Download Digestive System

Digestive (GI) System
(Gastrointestinal System)
Gastro = stomach
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Functions
–
–
INGESTION Taking food in by mouth
DIGESTION to break food down into simple
molecules
Mechanical: churning of food in the stomach,
manipulation of food with tongue, tearing and
grinding with teeth.
Chemical: breakdown of food with hydrochloric
acid
–
–
ABSORPTION nutrients enter capillaries
DEFECATION to eliminate solid waste
products
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Digestive
Organs
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Regional Terms
Upper GI
– Stomach and areas superior
Lower GI
– Areas inferior to the stomach
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Abdominal
Quadrants
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Peritoneum and Mesenteries
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Peritoneum and Mesenteries
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OMENTA
The liver is suspended by a mesentery
called the OMENTUM.
There are two omenta: greater and
lesser.
GREATER OMENTUM is flat, and is in
front of the intestines like an apron. Its
function is to store fat.
LESSER OMENTUM is smaller. It is just
some fat above the stomach.
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Mesenteries
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PERITONEAL CAVITY
Why is this important? The peritoneum
divides the abdominal cavity into three
distinct regions:
PERITONEAL CAVITY: digestive organs
are here
INFRAPERITONEAL CAVITY (inferior to
peritoneum); where the bladder is
RETROPERITONEAL CAVITY (posterior
to it); where the kidneys are
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PERITONEAL CAVITY
This is clinically important because if you tear
something in the GI tract (ruptured appendix),
bacteria go out into the peritoneal cavity, affects
all the organs there, which is the entire GI tract.
Bleeding in the kidney will accumulate in the
retroperitoneal cavity.
Infection in the urinary bladder doesn’t affect the
peritoneal cavity.
Bleeding and infection are confined to one
compartment.
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Mouth
Oral Cavity
– Hard and Soft Palate
Tongue
– Lingual Frenulum
Salivary Glands
– Parotid, Submandibular, Sublingual
Teeth
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ORAL CAVITY
Lined by non-keratinized stratified
squamous epithelium. The transition
between the skin (keratinized) and the
non-keratinized area is the LIPS. You
can see what happens when the lips dry
out; becomes cracked because the lips
don’t have as much keratin as the skin.
–
PALATE (ROOF of mouth)
HARD PALATE: bone
SOFT PALATE: soft tissue (can feel with tongue
on roof)
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Mouth
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Figure 22.8a
TONGUE
Your tongue is the only muscle in your body that is
attached at only one end.
The tongue is all muscle, but it is different than all
other muscles of the body, where the fascicles
are arranged in a particular order.
The fibers of the tongue go in all directions, and
have no fascicles  good ROM.
Some people can curl tongue, others can’t.
The LINGUAL FRENULUM is the flap of skin
under the tongue at the midline. If it is too
short, it limits mobility, called tongue-tied.
Treatment is to cut it.
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Figure 22.8b
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Salivary Glands
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SALIVARY GLANDS
Produce saliva
–
Names of some salivary glands:
Parotid (largest). Mumps is a virus that attacks here.
Submandibular
Sublingual
–
Functions of saliva
To moisten food so you can swallow, especially dry food
like crackers.
Saliva is made of mucus and water. The mucus in the
saliva is what moistens the food.
To inhibit growth of bacteria (which like dark, warm, moist
areas). What does this are the antibodies, enzymes, and
macrophages in the saliva.
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Saliva
Saliva is not used for digestion of food. There is
an enzyme in saliva that breaks down starch, but
it takes hours. It is used to break down food
stuck between the teeth so the bacteria can’t eat
it and cause cavities.
Saliva contains bactericidal enzymes that initiate
the digestion of carbohydrates, and bicarbonate
buffer. However, it does not contain enzymes
that begin the digestion of proteins; chemical
digestion begins in the stomach.
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TEETH
How many teeth does the average adult have?
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How many DECIDUOUS TEETH (baby teeth
that fall out)? 20
How many INCISORS (most anterior)? 8: for
cutting like scissors
How many CANINES? 4: for tearing
How many PRE-MOLARS(BICUSPIDS = 2
roots)? 8:For chewing, some tearing
How many MOLARS (TRICUSPIDS = 3
roots)? They are the most posterior; 12: For
chewing, some tearing. The 4 most posterior
ones are called WISDOM TEETH, which erupt
at age 20, but sometimes grow crooked, called
“impacted”
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STRUCTURE OF TOOTH
GINGIVA are the gums
CROWN is the area above the gingiva
ROOT is embedded in a socket in the bone. In the
maxilla, the root can extend into the maxillary sinus.
