Histology of the liver

1. Pamela.B.Lugwisha(M.D. MScAnatomy)

2. The liver:
 Is the largest gland in the body(largest mass of
glandular tissue in the body)
 Is located in the right upper quadrant(right
hypochondriac, epigastric region and extending
into the left hypochondriac region under the cover
of 5th to 10th ribs)
 Accounts for about 2% of body weight in adults and
about 5% in newborns.

5.  Receives a supply of arterial blood from hepatic
arteries, and a major supply of blood from veins of the
GIT, pancreas and spleen via hepatic portal vein.

6.  The liver is situated directly in the pathway of blood
vessels which convey substances absorbed in the
gastrointestinal tract, making it not only the first
organ to metabolize these substances, but also to be
the first organ to be exposed to ingested toxic
compounds.
 The liver has the ability to degrade toxic compounds,
but it can be overwhelmed and get damaged.

7. The liver:
 appears reddish brown in
color
 Has 2 surfaces;
diaphragmatic and
visceral surfaces
 Diaphragmatic surface;
is related to the concavity
of the inferior surface of
the diaphragm, this
surface is smooth and
dome shaped

8.  Visceral surface; Irregular in shape as this surface is
associated with structures such as the porta hepatis,
gallbladder
 NB; the porta hepatis contains structures that enter
and leave the liver such as portal vein, hepatic artery,
hepatic ducts, lymphatic vessels and autonomic nerve
fibers.

10. Porta hepatis:
 The porta hepatis or hilum of the liver found on the
posteroinferior surface, lies between the caudate and
quadrate lobes.
 In it lie:
The right and left hepatic ducts
The right and left branches of the hepatic artery
The portal vein
Sympathetic and parasympathetic nerve fibers
Hepatic lymph nodes

11. The visceral surface of the liver

12. Structural organization of the liver
 Most of the liver surface is covered by peritoneum
 Below the peritoneum, the liver is surrounded by
Glisson’s capsule
 At the porta hepatis, the connective capsule enters the
organ along with the portal vein, hepatic artery, bile
duct, nerves and lymphatic vessels.

13.  The neurovascular structures branch extensively in the
liver into the smallest branches
 E.g. the hepatic artery and portal vein branch into
smaller vessels that supply the liver lobule and pour
blood into sinusoids.
 Sinusoids are terminal blood channels that are
associated with hepatocytes(liver cells).

14.  The portal vein, hepatic artery and bile duct course
together as a triad, called portal triad
 The liver contains:
The hepatocytes
A stroma of connective tissue
Blood vessels, nerves, lymphatic and ducts

15. Sinusoids between plates of hepatocytes
A surrounding capsule of fibrous connective tissue
A serous cover(visceral peritoneum)
Histologically the liver is made up of:
Parenchyma
Stroma

16. Stroma of the liver:
 Is composed of connective tissue which consists of
three main parts;
First, the liver is covered with a thin connective tissue
capsule that contains collagen fibers and scattered
fibroblasts
The second type o0f connective tissue is the
intrahepatic connective tissue, also composed of
collagen fibers and scattered fibroblasts

17.  The intrahepatic connective tissue include septa that
branch from the capsule accompanying the bile ducts
and vasculature in the portal area to enter the liver
parenchyma.
 Thirdly, within the liver lobules, there is a fine
meshwork of reticular and collagen fibers around the
sinusoids and within perisinusoidal space.

18. Parenchyma of the liver:
 Is composed primarily of liver cells known as
hepatocytes.
 Hepatocytes;
Have centrally placed nuclei
Have cytoplasm filled all the organelles, glycogen
granules and prominent smooth endoplasmic reticula
Are arranged in rows and commonly anastomose with
each other surrounding the sinusoids and bile
canaliculi.

19.  Hepatocytes are polygonal in shape with six or more
surfaces
 These surfaces of hepatocytes:
May relate to a sinusoid
Some surfaces become closely applied to surfaces of
adjacent hepatocytes
 Surfaces of adjacent hepatocytes become partially
separated from each other to form bile a canaliculus.

