Download The Digestive System

The Digestive System
Lindsey Bily
Anatomy & Physiology
Austin High School
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Most of the food that we eat
is in a form that CANNOT
reach the cells.
Even if it could pass through
the intestines, it is too
complex for the cells to use.
Food has to modified and
broken down so that the
nutrients can be absorbed by
the cells.
What does the Digestive System
do?
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The main organs form a tube that goes through
your body and is open at both ends (mouthanus)
This is called the gastrointestinal (GI) tract.
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Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Appendix
Liver
Gallbladder
Pancreas
Organs of Digestion
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Made up of 4 layers that have blood
vessels and nerves traveling through
them.
◦ 1. mucosa: innermost layer and allows for
lubrication and easy flow.
◦ 2. submucosa: thicker and made up of
connective tissue. Contains the nerves and
blood vessels.
◦ 3. muscularis: thick layer of smooth muscle
that is innervated.
◦ 4. serosa: connective tissue outer layer that
covers the organs.
Walls of the GI Tract
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The mouth is called the “oral cavity”
◦ Lips: skin covers mucous
membranes. They are very
sensitive and easily irritated
(chapped lips).
◦ Cheeks: lined with mucous
membrane over the buccinator
muscle and fat. Has mucus
secreting glands that open by the
molars.
◦ Hard Palate: The top anterior part
of the mouth made up of bones.
◦ Soft Palate: The top posterior part
of the mouth made of muscle and
has the uvula hanging down. Forms
the partition between the mouth
and nasopharynx.
◦ Tongue: skeletal muscle covered
with mucous membrane. Helps to
ball up food and swallow.
The Mouth
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There are lots of
blood vessels
under the tongue
so some
medicines are
placed there to
dissolve and be
absorbed directly
into the blood
stream.
The Mouth

Salivary Glands- They secrete about 1
liter of saliva per day!
◦ Parotid Glands: located below the external ear.
◦ Submandibular Glands: under the mandible.
You can feel them.
◦ Sublingual Glands: located under the tongue.
The Mouth
Swollen and inflamed gland
salivary gland cyst
Teeth allow us to masticate (to chew).
They can cut, tear and grind our food so
that it ground into small bits which
increases the surface area.
 Increased surface area allows more
surface for the digestive enzymes to get
to.
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The Teeth
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Three main parts of a
tooth
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◦ Crown-exposed part that
you see made of enamel
which is 97% calcium.
◦ Neck- narrow part that is
covered by gum.
◦ Root- fits into the socket
of the maxillae and
mandible.
◦ Under the enamel is the
dentin that contains blood
vessels and nerves.
◦ You have 20 baby teeth
and then 32 permanent
teeth.
The Teeth
The mass of food that we swallow is made
into a round ball called a bolus.
 During swallowing, the bolus passes from
the mouth, through the pharynx to the
esophagus.
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Pharynx
About 25 cm long and goes from the
pharynx to the stomach through the
diaphragm.
 Lies posterior to the trachea
 Guarded by 2 sphincters at each end
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◦ Upper esophageal sphincter: makes sure you
don’t get air in your esophagus.
◦ Lower esophageal sphincter (cardiac
sphincter): opening of the esophagus and
stomach.
Esophagus
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Hiatal Hernia: The hole where the esophagus
passes through the diaphragm may get too big.
This causes the esophagus and sometimes the
stomach to bulge out.
Gastroesophageal reflux
disease (GERD): stomach acid
comes out of the stomach and
into the esophagus.
Sometimes caused by a hiatal
hernia or due to excess
stomach acid.
It HURTS!!
Esophagus
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The esophagus dilates
to form the stomach.
Normally the stomach
holds 1-1.5 Liters of
food.
Located under the liver
and the diaphragm.
When you eat a really
large meal, the
stomach pushes up on
the diaphragm and
heart giving you the
sensation that it is hard
to breathe.
The Stomach
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Flow into and out of the stomach is
controlled by 2 sphincters.
◦ Lower esophageal (cardiac) sphincter: between
the esophagus and stomach.
◦ Pyloric sphincter: between the end of the
stomach into the small intestine.
Stomach
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Stores food until it is partially digested and ready to move
to the intestines.
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Secretes gastric juice that contains acid and enzymes to
help digest food.
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Churns the food which breaks it into the small particles and
mixes it with the gastric juice.
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Secretes intrinsic factor that protects vitamin B12 from
being destroyed.
