Chapter 25 The Digestive System

1
Chapter 25The Digestive System

• (AKA GI Tract)

2
Digestive Functions

• Ingestion Eating, strapping on the feed bag,
  chowing down
• Digestion breakdown of food
• occurs in the gut
• Absorption nutrients going into the blood,
• occurs outside the gut
• Defecation elimination, number 2, etc

3
Stages of Digestion

• Mechanical digestion is physical breakdown
• teeth in the mouth
• churning action of stomach (has no teeth)
  intestines
• Chemical digestion is series of hydrolysis
  reactions that break macromolecules into their
  monomers

4
Digestion

• The digestive process has three parts
• Motility muscular contractions that break up
  food, mix it with enzymes move it along
• Secretion digestive enzymes hormones
• Membrane transport absorption of nutrients
• The digestive system has two parts
• Digestive tract (GI tract)
• 30 foot long tube extending from mouth to anus
• Accessory organs
• teeth, tongue, liver, gallbladder, pancreas,
  salivary glands

5
Layers of the GI Tract

• Slice an intestine and look in at it
• Mucosa
• Inside
• Submucosa
• Under the ______
• Muscularis externa
• Outer ______ layer
• Serosa
• The outside layer
• Also called the visceral peritoneum

6
4 Layers of the GI Tract
7
Inees and Outees

• The abdomen has a moist membrane called the
  peritoneum.
• The peritoneum has two parts
• parietal layer- this lines the back and front of
  the abdomen, it adheres to the walls
• visceral layer- this lines the?
• Between these two parts is the peritoneal cavity
• Increased fluid in this space is called- ascites
  (suggests liver dysfunction)
• If an organ is behind the peritoneum, if it
  overlaps the organ rather than the wall, we call
  this retroperitoneal (retro behind)
• the pancreas and the kidneys are retroperitoneal

8
Parts of the Peritoneum

• Mesentery
• Mesocolon
• Lesser omentum
• Greater omentum

9
More On the Peritoneum

• Visceral peritoneum suspends the GI tract
• Allows for great amount of movement for the
  intestinal muscles to mix and move its content
• Abdominal surgery may cause adhesions, what
  effect may this have on digestion?
• The liver is suspended by the falciform ligament
  which attaches to the anterior wall, this is the
  only organ attached to the anterior abdominal
  wall
• The mesentery is a folding of the peritoneum
• It contains blood vessels and binds the small
  intestine to the posterior abdominal wall
• Mesocolon is a fold of the peritoneum
• It contains blood vessels and binds the large
  intestine (colon) to the posterior abdominal wall

10
Mesentery and Mesocolon

• Mesentery of small intestines holds many blood
  vessels
• Mesocolon anchors the colon to the back body wall

11
The Lesser and Greater O

• The lesser omentum (small old man Tom) is a fold
  of the peritoneum hangs the duodenum (first part
  of the small intestine) and the stomach from the
  liver
• The greater omentum is the largest peritoneal
  fold, it is like a big O of fat on your belly
  (some more then others) may be responsible for
  Dunlaps disease
• Prevents spreading of infection due to lymph
  nodes

12
Lesser Greater Omentum

• Lesser attaches stomach to liver
• Greater covers small intestines like an apron

13
Peritonitis

• Inflammation of the _________
• Causes
• Side effect of abdominal opening example surgery
  (air in is not good?), trauma, disemboweled
  (would organs fall out?)
• Ruptured organ example appendix burst,
  perforated ulcer

14
Whats Coming

• GI System
• Mouth
• Esophagus
• Stomach
• Small intestine (3 parts, D.J. Illi)
• Large intestine (3 Parts A,T, D)
• Rectum
• Anus

15
The Mouth

• What is the purpose of the lingual frenulum?
  Uvula?
• What bone makes up the hard palate?

