Lecture 18: Histology of the Glandular GI System

Pancreas

Functions :Exocrine and Endocrine

• Secretes digestive enzymes that act in the small intestine

• Secretes hormones important for metabolism of absorbed nutrients

Endocrine Glands

What type of gland?

-produce hormones adn are always rich in capillaries

-hormones are released outside the body and picked up by blood vessels

Exocrine Glands

What type of gland?

-secrete substance to specific organs via duct systems

Islets

I

Serous Acini

A

Intralobular Ducts

D

Ducts and Blood Vessels

V

Pancreatic Cancer

-usually carcinoma of duct cells

-usually at the head of the organ near the duodenum

-tumor usually asymptomatic until growth and metastasis are advanced

Pancreatic Adenocarcinoma

the most common tumor arising in the pancreas

Pancreatic Adenocarcinoma

-arise form the pancreatic ductal epithelium

-arise in the head of the pancreas where they tend to obstruct the common bile duct

-pts present with painless obstructive jaundice

Courvoisier's Law

"A painless jaundice in the presence of a palpable gallbladder is rarely due to gallstones"

Exocrine Pancreas

Acini composed of serous cells

High rate of protein synthesis

Secretion of digestive enzymes

Duct Cells

-in the exocrine pancreas

-pale staining and secrete a solution of sodium bicarbonate

Pancreatic Acini

Secretin

-hormone that initiates centroacinar and intercalated duct cells to secrete HCO3- to hydrate, flush, and alkalinize enzymatic secretions

-Centroacinar Ducts

-Intercalated Ducts

-Intralobular Ducts

-Interlobular Ducts

name the Exocrine Pancreatic Ducts from Distal to Proximal

Higher

there is a _____________ pH in acini and ducts which keeps enzymes inactive

Acute Pancreatitis

-proenzymes may be activated and digest pancreatic tissues

-possible causes: infection, gallstones, alcoholism, drugs, and trauma

Pancreatitis

CCK

-stimulates enzyme secretion from acinar cells

Secretin

promotes water and HO3- secretion by duct cells

Islets of Langerhans (pancreatic islets)

-~1-2 million per pancreas, mainly in tail

-Origination from endoderm (same origin as acini)

Islets of Langerhans (pancreatic islets)

•Small polygonal or round lightly stained cells

•Separated by fenestrated capillaries

•Autonomic nerve fibers also found in association with each

Alpha Cells

-release glucagon

Raises concentration of glucose and fatty acids in blood - catabolic

More peripheral

Beta Cells

-release insulin and amylin

Decreases concentration of glucose in blood -anabolic

More central

Delta Cells

-release small amounts of somatostatin

Growth hormone inhibiting hormone

Regulates endocrine, neurotransmission, and cell proliferation

Epsilon Cells

-produce ghrelin

-Influences appetite and rate of energy use

PP Cells

-pancreatic polypeptide

-self regulates panceratic secretion

Alpha Cells

-acts on several tissues to make energy stored in glycogen and fat available thru glycogenolysis and lipolysis

-increases blood glucose content

Beta Cells

-acts on several tissues to cause entry of glucose into cells

-promotes decrease of blood glucose content

Delta Cells

-inhibits release of other islet cell hormones thru local paracrine action

-inhibits release of GH and TSH in anterior pituitary and HCl secretion by gastric parietal cells

PP Cells

-stimulates activity of gastric chief cells

-inhibits bile secretion, pancreatic enzyme, and bicarbonate secretion, and intestinal motility

Glucose

Activity of Alpha and Beta cells is regulated by

______________ levels

Decreased

___________________ glucose: stimulates Alpha cells and inhibits Beta cells

The Hilum

the liver is surrounded by a capsule which thickens where?

Hepatocytes

-synthesize and secrete major plasma proteins

-gluconeogensis

-detoxification

-deamination

-storage of vitamin A

-removal of erythrocytes

-storage of iron

-production of bile

-storage of glucose

Hepatocytes

Large polyhedral cells with spherical, centrally located nuclei arranged in cords

