Lipid digestion, absorption and transport Flashcards
What are lipids?
Lipids are fats
Name the different types of dietary lipids:
Triglycerides (most abundant in diet)
Phospholipids (cell membrane)
Steroids
Describe the structure of triglycerides
Glycerol
hydrocarbon backbone
attached to fatty acids
3 carbon atoms + 3 fatty acids
(phospholipids have 2 carbon atoms)
3 fatty acids
What is the structure of steroids?
have hydrocarbon in the from of ring structure
attached to fatty acids
Give examples of steroids
- Cholesterol (precursor for biosynthesis of below)
- Cortisol
- Estrogen
- Testosterone
Why do lipids require a special mechanism for digestion and absorption?
As they are hydrophobic and water insoluble
What are lipids made up of?
Fatty acids
Name the 2 difference classifications of fatty acids
- Saturated
- unsaturated
2. Unsaturated
What does it mean if a fatty acid is saturated?
each H atom is attached to carbon atom with single carbon bond
What does it mean if a fatty acid is unsaturated?
some carbon atoms have double covalent bonds
have less hydrogen
less attached to hydrogen
What can unsaturated carbons be further split into?
- Monounsaturated fatty acids
2. Poly unsaturated fatty acids
What does it mean if a fatty acid is Monounsaturated ?
It only has ONE double covalent bond between carbons
What does it mean if a fatty acid is poly unsaturated ?
Means there’s 1 or more double covalent bonds between carbon atoms (makes them less saturated with hydrogens) in the fattty acid chain
What state are saturated fatty acids found in?
SOLIDS
can withstand higher temp
Give examples of saturated fatty acids
Any fat eg
- Butter (solid at room temp as SATURATED)
- Ghee
- Coconut oil (solid at room temp)
- lard
What state are unsaturated fatty acids found in?
oils majorly
Give examples of unsaturated fatty acids
Any oils
eg olive oil= monounsaturated type
Give some functions of lipids (6)
1.2nd most used Energy source (after carbs)
- Helps body absorb important fat soluble vitamins
-> fat used to help these enter body cells/ circulation (otherwise can not) - supports key body processes such as synthesis of important hormones in body
e.g. cortisol = precursor for many other hormones
- Fat cushions internal organs and protects them from being damaged e.g. kidney, abdominal organs
- Fat layer below the skin insulated the body = subcutaneous fat
- Fat plays a general role in maintaining healthy skin + tissues + hair (and other organs/ tissues)
When do lipids serve as a source of energy?
Once calories from carbohydrates are used up if we are very active
body uses fats to make energy
Give examples of fat soluble vitamins
Vitamin A, D, E and K
for every gram of fat we burn, we get how many calories of energy?
9
What are some health issues associated with excessive dietary fat intake? (5)
obesity
diabetes
cancer
hypertension
atherosclerosis
What is the FDAs advice regarding fats?
max 35% of the total dietary intake should come from fat
What is the FDAs advice regarding saturated fat (most dangerous as well as trans fats)
No more than 10% of the total energy intake should come from saturated fat
What is the recommended daily value for total fat?
65g per day (based on a 2000 cal diet)
Which fatty acid comes from fatty fish?
Omega 3 fatty acids= good fats, lowers cholesterol
What does omega 3 fatty acid protect against ?
atherosclerosis
Should you take fish oil as a substitute for eating fatty fish?
No as they contain concentrated toxins accumulated by the fish §
How many fish meals are recommended per week?
2-3 to help our body get rid of cholesterol
Name the parts of the body involved in lipid digestion
- Oral cavity
- Stomach
- Small intestine
Where does digestion begin?
The oral cavity
How does digestion of lipids begin?
Chewing of fats increases surface area
Lingual lipase is released in the mouth which breaks down lipas
How are lipids digested in the stomach?
Lingual lipase and gastric lipase are relased
What do lingual and gastric lipase do?
They spilt triglycerides into fatty acids and diglycerides
What are lingual and gastric lipase also known as?
Acidic lipases
Why are lingual and gastric lipase known as acidic lipases?
As their activity is stimulated and increased by a acidic environment
Eating what can help protect you against atherosclerosis?
Eating foods high in omega 3 fatty acids
What process if very important in lipid digestion?
Emulsification
Why is emulsification important?
As emulsification helps fats to dissolve in water so that nutrients can be absorbed
Are fats soluble in water?
NO
What happens in emulsification?
Fat is spread out and the surface area is increased so that the fat can dissolve in water
What can lingual lipase do?
It has the capacity to emulsify fats
What else is present in the mouth other than lingual lipase that aids lipid digestion
Phospholipids
How do phospholipids aid lipid digestion?
They are slightly more soluble than triglycerides so they help with emulsification!
What is the activity of lipase stimulated and increased by?
By an acidic environment
how long does it take for 30% of triglycerides to be broken down into diglycerides + fatty acids?
after 2 hours of food reaching the stomach
this is way less than what happens in intestines later on!