16
Features of the Oral Cavity

• Cheeks and lips have two functions
• Speech
• Chewing
• keeps food between the teeth uses the Buccinator
  muscle
• Vestibule is space between teeth cheeks
• Tongue is sensitive, muscular manipulator of food
• Muscle of tongue is attached to hyoid, mandible,
  hard palate and styloid process
• Papillae are the bumps---taste buds
• Parts of oral cavity
• The floor the tongue
• The roof hard, soft palate and uvula
• allows breathing chewing at the same time

17
Permanent Baby Teeth

• Adult (32) between 6 and 25, Baby teeth (20) by 2
  years
• Differing structures indicate function incisors
  for biting, canines for tearing, premolars
  molars for crushing and grinding food

18
Tooth Structure

• Enamel
• hardest substance in body
• Dentin
• calcified connective tissue
• Periodontal ligament
• modified periosteum
• Root canal
• contains the root of the tooth such as the
  nerve blood vessels
• Cementum
• cements the teeth in the mouth
• Everyones Dentist Performs Root Canals

19
Digestion in the Mouth

• Mechanical digestion is called mastication
  (chewing)
• breaks into pieces
• ? surface area exposed to digestive enzymes
• mixes with saliva so it forms a bolus
• Chemical digestion
• amylase
• begins starch digestion at pH of 6.5 or 7.0 found
  in mouth
• when bolus enzyme hit the pH 2.5 gastric juices
  hydrolysis ceases
• lingual lipase
• secreted by glands in tongue
• begins breakdown of triglycerides into fatty
  acids and glycerol

20
Saliva

• Wets food for easier swallowing
• Dissolves food for tasting
• Bicarbonate ions buffer acidic foods
• bulimia---vomiting hurts the enamel on the teeth
• Chemical digestion of starch and fat begins
• salivary amylase enzyme starch digestion
• lingual lipase digests fat after reaches the
  stomach
• Helps destroy bacteria--- lysozyme
• Protects mouth from infection with its rinsing
  action---1 qt/ day

21
Salivary Glands

• Three glands All have ducts that empty into the
  oral cavity
• Parotid below your ear and over the masseter
• Myxovirus that attacks the parotid gland causing
  _______
• Submandibular is under lower edge of mandible
• Sublingual is deep to the tongue in floor of mouth

22
Salivation

• (What an evil preacher feels while counting the
  congregations offering)
• Increase salivation
• sight (see food diet), smell, sounds, memory of
  food, tongue stimulation (rock in mouth)
• Decreased salivation
• dry mouth when you are afraid
• Due to sympathetic nerves stimulation
• Anticholinergic drugs
• Which autonomic nervous system should be working
  when we eat?

23
Pharyngeal Arches

• Two skeletal muscles
• Palatoglossal muscle
• extends from palate to tongue
• forms the first arch
• posterior limit of the mouth
• Palatopharyngeal muscle
• extends from palate to pharyngeal wall
• forms the second arch
• Palatine tonsil between

24
Pharynx

• Funnel-shaped tube extending from internal nose
  to the esophagus (posterior) and larynx
  (anterior)
• Swallowing is facilitated by saliva and mucus
• starts when bolus is pushed into the oropharynx
• soft palate is lifted to close nasopharynx
• larynx is lifted as epiglottis is bent to cover
  glottis

25
Esophagus

• Collapsed muscular tube
• In front of vertebrae
• Posterior to trachea
• Posterior to the heart
• Pierces the diaphragm at hiatus
• hiatal hernia or diaphragmatic hernia
• Travel time is 6 seconds for solids and 1 sec for
  liquids

26
Swallowing- The 3 Blocks

• (a) Tongue forms food into bolus (yellow)
• (b) Three Blocks
• Bolus in esophagus
• 1. Tongue blocks oral cavity
• 2. Soft palate blocks nasal cavity
• 3. Epiglottis blocks larynx

27
The Esophagus

• (c) Bolus passes into esophagus
• (d) Peristaltic waves push bolus
• (e) Esophageal sphincter opens to allow food to
  enter stomach then it rapidly closes
• H20 is the most difficult to swallow
• Due to its lack of shape

