Liver Physiology Flashcards
(102 cards)
1
Q
What is the basic cellular structure of the liver?
A
Lobules
2
Q
What are lobules made of?
A
Ramifying columns of hepatic cells
3
Q
Where do portal vein and hepatic artery drain into?
A
Sinusoids
4
Q
What do sinusoids open into?
A
Central vein
5
Q
What are sinusoids? What is their function?
A
Special liver capillaries, blood flow regulation
6
Q
What is the dual blood supply to the liver?
A
Hepatic portal system
Hepatic artery
7
Q
Where does the hepatic portal system receive blood from?
A
Spleen
Intestines
Pancreas
Stomach
8
Q
Where does the hepatic portal system empty into?
A
Inferior vena cava
9
Q
What does the hepatic portal system supply?
A
Nutrient rich blood form the GI
10
Q
What % of blood to the liver does the hepatic portal system supply?
A
70 to 80%
11
Q
Why does the hepatic portal system store some blood?
A
It stores 450ml that can be shifted in times of stress
12
Q
What is the blood in the hepatic portal system like?
A
Incompletely saturated
13
Q
What kind of branch is the hepatic artery?
A
Primary branch from celiac artery which is one of the three main visceral branches of the aorta
14
Q
What % of blood does the hepatic artery supply to the liver?
A
20 to 30%
15
Q
What kind of blood does the hepatic artery bring to the liver?
A
Oxygen-rich blood
16
Q
What are the functions of the liver?
A
Metabolism
Detoxification
Bile Production
Storage
Hematologic Functions
Synthesis
Conversion
Cholesterol Production
Enterohepatic Circulation
17
Q
What kind of metabolic processes is the liver involved in?
A
Carbohydrate metabolism
Fat metabolism
Protein metabolism
18
Q
What is the carbohydrate metabolism like?
A
Converts glucose to glycogen for storage and vice versa
19
Q
What is the fat metabolism like?
A
Synthesis of fatty acids from glucose, breaks down fatty acids for energy and produces cholesterol
20
Q
What is the protein metabolism like?
A
Deaminates amino acids, forms urea from ammonia and synthesis plasma proteins
21
Q
What are the hematologic functions of the liver?
A
Synthesis of clotting factors
Hematopoiesis in the fetus
Recycling of haemoglobin
22
Q
What is the conversion process like?
A
Converts ammonia to urea, which is excreted in the urine
23
Q
What is cholesterol production like?
A
Produces cholesterol and excretes it in the bile
24
Q
What are hepatocytes responsible for?
A
Synthesis of most of the plasma proteins
25
What is albumin?
The major plasma protein and is almost exclusively synthesised by the liver
26
What other substances does the liver synthesise?
Non-essential amino acids
27
What is one of the benefits of the liver regarding the fat metabolism?
Extremely active in oxidising triglycerides to produce energy
28
Where does the liver get fatty acids from and what does it do with them?
Gathers fatty acids from the diet and breaks them down to acetyl-coA
29
Where does the liver export large quantities of acetoacerate into?
The blood
30
What does it convert insoluble lipids into?
Soluble forms (lipoproteins)
31
What % of cholesterol is produced by the liver?
85%
32
What is interesting about synthesis and degradation of fats?
Both synthesis and break down of fats take place in the liver
33
Where is acetoacetate produced? And from what?
In the mitochondria of the liver from acetyl-coA
34
What are the functions of cholesterol?
It makes cell membrane, sex hormones, bile acids and vitamin D
35
What does "endogenous" mean, and how does it relate to cholesterol?
Manufactured by our own cells, 85% of cholesterol is endogenous
36
Where does the rest of cholesterol come from (the remaining 15%)?
From the food we eat
37
What is the function of the liver in regards of detoxification?
Serves as a gatekeeper between the circulation and the absorbed substances
38
What is the First Pass?
Every substance absorbed in GIT passes through the liver
39
What does detoxification include?
Drugs, poison and metabolic products like ammonia, alcohol and bilirubin
40
What are the two mechanisms of detoxification?
Binds materials reversible to inactivate and chemically modify compound for excretion
41
What are the principles of detoxification?
Elimination of hydrophobic compounds from the body
Formation of polar/soluble products
42
What is bile?
A yellow-green liquid that is continuously secreted by hepatocytes
43
What is the bile secretion pathway?
Bile from hepatocytes enters bile canaliculi which empty into small bile ducts
Hepatic ducts join the cystic duct from the gallbladder to form common bile duct
44
What is the daily secretion of bile?
500ml
45
What is bile composed of?
Bile salts including bile acids (50%)
Phospholipids, Lecithin (40%)
Bile pigments, bilirubin (2%)
Cholesterol (4%)
Electrolytes & Water
46
What is the function of bile?
Emulsifying fats; aids in fat digestion and absorption
47
What are bile salts?
Amphipathic molecules
Ampipathic = hydrophobic and hydrophilic parts
48
What do hepatocytes secrete?
Organic components (bile acids, cholesterol and bilirubin)
49
What do bile ducts secrete?
Watery solution, sodium, bicarbonate
50
What are organic constituents like?
Highly concentrated
51
What happens to watery components?
Reabsorbed by the gallbladder mucosa
52
What is the function of the gallbladder?
Stores bile
Concentrates bile
Empties bile
53
What happens to most of the bile?
Most of the bile is recycled, 2 to 3 times during the digestion of a single meal --> Enterohepatic circulation
54
Which kinds of agents increase the formation of bile?
Cholerectic agents
55
Which is the rate limiting enzyme in the bile formation process?
Cholesterol 7-a-hydroxylase
56
When is cholesterol 7-a hydroxylase inhibited?