Damage to the sinus can be a lot of problems.
ENAMEL is the external layer of the tooth. It is stronger
than bone, but does wear out. It is suppose to be ivory
color, not white. Whitening procedures scrape away
outer oxidized layer, to expose the layer underneath,
which is white, but it will oxidize, too.
DENTIN is deep to the enamel. It is like bone, with living
tissues and cells.
PULP CAVITY with PULP is deep to the dentin. It has
blood vessels and nerves.
PERIODONTAL LIGAMENT attaches the tooth to the
bone. It’s like periosteum. Disease of this structure is
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the most common cause of tooth loss in adults.
Tooth
Structure
Figure 22.11
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Tooth Problems
When bacteria eat away at the enamel, what’s it called?
CARY (CAVITY)
The dentist removes a larger area than where the
bacteria destroyed, and fills it in.
If the cavity extends into the pulp cavity, there is no way
to clean it up. The treatment is to make a big hole,
scrape out the pulp, and fill up the whole thing = ROOT
CANAL. This is a dead tooth, but still there.
Bacteria between the gingiva and tooth causes
inflammation of the gingiva = GINGIVITIS.
When it gets worse, the gingiva pulls away from the
tooth and the bacteria extends down to the periodontal
ligament = PERIODONTITIS. This is the major cause of
tooth loss. The tooth loosens and falls out. That’s why
you need to floss.
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Cavity (called a “cary”)
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Plaque on Tooth
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X-ray of Teeth
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X-ray of Teeth
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Fun Facts
The enamel in your teeth is the hardest
substance in your body.
Your teeth start growing 6 months
before you are born.
If you are right handed, you will tend to
chew your food on the right side of your
mouth. If you are left handed, you will tend
to chew your food on the left side of your
mouth.
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Fun Facts
Termites chew up dirt and dung and make massive homes. If
they were the size of a human, they could make a home taller
than the Empire State Building. They also put in air
conditioning systems, covered walkways, stairs and gardens.
Every person has a unique tongue print.
A giraffe’s tongue is 22 inches long
What animal bite causes the most human deaths? Snakes
take their toll, but Mosquitoes cause millions of deaths a year.
The Komodo dragon has saliva so toxic with bacteria, it just
bites it's prey and waits for it to die of infection a few days
later.
The average human produces enough spit to fill two
swimming pools in their lifetime.
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VIDEOS
How Dentures are made VIDEO
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GI Tract
This is a tube through the body, forming
the esophagus, stomach, small and large
intestine. The GI tract functions to digest
and absorb.
– Esophagus
– Stomach
– Small Intestine
– Large Intestine
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NOTE
When you are referring to a structure that
has a cavity (stomach, esophagus, uterus,
eye, etc), the layer that touches the lumen
is considered the superficial layer, even
though from the outside of the body it
would be considered deeper.
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Layers of GI Tube
There are four layers:
1. MUCOSA (inner layer). The lining varies from region
to region.
– Epithelium
– Lamina Propria: Loose connective tissue
– Muscularis mucosae: very thin smooth muscle, causes little
twitches within the mucosa.
2. SUBMUCOSA (moderate dense connective tissue).
Lots of elastic fibers, blood vessels, and lymphatic
vessels.
3. MUSCULARIS EXTERNA (smooth muscle layer with
two parts:
– Circular Layer (inner)
– Longitudinal layer (outer)
4. Serosa
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Serosa
Mucosa
Muscularis Externa
Submucosa
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3. Muscularis Externa
Muscularis Externa is extremely important for
digestion.
It allows for 2 types of actions:
a. PERISTALSIS: a rhythmic contraction to push
something along. This pushes food down by smooth
muscle contraction.
b. SEGMENTATION: A back-and-forth squeezing
of the muscle to grind up food. Food moves forward then
backward a little, then forward again. Function is to
churn up the food inside.
Some areas have thicker smooth muscle = SPHINCTER.
Circular muscles open and closes an opening.
– Controls the flow of food from one region to another.
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Layers of GI Tube
4. SEROSA is not in all regions (none in
esophagus).
– Simple squamous epithelium
– Loose connective tissue
– From internal to external, the layers of
this tube are the mucosa, submucosa,
muscularis, serosa.
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Esophagus
Extends from the oropharynx (back of the throat)
to the stomach, about 25 cm long. The things
that are specialized in the esophagus are:
1. MUCOSAL EPITHELIUM (non-keratinized
stratified squamous epithelium).
Why do we want stratified squamous here?
