Gastrointestinal
System
Introduction
• Digestive tract runs from mouth to
anus
• Food broken down from large
items to small molecules for
absorption into bloodstream
• Molecules sent to area of body to
be used as energy, in synthesis of
proteins, and as enzymes for
essential reactions
• Nonessential elements excreted
through feces or urine.
Form and Function of the GI System
• Three main functions of GI system:
• Digestion
• Absorption
• Metabolism
• Controlled by
parasympathetic
system (peripheral
nervous system)
Ingestion
• Mouth - first apparatus where
food is mixed manually
(mechanical breakdown of food)
• Teeth chew food; salivary glands
secrete enzyme amylase for
chemical breakdown
• Three pairs of
salivary glands:
sublingual,
submandibular,
parotid
Ingestion
(Continued)
• Saliva moistens food for easy
swallowing (with help from tongue)
• Pharynx connects mouth to
esophagus, contains epiglottis
• Epiglottis closes off trachea to
prevent food entry
• Peristalsis propels
food down
esophagus to
stomach
Digestion
• Stomach - food enters acidic
environment and chemical
breakdown takes place
• Food activates gastric juices
secreted in stomach
• Gastric juice consists of intrinsic
factor enzymes and hydrochloric
acid (HCl)
Digestion
• Important chemical reaction:
pepsinogen becomes pepsin
(active enzyme)
• After breakdown, acidic mixture
becomes chyme (semisolid
state) - passes through pyloric
sphincter to
small intestine
Stomach
• pH of stomach is 2.0
• Inner mucosal lining - alkaline for
protection
• Protective mucosal lining prevents
acid from eating through stomach wall
• Extremely acidic environment kills
bacteria, activates
enzymes to break
down food
Absorption
• Vitamins, minerals move
through lining of intestine
• Molecules of glucose,
amino acids, fatty acids
circulate into
body fluids
• Blood carries
nutrients to cells
Absorption
• Intestinal secretions - alkaline pH
• Enzymes break down sugar,
protein, fat
• Acidic environment destroys
medications (special coatings
needed or use parenterals)
• Gallbladder releases bile to
disperse and absorb fats
Metabolism
• Nutrients used for energy and
as building blocks for larger
complex chemicals
• Anabolism: act of building
molecules
• Catabolism: act of breaking
down molecules to release
energy
• Metabolism = anabolism +
catabolism
Small Intestines
• Final area where
nutrients are absorbed
• Send remains that the
body can’t use to the
large intestines
Small Intestines
• Small intestines - three sections:
• Duodenum: 25 cm long; connected to
liver and pancreas; receives secretions
to mix with chyme
• Jejunum: 2.5 m long
• Ileum: 3.5 m long
Excretion
• Large intestine - main sections:
• Cecum, colon, rectum, anus
• Absorption limited to water and
electrolytes
• Substances - transformed to solid
fecal matter
Excretion (Cont)
• Rectum: shortest section;
connects to anal canal
• Empty except during defecation
• Time for normal passage of
fecal material: 3 to 5 days
• Sphincters:
• Internal sphincter - involuntary
• External sphincter - voluntary
Auxiliary Organ Functions
• Pancreas, liver, gallbladder:
all have ducts leading to
duodenum
• Proteins broken down into
peptides first by pepsin, then
by trypsin,
chymotrypsin
from
pancreas
Auxiliary Organ Functions (Cont)
• Carbohydrates: large sugar
molecules, broken down to
disaccharides, then to
monosaccharides; absorbed
and used for energy
• Fats: broken down by bile
(emulsification), then by lipases
(enzymes)
Appendix
• Appendix attached to cecum
of large intestine
• Appendicitis: inflammation of
lining of appendix
• Appendectomy:
surgical removal
of appendix
Mouth and Throat conditions
• Inflamed throat because of cold,
