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Histology > Digestive system: Glands > Flashcards

Digestive system: Glands Flashcards

1
Q

what are the extrinsic glands of the digestive system?

A
  • major salivary glands
  • pancreas
  • liver (+ gallbladder)

all found outside the wall of the digestive tract

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2
Q

what is the pancreas divided into and surrounded by?

A

the pancreas is surrounded by a slender connective tissue capsule.
it is dived into the exocrine pancreas, which secretes digestive enzymes, and the endocrine pancreas (islets of Langerhans), which produce hormones

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3
Q

describe the exocrine pancreas…

A

the exocrine pancrease is a serous compound tubuloacinar gland

pancreatic acinar cells are arranged around a central lumen. zymogen granules are membrane bound and densely packed in the apical region.

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4
Q

describe the duct system of the pancreas…

A

the initial intra-acinar portion, the intercalated ducts is formed by centroacinar cells.

from the initial portion, the intercalated ducts converge into a small number of intralobular ducts

which in turn empty into large interlobular ducts that empty into the main (or accessort) pancreatic duct

the main pancreatic duct fuses with the common bile duct, forming the ampulla of Vater, which secretes secreations of the exocrine pancreas and the contents of the gallbladder into the duodenum at the major duodenal papilla

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5
Q

what are pancreatic acinar cells?

A

pancreatic acinar cells are pyramidal serous cells arranged around a central lumen

they possess a round basal nucleus, abundant RER, an extensive Golgi complex, numerous mitochondria and many free ribosomes

zymogen (secretory) granules are membrane bound and densely packed in the apical region of pancreatic acinar cells. they contain enzymes and proenzymes packed in the golgi complex

their basal plasmalemma has receptors for cholecystokinin and acetylcholine

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6
Q

what are zymogen granules found in the pancreas?

A

zymogen (secretory) granules are membrane-bound and densely packed in the apical region of pancreatic acinar cells.

they contain enzymes and proenzymes packed in the golgi complex

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7
Q

what does the exocrine pancreas secrete?

- two classes

A
  • enzyme-poor alkaline fluid

- digestive enzymes

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8
Q

what is enzymes-poor alkaline fluid? (pancreas)

A

enzymes-poor alkaline fluid is released in large quantities by intercalated duct cells stimulated by secretin in conjunction with acetylcholine

it aids in the neutralisation of acidic chyme as it enters the duodenum.

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9
Q

what stimulates the release of enzyme-poor alkaline fluid from the pancrease?

A

secretin (with acetylcholine)
secretin is produced by a type of enteroendocrine cell found in the crypts of Lieberkuhn in the small intestine.

secretin regulates the secretions of the stomach and pancrease. and regulates water homeostasis throughout the body.

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10
Q

what digestive enzymes are produced by the exocrine pancrease?

A

enzymes are secreted as enzymes and proenzymes

enzymes: pancreatic amylase, pancreatic lipases, ribonuclease, deoxyribonuclease
proenzymes: trypsinogen, chymotrypsinogen, procarboxypeptidase and proelastase

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11
Q

how does the cells that manufacture trypsin protect themselves from the digestive enzyme?

A

cells that produce trypsin also produce trypsin inhibitor.

the secreted proenzymes trypsinogen cannot be converted into trypsin with in the cytosol

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12
Q

what is the function of pancreatic acinar cells?

A

pancreatic acinar cells synthesise and store digestive enzymes.
their release is stimulates by cholecytokinin and costimulate by acetylcholine released by postganglionic parasympathetic fibres.

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13
Q

what is the endocrine pancrease made of?

A

islets of langerhans

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14
Q

what are islets of langerhans?

A

islets of langerhans form the endocrine pancreas.
they are richly vascularised spherical clusters of endocrine cells surrounded by a fine network of reticular fibres.

each islet is 100-200um in diameter

they are scattered amoung the acini of teh exocrine pancreas at random.

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15
Q

what hormones are produced by islets of langerhans cells? (5)

A

each cell type produce only one hormone and can be differentiated using immunochemistry.

  1. glucogon - produced by a-cells (~20%)
  2. insulin - produced by ß-cells (~70%)
  3. somatostatin - produced by d-cells (<5%)
  4. gastrin - produced by Gastrin producing cells (rare)
  5. pancreatic polypeptide (rare)
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16
Q

what is the general structure of the liver?

