The document outlines the functions and anatomy of the digestive system, detailing the roles of ingestion, digestion, absorption, and elimination. It describes the components of the digestive tract, including the mouth, esophagus, stomach, small intestine, and large intestine, as well as associated organs like the liver and pancreas. Additionally, it explains the processes involved in digestion and absorption, highlighting the significance of various glands and enzymes.

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Chapter 16
Digestive System
Lecture Outline
Seeley’s ESSENTIALS OF
ANATOMY & PHYSIOLOGY
Eleventh Edition
Cinnamon VanPutte
Jennifer Regan
Andrew Russo
Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.

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Digestive System Functions
1. Ingestion and mastication – ingestion is the
consumption of solid or liquid food. Mastication is
chewing.
2. Propulsion and mixing - Propulsion is the movement of
food from one end of the digestive tract to the other.
Mixing is the movement of food back and forth in the
digestive tract to mix it with enzymes and facilitate
absorption.
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Digestive System Functions
3. Digestion and secretion - Digestion is the mechanical
and chemical breakdown of large molecules into smaller
molecules that can be absorbed. Secretion is the addition
of liquids, enzymes, and mucus to the ingested food.
4. Absorption - the movement of molecules out of the
digestive tract and into the blood or lymphatic system.
5. Elimination - Elimination is the removal of undigested
material, such as fiber from food, plus other waste
products from the body as feces.
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Anatomy of the Digestive System
The digestive tract consists of the:
• oral cavity (mouth)
• pharynx
• esophagus
• stomach
• small intestines
• large intestines
• anus
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Associated Organs
The digestive system includes some associated organs,
not directly in the digestive tract, that have ducts that lead
into the tract.
These associated organs are the:
• salivary glands
• liver
• gallbladder
• pancreas
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Layers of Digestive Tract Wall
The layers of the tract wall are also termed tunics.
1. Mucosa:
• innermost layer
• secretes mucus
2. Submucosa:
• above mucosa
• contains blood vessels, nerves, small glands
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Layers of Digestive Tract Wall
3. Muscularis:
• above submucosa
• longitudinal, circular, and oblique muscles
4. Serosa/adventitia:
• outermost layer
• If peritoneum is present- serosa
• If no peritoneum- adventitia
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Peritoneum and Mesentery
Visceral peritoneum - or serosa, is the serous membrane
that covers the organs.
Parietal peritoneum - is the serous membrane that lines the
wall of the abdominal cavity
Mesenteries - connective tissue sheets that hold organs in
place in the abdominal cavity
Lesser omentum - mesentery connecting lesser curvature
of stomach to liver and diaphragm
Greater omentum - mesentery connecting greater curvature
of stomach to transverse colon and posterior body wall
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Salivary Glands
Produce saliva which is a mixture of serous (watery) and
mucous fluids:
• Keeps the oral cavity moist
• Needed for normal speech
• Dissolves food particles so they can be tasted
• Protects against bacteria and neutralizes pH
• Begins the process of digestion
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Salivary Glands
Salivary Glands:
• Parotid - serous glands anterior to each ear.
• Submandibular - found along the inferior border of the
mandible; produce more serous than mucous secretions
• Sublingual - produce primarily mucous and lie below
the mucous membrane in the floor of the oral cavity.
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Salivary Glands
 Serous (liquid) portion of saliva contains enzymes
 Mucous portion of saliva contains mucin for lubrication
Amylase - digestive enzyme that breaks down
carbohydrates
Lysozyme - enzymes that are active against bacteria
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Pharynx
 Throat
 Connects the mouth to the
esophagus
It has three parts:
• nasopharynx
• oropharynx
• laryngopharynx
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Esophagus
 Tube that connects the pharynx to the stomach
 Transports food to the stomach
 Joins stomach at cardiac opening
Heartburn:
• occurs when gastric juices regurgitate into esophagus
• caused by caffeine, smoking, or eating or drinking in
excess
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Phases of Swallowing
Voluntary phase:
• bolus (mass of food) formed in mouth and pushed into
oropharynx
Pharyngeal phase:
• swallowing reflex initiated when bolus stimulates
receptors in oropharynx
Esophageal phase:
• moves food from pharynx to stomach
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Stomach
• Located in the abdomen
• Storage tank for food
• Can hold up to 2 liters of food
• Produces mucus, hydrochloric acid, protein digesting
enzymes
• Contains a thick mucus layer that lubricates and protects
epithelial cells on stomach wall from acidic pH (3)
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Regions of the Stomach
• The esophagus opens into the cardiac part.
• The fundus is to the left of, and superior to the cardiac
part.
• The body is largest part of the stomach.
• The body turns to the right, creating a greater
curvature and a lesser curvature.
• The body narrows inferiorly to form the funnel-shaped
pyloric part of the stomach.
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Stomach
Muscularis has 3 layers:
• outer longitudinal
• middle circular
• inner oblique to produce churning action
Rugae:
• large folds that allow stomach to stretch
Chyme
• paste-like substance that forms when food begins to be
broken down
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Stomach
Pyloric opening:
• opening between stomach and small intestine
Pyloric sphincter:
• thick, ring of smooth muscle around pyloric opening
which regulates movement of food into the small
intestine
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Epithelial Cells in the Stomach
Surface mucous cells - produce mucus that coats and
protects the stomach
Mucous neck cells - produce mucus
Parietal cells - produce hydrochloric acid and intrinsic factor
Endocrine cells - produce hormones and paracrine
molecules
Chief cells - produce pepsinogen, a precursor of the
protein-digesting enzyme pepsin
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Secretions of the Stomach
Hydrochloric acid
• Produces a pH of about 2.0 in the stomach.