Because that is the thickest type of epithelium.
It protects against things you swallow; pointy
potato chips, etc. Cuboidal would slough.
2. MUSCULARIS EXTERNUM in upper half =
skeletal muscle, is under voluntary control.
Lower half = smooth muscle, not voluntary.
Food gets caught in the lower half because it
hasn’t started peristalsis.
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Cardiac Sphincter
The esophagus goes through the thoracic
cavity.
It needs to go through the diaphragm’s
opening (esophageal hiatus).
It empties to the stomach through a
CARDIAC SPHINCTER = a thickening of
the muscularis externa. This is NOT A
TRUE SPHINCTER.
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Stomach Anatomy
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Stomach: Functions
Store Food
Mechanically churns food into a paste
called CHYME
Kill bacteria
Some digestion: of proteins
Some absorption: of water, alcohol
Gastric emptying is the release of food from the stomach
into the duodenum; the process is tightly controlled with
liquids being emptied much more quickly than solids.
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STOMACH FUNCTIONS
1. Store Food, so it can be slowly released into a small
intestine. Your whole Thanksgiving dinner can take your
stomach diameter from 2” to 8” diameter.
2. Mechanically Churns food. Secretions from the
stomach are added, turns everything into a gooey paste.
When you throw up, you can see the enzyme secretions
= CHYME.
3. Kill bacteria. The stomach is very acidic (pH 1) like
battery acid. Chyme will even eat through clothing.
4. Some digestion: of proteins.
5. Some absorption: of water, alcohol (alcohol is
absorbed in the mouth, too!)
Food takes four hours to completely leave the stomach.
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FUN FACTS
Body measurements
for food portions
1 oz = a handful
3 oz = palm size (meat)
cup = fist
teaspoon = tip of thumb
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REGIONS OF THE STOMACH
1.
2.
3.
4.
5.
Cardiac region (near heart)
Fundus (above the cardiac sphincter)
Body
Pyloric region
PYLORIC SPHINCTER (a true sphincter)
The lining of the stomach is folded over into
RUGAE, to allow for expansion of the stomach.
When the stomach is full, the rugae flatten out.
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The Stomach
Figure 22.14a
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The Stomach
Figure 22.14b
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HISTOLOGY OF THE STOMACH
Epithelium: simple columnar epithelium.
– Its function is for secretion and absorption.
Lamina Propria: contains gastric pits.
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The Stomach
Figure 22.15a-c
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Stomach Cells
CHIEF CELLS secrete an enzyme called
pepsinogen. When pepsinogen is exposed to
hydrochloric acid (HCl), it is cleaved into pepsin,
its active form. Pepsin digests proteins.
PARIETAL CELLS in the stomach secrete
hydrochloric acid.
They also secrete intrinsic factor, which is
needed to absorb vitamin B12, which is
needed to make red blood cells.
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Intrinsic Factor
A person who lacks intrinsic factor (such
as those who have a stomach stapling
procedure or gastric bypass) will not be
able to absorb vitamin B12 and they will
get a type of anemia called pernicious
anemia.
Treatment is injectable B12 shots monthly
for the rest of their lives. They also have a
new dissolvable oral form of vitamin B12
that enters the bloodstream directly from
the mouth.
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Gastric
gland
Figure 22.15a-c
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PARTICULARS OF STOMACH
Has a third layer of the muscularis
externum: an OBLIQUE LAYER to churn
food.
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The Stomach
Figure 22.14b
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Problems with the stomach
There are lots of goblet cells in the stomach which make mucus to
prevent the stomach from digesting itself. Bacterial infection can
erode this area = GASTRIC (or Peptic) ULCER.
Acid Reflux
– The acid in your stomach is strong enough to dissolve razor
blades. The acid can creep up the esophagus and erode the
lining there, causing heartburn.
– The acid can stay in the stomach and cause an ulcer. In severe
cases, the ulcers are so deep, they bleed, and the person might
even vomit blood.
– Tends to occur more when a person is under a lot of stress
because more acid is produced.
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Two major causes
of Peptic (stomach and
duodenum) Ulcers:
1) 60% of gastric and up to 90% of duodenal ulcers are
due to a bacterium called Helicobacter pylori.
– The body responds by increasing gastrin secretion,
which is a hormone that causes HCl to be secreted,
which erodes the stomach lining.
2) NSAIDs (non-steroidal anti-inflammatory drugs, such
as aspirin) block prostaglandin synthesis.
– Prostaglandins promote the inflammatory reaction.
They also are found in the stomach, protecting it from
erosion.