28
GastroEsophageal Reflux Disease (GERD)

• The esophageal sphincter is a physiological
  sphincter not a muscular one
• If lower sphincter fails to open
• distension of esophagus feels like a heart attack
• If lower esophageal sphincter fails to close
• stomach acids splash back into the esophagus
  cause heartburn (GERD)
• Control the symptoms
• Have stomach hydrochloric acid (HCL) evaluated,
  dont take Tums
• Strengthen diaphragm
• Be checked for hiatal hernia
• Dont lay down after meals
• Eat many small meals
• Elevate your bed 6-8 inches or use a wedge
  pillow, not pillows
• Sleep on your left side

29
Innervation and Circulation

• Innervation by parasympathetic fibers from vagus
  (CN ____) sympathetic fibers from the celiac
  plexus
• All blood drained from stomach is filtered
  through the liver before returning to heart

30
Gross Anatomy of the Stomach I

• Which side is it on?
• Size when empty?
• J shaped sausage, 4 quarts max
• stretches due to rugae
• Empties as small squirts of chyme leave the
  stomach through the pyloric valve
• Produces about 3 quarts of gastric juice/ day
  (H2O, HCl pepsin)
• Aspirin alcohol is absorbed in the stomach

31
Gross Anatomy of Stomach II

• Parts of stomach
• Cardiac region, Fundus---air on x-ray
• Body, Greater and lesser curvatures
• Pylorus---starts to narrow as approaches pyloric
  sphincter

32
Gross Anatomy of the Stomach III

• Cardiac region just inside cardiac orifice
• Fundus is superior and holds air seen on X-rays
• Body is main portion of organ
• Pyloric region is narrow inferior end
• Pylorus is opening to duodenum
• forms a sphincter

33
Unique Features of Stomach Wall

• Mucosa
• simple columnar glandular epithelium
• filled with gastric pits
• Muscularis externa has 3 layers
• inner oblique layers
• middle circular
• outer longitudinal
• These smooth muscles permits greater churning
  mixing of food with gastric juice

34
Gastric Pit and Gastric Gland

• Mucous cells
• protect stomach walls from being digested
• with thick layer of mucous
• Parietal cells secrete HCl acid
• Intrinsic factor
• absorption of vitamin B12 for RBC production
• Chief cells secrete pepsinogen
• HCl converts pepsinogen to pepsin

35
Functions of Hydrochloric Acid

• Activates enzymes pepsin lingual lipase
• Chyme is formed by liquefying food
• Hydrochloric acid breaks up connective tissues
  plant cell walls
• Iron ferric ions (Fe3) that cant be absorbed
  are converted to iron ferrous ions (Fe2) that
  can be absorbed utilized for hemoglobin
  synthesis (remember Ferric is ic, but Ferrous
  is good for us)
• Destroys ingested bacteria pathogens

36
Gastric Enzymes Intrinsic Factor

• Intrinsic factor (parietal cells )
• essential for absorption of B12 by small
  intestine
• necessary for RBC production (pernicious anemia)
• Gastric lipase (chief cell)
• gastric lipase splits the triglycerides in milk
  fat
• most effective at pH 5 to 6 (infant stomach)
• Pepsin --- (chief cell) protein digestion
• secreted as pepsinogen
• HCl converts it to pepsin (active form)

37
Gastric Motility

• Swallowing center signals stomach to relax
• Arriving food stretches the stomach activating a
  relaxation response
• Gentle ripple of contraction churns mixes food
  with gastric juice
• typical meal is emptied from stomach in 4 hours
• Increased fat, increases time in stomach

38
Vomiting (emesis)

• Contents of stomach squeezed between abdominal
  muscles and diaphragm and forced through open
  mouth
• Pylorospasm- often in infants
• Pyloric sphincter fail to relax trapping food in
  the stomach
• vomiting occurs to relieve pressure
• Pyloric stenosis
• narrowing of sphincter
• Often indicated by projectile vomiting

39
Healthy Mucosa Peptic Ulcer

• What are the symptoms of stomach and duodenial
  ulcer? Ulcers are due to increased or decreased
  acid in stomach? Why doesnt Tagamet work long
  term? What bug do they think causes this?

