltic waves mix
  food with gastric juice propel chyme into
  duodenum

48
(No Transcript)
49

• Chemical digestion of proteins begun by pepsin
• Absorption absorbs a few fat-soluble substances
• (aspirin, alcohol, some drugs)

50
D. Small Intestine Associated Accessory Organs

• Mechanical segmentation by smooth muscle of
  small intestine continually mixes contents with
  digestive juices moves food along tract
  through ileocecal valve at a slow rate allowing
  time for digestion absorption

51

• Chemical bile produced by liver emulsifies fats
  enhances fat digestion absorption of fatty
  acids, monoglycerides, cholesterol,
  phospholipids, fat-soluble vitamins

52

• alkaline mucus produced by intestinal glands
  bicarbonate-rich juice ducted in from pancreas
  help neutralize acidic chyme provide proper pH
  for enzymes

53

• Absorption breakdown products of carbohydrate,
  protein, fat nucleic acid digestion
• vitamins, electrolytes, water

54
E. Large Intestine

• Chemical some remaining food residues are
  digested by bacteria (also produce vitamin K B)

55

• Absorption absorbs most remaining water,
  electrolytes (NaCl), vitamins produced by
  bacteria

56

• Propulsion propels feces toward rectum by
  peristalsis, haustral churning, mass movements
  mucus produced by goblet cells eases passage of
  feces through colon

57

• Defecation reflex triggered by rectal
  distention eliminates feces from body

58
(No Transcript)
59
IV. Homeostatic Imbalances

• Peritonitis infection in the peritoneum
• Impacted teeth when teeth are embedded in the
  jaw bone (exert pressure and cause pain
  surgical removal)
• Gallstones crystallized cholesterol in the gall
  bladder due to bile being stored in the
  gallbladder for too long (pain)
• heartburn gastric juice backs up into the
  esophogus through the cardioesophogeal sphincter
• Hiatal hernia structural abnormality where
  superior part of stomach protrudes above the
  diaphram

60

• Peptic Ulcer erosion of mucosa of any part of
  GI tract. Cause thought to be stress though
  some are caused by acid-resistant bacteria
  Helicobacter pylori
• Diverticulitis mucosa protrudes through colon
  walls and becomes inflamed caused by lack of
  bulk in diet.
• Diarrhea result of any condition that speeds
  food through large intestine before water can be
  absorbed.
• Hyperthyroidism produces excessive metabolic
  rate causing body to catabolize fats and proteins
  - weight loss and weak bones/atrophy of muscles
  including heart.

61

• Hypothyroidism slowed metabolism obesity
  diminished thought processes.
• Cleft palate/lip congenital defect where
  palate/lip are unfused
• Phenylketonuria (PKU) cells cannot use
  phenylalanine (amino acid found in all protein
  foods). May cause brain damage must eat diet
  low in phenalalanine.