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Fat Metabolism Flashcards

1
Q

How is fat stored in the body

A
  • Most of the bodies fat is stored in adipocytes which form tissues called adipose tissues
  • Some is stored in hepatocytes
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2
Q

What are triglycerides made of

A

Triglycerides (TGs or TAGs) consist of 3 fatty acids bound to a glycerol molecule

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3
Q

How much do triglycerides account for in body energy stores

what about proteins and carbs

A

It accounts for 78% of energy stored in the body

Proteins account for 21% and carbohydrates account for 1%

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4
Q

95% of dietary lipids are triglycerides, the rest consist of

A

phospholipids, free fatty acids (FFAs), cholesterol and fat soluble vitamins

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5
Q

what are lipids

A

They are esters of fatty acids and certain alcohol compounds

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6
Q

function of lipids

A
  • Energy reserves
  • Structural part of cell membrane
  • Hormone metabolism
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7
Q

Function of Lipoproteins

A

They are used to transport cholesterol in the blood

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8
Q

Where is HDL made

A

liver

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9
Q

Function of HDL

A
  • Removeexcess cholesterol from blood and tissue
  • They then deliver this cholesterol to the liver which secretes it into the bileor converts it into bile salts
  • Referred to as “good” cholesterol, since it removes cholesterol from plasma
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10
Q

where is LDL formed

A

formed in the plasma

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11
Q

How are LDLs taken up by cells

A

LDLs bind to plasma membrane receptors specific for a protein component of the LDLs and are then taken up by the cells via endocytosis

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12
Q

why are LDLs said to be bad

A

LDL cholesterol is said to be “bad” due to the fact that high plasma concentrations can be associated with increased deposition of cholesterol in arterial walls and a higher incidence of heart attacks

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13
Q

But why is LDL important

A

However, LDL is essential in supplying cells with the cholesterol they require to synthesise cell membranes and for steroid hormone production in the gonads and adrenal glands + aldosterone + cortisol

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14
Q

LDL function

A

The main cholesterol carriers and they deliver cholesterol to cells throughout the body

is essential in supplying cells with the cholesterol they require to synthesise cell membranes and for steroid hormone production in the gonads and adrenal glands + aldosterone + cortisol

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15
Q

What Is VLDL where made

and function

A

synthesised in hepatocytes - carries triglycerides from glucose in liverto adipocytes

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16
Q

Under resting conditions approximately half the energy used by muscle, liver and the kidneys is derived from the

A

catabolism of fatty acids

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17
Q

Most cells store some degree of fat, but most of the body’s fat is stored in adipocytes
how so

A

almost the entire cytoplasm of each adipocyte is filled with a single large fat droplet

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18
Q

what is adipose tissue

A

Clusters of adipocytes form adipose tissue, most which is in deposits underlying the skin or surrounding internal organs

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19
Q

What is the purpose of adipocytes

A

The function of adipocytes is to synthesise and storetriglycerides during periods of food uptake and the, when food is not being absorbed from the small intestine, to release fatty acids and glycerol into the blood for uptake & use by other cells in order to provide the energy required for ATP formation

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20
Q

1 RELEASE OF FATTY ACID TO MAKE ATP PROCESS

What does CoEnzyme A do

A

Molecule of coenzyme A link to the carboxyl at the end of a fatty acid

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21
Q

2 RELEASE OF FATTY ACID TO MAKE ATP PROCESS

what happens when a Molecule of coenzyme A link to the carboxyl at the end of a fatty acid

A

This step is followed by the breakdown of ATP —> AMP + 2Pi3.

The coenzyme A derivative of fatty acid then proceeds through beta-oxidation reactions

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22
Q

3 RELEASE OF FATTY ACID TO MAKE ATP PROCESS

What happens in the beta oxidation reactions

A

A molecule of acetyl coenzyme A is split off from the fatty acid and two pairs of hydrogen atoms are transferred to coenzymes (one pair to FAD and the other pair to NAD+)

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23
Q

4 RELEASE OF FATTY ACID TO MAKE ATP PROCESS

what happens after two pairs of hydrogen atoms are transferred to coenzymes (one pair to FAD and the other pair to NAD+)

A

The hydrogen atoms from the coenzymes then enter the oxidative phosphorylation pathway to form ATP

Another coenzyme A attaches to the fatty acid and the cycle is repeated

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24
Q

5 RELEASE OF FATTY ACID TO MAKE ATP PROCESS

what happens each passage through this sequence

A

Each passage through this sequence shortens the fatty acid chain by two carbons atoms until all the carbon atoms have transferred to coenzyme A molecules