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Stomach (gastric) ulcer
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Risk and Transmission
The lifetime risk for developing a peptic ulcer is
approximately 10%.
In Western countries the prevalence of Helicobacter
pylori infections roughly matches age (i.e., 20% at age
20, 30% at age 30, 80% at age 80 etc.).
Prevalence is higher in third world countries.
Transmission is by food, contaminated groundwater, and
through human saliva (such as from kissing or sharing
toothbrushes or food utensils)
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Problems With the Stomach
The cardiac sphincter doesn’t close well, since it
is not a true sphincter; consequences:
– You can throw up (reverse peristalsis). Rats do have
a true cardiac sphincter, and can’t vomit!
– That’s why rat poison won’t kill people or dogs; they
can throw it up.
Another consequence: hiatal hernia.
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HIATAL HERNIA
Part of the stomach, protrudes through
esophageal hiatus, causing pain and
difficulty swallowing.
It is the most common of all hernias.
There is a great amount of acid reflux;
erodes walls of esophagus, causing
ulcerations of esophagus.
Treatment is surgical; pull down the
stomach, and tighten the hernia in a
laparoscopic procedure.
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Fun Fact
Astronauts can't belch - there is no gravity
to separate liquid from gas in their
stomachs.
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SMALL INTESTINE (Small bowels)
These are the longest part of the GI tract
(9-15 feet long, 1” diameter)
In a cadaver, they are even longer,
because the muscles relax.
The small intestine is the most important
region of the GI tract because almost all of
the digestion and absorption takes place
here.
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Small Intestine Structure
The small intestine needs a lot of surface area:
200 square meters, which is the floor space of a
typical house.
How do you get such a lot of surface area?
There are lots of folds called PLICAE
CIRCULARIS.
Each of these folds also has folds, called VILLI.
If you take velvet and fold it, the fold is the
plicae, and the velvet hairs are villi.
Each of the villi has epithelial cells called
MICROVILLI, which make a BRUSH BORDER.
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The Small Intestine
Crypt of Lieberkuhn
Figure 22.17a-c
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Small Intestine Regions
Duodenum “12 finger widths long”
Jejunum “hungry when empty”
Ileum “twisted”
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DUODENUM
This is the shortest region, only one foot
long.
It receives chyme from the stomach. This
is where digestion begins. There are two
ducts at the beginning of the duodenum
from the pancreas and gallbladder. It is
the site of action of liver and pancreas
secretions.
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The Duodenum
Figure 22.16
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Pancreas
PANCREAS is an endocrine gland, and also
participates in digestion (exocrine). Most of the
digestive enzymes are made here. They go out
the PANCREATIC DUCT to enter the small
intestine.
It also produces BICARBONATE (from a
hormone called SECRETIN) to increase the pH
(decrease the acidity) of the chyme coming from
the stomach. If there is too much acid there, get
a DUODENAL ULCER.
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PANCREAS
ACINAR CELLS: secretes digestive
enzymes
ISLETS OF LANGERHANS: secretes
insulin
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Pancreas Histology
Figure 22.25a
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Pancreas
Acinar cells
(secrete
enzymes)
Islet of
Langerhans
(secretes
insulin)
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Gall Bladder
GALL BLADDER stores and concentrates bile,
which emulsifies fat: It breaks down the fat into
microscopic droplets which can be broken down
by pancreatic enzymes.
Fat doesn’t dissolve in water, so when you go to
McDonalds and order the Big Mac, fries, and
shake, you get 200 grams of fat (one week
supply), which globs together in the intestine,
and that much more bile is needed to break it
down.
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What Ronald McDonald is doing
to your arteries
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GALL BLADDER
This is located inferior to the liver, and its
function is to store and concentrate bile.
Bile is a detergent/soap (not an enzyme) which
emulsifies fat: It breaks down the fat into
microscopic droplets which can be broken down
by pancreatic enzymes.
It does NOT make or secrete bile; that is done
by the liver.
Bile is made in the liver from Hemoglobin (Hgb),
and also contains cholesterol and other things.
The function of bile is to break down lipids (fats)
so they can be digested.
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Gallbladder and Pancreas
Figure 22.16
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Gall Bladder
As the liver produces bile, if there is no
food in the duodenum, the sphincter
closes and bile backs up into the gall
bladder. When there is food, the sphincter
releases the bile.
The gall bladder is similar to the stomach.
It is lined with RUGAE (allows organ
expansion). Has muscles around it to
push bile out.
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Gall Stones
One function of the gall bladder is to
concentrate the BILE, but if the bile salts
crystallize, GALL STONES can form.