Eosinophilic cytoplasm

Basophilic bodies

Glycogen granules

Fatty Liver Disease

-reversible condition

-large lipid droplets containing TGs accumulate in hepatocytes cia steatosis

-occurs in ppl with alcoholism or obesity

-may progessive to hepatitis or steatohepatitis

Venule

-branch of portal vein

-blood rich in nutrients but low in oxygen

Arteriole

-branch of hepatic artery

-brings oxygen

Bile Ductule

-branch of bile conducting system

-lined by cuboidal epithelium

Sinusoids

•Emerge from the peripheral branches of portal vein and hepatic artery

•Flow towards and converge on central vein

•Contain thin, discontinuous linings of fenestrated endothelial cells

Sinusoids

-allow plasma to fill Space of Disse and contact hepatocytes for uptake and release of proteins, toxins, and nutrients

Sinusoids

Contains:

-endothelial cells (fenestrated)

-Kupffer cells

-Stellate Cells

Kupffer Cells

Fixed macrophages that phagocytizeFixed macrophages that phagocytize particulate matter and senescent RBCs

Free heme and iron for reuse or storage in ferritin complex

May act as APC for bacteria particulate matter and senescent RBCs

Stellate Cells

-not distinguishable with light microscopy

Store vitamin A and fat soluble vitamins

Produce extracellular matrix, including collagen.

Smooth ER

location where bilirubin and bile acids taken up from perisinusoidal space

and secreted into bile canaliculi

RER

location of synthesis of plasma proteins for perisinusoidal space

Perisinusoidal Space

-location of stellate cells

-produces ECM and stores vitamin A

IVC

hepatic veins drain into the _________________-

oxygen and nutrient poor

describe the blood in the central vein

Nutrient Rich

describe the blood in the portal vein

Zone 1

What Zone?

-rely on aerobic metabolism, often active protein synthesis

-periportal

Zone 3

What Zone:

-lower oxygen and nutrients, involved in detoxification and glycogen metabolism

-most likely site of fatty accumulation and ischemic necrosis

-pericentral

Hepatic Acinus

supplies oxygenated blood to hepatocytes

Portal Lobule

drains bile from hepatocytes to the bile duct

Hepatic Lobule

-drains blood form the portal vein and the hepatic artery to the hepatic or the central vein

Zone 1

what zone is the MOST oxygenated?

Bile Canaliculi

form from grooves in surfaces of adjacent hepatocytes, with edges sealed by tight junctions

Smooth ER

location where bilirubin and bile acids taken up from perisinusoidal space and secreted into bile canaliculi

Canals of Hering

canaliculi empty into ___________________-

Cholangiocytes

Epithelial cells of hepatic ductules that modify the composition of bile.

Opposite

Bile and blood flow ______________ directions in the lobule

Bile Canaliculi

Bilirubin

-pigmented breakdown product of heme that is released from splenic macrophages primarily, but also from Kupffer cells,

-carried to hepatocytes bound to albumen.

Bilirubin

give feces and urine their characteristic colors.

Prehepatic

Jaundice classification:

-due to overproduction or impaired uptake by the liver

Hepatic

Jaundice Classification:

-decreased conjugation

Posthepatic

Jaundice Classification:

-decreased excretion

-intra or extrahepatic obstruction

Underdeveloped state of the Hepatocytes SER

frequent cause of jaundice in newborns

Blue light

what is a common treatment for jaundice in newborns?

Prehaptic Jaundice

assoc with unconjugated hyperbilirubinemia

Posthepatic Jaundice

assoc with conjugated hyperbilirubinemia

Canaliculi ---> Ductules ---> Ducts

flow of bile

Gallbladder

Mucosa - simple columnar epithelium (cholangiocytes)

Microvilli on surface

Many mitochondria for energy for pump to move sodium into the intracellular space (concentrating bile) then into intercellular space

Lamina propria and submucosa are thin : may contain mucous glands

Muscularis externa arranged in oblique spiral to propel bile out.

Gallbladder

saclike structure that stores and concentrates bile, and releases it into the duodenum after a meal.

CCK

Stimulation of the Gallbladder:

lipid in duodenum promotes release of ______________

CCK

-stimulates contraction of the gallbladder in order to empty bile into the duodenum

Bile

emulsifies fat facilitating hydrolysis of lipids by pancreatic lipases

Cholelithiasis

-presence of stones within the biliary system

Hepatocytes

-large eosinophilic cells with central nuclei and prominent nucleoli

-cells arranged in plates one cell thick with intervening sinusoids

-diverse metabolic functions

-secretion of bile into canaliculi

Liver

-fat metabolism

-carbohydrate metabolism

-protein metabolism

-storage of glycogen, vitamins, and iron

-intermediary metabolism

-interface between organs and blood supply

-secretion