Structure of the liver
The histological features of the liver are summarized below.
•
Structural
component of liver include
–
Connective
tissue stroma
–
Parenchyma
–
Portal
triad
–
Sinusoids
•
There
are three way to describe the structure of liver
–
The
classic lobule
–
The
portal lobule
–
Portal
acinus
Classical lobule
•
Connective
tissue stroma
– liver
is covered by a thin connective tissue capsule (Glisson's capsule) and extends
into its interior as numerous branching septa.
–
Blood
vessels, nerves, lymphatic vessels and bile ducts travel within these septa.
•
Parenchyma
– In
cross section, the substance of liver appears to be made up of hexagonal areas
that constitute the hepatic lobules. In certain animals (eg, pigs micrograph b
in adjacent figure), the lobules are separated by connective tissue septa (C). But in human (micrograph c in
adjacent figure) the septa are not distinct and the lobules appear to merge
with each other making it difficult to establish the exact limits between
different lobules.
– Each
lobule consists of interconnected plate of liver cells (hepatocytes). These
plates are one cell thick that branch and anastomose with each other to form
network.
–
The
center of the lobule is occupied by a central vein (V) which is a tributary of hepatic vein
– Along
the periphery of each lobule there are angular intervals filled by connective
tissue. These intervals are called portal canal/tract (T). Each portal tract
contains a venule (a branch of the portal vein), an arteriole (a branch of the
hepatic artery), a duct (part of the bile duct system).These three structures
collectively form a portal triad.
• venule
contains blood coming from the superior and inferior mesenteric and splenic veins.
• The
arteriole contains oxygen-rich blood coming from the celiac trunk of the
abdominal aorta.
• The
duct, carries bile synthesized by the hepatocytes and eventually empties into
the hepatic duct
Bile canaliculi
– Each
liver cell is cuboidal presenting six surfaces, out of which two surfaces are
related to the sinusoids and the remaining surface are in contact with the wall
of adjacent hepatocyte. Wherever two hepatocytes are in contact, they make a
tubular space between them known as the bile canaliculus
–
Bile
is synthesised by hepatocytes and secreted into bile canaliculi
–
Bile
canaliculi of adjacent hepatocyte plates merge to form canals of Hering
or bile ductules which latter finally drain into the bile duct in the
portal canal
Portal lobule
• The
portal lobule emphasizes the exocrine functions of the liver
• The
portal lobule includes the territory of liver tissue centered around a portal
triad, and is drawn by joining the central veins of the three adjacent liver
lobules
• The
territory of portal lobule includes those portion of three classic lobules that
secrete the bile that drains into its axial bile duct.
Liver acinus
• Liver
acinus is the structural unit that provides the best correlation between blood
perfusion and metabolic activity
•
It
consists of the area of liver tissue supplied by one hepatic arteriole running
along the line of junction of two hepatic lobule. Two central veins lie at the
ends of the acinus.
Structure of
Gall Bladder
The histological features of the gallbladder are summarized below.
The histological features of the gallbladder are summarized below.
• consists
of a mucosa composed of simple columnar epithelium and lamina propria,
fibromuscular layer, and a serous membrane
•
Mucous
membrane:
– lined
by is a single layer of tall columnar absorptive cells bearing numerous short
irregular microvilli . Goblet cells are absent.
– Mucosa
is highly folded, and the folds are called rugae.The submucosa (S) is relatively loose.
• The
fibromuscular coat: is composed of fibrous tissue (A) mixed with smooth muscle
cells (M) which are arranged loosely in longitudinal, circular and oblique
bundles but do not form distinct layers.
References
Gray's Anatomy
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy
Wheater's Functional Histology
References
Gray's Anatomy
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy
Wheater's Functional Histology