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Tuesday, July 04, 2017

The Liver: Anatomy, Physiology and Pathology

TABLE OF CONTENTS

INTRODUCTION
Anatomy of the liver 
Functions of the liver
Component of the liver
Histology of the liver
Diseases of the liver
Maintainance of the liver


INTRODUCTION


The liver is the largest organ inside the body.

It is  located behind the ribs in the upper right hand portion of the abdomen.

There are over 300 billion specialized cells in the liver that are connected by a well organized system of bile ducts and blood vessels called the biliary system. The liver is responsible for the production of several vital protein components of blood plasma, such as prothrombin, fibrinogen, and albumins.
The hepatocytes of the liver are responsible for important metabolic functions that support the cells of the body.



Blood return from the digestive system passes through the hepatic portal vein. the liver is responsible for metabolizing carbohydrate, lipids, and proteins into biologically useful materials.  Digestive system breaks down carbohydrates into the monosaccharide glucose, which cells use as a primary energy source.

Blood enter the liver through the hepatic portal vein that is extremely rich in glucose from digested food.

Hepatocytes absorb much of this glucose and store it as the macromolecule glycogen. A branched polysaccharide that allows the hepatocytes to pack away large amounts of glucose and quickly release glucose between meals.

The absorption and release of glucose by the hepatocytes helps to maintain homeostasis and protects the rest of the body from dangerous spikes and drops in the blood glucose level. Fatty acids in the blood.


Fatty acids in the blood passing through the liver are absorbed by hepatocytes and metabolized to produce energy in the form of ATP.

 Glycerol, another lipid component, is converted into glucose by hepatocytes through the process of gluconeogenesis.

Hepatocytes can also produce lipids like cholesterol, phospholipids, and lipoproteins that are used by other cells throughout the body.
Much of the cholesterol produced by hepatocytes gets excreted from the body as a component of bile.

Liver diseases are posing as a major health problem around the world. 

Hepatitis viral infection, toxic industrial chemicals, alcohol, aflatoxins, water pollutants are the major risk factors of liver diseases (paraskevi et al. 2006). 

Chronic liver damage is a widespread pathology characterized by a progressive evolution from steatosis to chronic hepatitis, fibrosis, cirrhosis and hepatocellular carcinoma.


ANATOMY OF THE LIVER



The liver is a triangular organ that extends across the entire abdominal cavity just inferior to the diaphragm (Moore, 2000). 

Most of the liver’s mass is located on the right side of the body where it descends inferiorly toward the right Kidney. 

The liver is made of very soft, pinkish-brown tissues encapsulated by a connective tissue capsule.

This capsule is further covered and reinforced by the peritoneum of the abdominal cavity, which protects the liver and holds it in place within the abdomen (moore, 2000).

 The peritoneum connects the liver in 4 locations: the coronary ligament, the left and right triangular ligaments (Paraskevi, 2006), and the falciform ligament.
These connections are not true ligaments in the anatomical sense; rather, they are condensed regions of peritoneal membrane that support the liver.

The wide coronary ligament connects the central superior portion of the liver to the diaphragm.

Located on the lateral borders of the left and right lobes, respectively (Satoliza et al., 1998).

The falciform ligament runs inferiorly from the diaphragm across the anterior edge of the liver to its inferior border. 
the falciform ligament forms the round ligament (ligamentum teres) of the liver and connects the liver to the umbilicus.(satoliza et al 1998).

The falciform ligament runs inferiorly from the diaphragm across the anterior edge of the liver to its inferior border. 
the falciform ligament forms the round ligament (ligamentum teres) of the liver and connects the liver to the umbilicus.(satoliza et al 1998).

The round ligament is a remnant of the umbilical vein that carries blood into the body during fetal development.

LIVER LOBES
The liver consists of 4 distinct lobes – the left, right, caudate, and quadrate lobes.
The left and right lobes are the largest lobes and are separated by the falciform ligament. The right lobe is about 5 to 6 times larger than the tapered left lobe.
The small caudate lobe extends from the posterior side of the right lobe and wraps around the inferior vena cava.
The small quadrate lobe is inferior to the caudate lobe and extends from the posterior side of the right lobe and wraps around the gallbladder (Srivastava 2006).