Where does the main bulk of digestion take place?
In the small intestine
What is chyme?
Food that has been churned and partially digested in the stomach
Where does the chyme go after the stomach?
The small intestine
What does chyme stimulate?
Stimulates mucosa cells to realise the hormone choleocystokinin
What does the enzyme choleocystokinin do?
It stimulates the gall bladder and pancreas to release bile and digestive enzymes
What type of pH does chyme have?
An acidic ph
What does bile contain?
Bile salts(acid)
Which enzymes does the pancreases release to aid lipid digestion?
Pancreatic lipase and other lipase
What does pancreatic lipase do?
It breaks down dyglycerides into 2- monoglycerides and fatty acids
What do bile salts do?
They help emulsify fat droplets thus increasing their surface area for digestion
Where does food that hasn’t been digested by the small intestine go?
To the large intestine for excretion
Where are bile salts secreted from/
The gall bladder
What do bile salts contain?
Cholesterol among other substance
What do bile salts do?
Emulsify lipids
How do bile salts emulsify lipids?
surround the fat droplets in the chyme
they break the fat droplet into smaller droplets
surround from all sides
form exterior of solubility:
so, make their membrane more soluble
+ SA for lipids to be digested
Describe the structure of bile salts
They have a hydrophobic head and hydrophilic tail
The hydrophobic side attaches itself to the lipids and emulsifies it
What does pancreatic lipase do to triglycerides?
Breaks them down into 2 fatty acids and 2-mono-glycerol
What stimulates the release of choleocystokinin?
The chyme moving from the stomach to the small intestine
Where is the hormone choleocystokinin released from?
The mucosa cells
What is a cholesteryl ester?
A cholesterol with a fatty acid attached by an ester linkage
Name the enzyme that breaks down cholesteryl esters into cholesterol and fatty acid?
cholesteryl ester hydrolase
What does cholesteryl ester hydrolase do to cholesteryl esters?
Breaks them down into cholesterol and 1 fatty acid
Name the enzyme that breaks does phospholipids
Phospholipase A2
What does Phospholipase A2 do to phospholipids?
Breaks them down into lysophopholipid and fatty acid
Name the enzyme that breaks down lysophopholipid
lysophopholipase
What does lysophopholipase do to lysophopholipids
Breaks them down into a glycerolphosphoryl base and a fatty acid
Name drugs used into the treatment of obesity
Orlistat or Xenical
How does Orlistat work?
They work by inhibiting the action of pancreatic lipase
-> triglycerides will not be broken down (undigested)
will just pass through large intestine for excretion
-> gets rid of dietary fat by mode of excretion
What is absorption?
Passing through the intestinal wall to the circulation (into blood stream)
A molecule has to be what to be able to pass through the intestinal wall?
Has to be water soluble
to help fats get inside intestinal epithelial lining cells (enterocytes)
fats need to be helped out
-> fats gathered together in small particles called micelles
What are micelles ?
They are small molecules of digestive triglycerides and phospholipids that are surrounded by bile salts/ acids
-> outer coating becomes soluble in water
aids the absorption of lipids
What are micelles surrounded by?
Bile salts/ acid
What are epithelial cells called?
Enterocytes
What are the 2 sides of the enterocytes
The apical border (brushed side) and the basolateral border (smooth side)
How do micelles enter the endocytes?
Pass through the brush border via simple diffusion
What is found outside the endocytes?
The lymphatic and vascular circulation
What happens to lipids once they enter the endocyte?
They re assemble themselves to form triglycerides (which are insoluble)
go back to OG form!
ER packages triglycerides with apoproteins, cholesterol, phospholipids
BIG VESICHLE in the golgi apparatus
leave cell using exocytosis
proteins help solubilit y
What do the endocytes do to the triglycerides to aid movement out of the cell?
The endoplasmic reticulum will package the triglycerides with apopoproteins, phospholipids, and a small amount of cholesterol to form chylomicrons (soluble)
Then this is packaged into a vesicle in the Golgi apparatus
By what process do lipids leave the cell?
The triglycerides are packaged with apopoproteins, phospholipids and cholesterol to form chylomicrons with are excreted out the cell via exocytosis
How do lipids exit the cells?
Chylomicrons are formed
On the basolateral side of the epithelial cells there lymph vessels called lacteals that take up chylomicrons and secrete them into the blood
Name the substances that form chylomicrons
Triacylglycerol + cholesterol + phospholipid + proteins form a lipoprotein complex called a chylomicron which transports the lipids in the circulation
Name the classes of lipoproteins
chylomicrons Very Low Density Lipoprotein (VLDL) Intermedial Density Lipoprotein (IDL) Low Density Lipoprotein (LDL) High Density Lipoprotein (HDL)
What are lipoproteins?
They are a mixture of lipids and proteins
Are chylomicrons made up of predominantly lipids or proteins
99% Lipids
1% Protein
If a molecule has a high Density Lipoprotein does it have more lipids or proteins?