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Absorbs some nutrients (some drugs, water, alcohol, and
some short chain fatty acids).
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Produces hormones gastrin (regulates digestion) and
ghrelin (increases appetite).
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Destroys some pathogens.
Stomach Functions
It is 1 inch wide and 20 feet long and fills
most of the abdominal cavity!
 Has three divisions…
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◦ duodenum: part where the stomach attaches.
◦ Jejunum: part where it turns abruptly forward
and downward. It is about 8 feet long.
◦ Ileum: The remaining 12 feet.
Small Intestine
The lining of the intestine has millions of
villi (fingerlike projections).
 This increases the surface area in which
to absorb nutrients.
 Each villus has an arteriole, a venule and
a lymph vessel.
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Small Intestine
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Diameter of 2.5 inches and a
length of 5-6 feet.
Has 3 divisions...
◦ Cecum: first 2-3 inches
◦ Colon:
 Ascending colon (goes up)
 Transverse colon (goes across)
 Descending colon (goes down)
 Sigmoid (S Shaped)
◦ Rectum: last 7 or 8 inches
 Last inch is the anal canal
 Anus is the opening to go
outside of the body
Large Intestine
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Vermis means “worm”
and forma means
“shape”. The appendix
is a wormlike tubular
structure.
3-4 inches long
It connects with the
cecum of the large
intestine.
Believed to be a
“breeding ground” for
the bacteria that live
in your large intestine.
Vermiform Appendix
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Large continuous sheet of membrane that
covers most of the organs and holds them
loosely in place.
Peritoneum
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Largest gland
in the body.
Weighs about
3-4 pounds
Lies right under
the diaphragm.
Has 2 lobes
(right and left)
and is
separated by
the falciform
ligament
The Liver
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Contains lots of tiny cylinders about 2 mm
high and 1mm in diameter called hepatic
lobules that are made from hepatic cells
and have branches of the hepatic vein and
hepatic artery going through them.
The Liver
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Blood comes into the hepatic lobules…
◦ From hepatic artery: cells get oxygen
◦ From hepatic portal vein: blood gets
“inspected”.
 Phagocytic cells eat bacteria, old RBCs, and other
foreign particles.
 Vitamins, minerals, and nutrients are absorbed by
the hepatic cells.
 Toxins are absorbed into the hepatic cells and are
detoxified (made harmless).
The Liver
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The hepatic duct emerges from the liver and
joins the cystic duct from the gallbladder and
opens into the duodenum of the small intestine
via the common bile duct.
Bile is formed by the liver cells.
The Liver-Bile Ducts
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Detoxifies lots of substances.
Secretes a pint of bile a day.
Metabolizes proteins, fats, and carbs.
Stores iron, vitamins A, B12, and D.
Produces plasma proteins and produces
RBCs in the fetus.
Liver-Functions
Bile is made up of bile salts, bile
pigments, and cholesterol.
 Bile salts are made from cholesterol by
the liver
 Aid in absorption of fats. If you don’t have
bile, you get really sick after eating a high
fat meal.
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Bile
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3-4 inch long sac
Holds 30-50 mL of bile
Lies under the liver
Stores bile and concentrates it.
After you eat, it squirts some of the concentrated bile into
the duodenum.
Jaundice is a yellow discoloration of the skin and mucosa.
Occurs when the bile cannot get into the duodenum. It
then can’t exit the body via feces. Instead it gets absorbed
into the blood.
Gallbladder
Cholecystitis: inflammation of the
gallbladder.
 Cholelithiasis: gallstone formation. They
are solid clumps of mostly cholesterol.
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Gallbladder Disorders
Grayish pink gland about 6-9 inches long.
 Has exocrine and endocrine glandular
tissue.
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◦ Exocrine: secretes digestive enzymes into the
duodenum.
◦ Endocrine: secrete insulin and glucagon into
the bloodstream.
Pancreas
Salivary gland diseases can cause a lack of saliva
which hinders effective digestion. Cancer or
inflammation of the glands can affect levels of
immunoglobin A which helps fight off oral
infections.
 Mumps: caused by a virus (remember your MMR
vaccine?) that swells the parotid glands. Usually
occurs in children 5-15, but can occur in adults.
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◦ A severe infection in adults. Can cause swelling of the
joints, pancreas, myocardium, kidneys and testes in
men.
