Lipid Metabolism

Question 1

What are the main types of lipids in the body?

Answer 1

Cholesterol (CL), Triglycerides (TG), Phospholipids (PL), Free Fatty Acids (FFAs).

Question 2

How are lipids transported in plasma?

Answer 2

Lipids are bound to proteins to form lipoproteins, making them hydrosoluble.

Question 3

What are the main classes of lipoproteins based on density?

Answer 3

Chylomicrons, VLDL, IDL, LDL, HDL.

Question 4

What is the role of LDL?

Answer 4

Transports cholesterol to peripheral cells.

Question 5

What is the role of HDL?


Answer 5

Removes excess cholesterol from tissues and transports it to the liver (reverse cholesterol transport).

Question 6

How does electrophoresis classify lipoproteins?

Answer 6

Chylomicrons
β-lipoproteins (LDL)
Pre-β-lipoproteins (VLDL)
α-lipoproteins (HDL)

Question 7

What enzymes are involved in lipid digestion?

Answer 7

Gastric and pancreatic lipases.

Question 8

What are the sources of cholesterol?

Answer 8

Exogenous (diet) and Endogenous (synthesized in the liver).

Question 9

How are chylomicrons formed?

Answer 9

From FFAs, monoglycerides, glycerol, and glucose in intestinal cells.

Question 10

What are the two metabolic pathways of LDL?

Answer 10

• Normal Pathway: LDL binds to LDL receptors (B/E receptors), leading to endocytosis, cholesterol release, and inhibition of HMG-CoA reductase.
  
  • Pathological (Macrophage) Pathway: Modified LDL is taken up by macrophages, leading to foam cell formation and atherosclerosis.

Question 11

What enzyme esterifies cholesterol in LDL?

Answer 11

Lecithin-Cholesterol Acyltransferase (LCAT).

Question 12

What is the function of Lipoprotein Lipase (LPL)?

Answer 12

Hydrolyzes triglycerides from chylomicrons and VLDL for tissue uptake.

Question 13

What is the role of Hepatic Lipase?

Answer 13

Converts IDL to LDL.

Question 14

What is the first step in atherosclerosis development?

Answer 14

Injury to the arterial wall and LDL infiltration.

Question 15

What role do macrophages play in atherosclerosis?

Answer 15

They engulf oxidized LDL, forming foam cells.

Question 16

What are the 6 stages of plaque progression?

Answer 16

1. Foam Cell Formation
   
   2. Fatty Streaks
   3. Intermediate Lesion
   4. Lipid Core Formation
   5. Atheromatous Plaque
   6. Complicated Plaque (thrombosis risk)

Question 17

What is the difference between stable and unstable plaques?

Answer 17

Stable plaques have a thick fibrous cap, while unstable plaques have a thin cap and are prone to rupture

Question 18

What is the balance required to prevent atherosclerosis?

Answer 18

Balance between Reactive Oxygen Species (ROS) and Antioxidant Defenses.

Question 19

When should a lipid profile be assessed in a patient?

Answer 19

• Obesity
  
  • Hypertension
  • Hypothyroidism
  • Cardiovascular symptoms
  • Liver disease
  • Family history of cardiovascular disease

Question 20

How long should a patient fast before a lipid assessment?

Answer 20

At least 12 hours.

Question 21

How is LDL measured?

Answer 21

Direct enzymatic assay or calculated using the Friedewald formula.

Question 22

What does a lactescent (milky) serum indicate?

Answer 22

High triglyceride levels.

Question 23

What are the types of dyslipidemia?

Answer 23

• Primary (Familial)
  
  • Secondary (due to diabetes, alcohol, drugs, etc.)

Question 24

What are the types of hyperlipoproteinemia?

Answer 24

• Primary: Genetic causes
  
  • Secondary: Diabetes, alcohol, drugs

Question 25

What is the Frederickson classification used for?

Answer 25

Categorizing hyperlipoproteinemias.

Question 26

what is atherosclerosis

Answer 26

chronic inflammatory disease involving many different cell types and is driven by elevated levels of cholesterol in the blood.

Question 27

What are the causes of primary hypolipoproteinemia?

Answer 27

• Hypobetalipoproteinemia (Apo B deficiency)
  
  • Hypoalphalipoproteinemia (low HDL, increased atherosclerosis risk)

Question 28

What conditions lead to secondary hypolipoproteinemia?

Answer 28

Hyperthyroidism, liver failure, malnutrition.

Question 29

What are the main classes of lipid-lowering drugs?

Answer 29

• Statins: Inhibit HMG-CoA reductase
  
  • Fibrates: Lower triglycerides
  • Ezetimibe: Inhibits cholesterol absorption
  • Monoclonal antibodies: Lower LDL

Question 30

30. A 52-year-old male presents with chest pain on exertion and shortness of breath. He has a history of hypertension and obesity (BMI: 32 kg/m²). His father had a myocardial infarction at age 54. Blood tests show:
    * Total Cholesterol: 2.5 g/L (high)
    * LDL: 1.9 g/L (elevated)
    * HDL: 0.4 g/L (low)
    * Triglycerides: 1.8 g/L (borderline high)
    * Fasting glucose: 1.2 g/L (mildly elevated)
    What is the most likely diagnosis, and what steps should be taken next?

Answer 30

Diagnosis: Dyslipidemia with high cardiovascular risk (likely metabolic syndrome and atherosclerosis risk).
Key Findings:
Elevated LDL → Atherogenic risk
Low HDL → Reduced cholesterol clearance
Borderline high TG → Suggestive of metabolic disturbance
Family history of early cardiovascular disease
Next Steps:
Lipid Profile Confirmation: Repeat fasting lipid profile after 3 months
Lifestyle Modifications: Diet, exercise, weight loss
Pharmacological Treatment: Statins to lower LDL, fibrates if triglycerides are very high
Monitor Cardiovascular Risk Factors: BP control, glucose monitoring
Key Concept: Atherosclerosis risk is directly proportional to LDL levels. Early intervention reduces cardiovascular event.