Accessory organs of the GI tract Flashcards
what are the three main digestive glands and what are their properties
Have lubricating , protective, digestive, and absorptive functions mediated by their secretory products
Major salivary glands: associated with the oral cavity through independent excretory ducts
Exocrine pancreas: secretes its alkaline aqueous and enzymatic product into the duodenum
Liver: endocrine and exocrine gland with extensive access to the blood circulation
Histology of the salivary gland and its characteristics
CT capsule with septa dividing the gland into lobes and smaller lobules
-route for neurovasculature
secretory cells organized in an acinus produce saliva via ANS control
released via ducts: acinus to the intercalated duct and through striated duct and finally out the excretory duct
differences histology between the mucous, serous, and mucoserous acini
Mucous acini are cloudier looking cytoplasm that produce thick glycoprotein rich product
Serous acini: clear staining cytoplasm that produce a water based product
Mucoserous: contain a core of mucous (black) cells surrounded by a serous demilune (yellow)
what are myoepithelial cells?
located between epithelial cells and basal lamina that assist in moving secretory products toward the excretory duct
what is the pathway flow of saliva?
Acinus
intercalated duct
-low cuboidal epithelium
striated duct
-simple cuboidal to columnar epithelium
excretory duct
-simple cuboidal to pseudostratified columnar or stratified cuboidal
which glands have the longest/shortest: intercalated duct, striated duct, and exretory duct
parotid: longest intercalated duct but shortest excretory duct
submandibular: longgest striated duct, shortest intercalated duct
sublingual: longest excretory and shortest striated duct
characteristics of the parotid gland
Largest salivary gland, adipocytes may be present
Acini consist primarily of serous secretory cells
- pyramidal cells with a basally located nucei
- prominent RER in basal region
- secretory granules visible in apical region
can sometimes see the CN VII pass through
Characteristics of the sublingual gland
Branched tubule-alveolar gland with both serous and mucous cells
-mixed gland but predominatly mucous
lacks defined capsule, but is divided by CT into small lobes
Interca;ated and striated ducts poorly developed
Characteristics of the Submandibular gland
Serous cells are predominant but mucous cells are present
mucous cell containing acini are capped by serous demilunes
-intercalated ducts are shorter and striated ducts are longer than in the parotid gland
what are the two components of the pancreas and what are some of its main features
Large gland with endocrine and exocrine functions but bulk gland is exocrine
THin layer of loose CT forms capsule
Divides gland into ill defined lobules, neurovasculature and ducts extend within the septa
Exocrine component: synthesizes/secretes enzymes that are essential for digestion in the intestine
endocrine component: synthesizes/secretes hormones into the blood that regulate the glucose, lipid, and protein metabolism
Characteristics of the exocrine pancreas
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 the acinus
- continuous with the low cuboidal epithelium of intercalated duct
- cells secrete HCO3-, Na+ and H20 and alkalinizes secretions
acinar cells stain intensely, centroacinar cells stin lightly
function and characterization of the Pancreatic acinar cell
Characterization:
- well developed RER
- prominent golgi apparatus
- apical domain of zymogen granules
Granules contain 20 different pancreatic enzymes
- trypsinogen, chymotrypsinogen digest proteins
- amylolytic enzyme a-amylase digest carbohydrates
- deoxyribonuclease, ribonuclease digest Nucleic acids
increase synthesis of proteases with protein rich diet
increase of amylases and decrease of proteases with a carbohydrate rich diet
Characteristics of the Endocrine pancreas and the 4 cell types
Spherical masses of endocrine cells surrounded by thin reticular capsule
Most islets contain several hundred cells, pancreas hs more than 1 million islets
islets arise from endodermal epithelial outgrowths
Islet cells:
- alpha cells = glucagon
- beta cells = insulin
- delta cells = spmatostatin
- PP cells - pancreatic peptide
Characteristics and the cells that make up the liver
Enclosed in thin CT capsule lined with mesotheilum of visceral peritoneum
lacking where directly adheres to the diaphragm or other organs
Hepatocytes: function in metabolism, storage, bile, production (exocrine)
-arranged in cellular cords
liver structure varies in regard to its functional unit:
- hepatic lobule
- portal lobule
- liver acinus
Characteristics of hepatocytes and bile
Large polygonal cells with eosinophillic cytoplasm and microvilli
Large spherical nuclei, many cells are binucleate, most are tetraploid
Numerous perioxisomes, lysosomes, extensive sER, large golgi
Hepatocytes secrete bile, mixture of H2O, bile salts and pigments, phospholipids, electrolytes
-drains into bile canaliculus which is a canal lined with cholangiocytes, located btwn adjacent hepatocytes
canaliculi join to eventually contribute to biliary tree
Bile functions in fat absorption and excretion of cholesterol, bilirubin, iron and copper
what make up the hepatic lobules and what is apart of the portal triad?
