 Omental bursa – a long, double fold of
mesentery that extends inferiorly from
the stomach before looping back to the
transverse
colon
to
create
a
cavity/pocket
 Mesentery proper – attaches the small
intestine to the posterior abdominal wall
DIGESTIVE SYSTEM


With the help of the circulatory system, is like a
gigantic ‘meals on wheels’, serving 100 T
customers the nutrients they need
Has its own quality control and waste disposal
methods
Retroperitoneal – abdominal organs that have no
mesenteries; duodenum, pancreas, ascending +
descending colon, rectum, kidneys, adrenal glands,
urinary bladder
FUNCTIONS (IDEA)
1. Ingestion of food.
2. Digestion of food.
3. Elimination of wastes.
4. Absorption of nutrients.
ANATOMY AND HISTOLOGY
Digestive Tract / Gastrointestinal Tract
 Oral cavity, pharynx, esophagus, stomach, small
intestine, large intestine, anus
Four Tunics
1. Mucosa
 Innermost tunic
 Consists of mucous epithelium, lamina propria
(loose CT), muscularis mucosae (thins SM layer)
 Mouth, esophagus, anus; resists abrasion
 Stomach, intestine; absorbs and secrets
2.


3.


4.



Submucosa
Thick layer of loose CT, consists of nerves, blood
vessels, small glands
Plexus – extensive network of nerve cell
processes (innervated by the autonomic nerves)
Muscularis
Consists of circular SM (inner), longitudinal SM
(outer)
Enteric nervous system – composed of the
nerve plexuses of the submucosa and
muscularis; controls movement and secretion
within the tract
Serosa
Outermost layer
Consists of the peritoneum (smooth epithelial
layer + underlying CT)
Adventitia – connective tissue; regions of the DT
not covered by the peritoneum
Peritoneum
1. Visceral Peritoneum / Serosa
membrane that covers the organs
2.
–
serous
Parietal Peritoneum – serous membrance that
covers the wall of the abdominal cavity
Mesenteries – CT sheets that hold the abdominal cavity
organs in place
a. Lesser omentum – connects the lesser curvature
of the stomack to the liver and diaphragm
b.
Greater omentum – connects the greater
curvature of the stomach to the transverse colon
and posterior body wall
ORAL CAVITY, PHARYNX, AND ESOPHAGUS
Anatomy of Oral Cavity
 Bounded by the lips and cheeks ++ contains the
teeth and tongue
Lips – muscular structures formed by the orbicularis
oris muscle
Cheeks – buccinators muscles flatten the cheeks against
teeth
Mastification – begins the process of mechanical
digestion
Tongue – plays a major role in the process of swallowing;
major sensory organ for taste; one of the major organs of
speech
 Frenulum – thin fold of tissue inferior to the
tongue
Teeth


1.
2.
3.
4.
5.
32 teeth in normal adult mouth
Located in the mandible and maxillae
Incisor – to cut
Canine – to tear
Premolars
Molars
Wisdom teeth – third molars
Permanent teeth – secondary teeth
Primary teeth – deciduous teeth; milk or baby teeth
Parts
a.
b.
c.
d.
Crown
Cusps
Neck
Root
Pulp cavity – center of the tooth; contains blood vessels
nerves, and pulp (connective tissue)
Dentin – bonelike tissue that surrounds the pulp cavity
Enamel – extremely hard, acellular substance that covers
the dentin of the tooth drown
Cementum – covers the surface of the dentin in the root;
anchors the tooth in the jaw
Alveoli (along the alveolar process of mandible x
maxillae) – where the teeth are rooted
Gingiva – dense fibrous CT and most stratified
squamous epithelium that covers the alveolar processes
Periodontal ligaments – CT fibers that extend from the
alveolar walls that hold the teeth in place
Dental caries / Tooth decay – result of the breakdown of
enamel by acids produced by bacteria on tooth surface
Periodontal disease – inflammation x degeneration of
the periodontal ligaments, gingiva, alveolar bone
Palate and Tonsils
Palate – roof of the oral cavity; prevents food from
passing into the nasal cavity during chewing and
swallowing
a. Hard palate – anterior part that contains bone
b. Soft palate – posterior portion that consists of
skeletal muscle _ CT
 Uvula – grape-like; posterior extension of the
soft palate
Tonsils – protect against pathogens from entering the
nose and mouth
Salivary Glands
 Produce saliva (serous + mucous fluids)
3 Pairs of SG
1. Parotid glands – largest; serous glands located
anterior to each ear
2. Submandibular glands – produce more serous
than mucous secretions
3. Sublingual
glands – smallest;
produce
primarily mucous secretions
Esophagus
 Muscular tube that ransports food from the
pharynx to the stomach
 Esophageal sphincters – regulate the movement
of food into and out of the esophagus
 Cardiac sphincter – lower ES
Swallowing / Deglutition
1. Voluntary Phase
 Bolus (mass of food) us formed in the mouth
 Bolus is pushed by the tongue forcing in into the
oropharynx
2.


