Transcript Digestive System

Digestive System
Digestion-Mechanical &
chemical breakdown of
food
into forms that cell
membranes can absorb
Alimentary Canal-wall
structure-4 layers
1. Mucosa-Mucus
membrane, has folds and
projections in lumen to
increase absorbing area,
protects tissue beneath it.
The mucosa carries out
secretion, digestion, and
absorption and consists
of epithelial cells
2. Submucosa- has blood
vessels that nourish
surrounding tissue and
carry away absorbed
materials. Lymphatic
vessels carry fatty acids
to the blood vessels, and
pathogenic organisms to
lymph nodes. The
vessels are held in place
by loose connective
tissue
3. Muscular Layer- 2 coats
of smooth muscle,
circular fibers contract,
causing diameter to
decrease. Longitudinal
fibers contract and the
alimentary canal shortens
4. Serosa-outer covering of the
tube. Cells secrete serous fluid
which moistens outer surface of
the tube so that organs in the
abdomen slide freely against
one another. This layer is known
as the visceral peritoneum.
• Movements of the tube
1. Mixing- in the stomach
Smooth muscles move
rhythmically to mix food
with digestive enzymes and
acid. Sphincters at both
ends of the stomach close
to keep chyme in stomach.
2. Propelling-peristalsis
Circular smooth muscles
contract, narrowing the
tube. As the contraction
moves down the tube, it
pushes food in front.
Simultaneously, muscle in
front of the food relax,
opening the tube and
allowing food to enter.
Organs
1. Mouth- chewing begins
digestion by mechanically
breaking down food and
mixing it with saliva.
2. Cheeks and Lips
contain muscles and sensory
receptors used to determine
temperature and texture of
food.
3. Tonguea. frendulum
Membrane which connects
the center of the tongue to
the floor of the mouth.
b. papilla
Rough projections which help
tongue move food. They also
contain taste buds.
c. lingual tonsils
Rounded mass of lymphatic
tissue found at the back of the
tongue where it attaches to
the hyoid bone.
4. Palate
Roof of mouth consists of the
anterior hard palate and the
posterior soft palate, which
extends to the cone-shaped
uvula.
5. Uvula is pulled up during
swallowing, closing off the
nasal cavity from the pharynx
6. Palantine Tonsils
Lymphatic tissue found in the
back of the throat below the
soft palate
7. Pharyneal Tonsils-adenoids
Lymphatic tissue on the
posterior wall of the pharynx above
the soft palate. The lymph tissue is
important in fighting infection.
Teeth
1. Primary-Deciduous
teeth
These teeth erupt through
the gums between 6 mo.
and 4 years. The teeth
are temporary and fall
out. There are 20
deciduous teeth, 10 in the
upper set, 10 in lower
jaw.
2. Secondary-Permanent
teeth
push the primary teeth
out of their socket, or
erupt in a new socket.
There are 32 secondary
teeth.
Incisors
Chisel-shaped teeth used
to bite off pieces of food
Cuspids
Cone-shaped teeth used
to grasp and tear food
Biscuspids and molars
have flattened surfaces
and are used to grind
food particles
2 portions to each tooth
1. Crown
the portion of the tooth
which projects above the gum
2. Root
the portion of the tooth
anchored into the jaw
Dentin is beneath the enamel
and is composed of bonelike material, although it is
harder.
Cementum is a thin layer of
bonelike material which
surrounds the root.
Peridontal Ligament surrounds
cementum and consists of
collagenous fibers attaching
tooth to jaw.
Pulp cavity contains blood
vessels, nerves, and
connective tissue (pulp)
which extend into the root
canal
Salivary glands secrete saliva,
which begins the chemical
digestion of carbohydrates
Parotid gland are below the
ear, and secrete a watery
fluid rich in amylase
Submandibular gland is just
above the mandible. The
gland has some mucous
cells, making it’s secretions
more viscous
Sublingual gland is below the
tongue and consists primarily
of mucous cells. Their
secretions are thick and
stringy
Pharynx is a cavity posterior to
the mouth and has 3 parts
Nasopharynx is an extension
of the nasal cavity, & allows
air to pass through
Oropharynx is posterior to
the soft palate and is the
passageway for food leaving
the mouth
Laryngopharynx is inferior to
the oropharynx and is the
passageway leading to the
esophagus
Esophagus is a collapsible
tube lined with mucous
glands, which secrete
mucous to moisten and
lubricate the tubes lining
Stomach is J shaped, with folds
called rugae which contain
mucosal and submucosal
layers. Contraction of the outer
muscle layer helps mix food
with stomach secretions.
Cardiac is the small region of
the stomach near the opening
to the esophagus
Fundic balloons above the
cardiac region & is a temporary
storage area for food
Body region is the main part of
the stomach and lies between
the fundic and pyloric regions
Pyloric region is adjacent to the
small intestine and contains the
pyloric sphincter
c
Stomach secretions: inner
lining of the stomach is the
mucous membrane which is
studded with gastric pits
which are at the end of the
tubular gastric glands. The
glands consist of 3 types of
secretory cells.