Mumps virus
Digestive Disorders
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Tooth decay: occurs on the tooth surfaces
where food debris, acid-secreting
bacteria, and plaque accumulate causing
a cavity. If not treated, you can get an
infection and loss of teeth.
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Gingivitis: inflammation of the gums.
Usually caused by poor hygiene (poor
flossing or brushing) but also by diabetes,
vitamin deficiency, or pregnancy.
Digestive Disorders
 Tooth
decay
 gingivitis
Inflammation of the periodontal ligament
that holds the tooth in the jaw.
 Usually occurs with untreated gingivitis
that spreads into the bony tissue of the
jaw.
 Leading cause of tooth loss in adults.
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Periodontis
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Wide spaces within teeth,
overlapping teeth, overbite or
underbite.
Contributes to headaches or
proper mastication of food.
Corrected by orthodontics
Malocclusion
Affects more than 60 million Americans
 Called heartburn or acid indigestion
 Backflow of gastric juices into the esophagus.
 Usually symptoms are mild and occur
infrequently.
 Avoid smoking, caffeine, alcohol, spicy foods,
acidic foods, chocolate or losing weight to fix the
problem.
 Antacids (TUMS) or H2-receptor antagonists
(Pepcid, Zantac, or Tagament)
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Gastroesophageal Reflux Disease
(GERD)
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Severe cases can cause
asthma attacks, severe chest
pain, bleeding or erosive
esophagitis.
Proton pump inhibitor drugs
decrease the production of
stomach acid (Nexium,
Prilosec, Prevacid)
Barrett’s esophagus is a
precancerous condition when
GERD is left untreated.
GERD
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Ulcers
Craterlike wound or sore
caused by tissue
destruction.
1 in 10 Americans will have
a gastric or duodenal ulcer
in their lifetime.
Cause burning pain and
may result in hemorrhage,
perforation, widespread
inflammation, or scarring.
Most are caused by an
infection of the bacteria H.
pylori.
The bacteria burrows in the
mucosa lining and impairs
the body to produce mucus.
Can also be caused by long
term use of NSAIDs (aspirin
and ibuprofen). They
interfere with the
prostaglandin function of
regulating the mucus lining
of the GI Tract.
Pylorospasm: common in infants. The
pyloric sphincter doesn’t relax to let food
out of the stomach, so the patient vomits
all of the food.
 Pyloric stenosis: narrowing of the pyloric
sphincter.
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Pyloric Sphincter Disorders
Inflammation of the
mucus lining of the
appendix.
 Can rupture if not treated
or removed in time. This
can be fatal as the
infection is released
throughout the body.
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Appendicitis
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The purpose of the digestive system is to
bring nutrients into the body so they are
available to the cells.
◦ Ingestion: food taken in
◦ Digestion: complex nutrients broken down into
smaller nutrients
◦ Motility: movement through the GI tract
◦ Secretion: digestive enzymes are secreted
◦ Absorption: nutrients move into the body from
the GI tract
◦ Elimination: materials not absorbed must be
excreted.
Digestive Physiology
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Includes all movement of food through the GI
tract.
◦ Mastication: chewing. Particle size is reduced.
◦ Deglutition: swallowing
◦ Peristalsis: the smooth muscles of the GI tract produce a
wavelike ripple of movement to propel the food forward
through the tract.
◦ Segmentation: Forward and back movement in one
region to break apart the food.
peristalsis
Segmentation
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Mechanical Digestion
It takes anywhere from 2-6 hours for food
to empty the stomach after a meal.
 Food is churned and mixed with gastric
juices to form a milky substance called
chyme.
 This slowly is squirted into the duodenum.
 It takes about 5 hours to travel through
the small intestine.
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Food Movement
The food undergoes hydrolysis reactions
(combines with water) to split into smaller
compounds.
 Digestive enzymes are organic catalysts
that speed up the breakdown of food.
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Most of the organs in the system secrete some
kind of enzyme.
Chemical Digestion
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Carbs are made up of saccharides
 Polysaccharides- starch and glycogen
 Disaccharides- sucrose, lactose, maltose
 Monosaccharides- glucose, fructose, galactose
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Amylases are enzymes that break apart
polysaccharides into disaccharides. (salivary
amylase and pancreatic amylase)
Maltase, sucrase, and lactase break down the
disaccharides into monosaccharides.
Carbohydrate Digestion
Proteins are made up of long folded amino
acid chains.
 Proteases break apart these chains by
hydrolysis.
