Download Anatomy of the Digestive System

Peritoneum
FIGURE 24.5
1. Recall that the abdominopelvic cavity is lined with a serous membrane called the
peritoneum.
A. The visceral peritoneum surrounds organs.
B. The parietal peritoneum lines the wall of the abdominopelvic cavity and covers certain
organs.
C. The peritoneal cavity, which is in-between the visceral and parietal peritoneum, is filled
with peritoneal fluid. The peritoneal fluid functions to reduce friction between organs.
2. Some organs are covered by (located behind) the parietal peritoneum and are called
retroperitoneal. Examples are the kidneys, adrenal glands, pancreas, ascending colon,
descending colon, and the urinary bladder.
3. Mesenteries are a double layer of peritoneum that extends from the abdominopelvic wall to
the organs within the lumen of the abdominopelvic cavity.
A. Functions of the mesenteries.
1) Mesenteries supports the abdominal organs.
2) Mesenteries are a bridgeway for blood vessels and nerves to reach the
abdominopelvic organs.
3) Mesenteries are a site of fat storage.
B. Important mesenteries of the digestive tract.
1) The coronary ligament (all double layers of peritoneum not called mesenteries are
called ligaments) attaches the liver to the diaphragm.
2) The falciform ligament attaches the liver to the anterior abdominal wall.
3) The lesser omentum attaches the liver to the lesser curvature of the stomach.
4) The greater omentum attaches the greater curvature of the stomach to the transverse
colon. The greater omentum folds over on itself to form a space called the omental
bursa.
5) The transverse mesocolon attaches the transverse colon to the posterior abdominal
wall.
6) The mesentery proper attaches the small intestine to the posterior abdominal wall.
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ORAL CAVITY
FIGURE 24.6
1. The oral cavity (mouth) is the part of the digestive tract bounded by the lips, fauces (opening
into the pharynx), cheeks, and palate.
2. The vestibule is the part of the oral cavity between the lips or cheeks and the alveolar
processes.
Lips and Cheeks
1. The lips are muscle (orbicularis oris) covered by keratinized stratified squamous epithelium.
They are important in communication.
2. The cheeks are muscle (mostly the buccinator) covered internally by moist stratified
squamous epithelium. They function in mastication (chewing) by holding food against the
teeth, and they function in communication.
Palate
1. The hard palate, composed of the maxillary bones and the palatine bones, functions to
separate the oral cavity from the nasal cavity.
2. The soft palate and uvula, composed of muscles, function to separate the oral cavity and the
nasal cavity. They also close off the opening to the nasal cavity during swallowing.
Tongue
FIGURE 10.13 (p. 333)
1. The tongue functions to move food about during mastication and swallowing and is also
involved in communication. The tongue consists of intrinsic tongue muscles, which change
the shape of the tongue. The extrinsic tongue muscles attach to the tongue and move it
about as a unit.
2. The anterior two thirds of the surface of the tongue is covered with papillae that give it a
rough texture. Some of the papillae contain taste buds. The posterior one third of the tongue
does not have papillae and has only a few taste buds.
3. The frenulum is a mucous membrane that attaches the tongue to floor of the mouth. If it
extends too far toward the tip of the tongue it can interfere with normal movement of the
tongue and normal speech, resulting in a person who is "tongue tied".
4. There are many superficial blood vessels under the tongue, making this location ideal for
administering certain medications, such as nitroglycerin, to increase blood flow to the heart.
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Tonsils
FIGURE 22.5 (p. 789)
1. Tonsils consists of lymphatic tissue and they are a part of the immune system, which helps to
protect against microorganisms.
2. There are three sets of tonsils.
A. The lingual tonsils are embedded within the posterior part of the tongue.
B. The palatine tonsils are in the lateral wall of the fauces.
C. The pharyngeal tonsil is located in the nasopharynx (back of the throat superior to the
uvula). The pharyngeal tonsil is often referred to as the adenoids.
Teeth
1. The teeth mechanically breakup food, and are involved in communication and defense.
2. Types of teeth.
FIGURE 24.7
A. Deciduous teeth are the first set of teeth. Usually they are all present by 2 years of age.
B. Permanent teeth replace the deciduous teeth between 6 to 17 years of age. The last
permanent teeth are molars called wisdom teeth, and they appear between 17 to 25 years
of age. Wisdom teeth may have to be removed because of lack of room.