The stones block the cystic duct, and
causes a lot of pain as the bile backs up.
Treatment is to cut the cystic duct and
remove the gall bladder.
Now that person can only eat small
amounts of fats at a time.
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Types of Gall Stones
Stones made out of cholesterol (most
common type). It has nothing to do with
the cholesterol levels in the blood.
Stones made from too much bilirubin in
the bile.
Gallstones are more common in women,
Native Americans and other ethnic groups,
and people over age 40. Gallstones may
also run in families.
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Jejunum
JEJUNUM (“empty”)
This is the part of the small intestine where
most absorption occurs.
It is 3 feet long.
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Ileum
ILEUM (“twisted”) is 5-10 feet long. It is
the terminal portion of the small intestine.
The rest of the absorption takes place
here.
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Histology of Small Intestine
The intestines are lined with simple columnar
epithelium with lots of goblet cells that make
mucus for protection.
However, the pancreatic enzymes can digest the
mucus and the epithelial cells, so the lining of
the small intestine is replaced every day.
The basic functions of this epithelium are
secretion and absorption.
Absorption is a digestive process in which
nutrients enter the capillaries.
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Crypt of Lieberkuhn
The INTESTINAL CRYPT (CRYPT OF
LIEBERKUHN) is where the new epithelial
cells come from, and they are pushed
upwards into the villi to replace the
digested cells.
Also in this crypt are cells that produce
enzymes and hormones.
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Crypt of Lieberkuhn
Lacteal
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Crypt of Lieberkuhn
Figure 22.17a-c
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Absorption in Small Intestine
In the villis is a fenestrated capillary bed (has
holes in the walls of the blood vessels), which
needs to absorb a lot of material.
The small intestine absorbs carbohydrates, fats,
and proteins (although protein enzymes have
already begun working earlier in the digestive
tract in the stomach).
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Intestinal Villi
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Lymphatics of Small Intestine
There are also large lymphatic capillaries
in each villis called LACTEALS, whose
function is to absorb breakdown products
of fat. The vessel is large so it won’t get
clogged up.
Under all this are the MUSCULARIS
MUCOSA muscles which can twitch to
move the villa so food does not get stuck.
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Inguinal Hernia
The inguinal canal is open in the male to allow for passage of the
spermatic cord. In the female, the area is closed, but weak.
When there is abdominal pressure (lifting a weight), a piece of small
intestine can push out of this canal, causing pain.
Symptoms and warning signs:
http://www.symptomfind.com/diseases-conditions/hernia-symptoms-warning-signs/
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Problem with Small Intestine
Crohn’s Disease
– Autoimmune disease of the GI tract
– Most common area affected is small intestine
– Inflammation causes pain and diarrhea (may
be bloody)
– Genetic cause (high risk if siblings have it)
– Usually occurs in males in their 20’s
– No cure; just treatment of symptoms
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Celiac disease
(Sprue; gluten intolerance)
Genetic autoimmune disorder of the small intestine,
causing chronic diarrhea. The person is allergic to
gluten. Causes destruction of microvilli and villi.
It is characterized by having pale, loose and greasy
stools (steatorrhoea) which are voluminous and
malodorous.
It often presents with abdominal pain and cramping,
abdominal distension, and sometimes mouth ulcers.
Without adjusting the diet, coeliac disease leads to an
increased risk of adenocarcinoma (small intestine
cancer).
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Celiac disease
(Sprue; gluten intolerance)
They may develop ulcerative jejunitis and stricturing (narrowing as a result
of scarring with obstruction of the bowel).
The changes in the bowel make it less able to absorb carbohydrates, fats,
minerals (calcium and iron), and the fat-soluble vitamins A, D, E, and K.
Anemia may develop in several ways: iron malabsorption may cause iron
deficiency anemia, and folic acid and vitamin B12 malabsorption may give
rise to megaloblastic anemia.
Calcium and vitamin D malabsorption may cause osteopenia (decreased
mineral content of the bone) or osteoporosis (bone weakening and risk of
fragility fractures).
A small proportion have abnormal coagulation due to vitamin K deficiency
and are slightly at risk for abnormal bleeding.
Coeliac disease is also associated with bacterial overgrowth of the small
intestine, which can worsen malabsorption or cause malabsorption despite
adherence to treatment.
95
Celiac disease
(Sprue; gluten intolerance)
Celiac disease is caused by an allergy to gluten.
Gluten is present in Wheat subspecies (such as spelt, semolina and
durum) and related species such as barley, rye, triticale and Kamut.
