Download PowerPoint to accompany

Chapter 17
Digestive System
1
Major Functions
• Ingestion
• Taking food into body
• Propulsion
• Passage of food along the gastrointestinal
tract
• Digestion
• Mechanical & Chemical
2
Major Functions
• Absorption
• Nutrients of food from GI tract diffuses
into cardiovascular & lymphatic systems
for distribution to cells
• Defecation
• Elimination of indigestible substances
from GI tract
3
Basic Organization
• Gastrointestinal Tract (GI tract)
– Alimentary canal
– Continuous tube running through the
ventral cavity from the mouth to the anus
– 9 meters
– Mouth, pharynx, esophagus, stomach, small
intestine, large intestine
4
Basic Organization
• Accessory Structures
– Teeth, tongue, salivary glands, liver, gall
bladder, pancreas (all lie outside GI tract
except teeth and tongue)
– Produce or store secretions that aid in the
chemical breakdown of food
– Secretions reach the GI tract through ducts
5
Major Organs
6
Alimentary Canal
7
Alimentary Canal Wall
• Mucosa (3 tissues)
– inner lining of the GI tract, mucous
membrane
– Epithelium
• stratified in mouth and esophagus and
simple throughout the rest of the GI tract
8
Alimentary Canal Wall
• Mucosa (3 tissues)
– Lamina propria
• Loose connective tissue connecting epithelial
layer to muscularis mucosa
• provides space for blood and lymphatic vessels
– Muscularis mucosa
• Smooth muscle that makes folds in the intestine
to increase the surface area
9
Alimentary Canal Wall
• Submucosa
– Dense connective tissue that binds the
mucosa to the muscularis
– Highly vascular
– Contains part of the autonomic nerve supply
to the muscularis mucosa
10
Alimentary Canal Wall
• Serosa
– Outermost layer of the GI tract
– Peritoneum
• Parietal peritoneum
– Lines the wall of the abdominal cavity
• Visceral peritoneum
– Lines some organs
• Peritoneal cavity
– Open space between the two peritoneums
11
Alimentary Canal Wall
• One extension of the parietal peritoneum is
called the mesentery
– Tip of the mesentery is attached to the
posterior abdominal wall
– Binds the small intestine to the wall
– Supply the small intestine with blood and
nerves
12
Alimentary Canal Wall
13
Movements of the Tube
• mixing movements
• peristalsis
14
Mouth
• Oral cavity/buccal cavity
• Formed by the cheeks,
hard palate, soft palate and
tongue
• Ingestion
• Mechanical digestion
• Prepares food for
chemical digestion
15
Mouth
• Uvula
– Tissue that
protrudes past the
end of the soft
palate
– Covers opening to
nasopharynx
during swallowing
16
Mouth
• Mechanical Digestion
– Mastication
• Tongue moves food, teeth grind food, and
food mixes with saliva
• Food reduced to a soft flexible mass called
a bolus
17
Tongue
18
Tongue
• Skeletal muscle covered by mucous membranes
– Medial septum
• Divides tongue into two equal halves
• Tongue attached inferiorly to the hyoid bone
– Lingual frenulum
• Attaches tongue to the floor of the mouth
• Limits the posterior movement of the tongue
– Superior surface covered by papillae--some of which
are “taste buds”
19
Palate
• roof of oral cavity
20
Primary Teeth
•Start appearing
about 6 months
• 8 incisors
• 4 cuspids
• 8 molars
21
Secondary Teeth
22
Secondary Teeth
•
•
•
•
•
•
Start appearing about 6 years
32 total
Jaw continues to grow until maturity
Age 6- 1st set of molars
Age 12- 2nd set of molars
Age 18- 3rd set of molars
– “wisdom teeth”
23
Section of a Tooth
24
Salivary Glands
25
Secretions of Salivary Glands
• Parotid glands
• Clear
• Water, serous fluid
• Rich in amylase
•Enzyme that starts
breakdown of starch
• Submandibular glands
• Primarily serous
fluid
• Some mucus
• Sublingual glands
• Primarily mucus
• Most viscous
26
Pharynx
27
Swallowing Mechanism
•Deglutition
•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
28
Swallowing Mechanism
• Voluntary Stage