3.


Pharyngeal Phase
A reflex initiated when a bolus of food
stimulates receptors in the oropharynx
Epiglottis – tipped posteriorly to cover the
larynx
Esophageal Phase
Responsible for moving food form the pharynx
to the stomach
Peristaltic waves – muscular contractions of the
esophagus
STOMACH
 Functions primarily as a storage and mixing
chamber for ingested food
Anatomy
Gastroesophageal opening
esophagus ino the stomach
–
opening
Cardiac
region
– region
of t
gastroesophageal opening; near the heart
from
the
around
the
Fundus – most superior part of the stomach
Mumps – inflammation of the parotid gland caused by
viral infection
Body – largest part of the stomach
 Greater curvature
 Lesser curvature
Saliva
 Helps keep the oral cavity moist
 Contains enzymes that begin the process of
digestion
Pyloric opening – opening from the stomach into the
small intestine
Salivary amylase – a digestive enzyme that breaks the
covalent bonds bet. glucose molecules (starch) and other
polysaccharides; enhances the sweet taste of food
Lysozyme – enzyme that has weak antibacterial action
Mastification
 Breaks large food particles into many small ones
 Increases the efficiency of digestion
Pharynx
 Throat
 Connects the mouth with the esophagus
 Oropharynx + laryngopharynx – transmit food
 Contains pharyngeal constrictor muscles
Pyloric sphincter – thick ring of smooth muscle
Pyloric region – region near the pyloric opening
Outer longitudinal, middle circular, and inner obique
layer – produce a churning action in the stomach
Rugae – large folds where the submucosa and mucosa
are thrown into when the stomach is empty
Gastric pits – openings for the gastric glands; formed by
simple columnar epithelium
Epithelial cells of the Stomach
1. Surface mucous cells – inner surface of stomach
& lining the gastric pits; coats and protects the
stomach lining
2. Mucous neck cells – produce mucus
3.
4.
5.
Parietal cells – produce hydrochloric acid &
intrinsic factor
Endocrine cells – produce regulatory chemicals
Chief cells – produce pepsinogen (precursor of
the protein digesting enzyme pepsin)
Secretions of the Stomach
Chyme – semifluid mixture (food + stomach secretions)
1.
2.
3.
4.
Hydrochloric acid kills microorganisms and
activates pepsin
Pepsin breaks covalent bond of proteins to form
smaller peptide chains.
Mucus lubricates and protects epithelial cells
from the damaging effect of acidic chime +
pepsin
Intrinsic factor binds with vit. B12 (DNA
synthesis and RBC prod.) and makes it more
readily absorbed in the small intestine
Regulation of Stomach Secretions
1. Cephalic phase – stomach secretions are
initiated by the sight, smell, taste, or thought of
food
2. Gastric phase – partially digested proteins and
distention of the stomach promote secretion
 Gastrin – hormone that enters the
circulation and is carried back to the
stomach
3. Intestinal phase – acidic chime in the
duodenum stimulates neuronal reflexes and the
secretion of hormones that inhibit gastric
secretions by negative feedback loops
 Secretin – hormone that inhibits gastric
secretions; released from the duodenum
in response to low pH
 Cholecystokinin – major inhibitor of
gastric motility; released from the
duodenum initiated by fatty acids and
peptides
Movement in the Stomach
 Increased motility = increases emptying
 Distention of stomach = increases gastric
motility
A. Mixing waves – thoroughly mix ingested food
with stomach secretions to form chime
 Fluid part of chime – pushed toward
the pyloric sphincter
 Solid center – moves back toward the
body of the stomach
B. Peristaltic waves – force the chime toward and
through the pyloric sphincter
