The document discusses the anatomy and functions of the digestive system. It begins by outlining the main functions as ingestion, digestion, absorption of nutrients, and elimination of waste. It then describes the major organs that make up the digestive tract, including the mouth, esophagus, stomach, and small and large intestines. It provides detailed information on the layers, tissues, and cell types that compose each organ. Throughout, it emphasizes the roles and secretions of each organ in the breakdown and absorption of food.

1. FUNCTIONS (IDEA)
1. Ingestion of food.
2. Digestion of food.
3. Elimination of wastes.
4. Absorption of nutrients.
ANATOMY AND HISTOLOGY
▪ 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
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. Submucosa
▪ Thick layer of loose CT, consists
of nerves, blood vessels, small
glands
▪ Plexus – extensive network of
nerve cellprocesses (innervated
by the autonomic nerves)
3. 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
4. ISerosa
▪ 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 – serous
membrane that covers the
organs
2. Parietal Peritoneum – serous
membrane thatcovers the wall
of the abdominal cavity
Mesenteries – CT sheets that hold the
abdominal cavityorgans in place
a. Lesser omentum – connects the
lesser curvatureof the stomach
to the liver and diaphragm
DIGESTIVE SYSTEM
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2. b. Greater omentum – connects
the greater curvature of the
stomach to the transverse colon
and posterior body wall
❖ 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
Retroperitoneal – abdominal organs
that have no mesenteries; duodenum,
pancreas, ascending + descending
colon, rectum, kidneys, adrenal
glands,urinary bladder
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
Mastication – 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 thetongue
Teeth
▪ 32 teeth in normal adult mouth
▪ Located in the mandible and
maxillae
1. Incisor – to cut
2. Canine – to tear
3. Premolars
4. Molars
5. Wisdom teeth – third molars
Permanent teeth – secondary teeth
Primary teeth – deciduous teeth; milk or
baby teeth
Parts
a. Crown
b. Cusps
c. Neck
d. 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 coversthe 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
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3. 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
Mumps – inflammation of the parotid
gland caused by viral infection
Saliva
▪ Helps keep the oral cavity moist
▪ Contains enzymes that begin the
process of digestion
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
Tongue – house taste buds and mucus
Mastication
• 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
Esophagus
▪ Muscular tube that ransports
food from thepharynx to the
stomach
▪ Esophageal sphincters –
regulate the movementof food
into and out of the esophagus
▪ Cardiac sphincter – lower ES
Swallowing / Deglutition
1. Voluntary Phase
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4. ▪ Bolus (mass of food) us formed
in the mouth
▪ Bolus is pushed by the tongue
forcing in into theoropharynx
2. Pharyngeal Phase
▪ A reflex initiated when a
bolus of food stimulates
receptors in the oropharynx
▪ Epiglottis – tipped posteriorly
to cover thelarynx
3. Esophageal Phase
▪ Responsible for moving food
form the pharynx to the
stomach
▪ Peristaltic waves – muscular
contractions of theesophagus
STOMACH
▪ Functions primarily as a
storage and mixing chamber
for ingested food
Anatomy
Gastroesophageal opening– opening
from theesophagus into the stomach
Cardiac region – region of
around the gastroesophageal
opening; near the heart
Fundus – most superior part of the
stomach
Body – largest part of the stomach
❖ Greater curvature
❖ Lesser curvature
Pyloric opening – opening from the
stomach into thesmall intestine
Pyloric sphincter – thick ring of smooth
muscle
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5. Pyloric region – region near the pyloric
opening
Outer longitudinal, middle circular,
and inner oblique layer – produce a
churning action in the stomach
Rugae – large folds where the
submucosa and mucosaare 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. Parietal cells – produce
hydrochloric acid &intrinsic
factor
4. Endocrine cells – produce
regulatory chemicals
5. Chief cells – produce
pepsinogen (precursor ofthe
protein digesting enzyme
pepsin)
Secretions of the Stomach
Chyme – semifluid mixture (food +
stomach secretions)
1. Hydrochloric acid kills
microorganisms and activates
pepsin
2. Pepsin breaks covalent bond of
proteins to form smaller
peptide chains.