– Bolus forced to the back of the mouth cavity and
into the oropharynx by the tongue pressing up and
back against the palates
• Pharyngeal Stage
– Bolus stimulates nerves in the oropharynx
– Impulses cause soft palate and uvula to move up and
seal off the nasopharynx
• Esophageal Stage
– Bolus pushed through the esophagus by involuntary
muscular movements called peristalsis
29
Swallowing Mechanism
– Peristalsis
• Function of the muscular that is controlled by the
medulla
• Circular fibers contract forcing food down
• Longitudinal fibers below bolus contract and
shorten the portion of the esophagus ahead of
bolus, increasing the opening above
• Solid food through esophagus about 4 to 8
seconds
• Liquids about 1 second
30
Swallowing Mechanism
31
Esophagus
32
Esophagus
• Muscular collapsible tube that lies
posterior to the trachea
• 22-26 cm long
• Passes trough the mediastinum just
anterior to the vertebral column
• Pierces the diaphragm through the
opening called the esophageal hiatus
33
Esophagus
34
Stomach
35
Stomach
• J-shaped
• Inferior to the
diaphragm
• Sphincter between
esophagus and
stomach is the
cardiac sphincter
36
Stomach
• Composed of 4 parts
– Cardia
• Closest to the
esophagus
– Fundus
• Rounded portion
above the cardia
– Body
• Central portion
– Pylorus
• Narrow, inferior
region prior to the
small intestine
37
Stomach
• Stomach can only
absorb some water,
electrolytes, certain
drugs (aspirin) and
alcohol
38
Lining of Stomach
39
Lining of Stomach
• Made of the same
four layers as the rest
of the GI tract (these
layers are modified)
• Rugae
– large folds on an
empty stomach
40
Lining of Stomach
• Chief cells
– secrete pepsin, which is
a protein splitting
enzyme
• Parietal cells
– secrete HCl
• converts pepsinogen
to pepsin
– intrinsic factor
• helps absorption of
vitamin B12
• Mucous cells
41
Lining of Stomach
• Enteroendocrine cells
– Produce gastrin
– Hormone that
stimulates HCl &
pepsin production
– Closes cardiac
sphincter and relaxes
pyloric sphincter
– Gastric juice
42
Phases of Gastric Secretion
• Cephalic phase
• Triggered by smell, taste, sight, or thought of food
• Parasympathetic impulses trigger gastric juice secretion
• Gastric phase
• Triggered by presence of food in stomach and
distention of stomach
• Partially digested proteins and caffeine stimulate
secretion of gastrin
• Gastrin increases production of gastric juice,
increases motility of GI tract, relaxes pyloric sphincter
43
Phases of Gastric Secretion
• Intestinal phase
Triggered by movement of food into small intestine
2-6 hours after ingestion
• Intestinal cells release intestinal gastrin
• Inhibits secretion of gastric juice
• Secretin
• Stimulates pancreatic secretions
•
• Cholecystokinin
• Induces the contraction of the gallbladder, which
releases which releases bile
• Gastric inhibiting peptide (GIP)
• Stimulates the release of insulin, which maintains
proper blood sugar level
44
Regulation of Gastric
Secretions
45
Mixing and Emptying Actions
46
Enterogastric Reflex
Regulates the rate at which chyme leaves the stomach
47
Pancreas
48
Pancreas
• Accessory structure of the GI tract
• Oblong gland 12.5 cm long and 2.5 cm thick
• Lies posterior to the greater curvature of the
stomach
• Connected by 2 ducts to the upper part of the
small intestine
49
Pancreas
• Pancreatic duct– Joins with the
common bile duct
from the gallbladder
to form the
hepatopancreatic
ampulla, which
empties into the small
intestine about 10 cm
below the pylorus
• 2.5 cm above the
hepatopancreatic
ampulla is the other duct
50
Pancreas
• Histology
– Groups of glandular epithelial cells
– About 1% of these cells are called the Islets of
Langerhan
• Endocrine part of the pancreas that secrete
hormones (insulin)
– Other 99% are called acini
