Microanatomy of liver, pancreas, salivary gland

Question 1

Liver development and portal system

Answer 1

-hepatic artery- supplies oxygenated blood to liver

-portal vein- provides nutrient rich blood from small intestine into liver, and then drains back into heart
>portal means there are multiple capillary beds in the venous system (in this example, one in gut, and one in liver)

Question 2

Where do vessels enter the liver?

Answer 2

-enter at hilus on visceral side

Question 3

Smallest vessels in portal canal

Answer 3

-interlobular portal venules and interlobular hepatic arteriole
>venules end directly in sinusoids
>arteriole mostly delivers blood to capillary network in interlobular connective tissue but a small amount also enters sinusoids through the terminal arterioles

Question 4

Hematopoiesis in liver

Answer 4

-during development, blood cells developed in liver

Question 5

Liver Histo

Answer 5

-capsule-dense irregular CT
-fibrous CT branches (CT septa) in liver extending throughout (interlobular CT)
>very prominent in pig (reason why not great to eat)
-hexonal structures=hepatic lobules
>have portal area (includes artery,vein, and bile duct)
-central vein/venule in each lobule
-lobules filled with hepatocytes making sheets called hepatic cords

Question 6

What supports hepatocytes and sinusoids?

Answer 6

reticular fibre network

Question 7

Central vein

Answer 7

-each lobule has central vein
-All central veins will eventually join up and drain to vena cava
-central vein is lined by endothelium resting on thin adventitia

Question 8

Portal area

Answer 8

*located in 3/6 corners of lobule
-interlobular arteriole (hepatic artery branch)
-interlobular bile duct
-interlobular portal venule (portal vein branch)

Question 9

Venous drainage of liver

Answer 9

-sinusoids converge towards and open in central vein (in center of hepatic lobule)
-central veins of all the lobules join to form sublobular veins at periphery of lobules, and eventually empty into hepatic veins and caudal vena cava

Question 10

Lymphatic drainage of liver

Answer 10

-lymph formed in perisinusoidal space, and flows towards periphery of the lobule and enter into intercellular space in portal area
-the lymph capillaries in the portal area then move lymph into large vessels that leave the hilus and enter the hepatic lymph nodes

Question 11

Hepatic sinusoids

Answer 11

-large dilated blood capillaries communicating with each other
-Basal lamina is interrupted (except ruminants who have more pores and continuous basal lamina) endothelium is separated from hepatocytes by perisinusoidal spaces (of disse)
>hepatocyte microvilli project into the space
-very porous allowing everything from digestive system to go through pores and reach hepatocytes
-contains Kupffer cells

Question 12

Blood movement

Answer 12

-moves from portal area into sinusoids/hepatocytes and then into the central venule of liver

Question 13

Stellate macrophages (Kupffer cells)

Answer 13

-highly phagocytic cells derived from monocytes; clean up system
-permanently in endothelium of liver scattered between endothelial cells
-They spread their pseudopodia through endothelial pores or between cells

Question 14

Glycogen stores in liver

Answer 14

-pinkish material is glycogen
-appear in clusters/rosettes
**will disappear after fasting as they are moved into other stores

Question 15

Hepatic cord size

Answer 15

-one-cell thick sheets

Question 16

Hepatocyte appearance

Answer 16

-contain centrally placed spherical nucleus and one or more prominent nucleoli
>can sometimes have binucleated hepatocytes
-numerous mitochondria, prominent golgi body, many lysosomes and ribosomes, well developed rER and sER

Question 17

Hepatocyte functions

Answer 17

-synthesize plasma proteins (rough ER)
-detoxification reactions (smooth ER)
-cholesterol and bile salt synthesis and exocrine secretion
-glycogen storage and blood glucose management
-gluconeogensis
-amino acid deamination and urea synthesis

Question 18

Hepatocyte surfaces

Answer 18

-6 surfaces
-microvillous surface- face perisinusoidal space
-canalicular surface- borders bile canaliculi
-contact surface- may have gap junctions and desmosomes among adjacent hepatocytes
-free surface faces the sinusoids

Question 19

Bile production

Answer 19

-hepatocytes absorb bilirubin from blood, and cells will conjugate and release bilirubin into bile along with bile salts, protein, and cholesterol

Question 20

Bile canaliculi

Answer 20

-form between 2 hepatocytes
-bile produced from hepatocytes will be released into bile canaliculi (microvilli project into lumen of canaliculis)
-bile flows from canaliculis into bile ductules (lined by simple cuboidal epithelium)
-then flows into interlobular bile ducts in the portal canals converge to form intrahepatic bile ducts

