Liver physiology Flashcards
What does the hepatic vein carry?
Deoxygenated blood from the liver to the heart via the inferior cava.
What does the hepatic portal vein carry?
Nutrient-rich but oxygen-poor blood from the GI tract towards the liver.
Where does the blood from the liver come from and leave?
25% if the output from the heart does to the liver
- 25% of this comes from the hepatic artery- oxygen rich
- 75% comes from the haptic portal vein- nutrient rich
then goes out of the liver by the hepatic vein to the vena cava.
Discuss the structure of the liver
The liver is the largest organ in the body and has left and right lobes that are divided into 8 segments called lobules.
Lobules:
- Hexagonal
- Has a central vein in the middle
- Outisde is the portal triad = branch of the hepatic artery, branch of the portal vein and branch of the bile duct.
- contain hepatocytes
- contains bile cannaliculi- gathers the bile made bu the hepatocytes
- Has sinusoids (capillaries)- join to the central vein.
- Other cells found in liver:
Kupfer cells- macrophages involved in phagocytosis of foreign substances e.g. bacteria
Fibrocytes
Hepatic stellate cells- these (and fribrocytes) support the hepatocytes and during liver disease these cells are responsible for the fiborsis (scarring) occurring.
What are the functions of the liver?
METABOLISM:
Involved in metabolism and storage of energy
- Carbohydrates:
Liver stores glucose as glycogen in case of fasting- this isn’t as energy dense as fats as it also needs storage of water.
Glycogenolysis in fasting breaks down the glycogen to glucose Gluconeogenesis- making of glucose from amino acids and fatty acids
- Lipids:
Liver synthesises up to 85% of cholesterol in the body which is then carries around in the blood via lipoproteins- VLDL, HDL, LDL- liver makes these also. Cholesterol is needed for the synthesis of cell membranes and some proteins.
- Protein: Synthesises non-essential amino acids in the liver ( the ones we can make ourselves, others are just dietary) e.g. glutamate and alanine
Also involved in the breakdown of amino acids to ammonia and then into urea ready for excretion.
DETOXIFICATION AND DEGREDATION:
- Liver is involved in the conversion of harmful ammonia to urea to be excreted by sweat and urine
- Detoxification:e.g. drugs and xenobiotics- foreign substances eg. food contaminants:
Phase I: reaction by CYP P450 enzymes
Phase II: conjugation with other compounds to become more hydrophilic and less toxic e.g. gluconosyltransferases
- Note this ability to detoxify and degrade can decrease with age, nutrition and genetics:
nutrition- some foods compete with these enzymes involved for metabolism
age- decreased efficacy of enzymes and also tend to take more meds as we age
ENDOCRINE FUNCTIONS:
- Involved in the modification of hormones:
- Vit D3 from the skin is converted to 25-hydroxy via D3 in the liver and then to 1,25-hydroxy vit d3 in the kidney
- thyroid hormone- conversion to T4 to more potent T3
- Insulin like growth factors produced by hepatocytes modify the action of growth hormones.
- Liver is majorly involved in hormone degradation also e.g. insulin + glucagon, oestrogens, parathyroid hormones and gastrin.
STORAGE:
- Stores fats- this is a problem in obesity as leads to a fatty liver which is the early stage of liver disease.
- stores glycogen as glucose
- trace elements e.g. copper and iron
- Vitamins:
fat-soluble e.g. vit A, D, K for a longtime
Some water-soluble vits for a very short time- except vit B12 which cane stored for a longer time
SYNTHESIS:
- Hormones e.g. insulin, thrombopoetin
- Plasma proteins e.g. coagulation factors for clotting, lipoproteins for cholesterol transport
- Angiotensinogen- involved in the RAS system
- proteins involved in iron transport and metabolism e.g. transferrin (transport in blood) and hepcidin (Inhibits iron uptake by gut)
- synthesises bile (in a mother flashcard)
IMMUNOLOGICAL FUNCTION:
Via the reticuloendothelial system, the kupfer cells phagocytose and degrade bacteria/antigens carried from the GI system in the portal vein
What does bile contain?
Bile salts
cholesterol
lecithin
bilirubin
Where is bile stores and then where does it go after a meal?
Bile is made in the liver and then released to be stored in the gall bladder. It is then released into the duodenum after a meal.
What are bile salts and lethicin and what do they do?
These are cholesterol derivatives that act as emulsifiers which convert large fat globules to a liquid emulsion as micelles. This allows for an increased surface area fo lipase in the gut to work.
How are bile salts excreted?
95% of bile salts are reabsorbed in the terminal ileum ad travel via the hepatic portal vein back to the liver for re-use
5% are lost in the faeces (bilirubin is excreted in this 5%)
How is bilirubin excreted?
- Bilirubin is a breakdown product of heam from red blood cell breakdown
- when RBCs are senescent, they get broken down
- The heme and haemoglobin is broken down to bilirubin in macrophages e.g. kupfer cells of the reticuloendothelial system via the enzyme haemoxygenase 1
- This bilirubin is unconjugated and is taken up by facilitates diffusion into the liver and conjugated with glucaronic acid
- This conjugated bilirubin is actively secreted into the bile and travels in the intestine
- in the colon section of the intestine, bacteria removes the glnucaronic acid part, resulting in free billirubin
- this is then converted to urobilinogen
- Some of the urobillinogen is reabsorbed from the gut and enters portal blood. this is transported to the kidney where it is converted to urobillin- this is what gives urine its characteristic yellow colour- it is excreted here
- A portion of urobilinogen stays in the colon and is oxidised by intestinal bacteria to the brows stercobilin (brown pigment of faececs)
- A portion is also entrered into the enterohepatic urobilinogen cycle = reabsorbed back to liver.