– Exocrine glands that secrete digestive enzymes
called Pancreatic juice
51
Pancreatic Juice
• Pancreatic amylase
• splits glycogen into disaccharides
• Pancreatic lipase
• breaks down triglycerides
• Trypsin, Chymotrypsin, and Carboxypeptidase
• digest proteins
• Nucleases
• Digest nucleic acids
• Bicarbonate ions
• Make pancreatic juice alkaline
52
Regulation of Pancreatic
Secretions
• Acidic chyme
stimulates release
of secretin
• Stimulates
release of
pancreatic juice
53
Liver
54
Liver
• Average size is about 1.4 kg
• Located under diaphragm in the right
hypochondrium and part of the
epigastrium of the abdomen
• 2 principal lobes
– Left and right
55
Hepatic Lobule
56
Hepatic Lobule
• Functional unit of the
liver
• Each lobule surrounds a
central vein
• Kupffer’s cells
– Line spaces between cells
– Destroy worn out RBC
and WBC, bacteria &
toxic substances
– Filters blood
• all things absorbed from
the GI tract go to the
liver first
57
The Paths of Blood and Bile in
Hepatic Lobule
58
Liver Functions
• Carbohydrate
metabolism
• Maintains normal blood glucose levels
• Produces glycogen from glucose
• Breaks down glycogen into glucose
• Converts noncarbohydrates to glucose
• Fat metabolism
• Synthesizes lipoproteins, phospholipids,
cholesterol
• Digest cholesterol
• Stores fat
• Converts carbohydrates and proteins into
fats
59
Liver Functions
• Protein metabolism
• Loss of this function results in death with in
a few days
• Removal of nitrates
• Conversion of NH3 into urea
• Synthesis of plasma proteins
• Synthesis of fibrinogen (blood coagulant)
• Synthesis of anticoagulants
• Conversion of one amino acid to another
60
Liver Functions
• Removal of drugs and hormones
• Detoxify penicillin, ampicillin
• Excrete or alter into bile, estrogen, or
aldosterene
• Excretion of bile
• Synthesis of bile salts
61
Liver Functions
• Storage
• glycogen, vitamins A, B12, D, E, K, iron,
copper
• Phagocytosis
• Kupffers cells
• Activation of vitamin D
62
Bile
• Yellow, brown, olive green liquid with a pH of 7.6-8.6
• Mostly water
• Bile salts
• Emulsification of fats
• Absorption of fatty acids, cholesterol, and fat-soluble
vitamins
• Bile pigments
• Cholesterol
• Electrolytes
63
Gallbladder
64
Gallbladder
•
•
•
•
Pear shaped sac
7-10 cm long
Accessory structure
Located in the fossa
of the visceral
surface of the liver
65
Gallbladder
• Stores and concentrates bile until small
intestine needs it
• Empty small intestine = closed
hepatopancreatic sphincter
• Bile flows back to gallbladder
• Chyme in small intestine opens the sphincter
66
Regulation of Bile Release
• Fatty chyme
entering duodenum
stimulates gallbladder
to release bile
• Hormonal
stimulation causes
smooth muscle
contraction &
squeezes contents into
the cystic duct &
common bile duct
67
Small Intestine
• 2.5 cm in diameter
• 6.35 m long
• Absorption and most
digestion occur here
68
Three Parts of Small Intestine
69
Three Parts of Small Intestine
• Duodenum (means 12)
• 1st 12 fingers width
from pyloric
sphincter (about
25cm)
• Jejunum (means empty)
• Ileum
• Longest part at 3.6m
long
• Joins the large
intestine at the
ileocecal sphincter
70
Small Intestine Histology
• Same 4 layers as the rest of the GI tract
– Mucosa and submucosa modified for digestion &
absorption
• Intestinal glands
– secrete juices
• Duodenal glands
– secrete alkaline mucous
71
Small Intestine Histology
• Large surface area = better absorption
• 4 things help the small intestine absorb better
• Length
• Microvilli
• Villi
– Projections about 1mm high
– 10 to 40 every square mm
– Gives lining of the small intestine a velvety
appearance
– Arteriole, venule, capillary network, and
lymphatic vessels
72
Small Intestine Histology
73
Small Intestine Histology
74
Small Intestine Histology
• Circular folds (plicae circulares)
