Histology of GI Glands Flashcards
Digestive Glands
- have lubricating, protective, digestive, absorptive functions mediated by their secretory products
What are the 3 main digestive glands?
1) Major salivary glands
2) Exocrine pancreas
3) Liver
Major Salivary glands
associated with the oral cavity through independent excretory ducts
Exocrine pancreas
- digestive glands
secretes its alkaline aqueous and enzymatic product into the duodenum
Liver
-main digestive glands
endocrine and exocrine gland with extensive access to the blood circulation
Exocrine glands
- secrete mucus, hormones, enzymes
- simple invagination of epithelium, or may lack contact with epithelial surface
Parts of exocrine glands
- Acinus
2. Duct
Acinus exocrine glands
blind-sac of secretory cells that synthesize and release product
Duct exocrine glands
conducting passageway for product to be released
Salivon
- what does it include?
basic secretory unit of salivary glands
- includes acinus, intercalated duct, excretory duct
Salivary Glands
- histology
- nerve innervation
- secretory cells produce saliva
- controlled by ANS
-CT capsule with SEPTA, dividing the glands into LOBES (interlobar septa) and smaller lobules ( interlobular septa)
Saliva
- lubricates and cleanses the oral mucosa, protecting it from dryness
- contains immunoglobulins, minerals, electrolytes, buffers, enzymes and metabolic waster
- aids in digestion of food via enzymes and maintenance of tooth integrity
How are secretory cells organized?
in an ACINUS
1) mucous acini
2) serous acini
3) mucoserous
4) myoepithelial cells
Mucous acini
cloudier-looking cytoplasm
- produce thick, glycoprotein-rich product
Serous acini
clear-staining cytoplasm
- produce a water-based product
Mucoserous
contain a core of mucous cells surrounded by serous demilune
Myoepithelial cells
located between epithelial cells & basal lamina
- assisted in moving secretory products toward the excretory duct
Mixed acini
contain serous and mucus-producing cells
Conventional fixation
serous cells have comprised the Demilune but this is an artifact of fixation
Rapid fixation
both mucous and serous cells are aligned in the same row to surround the lumen of secretory acinus
NO serous demilune is present
Effects of expansion of mucous cells during fixing
- increases volume
- displaces serous cells from their original position
Pathway of Saliva Flow
Acinus-> intercalated duct (low cuboidal epithelium)-> striated duct (simple cuboidal to columnar epithelium)-> excretory duct (simple cuboidal-> psuedostratified columnary or stratified cuboidal)
Parotid (Serous) Gland
- hallmarks
Largest salivary gland
- adipocytes scattered throughout
Acini consist mainly of serous secretory cells
- pyramidal cells with basally located nucleus
- Prominent RER in basal region
- Secretory granules visible in apical region
HALLMARK: SEROUS ONLY, LARGE AMOUNTS OF ADIPOSE TISSUE, CN VII PASS THROUGH
Sublingual Gland
- branched tubule-alveolar gland with both serous and mucus cells
- mixed gland, but predominantly mucous
- lack defined capsule, but is divided by CT into small lobes
- intercalated and striated ducts are poorly developed
Submandibular Gland
- serous cells are predominant, but mucous cells are present
- Mucous cell- containing acini are capped by serous demilunes (bonnet)
- Myoepithelia cells control serous secretions
- intercalated ducts are shorter and striated ducts are longer than those in parotid gland
Pancreas
- define
- description
- components
large gland with endocrine and exocrine functions (mostly exocrine)
thin layer of loose CT forms capsule
Divides glands into ill-defined lobules, neurovasculature &ducts extend within the septa
1) Exocrine component- synthesize / secretes enzymes that are essential for digestion in intestine
2) Endocrine component synthesize/secretes hormones (insulin & glucagon) into the blood -> regulate glucose, lipid, & protein metabolism
Pancreatic Histology
- characteristics
- cells
- Hallmarks
Serous acinus
- functional unit of exocrine pancreas and structurally unique
- contains pancreatic acinar cells
Intercalated duct begins within the acinus