A small minority of coeliac patients also react to oats. It is most
probable that oats produce symptoms due to cross contamination
with other grains in the fields or in the distribution channels.
Generally, oats are therefore not recommended.
Other cereals such as maize (corn), millet, sorghum, teff, rice, and
wild rice are safe for patients to consume, as well as non cereals
such as amaranth, quinoa or buckwheat. Non-cereal carbohydraterich foods such as potatoes and bananas do not contain gluten and
do not trigger symptoms.
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Gluten-free diet
Gluten is used in foods in some unexpected ways, for example as a
stabilizing agent or thickener in products like ice-cream and ketchup.
People wishing to follow a completely gluten free diet must also take
into consideration the ingredients of any over-the-counter or
prescription medications and vitamins. Also, cosmetics such as
lipstick, lip balms, and lip gloss may contain gluten and need to be
investigated before use. Glues used on envelopes may also contain
gluten.
Most products manufactured for Passover are gluten free.
Exceptions are foods that list matzah as an ingredient, usually in the
form of cake meal.
A blood test for IgA antiendomysial antibodies can detect coeliac
disease.
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Large Intestine
(Colon, or large bowel)
This is about 5 feet long, diameter of 4”.
Absorbs a LOT of water
Absorbs salts and electrolytes (Na, K, etc)
Stores feces for defecation (terminal portion)
Contains abundant bacteria (E. coli):
–
–
–
–
Make vitamins (B5, K, biotin)
Allow material to move through large intestine easier
Keep out harmful bacteria
They eat things you can’t digest
Fiber
Some sugars that we don’t have enzymes for
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Intestinal Gas
When these bacteria are happy and dividing, they
produce gas. If you are lactose intolerant, your are
missing the enzyme for lactose so the bacteria gets
more sugar and you get more gas! Beans also have
these sugars, so they give you gas.
Mexico has different strains of E. coli in their water; the
two strains battle it out and you get diarrhea.
Diarrhea is when the large intestine does not absorb
water  dehydration and electrolyte imbalance.
Cholera is a disease which attacks the large intestine,
preventing water absorption, and can be fatal in 24-48
hours.
The difference between diarrhea and constipation is the
amount of water absorbed from the large intestine.
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Regions of the Large Intestine
Cecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anus
101
Large Intestine
Figure 22.18a
102
Gross Anatomy of the Large
Intestine
The large intestine is divided into regions, but
they function the same.
The ileum enters into the first region of the large
intestine called the CECUM.
The ileo-cecal valve separates these and
controls the amount of chyme that enters into
the large intestine.
It also prevents the E. coli from leaving the large
intestine and getting into the small intestine,
where they would cause disease.
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Appendix
Below the cecum is the APPENDIX, which is a
lymph node, but it contains E. coli as well.
It might become inflamed, which closes off the
opening: APPENDICITIS
This is dangerous because It can rupture. Need
antibiotics and surgery or can be fatal.
Most common age for this is late teens to early
20’s because a child has a larger opening which
shrinks with age. When you’re done growing,
it’s done shrinking, so if you haven’t had a
problem by then, you might be ok.
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Large Intestine
Up from the cecum is the ASCENDING
COLON, TRANSVERSE COLON, and
DESCENDING COLON.
Then there is an “S” shaped section called
the SIGMOID COLON, which leads to the
RECTUM, and out the ANUS.
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SIGMOID COLON
This area allows for the passage of gas without passage
of feces. The LEVATOR ANI MUSCLE, when relaxed,
allows only gas to pas. When contracted, the feces can
pass.
Therefore, this muscle controls defecation by lifting
the anal canal superiorly around the feces.
Another thing that controls defecation is the INTERNAL
and EXTERNAL ANAL SPHINCTER. The internal one
is smooth muscle, and the external is skeletal muscle
(voluntary control).
The smooth muscles which line the large intestine work
in coordinated fashion to move the feces out.
It takes about 24 hours for food to be processed through
the entire digestive tract.
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Sigmoid Colon
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Problems with Large Intestine
DIVERTICULITITS
INFLAMMATORY BOWEL DISEASE
– Crohn’s Disease
– Ulcerative colitis
IRRITABLE BOWEL SYNDROME
COLON CANCER
HEMORRHOIDS
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DIVERTICULITITS
DIVERTICULUM (singular) DIVERTICUA
(plural) can form, which are small pouches
in the large intestine.
They can become inflamed, usually from a
small, hard piece of feces, causes the
condition known as DIVERTICULITITS.
These are painful and often need to be
surgically removed.