• Kills microorganisms, activates pepsin.
Pepsin
• breaks covalent bonds of proteins to form smaller peptide chains
Mucus
• A thick layer, which lubricates the mucosa of the stomach
• Protects mucosa from acidic chyme and pepsin
Intrinsic factor
• Binds with vitamin B12 making it more readily absorbed by small
intestine
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Movement in Stomach
Mixing waves:
• weak contraction
• thoroughly mix food to form chyme
Peristaltic waves:
• stronger contraction
• force chyme toward and through pyloric sphincter
Stomach empties every 4 hours after regular meal,
and 6 to 8 hours after high fatty meal
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Small Intestine
• Measures 6 meters in length
• Major absorptive organ of the gastrointestinal tract
• Chyme takes 3 to 5 hours to pass through
• Contains enzymes to further breakdown food
• Contains secretions for protection against the acidity of
chyme
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Anatomy of Small Intestine
Duodenum:
• first part
• 25 cm long
• contains absorptive cells, goblet cells, granular cells,
endocrine cells
• contains microvilli and many folds
• contains bile and pancreatic ducts
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Anatomy of Small Intestine
Jejunum:
• second part
• 2.5 meters long
• Primary site of nutrient absorption
Ileum:
• third part
• 3.5 meters long
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Mucosa of the Small Intestine
The mucosa of the small intestine is simple columnar
epithelium with four major cell types.
1. Absorptive cells, which have microvilli, produce digestive
enzymes, and absorb digested food
2. Goblet cells, which produce a protective mucus
3. Granular cells, which may help protect the intestinal
epithelium from bacteria; and
4. Endocrine cells, which produce regulatory hormones.
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Secretions of the Small Intestine
Secretions of mucus, ions, and water lubricate and protect
the intestinal wall from the acidic chyme and digestive
enzymes.
• Peptidases enzymatically breakdown proteins into amino
acids for absorption.
• Disaccharidases enzymatically breakdown disaccharides
into monosaccharides for absorption.
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Movement in the Small Intestine
• Peristaltic contractions along the length of the intestine
cause the chyme to move along the small intestine.
• Segmental contractions are propagated for only short
distances and mix intestinal contents.
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Liver Anatomy
Weighs about 3 lbs.
Located in the right upper quadrant of the abdomen under
the diaphragm
Consists of right, left, caudate, and quadrate lobes
Porta:
• gate where blood vessels, ducts, nerves enter and exit
• Receives blood from the hepatic artery and hepatic
portal vein
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Liver Ducts
Hepatic duct:
• transports bile out of liver
Common hepatic duct:
• formed from left and right hepatic duct
Cystic duct:
• joins common hepatic duct
• drains gallbladder
Common bile duct:
• formed from common hepatic duct and cystic duct
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Functions of the Liver
 Digestive and excretory functions
 Stores and processes nutrients
 Detoxifies harmful chemicals
 Synthesizes new molecules
 Secretes 700 milliliters of bile each day
Bile:
• dilutes and neutralizes stomach acid and breaks down
fats
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Pancreas
• Located posterior to stomach in inferior part of left upper
quadrant
• Head near midline of body
• Tail extends to left and touches spleen
• Endocrine tissues have pancreatic islets that produce
insulin and glucagon
• Exocrine tissues produce digestive enzymes that travel
through ducts to duodenum
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Pancreatic Secretions
The major protein-digesting enzymes are:
1. Trypsin
2. Chymotrypsin
3. Carboxypeptidase
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Pancreatic Secretions
• Pancreatic amylase continues the polysaccharide
digestion that began in the oral cavity.
• The pancreatic enzyme lipase is a lipid-digesting enzyme.
• The pancreatic nuclease enzymes degrade DNA and
RNA to their component ucleotides.
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Large Intestine
 Absorbs water from indigestible food and create
compact feces
 Contains cecum, colon, rectum, anal canal
Cecum:
• joins small intestine at ileocecal junction
• has appendix attached
Appendix:
• 9 cm structure that is often removed
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Large Intestine
Colon:
• 1.5 meters long
• contains ascending, transverse, descending, sigmoid
regions
Rectum:
• straight tube that begins at sigmoid colon and ends at
anal canal
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Large Intestine
Anal canal:
• last 2 to 3 cm of digestive tract
Food takes 18 to 24 hours to pass through large
intestine
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Large Intestine
• Feces formation is due to absorption of water and salts,
secretion of mucus, and action of microorganisms.
• The colon stores the feces until defecation.
• Every 8 to 12 hours strong contractions, called mass
movements propel the colon contents toward the anus.
• Movement of feces into the rectum distends the rectal wall
and stimulates the defecation reflex.
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Digestive Process
1. Digestion:
• Chemical and mechanical breakdown of food
2. Absorption:
• Most absorption occurs in the duodenum and jejunum,
although some occurs in the stomach and ileum
3. Transport:
• moves food through digestive tract, includes swallowing
and peristalsis
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