Centroacinar cells: duct cells inside of the acinus
- continuous with the low cuboidal epithelium of intercalated duct
- cells secrete HCO3-, Na+, and H2O alkalinizes secretions
Hallmarks: acinar cells stain intensely, centroacinar cells stain lightly, pancreas often confused with parotid
Pancreatic Acinar Cells
- characteristics (3)
- hormones (4)
- effects
Characterized by
1) well developed RER
2) prominent Golgi apparatus
3) apical domain of zymogen granules
Granules contain ~20 different pancreatic proenzymes
1) Trypsinogen, chymotrypisinogen : digest proteins
2) Amylolytic enzymes (alpha-amylase) : digest carbohydrates
3) Lipases: digest lipids
4) Deoxyribonuclease, ribonuclease: digest nucleic acid
increase synthesis of proteases with protein rich diet
increase of amylases, decreases in proteases with carbohydrate-rich diet
Pancreatitis
- describe
- cause
- results
-Zymogen granules contain inactive proenzymes normally activated in duodenum
- Premature activation of pancreatic enzymes, results in autodigestion of the pancreatic gland following their release
- particularly with trypsinogen-> trypsin and inactivation of trypsin inhibitor
Results in
1) acute pancreatitis
2) chronic pancreatitis
Acute Pancreatitis
- cause
- symptoms
usually following trauma, heavy meals, and excessive alcohol ingestion or bilary tract disease
symptoms:
severe abdominal pain, nausea, vomiting
Chronic Pancreatitis
characterized by fibrosis and partial/total destruction of pancreatic tissue
Cause
- alcoholism
can lead to permanent loss of pancreatic function (endocrine and exocrine)
Liver
- cells ( and function)
- enclosed in fibrous CT capsule
- serous covering surrounds the capsule, except where directly adheres to diaphragm/ other organs
- hepatocytes function in metabolism, storage, bile production ( exocrine)
- arranged in cellular cords
Functional unit of liver
1) hepatic lobule
2) portal lobule
3) liver acinus
Blood Supply to Liver
- transport (2)
- where they mix
- pathway for duct
1) Portal Vein ( 75-80% afferent blood volume)
- transports blood from GI tract, spleen, and pancreas
2) Hepatic artery
- supplies 2025% of oxygenated blood via the interlobar artery and interlobular arter pathway
Blood from branches of portal vein & hepatic artery mixes in the sinusoid of the lobules
- converges at the central venules-> sublobular veins
- blood returns to IVC ( via collecting and hepatic veins)
Right and left hepatic bile duct -> hepatic duct-> common bile duct-> gallbladder
Hepatocytes
- cell characteristics
- function
large polygonal cells with large spherical nuclei
- most are tetraploid
- many are binucleate
Functions:
- secrete bile, mixture of H2O, bile salts and pigments, phospholipds, electrolytes
- drains into bile canaliculus (canal lined with cholangiocytes, located btw adjacent hepatocytes)
- canaliculi join to eventually contribute to biliary tree
Bile
- function
fat absorption
excretion of cholesterol, bilirubin, iron, and copper
Bile and Lymph flow relationship
bile and lymph flow in the same direction, OPPOSITE of blood
Hepatocyte plates
separated by anastomosing sinusoids-> perfuse cells with portal and arterial blood
Terminal hepatic venule
- nickname
- function
aka central vein
collects blood from the sinsoids
Portal area/ portal canals
-position
positioned at angles of the hexagon, loose CT house portal triads
Periportal space of Mall
-location
located at edges of canals btw stromal CT and hepatocytes
- excess fluid in space of DIssee is collected here and is drained by lymphatic vessels
Hepatic Sinusoid
- lined with a thin discontinuous endothelium and discontinuous basal lamina
- large fenestrae, without diaphragms
- large gaps between neighboring cells
Kupffer Cells
specialized macrophages found along endothelial lining of hepatic sinusoid
- larger than endothelial cells
- detect and phagocytose effete erythrocytes
- distinguishes hepatic sinusoids
Bile Canaliculi
brown staining stick like structures located in between hepatocytes
Hepatic Lobule components
- central venule
- hepatocytes
- sinusoids
Portal Triad components
- bile ductules
- branches of hepatic a.
- branches of portal v.
