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D3: Functions of the Liver - Coggle Diagram
D3: Functions of the Liver
Blood Supply
Oxygenated blood from the hepatic artery
Leaves the liver through the hepatic vein (Deoxygenated blood). This vein joins the vena cava, which returns the blood to the heart
The liver also receives deoxygenated blood coming from the spleen, stomach, pancreas, gall bladder and intestines through the hepatic portal vein
(i) this vein carries foods (amino acids, glucose,
vitamins, minerals and other foods) absorbed
mainly in the small intestine.
Liver has a dual blood supply
(i) Oxygenated blood from the hepatic artery and deoxygenated blood from the hepatic portal vein
(ii) The blood from these two sources is mixed before entering the liver, its cells never receive fully oxygenated blood
sinusoids supply blood to the liver cells (hepatocytes) and macrophages (
Kupffer cells
)
Blood from the hepatic artery and the hepatic portal vein supply the sinusoids that bathe the hepatocytes and Kupffer cells. As blood passes through the liver, the hepatocytes monitor the contents of the blood and remove many toxic substances before they can reach the rest of the body.
Enzymes metabolise these toxins to render them harmless.
Many metabolic reactions take place in the liver. These reactions liberate heat, therefore when blood passes through the liver it is warmed up.
Structure
Liver lobules
The internal structure of each lobe has around 100,000 lobules, each consisting of a central venule coming from the hepatic vein surrounded by six venules coming from the hepatic portal vein and six arterioles from the hepatic artery.
blood vessels are connected by sinusoids
Sinusoids
: tubes that resemble capillaries but have a discontinuous endothelium.
Capillaries
:
(i) Very small pores
(ii) Continuous basement membrane
(iii) Cylindrical shape
(iv) Smaller
(v) Little intracellular space
(vi) Only small molecules can pass
Sinusoids
:
(iii) No definite shape
(iv) Larger
(ii) Discontinuous basement membrane
(v) Large intracellular space
(i) Fenestrated (with pores of approximately 175 nm diameter)
(vi) Leaky
Hepatocytes and Kupffer cells
Hepatocytes perform most of the liver functions, especially storage and metabolism.
Kupffer cells are white blood cells (macrophages) that break down red blood cells
Processing and Storage
Hepatocytes
in the liver absorb most of the glucose and store it as glycogen. When the body requires energy, this glycogen is broken down into glucose.
Fatty acids in the blood passing through the liver are absorbed by hepatocytes and metabolised to produce energy in the form of ATP
Hepatocytes also synthesise lipids such as triglycerides, cholesterol and phospholipids. These lipids can be bound to proteins forming lipoproteins, which are now soluble in blood plasma
Amino acids
entering the liver are transformed into other amino acids or are used in the synthesis of new proteins.
The acid group of the amino acid is used to produce energy or new glucose molecules while the amine group is converted into ammonia.
it is transformed into
urea
Endoplasmic reticulum and Golgi apparatus in hepatocytes produce
plasma proteins
.
erythrocytes and iron
Red blood cells or erythrocytes are cells modified to increase their capacity in the transport of oxygen. In order to do this, they have a biconcave shape and have lost their nucleus and organelles.
The biconcave shape increases their surface area:volume ratio, thus increasing the absorption of oxygen.
The lack of nucleus increases the amount of hemoglobin in each cell.
this means that they cannot reproduce, therefore they must be produced in the bone marrow from undifferentiated cells.
Erythrocytes
produced in the bone marrow and are liberated into the bloodstream
Dead erythrocytes are engulfed by macrophages in the liver, spleen or bone marrow by phagocytosis. In the liver, these macrophages are Kupffer cells
Kupffer cells, the hemoglobin is split into globin chains and heme groups
Globin is re-used in protein synthesis
The heme group is transformed into iron and bilirubin
Iron is carried back to the bone marrow where it is used to produce new red blood cells.
Bilirubin is secreted into bile that will be used in the emulsification of fats.
Cholesterol and Bile
Cholesterol
: Cholesterol is one of the most well-known fats. You ingest cholesterol in your diet, but it is not essential, as most cholesterol molecules are synthesised in the liver.
cholesterol is required for membrane synthesis, a small portion is added to the membranes of hepatocytes, and the rest is exported as lipoproteins or bile salts
High-density lipoproteins (HDL) contain more protein, while low-density lipoproteins (LDL) contain more lipids.
HDL Function: to transport cholesterol from tissues to the liver
LDL Function: to transport cholesterol from the liver to other organs
BUT LDL deposit in the blood vessels and can become oxidised. This will cause atherosclerosis of the walls of the arteries
LDLs and HDLs are both produced in the plasma; however a small amount is synthesised in the liver
Bile
: have a crucial role in digestion as they emulsify fats
Bile salts are synthesised by the liver from surplus cholesterol, and may be modified by bacteria in the intestines. Bile salts are reabsorbed from the intestines into the liver, but lots are lost in faeces.
The liver produces about one litre of bile per day. This fluid is carried by the bile canaliculi to the bile duct, which carries it to the gall bladder to be stored.
Diseases
Jaundice
: Jaundice is a condition where the skin and white of the eyes turn yellow. It is caused by the presence of bilirubin in extracellular fluid. (bilirubin is produced from haemoglobin breakdown in erythrocyte recycling in the liver)
Bilirubin in blood binds reversibly to albumin (a plasma protein), forming conjugated bilirubin that travels to the liver, which removes it from the plasma. When the liver is not able to remove the bilirubin from blood, its level may rise and the skin and eyes may begin to appear jaundiced.
Jaundice appears under....
Immaturity in the conjugation of bilirubin (greater in premature babies).
Genetic diseases (e.g. Gilbert syndrome).
Defects in the secretion of conjugated bilirubin from hepatocytes (in liver damage).
Defects in transit of bilirubin to intestines (e.g. with bile duct obstruction).
Alcohol and cirrhosis
: Cirrhosis is a disease where the damaged liver tissue is replaced by scar tissue
Affects the functioning of liver cells, but also interferes with the blood supply to these cells. The symptoms are weakness, fatigue, jaundice and bruising
There is no cure for this disease
Excessive alcohol or drug consumption may cause liver cirrhosis. Other causes of cirrhosis include chronic viral hepatitis B or C, chronic bile duct obstruction, fatty liver disease, excess of iron, cystic fibrosis
The greater the consumption, the greater the chances of dying of liver cirrhosis