L24 - liver anatomy & function Flashcards
can the liver regenerate?
yes
mass of liver
approx 1.5kg
describe liver structure
- 4 lobes (left, right, caudate, quadrate) NOTE: opposite way on diagrams
- diaphragmatic surface superior upper surface of the liver
- visceral surface faces abdominal organs (where gallbladder is located)
what is the liver made up of?
- lobules
- containing hepatocytes + kupffer cells
- blood vessels (sinusoids)
- bile caniculi
what is the portal triad?
- bile duct
- hepatic portal vein
- hepatic artery
describe liver blood flow
- liver receives blood from the heart & GI tract
- hepatic portal VEIN delivers deoxygenated blood from GI tract
- hepatic artery delivers oxygenated blood from heart
- the artery + vein divide into 2 and supply the left + right side of the liver
- blood flows from hepatic portal vein and hepatic artery through lobules into central vein
- bile flows in opposite direction
what are the exocrine (digestive) functions of the liver?
- secretes bile salts and HCO3-
- involved in cholesterol metabolism
- organic and drug metabolism
endocrine functions of liver
- secretes peptides & hormoes
- clotting and produces plasma clotting factors
- secretes plasma proteins
where is bile synthesised and stored?
synthesised in liver by HMG-CoA, stored in gallbladder
hepatocytes and their function in bile (exocrine function)
- create bile salts to solubilise fats
- cholesterol
- phospholipids (lectin)
- bile pigments ( extracts billirubin from rbc)
epithelial cells and their function in bile (exocrine function)
- HCO3- neutralises stomach acid
- secretion is triggered by secretion from small intestine in response to fatty acids in diet
during a meal what does the gallbladder do?
- contracts
- release bile into duodenum (SI)
- via Sphincter of Oddi
what is the contraction of gallbladder stimulated by during a meal?
cholecytoskinin from SI which is triggered by fatty acids
enterohepatic circulation
- flow of bile / bile salts
- release of bile. bile salts from gallbladder
- during fatty meal, bile salts are absorbed in SI but Na+ coupled transporters
- 95% is retired back to liver through hepatic portal vein: enterohepatic circulation
- hepatocytes absorb bile salts from blood and secrete back into the bile
- 5% lost in faeces and new bile salts synthesised from cholesterol
what are new bile salts synthesised from?
cholesterol
what does the liver do with cholesterol?
- extracts cholesterol from blood and secretes it into the bile and faeces
- can use to make more bile
describe cholesterol
- insoluble
- froms micelles
- forms lipoproteins in plasma
what happens when we eat dietary fibre?
- hides bile in SI preveting enterhepatic circulation (bile doesn’t return to liver through hepatic portal vein).
- so it removes the bile from the body and the cholesterol it contains
can cholesterol lower drugs?
yes
why do we need cholestrol?
- membrane + bile synthesis
- precursor to steroid hormones
- taken up by cells from blood for use
how does the liver use bile?
extracts cholesterol and secretes it into bile or metabolises it into bile salts
how are levels of cholesterol balance maintained?
increased dietary cholesterol suppresses HMG-CoA
bad cholesterol (LDL)
saturated fatty acids
- red meat
- cheese
- whole milk
increases plasma cholesterol
good cholesterol (HDL)
- polyunsaturated/ monounsaturated
- olive / peanut oil
decreases plasma conc
what do low density cholesterol do? (LDL)
deliver cholesterol to cells as they need a certain amount to make plasma membranes
what do high density cholesterol do? (HDL)
remove cholesterol from plasma and delivers to liver
too much cholesterol in body?
- causes deposition of cholesterol in artery walls (atherosclerotic disease)
- increased risk of heart attack
how to lower risk of athersosclerosis?
decrease LDL:HDL
what decreases HDL levels?
smoking
what increases HDL?
weight loss
what lowers LDL and raises HDL?
oestrogen
familial hypercholesterolaemia
decreased LDL receptors so increased circulating cholesterol
what are gallstones?
crystallisation of cholesterol in gallbladder
complications of gallstones
- can block gallbladder or bile duct, preventing fat digestion/ absorption
- decrease in absorption of fat soluble vitamins (A,D,E)
- clotting issues (K) and calcium deficiency
- bacteria acting on unabsorbed fat causes diarrhoea and fluid loss
- blocks pancreatic secretions
- causes build up of billirubin
- causes jaundice due to excess bilirubin
endocrine functions - synthesis of plasma proteins
most medicines are plasma protein bound
most abundant plasma protein?
- albumin
- made in liver
- circulate in plasma as too big to be take up into cells or filtered in kidney
- function in osmolarity of plasma
- carrier molecules for substances and drugs
globulins
immunoglobulins (antibodies)
fibrinogen
involved in blood clotting cascade
endocrine functions - synthesis of clotting factors
- liver makes them
- bile made by liver absorbs lipid soluble vitamin K from diet in SI
vitamin K
essential for production of prothrombin (precursor to thrombin) + other clotting factors
why can liver disease cause bleeding?
not making clotting factors and bile
endocrine function - liver makes peptides and hormones
- liver secretes insulin growth factor -1 (1GF-1) in response to increased levels of growth hormone (GH) from anterior pituitary
- liver hydroxylate enzymes metabolise dietary (D2) or sunlight derives (D3) vitamin D to active form
insulin growth factor -1 (IGF -1)
acts with grown hormone to cause bone chondrocytes for cell divison
what does calcitriol do?
stimulates SI absorption of calcium needed for bones
homeostatic function (endocrine) - peptides and hormones - angiotensinogen
- liver makes produces Angiotensinogen which is cleaved to form Angiotensin I by the action of
- renin is secreted by kidneys in response to drop in bp
- Activation of AngI to Ang II stimulates vasoconstriction and Na+/ H2O retention
immune function of liver
key detector of pathogens entering through GI tract.
Liver filters blood entering from hepatic portal vein
Pathogens detected by macrophage –like (Kupffer) cells
non-alcoholic liver disease
caused by obesity
hepatitis
viral infection or caused by alcohol
heaemochromatosis
genetic disease - build up of iron
cirrhosis
liver scarring and failure
hepatic medications
drug induced
liver function tests
blood test