May be caused by lack of fiber, causing
increased pressure in the colon.
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Inflammatory Bowel Disease (IBD)
IBD is a group of inflammatory conditions
of the colon and small intestine.
The major types of IBD are Crohn's
disease and ulcerative colitis
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Ulcerative Colitis
The main symptom is constant diarrhea mixed with
blood, of gradual onset.
An intermittent disease, with periods of exacerbated
symptoms, and periods that are relatively symptom-free
No known cause, but may be genetic
May be triggered by environmental factors
Dietary modification may reduce the discomfort
It is treated as though it were an autoimmune disease
(anti-inflammatory drugs, immunosuppression)
Colectomy (partial or total removal of the large bowel
through surgery) is occasionally necessary, and is
considered to be a cure for the disease.
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Ulcerative Colitis
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IRRITABLE BOWEL SYNDROME (IBS)
IBS is a diagnosis of exclusion.
Symptoms are chronic abdominal pain, bloating,
and alteration of bowel habits in the absence of
any detectable organic cause.
May manifest as diarrhea or constipation or may
alternate between the two.
May be caused by infection, stress, or onset of
maturity
No cure; treatments attempt to relieve
symptoms, including dietary adjustments,
medication and psychological interventions.
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COLON CANCER
This is the #1 most deadly cancer (kills more
people) because it metastasizes and there are
no symptoms. It can be suspected by seeing
blood in the stool; this is an easy test, but not
very accurate.
A more accurate test is a SIGMOIDOSCOPY. A
tube is inserted into the sigmoid colon, done in
the doctor’s office. The tube has a light, and
they look for growths on the walls of the intestine
= POLYPS, which are pre-cancerous growths.
A COLONOSCOPY is done under general
anesthesia since the tube has to go through the
entire colon, but it’s more effective.
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Colonoscopy Photos
Ileo-cecal valve
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HEMORRHOIDS
HEMORRHOIDS are varicose veins in the
rectum.
There are large veins along the rectum,
with nothing constricting them.
They are common in pregnant women and
in fighter pilots from the g-forces they pull.
They can be surgically removed.
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FUN FACTS ABOUT THE
RECTUM
A healthy individual releases 3.5 oz. of gas in
a single flatulent emission, or about 17 oz. in
a day.
The bombardier beetle combines chemicals
in his rear end and can squirt out boiling hot
acidic liquid which quickly neutralizes any
attack.
All land spiders breathe through a hole on the
rear part of their bodies.
The Fitzroy river turtle absorbs two-thirds of
the oxygen it needs through its rectum.
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FUN FACTS
HOW LONG DOES IT TAKE TO DIGEST
A MEAL? Should be about one day.
Because plant cells are made of cellulose
and we cannot digest that, you can
swallow a few kernels of corn (whole,
without chewing), and you’ll be able to
easily see them in your stools and find out
how long it takes to go all the way through
your digestive tract.
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Hepatic Portal System
Almost all of the blood coming from the digestive
system drains into a special venous circulation
called the portal circulation.
This is because it contains all the nutrients and
toxins that have been absorbed along the
digestive tract from ingested food.
Before these absorbed substances can go into
the systemic circulation (the main blood
circulation in the body), it must be filtered first to
remove or detoxify toxic substances first.
This filtering and detoxification is one of the 500+
functions of the liver.
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Hepatic Portal System
Many drugs that are absorbed through the GI
tract are substantially metabolized by the liver
before reaching general circulation. As a
consequence, certain drugs can only be taken
via certain routes.
For example, nitroglycerin cannot be swallowed
because the liver would inactivate the
medication, but it can be taken under the tongue
or transdermal (through the skin) and thus is
absorbed in a way that bypasses the portal
venous system.
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A portal system is one that has two separate
capillary beds between the arterial supply
and the final venous drainage.
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LIVER
This is the largest internal organ of the
body, located on the right side, below the
diaphragm, and extends below the costal
margin (can palpate).
It has many functions and is the most
complex organ except the brain.
The liver has 500+ known functions.
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Liver
Makes blood clotting factors
Makes blood proteins (albumin)
Makes bile
Regulates glucose levels
Processes fats
Makes cholesterol
Processes amino acids
Detoxifies chemicals
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Liver
It is also the only organ that can
regenerate.
As much as 80% of your liver could be cut
away and it would grow back to a full size
in approximately three months.
With only 1/6th of your liver present your
body could continue to function.
It is usually hard to determine if the liver is
damaged until the damage is quite
advanced.
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Liver
It has a right and left lobe, separated by
the FALCIFORM LIGAMENT.
