This document discusses lipids, including their definition, classification, functions, digestion and absorption. It notes that lipids are important for energy storage and cellular structure. They are broadly classified into simple lipids, compound/complex lipids, derived lipids, and neutral lipids. The document outlines the roles of the stomach, small intestine, bile salts, pancreatic enzymes, and peristalsis in emulsifying and digesting lipids into smaller particles that can be absorbed. It emphasizes how bile salts and degraded lipid products act as surfactants to reduce surface tension and promote emulsification for efficient lipid digestion.

1. Biochemistry
for
Dip.
In
Pharmacy
LIPIDS
BRAINSTROMIN
G
NOTES TO PRINT
Lipid Reveiw

2. Introduction:
 Lipids (greek: lipos-fat) are of great
importance to the body as the chief
concentrated storage form of energy,
 Besides their role in cellular structure
and various other biochemical functions.
 As such, lipids are a heterogenous group
of compounds and therefore, it is rather
difficult to define them precisely.

3. Definition
 Lipids may be regarded as organic
substances relatively insoluble in
water, soluble in organic solvent
(alcohol, ether etc) actually or
potentially related to fatty acids and
utilized by the living cells.

4. Classification of Lipids
 Lipids are broadly classified as :
1. Simple Lipids
2. Compound Lipids (Complex Lipids)
a) Phospholipids
i. Glycerophospholipids
ii. Sphingophospholipids
b) Glycolipids
c) Lipoproteins
d) Other complex lipids
3. Derived Lipids
4. Neutral Lipids

5. Terms
 Ester of fatty acid: The product
obtained from the combination of
alcohol and fatty acid.
 Fatty Acid: Saturated or unsaturated
carboxylic acid with long aliphatic
chain
 Carboxylic acid: organic compound
that contains a carboxyl group
(C(=O)OH)

6. Simple Lipids:
 Esters of fatty acids with alcohols.
 These are mainly of two types.
 a) Fats & oils (triacylglycerols): these are esters of
fatty acids with glycerol. The difference between fat
and oil is only physical. Thus, oil is a liquid while fat
is a solid at room temperature.
 b) Waxes: Esters of fatty acids with alcohols other
than glycerol. These alcohols may be aliphatic or
alicyclic. Crtyl alcohol is most commonly found in
waxes.

7. Compound Lipids (Complex
Lipids)
 Esters of fatty acids with alcohols containing additional
group such as phosphate, nitrogenous base,
carbohydrates, protein etc. they are further divided as:
 a) Phospholipids: Lipids containing phosphoric acids
 i. Glycerophospholipids: These phospholipids contains
glycerol as the alcohol. E.g. lecithin, cephalin.
 ii. Sphingophospholipids: Sphingosine is the alcohol in this
group of phospholipids e.g. sphingomyelin.
 b) Glycolipids: These lipids contain a fatty acids,
carbohydrate and nitrogenous base.

8. Derived Lipids:
 These are the derivative obtained on
the hydrolysis of group I and group 2
lipids which possess the
characteristic of lipids.
 Eg. glycerol and other alcohols, fatty
acids, mono- and diacylglycerols,
lipids soluble vitamins, steroids
hormones, hydrocarbons and ketone
bodies.

9. Neutral Lipids:
 These lipids which are uncharged
are referred to as neutral lipids.
These are mono-, di-, and
triacylglycerols, cholesterol and
cholesteryl esters.

10. Function of Lipids:
i. Are the concentrated fuel reserve of the body.
ii. Are the constituents of membrane structure and
regulates the membrane permeability.
iii. Serve are sources of fat soluble vitamins (K,E,D
& A).
iv. Are important as cellular metabolic regulators
(steroids hormones & prostaglandins).
v. Protects the internal organs, serve as insulating
materials and give shape and smooth
appearance to the body.

11. Thank You

12. Digestion and absorption of Lipids
 Daily consumption of the lipid:
◦ In Developed Country is 60-150 gram/day
◦ Poorer Section of Society <60 gram/day
 In lipid diet around 90% is fat (triacylglycerol).
 Remaining is made up of phospholipid, cholesterol, cholesteryl esters
and free fatty acids.
 In addition about 1-2 gram cholesterol and 3-5 gram phospholipids
are secreted into the intestine by bile.
 Lipids are insoluble or sparingly soluble in aqueous solution.
 The digestive enzymes, however are present in aqueous medium.
 This posses certain problem for the digestion and absorption of lipids.
 Fortunately, the digestive tract possesses specialized machinery to
◦ a) Increase the surface area of lipids for digestion.
◦ b) Solubilize the digestive products for absorption.
Cont….

13. Minor digestion of lipids in stomach:
 In adult:
◦ Digestion of lipid is initiated in the stomach,
catalysed by lingual lipase and gastric lipase
which can degrade fat containing short chain
fatty acids at neutral pH.
◦ Digestion of lipid in stomach is negligible in
adult.
 In Infant:
◦ Milk fat (with short chain fatty acids) can be
hydrolysed by gastric lipase to some extent
because of stomach pH of infant is close to
neutrality, i.e. ideal for gastric lipase action.
Cont….

14. Emulsification of lipids in the small intestine:
 Emulsification is the phenomenon of
dispersion of lipids into smaller
droplets due to reduction on the
surface tension.
 The process of emulsification
occurs by three complementary
mechanism:
a) Detergent action of bile salts.
b) Surfactant action of degraded lipids.
c) Mechanical mixing due to peristalsis.
Cont….

15. Detergent action of bile salts.:
 Bile salt is the most effective
emulsifying agents.
 They interact with lipids particles
and the aqueous duodenal contents
and convert them into smaller
particles.
 Further bile salt stabilize the
smaller particles by preventing

16. Surfactant action of degraded
lipids:
 The initial digestive products of
lipids namely free fatty acids,
monoacylglycerols promote
emulsification.
 These compounds along with
phospholipids are known as
surfactants.
 Surfactant gets absorbed to the
water lipids interfaces and

17. Mechanical mixing due to
peristalsis:
 Mechanical mixing due to
peristalsis also helps in the
emulsification of the lipids.
 The smaller lipids emulsion
droplets are good substrates for
digestion.
Cont….

18. Digestion of lipids by pancreatic
enzymes:
 The pancreatic enzymes are
primarily responsible for the
degradation of dietary
triacylglycerols, cholesteryl esters
and phospholipids.
Triglycerols

19. Thank You