1. Unit Thirteen: Metabolism and Temperature Regulation
Chapter 68: Lipid Metabolism
Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Lipid Metabolism
Classification of Lipids
Triglycerides (neutral fats)
Phospholipids
Cholesterol

3. Lipid Metabolism
Basic Chemical Structure of Triglycerides- three most
common are stearic aicd, oleic acid, and
palmitic acid

4. Transport of Lipids in the Body Fluids
Transport of Triglycerides from the GI Tract by Lymph
Chylomicrons-primarily triglycerides, they contain
small amounts of cholesterol, phospholipids and
protein
Transported upward through the thoracic duct and
emptied into the venous circulation at the juncture
of the subclavian and jugular veins

5. Transport of Lipids in the Body Fluids
Removal of Chylomicrons from the Blood
Chylomicron triglycerides are hydrolyzed by
lipoprotein lipase, and the fat is stored in adipose
tissue
Chylomicrons have a half-life of less than one
hour in plasma

6. Transport of Lipids in the Body Fluids
Fig Summary of major pathways for metabolism of chylomicrons synthesized in the intestine
and VLDL synthesized in the liver

7. Transport of Lipids in the Body Fluids
Free Fatty Acids- transported in the blood in
combination with albumin
Lipoproteins- 95% of the lipids in plasma are in the
form of lipoproteins
Types of Lipoproteins
VLDL- very low density lipoproteins
IDL- intermediate density
LDL- low density
HDL- high density

8. Transport of Lipids in the Body Fluids
Formation and Function of Lipoproteins- almost
all are formed in the liver; primary function is
to transport lipid components in the blood
Fat Deposits
Large quantities of fat are stored in two major
tissues of the body: adipose and liver
Adipocytes- modified fibroblasts that store almost
pure triglycerides

9. Transport of Lipids in the Body Fluids
Tissue lipases- when activated by hormones,
catalyze the splitting of triglycerides to
release free fatty acids
Triglycerides in fat cells are renewed every 2-3
weeks

10. Transport of Lipids in the Body Fluids
Liver Lipids- principal functions of the liver
in lipid metabolism are to:
Degrade fatty acids into small compounds that
can be used for energy
Synthesize triglycerides, mainly from cbh
Synthesize other lipids from fatty acids (i.e.
cholesterol and phospholipids)

11. Lipids Metabolism
Use of Triglycerides for Energy: ATP Formation
Hydrolysis of triglycerides
Entry of fatty acids into the mitochondria
Degradation of fatty acids to acetyl coA by
beta-oxidation
Oxidation of acetyl-CoA to enter the citric acid
cycle
Large amounts of ATP are formed by the
oxidation of fatty acids

12. Lipid Metabolism
Fig Beta-oxidation of fatty acids to yield acetyl coenzyme A

13. Synthesis of Triglycerides from Carbohydrates
Lipid Metabolism
Synthesis of Triglycerides from Carbohydrates
Fig Overall schema for synthesis of triglycerides from glucose

14. Lipid Metabolism
Efficiency of Carbohydrate Conversion into Fat-
about 15% of the energy is lost as heat, so 85% is
transferred to the stored triglycerides
Regulation of Energy Release
Cbhs are preferred over fats for energy when
excess cbhs are available
b. Absence of cbh leads to fat utilization for energy

15. Lipid Metabolism
Hormonal Regulation of Fat Utilization (7 hormones
in addition to insulin lack)
Epinephrine and norepinephrine
Glucocorticoids
Growth hormone
Thyroid hormone

16. Lipid Metabolism
Phospholipids and Cholesterol
Formation of phospholipids-essentially synthesized
in all cells but 90% in the liver
Specific uses-constituent of lipoproteins, thrombo-
plastin, nervous system, all membranes
Cholesterol-exogenous from the diet and
endogenous from the liver

17. Lipid Metabolism
Factors That Affect Plasma Cholesterol Concentration
Amount ingested each day
Highly saturated fat diet
Ingested of unsaturated fat in diet depresses the blood
cholesterol concentration
Lack of insulin or thyroid hormone increases levels
Genetic disorders

18. Lipid Metabolism
Fig Cholesterol

19. Lipid Metabolism
Specific Uses of Cholesterol
Used by the adrenal glands to produce adreno-
corticol hormones
Used by the ovaries to produce estrogen and
progesterone
Used by the testes to form testosterone
Precipitated in the corneum of the skin for
waterproofing

20. Lipid Metabolism
Atherosclerosis- disease of the larger arteries in
which fatty lesions develop on the inside
surfaces of the vessels; basic causes and risk
factors include:
Increased LDL
Physical inactivity and obesity
Diabetes mellitus
Hypertension
Hyperlidpidemia
Cigarette smoking
Low HDL (ratio)