Digestive System
Organization of the Digestive System
 The organs of the digestive system are divided into TWO main groups:
The ____________________________________ – also called the gastrointestinal (GI) tract
___________________________ – teeth, tongue, salivary glands, liver, gallbladder, pancreas
Gastrointestinal (GI) Tract
 A long, winding, continuous tube that extends from the ___________________________________
 Averages about 9 meters (___________________)
 Consists of: _____________________________________________________________________
_______________________________________________________________________________
Accessory Organs
 Located either ___________ the alimentary canal or _________________ it
 Communicates by way of _______________
 _________________ the organs of the alimentary canal in their functions
 Includes: _______________________________________________________________________
Digestive Processes
 Food needs to be turned into a ______________________________________________________
 This needs to be done by:
_______________________ reducing the food
_______________________ reducing the food
_______________________ the food into the blood through the intestinal wall
Carried by blood to the __________________________
Digestive Processes
 ____________________________
Taking food into the mouth (mechanical)
 ____________________________
Chewing (mechanical)
Salivary action (chemical)
 ____________________________
Swallowing (mechanical)
 ____________________________
Wavelike contractions that move food through the GI tract (mechanical)
 ____________________________
Passage of food molecules from GI tract into circulatory system (mechanical & chemical)
 ____________________________
Elimination of undigestible wastes (mechanical)
SPECIAL FEATURES OF THE DIGESTIVE SYSTEM
 Peritoneum: serous membrane, lubricating tissue (pericardium of the heart, pleurae of lungs)
Parietal Peritoneum: ________________________ of the abdominal cavity
Visceral Peritoneum: ____________________________
 Extensions of the Parietal Peritoneum
____________________________ – attaches liver to diaphragm & anterior body wall
_______________________ – extends between liver and the lesser curvature of the stomach
______________________ – extends from greater curvature of stomach to transverse colon
______________________ – supports the intestine
______________________ – supports large intestine
 Wall Structure of the Alimentary Canal
________________
Mucous membrane that ______________________________ of the alimentary canal
Consists of a thin layer of loose connective tissue & a small amount of smooth muscle in the external
layer
Major functions: _____________________________________________________
___________________________________________________________________
________________
External to the mucosa
Composed of loose connective tissue, rich in blood vessels, lymphatic vessels, nerve endings, & small
glands
________________
Smooth muscle that externally encircles the submucosa
Thickened at certain points along the alimentary canal to ______________________
____________________________________________________________
Provides the ________________ of food during mechanical digestion as well as the _______________
of food through the alimentary canal by ____________________
________________
The ______________________________________
DIGESTIVE ORGANS
 Mouth
Function: process of ____________________ (______________)
Moistening of food with saliva begins process of __________________________
Accessory organs associated with mouth: ________________________________________
Space between tongue and palate is called ___________________________
Cheeks and lips are separated by a space called the vestibule
Palate: forms the __________________________________
________________________: hard, bony anterior part of oral cavity
________________________: muscular, posterior part, forms archway bordering pharynx
______________________: along both sides of the archway
______________________: extends from the archway in a downward projection
 Tongue
Anchored to the floor of the mouth by a membranous fold extending from its midline along its
undersurface, called the lingual ____________________
Contains ______________________________________________ and also help to provide friction for
moving food
 Teeth
Provide mastication
Dentition: _________ different sets of teeth during normal development
First set: appear at about 6 months, continue to erupt until all ___________________ are present by
about 24 months
Referred to as deciduous teeth
Second set: appear between 6 and 12 years
By the end of adolescence, all permanent teeth have erupted except for the third molars, or wisdom teeth
(17 and 25 years)
In a full set, there are ____________________________________
Types:
_______________________ – pointed chisel (cutting)
_______________________ – cone-shaped (serve as tearing tool)
______________________________________________ – broad, flattened surfaces (grinding)
Tooth Structure
_____________: visible part of tooth above the gum line
_____________: buried below the gum line
_____________: covers the crown – hardest substance in the body
 Salivary Glands
Collection of accessory organs surrounding the mouth that secrete a fluid called saliva
Saliva consists of ___________________________________________________________
Medium for dissolving soluble food molecules
Solutes include mucus and enzymes
Lysozyme destroys bacteria
Salivary amylase ________________________________________________
Parotid Glands
___________________ salivary glands
Located in front of and slightly below each ear between the skin of the cheek and the masseter muscle
Secretes a _____________________ that is rich in __________________________
Submandibular Glands
Located along the inner surface of the jaw in the floor of the mouth
Secrete a more viscous fluid than parotids due to the mucus in their secretions
Sublingual Gland
Lies ___________________________
Secrete a _____________________________ fluid due to the abundance of mucus
 Digestion in the Mouth:
Digestion begins here
Mastication – ______________________________________________________________
Creates a __________________
 Pharynx
