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DIGESTIVE SYSTEM
The digestive system has four functions
a. INGESTION Taking food in by mouth
b. DIGESTION to break food down into simple molecules
i. Mechanical: churning of food in the stomach, manipulation of food with tongue, tearing
and grinding with teeth.
ii. Chemical: breakdown of food with hydrochloric acid
c. ABSORPTION nutrients enter capillaries
d. DEFECATION to eliminate waste products
REGIONAL TERMS
Upper GI
– Stomach and areas superior
Lower GI
– Areas inferior to the stomach
MOUTH
(Actually, digestion begins on the kitchen stove)
A. ORAL CAVITY is 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 they dry
out; becomes cracked.
a. PALATE (ROOF of mouth)
i. HARD PALATE: bone
ii. SOFT PALATE: soft tissue (can feel with tongue on roof)
B. 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.
C. SALIVARY GLANDS produce saliva
a. Names of some salivary glands:
i. Parotid (largest). Mumps is a virus that attacks here.
ii. Submandibular
iii. Sublingual
b. Functions of salivary glands
i. To moisten food so you can swallow, especially crackers. The mucus in the saliva is
what moistens the food.
ii. To inhibit growth of bacteria (which like dark, warm, moist areas). What does this are
the antibodies, enzymes, and macrophages in the 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 left in the mouth so the bacteria can’t eat it.
Saliva contains bactericidal enzymes, enzymes that initiate the digestion of carbohydrates, and
bicarbonate buffer. However, it does not contain enzymes that begin the digestion of proteins; that
begins in the stomach.
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D. TEETH: How many teeth does the average adult have? 32
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 points)? 8:For chewing, some tearing
How many MOLARS? (Most posterior)12: For chewing, some tearing
STRUCTURE OF TOOTH
A. GINGIVA are the gums
B. CROWN is the area above the gingiva
C. 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.
D. 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.
E. DENTIN is deep to the enamel. It is like bone, with living tissues and cells.
F. PULP CAVITY with PULP is deep to the dentin. It has blood vessels and nerves.
G. PERIODONTAL LIGAMENT attaches the tooth to the bone. It’s like periosteum. Disease of this
structure is the most common cause of tooth loss in adults.
When bacteria eat away at the enamel, what’s it called? CARIE (CAVITY)
The dentist removes a larger area where the bacteria are, 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 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.
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.
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STRUCTURE OF THE GI TUBE
There are four layers:
1. MUCOSA (inner layer). The lining varies from region to region.
a. Epithelium
b. Loose fibrous connective tissue = Lamina Propria
c. 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:
a. Circular Layer (inner)
b. Longitudinal layer (outer)
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.
4. SEROSA is not in all regions (none in esophagus).
a. Loose fibrous connective tissue
b. Simple squamous epithelium.
From internal to external, the layers of this tube are the mucosa, submucosa, muscularis, serosa.
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ESOPHAGUS
Extends from the oropharynx 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? It protects against things you swallow; pointy potato chips, etc. Cuboidal
would slough.
2. MUSCULARIS EXTERNUM in upper half = skeletal muscle. Lower half = smooth muscle.
Why? The upper half, skeletal muscle, is under voluntary control. Smooth muscle is not voluntary. Food gets
caught in the lower half because it hasn’t started peristalsis.
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 muscular externa.
This is NOT A TRUE SPHINCTER.
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 is 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.
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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FUN FACTS
Body measurements for food portions:
1 oz = a handful
3 oz = palm size (meat)
cup = fist
teaspoon = tip of thumb
REGIONS OF THE STOMACH
1. Cardiac region (near heart)
2. Fundus (above the cardiac sphincter
3. Body
4. Pyloric region
5. PYLORIC SPHINCTER (a true sphincter)
It is folded over into RUGAE, to allow for expansion of the stomach.
When the stomach is full, the rugae flatten out.
HISTOLOGY OF THE STOMACH
The stomach is lined with simple columnar epithelium; their function is for secretion and absorption.
There are gastric pits in the lamina propria.
PARIETAL CELLS in the stomach secrete hydrochloric acid and digestive enzymes which kill bacteria in the
stomach. They also secrete intrinsic factor, which is needed for absorption of vitamin B12.
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.
INTRINSIC FACTOR
The parietal cells in the stomach secrete INTRINSIC FACTOR. Vitamin B12 requires intrinsic factor in order
to be absorbed. 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.
PARTICULARS OF STOMACH
Has a third layer of the muscularis externum: an OBLIQUE LAYER to churn food.
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PROBLEMS WITH THE STOMACH
There are lots of goblet cells, the function of which is to make mucus to prevent the stomach from digesting
itself. Bacterial infection can erode this area = GASTRIC ULCER.
1. ACID REFLUX = heart burn.
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.
Two major causes of Peptic 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 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.
Does stress cause ulcers?
There is debate as to whether psychological stress can influence the development of peptic ulcers.
Helicobacter pylori thrives in an acidic environment, and stress has been demonstrated to cause the
production of excess stomach acid.