The liver gets blood from 2 sources:
Artery = Hepatic artery
Vein = Hepatic portal system = Blood from
the spleen, stomach, pancreas, small and
large intestines which all go through the
liver. The nutrients that are absorbed by
the GI tract go to the liver first for
processing, then to the rest of the body.
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Liver
Figure 22.22
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INTERNAL STRUCTURE OF
LIVER
The liver is made of hundreds of
thousands of LIVER LOBULES; each one
is the size of a sesame seed, giving the
liver a grainy texture when you eat it.
Each lobule carries out all of the functions
of the liver.
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LIVER LOBULE
It has a hexagonal shape, at each corner
are some vessels = HEPATIC TRIAD:
– ARTERIOLE from the hepatic artery
– VENUOLE from the hepatic portal vein
– BILE DUCT, which goes to the gall bladder.
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(Kupffer cells)
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Liver
Hepatic
Triad: Vein,
Artery, Bile
Duct
Figure 22.23a,132
c, d
Liver Lobules
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Liver: Central vein and sinusoids
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Sinusoids
LIVER SINUSOIDS are channels that blood can
flow through. Cells that line the sinusoids are
called HEPATOCYTES, and each one faces the
sinusoid and is in contact with blood.
The hepatocytes are what carry out all of the
functions of the liver.
If you made a machine to do the work of the
liver, it would have to be the size of a large oil
refinery.
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Liver: sinusoids and hepatocytes
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Function of Hepatocytes
Detoxification of poisons
Picking up and processing of nutrients
from the portal blood
– This includes picking up glucose from the
nutrient-rich blood coming from the small
intestine and stores it as glycogen (the
storage form of glucose) for when the body
needs it later.
Storage of the fat soluble vitamins
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Kupffer Cells
Within the sinusoids are KUPFFER CELLS,
which are macrophages. As blood flows through
the sinusoids, they phagocytize old erythrocytes.
The released Hgb is given to the hepatocytes,
which convert it to bilirubin, one of the main
components of BILE.
Bile flows through a series of channels called the
BILE CANNICULI to the bile duct.
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The Liver Destroys
Old Red Blood Cells
By the way, when you have dark circles
under your eyes, it is from hemoglobin and
iron deposits from broken RBC’s that
leaked out of the delicate capillaries under
the thin skin there.
Will skin creams remove this?
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Problems with the Liver
HEPATITIS
CIRRHOSIS
JAUNDICE
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Liver Problems
Infection of the liver = HEPATITIS (can be
deadly)
CIRRHOSIS is when the hepatocytes die
and are replaced by connective tissue.
This is often from alcoholism, which kills
the hepatocytes.
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Jaundice
One of the symptoms from any liver
disorder is a connection of the bile
canaliculi and the sinusoid so some
bilirubin can enter the blood.
Bilirubin is yellow-green (later in its
degradation it will turn brown and that is
what gives the feces its color).
The yellow color of bilirubin in the skin is
known as JAUNDICE.
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Jaundice
Jaundice is not a disease; it is a symptom of
liver disorder.
It first shows up in the sclera because it is white
there. The skin has other pigments, so yellow
doesn’t show up as well.
Newborns get jaundice from a lot of erythrocytes
being broken down, and the liver gets
overloaded, but it’s harmless.
The treatment is UV light or sunlight, goes away
in a few days.
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Liver Transplant
Adult-to-adult liver transplantation has
been done using the donor's right hepatic
lobe which amounts to 60% of the liver.
Due to the ability of the liver to regenerate,
both the donor and recipient end up with
normal liver function if all goes well.
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Situs Inversus
Congenital condition in which the major visceral organs
in the thorax and abdomen are reversed or mirrored from
their normal positions.
The heart is located on the right side of the thorax, the
stomach and spleen on the right side of the abdomen
and the liver and gall bladder on the left side.
The left lung is trilobed and the right lung bilobed, and
blood vessels, nerves, lymphatics and the intestines are
also transposed.
Situs inversus is generally an autosomal recessive
genetic condition, although it can be X-linked or found in
identical "mirror" twins.
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Situs Inversus
As long as there are no heart defects, the person has no
health issues.
However, donating an organ is more complicated, since
the connecting blood vessels are not in the same place!
People are not aware of their condition until an unrelated
health issue arises, such as appendicitis, presenting on
the left side instead of the right side. The doctor cannot
find the heart sounds in the proper location, either.
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40 lb Abdominal Tumor
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Warning!
The Government has issued a health
warning not to swallow chewing gum. The
following is a photo of what can happen:
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