3. Mucus lubricates and protects
epithelial cells from the
damaging effect of acidic chime
+ pepsin
4. 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
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6. 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 gastricmotility
A. Mixing waves – thoroughly
mix ingested foodwith
stomach secretions to form
chime
➢ Fluid part of chime –
pushed towardthe
pyloric sphincter
➢ Solid center – moves
back toward thebody
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;
contains absorptive cells, goblet
cells. Granular cells and
endocrine cells
2. Jejunum – 2.5 m long; makes
up 2/5
3. Ileum – 3.5 m long; makes up
3/5
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7. Common bile duct (liver) and
pancreatic duct
(pancreas) – join and empty into the
duodenum
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, producedigestive
enzymes, absorb digested
food
2. Goblet cells – produce a
protective mucus
3. Granular cells – help protect
the intestinalepithelium 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;
collection of lymphatic tissue
Ileocecal junction – where the ileum
connects to thelarge 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 toform
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 shotdistances;
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
Porta – gate through which blood
vessels, ducts, andnerves enter and
exit the liver
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8. Sources of Blood in the Liver
1. Hepatic artery – takes oxygen-
rich blood to theliver; supplies
liver with oxygen
2. Hepatic portal vein – oxygen-
poor blood butrich in nutrients
Hepatic veins – where blood exits the
liver and emptyinto the inferior vena
cava
Portal Triads
1. Hepatic artery
2. Hepatic portal vein
3. Hepatic duct
Hepatic cords – located bet. the center
and margins ofeach lobule
Hepatocytes – platelike groups that
form the hepaticcords
Hepatic sinusoids – blood channels
that separates thehepatic cords from
one another
Central vein – where mixed blood
flows toward thecenter of each lobule
Bile canaliculus – a cleftlike lumen bet.
the cells of eachhepatic 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 joindthe 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 – dilutes and neutralizes stomach
acid; dramatically increases the
efficiency of fat digestion and
absorption; stimulated by secretin
Bile salts – emulsify fats
Bilirubin – bile pigment that results
from the breakdown of hemoglobin
Anatomy of Pancreas
1. Head – near the midline of the
body
2. Tail – extends to the left
Pancreatic islet / Islets of Langerhans
– endocrine part;produce insulin and
glucagon
Compound acinar gland – exocrine
part
Acini – produce digestive enymes
Pancreatic duct – formed by larger
ducts from clustersof acini
Functions of the Pancreas
Major Proteolytic enzymes – continue
protein digestionthat began in the
stomach
1. Trypsin
2. Chymotrypsin
3. Carboxypeptidase
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9. Pancreatic amylase – continues
polysaccharide digestionthat began in
the oral cavity
Lipase – lipid-digesting enzyme
Nucleases – enzymes that degrade
DNA and RNA totheir component
nucleotides
LARGE INTESTINE
Anatomy Cecum
▪ Proximal end of the large
intestine
Appendix – 9 cm tube attached to the
cecum
Colon
1. Ascending colon
2. Transverse colon
3. Descending colon
4. 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)
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
1. Feces production
2. Water absorption
Feces – converted chyme
Defecation – elimination of feces from
the colon
Mass movements – strong contractions
in the large partsof 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
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10. sugar), and lactose (milk sugar)
Polysaccharides – large carbohydrates
that consist of many sugars linked by
chemical bonds
Salivary amylase – begins the digestion
of carbohydrates in the mouth
Pancreatic amylase – continues
digestion of carbohydrates
Disaccharides – two sugars; broken
down polysaccharide
Disaccharidase – group of enzymes
that break the disaccharides to
monosaccharides
Monosaccharides – single sugars;
glucose, galactose, and fructose
Lipids
▪ Molecules which are insoluble
or slightlysoluble 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
Lipase – secreted by pancreas; digests
lipid molecules
Micelles – aggregated bile salts around
small droplets ofdigested lipids
Chylomicrons – packaged lipid-
protein complexes (lipoproteins)
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 digestivetract
▪ Approximately 2 L from food
& drink &remaining 7 liters is
from digestive secretions
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