Detail structure and functions of liver and gall bladder

1. LIVER
The liver, the largest visceral organ lies in the right hypochondriac
and epigastric regions mainly. It is firm, wedge shaped, reddish
brown and weighs about 1.5 kg approximately. Its main functions
include metabolic and haematological regulation and production
of bile.

2. Gross Anatomy
The liver lies immediately below the diaphragm. It extends upwards under the rib
cage up to the level of 5 rib. The upper border lies at the level of xiphisternal joint
while the inferior border crosses the midline at the level of L, vertebra. The liver is
covered by a layer of visceral peritoneum. On the anterior surface, the double
peritoneal fold; known as falciform ligament is attached thereby dividing the liver
into smaller left lobe and larger right lobe. On the posterior surface position of
inferior vena cava separates the right lobe from a small caudate lobe. Inferior to the
caudate lobe lies the quadrate lobe in between the left lobe and the gall bladder.

3. The liver has five surfaces: anterior, superior, posterior, inferior
and right lateral. There are no distinct demarcations between
these surfaces. The superior border is rounded and separates
superior from the posterior surface. The inferior border is well
defined, sharp border which separates the inferior from anterior
surface. It presents: (i) a cystic notch for the gall bladder and (ii)
notch for the ligamentum teres.

7. Peritoneal reflections
The visceral layer of peritoneum extends as a double fold of peritoneum from
anterior abdominal wall and covers the anterior surface (falciform ligament). At
the superior surface, the two layers diverge. The right layer is continuous with
the superior layer of Coronary ligament on the right lobe and the left layer is
continuous with the anterior layer of the left triangular ligament on the left
lobe. From the posterior surface of liver, the coronary ligaments pass to the
diaphragm thereby leaving a part of the surface of liver without the covering of
peritoneum. This is called as bare area of liver. Besides this, there are a few
more bare areas located on the posterior and inferior surface of the liver.

8. The right and left peritoneal triangular ligaments connect the upper surfaces of
right and left lobes of liver to the diaphragm. Their anterior layers are
continuous with falciform ligament while the posterior layer of right triangular
ligament becomes continuous with lesser omentum on the inferior surface of
liver.
Lesser Omentum: It is the fold of peritoneum which connects the stomach and
first 2.5 cm of duodenum to the inferior surface of the liver. Its right margin is
free and conveys blood vessels to the liver. It contains (i) Portal vein (ii) Hepatic
artery (ii) Bile duct.

9. Ligamentum Venosum: It is the remnant of a fetal venous channel (ductus venosus) which was an
anastomosis between portal vein and inferior vena cava.
These folds of peritoneum cover almost all surfaces of liver, except a few regions where peritoneum gets
reflected to get attached to diaphragm leaving those areas, without the covering of peritoneum. These
are called “bare areas’ of liver. These are located on:
i) On the posterior surface of liver
ii) Groove for IVC on the posterior surface of liver
iii) Groove for ligamentum venosum on the inferior surface.
iv) Fossa for gall bladder on the inferior surface
v) Fissure for porta hepatis on the inferior surface

10. Relations of Liver
Anterior: Anterior Abdominal wall and diaphragm
Posterior: Inferior vena cava, aorta, gall bladder
Superior: Diaphragm
Inferior: Right kidney, right suprarenal gland, Ist & IInd part of duodenum,
stomach.
Important features of the Liver
Groove for the inferior vena cava (IVC) is located on the posterior surface of
liver. A segment of the IVC is firmly attached to the surface of liver. This part of
IVC receives 2-5 hepatic veins from the lobes of liver.

11. Fossa for the gall bladder: Present on the inferior surface and is devoid of
peritoneum. Usually the fundus of gall bladder is not attached to the surface of
liver.
Fissure for the ligamentum teres: The ligamentum teres is enclosed within
layer of falciform ligament near its free edge and passes from umbilicus to the
inferior border of liver. It encloses the remnants of left umbilical vein which
was functional in fetal life.
Porta hepatis: Also called as the ‘hilum of the liver’ the porta hepatis is a
transverse groove on the inferior surface in between caudate and quadrate
lobes of liver. The hepatic artery and portal vein enter the liver here while the
bile duct leaves at this site.

12. Segments of liver:
As discussed earlier, the liver has four lobes: right, left caudate and quadrate.
In addition, the liver is divided into eight hepatic segments. These segments
are not as well defined as the bronchopulmonary segments of the lungs.
However, each segment is supplied by separate branch of the hepatic artery;
therefore, it can be removed in one segment. The veins draining the segments
drain more than one segment. Out of these 8, I to IV segments are on left side
and V to VIII on the right side. Segment 1 corresponds to the caudate lobe and
segment IV corresponds to the quadrate lobe. There is no demarcation visible
on the surface of liver.

13. Blood Supply
The liver is supplied by two sources
1) Hepatic artery20% of total volume (arterial oxygenated blood).
2) Portal vein80% of total volume (venous blood rich in nutrients).
Venous drainage: 2-5 hepatic veins which drain directly into the IVC where it is
lodged in the groove on posterior surface.
Lymphatic drainage
Hepatic lymph nodes which drain into coeliac nodes
Posterior mediastinal lymph nodes

14. Nerve Supply
Sympathetic: from coeliac plexus
Parasympathetic: Vagus nerve
The pain due to liver infections passes through sympathetic fibres and is often referred
to epigastrium.