Chamber located ________________________________ extending from the internal nares to the
larynx
Its walls are composed of skeletal muscle ________________________________________
Divided into ________________________: nasopharynx, oropharynx, and laryngopharynx
Function: transports food from ________________________________________
Plays an important role in the act of swallowing
 Act of Swallowing:
Begins as food ____________________________________ from the mouth into the pharynx by the
tongue
_______________________________________ to keep food from entering the nasal cavity
Followed by contraction of muscles in the wall of the pharynx, which moves the larynx upward as the
epiglottis presses downward (__________________________)
Muscles in lower pharynx relax, opening the passage into the ____________________
The food bolus is pushed into the esophagus and onward to the stomach by
______________________________, which begins in the pharynx and continues along the length of the
esophagus
 Esophagus
Muscular tube that extends from the pharynx to the stomach for about 25 cm (___________)
Located ____________________________________ in the neck and upper thorax
_________________________________________________________________________
_________________________________ (lower esophageal sphincter/ cardiac sphincter) near its union
with the stomach
Acts as a valve to ______________________________________ from the stomach
Opens as peristaltic waves reach the stomach
 Stomach
______________________________ that is about 25 cm (10 inches) long and in most people can hold
over 2 liters of food
When empty, its inner linings form deep folds known as _______________ (ROO-JE)
The convex lateral margin of the stomach is called the ______________________________
The greater omentum extends from the greater curvature
The concave medial margin is known as the __________________________________
The lesser omentum extends from the lesser curvature
 Parts of the stomach
_____________________ – small area surrounding the opening that receives food from the esophagus
_____________________ – expanded region that bulges above the cardia; serves as a temporary holding
area for food
_____________________ – main part of the stomach; lies between the fundus and the pylorus
_____________________ – narrowed, inferior region
At the terminal end is the _____________________
Serves as a valve to control the movement of food from the stomach to the small intestine
 Stomach Wall – MUCOSA
Characterized by millions of tiny openings that can be seen only with a magnifying lens or microscope
called gastric pits
Gastric pits lead into tube-like gastric glands that secrete a collection of chemicals called
_____________________
_____________________ of gastric juice pour out from these glands each day
Glands contain secratory cells called _____________________________, which secrete digestive
enzymes
___________________________________________________________________
Mucous cells secrete __________________
_________________ will develop if this lining breaks down
 Functions of the Stomach:
Mechanical Digestion – accomplished by mixing and churning actions
Chemical Digestion – provided by gastric juice
Several enzymes are present, but most importantly, _______________ is present – secreted by
zymogenic cells in an inactive form called pepsinogen
Pepsin is a powerful _________________________________ capable of beginning the breakdown of
nearly all proteins
Pepsin and its acidic environment are kept from digesting the stomach wall by the protective layer of
mucus that coats the ________________________
Absorption
Limited amount of absorption takes place across the stomach lining
Materials the can cross this barrier are: ____________________________________
___________________________________________________________________
Propulsion
Provided by _____________________________________________
The material that is ready to enter the small intestine has been converted by mechanical and chemical
digestion into a semi-fluid paste of small food particles and gastric juice known as
______________________
 Additional role of the stomach:
Secretes a substance called _____________________, which _________________________
_______________________________________________________________ (vital for survival due to its
role in the production of mature red blood cells)
 Pancreas
An accessory organ of the digestive system and has an ______________________ function
Soft, oblong organ that lies _____________________________________________ in the upper
abdominal cavity
Extends across the abdomen from its ____________ near the duodenum to its __________, which
touches the spleen – middle portion is the _______________
Within the pancreas are groups of exocrine secretory cells called ______________
The secretory cells release a mixture of enzymes known as ___________________________ into the
duct
The ducts from all the acini drain into the pancreatic duct, which fuses with the ___________
_______________________ before entering the small intestine
Scattered among the acini are clusters of endocrine cells called the _____________________
_______________________, which contain the cells that produce the hormones _________
_________________________________ and release them right into the blood
 Functions of the pancreas
Digestive function of the pancreas is the secretion of pancreatic juice, which finds its way into the
duodenum of the small intestine
In an average adult, about 1500mL of this watery, clear fluid is produced daily
The pancreatic enzyme responsible for digesting carbs is known as _____________________
The enzyme that aids in the digestion of fats is called _____________________
The enzymes that digest nucleic acids are called _____________________
 Liver
____________________ visceral organ of the body
Occupies the _____________________ of the abdominal cavity and presses against the diaphragm
Like the pancreas, the liver is associated with the small intestine by way of the common bile duct
One of its primary functions is the production of _______ that is necessary in ____________
____________________________________
 Structure of the Liver
Divided into two main sections, called _______________
The large right lobe and the smaller left lobe