A

the liver is made up of only one type of parenchymal cell, hepatocytes.

the liver is surrounded by a dense, irregular collagenous connective tissue known as the Glisson capsule, which gives rise to the septa that subdivide the liver into the lobes and lobules

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17
Q

what is the Glisson capsule?

A

the glisson capsule is a dnse, irregular collagenous connective tissue that surrounds the liver.
it gives rise to the septa that subdivide the liver into lobes and lobules.

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18
Q

what are the 3 defined types of liver lobules?

A
  1. classic liver lobule
  2. portal lobule
  3. hepatic acinus of Rappaport
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19
Q

what is the definition of the classic liver lobule?

A

the classic liver lobule is a hexagonal mass of tissue primarily composed of plates of hepatocytes, which radiate from the region of the central vein toward the periphery.

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20
Q

what are the portal areas?

  • portal canals
  • portal triads
A

the portal areas are regions of the connective tissue between lobules that contain branches of the portal vein, hepatic artery, lymph vessel and bile duct. (portal triad)

the portal triads are present at alternate corners of a classic liver lobule

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21
Q

what are liver sinusoids?

A

liver sinusoids are sinusoidal capillaries that arises at the periphery of a lobule and run between adjacent plates of hepatocytes.

they deliver blood from the vessels in the portal areas and deliver it the the central vein

they are lined by sinusoidal lining cells (endothelial cells) that have large discontinuties between them, display fenestrations and lack basal lamina.

they also contain phagocytic cells, Kupffer cells, derived from monocytes

22
Q

what are Kupffer cells?

A

Kupffer cells are phagocytic cells found in liver sinusoids, forming part of the lining of the sinusoids. they are dirived from monocytes
they remove debris, old erythrocytes and cellular fragments from the blood stream.

23
Q

what are the spaces of Disse?

- function

A

the space of disse is the subendothelial space between hepatocytes and sinusoidal lining cells.

the space of Disse centains short microvilli of hepatocytes, reticular fibres and occassional nonmyelinated nerve fibres

the space of Disse also contains stellate fat-storing cells; preferentially store vitamin A.

the space of Disse functions in the exchange of material between the bloodstream and hepatocytes. hepatocytes DO NOT directly contact the bloodstream

24
Q

what is the definition of the portal lobule?

A

the portal lobule is defined in terms of bile flow. in this concept of liver lobulation, the bile duct is in the centre of the lobule

it contains portions of adjacent classic liver lobules

the portal lobule, viewed in 2-dimensions, is a triangular region with three apices that are neighbouring central veins and a centre in a portal vein.

25
Q

what is the definition of hepatic acinus of Rappaport?

A

this concept of liver lobulation is defined in terms of blood flow from the distributing vessels in a single portal area.

hepatic acinus of Rappaport, veiwed in 2-dimensions, is a diamond shaped region encompassing triangular sections of two adjacent classic liver lobules and is divided by the common distributing vessels

the hepatic acinus of Rappaport can be divided into 3 zones on the basis of the proximity of the hepatocytes to the incoming blood.

26
Q

describe the blood flow to the liver….

A

blood flow into the liver is derived from two sources and is diverged from the portal triads at the periphery of each classic liver lobule toward the central vein.

  1. the hepatic artery brings rich-oxygenated blood from the abdominal aorta and supplies 20-30% of the livers blood
  2. the portal vein brings nutrient-rich blood from the alimentary canal and pleen; it supplies 70-80% of the livers blood.
27
Q

describe the blood flow out of the liver…

A

the blood flow out of the liver occurs via the hepatic vein, formed by the union of numerous sublobular veins, which collect blood from the central veins

28
Q

how is bile collected from hepatocytes to the gallbladder?

A

blie flow is directed toward the periphery of the classic liver lobule (opposite direction of blood flow).

blie is carried in a system of ducts that culminate in the left and right hepatic ducts, which leave the liver and carry blie to the gallbladder.

  • blie canaliculi
  • blie ducts
29
Q

what are bile canaliculi?

A

bile canaliculi are expanded intracellular spaces between adjacent hepatocytes that form tiny canals for the initial flow of bile

the recieve the liver’s exocrine secretion (bile) and carry it to the canals of Hering (bile ductules) at the very periphery of classic liver lobules

30
Q

what are canals of Hering?

A

canals of Hering are bile ductules formed by the combination of bile canaliculi

31
Q

what are hepatic ducts?