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25
6 RELEASE OF FATTY ACID TO MAKE ATP PROCESS what happens when all the carbon atoms have transferred to coenzyme A molecules
These molecules then lead to the production of CO2 & ATP via the Kreb’s cycle & oxidative phosphorylation
26
function of Lipoprotein lipase
Hydrolyses triglycerides in lipoproteins (chylomicrons & VLDLs) into 2 free fatty acids & 1 glycerol molecule
27
Function of Hepatic lipase
- Expressed in the liver and adrenal glands - Converts IDL (intermediate density lipoprotein) into LDL thereby packaging it with more triglycerides to be released in the body
28
What secretes bile
Secreted in the liver by hepatocytes more or less continuously
29
function of bile
Used to emulsify fats | Also serves as an excretory pathway for most steroid hormones, many drugs as well some toxins metabolised by the liver
30
Where is bile stored and concentrated
Stored & CONCENTRATED in the gall bladdersince some NaCl & water are absorbed into the blood
31
Where does the gall bladder lie
The gall bladder, lies at the junction of the right-mid-clavicular line & costal margin
32
how is liver connected to GI TRACT
The livers connection with the GI tract is via the portal vein which collects blood from the superior mesenteric vein (which in turn is effectively the venous drainage of both the small and large intestines)
33
What drains small and large intestine
superior mesenteric which drains into portal vein
34
The functional unit of the liver is
the hepatic lobule (formed by hepatic plates stacked on top of each other)
35
What is a hepatic lobule
Hepatic lobules are hexagonal in cross-section with a portal triad at each corner
36
what does the portal triad consist of
- A hepatic portal vein - Hepatic artery - Bile duct
37
Running up the centre of the lobule is the what
central vein which eventually becomes the hepatic vein
38
what is the hepatic sinusoid
type of blood vessel (with fenestrated, discontinuous endothelium)
39
Histology of hepatic sinusoid
type of blood vessel (with fenestrated, discontinuous endothelium)
40
What happens at the hepatic sinusoid
Substances absorbed from the small intestine wind up in the hepatic sinusoid, (where oxygen-rich blood from the hepatic artery and nutrient richblood from the portal vein is found hepatocytes are separated from the sinusoids by the space of disse) either to reach the vena cava via the central vein or are taken up by the hepatocytes in which they can be modified
41
what separates the sinusoids from the hepatocytes
space of disse
42
what are the hepatic lobules
The hepatic lobules are wedge-like arrangements of hepatocytes around 1 to 2 cells deep which are surrounded by sinusoids (containing mixed portal/hepatic artery blood)
43
Blood supply of liver
The liver is unique in that the majority of its blood supply comes from a vein - the portal vein - which is responsible for 80% of the supply with the remaining 20%supplied by the hepatic artery
44
When the branches of artery and vein leave the portal triadthey join and blood is mixed as it enters the sinusoids where does it exit
It flows through the centre and exits via the central vein
45
The sinusoids are lined with what
a continuos layer of specialised endothelial cells interspersed with Kupffer cells (the resident macrophage population)
46
The formed bile heads are in what in relation to the blood
in the opposite direction to the blood
47
purpose of stellate cells
On the undersurface there are cells called stellate cells which are responsible for producing the extracellular matrix in the space of disse
48
what are bile canaliculi
Between adjacent hepatocytes are bile canaliculi - these are not true vessels (they do not have specialised walls) but are like a groove running along the side of the hepatocytes, they are bound together by tight junctions, gap junctions & desmosomes which crossboth cell membranes. Actin filaments are found in the areas around the canaliculi and serve to pump the formed bile toward the bile ducts
49
function of bile canaliculi
Actin filaments are found in the areas around the canaliculi and serve to pump the formed bile toward the bile ducts
50
what forms the common bile duct
The bile ducts in the the hepatic lobules join either into the left or right hepatic ducts which in turn join to form the common hepatic duct
51
what does the cystic duct do
joins the common hepatic duct to gall bladder , allowing bile to collect in the gall bladder
52
what joins to form the common bile duct
After the cystic duct had joined the common hepatic duct, the duct becomes the common bile duct
53
what is the ampulla of vater
the point where the common bile duct and the pancreatic duct join
54
where does the pancreatic duct and the common bile duct enter the duodenum at what
These two ducts then enter the duodenum at the major duodenal papilla (2nd part duodenum)
55
what is the sphincter of oddi
A sphincter around the two ducts, to regulate the entry of bile into the duodenum is
56
6 major ingredients of the bile
- Bile salts-Lecithin (a phospholipid) - HCO3 - and other salts - Cholesterol - Bile pigments - Trace metals
57