By high levels of bile acids
57
What are the bile formation processes?
Primary bile acids formation
Secondary bile acids formation
58
Where are primary bile acids formed?
Hepatocytes
59
How are secondary bile acids formed?
In the large intestine, bacteria convert a portion of each primary bile acid to a secondary one
60
What are the primary bile acids?
Cholic acid and Chenodeoxycholic acid
61
What are the secondary bile acids?
Deoxycholic acid and lithocholic acid
62
What are the two pathways used for bile acid synthesis?
Classic and alternative pathways
63
Explain the classic pathway of the bile acid synthesis process
Cholesterol --> 7a hydroxylate --> Sterol 12-a hydroxylate OR CYP27A1 --> Cholic acid OR Chenodeoxycholic acid
64
What do gut microbiota do?
15% of conjugated bile acids are deconjugated by intestinal bacteria
65
What are the enzymes used by gut microbiota to deconjugate the bile acids?
Bacterial bile salt hydrolase
Bacterial 7 a dehydroxylase
66
What is the alternative pathway process?
Cholesterol --> 27 hydroxylase --> Oxysterol 7a hydroxylase --> Chenodexycholic acid
67
What is the final step of bile acids synthesis?
It goes into the terminal ileum and colon and it becomes DCA, LCA and UDCA
68
What is the process of formation of canicular bile?
Bile salts and bile acids are formed by hepatocytes
Bile pigments are picked up from blood sinusoids
Conjugation of bilirubin occurs in hepatocytes
69
What is bilirubin?
A metabolite of heme that is potentially toxic to the body
70
What is one of the key characteristics of bilirubin?
It is capable of crossing the BBB
71
Where does most of the bilirubin come from?
RBCs
72
Where does the minority of bilirubin come from?
Heme-containing proteins in other tissues (skeletal muscle and liver)
73
What does bilirubin provide colour to?
Bile, feaces, and to a lesser extent urine
74
What are the three fates of bilirubin in the intestines?
1. Reabsorption into the blood
2. Excretion in feaces
3. Conversion by intestinal flora to urobilinogen
75
How does bilirubin relate to jaundice?
Bilirubin accumulation in the blood stream, often due to liver diseases, leads to jaundice which manifests as the yellow discolouration of the skin and the conjunctiva
76
How does jaundice develop in newborn babies?
Red blood cells die in large numbers after birth,
A lot of bilirubin is created,
The liver is not mature yet so it processes bilirubin very slowly,
Very little bilirubin actually leaves the body,
The excess, unprocessed bilirubin builds up everywhere in the body --> yellow discolouration in skin and eyes
77
What are the functions of the gallbladder?
Storage of bile
Release of bile
Regulation of bile flow
Bile pH regulation
78
How is storage of bile in the gallbladder important?
Bile is stored and concentrated in the gallbladder, aids in digesting fats
79
What happens during the release of bile in the gallbladder?
After consuming fatty meals, the gallbladder releases bile into the small intestine to emulsify fats --> Aids absorption
80
How is the bile flow regulated in the gallbladder?
Gallbladder controls bile flow into the small intestine by contracting and relaxing its muscles, ensuring bile is released in a controlled manner
81
What happens if bile becomes too acidic?
It can lead to gallstones
82
What is the neurohormonal control of gallbladder contraction and biliary secretion?
Bile is released in response to signals that simultaneously relax the sphincter of Oddi and contract the smooth muscle that encircles the gallbladder epithelium
83
What is hormonal control mechanism of biliary secretion?
CCK
84
What are the neural control mechanisms of biliary secretion?
Parasympathetic (vagal nerve)
Sympathetic
85
What is the effect of the parasympathetic neural control on biliary secretion?
Contraction of gallbladder
Relaxation of sphincter of Oddi
Increased bile formation
86
What is the effect of the sympathetic neural control on biliary secretion?
Reduced bile secretion
Relaxation of gallbladder smooth muscle
87
What is the enterohepatic circulation?
The recirculation of bile salts
88
Where are specialised cells contained and what are their function regarding bile salts?
The terminal ileum contains specialised cells that are responsible for the absorption of primary and secondary bile salts by active transport
89
Why is enterohepatic circulation important?
It is necessary because of the limited pool of bile salts
90
What does resection of the ileum lead to?
Prevents absorption of bile salts which leads to steatorhea
91
How could fats and bile salts increase water content of feaces?
By promoting the influx of water into the lumen of the colon
92
How is ammonia primarily produced?
Through the breakdown of amino acids during protein metabolism
93
Where is ammonia derived from?
The colon by bacterial creases (50%)
The kidney (40%
Deamination of amino acids (liver and metabolic processes in muscle cells) (10%)
94
What is the only tissue in the body that can convert ammonia to urea?
The liver
95
What does ammonia do to CNS?
It is toxic
96
What is the purpose of converting ammonia to urea in the liver?
To prevent toxic accumulation of ammonia in the bloodstream
97
What are the key enzymes in the urea cycle?
Carbamoyl phosphate synthase I
Ornithine Transcarbamylase
98
What is the toxic effect of urea oil comparison to ammonia?
Urea is much less toxic than ammonia so it is released into the bloodstream and transported to the kidney
99
Where is urea excreted?
In the urine
100
How does liver disfunction lead to hyperammonemia?
Liver disease impairs the liver's ability to function properly leading to increased ammonia levels in the blood
101
What kind of liver disease can lead to hyperammonemia?
Cirrhosis or hepatitis
102
What can hyperammonemia lead to?
Encephalopathy, CNS impairment (confusion and disorientation)