• Permanent ridges about 10 mm high
• Start near the proximal portion of
duodenum and stop at the midpoint of the
ileum
• Causes chyme to spiral, which enhances
absorption by increasing the contact with
villi
75
Small Intestine Histology
76
Physiology of Digestion
• Mechanical
• Segmentation
• Major movement of small intestine
• Localized contraction to mix the chyme
• DOES NOT move chyme downward
• Peristalsis
•
•
•
•
Moves chyme down
Weak compared to in the esophagus
Chyme moves at 1 cm per minute
Food stays in the small intestine about 3 to 5 hours
• Over-distended wall triggers peristaltic rush
resulting in diarrhea
77
Physiology of Digestion
• Chemical
• Pancreatic juice, bile and intestinal juice
complete the breakdown of carbohydrates,
proteins and lipids
78
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
79
Secretions of Small Intestine
• 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
80
Physiology of Absorption
• Food pieces need to be small enough to pass
through epithelial tissue in villi
• Depends on diffusion, facilated diffusion, osmosis,
and active transport
• Absorbed into blood
• Carbohydrates
• Monosacharides
• Proteins
• amino acids
• Fats, lipids
• fatty acids, glycerol, and glycerides
81
Physiology of Absorption
• Micelles
– Container for fatty acids and glycerides
– When they come in contact with epithelial cells they
allow contents to diffuse out of the “bubble”
– The micelle stays in the small intestine
• Lipids hitch rides with protein transporters to
form lipoproteins
82
Physiology of Absorption
• HDL’s (high density lipoproteins)
– Remove cholesterol from arteriole walls to take to
the liver
– Good
• LDL’s (low density lipoproteins)
– Transport cholesterol to tissues for hormone and
membrane production
– Cause cholesterol to build up in your arteries
– Bad
83
Physiology of Absorption
• Water
– Absorbed by osmosis
– Average of 9 liters of water enter the small
intestine a day
– All but 1 liter is absorbed
84
Mesentery
• Suspends portions of
the small intestine from
the posterior abdominal
wall
85
Large Intestine
86
Large Intestine
• 1.5 Meters in length and 6.5 cm in diameter
• Cecum
– Portion below the ileocecal sphincter
– The appendix is attached to the pouch of the mecum
• Colon (4 parts)
–
–
–
–
Ascending- up
Transverse- across
Descending- down
Sigmoid- angles toward the midline of the body
87
Large Intestine
• Rectum
• last 20 cm of the gastrointestinal tract
• Anal Canal
• last 2 to 4 cm of the rectum
• Anus
• Opening of the canal
• Internal anal sphincter- smooth “involuntary
muscle”
• External anal sphincter- skeletal muscle
88
Large Intestine
• Histology
–
–
–
–
Same four layers as the rest of the GI tract
No villi
No circular folds
Simple columnar epithelial cells absorb
water
– Goblet cells secrete mucous
89
Large Intestinal Wall
90
Functions of Large Intestine
• Little or no digestive function
• Absorbs water and electrolytes
•Less than 10% of total amount
• Secretes mucus
• Houses intestinal flora
91
Functions of Large Intestine
• Forms feces
• Chyme stays in the large intestine for 3 to 10
hours
• Becomes a semi-solid due to the absorption of
water
• All but about 100 mL of water is absorbed
• Water, inorganic salts, sloughed off epithelial
cells, products of bacterial decomposition and
undigested parts of food
• Bile pigments altered by bacteria provide color
• Smell produced by bacterial compounds
92
Functions of Large Intestine
• Carries out defecation
• Emptying of rectum
• Triggered by distention of the rectum
93
Movements of Large Intestine
• Slower and less frequent than those of small
intestine
• Mixing movements
• Peristalsis
• Mass movements usually follow meals
94
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
95
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
96