2. THE CARDIAC SPHINCTER DOESN’T CLOSE WELL, since it is not a true sphincter; consequences:
– You can throw up (reverse peristalsis). Rats don’t have a sphincter, and can’t vomit!
– That’s why rat poison won’t kill people or dogs; they can throw it up.
3. HIATAL HERNIA occurs when 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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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.
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.
Regions of the Small Intestine
1. DUODENUM (12 finger widths long) 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 secretions (bile) and pancreas
secretions (digestive enzymes and bicarbonate).
PANCREAS is an endocrine gland, and also participates in digestion. 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 reduce the pH of the chyme coming from
the stomach. If there is too much acid there, get a DUODENAL ULCER.
ACINAR CELLS: secretes digestive enzymes
ISLETS OF LANGERHANS: secretes insulin and glucagon
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.
The gall bladder 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.
The gall bladder does NOT make or secrete bile; that is done by the liver.
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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.
Two HEPATIC DUCTS join to form the COMMON BILE DUCT, which enters the small intestine
along with the PANCREATIC DUCT. At the entrance is a SPHINCTER.
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.
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.
Two main types of gallstones:
 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.
The following also make you more likely to develop gallstones:
Failure of the gallbladder to empty bile properly (this is more likely to happen during pregnancy)
Medical conditions that cause the liver to make too much bilirubin, such as chronic hemolytic anemia,
including sickle cell anemia
Liver cirrhosis and biliary tract infections (pigmented stones)
Diabetes
Bone marrow or solid organ transplant
Rapid weight loss, particularly eating a very low-calorie diet
Receiving nutrition through a vein for a long period of time (intravenous feedings)
May be asymptomatic or have sudden and rapidly intensifying pain in the upper right portion of the abdomen,
lasting several minutes to a few hours.
The doctor may order the following blood tests:
 Bilirubin
 Liver function tests
 Pancreatic enzymes
Treatment for gall stones
Symptomatic patients usually have surgery. Medicines called chenodeoxycholic acids (CDCA) or
ursodeoxycholic acid (UDCA, ursodiol) may be given in pill form to dissolve cholesterol gallstones. However,
they may take 2 years or longer to work, and the stones may return after treatment ends.
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2. JEJUNUM (“hungry when empty”) where most digestion and absorption occurs. It is 3 feet long.
3. ILEUM (“twisted”) is 5-10 feet long. It is the terminal portion of the small intestine. Much of the
absorption takes place here.
Histology
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
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.
In the villis is a fenestrated capillary bed, 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).
There are also large lymphatic capillaries in each villa 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 things don’t get stuck.
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)
– 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).
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.
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 carbohydrate-rich
foods such as potatoes and bananas do not contain gluten and do not trigger symptoms.
Gluten-free diet
Several grains and starch sources are considered acceptable for a gluten-free diet. The most frequently
used are corn, potatoes, rice, and tapioca (derived fromcassava). Other grains and starch sources
generally considered suitable for gluten-free diets include amaranth, arrowroot, millet, montina, lupin,
quinoa, sorghum(jowar), taro, teff, chia seed, and yam. Various types of bean, soybean, and nut flours
are sometimes used in gluten-free products to add protein and dietary fiber. Almond flour is a lowcarbohydrate alternative to flour, with a low glycemic index. In spite of its name, buckwheat is not
related to wheat; pure buckwheat is considered acceptable for a gluten-free diet, although many
commercial buckwheat products are actually mixtures of wheat and buckwheat flours, and thus not
acceptable. Gram flour, derived from chickpeas, is also gluten-free (this is not the same as Graham flour
made from wheat).
Gluten is used in foods in some unexpected ways, for example as a stabilizing agent or thickener in
products likeice-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”.
This intestine is important for several reasons:
1. Absorbs a LOT of water and salts
2. Absorbs electrolytes (Na, K, etc)
3. Stores feces for defecation
4. Contains bacteria (E. coli), about 3 pounds of it! These bacteria have functions:
a. Make vitamins (B5, K, biotin)
b. Allow material to move through large intestine easier
c. Keep out harmful bacteria
d. They eat things you can’t digest
i. Fiber
ii. Some sugars that we don’t have enzymes for
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. 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.
Gross Anatomy
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.
Below the cecum is the APPENDIX, which is a lymph node. It contains E coli as well. It is about the size of
your little finger. 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.
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 muscle 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.
Problems with Large Intestine
DIVERTICULITITS
INFLAMMATORY BOWEL DISEASE
– Crohn’s Disease
– Ulcerative colitis
IRRITABLE BOWEL SYNDROME
COLON CANCER
– SIGMOIDOSCOPY or a COLONOSCOPY
POLYPS
HEMORRHOIDS
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DIVERTICULUM (Diverticula is plural) can form, a small pouch 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.
Inflammatory Bowel Disease (IBS)
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
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 symptomfree
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.
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.
COLON CANCER
This is the #1 most deadly cancer (kills more people) because it metastasizes and there are no symptoms. It can
be diagnosed by seeing blood in the stool; this is an easy test, but no very accurate. A more accurate test is a
SIGMOIDOSCOPY or a COLONOSCOPY. 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 precancerous growths. A colonoscopy is done under general anesthesia since the tube has to go through the entire
colon, but it’s more effective.