SMALL INTESTINE
 Major site of digestion and absorption of food
 Major function is the absorption of nutrients
Anatomy
1. Duodenum – 12 in. long
2. Jejunum – 2.5 m long; makes up 2/5
3. Ileum – 3.5 m long; makes up 3/5
Common bile duct (liver) and pancreatic
(pancreas) – join and empty into the duodenum
duct
Increased surface area
1. Circular folds – formed by mucosa and
submucosa that run perpendicular to the long
axis of the digestive tract
2. Villi – formed by tiny, fingerlike projections of
the mucosa
3. Microvilli – numerous cytoplasmic extensions
on the surface of the villi
Lacteal – lymphatic capillary
Simple Columnar Epithelium
1. Absorptive cells – have microvilli, produce
digestive enzymes, absorb digested food
2. Goblet cells – produce a protective mucus
3. Granular cells – help protect the intestinal
epithelium from bacteria
4. Endocrine cells – produce regulatory hormones
Intestinal glands – epithelial cells produced within
tubular galnds of mucosa
Duodenal glands – mucous glands in the submucosa of
the duodenum
Peyer patches – clusters of lymphatic nodules along the
digestive tract
Ileocecal junction – where the ileum connects to the
large intestine
Ileocecal sphincter – ring of smooth muscle
Ileocecal valve – allow intestinal contents to move from
the ileum to the large intestine; but not in opposite
direction
Secretions of the Small Intestine
1. Peptidases – break peptide bonds in proteins to
form amino acids
2.
Disaccharidases – break down disaccharides
(maltose) into monosaccharides (glucose)
Movement of the Small Intestine
A. Peristaltic contractions – proceed along the
length of the intestine for variable distances;
causes the chime to move along the small
intestine
B. Segmental contractions – propagate for shot
distances; mix intestinal contents
LIVER AND PANCREAS
Anatomy of Liver
Major Lobes
1. Right lobe
2. Left lobe
Falciform ligament – CT septum that separates the right
and left lobe of the liver
Smaller Lobes
1. Caudate lobe
2. Quadrate lobe
Pancreatic islet / Islets of Langerhans – endocrine part;
produce insulin and glucagon
Porta – gate through which blood vessels, ducts, and
nerves enter and exit the liver
Sources of Blood in the Liver
1. Hepatic artery – takes oxygen-rich blood to the
liver; supplies liver with oxygen
2. Hepatic portal vein – oxygen-poor blood but
rich in nutrients
Hepatic veins – where blood exits the liver and empty
into the inferior vena cava
Portal Triads
1. Hepatic artery
2. Hepatic portal vein
3. Hepatic duct
Acini – produce digestive enymes
Pancreatic duct – formed by larger ducts from clusters
of acini
Functions of the Pancreas
Major Proteolytic enzymes – continue protein digestion
that began in the stomach
4. Trypsin
5. Chymotrypsin
6. Carboxypeptidase
Pancreatic amylase – continues polysaccharide digestion
that began in the oral cavity
Hepatic cords – located bet. the center and margins of
each lobule
Hepatocytes – platelike groups that form the hepatic
cords
Hepatic sinusoids – blood channels that separates the
hepatic cords from one another
Central vein – where mixed blood flows toward the
center of each lobule
Bile canaliculus – a cleftlike lumen bet. the cells of each
hepatic cord
Common hepatic duct – right + left hepatic ducts
Common bile duct – common hepatic duct + cystic duct
Gallbladder – stores and concentrates bile
Duodenal papilla – where the common bile duct joind
the pancreatic duct and opens into the duodenum
Functions of the Liver
1. Digestion
2. Excretion
3. Nutrient storage
4. Nutrient conversion
5. Detoxification of harmful chemicals
6. Synthesis of new molecules
Bile salts – emulsify fats
that
results
Anatomy of Pancreas
