Download - Histology. Digestive system
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Digestive System III
Liver
Gallbladder
Pancreas
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Liver
occupies the upper right region
of the abdominal cavity
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Liver is the largest internal organ
is subdivided into
two large lobes (right and left)
two small lobes (quadrate and caudate) is enclosed in a capsule (capsule of Glisson) is partially covered by the visceral peritoneum is associated with the gallbladder
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Liver composition
Parenchyma - consists of epithelial cells - hepatocytes
- arises from the endoderm
Stroma - consists of connective tissue trabeculae
- contains blood and lymphatic vessels,
nerves, and bile ducts
- divides parenchyma into lobules
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Connective tissue is poor-developed in the human liver
the human liver
connective tissue in the pig liver ⇒
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Liver functions
Bile production – exocrine function
⇓
⇑so-called “endocrine” functions
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Liver is involved in many metabolic pathways
produces blood plasma proteins
(albumins, prothrombin, fibrinogen,
nonimmune α- and β-globulins, etc.) stores the blood glucose as glycogen and
releases glucose back after glycogenolysis stores lipid-soluble vitamins – A, D, K synthesizes and stores cholesterol stores iron ions as ferritin or hemosiderin synthesizes urea from ammonium ions
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Liver degrades drugs, toxins, alcohol, and hormones
Detoxication and degradation
- occur in hepatocyte sER ⇒- include
oxidation
conjugation
conversation
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Liver blood supply
Liver receives blood from two blood vessels
the hepatic artery
the portal vein
the liver hilum or porta hepatis ⇒
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Portal vein carries the venous blood
from the digestive tract, spleen,
and pancreas ⇒
portal blood contains– nutrients and toxic materials – erythrocyte breakdown products– hormones
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Blood vessels pass in connective tissue with bile ducts
Triad (portal area) includes interlobular– artery– vein (from v. porta)– bile duct
⇓
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Interlobular vessels give rise to capillaries
capillaries (hepatic sinusoids) – pass trough lobule– empty into the central vein
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Hepatic sinusoids carry mixed blood
hepatic sinusoids
⇓
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Central vein is a terminal venule
receives blood from sinusoids
⇔
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Central vein begins the vinous blood outflow
a central vein
⇓
the sublobular veins
⇓the hepatic vein
⇓the inferior vena cava
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Hepatic lobules
are the liver morphofunctional units
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Hepatic lobule composition
hepatocytes arranged in plates hepatic sinusoids perisinusoidal spaces (spaces of Disse) bile capillaries (canaliculi) central veins
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Classic hepatic lobule
is a hexagonal mass of tissue a central vein is at the center the triads are at the angles
hepatic plates radiate from the center to periphery sinusoids travel between plates blood flows from the periphery towards the center bile flows from the center towards the periphery
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Portal lobule emphasizes the liver exocrine function
is a triangular mass of tissue the central veins are at the angles the triad is at the center blood flows from the center to the periphery bile flows from the periphery to the center
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Liver acinus
is a diamond-shaped mass of tissue the short axis is between the triads the long axis is between the central veins
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Plates of hepatocytes
consist of two anastomosing cell rows bile canaliculus is between the rows are surrounded by the blood sinusoids
delicate network of the reticular fibers
supports plates
⇐
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Hepatocytes
are large polygonal cells contain 1 or 2 nuclei with several nucleoli may be tetraploid
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Hepatocytes are rich in organelles
rER and sER mitochondria Golgi apparatus peroxisomes
⇔⇒⇑
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Hepatocyte inclusions
glycogen clumps
⇓
⇔
lipid droplets
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Hepatocyte polarization
Vascular pole
- faces blood sinusoids
- is involved in the “endocrine” function
(blood-hepatocyte exchange)
Biliar pole
- faces bile canaliculi
- is involved in the exocrine function
(bile secretion)
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Hepatocytes are capable for regeneration
Physiologic regeneration
hepatocyte lifespan is about 5 months
hepatocytes can be renewed
Reparative regeneration
occurs when liver substance is lost after trauma or surgery
undifferentiated cells are
in the periportal areas ⇒
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Bile canaliculi
are intercellular gaps within the hepatic plates
⇔
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Bile canaliculi lack their own wall
are isolated by the hepatocyte tight junctions
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Bile canaliculi empty into the bile duct
bile duct is a part of the triad
⇓
⇔
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Bile duct is lined with cuboidal epithelial cells
⇔
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Hepatic blood capillaries – hepatic sinusoids
are sinusoidal fenestrated and discontinuous
⇑are lined with fenestrated endothelial cells
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Hepatic sinusoids contain Kupffer cells
Kupffer cells are hepatic macrophages
⇔
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Kupffer cells
belong to the mononuclear
phagocytotic system arise from blood monocytes
pit-cell is a large granulated lymphocyte
⇑
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Kupffer cell functions
degradation of damaged or senile erythrocytes conversation ferritin to hemosiderin phagocytosis of bacteria and antigens initiation of immune reactions
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Perisinusoidal space (space of Disse)
is between vascular hepatocyte pole and sinusoid contains a few reticular fibers and amorphous substance
⇑ hepatocytes project microvilli into space of Disse
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Space of Disse is a site of
exchange between blood and hepatocytes hepatic lymph origination hemopoiesis in the fetal period and
in cases of chronic anemia in the adult
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Space of Disse contains lipocytes (stellate or Ito cells)