The higher the density the more proteins the molecule has
Are VLDLs made up of predominantly lipids or proteins
92% lipids
8% protein
Are IDLs made up of predominantly lipids or proteins
85% lipids
15% protein
Are LDLs made up of predominantly lipids or proteins
80% Lipids
20% protein
Are HDLs made up of predominantly lipids or proteins
50% lipids
50% protein
Where are Chylomicrons assembled?
In the intestinal mucosal cells
How do Chylomicrons enter the lymphatic system?
Via the thoracic duct
Which tissues in the body take up triglycerides, proteins etc?
Fat tissue like adipose
What are Chylomicrons contain mostly?
TAG
What is the main function of Chylomicrons?
They transport dietary TAG to the adipose tissues where it can be stored as fat or to muscles
Where are VLDLs synthesised?
By the liver
What are VLDLs a product of?
The Chylomicrons when they lose a lot of triglycerides
What is the purpose of VLDLs?
They deliver triglycerides, cholesteryl esters, and cholesterol to peripheral tissues
What do VLDLs give rise to and why?
Gives rise to IDLs as their triglyceride content is largely depleted at target tissues
What are LDLs derived from?
Derived from VLDLs and IDLs in the plasma
What do LDLs contain ?
A large amount of cholesterol and and cholesteryl esters.
What is the main role of LDLs?
To deliver cholesterol and cholesteryl esters to peripheral tissues
What proportion of cholesterol and its ester found in the plasma associated with LDLs?
2/3
Are VLDLs good for the body?
bad
What is the general rule of thumb regarding lipoproteins and health?
The lower the protein density the higher the risk
so the higher the lipid density the higher the risk
Which of the classes of lipoproteins is the smallest?
The HDLs
What do HDLs play a primary role in in?
The removal of excess cholesterol from cells and returning them to the liver
What happens to excess cholesterol cells in the liver?
They are metabolised to bile acids and salts
What do LDLs and HDLS play a major role in?
Maintain the cholesterol balance in the body
What is a high ratio of HDL to cholesterol associated with/
Correlates well with a lower incidence of disease in humans
What do blood cholesterol have a high correlation with?
atherosclerosis
What is known as the bad cholesterol?
LDLs
What happens if theres a high concentration of LDLs in the body?
The LDLs can form fatty deposits in your arteries and damage their lining
What can having fatty deposits in your arteries increase your risk of getting?
Coronary heart diseases and stroke
What is known as the good cholesterol?
HDLs
Why are HDLs known as the good cholesterol?
As they remove other forms of cholesterol from the body
What are higher levels of HDLs associated with?
A lower risk of heart disease
Name some HDLs that are highly recommend to lower the risk of cardiovascular disease?
Omega 3 and fish oils
Which molecules play a major role in balancing the bodies cholesterol levels?
HDLs and LDLs
How is Hyperlipidaemia treated?
By statins
People with type 2 diabetes prescribed
statins
What is cholesterol synthesised by?
synthesised in the liver by a HMG-CoA reductase enzyme.
Why are diabetes prescribes with statins?
To reduce their risk of getting atherosclerosis and lower the risk of heart attack and cardiovascular diseases
How fo stratins work?
They are a competitive inhibitor of HMG-CoA reductase as they mimic the natural cholestero and compete for binding to the HMGCoA-R enzyme.
What does HMG-CoA reductase do?
Synthesises cholesterol
What is the natural way or treating high blood cholesterol?
By lowering your dietary intake of dietary lipids and fats
And by eating more fibre
Why is increasing your fibre content a good way to reduce blood cholesterol ]?
As fibres stick to the fats and they are not easily digested
what are fatty acids?
major components of all lipids
difference between oil and fat?
oil= liquid as it is unsaturated
oils have limit temp before they become toxic
so some unsaturated oils can not be used in frying because they become toxic after a certain temp
what is falling kidney?
kidneys fall a little bit in body cavity
if very quickly deprived of fat which is protecting kidney
= fatal condition
what does gastric lipase do?
in the stomach, lingual lipase continues it’s action
gastric lipase breaks down fats which were emulsified by lingual lipase -> diglycerides/ fatty acids
which lipid is most present in our diet?
triglycerides
con of Orlistat?
a lot of fat depletion
= harmful for body
diet doctors must weight risks/ benefits
so 3 enzymes involved in enzymic digestion of lipids in small intestine?
1) phospholipase A2
2) gastric, pancreatic, lingual lipase
3) cholesterol ester hydrolase
why can phospholipids enter into the lumen of the enterocytes?
they are partially soluble
as they make up the membrane (phospholipid bilayer)
how do micelles enter the brush border?
via simple diffusion
what is outside of the basolateral border of the enterocytes?
lymphatic circulation
blood circulation
what are fats transported by because of the lacteals?
jugular vein
thoracic duct