15. Microscopic structure of the Liver
Each lobe of the liver is divided by connective tissue into liver lobules which are
the basic functional units of the liver.
The lobules are separated from each other by an interlobular septum. The liver
cells called as hepatocytes form one cell thick series of irregular plates. The
plates are arranged like spokes of a wheel. In between these plates, there are
irregular vascular spaces called sinusoids. In the centre of each lobule there is a
central vein, a branch of hepatic vein. The lobules are hexagonal in shape and
at each corner of the lobule, there are branches of portal vein (ii) hepatic
artery (iii) bile duct. These areas are called portal triad.

16. In addition to the hepatocytes, liver also contains a large number of Kupffer
Cells which engulf pathogens, cell debris and damaged blood cells
(Phagocytoses).
The hepatocytes produce bile which is transported to a branch of bile duct in
the portal triad. All these ducts join to form the right and left hepatic ducts
which. unite to form the common hepatic duct. The bile ultimately reaches the
duodenum for the breakdown of carbohydrates and lipids in the food. Some of
the bile will pass to gall bladder for storage.

17. The blood enters the liver sinusoids from branches of portal vein and hepatic
artery. The hepatocytes absorb solutes from the plasma. The sinusoids direct
the blood to enter the central vein of the lobule. The central veins ultimately
merge to form the hepatic veins which drain into hepatic part of IVC.

19. Extrahepatic Biliary Apparatus
It consists of the parts for storage and drainage of the bile from liver to the
second part of duodenum. It includes the following:
Hepatic ducts
Common hepatic duct
Gallbladder and cystic duct
Bile duct
The right and left hepatic ducts drain the bile from respective lobes of liver.
They join to form common hepatic duct at the right end of porta hepatis.

22. The common hepatic duct, 3 cm in length, runs downwards and joins cystic
duct to form bile duct.
The gallbladder is situated in fossa for the gallbladder on the right lobe of
the liver. It is flask-shaped, 7-10 cm in length with a capacity of 50 cm3, It is
covered by peritoneum on its free surface and directly related to liver on its
deep surface. However, it may have short mesentery.
Parts and relations
Fundus, lowest part, projects beyond inferior margin of liver and lies behind
right ninth costal cartilage where lateral margin of right rectus abdominis
crosses the costal margin.

23. Body of the gallbladder lies anterior to the second part of duodenum
and right end of the transverse colon.
Neck of the gallbladder lies at the medial end of porta hepatis. Its dilated
lateral end forms Hartmann’s pouch. The mucosal fold of neck continues
with that of cystic duct. The neck continues with cystic duct.
The cystic duct, 3—4 cm in length, starts from the neck of the
gallbladder and runs parallel to the common hepatic duct, before joining
it. It shows 5-12 crescentic folds of mucosa called spiral valve of Heister.

24. Bile duct, also known as common bile duct, is formed by union of cystic
duct with common hepatic duct at porta hepatis. It is 8-10 cm in length
and 6 mm in diameter. It descends in right free margin of lesser
omentum with hepatic artery to its left and portal vein behind it. It then
passes behind the first part of duodenum, pierces posteromedial wall of
the second part of duodenum and joins the main pancreatic duct to
form hepatopancreatic ampulla (of Vater). The ampulla is surrounded by
circular muscle forming sphincter of Oddi. It opens at major duodenal
papilla.

25. Blood Supply
Arterial supply The gallbladder is supplied by cystic artery from right hepatic
artery. The common bile duct is supplied by branches from cystic artery in
the upper one-third, common hepatic artery in the middle one-third and
gastroduodenal artery in the lower one-third. However, all branches
communicate with each other.
Venous drainage The gallbladder drains by many small cystic veins that enter
the liver to join portal vein. The hepatic and bile ducts drain into portal vein.
Lymphatic drainage The gallbladder and all extrahepatic biliary ducts drain
into cystic node situated above cystic duct.

26. Nerve Supply
The gallbladder and extrahepatic biliary ducts are supplied by autonomic
autonomic nerves from hepatic plexus.
Microscopic Structure
The gallbladder shows the following:
— Outer serous coat
— Middle fibromuscular coat, made of circular and longitudinal smooth
muscle fibres interlacing with fibrous connective tissue (this arrangement
arrangement allows distention of the bladder)

27. Mucosa shows folds with tall columnar epithelium.
The gallbladder lacks submucosa and muscularis mucosa (as there are
no glands).

29. Filling of Gallbladder
During fasting, bile that is secreted gets collected in gallbladder and is
stored there. Opening of common bile duct in the duodenum is
surrounded by sphincter of Oddi. During fasting, the sphincter is in
contracted state and keeps the opening of the common bile duct closed.
As bile is continuously secreted by liver, it gets collected in common bile
duct (it cannot come to the intestine as duodenum closes the opening)
and the pressure in common bile duct increases, which forces the bile
through cystic duct into gallbladder.

30. Emptying of Gallbladder
When food reaches upper intestine, gallbladder empties its bile into the
duodenum. This occurs due to the contraction of wall of gallbladder with
simultaneous relaxation of sphincter of Oddi. This is mainly controlled as
follows:
Cholecystokinin Presence of fat in upper intestine causes release of
hormone CCK from the mucosa of small intestine. This hormone is
absorbed in blood and when it reaches the gallbladder, it causes
contraction of gallbladder and relaxation of sphincter of Oddi.

31. Vagus stimulation It occurs during cephalic phase and during various
vagal reflexes and causes contraction of gallbladder and relaxation of
sphincter of Oddi.