LJGC
DIGESTIVE SYSTEM
1. Mucosa:
-
Innermost layer
Secretes mucus
consists of three layers:
a. the
inner
mucous
epithelium
b. loose connective tissue
called the lamina propria
c. thin outer layer of smooth
muscle, the muscularis
mucosae
2. Submucosa:
-
Above mucosa
Contains blood vessels, nerves,
small glands
3. Muscularis:
-
Above submucosa
Smooth muscles
 Circular – inner layer
 Longitudinal – outer layer
4. Serosa/Adventitia:
-
Functions:
1. Ingestion - is the consumption of solid or
liquid food, usually through the mouth.
2. Digestion - breakdown of large organic
molecules into smaller molecules that can be
absorbed.
 Mechanical – breakdown of food into
digestible particle mainly by the teeth
 Chemical – refers to the process by
which compounds with a high
molecular weight into food are broken
down to small substances that can be
absorb by the body
3. Absorption - movement of molecules out of
the digestive tract and into the blood or
lymphatic system
4. Elimination - removal of undigested
material, such as fiber from food, plus other
waste products from the body as feces
-
Outermost layer
Serosa
 Peritoneum: which is a
smooth epithelial layer, and
its underlying connective
tissue
Adventitia
 No
peritoneum:
continuous
with
the
surrounding
connective
tissue
Peritoneum




Serous membrane
Layer of smooth epithelial tissue
Visceral peritoneum
- Covers the organs
Parietal peritoneum
- Lines the wall of abdominal cavity
Digestive System
- consists of the digestive tract, or
gastrointestinal plus specific associated
organs
Layers of Digestive System
Mesenteries
-
Connective tissue sheets holds the
organs in abdominal cavity in place
provide a route for blood vessels and
nerves from the abdominal wall to the
organs
Consist of two layers of serous
membranes with a thin layer of loose
connective tissue between them
LJGC
Lesser omentum
-

Tongue
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
-

Teeth
-
Oral Cavity




First part of digestive system
Bounded by lips and cheeks
Contains the teeth and tongue
Lips
o
o
o
o
Orbicularis oris muscle
Outer surface covered by skin
(keratinized stratified epithelium)
The color from the underlying blood
vessels can be seen through the thin,
transparent epithelium, giving the lips
a reddish-pink appearance
Internal margin of the lips – moist
stratified squamous epithelium
Large, muscular organ
Attached at posterior part of the
oral cavity
Anterior part – relatively free
except for an anterior attachment
to the floor – FRENULUM
Anterior 2/3
 Covered by papillae
 Contains taste buds
Posterior 1/3
 Idevoid of papillae
 Few scattered taste buds
 Contains lingual tonsils
-
3 regions
 Crown
 Visible portion of a
tooth
 Neck
 Root
 Largest
 Anchors
in
jawbone
Center of tooth is pulp cavity
Dentin – living, cellular, calcified
tissue suurounding the pulp
cavity
Enamel is hard covering protects
against abrasions
Cementum – helps anchor tooth
in the jaw
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
Salivary Glands
-
-
Produce saliva which contains enzymes
to breakdown carbohydrates into glucose
Cleanse mouth
Dissolve and moisten food
Parotid glands
- Largest glands located just
anterior to each ear
Submandibular glands
- Produce more serous than
mucous secretion
- Located along the inferior border
of mandible
Sublingual glands
- Smallest
- Produce mucous secretions
- Lie below the mucous membrane
in the floor of the oral cavity
Dental caries
- Tooth decay: result of the breakdown of
enamel by acids produced by bacteria on
the tooth surface
Periodontal disease
- Inflammation and degeneration of the
periodontal ligaments, gingiva, and
alveolar bone
- Most common cause of tooth loss in
adults

Palate
-
Roof of the oral cavity
Hard palate
o Anterior part: anterior part
contains bone
Soft palate
- Posterior part: consists of skeletal
muscle and connective tissue
 Mumps
o Inflammation of the parotid gland
caused by a viral infection
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 Saliva
-
Contains enzymes
1L per day
Amylase
- Produced
by
parotid
and
submandibular glands serous
part of the saliva
- Salivary enzyme that breaks
down carbohydrates
Lysozyme
- Salivary enzymes that are active
against bacteria
Mucin
- Proteoglycan that gives a
lubricating
quality
to
the
secretions of the salivary glands
-
 Mastication
Incisors and canine – cut and tear food
Premolars and molars – crush and grind
Breaks large food particles into small
ones



 Pharynx
o
o
Throat
Connects mouth to esophagus
 Esophagus
o
o
o
o
o
Tube that connects pharynx to stomach
25cm long
Lies anterior to the vertebrae and
posterior to the trachea
Upper 2/3 – skeletal muscle
Lower 1/3 – smooth muscle

