Lecture 10-Digestive Glands Flashcards
Digestive glands
-General functions?
Lubricative, protective, digestive, and absorptive functions
Digestive gland functions are mediated by?
Their secretory products released into the oral cavity and duodenum
3 major digestive glands?
- Salivary (parotid, submandibular, and sublingual)
- Exocrine pancreas
- Liver (gallbladder)
Exocrine glands are glands that?
secrete their products into ducts
Classification of exocrine glands
-Structure?
- simple-unbranched
- compound-branched
Classification of exocrine glands
-Structure of the secretory unit?
- Tubular
- Alveolar (acinar)
Classification of exocrine glands
-Secretory product?
Mucus or serous (watery fluid with zymogen/proenzyme granules)
Classification of exocrine glands
-3 secretory mechanisms?
- Merocrine
- Holocrine
- Apocrine
Classification of exocrine glands
-Secretory mechanism-merocrine?
Exocytosis
Classification of exocrine glands
-Secretory mechanism-Holocrine?
Whole cell
Classification of exocrine glands
-Secretory mechanism-Apocrine?
Gland releases its product together with a small amount of the apical cytoplasm of the secretory cell
Major salivary glands
-Classified as?
Branched tubuloalveolar glands
Major salivary glands
-Excretory ducts open into?
The oral cavity
Saliva contains 5 components?
- Proteins
- Glycoproteins (mucus)
- Ions
- Water
- IgA
Submadibular gland
-produces?
Most of the saliva
Parotid gland
-produces? Rich in?
Some saliva-amylase rich
Production of saliva is under the control of?
The ANS
Striated duct
- This epithelium is involved in?
- Well developed in which glands?
- Transport of ions and water
- Well developed in submandibular and parotid glands
Protective function
-3 constituents of saliva and their functions?
- Lysozyme-attacks bacteria
- Lactoferrin-chelates iron necessary for bacterial growth
- IgA-neutralizes pathogens
Digestive function
-relies on?
- Amylase-initiates digestion of carbs
- Lingual lipase-hydrolysis of dietary lipids
Slide 10?
?
Salivary glands
-Parotid?
Exclusively serous acini
Salivary glands
-Sublingual gland?
- Mixed serous and mucus
- Mucus acini predominate
Salivary glands
-Submandibular gland?
- Mixed serous and mucus
- Serous demilunes
- Pure mucus acini rare
Parotid gland
-Enzymes?
Amylase, peroxidase, lysozyme
Parotid gland-Clinical significance
-primary target of?
The rabies and mumps viruses-transmitted in saliva containing the virus
The mumps virus causes?
Transient swelling of the parotid gland and confers immunity (can’t get it again)
Two complications of mumps?
Orchitis and meningitis
Bilateral orchitis caused by the mumps virus can result in?
Sterility
Parotid gland-most frequent site for slow growing benign salivary gland tumors
-Surgical removal is complicated by?
The location of the facial nerve
Submandibular glands
-Mucus cells secrete?
- Mucus cells secrete mucin which aids in the lubrication of the food bolus as it travels through the esophagus
- In addition, the serous cells produce salivary amylase-aids in the breakdown of starches
Sublingual gland
-2 types of cells?
- Serous and mucous cells
- Most secretory units are mucous
Exocrine pancreas-the pancreas is a combined endocrine and exocrine gland
-Endocrine component?
Islet of Langerhans (represents only 2% of pancreas volume)
The main function of the endocrine pancreas?
Regulation of glucose metabolism by hormones secreted into the bloodstream
The functional histologic unit of the exocrine pancreas?
Acinus
Initiation of the secretory-excretory duct system?
Lumen of the acinus
Lumen of the acinus contains?
Centroacinar cells (unique to the pancreas)
Centroacinar cells are continuous with the low cuboidal epithelial lining of the intercalated duct
-Exocrine pancreas lacks?
Striated ducts and myoepithelial cells
Intercalated ducts converge to form?
