BIOD 331 Module 7 Pathophysiology: (Gastrointestinal Tract
Disorders, Anatomy and Physiology Review II, Motility/Diarrhea,
Irritable Bowel Syndrome & Inflammatory Bowel Disease, GERD &
PUD, Jaundice, Cirrhosis & Cholecystitis)
Module 7: Gastrointestinal Tract Disorders
7.1: Anatomy and Physiology Review
● Main functions of the GI tract are to digest food and absorb nutrients into the
bloodstream. The GI tract is a long muscular tube that extends from mouth to
anus. The upper GI tract contains the mouth, esophagus, and stomach. The middle
GI tract contains the duodenum, jejunum, and ilium. The lower tract contains the
cecum, colon, and rectum. The accessory organs include the salivary glands, liver,
and pancreas
● Mouth begins process of digestion. Food is masticated while tongue and salivary
glands assist, preparing food to be swallowed. The salivary glands produce saliva
which both lubricates the food to ease of swallowing and aids in the breakdown of
food. Saliva contains multiple enzymes such as salivary amylase, which breaks down
carbohydrates, and lipase which breaks down fats
● Esophagus passes food from the pharynx to the stomach. Contains smooth muscle
layers that use peristalsis to move food through GI tract. The pharyngoesophageal
sphincter is located in the upper esophagus and prevents air from entering the
esophagus and stomach during breathing. The gastroesophageal sphincter is located
in the lower region of the esophagus connecting it to the stomach. It prevents
reflux of gastric contents into the esophagus
● The stomach holds food in storage during the early stages of digestion.
Carbohydrate and protein digestion by pepsin occur here. The area where the
esophagus opens into the stomach is called the cardiac region. The dome-shaped
portion is called the fundus, and the middle portion is the body. The region that
connects the stomach to the small intestine is called the pyloric region. The pyloric
sphincter controls the emptying of stomach contents into the small intestine and
prevents the backflow of contents into the stomach
● The small intestine is made up of the duodenum, jejunum, and ileum. The duodenum
is approximately 10 inches long. The jejunum and ileum have a combined length of
approx 9-20 feet which can vary greatly depending on the size of the person. The
small intestine is where the majority of digestion and absorption takes place. Bile
, and pancreatic juices enter intestine through the common bile duct and main
pancreatic duct to assist in digestion. For lipid digestion to occur, fat must be
broken down into smaller pieces so that the water-soluble digestive enzymes can
act on the surface molecules. This process, known as emulsification, starts in the
stomach with agitation (or mechanical digestion) and continues in the duodenum
with the help of bile and pancreatic lipase (chemical digestion). The small intestine
contains a large surface area composed of villi and circular folds, which allow for
absorption of nutrients. Absorption is process of moving nutrients and other
materials from the external environment of the GI tract into the internal
environment
● The large intestine is approx 4.5-5 feet long and 2.4-2.7 inches in diameter.
Comprised of cecum, colon, rectum, and anal canal. The ileocecal valve is located at
the cecum and prevents feces from flowing back into the ileum. The colon is
further divided into the ascending, transverse, descending, and sigmoid sections.
The rectum connects the sigmoid colon to the anus. The anal canal has strong
sphincter muscles that prevent incontinence. The large intestine reabsorbs mainly
water & serves as storage for waste until defecation occurs
● Liver is largest visceral organ in the body, weighs 3 lbs in an adult. Receives 25% of
resting cardiac output. Has venous portal blood supply through the hepatic portal
vein that receives about 75% of blood per minute, and an arterial supply through
the hepatic artery that receives remaining 25% of blood. The venous blood comes
from the digestive tract, pancreas, and spleen
○ Hepatic vein in the liver drains into the inferior vena cava below the level of
the diaphragm. Due to this pressure difference, the liver can store approx
500-1000 mL of blood. This is helpful during times of hypovolemia and shock
as this blood can be moved back into circulation. When there is an
accumulation of blood in the periphery as seen in right sided heart failure, it
accumulates in the liver
○ Several important functions in the body. Produces bile, metabolizes hormones
and drugs, synthesizes proteins, glucose, and clotting factors, stores
vitamins and minerals and converts them to useable material the body can
utilize, changes ammonia to urea, and converts fatty acids to ketones
○ The liver can store large amounts of glucose as glycogen through glycogenesis.
