reversed to form very low density lipoprotein (VLDL)from chylomicra.
Other digested materials travel through the hepatic portal veinto the liver
where hepatocytes process the digested nutrients.
Cell types in the small intestine include enterocytes (absorption),
Paneth cells (production of lysozyme, defensins, and cryptidins), gob-
let cells (mucus),andenteroendocrine cells (secretion of peptide hor-
mones).All of those cells originate from a single stem cellin the crypt.
New cells are born in the crypt, move up the villus, die by apoptosis, and
are sloughed off at the tip. The primary function of the colon,which
appears histologically as crypts with prominent goblet cellsandnovilli,
is water resorption.
The major salivary glands (parotid, submandibular,andsublingual)
are exocrine glands that secrete amylaseand mucus, primarily regulated
by the autonomic nervous system.In contrast, the pancreashas both
exocrine (acinar cells)andendocrine (islet cells)components that syn-
thesize pancreatic juice and blood sugar–regulating hormones, respectively.
The exocrine pancreas is primarily regulated by the hormones cholecys-
tokinin (CCK) and secretin, which primarily regulate acinar and ductal
secretion, respectively.
Theliveris also a dual-function gland whose exocrine product is bile,
synthesized by hepatocytes, and transported by a duct system to the gallblad-
der for storage and concentration. Bile emulsifies lipidsfor more efficient
enzymatic access. The endocrine products include glucoseandmajor blood
proteins (albumin, fibrinogen, coagulation proteins).The liver subserves
numerous other functions including synthesis of cholesterol and detoxifica-
tion of lipid-soluble drugs,such as phenobarbitalby the SER(using the
P450 enzyme system).Alcohol detoxificationis one of the major processes
carried out in the hepatocyte. Alcohol detoxification involves alcohol dehy-
drogenase (ADH), MEOS (microsomal ethanol oxidation system, P450
enzymes in the SER), and catalase in peroxisomes. The primary metabolic
pathway is ADH. At higher alcohol levels the MEOS and even catalase systems
are activated. The bile canaliculusis defined as apical,thejunctional com-
plexesaslateral,and the blood surface with the space of Disseandhepatic
sinusoidsis considered basal.The sinusoids are lined by hepatic stellate
cells,endothelial cells, and Kupffer cells.Thehepatic stellate cellsare
affected following chronic alcohol toxicity and are converted into myofibrob-
lastsduring the onset of cirrhosis.Those cells synthesize large quantities of
30 Anatomy, Histology, and Cell Biology