40
Three Phases of Gastric Secretion and Motility

• Cephalic phase- stomach controlled by the brain
• Gastric phase- stomach controlled by itself
• Intestinal phase- stomach controlled by the small
  intestine

41
Cephalic Phase Stomach Getting Ready

• Cephalic phase
• vagus nerve stimulates gastric secretion
  motility just with sight, smell, taste or thought
  of food (control from brain)

42
Gastric Phase Stomach Working I

• Nervous control (of stomach itself) keeps stomach
  active
• stretch receptors chemoreceptors provide
  information
• vigorous peristalsis and glandular secretions
  continue
• chyme is released into the duodenum

43
Gastric Phase Stomach Working II

• Endocrine influences over stomach activity
• distention and presence of caffeine or protein
  cause G cells secretion of gastrin into
  bloodstream
• gastrin hormone increases stomach glandular
  secretion
• gastrin hormone increases stomach churning and
  sphincter relaxation

44
Intestinal Phase Stomach Emptying

• Duodenum regulates gastric activity through
  hormones nervous reflexes
• enterogastric reflex duodenum inhibiting
  stomach by sympathetic nerves
• chyme stimulates duodenal cells to release
  hormones that suppress gastric secretion
  motility

45
Gross Anatomy of Liver

• Liver
• weighs 3 lbs., below diaphragm
• right lobe larger, gallbladder on right lobe
• size causes right kidney to be lower than left
• 4 lobes -- right, left, quadrate caudate
• falciform ligament separates left and right
• round ligament is remnant of umbilical vein

46
Inferior Surface of Liver- Blood Supply

• Hepatic portal vein
• nutrient rich blood from stomach, spleen
  intestines
• Hepatic artery from branch off the aorta

47
Microscopic Anatomy of Liver

• Tiny cylinders called hepatic lobules
• Like an open book
• Central vein surrounded by sheets of hepatocyte
  cells separated by sinusoids lined with
  fenestrated epithelium
• Blood filtered by hepatocytes on way to central
  vein
• nutrients, toxins, bile pigments, drugs, bacteria
  debris filtered

48
Histology of Liver -- Hepatic Triad

• 3 structures found in corner between lobules
• hepatic portal vein brings nutrition rich blood
  from the intestines to the liver
• hepatic artery bring oxygen rich blood to the
  liver from the heart
• bile duct collects bile from the liver
• Central vein is the main drain that takes the
  processed blood from the liver to the inferior
  vena cava and then to the heart

49
Major Liver Functions

• Metabolism of carbohydrates
• Metabolism of Proteins
• Metabolism of fats
• Liquor detoxification and other drugs hormones
  (thyroid estrogen)
• Ingests or phagocytizes worn out blood cells
  bacteria
• Vitamin/ mineral storage and activation
• Emulsification of fats by release of bile salts
• Removes waste products--bilirubin
• MMM, Liver!

50
Ducts of Gallbladder Liver

• Bile passes to right left hepatic ducts
• Right left ducts join outside the liver to form
  common hepatic duct
• Cystic duct from gallbladder joins common hepatic
  duct to form the bile duct

51
Ducts of Gallbladder Pancreas

• Duct of pancreas and bile duct combine to form
  hepatopancreatic ampulla emptying into the
  duodenum at the major duodenal papilla
• sphincter of Oddi (hepatopancreatic sphincter)
  regulates release of bile pancreatic juice

52
Gallbladder and Bile

• Sac on underside of liver 4 inches long
• About 4 cups of bile are secreted daily from
  liver
• Gallbladder stores concentrates bile
• Yellow-green fluid containing minerals, bile
  acids, cholesterol, bile pigments phospholipids
• bilirubin pigment from hemoglobin breakdown
• intestinal bacteria convert to urobilinogen
  brown color
• Color of fecal matter
• bile salts emulsify fats aid in their digestion
• enterohepatic circulation - recycling of bile
  salts from ileum

53
Gross Anatomy of Pancreas

• Retroperitoneal gland posterior to stomach
• head- close to curve in C-shaped duodenum
• body
• tail- like a flag waves to the left under the
  stomach
• Endocrine and exocrine gland
• ENDOCRINE- secretes insulin glucagon into the
  blood
• EXOCRINE- secretes pancreatic juice into duodenum
• Pancreatic duct runs length of gland to open at
  sphincter of Oddi
• accessory duct opens independently on duodenum