Heartburn
o
o

Occurs when gastric juices reguritate
into esophagus
Caused by coffeine smoking, or
eating or drinking in excess
Swallowing
o
Three phases:
 Voluntary phase – bolus
(mass of food) formed in
mouth and pushed into
oropharynx
 Pharyngeal
phase
–
swallowing reflex initiated
when
bolus
stimulates
receptors intoi oropharynx
 Esophageal phase – moves
food from pharynx to stomach
 Peristalsis: wave-like
contractions moves
food through digestive
tract
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 Stomach
o
o
o
o
o
o
o
o
o
o
o
o
o
Houses
food
for
mixing
with
hydrochloric acid and other secretions
Enlarged segment of digestive tract in
the left superior part of abdomen
Gastroesophageal opening
 Opening of esophagus into the
stomach
Cardiac region
Fundus
 Most superior part
Body
 Largest part
Greater and lesser curvature
Pyloric opening
 Opening into the small intestine
 Pyloric sphincter: thick ring of
smooth muscle
Pyloric region
Muscle layers
- Outer longitudinal
- Middle circular
- Inner oblique
Rugae
- Wrinkles
- Large folds
Simple columnar epithelium
Gastric pits
- Opening for gastric glands
Secretions of the stomach

Chyme
o

Hydrochloric acid
o

o
o
o
o
5 groups of epithelial cells
- Surface mucous cells
- 4 epithelial cells located in gastric
glands
 Mucous neck cells
 Parietal cells
 Endocrine cells
 Chief cells
Binds with vitamin B12 and make it
really absorbed in small intestine
Heart burn
o
o
o
Thick layer
Lubricates the epithelil cells of
stomach wall
Protects from damaging effect of
acidic chyme and pepsin
Instrinsic Factor
o

Converted from its inactive form –
Pepsinogen
Breaks covalent bonds oif protein
form smaller peptide chains
Mucus
o
o

Produces 2.0 pH
Pepsin
o

Paste-like substance that form when
food begins to be broken down
Gastritis
Painful or burning sensation in the
chest usually associated with an
increase in gastric acid secretion
and/or backflush of acidic chyme into
the esophagus
Causes
 Overeating:
eating
fatty
foods,
lying
down
immediately after a meal,
consuming too much alcohol
or caffeine, etc.
Treatment: medications
Regulation of Stomach Secretion
 Approximately 2L gaastric juice produced each
day
 Regulated by nervous and hormonal
mechanism
 Neural mechanism – CNS reflexes intergated
within medulla oblongata
 Local relfexes – enteric plexus
LJGC
 3 Phases:
1. Cephalic – get started
2. Gastric – go for it
3. Intestinal – slow down

Cephalic phase:
- 1st phase
- Stomach secretions are initiated
by sight, smell, taste, or food
thought
Gastrin
- Source: gastric glands
- Increases gastric secretions

Gastric phase:
- 2nd phase
- Partially digested proteins and
distention of stomach promote
secretion

Intestinal phase:
- 3rd phase
- Acidic chyme stimulates neuronal
reflexes and secretions of
hormones that inhibit gastric
secretions by negative feedback
loops
Movement in Stomach
 2 types


Mixing waves
 Weak contraction
 Thoroughly mix food to form
chyme
Peristaltic waves
 Stronger contraction
 Force chyme forward and
through pyloric sphincter
 Hunger pangs
-
Uncomfortable sensations
Occur foir about 2-3 minutes
Usually begins 12 to 24 hours
after the previous meal
- Stomach “growling”
 Stomach empties every 4 hours after regular
meal, and 6-8 hours after high fatty meal
 Hormonal and neural mechanism stimulate
stomach secretions
Small Intestine







Measures 6 meters in length
3 parts
- Duodenum
- Jejunum
- Ileum
Major absorptive organ
Chyme takes 3-5 hours to pass through
Contains enzymes to further breakdown
food
Contains secretions for protection
against chyme’s acidity
Three modifications: increase its surface
are
- Circular folds
 Run perpendicular to the
long axis of digestive tract
- Villi
 Tiny fingerlike projections
of mucosa
 0.5 – 1.5 mm long
- Microvilli
 Cytoplasm extensions
LJGC
Secretions of Small Intestine




Contains mainly mucus, ion, water
Lubricate and protect the intestinal wall from
the acidic chyme and the action of digestive
enzymes
Peptidases
- Digest proteins to form amino
acids
Disaccharidases
- Digest small sugars
Movement in the Small Intestine




4 major cell types
- Absorptive cells
- Goblet cells
- Granular cells
- Endocrine cells
Intestinal glands – crypts of lieberkuhn
- Epithelial cells are located
- Granular and endocrine located
at bottom of the glands
Duodenal glands

Peristatic contractions
- Proceed along the length of the
intestine causing chyme to move
along the small intestine
Segmental contractions
- Propagated for only short
distance and mix intestinal
contents
Cecum




Proximal end of the large intestine
Located in the right lower quadrant of the
abdomen near iliac fossa
Sac, extending inferiorly about 6cm past
ileocecal junction
Apendix
o Tube about 9cm long
o Attached to cecum
Appendicitis