The tubes that carry bile through the liver and gallbladder are known as bile ducts and form a branched structure known as the biliary tree. Bile produced by liver cells drains into microscopic canals known as bile canaliculi. The countless bile canaliculi join together into many larger bile ducts found throughout the liver.

THE BILIARY SYSTEM

These bile ducts next join to form the larger left and right hepatic ducts, which carry bile from the left and right lobes of the liver (Satoliza, 1998). 
Those two hepatic ducts join to form the common hepatic duct that drains all bile away from the liver. 
The common hepatic duct finally joins with the cystic duct from the gallbladder to form the common bile duct, carrying bile to the duodenum of the small intestine

Most of the bile produced by the liver is pushed back up the cystic duct by peristalsis to arrive in the gallbladder for storage, until it is needed for digestion (Satoliza 1998).

BLOOD VESSEL OF THE LIVER
The blood supply of the liver is unique among all organs of the body due to the hepatic portal vein system. 

Blood traveling to the spleen, stomach, pancreas, gallbladder, (Shi et al., 2003) and intestines passes through capillaries in these organs and is collected into the hepatic portal vein.

LOBULES

The internal structure of the liver is made of around 100,000 small hexagonal functional units.
 known as lobules. Each lobule consists of a central vein surrounded by 6 hepatic portal veins and 6 hepatic arteries.
These blood vessels are connected by many capillary-like tubes called sinusoids, (Rajagopal et al., 2003) which extend from the portal veins and arteries to meet the central vein like spokes on a wheel.

IMPORTANT OF THE LIVER

The liver is such an important organ that we can survive only one or two days if it shuts down.

if the liver fails, your body will fail too. 

Fortunately, the liver can function even when up to 75% of it is diseased or removed. 

This is because it has the amazing ability to create new liver tissue 

(i.e. it can regenerate itself) from healthy liver cells that still exist (Brasga et al., 1999).

LIVER FUNCTION

Stores vitamins, sugar and iron to help give your body energy.

Controls the production and removal of cholesterol.

Clears  blood of waste products, drugs, and other poisonous substances.

Produces immune factors and removes bacteria from the bloodstream to combat infection.

Releases a substance called “bile” to help digest food and absorb important nutrients. 

Makes clotting factors to stop excessive bleeding after cuts or injuries (Moore, 2000)

DIGESTION

The liver plays an active role in the process of digestion through the production of bile. 

Bile is a mixture of water, bile salts, cholesterol, and the pigment bilirubin. 

Hepatocytes in the liver produce bile, which then passes through the bile ducts to be stored in the gallbladder. 

When food containing fats reaches the duodenum, the cells of the duodenum release the hormone cholecystokinin to stimulate the gallbladder to release bile.

 Bile travels through the bile ducts and is released into the duodenum where it emulsifies large masses of fat. 

The emulsification of fats by bile turns the large clumps of fat into smaller pieces that have more surface area and are therefore easier for the body to digest.

Bilirubin present in bile is a product of the liver’s digestion of worn out red blood cells.

 Kupffer cells in the liver catch and destroy old, worn out red blood cells and pass their components on to hepatocytes. 

Hepatocytes metabolize hemoglobin, the red oxygen-carrying pigment of red blood cells, into the components heme and globin.

Globin protein is further broken down and used as an energy source for the body. 
The iron-containing heme group cannot be recycled by the body and is converted into the pigment bilirubin and added to bile to be excreted from the body. 
Bilirubin gives bile its distinctive greenish color. 
Intestinal bacteria further convert bilirubin into the brown pigment stercobilin, which gives feces their brown colour.

METABOLISM

The hepatocytes of the liver are tasked with many of the important metabolic jobs that support the cells of the body. 

Because all of the blood leaving the digestive system passes through the hepatic portal vein.

the liver is responsible for metabolizing carbohydrate, lipids, and proteins into biologically useful materials. 

Our digestive system breaks down carbohydrates into the monosaccharide glucose, which cells use as a primary energy source. 

Blood entering the liver through the hepatic portal vein is extremely rich in glucose from digested food. 