Mucus cells or goblet cells
secrete mucus which coats
and protects the stomach
wall from HCl
Chief cells secrete pepsinogen
which is converted to pepsin
by HCl. Pepsin breaks down
proteins
Parietal cells secrete HCl
The 3 products together make
up gastric juice
Gastrin
is an important digestive
hormone which increases
secretions from the gastric
glands
Absorption
is the movement of
substances across the cell
membrane into the cell
Peptic ulcers
are open sores in the mucous
membrane of the GI tract
Gastric ulcers
are ulcers in the stomach
Duodenal ulcers
are in the small intestine
nearest the stomach
For many years, ulcers were attributed
to stress. Helicobacter pylori, a bacteria
growing in the stomach was found to
cause gastric ulcers which can be
cured with antibiotics in combination
with acid-lowering drugs.
Stomach muscle contraction is used for mixing food,
producing a semi-liquid paste called chyme which
accumulates near the pyloric sphincter. Then the pyloric
sphincter muscle begins to relax, allowing the chyme to
enter the duodenum.
The amount of time the chyme remains in the stomach
varies. Liquids pass through the stomach rapidly, but
solid food remain in the stomach until they are
completely mixed with gastric juice
fatty foods
remain in the stomach 3-6 hours
proteins
are kept in the stomach or < 3 hours
carbohydrates
pass through the stomach faster than fatty foods &
proteins
Pancreas has acinar cells that
make up most of the organ. The
cells surround a tube, into which
they release their secretions.
Many of these tubes merge to
form the pancreatic duct,
which carries the secretions
to the duodenum.
Pancreatic juice contains
enzymes that digest proteins,
carbohydrates, and nucleic
acids.
Pancreatic Enzymes
1. Pancreatic amylase breaks
down starch and glycogen
into disaccharides
2. Lipase breaks triglycerides
into fatty acids and glycerol
3. Trypsin, chymotrypsin,
carboxypeptidase break down
proteins. These enzymes are
secreted in an inactive form
until activated by an enzyme
(enterokinase) in the small
intestine
If trypsinogen is converted to
the active enzyme trypsin in
the pancreas, it starts to
digest the pancreas. This
condition is called
pancreatitis, and occurs if the
bile duct becomes blocked.
Blockage is caused by
alcoholism, gallstones,
infections, traumatic injury, or
side effects of some drugs.
Secretin is a hormone that
stimulates secretion of
pancreatic juice, which has a
high concentration of
bicarbonate ions, which
neutralize the acid of chyme,
preventing ulcers.
Pancreas destroyed by
pancreatitis
Liver- consists of two lobes,
right and left.
The functional units are
called lobules which
consist of hepatic cells
radiating outward from a
central vein. Hepatic
sinusoids separate
groups of cells and
supply them with
nutrients brought directly
from the intestine by the
hepatic portal vein.
Functions of the liver
1. When blood sugar levels are high, glucose is absorbed by the
liver and converted to glycogen. This is reversed as blood
glucose levels drop. These actions are controlled by two
hormones, insulin and glucagon.
2. Converts excess food to fats which are sent to adipocytes for
storage. Proteins are also metabolized by the liver.
3. Kupffer cells (stationary phagocytes) remove bacteria and
other foreign particles by phagocytosis. Removes and
destroys damaged red blood cells.
4. The liver is the major detoxification unit of the body. Toxins are
broken down and prepared for excretion. Lipid soluble toxins
are metabolized into water soluble materials (so they do not
diffuse across the intestinal cell membrane). Metabolized
toxins are secreted with the bile
Remember that the hepatic portal vein brings blood directly to the
liver from the intestine. Makes sense, doesn’t it!
Bile yellow/green liquid made up of bile
salts, bile pigments (bilirubin),
cholesterol, and electrolytes including
metabolized toxins. Bile is stored in the
gallbladder.
Bile salts break fat into smaller droplets (
emulsification) so they can be more
effectively digested.
Bilirubin is a breakdown product of
hemoglobin which is secreted in the
bile.
Jaundice turns the skin and eye whites
yellow. This is due to the build-up of
bilirubin. Jaundice is caused by 1. liver
disease (hepatocellular jaundice), 2.
blockage of the bile duct (obstructive
jaundice), or 3. rapid breakdown of
RBC (hemolytic jaundice).
Person w/ Jaundice
Gallbladder
• Hepatitis is an inflammation
of the liver, caused by a
virus.
• Hepatitis A is spread by
objects contaminated with
infected feces. This is a mild
form of the disease.
• Hepatitis B is transmitted by
body fluids (blood
transfusions, shared
needles, sexual activity).
• Hepatitis C accounts for
>50% of all hepatitis cases. It
is transmitted in blood
(shared needles etc and from
mother to fetus). Often it is a
chronic disease.
• Hepatitis D occurs in those
infected with hepatitis B.
>20% die.
Liver destroyed by hepatitis.
Note the normal piece of liver
to the far right.
Hepatitis E is transmitted in
water contaminated by feces.
Problem for visitors in 3rd
world countries.
Gall stones- cholesterol in bile
may form crystals that enter
the common bile duct &
cause severe pain.
The stones can be removed
surgically.
Sometimes, doctors use
ultrasound to break up
stones. The fragments can
than pass through the ducts.
Patients who persistently form
gall stones may have the
gallbladder removed.
What problem do you think this
can cause? What do you
think these people are forced
to do?