Download Digestive System Day 2

NOTES – DIGESTIVE SYSTEM ANATOMY
Interesting Digestive System Facts
After you eat how long does
it take for the stomach to
empty?
Within 2-6 hours, all food is
emptied into the small
intestine.
How many
pounds of food
does the
average person
eat in a year?
1,100
How many feet long are your
intestines?
about 20-30 ft long.
NOTES – DIGESTIVE SYSTEM ANATOMY
• Oral Cavity
• mouth, pharynx, esophagus
• MOUTH
• SALIVARY GLANDS – produce saliva
• Saliva Components
• Mostly water – about 99.5%
• SALIVARY AMYLASE – digests starch
• LYSOZYME – antibacterial action
• MUCIN – lubricant
• chewing and saliva with food form a
BOLUS
• PHARYNX
• common area for food and air
• Epiglottis
• prevents food from entering the
trachea (wind pipe)
• ESOPHAGUS
• transports bolus from pharynx to
stomach
Pierces diaphragm and joins stomach
at cardiac sphincter
• involuntary muscular movement of
food - PERISTALSIS
Homeostatic Imbalance
• Heartburn
– Stomach acid regurgitates into esophagus
– Likely with excess food/drink, extreme obesity,
pregnancy, running
– Also with hiatal hernia - structural
abnormality
• Part of stomach above diaphragm
• Can  esophagitis, esophageal ulcers,
esophageal cancer
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Esophagus
• Esophageal mucosa contains stratified
squamous epithelium
– Changes to simple columnar at stomach
• Esophageal glands in submucosa secrete
mucus to aid in bolus movement
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Figure 23.12a Microscopic structure of the esophagus.
Mucosa
(stratified
squamous
epithelium)
Submucosa
(areolar
connective
tissue)
Lumen
Muscularis
externa
• Circular layer
• Longitudinal
layer
Adventitia
(fibrous
connective
tissue)
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Figure 23.12b Microscopic structure of the esophagus.
Mucosa
(stratified
squamous
epithelium)
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Esophagus-stomach
junction
Simple columnar
epithelium of stomach
• STOMACH
• a storage & mixing chamber
• secretions
• mucus
• hydrochloric acid (HCl)
• HCl activates pepsinogen to pepsin
which is main enzyme that digests
protein
Figure 23.14a Anatomy of the stomach.
Cardia
Fundus
Esophagus
Muscularis
externa
• Longitudinal layer
• Circular layer
• Oblique layer
Serosa
Body
Lumen
Lesser
curvature
Rugae of
mucosa
Greater
curvature
Duodenum
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Pyloric sphincter
(valve) at pylorus
Pyloric
canal
Pyloric
antrum
Figure 23.14b Anatomy of the stomach.
Liver
(cut)
Fundus
Body
Spleen
Lesser
curvature
Greater
curvature
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Stomach: Microscopic Anatomy
• Mucosa
– Simple columnar epithelium composed of
mucous cells
• Secrete two-layer coat of alkaline mucus
– Surface layer traps bicarbonate-rich fluid beneath it
– Dotted with gastric pits  gastric glands
• Gastric glands produce gastric juice
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Figure 23.15b Microscopic anatomy of the stomach.
Gastric pits
Surface epithelium
(mucous cells)
Gastric
pit
Mucous neck cells
Parietal cell
Gastric
gland
Chief cell
Enteroendocrine cell
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Enlarged view of gastric pits and
gastric glands
Figure 23.30b Mesenteries of the abdominal digestive organs.
Liver
Gallbladder
Lesser omentum
Stomach
Duodenum
Transverse colon
Small intestine
Cecum
Urinary bladder
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Homeostatic Imbalance
• Gastritis
– Inflammation caused by anything that
breaches mucosal barrier
• Peptic or gastric ulcers
– Erosions of stomach wall
• Can perforate  peritonitis; hemorrhage
– Most caused by Helicobacter pylori bacteria
– Some by NSAIDs
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Figure 23.16 Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it.