Hepatocytes absorb much of this glucose and store it as the macromolecule glycogen.

 a branched polysaccharide that allows the hepatocytes to pack away large amounts of glucose and quickly release glucose between meals. 

The absorption and release of glucose by the hepatocytes helps to maintain homeostasis .

and protects the rest of the body from dangerous spikes and drop in the blood glucose level.


Fatty acids in the blood passing through the liver are absorbed by hepatocytes and metabolized to produce energy in the form of ATP. 

Glycerol, another lipid component, is converted into glucose by hepatocytes through the process of gluconeogenesis. 

Hepatocytes can also produce lipids like cholesterol, phospholipids, and lipoproteins that are used by other cells throughout the body.

 Much of the cholesterol produced by hepatocytes gets excreted from the body as a component of bile.

DETOXIFICATION

As blood from the digestive organs passes through the hepatic portal circulation.

 the hepatocytes of the liver monitor the contents of the blood and remove many potentially toxic substances before they can reach the rest of the body.

 Enzymes in hepatocytes metabolize many of these toxins such as alcohol and drugs into their inactive metabolites.
 And in order to keep hormone levels within homeostatic limits, the liver also metabolizes and removes from circulation hormones produced by the body’s own glands.

STORAGE

The liver provides storage of many essential nutrients, vitamins, and minerals obtained from blood passing through the hepatic portal system.

 Glucose is transported into hepatocytes under the influence of the hormone insulin and stored as the polysaccharide glycogen (Crustic et al., 2012).
Hepatocytes also absorb and store fatty acids from digested triglycerides. 
The storage of these nutrients allows the liver to maintain the homeostasis of blood glucose. 

Our liver also stores vitamins and minerals - such as vitamins A, D, E, K, and B12, and the minerals iron and copper - in order to provide a constant supply of these essential substances to the tissues of the body (Crustic, 2000).

PRODUCTION

The liver is responsible for the production of several vital protein components of blood plasma: prothrombin, fibrinogen, and albumins.
Prothrombin and fibrinogen proteins are coagulation factors involved in the formation of blood clots.

 Albumins are proteins that maintain the isotonic environment of the blood so that cells of the body do not gain or lose water in the presence of body fluids.

IMMUNITY OF THE LIVER

The liver functions as an organ of the immune system through the function of the Kupffer cells that line the sinusoids. 

Kupffer cells are a type of fixed macrophage that form part of the mononuclear phagocyte system along with macrophages in the spleen and lymph nodes. 

Kupffer cells play an important role by capturing and digesting bacteria, fungi, parasites, worn-out blood cells, and cellular debris. 

The large volume of blood passing through the hepatic portal system and the liver allows Kupffer cells to clean large volumes of blood very quickly (Crustic et al., 2012).

SINUSOIDS

Each sinusoid passes through liver tissue containing 2 main cell types: Kupffer cells and hepatocytes.
Kupffer cells are a type of macrophage that capture and break down old, worn out red blood cells passing through the sinusoids.
Hepatocytes are cuboidal epithelial cells that line the sinusoids and make up the majority of cells in the liver.
 Hepatocytes perform most of the liver’s functions – metabolism, storage, digestion, and bile production. 

Tiny bile collection vessels known as bile canaliculi run parallel to the sinusoids on the other side of the hepatocytes and drain into the bile ducts of the liver.

Dietary proteins are broken down into their component amino acids by the digestive system before being passed on to the hepatic portal vein.

 Amino acids entering the liver require metabolic processing before they can be used as an energy source. 
Hepatocytes first remove the amine groups of the amino acids and convert them into ammonia and eventually urea.

 Urea is less toxic than ammonia and can be excreted in urine as a waste product of digestion.
 The remaining parts of the amino acids can be broken down into ATP or converted into new glucose molecules through the process of gluconeogenesis.

HEPATOCYTES FUNCTION

As blood from the digestive organs passes through the hepatic portal circulation, 

the hepatocytes of the liver monitor the contents of the blood and remove 

many potentially toxic substances before they can reach the rest of the body.

