histo- gallbladder & pancreas.doc

7/28/2019 histo- gallbladder & pancreas.doc

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GALLBLADDER (histo)- pear-shaped hollow organ occupying a shallow fossaon the inferior surface of the liver- consists of a fundus, body & neck that continues intothe cystic duct- variable in shape- frequently the site of pathological processes

Fxns: store, concentrate & release into the duodenum thebile secreted by the liver

- all but the hepatic surface is covered by a serosacontinuous with that covering the liver- wall consists of a thin subserosal layer of CToverlying a layer of smooth muscle

I. MucosaEpithelium - simple columnar with oval nuclei & faintlyeosinophilic cytoplasm

- microvilli are shorter & less regular in theirorientation- tips of microvilli bear minute filiformappendages similar to glycocalyx- intercellular cleft in the upper ½ is wide &

sealed by Zonula Occludens- width is narrow in inactive condition- distended when bile is beingconcentrated by transport of H2O acrossthe epithelium

Lamina propria - highly vascular- loose organization of collagenous &elastic fibers provides flexibility- simple tubuloalveolar glands near theneck of the gallbladder extending into themuscular layer (mucus secretion)- Rockitansky-Aschoff sinuses -- largeinpocketings mistaken for glands- lining continuous with the surfaceepithelium- may represent a pathological changethat permits evagination of the mucosa

Convoluted folds - variable in height that delimitnarrow base or clefts

- in contracted gallbladder -- tall &closely spaced- parallel course- when gallbladder is distended -- short &more widely spaced- reduced to low ridges- branch & anastomose

II. Muscularis - irregular loose network of longitudinaltransverse & oblique bundles of smooth muscle

- spaces between the bundles are occupied bycollagenous & elastic fibers- occasional fibroblasts

III. Serosa - dense CT- rich in collagen & elastin- component cells: fibroblasts, macrophages,occasional clusters of adipose cell- blood vessels, nerves & lymphatics run in thislayer & send branches through the muscular layerto the mucosa

Luschka ducts - peculiar duct-like structure- may be found on the hepatic surface near theneck of the gallbladder- none open into the lumen- some connect with the bile ducts- may be aberrant bile ducts

Cystic duct - continues from the neck of the gallbladder & joins the Common Hepatic Duct (Common BileDuct) which courses downward behind the headof the pancreas

- the 2 pass together to the through themuscularis of the duodenum

Ampulla of Vater (Hepatopancreatic ampulla) - union of cystic duct & common bile duct in their oblique coursethrough the submucosa

- opens into the lumenof the duodenum

Sphincter of Oddi - band of smooth muscle- encircles the bile & pancreatic ducts in thewall of duodenum

- parts:

1. Sphincter choledochus - strong circular band of smooth muscle around the terminal portion of the bileduct

- contraction stops theflow of bile

2. Sphincter pancreaticus - around the pancreatic duct3. Fasciculus longitudinalis - longitudinal bundles of smooth muscle in the space between the ducts

- shorten the intramural portion of the ducts- facilitate the flow of bile into the duodenum

4. Sphincter ampullae - meshwork of muscle fibersaround the ampulla

- undesirable effect of causing reflux of bile intothe pancreatic duct pancreatitis

Blood supply - Cystic arteryVeins - empty into the small veins of the liver with only afew joining the cystic branch of the portal vein

Lymphatic vessels:Rich supply of lymphatic vessels in 2 plexuses: in thelamina propria & outer CT layerLymphatic plexuses drain into larger lymphatics thatpass to the lymph node or nodes at the neck of thegallbladder accompany the cystic & common bileducts traverse several nodes near the duodenumempties into the Cisterna Chyli

Nerve supplyBranches of the Splanchnic sympathetic & Vagus

nerves - both contain contain excitatory & inhibitoryfibersSensory nerve endings - over distension of thegallbladder or spasm of the extrahepatic biliary tractinitiate reflex disturbances in the gut

Histophysiology of the gallbladder- entry of food enteroendocrine cells in the intestinalmucosa release Cholecystokinin carried in the bloodto the gallbladder induces rhythmic contractions of the wall

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- as waves of smooth muscle relaxation pass theampulla of Vater in duodenal peristalsis sphincter of Oddi relaxes permitintermittent outflow of bile- ion channels present in the apical membrane permitfree passage of Na ions- basolateral membranes contain Na,K-pumps- increased solute conc. creates a concentrationgradient that moves H2O across the epitheliumthereby concentrating the bile in the lumen

- functional capacity of the gallbladder is assessedclinically by observing its ability to concentratehalogen salts of phenolphthalein that are radio-opaque- failure to clearly visualize the gallbladder in x-raysindicates that the organ has lost its concentratingpower

