Download Liver

Pharynx
• Oropharynx and laryngopharynx
• Allow passage of food, fluids, and air
• Skeletal muscle layers: inner longitudinal,
outer pharyngeal constrictors
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Esophagus
• Flat muscular tube from laryngopharynx to
stomach
• Travels through the diaphragm via an
opening called the esophageal hiatus
• Joins stomach at the cardiac orifice
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Esophagus
• Esophageal glands secrete mucus to lubricate and
aid in bolus movement
• Muscularis: consists of skeletal muscle superiorly;
smooth muscle inferiorly
• Contains upper and lower esophageal sphincters:
upper and lower that act as “gateways” for food
• Lower esophageal sphincter prevents
backflow of stomach contents into the
esophagus
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(a)
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Mucosa
(contains a stratified
squamous epithelium)
Submucosa (areolar
connective tissue)
Lumen
Muscularis externa
• Longitudinal layer
• Circular layer
Adventitia (fibrous
connective tissue)
Figure 23.12a
Digestive Processes: Mouth
• Ingestion
• Mechanical digestion
• Mastication is partly voluntary, partly
reflexive
• Chemical digestion (salivary amylase and
lingual lipase)
• Propulsion
• Deglutition (swallowing)
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Deglutition – 2 major phases
• Involves the tongue, soft palate, pharynx,
esophagus, and 22 muscle groups
• Buccal (oral) phase
• Voluntary contraction of the tongue
• Pharyngeal-esophageal phase
• Involuntary (sensory receptors initiate the
swallowing reflex)
• Control center in the medulla and lower pons
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Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
1 Upper esophageal sphincter is contracted. During
the buccal phase, the tongue presses against the hard
palate, forcing the food bolus into the oropharynx
where the involuntary phase begins.
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Figure 23.13, step 1
Uvula
Bolus
Epiglottis
Esophagus
2 The uvula and larynx rise to prevent food from
entering respiratory passageways. The tongue blocks
off the mouth. The upper esophageal sphincter
relaxes, allowing food to enter the esophagus.
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Figure 23.13, step 2
Bolus
3 The constrictor muscles of the pharynx contract,
forcing food into the esophagus inferiorly. The upper
esophageal sphincter contracts (closes) after entry.
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Figure 23.13, step 3
Relaxed muscles
Circular muscles
contract
4 Food is moved through
the esophagus to the
stomach by peristalsis.
Bolus of food
Longitudinal muscles
contract
Gastroesophageal
sphincter closed
Stomach
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Figure 23.13, step 4
Relaxed
muscles
5 The gastroesophageal
sphincter opens, and food
enters the stomach.
Gastroesophageal
sphincter opens
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Figure 23.13, step 5
Bolus of food
Tongue
Uvula
Pharynx
Bolus
Epiglottis
Epiglottis
Glottis
Trachea
Bolus
Esophagus
1 Upper esophageal sphincter is
contracted. During the buccal phase, the
tongue presses against the hard palate,
forcing the food bolus into the oropharynx
where the involuntary phase begins.
Relaxed muscles
2 The uvula and larynx rise to prevent food
from entering respiratory passageways. The
tongue blocks off the mouth. The upper
esophageal sphincter relaxes, allowing food
to enter the esophagus.
4 Food is moved
through the esophagus
to the stomach by
peristalsis.
Circular muscles
contract
Bolus of food
3 The constrictor muscles of the
pharynx contract, forcing food
into the esophagus inferiorly. The
upper esophageal sphincter
contracts (closes) after entry.
Relaxed
muscles
5 The gastroesophageal
sphincter opens, and food
enters the stomach.
