Biochemistry of liver

Functions of liver (enumeration)

1 – regulatory-homeostatic

2 – structural

3 – energetical

4 – protective (antitoxic)

5 – secretory-excretory

Regulatory-homeostatic function

Liver takes part in regulation of level of numerous substances in blood. After absorption the concentration of absorbed products in portal vein is variable, but the level of these compounds in blood effluxed from liver is permanent (glucose, cholesterol etc), e.g. glucostatic function of liver (describe, please)

Antitoxic function of liver

The detoxification in liver may occur by 2 stages: 1^st one are oxidation, reduction, hydrolysis; 2-nd one is conjugation.

The oxidation usually occurs in microsomes. This is microsomic oxidation (enzymes are cytochromes b5, P450). There is a peroxisomic oxidation (enzymes are oxydases). During 1-st stage some functional groups arrear – OH, NH2, COOH. These groups serves for conjugation with glucuronic acid (e.g. formation of direct bilirubin).

The synthesis of urea is appearance of antitoxic function of liver too because this process is detoxification of ammonia

Secretory-excretory function of liver

The bile is secreted permanently (500-700ml/day). Hepatic bile enters the gall bladder and it is concentrated due to the removal of water and electrolytes. Gall bladder’s bile enters the small intestine. But hepatic bile may enter the small intestine at once.

The secretory-filtratory theory of formation of bile:

Water, cholesterol, bile acids, bile pigments and phospholipids enter from hepatocytes and extracellular space into biliary cappilaries. This is primary bile. It contacts with blood and saturated by plasma blodd cations, anions, albumins, creatine etc. This is hepatic bile. It enters the gall bladder and concentrated there due to the removal of water and electrolytes. Albumins are absent in gall bladder bile. Here are mainly mucins.

The composition and properties of bile

Hepatic bile: gold-yellow color, gravity is 1.010, pH is 6.8; water – 97.4%, dry part – 2.6%; bile acids – 0.6%; bile pigments – 0.5%; proteins – 2%; lipids – 0.3%; cholesterol – 0.06%; inorganic compounds – 0.84%

Gall bladder bile: green-brown color, gravity is 1.026-1.050; pH is 7.5; water – 86.6%; dry part is 13.4%; bile acids – 7%; bile pigments – 3%; proteins4.5%; lipids – 1.9%; cholesterol – 0.26%; inorganic compounds- 0.65%

The role of bile:

bile acids participate in digestion and absorption of lipids (they activate pancreatic lipase and form micelles)

excretory role – the liver eliminate waterinsoluble compounds

bile neutralizes acidic products from gaster

protective role – proteins of bile bind pepsin and other proteases of gastric juice

bile acids and phospholipids promote the solubilization of cholesterol in bile. Their lack results in bile stones formation

HORMONES

(REGULATION OF METABOLISM)

1. Neuro-gliale through receptors with very big velocity (rate). Molecular base – the change of cons and mediators concentration into and out side of neurons.

2. Change of enzymatic activity.

3. Special separation of different biochemical processes: in mitochondria – CAC, respiratory chain, boxidation; in nucleus – enzymes of replication and transcription. Different processes in different organelle bond each other through metabolites.

4. Neuroendocrinic regulation through hormones.

Hormones – compounds, which are formed in glands, are secreted in the blood, and they regulate metabolism (see scheme neurohumoral regulation). Due to this regulation 200 kinds of different cells, 75 trillion of cells in organism act as united system. The name “hormone” was offered by Beilis and Starling, from hormao – excite.