Perisinusoidal Space
- nickname
- describe
- location
aka Space of Disse
- site of exchange of materials between blood and liver cells
- found btw basal surfaces of hepatocytes and those of endothelial cells and Kupffer cells lining the sinusoids
- microvilli project into this space from the basal surface of the hepatocytes
- Because of the large gaps in the endothelial layer and the absence of a continuous basal lamina, no significant barrier exists between the blood plasma in the sinusoid and the hepatocyte plasma membrane
- protein and lipoproteins synthesized by hepatocytes are released into the blood in the perisinusoidal space
Portal Lobule
- how to find it ( 3 steps)
- signficance
Central axis is bile duct (portal triad)
ID portal triad-> draw imaginary lines between 3 central veins-> portal lobule
- triangular block of tissue
- outlines bile drainage pathway from adjacent lobules into the same bile duct
- provide a description comparable to that of other exocrine glands
Liver Acinus
- diamond-shaped and occupies part of adjacent classic lobules
- hepatocytes are arranged in concentric zones around short axis
- based on O2 gradient along sinusoids of adjacent lobules
- flow of arterial blood creates gradient of O2/nutrients
- Cells within each zone have different metabolicc functions and distribution of hepatic enzymes
- Explains distribution of liver damage resulting from ischemia and/or exposure to toxic substances
What pathological changes do you see in Congestive heart failure?
- zones
- cell type
ischemic necrosis
- most severe in hepatocytes in zone 3
- presence of multiple round vacuoles, which indicates extensive lipid accumulation
No noticeable changes are seen in the periphery of the lobule which is zone 1 and much of zone 2
Classic Lobule
emphasizes endocrine function of hepatocytes as blood flows toward the central vein
Portal Lobule
emphasizes hepatocytes exocrine function and flow of bile from the classic lobules toward bile duct in portal triad
- area drained by each bile duct is roughly triangular
Hepatic Acinus
emphasizes different oxygen and nutrient contents of blood at different distances along the sinusoids (blood from each portal area supplies 2+ classic lobules)
- major activity of each hepatocyte is determined by location along oxygen/nutrient gradient: periportal cells of zone 1
- increase [oxygen/nutrients] in zone 1 AND 2 AND 3
Hereditary Hemachromatosis
pathology characterized by increased iron absorption and accumulation in lysosomal hepatocytes
- complications include cirrhosis and cancer of the liver
WIlson’s disease
hereditary disorder of copper metabolism in which excessive deposits of copper in liver and brain lysosomes produce chronic hepatitis
Chronic liver disease
perisinusoidal cells remain in quiescent, nonproliferative state, but can proliferate when activated by Kupffer cells and hepatocytes
leads to fibrosis and inflammatory cells (lymphocytes and macrophages) in distorted portal space
Long-term consumption of ethanol
can result in fatty liver (reversible if EtOf consumption is discontinued)
- steatohepatitis
- cirrhosis
Steatohepatitis
fatty liver accompanied by an inflammatory reaction
Cirrhosis
collagen proliferation of fibrosis
Hepatitis
inflammatory condition due to viruses, but can also result from bacteria and parasites
Acute hepatitis
characterized by loss of appetite, nausea, vomiting, jaundice
Chronic hepatitis
presence of fibrosis, together with hepatocyte necrosis and inflammatory lymphtocytic activity
Viral hepatitis
caused by hepatitis virus A, B, C
HAV
hepatitis virus A
infections caused by spread through ingestion of contaminated food/water
- causes acute hepatitis that rarely becomes chronic
HBV
Hepatitis Virus B
via sexual contact and blood/serum transfer through shared needles in drug abused
~10% of individuals develop chronic hepatitis
HCV
Hepatitis Virus C
largely caused by blood transfusion (~90% of the cases)
- 50-70% of the affected individuals develop chronic hepatitis
Therapy
-oral administration of antiviral agents
Gallbladder
Sac-like structures that stores and concentrate bile
-releases it into duodenum after a meal
Gallbladder Histology
- think four layers
highly folded mucosa with simple columnar epithelium with microvilli overlying a lamina propria
Muscularis with bundles of muscle fibers oriented in all directions to facilitate emptying of the organ
** external adventitia where it is against the liver
Serosa exposed to peritoneal cavity
Rokitansky-Aschoff sinuses
deep diverticular of the mucosa that may extend through muscularis externa
- develop as the result of hyperplasia and herniation of epithelial cell through muscularis externa
- bacteria may accumulate, causing chronic inflammation
- increased risk for gallstones
Perisinusoidal space of Disse
separates hepatocyte plates from blood sinusoidal space
-site of material exchange