54
Activation of Zymogens

• Zymogens are inactive proteins. Converted to
  active enzymes by losing a part of themselves
  (usually renamed without the -ogen
• Note the sphincter of Oddi going into the
  duodenum
• Acute pancreatitis---associated with heavy
  alcohol intake or biliary tract obstruction
• result is patient secretes trypsin in the
  pancreas starts to digest himself

55
Hormonal Control of Secretion

• Cholecystokinin released from duodenum in
  response to arrival of acid and fat
• causes contraction of gallbladder, secretion of
  pancreatic enzymes, relaxation of
  hepatopancreatic sphincter
• Gastrin from stomach duodenum weakly stimulates
  gallbladder contraction pancreatic enzyme
  secretion
• Secretin released from duodenum in response to
  acidic chyme
• stimulates all ducts to secrete more bicarbonate.
  Why?
• Because HCO3 (bicarbonate) H becomes H2CO3
  which dissociates into H2O CO2

56
Small Intestine

• Nearly all chemical digestion and nutrient
  absorption occurs in the small intestine
• Food in stomach causes gastroileal reflex
  (relaxing of illiocecal valve filling of cecum)

57
Gross Anatomy of Small Intestine

• Duodenum curves around head of pancreas (10 in.)
• retroperitoneal along with pancreas
• receives stomach contents, pancreatic juice
  bile
• neutralizes stomach acids, emulsifies fats,
  pancreatic enzymes
• Jejunum is next 8 ft. (in upper abdomen)
• Ileum is last 12 ft. (in lower abdomen)
• ends at ileocecal valve
• D. J. Ilee

58
Large Surface Area of Small Intestine

• Circular folds up to ½ inch tall
• chyme flows in spiral path causing more contact

• Villi are fingerlike projections 1 mm tall
• nutrient absorption
• Microvilli 1 micron tall

59
Intestinal Villi
Villi of Jejunum Histology of duodenum
60
Segmentation in the Small Intestine

• Purpose of segmentation is to mix churn not to
  move material along as in peristalsis
• Churns chyme to increase contact for absorption

61
Peristalsis

• Move material along
• to the colon
• Begins after absorption occurs
• Stomach pain is really duodemum pain refered to
  as periumbilical pain

62
Anatomy of Large Intestine

• 5 feet long and 2.5 inches around
• Appendix
• Cecum in RLQ
• Ascending, Transverse and Descending colon
• Sigmoid colon is S-shaped
• Rectum ending at Anal canal
• A CAT Digests Some Rats Always

63
Appendicitis, Flora Gas

• Inflammation of the appendix due to irritation
• Prolonged inflammation gives symptoms of
• high fever, elevated WBC count, neutrophil count
  above 75
• pain localizes in right lower quadrant, rebound
  test, periumbilcal pain is usually a precursor
• May progress to peritonitis from rupture
• Bacterial flora populate large intestine
• Ferments cellulose other undigested
  carbohydrates
• synthesize vitamins B and K
• Flatus (gas)
• average person produces 17 ounces per day
• most is swallowed air but it can contain methane
  that produces the odor

64
Absorption and Motility

• Mouth to anus transit time is 17 hours average
• Feces consist of water solids
• Haustral contractions occur every 30 minutes
• distension of a haustrum stimulates it to
  contract
• Gastrocolic reflex
• filling of the stomach stimulates motility (GIGO)
  of the colon
• A good remedy for _________ is to take fiber,
  exercise, water and read a good book while
  sitting for ten minutes.

65
Anatomy of Anal Canal

• Anal canal is about an inch long
• Hemorrhoids are permanently distended veins, from
  straining at stool, Psoas muscle spasm, coccyx
  subluxation

66
Neural Control of Defecation

• 1. Filling of the rectum
• 2. Reflex contraction of rectum relaxation of
  internal anal sphincter
• 3. Voluntary relaxation of external sphincter
• The END