Bilirubin | Production| Effects | Liver

                                      Bilirubin Production| Effects |Liver

This article discusses different features of bilirubin. It is used to diagnose liver diseases. Here, learn about the tests, procedures, indications, and more. This article is intended for an international audience of medical care providers and learners.

Keywords:  Human Physiology| jaundice Liver |δ bilirubin| haem oxidase|2UDPGlucuronic acid| stercobilin| urobilin| Conjugated|Unconjugated |cellular antioxidant| isomer zz| ez isomer

Table of contents

1.	Introduction
2.	Types of bilirubin
3.	Production
4.	Functions
5.	Links

 

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Introduction:

Bilirubin is an orange-yellow pigment present in the blood. It is a degraded product of the hemoglobin of red blood cells. Bilirubin occurs in the normal catabolic pathway of red blood cells. The average total bilirubin level is 1.2 mg/dL of blood. It occurs in two parts

Types:

1.    Unconjugated bilirubin or indirect bilirubin 0.9 mg/dL of blood.

2.    Conjugated bilirubin or direct bilirubin           0.3mg/dL of blood.

3.    δ bilirubin is covalently bound to albumin, which appears in the blood when hepatic excretion of conjugated bilirubin is less in a patient with hepatobiliary diseases. Direct bilirubin includes Conjugated bilirubin and δ bilirubin. So, conjugated bilirubin is not the same as direct bilirubin.

Types of Bilirubin in the human body

Production: 

Senile or abnormal red blood cells are destroyed in the cells of the reticuloendothelial system, especially in the spleen, and some destruction

 occurs in the liver. Haemoglobin comes out from red blood cells.

Hemoglobin breaks in haem and globin. The globin is utilized and incorporated into the amino acid pool. Haem is an iron-containing porphyrin compound from which iron is removed by haem oxidase. This removal of iron is the first step in bilirubin production. This iron combines with apoferritin and is used by the body. The close chain of porphyrin is straightened, forming an open-chain tetrapyrrole.

Biliverdin reductase converts biliverdin into bilirubin, which is an open-chain tetrapyrrole. In other words, open-chain tetrapyrrole is formed by oxidative cleavage of the porphyrin in the haem.

 

 

This bilirubin binds with albumin by a non-covalent bond and is transported. In the liver, bilirubin dissociates from the carrier albumin and enters hepatocytes. In the hepatocyte, bilirubin binds to intracellular protein -ligandin and z protein. Salicylates and sulphonamides displace bilirubin from albumin, causing a rise in bilirubin levels. Bilirubin is not water-soluble. In the liver, bilirubin gets conjugated.

    2UDPGlucuronic acid     2UDP( Uridine diphosphate)                        Bilirubin- -----bilirubin glucuronyl transferase----------> bilirubin monoglucuronide.

                       2UDPGlucuronic acid     2UDP( Uridine diphosphate

Bilirubin monoglucuronide--- bilirubin glucuronyl transferase-->bilirubin diglucuronide.

 In the hepatocyte, bilirubin is conjugated with glucuronic acid to form bilirubin monoglucuronide. In the second step, bilirubin  monoglucuronide  is converted into bilirubin diglucuronide.In this process, 2UDPGlucuronic acid provides glucuronic acid in the presence of the enzenzyme' bilirubin glucuronyl transferase.' The conjugated bilirubin is water-soluble and secreted in the bile, which enters the small intestine.

In the colon, gut flora removes glucuronic acid from conjugated bilirubin. The free bilirubin is reduced to stercobilin and urobilinogen in an 80% and 20% ratio.

 The stercobilinogen is not absorbed and oxidized to stercobilin and excreted into the stool. Stercobilin is responsible for the brown color of the stool.

 Urobilinogen is absorbed in the colon. It reaches the liver via enterohepatic circulation and is excreted in the urine. This urobilinogen is responsible for the straw color of urine. Urobilinogen is oxidized to urobilin.

In obstructive jaundice or when bilirubin is not soluble, there is no stercobilin, and stool becomes clay-colored.

Urobilin is also present in plants. Bilirubin is structurally similar to the pigment Phycobilin in some algae and phytochrome plants that capture light energy.

Some of the double bonds in bilirubin isomerize when exposed to light. The isomer zz usually is present in the bilirubin. This isomer changes to an 'ez' isomer when exposed to sunlight. The ez isomer is more water-soluble than the unilluminated 'zz' i'omer, so increased water solubility allows the excretion of bilirubin in bile. This is the basis of phototherapy in case of jaundice, especially in infants.

Functions of Bilirubin:  

Bilirubin, when oxidized, becomes biliverdin. Its primary physiological role is as a cellular antioxidant. The antioxidant action of bilirubin is vital in the brain. Bilirubin prevents excitotoxicity and neuronal death by scavenging superoxide during N-methyl D –aspartic acid neurotransmission.

High total bilirubin levels provide various health benefits without liver disease. Serum bilirubin levels are inversely related to the risk of certain heart diseases.

Hyperbilirubinemia is a condition in which total bilirubin is more than the normal range.

Bilirubin encephalopathy is common in infants, as their blood-brain barrier is underdeveloped. Bilirubin enters brain tissue and deposits in brain cells, especially basal ganglion cells. This condition is known as kernicterus.

Importance:

The conjugated and unconjugated bilirubin levels give more reliable information than AST in suspected liver diseases –hepatitis, cirrhosis, and jaundice.

Conjugated and unconjugated bilirubin levels are measured in cases of suspected liver diseases.

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Internal link:

https://totalphysology20.blogspot.com/2021/02/glands-we must know

https://totalphysology20.blogspot.com/2021/03/small intestine  we must  know

https://totalphysology20.blogspot.com/2021/05 /bile- we must  know

https://totalphysology20.blogspot.com/2021/05 /Gall bladder- we must  know

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https://www.healthline.com>nutrition

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Hashtags: Human physiology # Liver# Jaundice#english# isomer zz# ez isomer#δ bilirubin # cellular antioxidant# urobilin# stercobilin# 2UDPGlucuronic acid.