Question 21

Classic hepatic lobule

Answer 21

-drain blood from the portal vein and hepatic artery to the hepatic or central canal
>around one lobule (hexagon shape)

Question 22

Portal lobule

Answer 22

-portal area drains to surrounding lobule central canals (triangle)= exocrine function
-drain bile from hepatocytes to the bile duct

Question 23

Portal acinus

Answer 23

-diamond shaped drainage to nearby central canal
>least oxygenated closer to central canal (zone III), most oxygenated near portal area (zone I)
-supplies oxygenated blood to hepatocytes

Question 24

Acinus zones

Answer 24

-acinus is divided into zones that correspond to distance from arterial blood supply
>hepatocytes closest to arterioles (portal area; zone I) are most oxygenated; hepatocytes farthest away are least oxygenated (zone III)
»zone I are the first to see and potentially absorb blood-borne toxins. Most metabolically active

Question 25

Gallbladder

Answer 25

-bile being produced continuously by hepatocytes in liver and drained into gallbladder
-cystic duct from gallbladder than moves it to duodenum

Question 26

Gallbladder histo

Answer 26

-simple columnar epithelium that extends into mucosal crypts. Tight junctions between epithelial cells, and microvilli present
-goblet cells in ruminants
-stores and concentrates the bile by water reabsorption and inorganic salt absorption

Question 27

Layers of gallbladder

Answer 27

-Tunica muscalaris: circularly arrangedsmooth muscle cell layer
-Tunica serosa on free side
-Tunica adventitia in hepatic attachment area

Question 28

Secretory units

Answer 28

-serous (zymogens), mucous, or seromucous glands possible depending on salivary gland
-myoepithelial cells are located between secretory cells and the basal lamina

Question 29

Dog parotid gland

Answer 29

serous

Question 30

Horse mandibular gland, dog and cat sublingual land

Answer 30

-seromucous
-serous demilune possible

Question 30

Mandibular gland dog/cat, sublingual ox,sheep,pig

Answer 30

mucous

Question 31

Intercalated ducts

Answer 31

-short ducts lined by cuboidal epithelium
-connect secretory acini with striated ducts

Question 32

Striated ducts (salivary or intralobular ducts)

Answer 32

-largest structures in lobules
-lined by simple columnar epithelium
-cells form basal folding containing mitochondria
-basal membrane has energy requiring pumps
-participate in secretory process

Question 33

Interlobular ducts

Answer 33

-located in interlobular connective tissue
-lined by simple columnar epithelium which changes to stratified columnar or stratified cuboidal epithelium

Question 34

Main duct

Answer 34

-single duct that leaves the salivary gland
-lined by stratified columnar or stratified cuboidal epithelium

Question 35

Parotid salivary gland

Answer 35

-lobules (anything inside is intralobular)
-inbetween lobules are interlobular)
-acinar cells releasing zymogens

Question 36

Mandibular salivary gland (dog and cat)

Answer 36

-predominantly mucous producing
-striated ducts present

Question 37

Mandibular salivary gland of horse

Answer 37

-seromucous glands

Question 38

Pancreas

Answer 38

-encapsulated, lobulated, compound, serous tubule-acinar gland containing endocrine and exocrine parts
>Exocrine part: produce enzymes (amylase, lipase, trypsin)
>Endocrine part: produce hormones (insulin, glucagon)

Question 39

Exocrine part of pancreas

Answer 39

-organized into lobules containing intralobular ducts (non-striated)
-tubuloacinar secretary units with centroacinar cells
-glandular epithelial cells produce enzymes

Question 40

Duct system of pancreas

Answer 40

-intercalated ducts begin in middle of glandular unit at acinus (surrounded by centroacinar cells) and drain to intralobular ducts (cuboidal epithelium; non-striated) and then into interlobular ducts (simple columnar)

Question 41

Endocrine part of pancreas

Answer 41

-pancreatic islets located between exocrine pancreas (acini)
-contain A, B, C, D, and F cells (spprox. 75% are B cells producing insulin; A cells produce glucagon)

Question 42

Pancreatic acinus

Answer 42

-acinar cells secreting enzymes, and then move into intralobular duct, and then eventually interlobular duct
-centroacinar cells (cells of duct system)- duct system extends into excretory units (acinar cells)

Question 43

Centroacinar cells

Answer 43

-cells of intercalated duct that insert into acinar lumen
-secretin from enteroendocrine cells in the duodenum and jejunum cause release of serous secretion rich in bicarbonate to neutralize the acidic gastric contents entering the duodenum

Question 44

Acinar cells

Answer 44

-stimulated by cholecystokinin
- release zymogen granule contents (trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase, pancreatic amylase, lipases)