When blood glucose levels are low, glycogen is converted back to glucose.
The liver can also synthesize glucose from amino acids, glycerol, and lactic
acid during times of fasting or increased demand in a process called
, gluconeogenesis. Can also convert excess carbohydrates to triglycerides for
storage in a dipose tissue, and is a major site for protein synthesis and
degradation
○ Liver produces approx 500-600 mL of bile daily. Bile is needed for dietary fat
digestion and absorption. The bile salts contained in bile, which are formed
from cholesterol, are the important component of digestion
● GI wall Structure
○ 4 layers to the GI wall structure starting below the upper third of the
esophagus. They are the mucosal layer, the submucosal layer, the muscularis
externa, and the serosal layer.
■ The mucosal layer is the inner layer, made up of epithelium, an
underlying connective tissue called the lamina propria, and smooth
muscle cells that can contract and change the shape and surface area
of the mucosal layer. Mucosal layer functions in producing mucus that
lubricates and protects inner surface of alimentary canal, secretes
digestive enzymes and substances that break down food, absorbs the
breakdown products of digestion, and maintains a barrier to prevent
the entry of noxious substances and pathogenic organisms. These
epithelial cells are constantly being replaced every 5 days, injury to
this layer heals rapidly
■ Submucosal layer: contains dense connective tissue and some adipose
tissue. This layer has blood vessels, nerves, and structures that
secrete digestive enzymes
■ Muscularis externa: consists of an inner layer of circularly arranged
smooth muscle layers. These layers alternately contract to help move
the contents through the GI tract via peristalsis
■ Serosal layer: serous membrane, outermost layer of organs and is also
called visceral peritoneum. The peritoneum is the largest serous
membrane in the body. It is comprised of 2 continuous layers, the
visceral and parietal peritoneum. The parietal peritoneum lines the
wall of the abdominopelvic cavity. Between the 2 layers is the
peritoneal cavity, a potential space containing fluid secreted by the
serous membranes. This serous fluid keeps a moist surface to
prevent friction between the moving abdominal organs
○ The mesentery is the double layer of peritoneum that encloses some or all of
the abdominal viscera and attaches it to the abdominal wall. Included in the
Disorders, Anatomy and Physiology Review II, Motility/Diarrhea,
Irritable Bowel Syndrome & Inflammatory Bowel Disease, GERD &
PUD, Jaundice, Cirrhosis & Cholecystitis)
Module 7: Gastrointestinal Tract Disorders
7.1: Anatomy and Physiology Review
● Main functions of the GI tract are to digest food and absorb nutrients into the
bloodstream. The GI tract is a long muscular tube that extends from mouth to
anus. The upper GI tract contains the mouth, esophagus, and stomach. The middle
GI tract contains the duodenum, jejunum, and ilium. The lower tract contains the
cecum, colon, and rectum. The accessory organs include the salivary glands, liver,
and pancreas
● Mouth begins process of digestion. Food is masticated while tongue and salivary
glands assist, preparing food to be swallowed. The salivary glands produce saliva
which both lubricates the food to ease of swallowing and aids in the breakdown of
food. Saliva contains multiple enzymes such as salivary amylase, which breaks down
carbohydrates, and lipase which breaks down fats
● Esophagus passes food from the pharynx to the stomach. Contains smooth muscle
layers that use peristalsis to move food through GI tract. The pharyngoesophageal
sphincter is located in the upper esophagus and prevents air from entering the
esophagus and stomach during breathing. The gastroesophageal sphincter is located
in the lower region of the esophagus connecting it to the stomach. It prevents
reflux of gastric contents into the esophagus
● The stomach holds food in storage during the early stages of digestion.