Longitudinal muscles
contract
Gastroesophageal
sphincter closed
Gastroesophageal
sphincter opens
Stomach
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Figure 23.13
The Stomach
Four Main Functions:
1. Temporary storage for ingested food
2. Mechanical breakdown of food
3. Chemical breakdown of food
4. Production of intrinsic factor,
necessary for absorption of vitamin
B12
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Stomach: Gross Anatomy
• Cardiac region (cardia)
• Surrounds the cardiac orifice
• Fundus
• Dome-shaped region beneath the diaphragm
• Body
• Midportion
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Stomach: Gross Anatomy
• Pyloric region: antrum, pyloric canal, and
pylorus
• Pylorus is continuous with the duodenum
through the pyloric valve (sphincter)
• Greater curvature
• Convex lateral surface
• Lesser curvature
• Concave medial surface
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Cardia
Esophagus
Muscularis
externa
• Longitudinal layer
• Circular layer
• Oblique layer
Lesser
curvature
Fundus
Serosa
Body
Lumen
Rugae of
mucosa
Greater
curvature
Duodenum
(a)
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Pyloric
Pyloric
canal
antrum
Pyloric sphincter
(valve) at pylorus
Figure 23.14a
Stomach: Gross Anatomy
• Lesser omentum
• From the liver to the lesser curvature
• Greater omentum
• Drapes from greater curvature
• Anterior to the small intestine
• Protects abdominal viscera
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Falciform ligament
Liver
Gallbladder
Spleen
Stomach
Ligamentum teres
Greater omentum
Small intestine
Cecum
(a)
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Figure 23.30a
Liver
Gallbladder
Lesser omentum
Stomach
Duodenum
Transverse colon
Small intestine
Cecum
Urinary bladder
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(b)
Figure 23.30b
Stomach: Microscopic Anatomy
• Still has four tunics
• Muscularis and mucosa are modified
• Muscularis externa
• Three layers of smooth muscle
• Inner oblique layer allows stomach to
churn, mix, move, and physically break
down food
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3 muscular layers
•Longitudinal
•Circular
•Oblique
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Figure 23.15a
Stomach: Microscopic Anatomy
• Mucosa
• Simple columnar epithelium composed of
mucous cells
• Produce a layer of mucus that traps
bicarbonate-rich fluid beneath it
• Protects the epithelial cells from acids,
enzymes and abrasive materials
• Gastric pits lead into gastric glands
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Gastric pits
Surface epithelium
(mucous cells)
Gastric
pit
Mucous neck cells
Parietal cell
Chief cell
Gastric
gland
Enteroendocrine cell
(b) Enlarged view of gastric pits and gastric glands
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Figure 23.15b
Gastric Glands
• Cell types
• Mucous neck cells (secrete thin, acidic
mucus)
• Parietal cells
• Chief cells
• Enteroendocrine cells
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Pepsinogen
HCl
Pepsin
Mitochondria
Parietal cell
Chief cell
Enteroendocrine
cell
(c) Location of the HCl-producing parietal cells and
pepsin-secreting chief cells in a gastric gland
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Figure 23.15c
Gastric Gland Secretions
• Glands in the fundus and body produce most of
the gastric juice
Parietal cell secretions
• HCl
•  pH 1.5–3.5 denatures protein in food, activates
pepsin, and kills many bacteria
• Intrinsic factor
• Glycoprotein required for absorption of vitamin
B12 in small intestine
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Gastric Gland Secretions
• Chief cell secretions
• Inactive enzyme pepsinogen
• Converted to pepsin by HCl and by pepsin
itself
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Homeostatic Imbalance
• Gastritis: inflammation caused by anything
that breaches the mucosal barrier
• Peptic or gastric ulcers: erosion of the
stomach wall
• Most are caused by Helicobacter pylori
bacteria
• Cause 80% of gastric ulcers
• Treated successfully with antibiotics
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Bacteria
Mucosa
layer of
stomach
(a) A gastric ulcer lesion
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(b) H. pylori bacteria
Figure 23.16
Digestive Processes in the Stomach
• Physical digestion
• Denaturation (breakdown) of proteins
• Enzymatic digestion of proteins by pepsin
(and rennin in infants)
• Secretion of intrinsic factor required for
absorption of vitamin B12
• Lack of intrinsic factor  pernicious anemia
• Delivers chyme to the small intestine
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Regulation of Gastric Secretion
• Regulated by CNS and hormonal
mechanisms
• Events occur in three phases:
1. Cephalic (reflex) phase: few minutes
before food entry:
• sight, smell, taste or thought of food
initiates gastric secretion
• Prepares the stomach to receive food
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Regulation of Gastric Secretion
2. Gastric phase: lasts for 3–4 hours after food
enters the stomach (distending stomach)
•
Stimulates stretch receptors
•
Gastrin is released increasing gastric
secretion production
•
Distension and gastrin increase force
of contraction
3. Intestinal phase: brief stimulatory effect as
partially digested food enters the duodenum,
followed by inhibitory effects to slow gastric
activity down giving the intestine time to do
its job
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Pyloric
valve
closed
1 Propulsion: Peristaltic
waves move from the
fundus toward the
pylorus.
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Pyloric
valve
closed
2 Grinding: The most
vigorous peristalsis and
mixing action occur
close to the pylorus.
Pyloric
valve
slightly
opened
3 Retropulsion: The pyloric
end of the stomach acts as a
pump that delivers small
amounts of chyme into the
duodenum, simultaneously
forcing most of its contained
material backward into the
stomach.