PANCREAS- pinkish-white organ lying retroperitoneally on theposterior wall of the abdominal cavity- at the level of L2-L3head - lodged in the concavity of the C-shapedduodenumbody & tail - extend traversely across the posteriorwall of the abdomen to the hilus of the spleen

Length: 20-25cmWeight: 100-150 g

- covered by a thin layer of CT which doesn’t form anopaque capsule- lobulated & the outlines of the larger lobules can beseen with the naked eye- 2nd largest gland associated with the alimentary tract- portions:

Exocrine

Secretion secretes daily about 1.2 L of an enzyme-richfluid

Function Digestion of dietary fats, carbohydrates &

protein

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EXOCRINE

Acinar Tissue - compound acinous gland- made up of many small lobules boundtogether by loose CT- acini -- round or slightly elongated

- consist of 40-50 pyramidal epithelialcells around a narrow lumen

- lumen -- wider during active secretion- cytoplasm near the base of the acinar cells isstrongly basophilic owing to high conc of ribonucleoproteins- prominent nucleolus & peripheral clumps of heterochromatin- apical cytoplasm is filled with secretorygranules- Zymogen granules -- more abundant in acinartissue fixed during fasting

- reduced in # after thecopious secretion induced by ameal- fluid content

- rough ER (20% of cell volume)- free polyribosome- occasional lipid droplets & lysosomes

- no granules in the lumen

Duct Systemcentroacinar cells - cuboidal or squamous cells liningthe duct extend a short distance into the acinus- paleIntercalated ducts intralobular ducts interlobularducts (columnar w/ goblet cells) main pancreaticducts

Duct of Wirsung - larger main pancreatic duct- begins in the tail & runs through the length of thegland- in the head of pancreas, it runs parallel to thecommon bile duct (ductus choledochus) with which itmay have a common opening into the duodenum atthe Ampulla of Vater- sphincter of Oddi controls the opening & closing of the common outlet

Duct of Santorini - always present- lies cranial to the duct of Wirsung- length: 6 cm

Blood SupplySplenic arterypancreaticoduodenal branches of the hepatic &superior mesenteric arteries- walls of capillaries have continuous endothelium

(fenestrated in endocrine)

Veins - join the portal, splenic & superior mesenteric veins

Lymphatic VesselsLymphatic capillaries end blindly among the acini& drain via larger lymphatics that follow thecourse of the blood vessels to reachPancreaticosplenic lymph nodes distributed alongthe upper border of the gland.

Nerve SupplyVagus & Splanchnic nerves via the Splenic nerveplexus

stimulation results in exocytosis & accumulationof secretion in the lumen of the acini & in smallducts

- there is little outflow of secretion from thegland because only very small amount of H2O &electrolytes are added to the secretion

- small clusters of Autonomic ganglion cells- Axons - occasionally penetrating the basallamina & ending in intimate contact with the baseof an acinar cell

- terminations of branches of the vagus nerve

Histophysiology of the Exocrine Pancreas- proenzymes & enzymes:

Trypsinogen trypsin - most abundantChymotrypsinogenProcarboxypeptidaseRibonucleasedeoxyribonucleaseLipaseElastaseAmylase Trypsin inhibitor - CHON

- acinar cells secrete enzymes for digestion of protein,lipid, carbohydrate & other constituents of the food

ingested- to protect the integrity of the gland, secretions areproduced in an inactive form & activated only afterthey are secreted into the lumen of the intestine- Acute Pancreatitis -- proteolytic enzymes areactivated & pancreas is rapidly digested by its ownenzymes often with fatal outcome- secretory activity has a rhythmical cycle with a lowbasal rate of continuous secretion which is greatlyincreased periodically by hormonal stimulationassociated with the ingestion of food

Presence of food in the gastric antrum & passage of acidic products of gastric digestion into the duodenumstimulate release of 2 intestinal hormones:

Secretin - small peptide of 27 AA- when carried in the bloodstream to thepancreas, it stimulates the secretion of alarge volume of fluid containing a high conc.of HCO3- doesn’t stimulate acinar cells- copious alkaline fluid -- produced byepithelial lining of the smaller ducts

- little or no enzymaticactivity- neutralize the acidicchyme entering theintestine from thestomach

Cholecystokinin - 33 AA

- secreted by the mucosa of theduodenum & upper jejunum- when transported in the blood to thepancreas, it binds to specificreceptors in the basolateralmembranes of the acinar cells &induces their release of highlyconcentrated digestive enzymes- acting alone, doesn’t significantlyincrease the outflow from pancreaticducts- coordinated action with secretinresults in secretion of a large volumeof enzyme-rich pancreatic juice

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histo- gallbladder & pancreas.doc