Bacteria
Mucosa
layer of
stomach
A gastric ulcer lesion
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H. pylori bacteria
Homeostatic Imbalance
• Vomiting (emesis) caused by
• Extreme stretching
• Intestinal irritants, e.g., bacterial toxins, excessive
alcohol, spicy food, certain drugs
• Chemicals/sensory impulses  emetic
center of medulla
• Excessive vomiting  dehydration,
electrolyte and acid-base imbalances
(alkalosis)
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• movement
• mixing waves - peristalsis
• bolus becomes chyme
• SMALL INTESTINE
• parts: duodenum, jejunum, ileum
• Function:
• digestion and absorption
• intestinal juice – water & mucus
• epithelial cells have digestive
enzymes to digest ALL classes of
food
Duodenum
• Curves around head of pancreas; shortest
part – 25 cm
• Bile duct (from liver) and main pancreatic
duct (from pancreas)
– Join at hepatopancreatic ampulla
– Enter duodenum at major duodenal papilla
– Entry controlled by hepatopancreatic
sphincter
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Figure 23.21 The duodenum of the small intestine, and related organs.
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Tail of pancreas
Pancreas
Jejunum
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Main pancreatic duct and sphincter
Duodenum
Head of pancreas
Jejunum and Ileum
• Jejunum
– Extends from duodenum to ileum
– About 2.5 m long
• Ileum
– Joins large intestine at ileocecal valve
– About 3.6 m long
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Figure 23.30c Mesenteries of the abdominal digestive organs.
Greater omentum
Transverse colon
Transverse
mesocolon
Descending colon
Jejunum
Mesentery
Sigmoid
mesocolon
Sigmoid colon
Ileum
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Structural Modifications
• Increase surface area of proximal part for
nutrient absorption
– Circular folds (plicae circulares)
– Villi
– Microvilli
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Structural Modifications
• Circular folds
– Permanent folds (~1 cm deep) that force
chyme to slowly spiral through lumen  more
nutrient absorption
• Villi
– Extensions (~1 mm high) of mucosa with
capillary bed and lacteal for absorption
• Microvilli (brush border) – contain
enzymes for carbohydrate and protein
digestion
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Figure 23.22a Structural modifications of the small intestine that increase its surface area for digestion and
absorption.
Vein carrying
blood to
hepatic portal
vessel
Muscle
layers
Circular
folds
Villi
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Lumen
Figure 23.22b Structural modifications of the small intestine that increase its surface area for digestion and
absorption.
Microvilli
(brush border)
Absorptive
cells
Lacteal
Goblet
cell
Blood
capillaries
Mucosaassociated
lymphoid
tissue
Intestinal
crypt
Muscularis
mucosae
Duodenal
gland
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Villus
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
Figure 23.22c Structural modifications of the small intestine that increase its surface area for digestion and
absorption.
Absorptive cells
Goblet
cells
Villi
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Intestinal crypt
Figure 23.23 Microvilli of the small intestine.
Mucus
granules
Microvilli
forming the
brush border
Absorptive cell
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Homeostatic Imbalance
• Chemotherapy targets rapidly dividing
cells
– Kills cancer cells
– Kills rapidly dividing GI tract epithelium 
nausea, vomiting, diarrhea
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• LIVER
• performs many functions – main
blood filter in digestive system
• in digestion it secretes BILE into
the gall bladder
• the gall bladder then dumps bile
into small intestine
Figure 23.24a Gross anatomy of the human liver.
Sternum
Nipple
Bare area
Liver
Falciform
ligament
Left lobe of
liver
Right lobe of liver
Gallbladder
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Round ligament
(ligamentum
teres)
Figure 23.24b Gross anatomy of the human liver.
Lesser
omentum
(in fissure)
Left lobe
of liver
Porta hepatis
containing
hepatic
artery (left)
and hepatic
portal vein
(right)
Quadrate
lobe of liver
Ligamentum
teres
Bare area
Caudate lobe
of liver
Sulcus for
inferior
vena cava
Hepatic vein
(cut)
Bile duct
(cut)
Right lobe
of liver
Gallbladder
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Figure 23.21 The duodenum of the small intestine, and related organs.
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Tail of pancreas
Pancreas
Jejunum
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Main pancreatic duct and sphincter
Duodenum
Head of pancreas
Figure 23.25a–b Microscopic anatomy of the liver.