Inflammation of the appendix
Usually because of an obstruction
Symptoms:
o Sudden abdominal pain (right lower
quadrant):
 McBurney Point
- Midway between
uimbilicus
and
right superior iliac
sine of the coxal
bone
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
o Slight fever
o Loss of appetite
o Constipation or diarrhea
o Nausea and vomiting
Treatment:
o Surgery (appendectomy)
Colon



4 parts
o Ascending colon
- Extends superiorly from the
cecum to the right colic flexure
o Transverse colon
- Extends from right colic flexure to
left colic flexure near the spleen
o Descending colon
- Extends from left colic flexure to
the pelvis
o Sigmoid colon
- S shaped tube
- Extends
medially
and
inferiorlyinto pelvic cavity
Crypts
o Contains many mucus producing
goblet cells
Teniae coli
o Three bands
Rectum


Straight muscular tube
Composed of thick smooth muscle
Liver Anatomy
-
-
-
-
Anal Canal




Last 2-3cm of digestive tract
Internal anal sphincter – smooth muscle
External anal sphincter – skeletal muscle
Hemorrhoids
- Enlarged or inflamed rectal or
hemorrhoidal veins that supply
the anal canal
- Treatment:
 Fiber diet
 Sitz bath
 Hydrocortisone
suppositories
Large Intestine






18-24 hours for material to pass through
Chyme converted to feces
Defecation:
o Process of eliminating feces
Numerous microorganisms inhabit colon
o Some bacteria synthesize vitamin K
Mass movement
Defecation reflex
Bile
Weighs about 3lbs
In right upper quadrant of
abdomen under diaphragm
Hepatic artery
 Delivers
oxygenated
blood to liver
Hepatic portal vein
 Carries nutrient rich blood
from digestive tract to liver
Hepatic veins
 Blood exits the liver
 Empty into inferior Vena
Cava
Lobules
 Divisions of liver with
portal triads of corners
Portal triad
 Contain hepatic artery,
hepatic
portal
vein,
hepatic duct
Hepatic cords
 Between center margins
of each lobule
 Separated by hepatic
sinusioids
Liver Ducts
-
-
Hepatic duct
 Transport bile out of liver
Common hepatic duct
 Formed from left and right
hepatic duct
Cystic duct
 Joins common hepatic
duict
 From gallbladder
Common bile duct
 Formed from common
hepatic duct and cystic
duct
Gallbladder
-
Small sac on inferior surface of
liver
Stores and concentrates bile
LJGC
Liver Functions
-
Bile
o
o
-
Important for digestion
Dilutes and neutralizes stomach acid
-
Bile salts
o
Emulsify fats, breaking the fat globules
into smaller droplets
Bilirubin
o
Bile pigments results from breakdown of
hemoglobin
Functions of Pancreas
-
Gallstones
o






Form it amount of cholesterol secreted by
liver becomes excessive and is not able
to be dissolved by bile salts
Digestion
Excretion
Nutrient storage
Nutrient conversion
Detoxicification of harmful chemicals
Synthesis of new molecules
Exocrine
tissues
produce
digestive enzymes
Exocrine part- compound acinar
gland
Acini
 Produce
digestive
enzymes
-
Pancreatic enzymes
Major protein digesting enzymes
 Trypsin
 Chymotrypsin
 Carboxypeptidase
Pancreatic amylase
Lipase
Nucleases
Digestive Process
1. Digestion: (Mechanical and Chemical)
 Breakdown of food occurs in
stomach and mouth
2. Propulsion
 Moves food through digestive tract
includes swallowing and peristalsis
3. Absorption
 Primarily in duodenum and jejunum
of small intestine
4. Defecation
 Elimination of waste in the form of
feces
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 islet that produce
insulin and glucagon
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Carbohydrate Digestion
-
-
-
Polysaccharides
split
into
disaccharides
 Salivary and pancreatic
amylases
Disaccharides broken down into
monosaccharides
 Disaccharides on surface
of intestinal epithelium
Glucose
is
absorbed
by
cotransport with Na+ into
intestinal epithelium
Glucose is carried by hepatic
portal vein to liver and enters
most
cells
by
facilitated
diffusion
Lipid Digestion
-
-
Bile salts emulsify lipids
Lipase breaks down lipids which
form micelles
Micelles are in contact with
intestinal epithelium and diffuse
with cells where they are package
and released into lacteals
Lipids are stored in adipose
tissue and liver
Water and Minerals
-
Water can move across intestinal
wall in either direction
Depends on osmotic conditions
99% of water entering intestine is
absorbed
Minerals are actively transported
across wall of small intestine
Diarrhea
-
-
Any change in bowel habits
involving
increase
stool
frequency or volume or increase
stool fluidity
Not a disease in itself
Symptom of a wide variety of
disorders
Acute and Chronic
Effects of Aging
-
With advancing age, layers of the
digestive tract thin and the blood
supply decreases
Mucus secretion and motility also
decrease in the digestive tract
Defenses of the digestive tract
declines
Tooth enamel becomes thinner
and gingiva recedes