20. Functions of hepatocytes:
 Synthesis of glycogen and secretion of glucose when
blood levels of glucose fall
 Synthesis of blood proteins concerned with blood
coagulation such as albumin, fibrinogen and globulins
 Control the level of lipids in the blood by synthesizing
lipoproteins.

21. Medical application of lipoproteins
 Lipoproteins are multicomponent complexes of
proteins and lipids that are involved in the transport of
cholesterol and triglycerides.
 Cholesterol and triglycerides do not circulate free in
the plasma because lipids on their own would be
unable to remain in suspension.

22.  The association of the protein with the lipid core
makes the complex sufficiently hydrophilic to be
suspended in the plasma.
 Five classes of lipoproteins have been defined by their
characteristic density, molecular weight, size and
chemical com position.

23.  These are from the largest and least dense to the
smallest and most dense:
Chylomicrons
Very low density lipoproteins(VLDL)
Intermediate density lipoproteins(IDL)
Low density lipoproteins(LDL)
High density lipoproteins(HDL)

24.  The lipoproteins serve a variety of functions in the
cellular membranes and the transport and
metabolism of lipids.
 Precursors of the lipoproteins are produced in
hepatocytes.
 The lipid component is produced in the sER, the
protein component in the rER.

25.  The lipoprotein complexes pass to the Golgi complex
where secretory vesicles containing electron dense
lipoproteins particles bud off and then are released
into the plasma at the cell surface bordering the space
of Disse.

26.  High levels of LDL are directly correlated with
increased risk of developing cardiovascular disease,
high levels of HDL or low levels of LDL have been
associated with decreased risk.

27. Continued; functions of
hepatocytes
 Detoxification of toxic substances such as drugs and
alcohol
 Excretion of unwanted materials from the body
 Secretion of bile
 Bile is secreted by hepatocytes(appears as greenish
yellow fluid), bile contains water, lecithin, bile
pigments(bilirubin& biliverdin) and bile salts(sodium
glycocholate and sodium taurocholate)

28.  Bile has three purposes;
Bile emulsifies fats in the duodenum(during
emulsification, bile salts combine with phospholipids
to break down fat globules, this process of
emulsification allows fats to be absorbed and enhances
absorption of lipid soluble vitamins)
Bile serves as a route for the excretion of bilirubin from
the body
Bile salts neutralize acids that come from the stomach.

29.  Sinusoids: are a type of capillaries that are leaky(their
wall and basement membranes have minute pores)
 Sinusoids have a wide lumen and are closely associated
with phagocytic cells of the liver, the kupffer cells
 Sinusoids receive:
Venous blood from interlobular branches of portal
vein
Arterial blood from interlobular branch of hepatic
artery
 Sinusoids pour blood into the central veins.

32.  As nutrients pass through the sinusoids, the
hepatocytes will act on the nutrients, detoxifying
toxins contained, modify nutrients and at the end, the
sinusoid blood will be purified and cleared of harmful
materials.
 Also hepatocytes will synthesize molecules and secrete
the newly synthesized molecules into the sinusoid
blood.

33.  There is a narrow space between the plasma
membranes of hepatocytes and endothelial wall of
sinusoid
 The space is called perisinusoidal space of Disse
 The perisinusoidal space of Disse contains:
Reticular fibers
Microvilli of adjacent hepatocytes
A small number of fat cells(Ito cells)

35.  The plasma membrane of hepatocytes that borders the
sinusoids is highly folded and contains microvilli
 These surface modifications increase:
Surface area of hepatocytes
The capacity for liver cells to perform physiological
activities such as absorption and secretion.

36.  Portal blood contains nutrients and other materials
absorbed from the gastrointestinal tract.
 The interlobular branches of the portal vein and
hepatic artery, which pour blood into the sinusoids,
are located in the portal areas.
 The liver has many portal areas.