Figure 23.19
Regulation of Gastric Emptying
• As chyme enters the duodenum in 3 ml spurts
• Receptors respond to stretch and chemical
signals
• Enterogastric reflex and enterogastrones
inhibit gastric secretion and duodenal filling
• Carbohydrate-rich chyme moves quickly
through the duodenum
• Fatty chyme remains in the duodenum 6 hours
or more
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Small Intestine: Gross Anatomy
•
Major organ of digestion and absorption
•
2–4 m (7-13 ft) long; from pyloric
sphincter to ileocecal valve
•
Three Subdivisions
1. Duodenum – contains the bile duct and
main pancreatic duct
2. Jejunum
3. Ileum
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Mouth (oral cavity)
Tongue
Esophagus
Liver
Gallbladder
Duodenum
Jejunum
Small
intestine Ileum
Anus
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Parotid gland
Sublingual gland Salivary
Submandibular
glands
gland
Pharynx
Stomach
Pancreas
(Spleen)
Transverse colon
Descending colon
Ascending colon
Large
Cecum
intestine
Sigmoid colon
Rectum
Vermiform appendix
Anal canal
Figure 23.1
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Tail of pancreas
Pancreas
Jejunum
Duodenum
Main pancreatic duct
and sphincter
Head of pancreas
Figure 23.21
Structural Modifications
• Increase surface area of proximal part for
nutrient absorption
• Circular folds (plicae circulares)
• Villi
• Microvilli
• Circular folds
• Permanent ridged
• Force chyme to slowly spiral through lumen
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Vein carrying blood to
hepatic portal vessel
Muscle
layers
Circular
folds
Villi
Lumen
(a)
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Figure 23.22a
Structural Modifications
• Villi
• Motile fingerlike extensions of the
mucosa
• Villus epithelium
• Simple columnar absorptive cells
(enterocytes)
• Goblet cells
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Structural Modifications
• Microvilli
• Projections (brush border) of absorptive
cells
• Contain brush border enzymes which
complete carbohydrate and protein
digestion in the small intestine
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Microvilli
(brush border)
Absorptive cells
Lacteal
Goblet cell
Blood
capillaries
Mucosa
associated
lymphoid tissue
Intestinal crypt
Muscularis
mucosae
Duodenal gland
(b)
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Vilus
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
Figure 23.22b
Intestinal Juice
• Secreted in response to distension or
irritation of the mucosa
• Slightly alkaline and isotonic with blood
plasma
• Largely water, enzyme-poor, but contains
mucus
• Facilitates transport and absorption of
nutrients
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Liver
• Largest gland in the body
• Four lobes—right, left, caudate, and
quadrate
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Liver
• Falciform ligament
• Separates the (larger) right and (smaller)
left lobes
• Suspends liver from the diaphragm and
anterior abdominal wall
• Round ligament (ligamentum teres)
• Remnant of fetal umbilical vein along free
edge of falciform ligament
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Sternum
Nipple
Liver
Bare area
Falciform
ligament
Left lobe of liver
Right lobe
of liver
Gallbladder
(a)
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Round ligament
(ligamentum
teres)
Figure 23.24a
Sternum
Nipple
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
(b)
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Figure 23.24b
Liver: Associated Structures
• Lesser omentum anchors liver to stomach
• Hepatic artery and hepatic portal vein
• Bile ducts
• Common hepatic duct leaves the liver
• Cystic duct connects to gallbladder
• Bile duct formed by the union of the above
two ducts
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Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Gallbladder
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Tail of pancreas
Pancreas
Jejunum
Duodenum
Main pancreatic duct
and sphincter
Head of pancreas
Figure 23.21
Liver: Microscopic Anatomy
• Liver lobules
• Hexagonal structural and functional units
• Filter and process blood
• Composed of hepatocytes (liver cells)
• Longitudinal central vein
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(a)
Lobule
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(b)
Central vein
Connective
tissue septum
Figure 23.25a, b
Liver: Microscopic Anatomy
• Portal triad at each corner of lobule
• Bile duct receives bile from bile canaliculi
• Portal arteriole is a branch of the hepatic
artery
• Hepatic venule is a branch of the hepatic
portal vein
• Liver sinusoids are leaky capillaries between
hepatic plates
• Kupffer cells (hepatic macrophages) in liver
sinusoids
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Interlobular veins
(to hepatic vein)
Central vein
Sinusoids
Bile canaliculi
Plates of
hepatocytes
Bile duct (receives
bile from bile
canaliculi)
Fenestrated
lining (endothelial
cells) of sinusoids
Portal vein
Hepatic
macrophages
in sinusoid walls
Bile duct
Portal venule
Portal arteriole
Portal triad
(c)
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Figure 23.25c
Liver: Microscopic Anatomy
• Hepatocyte functions
• Process bloodborne nutrients
• Store fat-soluble vitamins
• Perform detoxification
• Produce ~900 ml bile per day
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Bile
• Yellow-green, alkaline solution containing
• Bile salts: function in fat emulsification and
absorption
• Bilirubin: pigment formed from heme
• Cholesterol, triglycerides, phospholipids,
and electrolytes
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Bile
• Enterohepatic circulation
• Recycles bile salts
• Bile salts  duodenum  reabsorbed from
ileum  hepatic portal blood  liver 
secreted into bile
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The Gallbladder
• Thin-walled muscular sac on the ventral
surface of the liver
• Stores and concentrates bile by absorbing
its water and ions
• Releases bile via the cystic duct, which
flows into the bile duct
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