Carbohydrate and protein digestion by pepsin occur here. The area where the
esophagus opens into the stomach is called the cardiac region. The dome-shaped
portion is called the fundus, and the middle portion is the body. The region that
connects the stomach to the small intestine is called the pyloric region. The pyloric
sphincter controls the emptying of stomach contents into the small intestine and
prevents the backflow of contents into the stomach
● The small intestine is made up of the duodenum, jejunum, and ileum. The duodenum
is approximately 10 inches long. The jejunum and ileum have a combined length of
approx 9-20 feet which can vary greatly depending on the size of the person. The
small intestine is where the majority of digestion and absorption takes place. Bile
, and pancreatic juices enter intestine through the common bile duct and main
pancreatic duct to assist in digestion. For lipid digestion to occur, fat must be
broken down into smaller pieces so that the water-soluble digestive enzymes can
act on the surface molecules. This process, known as emulsification, starts in the
stomach with agitation (or mechanical digestion) and continues in the duodenum
with the help of bile and pancreatic lipase (chemical digestion). The small intestine
contains a large surface area composed of villi and circular folds, which allow for
absorption of nutrients. Absorption is process of moving nutrients and other
materials from the external environment of the GI tract into the internal
environment
● The large intestine is approx 4.5-5 feet long and 2.4-2.7 inches in diameter.
Comprised of cecum, colon, rectum, and anal canal. The ileocecal valve is located at
the cecum and prevents feces from flowing back into the ileum. The colon is
further divided into the ascending, transverse, descending, and sigmoid sections.
The rectum connects the sigmoid colon to the anus. The anal canal has strong
sphincter muscles that prevent incontinence. The large intestine reabsorbs mainly
water & serves as storage for waste until defecation occurs
● Liver is largest visceral organ in the body, weighs 3 lbs in an adult. Receives 25% of
resting cardiac output. Has venous portal blood supply through the hepatic portal
vein that receives about 75% of blood per minute, and an arterial supply through
the hepatic artery that receives remaining 25% of blood. The venous blood comes
from the digestive tract, pancreas, and spleen
○ Hepatic vein in the liver drains into the inferior vena cava below the level of
the diaphragm. Due to this pressure difference, the liver can store approx
500-1000 mL of blood. This is helpful during times of hypovolemia and shock
as this blood can be moved back into circulation. When there is an
accumulation of blood in the periphery as seen in right sided heart failure, it
accumulates in the liver
○ Several important functions in the body. Produces bile, metabolizes hormones
and drugs, synthesizes proteins, glucose, and clotting factors, stores
vitamins and minerals and converts them to useable material the body can
utilize, changes ammonia to urea, and converts fatty acids to ketones
○ The liver can store large amounts of glucose as glycogen through glycogenesis.
When blood glucose levels are low, glycogen is converted back to glucose.
The liver can also synthesize glucose from amino acids, glycerol, and lactic
acid during times of fasting or increased demand in a process called
, gluconeogenesis. Can also convert excess carbohydrates to triglycerides for
storage in a dipose tissue, and is a major site for protein synthesis and
degradation
○ Liver produces approx 500-600 mL of bile daily. Bile is needed for dietary fat
digestion and absorption. The bile salts contained in bile, which are formed
from cholesterol, are the important component of digestion
● GI wall Structure
○ 4 layers to the GI wall structure starting below the upper third of the
esophagus. They are the mucosal layer, the submucosal layer, the muscularis
externa, and the serosal layer.
■ The mucosal layer is the inner layer, made up of epithelium, an
underlying connective tissue called the lamina propria, and smooth
muscle cells that can contract and change the shape and surface area
of the mucosal layer. Mucosal layer functions in producing mucus that
lubricates and protects inner surface of alimentary canal, secretes
digestive enzymes and substances that break down food, absorbs the
breakdown products of digestion, and maintains a barrier to prevent
the entry of noxious substances and pathogenic organisms. These
epithelial cells are constantly being replaced every 5 days, injury to
this layer heals rapidly
■ Submucosal layer: contains dense connective tissue and some adipose
tissue. This layer has blood vessels, nerves, and structures that
secrete digestive enzymes
■ Muscularis externa: consists of an inner layer of circularly arranged
smooth muscle layers. These layers alternately contract to help move
the contents through the GI tract via peristalsis
■ Serosal layer: serous membrane, outermost layer of organs and is also
called visceral peritoneum. The peritoneum is the largest serous
membrane in the body. It is comprised of 2 continuous layers, the
visceral and parietal peritoneum. The parietal peritoneum lines the
wall of the abdominopelvic cavity. Between the 2 layers is the
peritoneal cavity, a potential space containing fluid secreted by the
serous membranes. This serous fluid keeps a moist surface to
prevent friction between the moving abdominal organs
○ The mesentery is the double layer of peritoneum that encloses some or all of
the abdominal viscera and attaches it to the abdominal wall. Included in the