37.  Each portal area contains:
Interlobular portal vein
Interlobular hepatic artery
Interlobular bile ductule
Branches of autonomic
nerves
A Lymphatic channel

38.  Bile canaliculi:
 Are minute intrahepatic bile channels situated
between adjacent hepatocytes
 They form an anastomosing network which is
present on almost all surfaces of the hepatocytes
except where hepatocytes relate to sinusoids
 They are not like ducts because they do not have
their own walls or epithelial linings
 They are limited on all sides by cell membranes of
concerned hepatocytes.

40.  When liver cells secrete bile, they secrete into bile
canaliculi.
 The bile canaliculi join to form intralobular bile
ductules which drain into interlobular bile ductules
present in the portal areas.
 From the portal areas the bile canaliculi unite and
ultimately large ducts are formed(right and left hepatic
ducts)

41. Hepatic lobules
 There are three types of hepatic lobules described by
considering the position of the central vein and
portal area.
 Understanding the morphology of these lobules is
important in the understanding of the morphology of
the liver, and how the liver works.
 The hepatic lobules are:
Classical hepatic lobule
Portal lobule
Liver acinus

42.  Portal areas are special regions of the liver that contains
five structures:
 Tributaries of portal vein
 Branches of hepatic artery
 Branches of bile ducts
 Lymphatic channels
 Autonomic nerve fibers
 The tributaries of portal vein and branches of hepatic
artery together pour blood into the sinusoids, so the
sinusoids contain both oxygenated and deoxygenated
blood.

43.  Central veins:
Are initial venous tributaries that receive blood from
sinusoids
Are tributaries of hepatic veins

44.  Classical hepatic lobule:
Hexagonal in shape
The central vein is at the center of the hexagon
Portal areas are located at the angles of the hexagon
Sinusoids are seen separated by hepatocytes
Hepatocytes are arranged in plates radiating fro the
central vein to the periphery of the hexagon
Blood flows from the periphery through the sinusoids
to the central vein.

46.  The classical hepatic lobule emphasizes the
architecture of the liver, and the floe of blood and bile.
 Blood flows from the periphery(portal area)through
sinusoids to the central vein.
 Bile is secreted by the hepatocytes and flow to the
small bile ducts at the periphery.

47.  Portal lobule:
Triangular in shape
Has central vein at the angles of the triangle
Here the central structure is the portal area
One portal lobule incorporates three adjacent classic
hepatic lobules, each lobule secreting bile into the bile
canaliculi located at its center
Portal lobules emphasize the flow of bile(the central
structure which is the portal area, receives bile).

48.  Liver acinus:
A diamond shaped lobule with two opposing central
veins and two opposing portal areas
Considered the smallest functional unit of the liver
The long axis of the liver acinus represents a line
extending between the two opposite central veins abd
the short axis a line extending between the two
opposing portal areas.

50.  The liver acinus:
 emphasizes circulation of blood
Is an important lobule that allows interpretation of
liver pathology such as liver degeneration and toxic
effects to the liver.
The hepatocytes closest to the portal areas will be
more affected in degeneration of the liver or will be
first destroyed when the liver is poisoned.
And they will also regenerate first during the process
of regeneration.

51.  Hepatocytes in the liver acinus are described as being
in three zones:1,2 and 3
 The zones are elliptical zones around the short axis of
the liver acinus.
 Cells in zone 1 are those hepatocytes closest to the
short axis of the acinus, the hepatocytes furthest from
the short axis are in zone 3 and those in between are in
zone 2.

53.  Hepatocytes in zone 1 therefore are most exposed to
nutrients and toxins and will be the first to show
pathological changes in case of liver degeneration or
poisoning.
 Hepatocytes in zone 3 are poorly supplied and
therefore they are the first to show ischemic necrosis
in case of poor liver perfusion
 They are also the first to undergo fatty degeneration.