Type of Tooth
Incisor
Canines
Premolar
Molar
TOTAL
Deciduous
8
4
0
8
20
Permanent
8
4
8
12
32
Function
Cutting
Tearing
Grinding
Grinding
3. The teeth extend into the alveoli (sockets) of the mandible and the maxillary bones. The
gums or gingiva (dense fibrous connective tissue) cover the alveoli and jaw bones.
4. General parts of a tooth.
FIGURE 24.8
A. The crown is the part of the tooth above the gum line. The crown is the cutting or
chewing surface of the tooth. [The clinical crown is the part of the crown exposed in the
oral cavity. The anatomical crown is the enamel covered part of the tooth.]
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B. The neck is the constricted part of the tooth at the gum line.
C. The root is the part of the tooth below the gum line that extends into the alveolus.
5. Detailed description of a tooth.
A. Teeth consist of a hard bony material called dentin.
1) Enamel covers the dentin of the crown. Caries or cavities are usually a breakdown of
the enamel caused by acids produced by bacteria. Fluoride treatment increases the
resistance of the enamel to acid.
2) Cementum covers the dentin of the root and neck. It anchors the tooth to the
periodontal ligaments.
3) The periodontal ligaments extend from the tooth to the bone of the alveoli. They
hold the tooth in place. Periodontal gum disease is destruction of the periodontal
ligaments caused by bacterial activity. The result is the tooth falls out. This kind of
tooth loss can be reduced by regular cleaning and flossing of the teeth.
B. The pulp cavity contains pulp (connective tissue), blood vessels, and nerves.
C. The root canal is a passageway for blood vessels and nerves into the pulp cavity. The
opening into the root canal is the apical foramen. If an infection occurs inside the tooth,
the top of the tooth is removed, pulp is removed from the root canal and replaced with a
packing material (a procedure called a “root canal”), and an artificial crown is attached to
the tooth.
Mastication
1. Mastication is the process of chewing food.
2. Mastication mixes food with saliva to form a bolus of food. Breaking the food down into
smaller pieces increases the surface area of the food, which promotes digestion by various
secretions.
3. The muscles of mastication move the mandible, providing the force necessary for the teeth to
cut, tear, and grind food.
FIGURE 10.11 (p. 334)
4. Mastication is controlled primarily by the mastication reflex, which alternately causes the
muscles of mastication to contract and relax. Mastication can be voluntarily started and
stopped.
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Salivary Glands
FIGURE 24.9
1. The salivary glands produce saliva, which moistens food and begins the process of digesting
carbohydrates.
2. There are three pairs of salivary glands.
A. The parotid salivary glands are located anterior to the ear. They are the largest salivary
glands and can become swollen in mumps.
B. The submandibular glands are located along the border of posterior half of each
mandible.
C. The sublingual glands are located in the floor of the mouth.
4. The salivary glands produce approximately 1 - 1.5 L of saliva per day.
A. Saliva is mostly water. The water makes it possible to taste food and makes the food
easier to swallow.
B. Salivary amylase starts starch digestion by splitting starch into maltose (a disaccharide)
and isomaltose.
C. Lysozyme (an enzyme) and IgA (an antibody) kill some bacteria. The mouth still harbors
many bacteria, and human bites can easily cause infections.
D. Mucus is a secretion of the mucous membranes, consisting of mucin, epithelial cells,
white blood cells, and inorganic salts suspended in water. Mucin is a proteoglycan
(polysaccharides attached to a protein core) that makes mucus very slippery. Mucus acts
as a lubricant.
5. Regulation of saliva secretion.
A. Stimulation of saliva production.
1) Taste or smell stimuli that act through conditioned reflexes.
2) Tactile stimuli in the mouth.
3) Thoughts (e.g., lemon) or nausea.
4) Irritating substances in the stomach and small intestine. Saliva may help to dilute the
irritating substance.
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B. Inhibition of saliva production.
1) Dehydration.
2) Fear, anxiety, or intense mental effort.