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Examples:
pepsin- in the gastric juice
trypsin and chymotrypsin- in pancreatic juice
peptidases- in the intestine
Protein Digestion
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Fats are insoluble (don’t
dissolve) in water.
They have to be EMULSIFIED
first. They are broken down
into tiny droplets.
◦ Bile and lecithin are formed in the
liver and are emulsifiers.
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Lipases are enzymes that then
can break down the fats into
smaller particles.
◦ Lipases are found in pancreatic
juice
Fat digestion
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Mostly water that helps to
liquefy the food
Contains salivary amylase to
break down polysaccharides.
Also contains lipase but really
doesn’t have enough time to do
any digestion of fats.
Contains NaHCO3 which makes
it slightly basic. Amylase works
best is a higher pH.
Contains mucus so the food can
slide through the GI tract easier
Saliva
Contains water and mucus just like saliva, but
also…
 Chief cells in the stomach secrete pepsinogen.
This is an inactive form of pepsin (digests
proteins). It is activated by HCl.
 Parietal cells produce the HCl in the stomach.
 Parietal cells also produce intrinsic factor which
protects Vitamin B12 from being “eaten” by the
acid and enzymes.
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Gastric epithelium. Red
large cells are gastric cells,
the yellow are mucus
secreting cells.
Gastric Juice
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Pancreatic juice is mostly water but has
lots of different enzymes
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trypsin- a protease
Chymotrypsin-a protease
Various lipases
Various nucleases (digest RNA and DNA)
Amylase
The pancreas secretes bicarbonate to
neutralize the acidic pH of the chyme as it
comes from the stomach.
Pancreatic Juice
The intestines secrete bicarbonate to keep
the buffer the pH of the chyme.
 Also contains mucus.
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Intestinal Juice
Absorption is when the digested food,
water, salts and vitamins move from the
GI tract through the intestinal mucosa
and into the blood or lymph.
 Most absorption occurs in the small
intestine which have tons of villi.
 Water is absorbed by osmosis.
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Absorption
Glucose, fats, amino acids, are co-transported
into the intestine with the aid of a co-transporter
molecule (ex. Bile, lecithin, Na+)
 Vitamins A,D,E, and K are “fat soluble” vitamins
and depend on bile salts to be absorbed.
 Most drugs are water soluble and absorbed by
simple diffusion or are lipid soluble.
 All of the things that are absorbed in the
intestine then go to the liver for inspection.
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Absorption
Elimination is the getting rid of the
residues of digestion called feces.
 Expelling of the feces is called defecation.
 It is a reflex caused by the stimulation of
receptors in the rectum as fecal matter is
moved to the rectum.
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Elimination
Constipation: The movement of fecal
matter has slowed down so extra water is
absorbed making the feces hard.
 If constipation is chronic, then you can
get a fecal impaction.
 This can cause ulcers and necrosis of the
large intestine. It can be fatal!
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Elimination
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Gastroenteritis (aka gastritis): stomach inflammation
Nausea: unpleasant feeling that often leads to vomiting
Emesis: vomiting
Diarrhea: elimination of liquid feces, sometime with
abdominal cramps.
Stomach cancer: linked to excessive alcohol consumption,
chewing tobacco, eating smoked or heavily preserved food.
◦ Usually the cancer has already spread before the patient is
diagnosed. The early warning signs are belching, heartburn
and nausea, so patients usually treat themselves.
◦ Later symptoms are chronic indigestion, vomiting, anorexia,
stomach pain, and blood in the feces.
Disorders of the GI Tract
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Malabsorption Syndrome: general term
for anything that causes the small
intestine to not absorb nutrients properly.
Diverticulosis: abnormal saclike pouches
that come out of the large intestinal wall.
Common in people over 50.
The diverticuli can become inflamed,
called diverticulitis (pain, tenderness,
fever, blood in stool).
Disorders of the GI Tract
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Colitis: inflammation of the large
intestine. Symptoms are diarrhea,
cramps, constipation, bleeding, ulcers.
◦ Crohn disease and ulcerative colitis are
autoimmune diseases
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Irritable Bowel Syndrome (spastic colon):
chronic noninflammatory condition that
usually occurs with stress.
◦ Symptoms are constipation and diarrhea
usually with abdominal pain.
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Colorectal Cancer: malignancy of the
colon cells.
Disorders of the GI Tract
Colorectal Cancer