Liver parenchyma are organixed as hepatic lobules
- hepatocytes from irregular plates radiating from a central vein
- plates are supported by a stroma or reticular fubers
- plates separated by sunusoids
Blood flows toward the central vein
Peripheral angles of each lobe contain a portal triad”
- Venule branch of the portal vein (high in nutrients and low in O2)
- arteriole branch of the hepatic artery supplies O2
- Bile ductules (1-2) branches of the bile conducting system
blood and bile flow in opposite directions
what are the hepatic sinusoids and what are the two cell types found among them
Anastomosing capillaries that perfuse hepatocytes with portal and arterial blood
Kupffer cell:
- stellate macrophages within the endothelium of the sinusoid
- larger than the endothelial cells
- detect and phagocytose effete erythrocytes
- distinguishes the hepatic sinusoids
Hepatic stellate cells: Ito cells, cells with small lipid droplets that store vitamin A and other fat soluble vitamins
what is the perisinusoidal space of Disse
Located between the hepatocytes and sinusoidal endothelium (discontinuous capillaries)
Creates a potential space for exchange of materials between blood and hepatocytes
- microvilli project into this space
- plasma fills the space and directly bathes microvilli
- increase SA available for material exchange
Facilitates uptake/release of nutrients proteins and potential toxins
what are the bile canaliculi and how does bile flow
Anastomosing network of channels formed by the hepatocyte plates
-end near the portal triads
Bile flow occurs from center of the lobule to the periphery
-bile canliculi drain into canals of hering, composed of cuboidal epithelial cells caled cholangiocytes
bile flow:
- baile canaliculi
- canals of hering
- bile ductiles
- merge and enlarge
- right and left hepatic ducts
what is a portal lobule
Central axis is the bile duct (portal triad)
ID portal triad and draw imaginary lines btwn 3 central veins
- triangular block of tissue
- outlines bile drainage pathway from adjacent lobules into the same bile duct
Provides a description comparable to that of other exocrine glands
What is the liver acinus
Diamond shaped and occupies parts of adjacent classic lobules
Hepatocytes are arranged in concentric zones around short axiis
Based on O2 concentration gradient along sinusoids of adjacent lobules
Cells within each zone have different metabolic functions and distribution of hepatic enzymes
-explains distribution of liver damage resulting of ischemia and or exposure to toxic substances
level 1: most nutrients and and O2
level 3 = least
what is the structure and function releastionship of the 3 different lobules
Classic lobule: emphasizes endocrine function of hepatocytes as blood flows toward central vein
Portal lobule: emphasizes hepatocytes exocrine function and flow of bile from the classic lobules toward bile duct in portal triad
-triangular
Hepatic acinus: emphasizes different ozygen content and nutrient content of blood at different distances along the sinusoid
- activity determined by nutrient concentration
- level 1 = most nutrients
- level 3 = least nutrients
characteristics of the gall bladder
Sac like structure that stores and concentrates bile
Releases it into the duodenum after a meal
Highly folded mucosa with a simple columnar epithelium with microvilli overlying the lamina propria
muscularis with bundles of muscle fibers orientated in al directions to facilitate emptying of the organ
External adventitia is where it is against the liver but serosa where it is supposed to the peritoneal cavity
What are Rotikansky-Aschoff sinuses?
deep diverticua of the mucosa that may extend through the muscuaris externa
develop as the result of hyperplasia and herniation of epithelial cells through the muscuaris externa
Bacteria may accumulate causing chronic inflammation and increased risk for gallstones
