CHAPTER 16
Digestive Glands and Associated Organs
317
1
2
3
Central vein
Central
vein
Hepatic acinus
( 2 central veins +2 portal triads)
Sublobular
vein
Portal lobule
(3 central veins +1 portal triad)
Portal triad
Portal triad
Bile ductule
Bile ductule
Bile
canaliculus
Portal vein
Portal vein
Hepatic artery
Hepatic artery
Hepatic
arteriole
Left lobe
Gallbladder
Inferior
vena cava
Portal
vein
Classic lobule
( 6 portal triads + 1 central vein)
Bile
duct
Aorta
Falciform
ligament
Right
lobe
Venous
(hepatic)
sinusoids
Hepatocytes
(hepatic plate)
Central
vein
SYNOPSIS 16-1
Functions of the Liver
Exocrine function
:
secretion of bile into the duodenum to help digest fat and eliminate waste products, such as bilirubin
and excess cholesterol. The main components of bile include water, bile salts, bilirubin, cholesterol, fatty acids, lecithin,
and electrolytes.
Endocrine function
:
synthesis of majority of plasma proteins such as F
brinogen, prothrombin, lipoproteins, and albumins,
and their release into the bloodstream.
Metabolism and detoxiF
cation
:
breakdown of proteins, toxic substances, and many drugs; oxidation and conjugation of
toxins, estrogens, and other hormones; and elimination via bile or urine.
Storage
:
storage of iron; blood; glycogen; triglycerides (lipid droplets); and vitamins A, D, and B12.
Figure 16-11.
General structure of the liver.
The
liver
is the largest gland and the largest visceral organ in the body. It has left and right lobes and is covered by a thin capsule called the
Glisson
capsule
. The liver is located in the superior right and superior left quadrants of the abdominal cavity (see ±ig. 16-1). The liver contains numerous
hepatocytes
arranged in plates;
venous sinusoids
(
hepatic sinusoids
) run between these hepatic plates. The liver has a rich vascular supply; it receives
blood from both the
portal veins
and the
hepatic artery
. Secretory products and waste drain out of the liver by three routes: (1) the
hepatic venous
system
, in which blood drains from the hepatic sinusoids (
white arrows in detail view above
) to the central vein, then to the sublobular vein, and
F nally to the large hepatic veins; (2) the
duct system for bile
, in which bile drains from bile canaliculi (
green arrow in the detail view above
) to the
bile ductules, from the ductules into the hepatic ducts, which then join the
cystic duct
from the gallbladder; and (3) the
lymphatic vessel system
, in
which lymph from the liver drains into the hepatic lymph vessels and passes through the lymph nodes near the liver to then drain into the thoracic
duct. The liver has many lobules. These can be classiF ed into three types based on their structure and function. (1)
Classic lobule
(
hexagon shape
)
is the traditional way to describe liver lobules based on the direction of the blood fl ow. Each lobule contains six portal triads and one central vein;
blood fl ows from portal triads into a central vein. (2)
Portal lobule
(
triangular shape
) emphasizes the exocrine functions of the liver (production
of the bile). This classiF cation is based on the direction of the bile fl
ow. Each lobule contains three central veins and one portal triad in the center.
The bile is produced by hepatocytes and enters the bile canaliculi to then drain into the bile ductule in the portal triad. (3)
Hepatic acinus
(
diamond
shape
), which includes two central veins and two portal triads in each lobule. This classiF
cation is based on the blood oxygen level, nutrient supply,
and metabolic activity. It is an important concept for liver pathology. The hepatic acinus can be subdivided into three zones:
zone 1
,
zone 2
, and
zone 3
(±ig. 16-12A).
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