 Enzymes in hepatocytes metabolize many of these toxins such as alcohol and drugs into their inactive metabolites.
And in order to keep hormone levels within homeostatic limits, the liver also metabolizes and removes from circulation hormones produced by the body’s own glands.

DISEASE OF THE LIVER

Hepatitis: This is known as any forms of inflammation of the liver.
 that could have rendered the liver disease (Naik et al., 2004) .

It could be divided into two type,which are:

Hepatitis A and Hepatitis B (Naik 2004).

Hepatitis B: Hepatitis B is the most common serious liver infection in the world. 

It is caused by the hepatitis B virus (HBV), which attacks liver cells and can lead to cirrhosis, liver cancer, or liver failure if it is not detected and managed. 

The virus is transmitted through contact with infected blood and bodily fluids that contain blood.

 Approximately 10% of adults, 30-50% of children, and 90% of babies will not get rid of the virus and will develop a chronic HBV infection. 

Chronically infected people can pass the virus on to others and are at increased risk for liver problems later in life.
HBV is 100 times more infectious than the AIDS virus.
Yet, hepatitis B can be prevented with a safe and effective vaccine.

 For the 400 million people worldwide who are chronically infected with HBV, the vaccine is of no use.  However, there are promising new treatments for those who live with chronic hepatitis B. 

FIBROSIS AND  CIRRHOSIS

Fibrosis: After becoming inflamed, the liver tries to repair itself by forming tiny scars. 

This scarring, called "fibrosis," makes it difficult for the liver to do its job. 

As damage continues, many scars form and begin to join together, leading to the next stage, cirrhosis.

Cirrhosis: With a chronic HBV infection, large areas of the liver can become permanently scarred and nodules may form.

 Blood cannot flow freely through scarred liver tissue. This causes the liver to begin to shrink and become hard.

LIVER FAILURE

Liver Failure: If cirrhosis becomes very severe, liver failure can occur. 

This means the liver is unable to filter wastes, toxins, and drugs from the blood. 

It can no longer produce the clotting factors neces-sary to stop bleeding. 

Liver failure can lead to death.

LIVER CANCER

Cirrhosis can sometimes set the stage for liver cancer. 
One explanation for this is that damage to liver cells may alter the genes inside the cells in such a way that they can become cancerous.

BILE

One of the liver’s primary jobs is to store energy in the form of glycogen, which is made from a type of sugar called glucose. 

The liver removes glucose from the blood when blood glucose levels are high. 

Through a process called glycogenesis, the liver combines the glucose molecules in long chains to create glycogen, a carbohydrate that provides a stored form of energy.
When the amount of glucose in the blood falls below the level required to meet the body’s needs, the liver reverses this reaction, transforming glycogen into glucose.

Another crucial function of the liver is the production of bile - a yellowish-brown liquid containing salts necessary for the digestion of lipids, or fats. 

These salts are produced within the lobules.  Bile leaves the liver through a network of ducts and is transported to the gallbladder, which concentrates the bile and releases it into the small intestine.

COMPONENT OF THE LIVER 

GALLBLADDER

Gallbladder, muscular organ that serves as a reservoir for bile, present in most vertebrates.

 In humans, it is a pear-shaped membranous sac on the undersurface of the right lobe of the liver just below the lower ribs. 

It is generally about 7.5 cm (about 3 in) long and 2.5 cm (1 in) in diameter at its thickest part; it has a capacity varying from 1 to 1.5 fluid ounces. 
The body (corpus) and neck (collum) of the gallbladder extend backward, upward, and to the left. 

The wide end (fundus) points downward and forward, sometimes extending slightly beyond the edge of the liver.  Structurally, the gallbladder consists of an outer peritoneal coat (tunica serosa); a middle coat of fibrous tissue and unstriped muscle (tunica muscularis); and an inner mucous membrane coat (tunica mucosa).

FUNCTION OF GALLBLADDER

The function of the gallbladder is to store bile,.

secreted by the liver and transmitted from that organ via the cystic and hepatic ducts,

 until it is needed in the digestive process. The gallbladder, when functioning normally,

 releases bile through the biliary ducts into the duodenum to aid digestion by promoting 

peristalsis and absorption, preventing putrefaction, and emulsifying fat. See Digestive System.

