Histology                                                                                                                     Stanley Shostak
BioSc 1450                                                                                                                  Spring 04

Lecture 14. Pancreas, Liver and Gallbladder

Pancreas: compound (mixed) gland (endocrine and exocrine); releases enzymes as proenzymes (chymotrypsin, trypsin, elastase, carboxypeptidase) and active enzymes (DNase, RNase, pancreatic lipase, pancreatic amylase); release controlled by secretin from APUD; paracrine hormones
exocrine pancreas: compound tubuloalveolar (tubuloacinar) gland; capsule gives rise to septa; separates gland into lobules;acinar (alveolar) cells (basally basophilic with apical eosinophilic zymogen granules) coupled to centroacinar cells (with pale, vesicular nuclei) and intercalated ducts release alkaline secretion rich in digestive enzymes > interlobular ducts > main duct

proteases: break down polypeptides to dipeptides
lipase: breaks down lipids to fatty acids, monoglycerides and glycerol within dudoenum and proximal jejunum
endocrine pancreas = pancreatic islets (= islets of Langerhans) scattered among serous acini; 5 cell types distinguished histochemically: a (A) cells (generally peripheral [human], central [monkey]) > glucagon;
b (B) cells (most populas; located centrally [human], peripherally [monkey]) > insulin;
(D/C cells: least numerous)
G (C) cells > gastrin;
d (D) cells > somatostatin; PP cells > pancreatic polypeptide

Liver: stroma of capsule (Glissons capsule) and septa (pig, not in dog or monkey) separating hexagon-shaped lobules; reticular fibers support sinusoidal/plates structure; lobes divided into lobules

multiple functions: especially regulates blood-glucose levels; detoxification of various drugs, metabolic byproducts, hemoglobin by action of microsomal mixed-function oxidase of sER and peroxidase of peroxisomes; endocrine (kind of): plasma proteins and components: fibrinogen, albumin, prothrombin, and lipoproteins; storage of glycogen and lipids; gluconeogenesis from noncarbohydrate sources; transport of IgA into bile; deamination (anticipates CHO storage) and urea formation
 

parenchymal cells = hepatocytes (polygonal cells, 1 to 2 nuclei, with bile canaliculus between them; defined by occluding junctions) arranged in anastomosing plates = trabeculae (1 to 2 cells thick; radiate from central vein); regulated by paracrine hormones of APUD cells in alimentary tract

sinuoids: lined by fenestrated endothelium (sinusoidal lining cells); discontinuous capillaries = sinusoids (incomplete endothelium running between plates of hepatic cells [single cell thick]) > central (terminal) vein > sublobular veins > hepatic vein

hepatic fixed macrophages (= Kupffer cells): macrophages derived from monocytes; linine sinusoids (see phagocytosis slide).

fat-storing (Ito) cells in (space of Disse): may accumulate vitamin A.

Classic Lobule: sinusoid drains to central vein; portal areas = apices (= site of triad [cross section]); triad = hepatic artery, portal vein, and bile duct. Terminal plates = peribiliary area

Portal Lobule (follows bile flow): area surrounding triad (cross section); bile drains to bile duct; portal confluence central

exocrine function: production of bile; note: bilirubin glucuronide is water-soluble conjugate of nonsoluble bilirubin (toxic breakdown product of hemoglobin)
bile ductules > cholangioles (= canals of Hering) > bile duct (in portal areas) > cystic and common hepatic (bile) ducts > gallbladder > cystic and common hepatic (bile) ducts > duodenum Portal Acinus of Rappaport (brings hepatic arterioles into picture; follows blood flow): area surrounding (longitudinal section) hepatic artery (and portal vein); supplies adjacent parts of lobule with freshest blood; drains toward central vein.

Gallbladder: stores and concentrates bile.

lamina propria lined by simple columnar epi thrown into highly convoluted folds which disappear on distention; occasional tubuloalveolar mucous glands.
muscularis externa: obliquely oriented smooth muscle.
serosa = adventitia: binds to liver;
cholecystokinin: released by intestinal APUD cells
last revised: -3-04-04