flu, strained vocal cords
• Treatments: mouthwashes,
sprays, lozenges, troches
• Agents contain alcohol, phenol
bases; antiseptics
• Anesthetics: benzocaines,
phenols, menthol
• Oral antibiotics: swished and spit
out or swallowed per doctor’s
orders
Conditions Affecting GI System
• Constipation, diarrhea
• Crohn’s disease (severe illness)
• Bacterial infections
• Food allergies
• Tumors
• Genetic defects: lack of
chemicals
Stomach conditions
• Stomach conditions caused by
high acid content (upset
stomach, heartburn,
indigestion)
• Three main conditions:
• Hyperacidity
• GERD
• Peptic ulcers
(H. pylori
bacterium)
Stomach - GERD
• Occurs when cardiac sphincter
relaxes
• Acidic contents back up into
esophagus; causes burning
sensations in chest and throat
• Antacids used and purchased
OTC
Stomach (Continued)
• OTC medications contain
simethicone and antacids
• Flatulence (gas) accompanies
gastric upsets
• Gas - side effect of carbonates
(major ingredient in antacids)
Antacids Used to Treat Hyperacidity
and GERD
• Ion additives used: aluminum
carbonate, sodium bicarbonate,
calcium carbonate, magnesium
hydroxide, aluminum hydroxide
• Aluminum causes constipation
• Magnesium causes diarrhea
• Buffers decrease acidity within
stomach
Calcium & Magnesium Content of
Common OTC Antacids
800
700
600
500
400
mg Calcium
mg Magnesium
300
200
100
0
Tums ES
Rolaids
Pepto-Bismol
Maalox
Gaviscon
OTC Antacid Agents
Trade
Alu-Cap
Tums
Uro-Mag
Riopan
Combination Agents
Gaviscon Chew tabs
Rolaids
Maalox Suspension
Titralac Ex-stg tabs
Mylanta Gelcaps
Generic
Aluminum hydroxide gel
Calcium carbonate
Magnesium oxide
Magaldrate
Aluminum hydroxide,
sodium bicarbonate
Magnesium hydroxide,
calcium carbonate
Aluminum hydroxide,
sodium bicarbonate
Calcium carbonate,
saccharin
Calcium carbonate,
magnesium carbonate
Prescriptions for Stomach
• H2 antagonists - block H2
receptors in lining of stomach
• Examples: cimetidine and
ranitidine
• Proton-pump inhibitors - inhibit
gastric acid secretion by
blocking last enzymatic reaction
before acid secretion takes
place
• Example: Prilosec
Peptic Ulcer Disease
• H. pylori - gram-negative
bacillus - embeds itself in
mucosal lining of stomach,
duodenum, rectum
• Cause of inflammation, peptic
ulcers, linked to stomach
cancer
• Treatments: 2 to 4 agents
given simultaneously
• Most effective: bismuth,
metronidazole, tetracycline,
omeprazole
Emesis
• Emesis - extreme nausea and
vomiting - caused by
chemotherapy treatments
• Medulla oblongata - control
center
• Chemoreceptor trigger zone or
nausea center activated by smell,
pain, medication, motion
sickness, emotions
• Treat with antiemetics
Diarrhea
• Agents: OTC and prescription
• OTC - Kaopectate, FiberCon,
Pepto-Bismol
• Potent/controlled substances:
Lomotil, Paregoric (short-term
use)
• Lack of normal intestinal
bacteria - cause of diarrhea
(Lactobacillus - bacterial
replacement therapy used)
Constipation
• Symptoms: lack of defecation, dry
and hard stools
• Causes: lack of fiber in diet
• Treatment:
• Bulk-forming agents - absorb water
from the body, increase moisture, bulk
up stool for easier elimination
• Stool softeners pull water and fatty
compounds into intestines to aid
elimination
• Hyperosmotic agents increase
pressure within bowels by drawing in
water
• Stimulants if severe
Flatulence
• Gas caused by byproduct of
microbial breakdown of food
• Foods that produce gas:
broccoli, onions, garlic
• Symptoms: discomfort, pain
• OTC: simethicone (tablets,
chew tablets, liquid)
Poisoning
• Ipecac syrup for removal of
substance before digested –
still available, but no longer
recommended by
Pediatricians
• Activated charcoal:
absorption of toxins