Download The liver is the largest gland in the body, weighing about 1.4 Kg. It is

liver
The liver is the largest gland in the body, weighing about 1.4 Kg. It is
located under the diaphragm, within the rib cage in the upper right
quadrant of the abdomen. The liver is an accessory digestive gland
.liver consist of 4 Lobes
Major: Left and right and Minor: Caudate and quadrate
Ducts Common hepatic Cystic From gallbladder Common bile Joins
pancreatic duct at hepatopancreatic ampulla The liver is composed
of liver lobules which are roughly hexagonal structures consisting of
hepatocytes. The hepato-cytes radiate outward from a central vein.
At each of the six corners of a lobule is a portal triad. Between the
hepatocytes are the liver sinusoids.
The hepatocytes produce bile which flows through canals, called bile
canaliculi to a bile duct. The bile ducts eventually leave the liver via
the common hepatic duct.
The hepatocytes also process nutrients into macromolecules, store
fat-soluble vitamins, and play an important part in detoxification.
The total blood flow through the Liver is about 1450 ml / minutes. It
has double blood
supply from hepac ar ter y 20% and por tal vei n 80%. The por tal vei n
drains the
digestive tract, the spleen, pancreas and gallbladder.
The liver empties into the hepatic vein and into vena cava. The
venous sinusoids are lined by two types of cells; 1- Endothelial cells.
2- Large kupffer cells which are tissue macrophages capable of
phagocytizing bacteria and other foreign matter in the blood.
Endothelial cells have large pores, plasma substances even proteins
can move freely from blood to hepatic cells. Plasma proteins can pass
to interstitial spaces, therefore, the lymph draining from liver has a
protein concentraon about 6 gm / dl .
Permeability of liver
sinusoids allow a large quantities of lymph to form, therefore, about
one half of all the lymph formed in the body under resting condition
in the liver
Metabolic function of the liver:
1- Carbohydrate metabolism:
A- Storage of glycogen; the liver is important for maintaining a
normal blood glucose. The liver remove excess glucose from blood, in
form glycogen and return it to the blood when blood glucose
concentration fall too low.
Adrenaline and glucagon mobilize this liver glycogen to blood glucose
by glucose-6-phosphatase which is necessary for breakdown of
glycogen and only liver has it.
B- Conversion of galactose and fructose to glucose.
C- Gluconeogenesis when glucose concentration begins to fall below
normal. Large amount of amino acid are converted into glucos
2- Fat metabolism:
A- Bile salt produced; which is essential for the digestion and
absorption of fat.
B- Fat-soluble vitamin are stored in the liver; such as vitamin A and D.
water soluble vitamin B 12are also stored.
C- Mobilization of depot fat in the form ketone bodies, which are
metabolized by other tissues with production of heat and energy.
D- Site of synthesis of cholesterol and phospholipids.
E- Site of conversion of carbohydrate and protein to fat
3-Protein metabolism:
A- Deamination of amino acids; with production of ammonia.
B- Convert ammonia to urea.
C- Synthesis certain amino acids; that non essential amino acids.
4-The blood:
A- Formation and destruction of RBC.
B- Site of formation of RBC; in fetal life.
C- Store of iron and B12 ; for maturation of RBC.
D- Excretion the bilirubin in the bile duct; into duodenum as a bile
pigments from broken RBC in blood.
E- Manufactures of plasma proteins; with exception of some globulin
fraction which is mainly formed by plasma cells in lymph tissue of the
blood.
F- Formation of clotting factors; such as prothrombin and fibrinogen
5-Detoxification: Poisons, physiological substances as well as drugs
are modified by the liver for excreted by kidneys.
Bilirubin metabolism :It is a greenish-yellow pigment, it is formed as end product of Hb. It is
fat soluble, very toxic, its secretion is one of important function of
the liver. It combines with plasma albumin, called free or
unconjugated bilirubin (indirect). This type of bilirubin can not be
excreted by kidney because it is insoluble in water. In premature
infant unconjucated bilirubin entering the nervous system where it
deposited in basal ganglia leading to kernicterus.
The unconjugated bilirubine is absorbed through the hepatic cell ,
released from the plasma albumin. 80% of it conjugates with
glucuronic acid by enzyme glucuronyl transferase. 10% of it
conjugates with sulfate to form bilirubin sulfate. 10% of it conjugates
with other substances. Conjugated bilirubin is water soluble excreted
in urine. It is not toxic to nervous system. Some of conjugated
bilirubin return to plasma
I n the intestine half of bilirubin is converted by bacterial action into
urobilinogen which responsible for brown color of stool. Some of
urobilinogen is reabsorbed through intestinal mucous to the blood,
most of it is re-excreted by liver back into the gut but 5% is excreted
by kidneys into urine.
Figure (16)Bilirubinmetabolism
senescent
RBC
BilirubinAlbumin
Adduct
Macrophages
(spleen)
heme
Bilirubin (indirect)
Feces
(stercobilin)
Urine Systemic Circulation
(urobilin)
BilirubinGlucuronide
Portal Circ.
Urobilinogen
Intestinal Flora
Bile Duct
Hepatocyte