PHARYNX
1. The pharynx (G. throat), or throat, is divided into three interconnected parts.
FIGURE 23.2 (p. 827)
A. The nasopharynx is connected to the nasal cavity.
B. The oropharynx is connected to the oral cavity.
C. The laryngopharynx is connected to the esophagus.
2. Pharyngeal constrictors are muscles that move food through the pharynx to the esophagus.
FIGURE 10.14b (p. 338)
ESOPHAGUS
FIGURE 24.1
1. The esophagus is a muscular tube that connects the laryngopharynx with the stomach.
2. Sphincters.
A. The upper esophageal sphincter regulates movement into the esophagus.
B. The lower esophageal sphincter (cardiac sphincter) regulates movement into and out of
the stomach.
3. The esophagus is lined with moist, stratified squamous epithelium that provides protection
against abrasion.
4. Mucous glands produce mucus that lubricates the surface of the epithelium.
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Liver
FIGURE 24.17
1. The liver is located in the right-upper and left-upper quadrants of the abdominopelvic cavity.
2. The liver is divided into four lobes: two major lobes (right and left) and two minor lobes
(caudate and quadrate).
A. The division of the liver into four external lobes is based on surface markings formed by
the ligaments of the liver.
B. The internal divisions of the liver are based on the branching pattern of blood vessels and
ducts entering or exiting the liver (see below). Based on this pattern, the “internal” left
lobe consists approximately of the “external” left lobe, caudate lobe, and quadrate lobe.
The “internal” right lobe consists of the remainder of the liver.
C. The “internal” lobes are further subdivided into 7 to 9 segments, depending on the
classification scheme used. There are no surface markings for these divisions, which
must be determined using radiographic techniques.
D. Liver transplants typically involve transplanting the whole liver from a recently deceased
person. Sometimes the liver is split into right and left “internal” lobes to provide two
recipients.
E. There is a shortage of livers for transplantation into children. One procedure removes
two segments from an adult “external” left lobe, achieving a better size match. In some
cases, a living parent donates part of a liver.
3. The porta (gate), on the inferior surface of the liver, is where vessels, ducts, and nerves enter
or exit the liver.
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4. Blood enters the porta (gate) of the liver from two sources.
FIGURE 24.20
A. The hepatic artery, which brings oxygenated blood from the aorta (a major blood vessel
arising from the heart).
B. The hepatic portal vein drains the digestive tract and carries deoxygenated, nutrient rich
blood to the liver.
5. The liver segments are subdivided into lobules.
FIGURE 24.19
A. The tissue of the lobules consists of hepatic cords, which are columns of hepatocytes,
the functional cells of the liver.
B. On the outside of the lobules are portal triads, which consist of the branches of the
hepatic artery, hepatic portal vein, and hepatic duct (to be discussed below).
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C. Branches of the hepatic artery and hepatic portal vein empty into the hepatic sinusoids,
which are enlarged blood capillaries, located between the hepatic cords.
1) The blood from the hepatic arteries supplies the hepatocytes with oxygen.
2) The blood from the hepatic portal veins brings the hepatocytes nutrients that are
processed.
D. The hepatic sinusoids connect to a central vein in the center of the lobule. The central
veins from the lobules empty into the hepatic veins.
E. Blood leaves the liver through the hepatic veins, which do not pass through the porta.
The hepatic veins join the inferior vena cava as it passes by the posterior side of the liver.
Given the following structures:
1. central vein
2. hepatic artery
3. hepatic portal vein
4. hepatic sinusoid
5. hepatic vein
Make a list of the structures in the order blood passes through them as the blood moves
from the GI tract into and out of the liver (note that not all of the structures listed need to
be used).
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6. Bile ducts.
FIGURE 24.18
A. Bile, the secretion of the liver, is produced by the hepatocytes.
B. Bile from the hepatocytes enters bile canaliculi, which lie between the hepatic cords.
The bile canaliculi join the small hepatic ducts of the portal triads.
C. The small hepatic ducts within the liver tissue join together to form the right and left
hepatic ducts. The right hepatic duct drains the right half of the liver and the left hepatic
duct drains the left half of the liver.
D. The right and left hepatic ducts join to form the common hepatic duct.
E. The cystic duct from the gallbladder joins the common hepatic duct to form the common
bile duct.
