BI SC 004
Human Body:
Form and Function
STUDY GUIDE
The Digestive System
Dr. Martha Aynardi
aynardi@psu.edu
Chapter Learning Objectives

Upon completion of this chapter, you should be able to:
◦ Identify the organs of the alimentary canal and the accessory organs of
the digestive tract and identify the main functions of each structure.
◦ List the 5 functions of the digestive system.
◦ Differentiate between digestion and absorption.
◦ Describe the role of digestive enzymes.
◦ Describe the importance of regulating pH during digestion.
◦ Identify the 4 major layers of the wall of the alimentary canal and recall
the function of each.
◦ Differentiate between the structure and function of villi and microvilli in
the intestinal wall.
◦ Describe and give cause of the following diseases and conditions of the
digestive system: GERD, gallstones, hepatitis, pancreatitis, perforated
ulcer, ulcerative colitis.
Identify the organs of the alimentary canal and the accessory organs
of the digestive tract and identify the main functions of each structure
(pg. 516).
List and differentiate between the 5 functions of the digestive system.
◦
◦
◦
◦
◦
Ingestion
Mechanical Processing
Digestion
Secretion
Absorption
Differentiate between digestion and absorption (pg. 516).
◦ Digestion refers to the chemical breakdown of food into small organic
fragments that can be absorbed by the digestive epithelium.
◦ Absorption is the movement of small organic molecules, electrolytes,
vitamins, and water across the digestive epithelium and into the
interstitial fluid of the digestive tract.
Describe the role of digestive enzymes (pg. 531).
◦ Recall that an enzyme is a protein that catalyzes (speeds up) a specific
biochemical reactions.
◦ Digestive enzymes are needed to break down the complex materials
found in our diet.
For example: when food enters the stomach, it is
saturated with gastric juices and is exposed to the effects of a strong acid
(HCI) and the proteolytic enzyme, pepsin.
Describe the importance of regulating pH (pg. 38-39; 58) during
digestion (pg. 525; 531-532).
◦ Variations in pH outside the normal range of 7.35 to 7.45 can damage
cells and disrupt normal cellular functions because the chemical
processes of the cell are very sensitive to the concentration of hydrogen
and hydroxide ions present.
◦ In digestion, buffers stabilize pH by either removing or replacing
hydrogen ions.
◦ Different digestive enzymes vary in optimum pH according to where in
the digestive tract they normally function.
◦ A change in pH can change the shape of an enzyme and alter its function.
◦ All human enzymes have a temperature optimum near 37 0C or 98.60F.
Identify the 4 major layers of the wall of the alimentary canal and
recall the function of each (pg. 517-518).
1. The mucosa (inner layer of the digestive tract) is a mucous membrane.
Along most of the digestive tract, the mucosa is thrown into folds that
both increase the surface area available for absorption and permit
expansion after a large meal.
2. The submucosa contains blood vessels, lymphatic vessels, nerves, and
some glands that secrete lubricating mucus into the lumen.
3. The muscularis externa are concentric layers of smooth muscle
responsible for muscle contractions that mix foods with digestive juices
and then propel these materials through the digestive tract.
4. The serosa is the thin outermost layer of connective and epithelial tissue.
Its secretions lubricate and prevent friction between the digestive organs
and the surrounding viscera.
With the mesentery it helps to stabilize the
positions of the viscera in the abdomen.
Differentiate between the structure and function of villi and
microvilli in the intestinal wall (pg. 528).
◦ Villi are microscopic fingerlike folds of the mucosa (epithelial cells held
together by tight junctions) that project into the intestine and which serve
to increase the surface area for absorption ~10X.
◦ Microvilli are microscopic folds found at the apical surface of each
epithelial cell membrane that project from the epithelium of the villi like
bristles on a brush into the lumen of the digestive tract (they are
therefore referred to as the brush border).
In addition to increasing the
surface area for absorption ~20-30X, the membranes of the microvilli
contain digestive enzymes involved in digestion.
Describe and give cause of the following diseases and conditions of
the digestive system: GERD, gallstones, hepatitis, pancreatitis,
perforated ulcer, ulcerative colitis.
◦ GERD - GastroEsophageal Reflux Disease, reflux or backflow from the
stomach that are responsible for the symptoms of “heartburn”.
◦ Gallstones – deposits of minerals, bile salts, and cholesterol that form if
bile becomes too concentrated.
◦ Hepatitis – a virus-induced disease of the liver; the most common forms
include hepatitis A, B, and C.
◦ Pancreatitis – the inflammation of the pancreas.
◦ Perforated ulcer – a particularly dangerous ulcer in which gastric acids
erode through the wall of the digestive tract, allowing its contents to
enter the peritoneal cavity.
◦ Ulcerative colitis (inflammatory bowel disease) – a chronic inflammation
of the digestive tract, most commonly affecting the colon.
Key Terms
◦ Digestion
◦ Absorption
◦ Enzymes
◦ Digestive
◦ Mucosa
◦ Submucosa
◦ Muscularis externa
◦ Serosa
◦ Villi
◦ Microvilli
Chapter Review Questions
Can you answer the following questions?
◦
Can you identify the organs of the alimentary canal and the accessory
organs of the digestive tract and recall the main functions of each
structure?
◦
What are the 5 functions of the digestive system (discussed in class)?
◦
What is the difference between digestion and absorption?
◦
What is the role of digestive enzymes?
◦
Can you describe the importance of regulating pH during digestion?
◦
Can you identify the 4 major layers of the wall of the alimentary canal
and recall the function of each?
◦
What is the difference between the structure and function of villi and
microvilli in the intestinal wall?
◦
Can you describe and give cause of the following diseases and
conditions of the digestive system: GERD, gallstones, hepatitis,
pancreatitis, perforated ulcer, ulcerative colitis?
Questions to consider when studying for the exam
◦ How does structure relate to function?
◦ Are you able to recognize examples and apply knowledge?
◦ Do you know the sequential steps of any mechanisms discussed?