HEMORRHOIDS are varicose veins. 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.
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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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.
A portal system is one that has two separate capillary beds between the arterial supply and the final
venous drainage.
The first capillary bed is in the small intestines.
The blood enters the liver via the portal vein (which drains blood into the liver, not from the liver). The
portal vein then branches into many smaller vessels that open into hepatic sinusoids.
The second capillary bed is the sinusoids.
The blood is then cleaned by the hepatocytes and macrophages of the liver, before draining into the
hepatic veins, which drains into the inferior vena cava.
The hepatic portal system has two distinct capillary beds separated by a portal vein. The functions
of these two capillary beds are that the first picks up nutrients and the second delivers these
nutrients to liver cells.
Therefore, this system is a capillary system within a venous system.
Because one capillary bed empties into another capillary bed, there is some oxygen left in the hepatic
portal vein.
Hepatic portal vein: oxygen not-poor and nutrient rich.
Capillary – Portal Vein – Capillary
the first picks up nutrients, the second delivers these nutrients to liver cells.
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). Its function is the most complex organ except the brain. The liver has 500+
known functions.
1. Makes blood
2. Makes blood proteins (clotting factors)
3. Regulates glucose levels
4. Processes fats (if the liver is damaged, it will interfere with digestion of lipids)
5. Makes cholesterol
6. Processes amino acids
7. Detoxifies chemicals (That’s why CSI autopsies look at the liver for poisons)
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.
Most systemic venous blood is both oxygen poor and nutrient poor.
However, systemic venous blood that is oxygen not poor and nutrient rich occurs in the hepatic portal
vein.
It is nutrient rich because it receives blood from the small intestine right after it has absorbed the
nutrients.
It is not completely oxygen poor because it has a capillary  vein  capillary system that has more
oxygen than just one capillary  vein.
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INTERNAL STRUCTURE
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.
LIVER LOBULE
It has a hexagonal shape, at each corner are some vessels = HEPATIC TRIAD:
1. ARTERIOLE from the hepatic artery
2. VENUOLE from the hepatic portal vein
3. BILE DUCT, which goes to the gall bladder.
The HEPATIC TRIAD vessels enter the liver lobule through a capillary, then join to combine the blood 
becomes a CAPILLARY VEIN, which drains into the CENTRAL VEIN at the center of the lobule 
HEPATIC VEIN  INF. VENA CAVA.
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 carries 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.
BLOOD FLOW IN THE LIVER
Blood flow to the liver is unique in that it receives both oxygenated and deoxygenated blood.
Nutrient-rich, oxygen-poor blood from the intestine enters the liver by the hepatic portal vein. It flows
through the sinusoids for detoxification.
Oxygen-rich blood enters the liver by the hepatic artery. It flows through the sinusoids to supply them
with oxygen.
All of the blood mixes together, and when the oxygen demand of the hepatocytes is satisfied, and the
toxins have been removed, the oxygen-depleted blood collects in a central vein within each lobule,
which drains into the hepatic vein. The hepatic vein subsequently drains into the inferior vena cava and
back to the heart. Because of the mixture of oxy and deoxy blood in the liver, the partial pressure of
oxygen (pO2) and perfusion pressure of portal blood are lower than in other organs of the body.
Partial Pressure of oxygen means the amount of dissolved oxygen.
Perfusion pressure is the amount of pressure required to deliver nutrients to cells.
These low pressures in tissues allow the nutrients to leave the circulation and enter the tissues better.
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Function of hepatocytes
A) detoxification of poisons
B) 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.
C) storage of some vitamins
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.
The liver destroys old red blood cellsBy 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?
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.
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 (a lot of it is brown and is what gives the feces its
color). The yellow color is known as 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.
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.
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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PERITONEUM and MESENTERIES
The peritoneum is the lining of the GI tract and abdominal wall, similar to the pleura and pericardium. It is
made of simple squamous epithelium with underlying loose connective tissue.
A mesentery is a double layer of peritoneum, fused back-to-back, that extends from the body wall to the
digestive organs.
CROSS SECTION OF ABDOMEN
In the center is the GI tract. The PARIETAL PERITONEUM lines the wall, the VISCERAL
PERITONEUM lines the organs, and in between is the PARIETAL CAVITY. But the organ can’t just float
in space; it has to be attached. The MESENTERY is what attaches the GI organs to the peritoneum (like
hanging a pipe from the ceiling by another pipe).
Blood vessels and nerves go through the mesentery, that’s why they are called MESENTERIC VESSELS. In
some regions of the GI tract, there are accessory organs (liver, kidney, pancreas, etc). The peritoneum
continues around each organ.
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,
especially in men. LESSER OMENTUM is smaller.
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Why is this important? The peritoneum divides the abdominal cavity into three distinct regions:
1. PERITONEAL CAVITY
2. INFRAPERITONEAL CAVITY (inferior to peritoneum)
3. RETROPERITONEAL CAVITY (posterior to it)
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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