Interlobular ducts
-lined by a columnar epithelium with a few goblet cells and occasional enteroendocrine cells
Centroacinar cells
- Function?
- Stimulated by?
- Secrete aqueous bicarbonate sol’n
- Stimulated by the hormone secretin
CCK
- Binds to?
- Function?
Binds to specific receptors of acinar cells and stimulates the release of zymogen
Acinar pancreatic cells secrete the inactive forms of what enzymes?
Trypsin, chymotrypsin, and carboxylpeptidase
An increase in the synthesis of proteases is associated with?
A protein-rich diet
An increase in the synthesis of amylases and a decrease in the synthesis of proteases is often associated with?
A carb-rich diet
Amylase gene expression is regulated by what hormone?
Insulin (internal circulation within the pancreas (insuloacinar portal system) is functionally very important)
Acute pancreatitis
-Pathology?
-Premature activation of pancreatic enzymes (trypsinogen to trypsin) and inactivation of trypsin inhibitor result in autodigestion of pancreatic acini
Acute pancreatitis
-Usually follows?
Heavy meals or excessive alcohol ingestion
Acute pancreatitis
-Clinical signs?
- SEVERE abdominal pain, nausea and vomiting
- Rapid elevation of amylase and lipase in serum (within 24-72 hrs)
Liver
-Blood is supplied to the liver by?
- Portal vein to be filtered
- Hepatic artery-supplies hepatic tissue
Liver
-Blood from branches of the portal vein and the hepatic artery mixes in the sinusoids of the liver lobules and converges at the?
Central venule of the liver lobule
Liver
-Central venules converge to form?
Sublobular veins and blood returns to the IVC
Structural and functional unit of the liver?
Hepatic lobule
Hepatic lobule
- Consists of anastomosing plates of hepatocytes limiting blood sinusoidal spaces
- A central venule in the core of the hepatic lobule collects the sinusoidal blood containing a mixture of blood supplied by the portal vein and hepatic artery
The liver lobule can be conceptualized as?
- Classic hepatic lobule
- Portal lobule
- Liver acinus
Classic hepatic lobule
- Hexagonal lobule
- Surrounding a central vein
- Portal triads at the angles
Portal lobule
- Triangular arrangement
- Center of the triangle is bile duct collecting from 3 hepatic lobules
- Angles are the central veins of three hepatic lobules
Liver acinus
- Based on the oxygen gradient of venous sinusoids of adjacent lobules
- Divided into 3 zones based on the blood supply to the hepatocytes from the branch of the hepatic artery
Liver acinus
-The direction of arterial flow determines a?
The direction of arterial flow determines a metabolic gradient from the periportal space near the portal triad (zone I) to the zone of drainage (zone III)
Microscopic structure of lobule?
-Mostly made up of what type of cell?
Mostly made up of hepatocytes arranged in thin layers that radiate from the central canal vein to the periphery of the lobule
Microscopic structure of lobule?
-Between the radiating rows of hepatocytes?
Small blood vessels called sinusoids
Microscopic structure of lobule?
-Sinusoids receive?
- Oxygen rich blood from the hepatic artery and nutrients from the the intestines via the portal vein
- The oxygen and nutrients diffuse through the capillary walls into the liver cells
Microscopic structure of lobule?
-Within the sinusoids?
Specialized macrophages called Kupffer cells
-Involved in the recycling of old RBCs
Microscopic structure of lobule?
-At the corner of each lobule?
At the corner of each lobule is the portal triad, composed of branches of the hepatic portal vein, hepatic artery, bile duct and nerve
Microscopic structure of lobule?
-Bile drains from?
-Bile drains from the hepatocytes by the many small bile ducts that unite to form the main bile duct of the liver, the hepatic duct
The hepatic duct joins with the?
Cystic duct (coming from gall bladder) to form the common bile duct, which drains into the duodenum
The endothelium which lines liver sinusoids
-Characteristics?
- Fenestrated
- Lacks a continuous basement membrane (discontinuous capillaries)
The space between the fenestrated endothelium and the cords is called?