are located between hepatocytes lack contact with bile canaliculi contain numerous lipid droplets
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Lipocyte functions
storage of vitamin A synthesis of reticular fibers and amorphous substance
In pathology
- lose their lipids and differentiate into myofibroblast-like cells
- synthesize collagen fibers resulting in liver fibrosis
- may contract resulting in portal hypertension
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Gallbladder
is attached to the visceral surface of the liver
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Gallbladder functions
bile storage bile concentration bile release to the duodenum as required
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Bile takes part in digestion
emulsifies lipids activates pancreatic lipases facilitates fatty acid absorption
Bile composition:waterelectrolytesphospholipidscholesterolbile acidsbile pigments (bilirubin)
⇔
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Gallbladder wall structure
Mucosa Mascularis externa Adventitia/Serosa
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Gallbladder mucosa
epithelium lamina propria
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Gallbladder epithelium
simple columnar striated
⇔
brush border
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Hormone cholecystokinin regulates the bile injection
is produced by enteroendocrine cells of the duodenum is released in response to a fatty chyme induce the gallbladder muscle contractions
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Pancreas
is located behind the stomach is enclosed in a capsule and
partially covered with serosa is subdivided into
head
body
tail
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Pancreas composition
Parenchyma
- consists of epithelial cells
- arises from the endoderm Stroma
- consists of connective tissue trabeculae
- contains blood and lymphatic vessels,
nerves, and ducts
- divides parenchyma into lobules
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Pancreas is mixed gland
Exocrine component
produces pancreatic juice
Endocrine component
secretes hormones
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Exocrine pancreas
is compound
branched
tubulo-alveolar
serous (protein-producing) gland
main and accessory pancreatic ducts empty into the duodenum ⇑
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Pancreatic secretory unit - acinus
is round with narrow lumen
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Acinar cells
are pyramidal nuclei are round and centrally located broad basal portion is basophilic due to rER apical portion is acidophilic due to secretory (zymogen) granules
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Acinar cell ultrastructure
zymogen granules in the apical pole ⇒
rER in the basal pole ⇒
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Acinar cells secrete a variety of digestive enzymes
Trypsin, chymotrypsin, peptidases – digest proteins up to amino acids
Amylase – digests carbohydrates up to glucose
Lipases – digest lipids up to glycerol and fatty acids
Nucleases – digest nucleic acids up to nucleotides
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Zymogen granules contain inactive enzymes
proenzymes are activated when reach
the intestinal lumen ⇓
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Exocrine pancreas duct system
Intercalated ducts Intralobular ducts Interlobular ducts
Main and accessory pancreatic ducts ⇒
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Intercalated duct
is narrow tubule lined with squamous or cuboidal cells may begin within the acinus (compound acinus) its cells in the acinus are called centroacinar cells
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Centroacinar cells exist in the compound acinus
but belong to the intercalated duct ⇒⇓
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Intercalated duct takes part in secretion
Adds
water
sodium
bicarbonate to the pancreatic juice
Intercalated duct secretion
- neuyralizes acidic gastric chyme
- establishes the optimal pH for pancreatic enzyme activity
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Intralobular and interlobular ducts
are lined with simple cuboidal epithelium
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Pancreas exocrine secretion hormonal regulation
Hormones of enteroendocrine cells from the duodenum
pancreozymin ⇒ stimulates acinar cells
secretin ⇒ stimulates intercalated duct cells
Pancreatic hormones
insulin and VIP ⇒ stimulate exocrine secretion
glucagon and PP ⇒ inhibit exocrine secretion
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Pancreas exocrine secretion nervous regulation
parasympathetic fibers stimulate both acinar and duct cells
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Endocrine pancreas
consists of pancreatic (Langerhans) islets
islets are scattered throughout the gland
⇒
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Islet composition
endocrine cells fenestrated sinusoidal capillaries
⇔
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Islet endocrine cell types
B cells A cells D cells D1cells
PP cells
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B cells constitute about 70% of the islet population
occupy the islet central portion secrete insulin
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Insulin decreases blood glucose levels
Effects hepatocytes and skeletal muscles – stimulates uptake of glucose from circulation– activates glycogen synthesis
Effects the white adipose cells– stimulates uptake of glucose from circulation– stimulates glycerol synthesis– inhibits lipase activity
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A cells constitute 15-20% of the islet population
occupy the islet periphery secrete glucagon
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Glucagon increases blood glucose levels
Stimulates glucose release into the bloodstream glycogenolysis (breakdown of glycogen) gluconeogenesis (synthesis of glucose from amino acids) lipase and lipid mobilization in adipose cells
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Insulin and glucagon are antagonists
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D cells constitute about 5-10% of the islet population
occupy the islet periphery secrete stomatostatin
inhibits both insulin and glucagon secretion
inhibits acinar cell
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Minor cell types in pancreatic islets
D1 cells ⇒ vasoactive intestinal peptide (VIP)
– stimulates endocrine and exocrine pancreatic secretion– decreases blood pressure
PP cells ⇒ pancreatic polypeptide– stimulates gastric chief cells– inhibits
bile secretion
pancreatic juice production
intestinal motility
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Regulation of the islet activity
Blood glucose levels increase ⇒ stimulate insulin productiondecrease ⇒ stimulate glucagon production
Nervous regulation parasympathetic fibers ⇒ stimulate both insulin and glucagon secretionsympathetic fibers ⇒ stimulate glucagon release but inhibit insulin secretion
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The End
Thank you for attention!