The falciform ligament, a fold of the peritoneum, separates the right and left lobes and suspends the liver
from the diaphragm and anterior abdominal wall
Each lobe is further divided into numerous liver lobules
Liver cells, which are known as ____________________________, are arranged within each liver lobule
into columns that converge toward a central vein
Columns are separated from adjacent columns by channels lined with endothelial cells
These channels are filled with flowing blood and are called _______________________
___________________ remove bacteria arriving with blood from the digestive tract
Bile canaliculi carry a fluid secreted by hepatocytes known as ___________
Bile is a _______________________________ that contains water, bile salts, bile pigments, cholesterol,
and electrolytes
 Functions of the Liver
Digestive role of the liver is the _____________________
Emulsification – breaking apart clumps of _____________________ into tiny droplets
HDL (high density lipoproteins) – _______ lipoproteins
LDL (low density lipoproteins) – ___________________, can cause health problems
 Gallbladder
The gallbladder is a small, thin-walled sac that serves as an accessory organ associated with the liver
It is located immediately behind the liver, where it lies in a shallow depression tucked in against the lower
margin of the right lobe
The main function of the gallbladder is to ________________________________________
_______________________________________________________________
 Small Intestine
Body’s ________________________________ digestive organ
It completes the processes of mechanical and chemical digestion, and is the ______________
_______________________________________________________________
Longest segment of the alimentary canal
Extends from the stomach to the large intestine for about 6 m (_____________)
It is 2.5cm (_____________) in diameter
Suspended in the abdominal cavity by the _____________________, which anchors it to the abdominal
wall
It is framed by the large intestine
Has three segments: duodenum, jejunum, and ileum
Segments of the Small Intestine
_____________________
Receives chyme from the stomach through the pyloric sphincter
Only about 25cm (10 inches) long and is relatively immovable
At the distal end of the duodenum, the small intestine continues as the more mobile jejunum
_____________________
Extends for about 2.5m (8 feet) to the third segment, the ileum
_____________________
Longest segment at about 3.6m (12 feet)
It unites with the large intestine at the _____________________, which helps regulate the flow of
material from the ileum to the large intestine
 Small Intestine Wall
Mucosa
Extremely __________________________________________________________
Has tiny projections known as intestinal ____________
Villi project about 1mm into the lumen of the small intestine where they come in contact with its contents
Covering each villus is the mucosa, whose cells are bristled with thousands of tiny microprojections called
________________________
Within each villus are capillaries and a lymphatic vessel (called a lacteal), which carry absorbed nutrients
away with blood
Submucosa
Contains numerous lymphatic nodules, known as _____________________, which protect the body
against infectious microorganisms that try to penetrate the intestinal wall
Also contains a collection of mucous glands, called __________________________, found only in the
duodenum – help _______________________________________
 Functions of the Small Intestine
Chemical Digestion
____________________________________ by using a mixture of enzymes and bile
Receives a wide spectrum of pancreatic enzymes from the pancreas and bile from the liver by way of the
common bile duct
Breaks down a wide spectrum of food (maltase, lactase, sucrase, and dextrase – all digest
monosaccharides, which are carbs)
Absorption
Small intestine is the main site of nutrient absorption
Effectiveness is due to the vast surface area of its mucosa (villi)
Carb digestion begins in the mouth and ends in the small intestine
Protein digestion by pepsin in the stomach and later in the small intestine by enzymes from the pancreas
and intestinal mucosa results in the availability of amino acids
Fat digestion occurs by the action of bile salts and enzymes within the small intestine
Propulsion
The propulsion of chyme through the small intestine is done by peristalsis
Slow propulsion that takes between _____________________ to move chyme all the way through
Large quantities of water and electrolytes are also absorbed by the villi
Out of ____ liters of water, only _____ passes through to the large intestine
If infection occurs, peristaltic contractions may dramatically increase, causing a very rapid movement of
material through it, __________________________
 Large Intestine
Extends about 1.5m (_____________) from its union with the small intestine at the _______
__________________________________________
Its large diameter, which measures about 7cm (almost _____________), provides it with its name
The main functions of the large intestine are to ____________________________________ by
absorbing water, and to __________________________________________
 Structure of the Large Intestine
Divided into 4 main segments
____________________: receives material from small intestine
Attached to the cecum is the _______________________
Colon: ____________________________________________________________
_______________________________________________________________
Rectum: located against the sacrum in the pelvic cavity; extends downward as a straight tube until it
converges with the last segment of the large intestine, the anal canal
Anal canal
 Wall of the Large Intestine
Its mucosa _____________________ that are found in the small intestine
In the mucosal lining are _____________________________________________________ to allow for
easy passage of fecal matter
Muscular structure is called _____________________
The propulsion of feces through the large intestine and out through the anus is called
_____________________
It normally takes _____________________ for material to pass through the 1.5m of the colon, whereas
it takes only 3 – 10 hours to pass through the 6m of the small intestine