D3 - Liver Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Liver

A

lobed organ located below the diaphragm that functions to regulate the chemical composition of blood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Liver blood flow

A

It receives oxygenated blood via the hepatic artery, which is used to sustain liver cells (hepatocytes)
It also receives nutrient rich blood from the gut via the portal vein
Deoxygenated blood is transported from the liver via the hepatic vein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Liver functions

A

t is responsible for the storage and controlled release of key nutrients (e.g. glycogen, cholesterol, triglycerides)
It is responsible for the detoxification of potentially harmful ingested substances (e.g. amino acids, medications, alcohol)
It produces plasma proteins that function to maintain sustainable osmotic conditions within the bloodstream
It is responsible for the breakdown of red blood cells and the production of bile salts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Hepatic lobules

A

The liver is composed of smaller histological structures called lobules, which are roughly hexagonal in shape

Each lobule is surrounded by branches of the hepatic artery (provide oxygen) and the portal vein (provide nutrients)
These vessels drain into capillary-like structures called sinusoids, which exchange materials directly with the hepatocytes
The sinusoids drain into a central vein, which feeds deoxygenated blood into the hepatic vein
Hepatocytes also produce bile, which is transported by vessels called canaliculi to bile ducts, which surround the lobule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Sinusoids

A

Sinusoids are a type of small blood vessel found in the liver that perform a similar function to capillaries (material exchange)

Sinusoids have increased permeability, allowing larger molecules (e.g. plasma proteins) to enter and leave the bloodstream

The increased permeability of sinusoids is important for liver function and is due to a number of structural features:

The surrounding diaphragm (basement membrane) is incomplete or discontinuous in sinusoids (but not in capillaries)
The endothelial layer contains large intercellular gaps and fewer tight junctions (allowing for the passage of larger molecules)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Nutrient supply and conversion

A

The liver plays an important role in regulating the levels of nutrients in the bloodstream

Nutrients absorbed by the small intestine are transported by the hepatic portal vein to the liver for metabolism
The liver converts these nutrients into forms that can be stored or used and mediates their transport to various tissues
Nutrients stored within the liver include glycogen, iron, vitamin A and vitamin D

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Carbohydrate metabolism

A

Excess glucose in the bloodstream (e.g. after meals) is taken up by the liver and stored as glycogen
When blood glucose levels drop, the liver breaks down glycogen into glucose and exports it to body tissues
When hepatic glycogen reserves become exhausted, the liver synthesises glucose from other sources (e.g. fats)
These metabolic processes are coordinated by the pancreatic hormones – insulin and glucagon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Protein metabolism

A

The body can not store amino acids, meaning they must be broken down when in excess
Amino acid breakdown releases an amine group (NH2), which cannot be used by the body and is potentially toxic
The liver is responsible for the removal of the amine group (deamination) and its conversion into a harmless product
The amine group is converted into urea by the liver, which is excreted within urine by the kidneys
The liver can also synthesise non-essential amino acids from surplus stock (via transamination)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Fat metabolism

A

The liver is the major site for converting excess carbohydrates and proteins into fatty acids and triglycerides
It is also responsible for the synthesis of large quantities of phospholipids and cholesterol
These compounds are then stored by the liver or exported to cells by different types of lipoproteins
Low density lipoprotein (LDL) transports cholesterol to cells, for use in the cell membrane and in steroid synthesis
High density lipoprotein (HDL) transports excess cholesterol from cells back to the liver (for storage or conversion)
LDL is considered ‘bad’ as it raises blood cholesterol levels, while HDL lowers cholesterol levels and is therefore ‘good’
Surplus cholesterol is converted by the liver into bile salts, which can be eliminated from the body via the bowels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Toxins in bloodstream

A

Many of these toxic compounds are fat soluble, making them difficult for the body to excrete
These compounds are converted into less harmful and more soluble forms, which are then excreted from the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Detoxification

A

Toxins are converted into less harmful chemicals by oxidation, reduction and hydrolysis reactions
These reactions are mediated by a group of enzymes known as the cytochrome P450 enzyme group
These conversions produce damaging free radicals, which are neutralised by antioxidants within the liver
The converted chemical is then attached to another substance (e.g. cysteine) via a conjugation reaction
This renders the compound even less harmful and also functions to make it water soluble
The water soluble compounds can now be excreted from the body within urine by the kidneys

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Plasma proteins

A

proteins present in the blood plasma and are produced by the liver (except for immunoglobulins)

The proteins are produced by the rough ER in hepatocytes and exported into the blood via the Golgi complex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Types of plasma proteins

A

Albumins regulate the osmotic pressure of the blood (and hence moderate the osmotic pressure of body fluids)
Globulins participate in the immune system (i.e. immunoglobulins) and also act as transport proteins
Fibrinogens are involved in the clotting process (soluble fibrinogen can form an insoluble fibrin clot)
Low levels of other plasma proteins have various functions (e.g. α-1-antitrypsin neutralises digestive trypsin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Erythrocyte recycling

A

In humans, red blood cells possess minimal organelles and no nucleus in order to carry more haemoglobin

Consequently, red blood cells have a short lifespan (~120 days) and must be constantly replaced

The liver is responsible for the break down of red blood cells and recycling of its components

These components are used to make either new red blood cells or other important compounds (e.g. bile)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Function of Kupfter cells

A

Kupffer cells are specialised phagocytes within the liver which engulf red blood cells and break them down

Kupffer cells break down haemoglobin into globin and iron-containing heme groups
Globin is digested by peptidases to produce amino acids (which are either recycled or metabolised by the liver)
Heme groups are broken down into iron and bilirubin (bile pigment)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Iron storage

A

The released iron must be complexed within a protein in order to avoid oxidation to a ferric state

Iron can be stored by the liver within a protein shell of ferritin
Iron can be transported to the bone marrow (where new haemoglobin is produced) within the protein transferrin

17
Q

Jaundice - symptoms

A

The main consequence of jaundice is a yellowish discoloration of the skin and whites of the eyes (sclera)

Other common symptoms include itchiness, paler than usual stools and darkened urine

18
Q

Jaundice - cause

A

Jaundice is a condition caused by an excess of bile pigment – bilirubin – within the body

Bilirubin is produced as part of the natural breakdown of haemoglobin by the liver
Normally, the liver conjugates this bilirubin to other chemicals and then secretes it in bile
When there is an excess of bilirubin, it may leak out into surrounding tissue fluids

19
Q

Jaundice - underlying causes

A

Jaundice may be caused by any condition which impairs the natural breakdown of red blood cells, including:

Liver disease – impaired removal of bilirubin by the liver may cause levels to build within the body
Obstruction of the gall bladder – preventing the secretion of bile will cause bilirubin levels to accumulate
Damage to red blood cells – increased destruction of erythrocytes (e.g. anemia) will cause bilirubin levels to rise

20
Q

Jaundice - treatment

A

Jaundice may be resolved by treating the underlying cause for the build up of bilirubin within the body