A

hepatic ducts are formed by the fusion of enlarged bile ducts.
hepatic ducts leave the liver at the porta hepatis.

32
Q

describe hepatocytes…

A

hepatocytes are large polyhedral cells (20-30um in diameter) that possess abundant RER and SER; numerous mitochondria, lysosomes, and perioxisomes; several golgi complexes and many lipid droplets and glycogen deposits.

they contain one round nucleus; about 25% of cells are binucleated; occassionally, nuclei are polyploid.

33
Q

describe the surfaces of hepatocytes…

A
  • hepatocyte surfaces facing the space of disse possess microvilli (facilitate the transfer of materials between the hepatocytes and the blood
  • abutting surfaces of adjacent hepatocytes
    1. frequently delineate bile canaliculi, small, tunnel-like expansions of the intercellular space.
    2. possess microvilli that extend into the bile canaliculus
    3. also have gap junctions.
34
Q

what are the functions of the hepatocyte? (6)

A
  1. exocrine secretion
  2. endocrine secretion
  3. storage of metabolites
  4. gluconeogenesis
  5. detoxification
  6. IgA transfer
35
Q

what is the exocrine function of the hepatocyte?

A

exocrine secretion os hepatocytes involves the production and release of 600-1200ml of bile per day

36
Q

what is bile?

A

bile is a fluid composed of bilirubin glucuronide (bile pigment), bile acids (bile salts), cholesterol, lecithin, phospholipids, ions, IgA and water.

37
Q

what is the metabolic fate of hydrophobic bilirubin?

A

hydrophobic bilirubin (a breakdown product of haemoglobin) is converted into water-soluble bilirubin glucuronide (a nontoxic compound) on the SER of the hepatocytes

38
Q

what is the endocrine function of hepatocytes?

A

the endocrine secretion of hepatocytes involves the production and release of several plasma proteins and urea).

hepatocytes can also manufacture and release nonessential amino acids.

39
Q

what are the plasma proteins produced and released by hepatocytes?

A

plasma proteins:

1. prothrombin 
2. fibrogen
3. albumin
4. factor III
5. lipoproteins
40
Q

what metabolites are stored in hepatocytes?

A

metabolites are stored in the form of glygogen (stored glucose) and triglycerides (stored lipids)

vit A, vit D iron

41
Q

how does the gallbladder communicate with the common hepatic duct?

A

via the cystic duct

- which originates at the neck of the gallbladder

42
Q

what are the 4 layers that make up the wall of the gallbladder?

A
  1. the mucosa is composed of a simple columnar epithelium and a richly vascularised lamina propria. when the gallbladder is empty, the mucosa displays highly convoluted folds.
  2. the muscle layer is composed of a thin, oblique layer of smooth mucle cells
  3. the conneective tissue layer consists of dense, irregular collagenous connective tissue and houses nerves and blood vessels
  4. the serosa covers most if the gallbladder, but adventitia is present wher the organ is attached to the liver
43
Q

what is the main function of the gallbladder?

A

the gallbladder concentrates, stores and releases bile by the contraction of its muscular walls, stimulated by cholecytokinin.
the contraction forces bile from its lumen into the duodenum.

44
Q

what does the liver weigh?

what is the location of the liver?

A

the liver weighs ~1500g and accounts for ~2.5% of adult body weight.
the liver is the largest mass of glandular tissue and the largest internal organ of the body.

the liver is located in the upper right and partially in the upper left quadrants of the abdominal cavity, protected by the ribcage

45
Q

in the embryo, how does the liver develop?

A

the liver develops as an endodermal evagination from the wall of the foregut to form the hepatic diverticulum

the diverticulum proliferates, giving rise to the hepatocytes, which become arranged in cellular cords, thus forming the parenchyma of the liver.

the original stalk of the hepatic diverticulum becomes the common bile duct. an outgrowth from the common bile duct forms the cystic diverticulum that gives rise to the gallbladder and cystic duct

46
Q

describe liver sinusoids…

A

liver sinusoids are lined by fenestrated endothelial cells, lack a basal lamina and deliver blood directly to the central vein

47
Q

what do pancreatic a-cells secrete?

A

glucagon

48
Q

what do pancreatic b-cells secrete?

A

insulin

49
Q

what do submandibular cells secrete?

A

lysozyme

50
Q

what do hepatocytes secrete?

A

plasma proteins:

  • fibrinogen
  • prothrombin
  • albumin

Histology (16 decks)

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