DISORDER OF GALLBLADDER

The major disorder associated with the gallbladder is the presence of gallstones, varying in shape and size from a pea to a small pear. 

Accreted from the constituent salts in the bile, they are most common in diabetic patients, in blacks, and in women; their presence increases with age.

 Two of the reasons for the growth of gallstones are believed to be the presence of excessive amounts of substances such as calcium and cholesterol in the bile and the retention of bile in the gallbladder for a long period of time. 

The usual treatment for gallstones is surgical removal.

 Two naturally occurring bile salts, chenodeoxycholic acid and ursodeoxycholic acid, taken orally dissolve gallstones in some patients.

 Ultrasound (see Ultrasonics) treatment to shatter the stones also eliminates the need for surgery in some cases.

Disorder of Gallblader

Another common disorder of the gallbladder is cholecystitis or inflammation of the organ, which is believed to be a result of the presence of highly concentrated bile.  Chronic cholecystitis is sometimes aggravated by bacterial infection, leading to perforation and peritonitis. 

Less common is the growth of malignant tumors, which are associated with gallstones and constitute about 3 percent of all cancer in humans.

THE SPLEEN

Spleen, flattened, oblong organ that removes disease-producing organisms and worn-out red blood cells from the bloodstream. 

The spleen is situated in the upper left abdominal cavity, in contact with the pancreas, the diaphragm, and the left kidney. 

It is supported by bands of fibers that are attached to the peritoneum (the membrane lining the abdominal cavity). 

The spleen varies in size but, in adult humans, it is about 13 cm (about 5 in) long, up to 10 cm (4 in) wide and 3.8 cm (1.5 in) thick, and weighs about 200 g (about 7 oz). 

The spleen is fed by the splenic artery, and venous blood from the spleen enters the liver.

The spleen removes iron from the hemoglobin of red blood cells for use in the body. 

It also removes such waste materials as bile pigments for excretion as bile by the liver. 

The spleen produces antibodies against various disease organisms and manufactures a variety of blood cells. 

In the unborn child, the organ functions primarily to produce red blood cells, a function that is normally taken over by the bone marrow after birth. 

However, if diseases slow down this function in the bone marrow, the spleen may again start to produce red blood cells.

Many diseases affect the spleen. In splenomegaly, the spleen enlarges.
This condition is usually an indication of bacterial, parasitic, and viral infections, such as infectious mononucleosis, tuberculosis, malaria, rheumatoid arthritis, and histoplasmosis.

SPLENOMEGALY

Splenomegaly may also be caused by cirrhosis of the liver. 
In hypersplenism, a malfunctioning or hyperactive spleen may so increase its normal rate of destroying red blood cells as to cause a variety of hemolytic anemias. 

Hemorrhage of an enlarged spleen may magnify anemia and also cause an iron deficiency.

. Small splenic abscesses may run a benign course without detection.

 Large splenic abscesses, however, may rupture into the bowel cavity to cause peritonitis .

and the infection may invade the bloodstream and be carried to the liver, where it may form additional abscesses.

 Splenic cysts are rare, and the spleen is seldom the site of a carcinoma, or cancer.

A hyperactive spleen may sometimes be treated with radiation or corticosteroids (steroids that are extracted from the adrenal cortex). 

Abscesses are treated with broad-spectrum antibiotics or surgical drainage. 

Surgical removal of the spleen is required if the spleen or the splenic artery ruptures.


DIAGRAMs OF A DAMAGED LIVER




CONCLUSION

The liver is one of the vital organ in the living system.
That perform storage and degradative functionof some vital element and macromolecle needed by the body.
Liver disease are possing as a major parthological issue ranging from:
Fibrousis,cirrhosis, and hepatic carcinoma.
leading to inflamation of the hepatic segement and lobules of the liver

With mostly causative agent of hepatities B or C virus respectively.


RECOMMENDATION

It is recommended that you have your liver checked today.

Take the hepatitis vaccine immediately if tested negative.

Also start treatment  and effective management of the liver now if tested positive ti hepatities virus.

Visit your health care provider.


Thank you for reading.




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