The space of Disse
Space of Disse
-The fenestrations permit blood plasma to?
wash freely over the exposed surfaces of the hepatocytes through the space of Disse
Space of Disse
-Microvilli of hepatocytes extend into this space, allowing?
Microvilli of hepatocytes extend into this space, allowing proteins and other plasma components from the sinusoids to be absorbed by the hepatocytes
Bile canaliculus
Hepatocytes secrete bile
Ito cells
- What are they?
- Where are they located?
- Function?
- Stellate cells of the liver
- Located at intervals within the space of Disse
- These cells function as storage sites for fat and vitamin A
Bile
- produced by?
- pathway?
- Produced by hepatocytes
- Flows in opposite direction to the blood
- Transported through bile canaliculi into the canal of Hering then to the bile duct in the portal triad space
Hepatocytes-Functional endocrine and exocrine cell of the liver
-Basolateral domain?
- Abundant microvilli extending into the space of Disse
- Participates in the absorption of blood-borne substances (bili, peptide/steroid hormones, vitamin B12, substances to be detoxed)
- Secretion of plasma proteins (albumin, fibrinogen, prothrombin, coag factors, c’ proteins)
Hepatocytes
-Contain smooth ER associated with?
Glycogen inclusions
Hepatocytes
-4 Functions of the SER?
- Synthesis of cholesterol and bile salts
- Conjugation of bili, steroids, drugs
- Breakdown of glycogen into glucose
- detox of lipid soluble drugs (phenobarbital)
Hepatocytes
-Rough ER and golgi participate in?
The synthesis and glycosylation of the secretory proteins indicated above
Hepatocytes
-Peroxisomes-function?
- Prominent in hepatocytes
- generate hydrogen peroxidase (which is broken down into oxygen and water)
Bile
- A mixture of organic and inorganic substances produced by the hepatocyte
- Participates in the excretion of cholesterol, phospholipids, bile salts, conjugated bili, electrolytes
Bile
-Fat absorption in the intestinal lumen depends on?
the fat emulsifying function of bile salts
Bile transports IgA to?
The intestinal mucosa and inhibits bacterial growth in the small intestine
The secretion of bile into the bile canaliculus is an ATP mediated process involving?
- Multidrug resistance 1 and 2 transporters
- Multispecific organ anionic transporter
- Biliary acid transporter
Metabolism of bilirubin
Bili is the end product of heme catabolism-comes from old RBCs being destroyed in the spleen by macrophages
Bilirubin formation?
-Macrophages convert heme into?
Biliverdin–>unconjugated bili (in blood)–>forms complex with albumin–>hepatic sinusoids–>albumin detaches–>bili is internalized by hepatocyte
Alcoholism and fatty liver
- Hepatocytes participate in the metabolism of ethanol
- Long term consumption of ethanol results in fatty liver
- Reversible process if alcohol ingestion discontinued
- Cirrhosis
- Hepatocellular carcinoma
Cirrhosis
-collagen proliferation of fibrosis of the liver
Gallbladder
-Main functions?
Storage, concentration, and release of bile (into common bile duct then liver)
Dilute bile from the hepatic ducts is transported through?
The cystic duct into the gall bladder
After concentration, what happens to bile?
Bile is discharged into the common bile duct
Gallstones
-What are they?
- Pieces of solid material that form in the gallbladder
- These stones develop because cholesterol and pigments in bile sometimes form hard particles
Gallstones
-Two main types?
- Cholesterol stones
- Pigment stones
Gallstones
-Cholesterol stones
- Usually yellow-green in color
- Most gallstones are cholesterol stones
Gallstones
-Pigment stones?
These stones are smaller and darker and are made up of bilirubin
What type of cell predominates in the sublingual gland?
Mucous cells
What type of cell predominates in the submandibular gland?
Serous cells
What gland produces IgA?
Parotid gland
Serous demilunes
Serous cells are located at the fundus of the acinus forming a crescent shaped structure embracing the mucus cells located closer to the opening of the acinus into the intercalated duct