1. Head – near the midline of the body
2. Tail – extends to the left
Lipase – lipid-digesting enzyme
Nucleases – enzymes that degrade DNA and RNA to
their component nucleotides
LARGE INTESTINE
Anatomy
Cecum
 Proximal end of the large intestine
Appendix – 9 cm tube attached to the cecum
Colon
5.
6.
7.
8.
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Crypts – straight, tubular glands in the mucosal lining of
the colon
Teniae coli – three bands
Rectum
 Straight, muscular tube that begins at the
termination of sigmoid colon & ends at the anal
canal
Anal Canal
 Begins at the inferior end of the rectum and ends
at the anus (external digestive tract opening)
Bile – dilutes and neutralizes stomach acid; dramatically
increases the efficiency of fat digestion and absorption;
stimulated by secretin
Bilirubin – bile pigment
breakdown of hemoglobin
Compound acinar gland – exocrine part
from
the
Internal anal sphincter – smooth muscle layer at
superior end
External anal sphincter – skeletal muscle at inferior end
Hemorrhoids – enlarged or inflamed rectal or
hemorrhoidal, veins that supply the anal canal; may
cause pain, itching, bleeding around anus
Functions of Large Intestine
3. Feces production
4. Water absorption
Feces – converted chyme
Lipase – secreted by pancreas; digests lipid molecules
Defecation – elimination of feces from the colon
Micelles – aggregated bile salts around small droplets of
digested lipids
Mass movements – strong contractions in the large parts
of the colon; propel the colon contents a considerable
distance towards the anys
Defecation reflex – local (weak contractions)
parasympathetic (strong contractions) reflexes
+
DIGESTION, ABSORPTION, AND TRANSPORT
Digestion – breakdown of food to molecules tha are
small enough to be absorbed into the circulation
a. Mechanical digestion – breaks large good
particles into smaller ones
b. Chemical digestion – breaking of covalent
chemical bonds in organic molecules by
digestive enzymes
Absorption – begin in stomach; lipid-soluble molecules
diffuse through the stomach epithelium into the
circulation
Transport – requires carrier molecules and includes
facilitated diffusion, cotransport, and active transport
Carbohydrates
 Consist primarily of starches, cellulose, sucrose
(table sugar), small amounts of fructose (fruit
sugar), and lactose (milk sugar)
Polysaccharides – large carbohydrates that consist of
many sugars linked by chemical bonds
Salivary amylase – begins
carbohydrates in the mouth
Pancreatic
amylase
carbohydrates
Disaccharides
polysaccharide
–
–
two
the
digestion
of
continues
digestion
of
sugars;
broken
down
Disaccharidase – group of enzymes that break the
disaccharides to monosaccharides
Monosaccharides – single sugars; glucose, galactose,
and fructose
Lipids
 Molecules which are insoluble or slightly
soluble in water
Triglycerides – most common type of lipid; 3 fatty acids
bound to glycerol
Saturated – fatty acids have only single bonds
Unsaturated – fatty acids have one or more double
bonds
Emulsification – large lipid droplets are transformed
into much smaller droplets
Chylomicrons
(lipoproteins)
–
packaged
lipid-protein
complexes
Chyle – lymph containing late amounts of absorbed
lipid
Proteins
 Chains of amino acids
Pepsin – enzyme secreted by stomach that breaks down
proteins
Polypeptides – shorter amino acid chains
Trypsin, Chymotrypsin, Carboxypeptidase – enzymes
produced by pancreas that continue the digestive
process
Peptidases – small peptides
Water and Minerals
 Approximately 9 L of water enters the digestive
tract
 Approximately 2 L from food & drink &
remaining 7 liters is from digestive secretions