what are bile salts manufactured by
hepatocytes
58
Bile salts, cholesterol & lecithin are aggregated into mixed micelles and MAINTAIN this aggregation in the gall bladder even when concentrated what is the main reason for this
The main reason for this is that bile salts are powerful detergents which they need to be for their fat emulsification function (derived due to the fact that bile salts are anionic(negative)). However they are also capable of damaging cell membranes and so they are separated in micelles to reduce damage until they are required
59
Function of H3CO3-
helps neutralise the acids in the duodenum
60
The components of bile are secreted by TWO different cell types:
- Hepatocytes; bile salts, cholesterol, lecithin & bile pigments - Epithelial cells lining the bile ducts; most of the HCO3- rich solution
61
what stimulates the secretion of the HCO3- Rich solution by the bile ducts
Secretion of the HCO3- rich solution by the bile ducts, just like the secretion by the pancreas, is stimulated by secretin in response to the presence of acid in the duodenum
62
Where does the gall bladder get its bile from
The gallbladder receives its bile from the common hepatic duct which is formed by the the left and right hepatic ducts
63
how does bile enter the gallbladder and what happens here
The hepatic bile enters the gallbladder via the cystic duct and is stored & concentrated here - hepatic bile is relatively dilute and is then concentrated in the gallbladder
64
Bile remains in the gall bladder until what
until the gallbladder contracts under the action of cholecystokin (CCK) - CCK is released due to amino + fatty acids in duodenum
65
How is the vasculature of the gall bladder strange
The vasculature of the gallbladder is strange in that it the cystic artery supplied oxygenated blood to the gallbladder but it has no venous drainage. The gallbladder is stuck to the liver bed & blood drains from the gallbladder directly into the liver with no identifiable venous pathway
66
What happens to the bile which is secreted into the intestinal tract
During the digestion of a fatty meal, most of the bile salts entering the intestinal tract via the bile are absorbed by specific Na+-coupled transporters in the jejunum and terminal ileum (largest amounts absorbed here)
67
what happens to the bile salts which are absorbed from the intestinal tract
The absorbed bile salts are returned via the portal vein to the liver, where there are once again secreted into the bile
68
what drives the uptake of bile salts from the portal blood
Uptake of bile salts from the portal blood into hepatocytes is driven by secondary active transport coupled to Na+
69
what is the enterohepatic circulation
refers to the circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver basically This recycling pathway from the liver to the intestine
70
How much bile is lost in faeces what replaces this
A small amount (5%) of the bile salts escape this recycling and is lost in faeces, but the liver synthesises new bile salts from cholesterol to replace it
71
how often will bile be recycled during a meal
During the digestion of a meal, the entire bile salt content of the body may be recycled several times via the enterohepatic circulation
72
what is bile made from
Bile is synthesised from cholesterol The liver also secretes cholesterol extracted from the blood into the bile
73
what is one of the mechanisms for maintaining cholesterol homeostasis in the blood
Bile secretion, followed by excretion of cholesterol in the faeces, is one of the mechanisms for maintaining cholesterol homeostasis in the blood
74
How is cholesterol made insoluble in water but soluble in bile
Cholesterol is insoluble in water, and it solubility in bile is achieved by its incorporation into micelles (whereas in blood, cholesterol is incorporated into lipoproteins)
75
when is bile secretion greatest
Although bile secretion is greatestduring & just after a meal, the liver is always secreting some bile
76
What happens to hepatic bile when the sphincter of oddi is closed
When this sphincter is closed, the dilute bile secreted by the liver is shunted into the gallbladder - here the bile is concentrated as some of the NaCl & water is absorbed into the blood
77
Surrounding the common bile duct at the ampulla of vater is a ring of smooth muscle known as the
sphincter of Oddi.
78
what kind of system is the bile system
low pressure
79
how is the bile system low pressure
So when the gallbladder fillswith bile it must exhibit adaptive relaxation - which is where the size increases but the pressure doesn't (opposite of what happens when you blow up a balloon)
80
Shortly after the beginning of a fatty meal what hormone is released, in response to what
the hormone cholecystokinin (CCK) is released in response to the presence of fat in the duodenum
81
what does CCK do
CCK causes the gallbladder to contract & the sphincter of Oddi to relax resulting in the flow of bile down the cystic duct through the common bile duct and into the duodenum where it mixes with the food in the duodenum & lipid digestion occurs

LIVER & FRIENDS (11 decks)

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