F. The common bile duct empties into the hepatopancreatic ampulla, an enlarged duct
formed by the union of the common bile duct and the main pancreatic duct.
1) The hepatopancreatic ampulla empties through the major duodenal papilla into the
duodenum.
2) The opening of the hepatopancreatic ampulla is usually closed by the
hepatopancreatic ampullar sphincter.
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Given the following structures:
1. bile canaliculus
2. common bile duct
3. common hepatic duct
4. major duodenal papilla
5. hepatopancreatic ampulla
6. right and left hepatic ducts
7. small hepatic ducts of the portal triads
Make a list of the structures in the order bile passes through them, starting with the
secretion of bile from hepatocytes and ending with movement of bile into the duodenum.
Functions of the Liver
1. Bile Production. The liver produces about 700 ml of bile per day.
A. Bile contains bile salts. The bile salts emulsify fats, i.e., break fat globules into smaller
pieces. This is important because it allows digestive enzymes to act on the fat molecules.
B. Bile contains bicarbonate ions, which neutralize acid from the stomach. It is necessary to
raise pH in the small intestine so that enzymes from the pancreas and the wall of the
digestive tract can function optimally.
C. Bile contains excretory products such as bile pigments (breakdown product from old red
blood cells), cholesterol, and hormones. Bile pigments are responsible for the color of
feces. Failure to secrete bile can result in bile movement into the blood, producing the
condition of jaundice.
2. Storage. The liver stores a variety of substances.
A. The liver stores glycogen, fats, fat soluble vitamins (A, D, E, and K), copper, and iron.
B. The liver stores harmful substances that cannot be broken down or excreted (e.g., DDT).
C. The liver functions to regulate blood glucose (sugar levels) by storing glucose. When
blood glucose levels are high, the liver removes glucose and stores it as glycogen. When
blood glucose levels are low, the liver releases glucose into the blood.
3. Nutrient Interconversion.
A. The liver processes nutrients, helping to ensure that the body has the proper amounts of
carbohydrates, fats and proteins. For example, excess proteins, resulting from a high
protein diet, can be converted into carbohydrates and lipids.
B. The liver transforms substances into a useful form. For example, inactive vitamin D is
converted to active vitamin D.
4. Detoxification. The liver detoxifies harmful substances. For example, ammonia is converted
to the less harmful substance, urea.
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5. Phagocytosis. Hepatic phagocytic cells (Kupffer cells) in the liver remove bacteria, worn out
red blood cells, and foreign substances from the blood.
6. Synthesis. The liver produces many new, unique substances, such as important blood
proteins (e.g., albumin, prothrombin, fibrinogen, heparin, etc.).
GALLBLADDER
FIGURE 24.18
1. The gallbladder is a small sac located on the inferior surface of the liver.
2. The gallbladder has three layers or tunics.
A. The inner layer is a mucous membrane arranged into rugae.
B. The middle layer is smooth muscle that can contract causing the gallbladder to empty.
C. The outer layer is visceral peritoneum.
3. The gallbladder functions to store and concentrate bile. Note that the gallbladder does not
produce bile.
A. When the small intestine is empty the hepatopancreatic ampullar sphincter is closed.
B. Bile produced by the liver backs up the common bile duct to the cystic duct and then into
the gallbladder.
Given the following structures:
1. bile canaliculus
2. common bile duct
3. common hepatic duct
4. cystic duct
5. right and left hepatic ducts
6. small hepatic ducts of the portal triads
Make a list of the structures in the order bile passes through them, starting with the
secretion of bile from hepatocytesing with movement of bile into the gallbladder.
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Given the following structures:
1. common bile duct
2. common hepatic duct
3. cystic duct
4. major duodenal papilla
5. hepatopancreatic ampulla
Make a list of the structures in the order bile passes through them, starting in the
gallbladder and ending with movement of bile into the duodenum (note that not all of the
structures listed need to be used).
4. Cholesterol in bile can precipitate to produce gallstones. Gallstones can enter the cystic duct
or common bile duct and block the passage of bile. Blockage of the common bile duct can
cause jaundice. Spasms of smooth muscles in the ducts produce the pain of biliary colic.
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