Lobule
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Central Connective
vein tissue septum
Liver: Microscopic Anatomy
• Hepatocytes – increased rough & smooth
ER, Golgi, peroxisomes, mitochondria
• Hepatocyte functions
– Process bloodborne nutrients
– Store fat-soluble vitamins
– Perform detoxification
– Produce ~900 ml bile per day
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Liver
• Regenerative capacity
– Restores full size in 6-12 months after 80%
removal
– Injury  hepatocytes  growth factors 
endothelial cell proliferation
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Homeostatic Imbalance
• Hepatitis
– Usually viral infection, drug toxicity, wild
mushroom poisoning
• Cirrhosis
– Progressive, chronic inflammation from
chronic hepatitis or alcoholism
– Liver  fatty, fibrous  portal hypertension
• Liver transplants successful, but livers
scarce
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• bile EMULSIFIES fats – breaks fat
into smaller pieces – easier for fat
digesting enzymes to do their work
Normal liver
fatty liver
Cirrhosis of the liver
• PANCREAS
• pancreatic enzymes are important for
the digestion of all major classes of food
• four enzymes and bicarbonate
• all are dumped into small intestine
Figure 23.26a Structure of the enzyme-producing tissue of the pancreas.
Small
duct
Acinar cell
Basement
membrane
Zymogen
granules
Rough
endoplasmic
reticulum
Duct cell
One acinus
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Figure 23.26b Structure of the enzyme-producing tissue of the pancreas.
Acinar cells
Pancreatic
duct
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• LARGE INTESTINE
• Parts: ascending colon,
transverse colon, descending colon,
sigmoid colon
• chyme is converted to feces
• absorption of water & salts
• E. coli bacteria synthesizes
vitamin K
Figure 23.29a Gross anatomy of the large intestine.
Left colic
(splenic) flexure
Right colic
(hepatic) flexure
Transverse
mesocolon
Transverse colon
Epiploic
appendages
Superior
mesenteric artery
Descending colon
Haustrum
Ascending colon
IIeum
Cut edge of
mesentery
IIeocecal valve
Tenia coli
Sigmoid colon
Cecum
Appendix
Rectum
Anal canal
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External anal sphincter
Figure 23.30d Mesenteries of the abdominal digestive organs.
Liver
Lesser omentum
Pancreas
Stomach
Duodenum
Transverse mesocolon
Transverse colon
Mesentery
Greater omentum
Jejunum
Ileum
Visceral peritoneum
Parietal peritoneum
Urinary bladder
Rectum
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Homeostatic Imbalance
• Low fiber diet  narrowed colon  strong
contractions  increased pressure on
walls  diverticula (herniations of
mucosa)
• Diverticulosis commonly in sigmoid colon
– Affects ½ people > 70 years
• Diverticulitis
– Inflamed diverticula; may rupture and leak into
peritoneal cavity; may be life threatening
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Homeostatic Imbalance
• Irritable bowel syndrome
– Functional GI disorder
– Recurring abdominal pain, stool changes,
bloating, flatulence, nausea, depression
– Stress common precipitating factor
• Stress management important in treatment
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Malabsorption of Nutrients
• Gluten-sensitive enteropathy (celiac
disease)
– Immune reaction to gluten
– Gluten causes immune cell damage to
intestinal villi and brush border
– Treated by eliminating gluten from diet (all
grains but rice and corn)
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Developmental Aspects
• Oral membrane  mouth opening
• Cloacal membrane  anus
• By week 5 alimentary canal continuous
tube from mouth to anus
• Shortly after, accessory organs bud from
mucosa
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Figure 23.36 Embryonic development of the digestive system.
Lung bud
Brain
Oral membrane
Heart
Yolk sac
Stomodeum
Foregut
Liver
Site of liver
development
Body stalk
Gallbladder
Hindgut
Cystic duct
Ventral pancreatic bud
Proctodeum
Endoderm
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Bile
duct
Midgut
Spinal cord
Cloacal
membrane
Stomach
Dorsal
pancreatic
bud
Duodenum
Homeostatic Imbalance
• Cleft palate and cleft lip
• Tracheoesophageal fistula
– Opening between esophagus and trachea
• Cystic fibrosis
– Genetic disease  thick mucus  can block
pancreatic duct
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Developmental Aspects
• Fetal nutrition via placenta, but GI tract
stimulated to mature by amniotic fluid
swallowed in utero
• Newborn's rooting reflex helps infant find
nipple; sucking reflex aids in swallowing
• Newborns double birth weight in six
months; adult diet by 2 years
• Cholecystitis, ulcers – problems of middle
age
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Developmental Aspects
• During old age
– GI tract activity declines, less digestive juice,
absorption less efficient, peristalsis slows 
less frequent bowel movements
– Taste/smell less acute; periodontal disease
often develops
– Diverticulosis, fecal incontinence, and cancer
of GI tract fairly common
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Cancer
• Stomach and colon cancers rarely have
early signs or symptoms
• Metastasized colon cancers frequently
cause secondary liver cancer
• Prevention
– Regular dental and medical examination
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