Chapter 69 - Lipid Metabolism Flashcards
4 Forms of Lipids in Food
- Neutral fats - triglycerides
- Phospholipids
- Cholesterol
- Others
What is the basic lipid moiety of triglycerides and phospholipids?
Fatty acids
Name CH3(CH2)14COOH
Palmitic acid
Lipid Functions (#3)
- Provide energy for metabolic processes
- Form membranes of all cells
- Perform other essential cellular functions
What are the components of a triglyceride structure?
3 fatty acids and a glycerol backbone
18 carbon chain fatty acid fully saturated with hydrogen atoms
Stearic acid
18 carbon chain fatty acid with one double bond at the middle of the chain (unsaturated)
Oleic acid
16 carbon chain fatty acid, fully saturated
Palmitic acid
3 most commonly found fatty acids in the human body
- Stearic acid
- Oleic acid
- Palmitic acid
Chylomicron concentration in plasma:
1. After meal - plasma appearance
2. After a few hours - plasma appearance
Half life of chylomicrons?
- Chylomicrons rise to 1% - 2% of plasma, plasma is yellow and turbid (large size of chylomicrons)
- Back to normal, plasma is clear
Chylomicron half-life is less than 1hr
Total concentration of lipoproteins in the plasma
700 mg per 100 ml of plasma (700 mg/dl)
Adipose Triglycerides are Transported as FFA in Blood for Energy via Hydrolysis
(Stimuli for triglyceride hydrolysis)
- Inadequate glucose stores > insufficient amount of glucose breakdown product:
alpha-glycerophosphate > glycerol portion of triglycerides is not maintained > hydrolysis to FFA - Activation of hormone-sensitive cellular lipase
Forms of fatty acids in plasma
- Free Fatty Acids or Nonesterified Fatty Acids (fatty acids ionically combined with albumin)
- Fatty acids as esters of glycerol
- …as cholesterol
- …as other substances
Concentration of free fatty acids in the plasma in resting conditions
Turnover time of FFA
15 mg/dl or 0.45g
Replacement of half the plasma fatty acid every 2-3 mins
Conditions where plasma FFA can increase up-to five to eight-fold
Starvation and Diabetes Mellitus
(Body cells have little to no metabolic energy from carbohydrates)
Lipid transport in blood varies accdg. to physiological need of the body. Number of FFA molecules one albumin protein can transport at a time
3 to 30 molecules
Major function of triglyceride storage in adipose tissue
- Storage of FFA as triglyceride for energy
- Heat insulation
- Secretion of hormones for appetite and energy expenditure: leptin and adiponectin
Appetite suppressant hormone
Leptin
Adipocyte hormone that (1) decrease hepatic glucose production, (2) increase fatty acid oxidation in liver and skeletal muscle, and (3) decrease vascular inflammation
Adiponectin
Triglycerides in fat cells are renewed every
2 to 3 weeks
Principal functions of the liver in lipid metabolism
- Degrade fatty acids to small compounds for energy
- Synthesize triglycerides from carbohydrates and proteins
- Synthesize cholesterol and phospholipids from fatty acids
- Desaturates fatty acids producing unsaturated triglycerides
Increased triglycerides in liver during:
- early stages of starvation
- diabetes mellitus
- conditions where fat is used for energy
- obesity
- lipodystrophy - deficiency in adipocytes
Normal combined concentration of acetoacetic acid and beta-hydroxybutyric acid in plasma
< 3 mg/dl
Explain in your own words:
TRANSPORT OF TRIGLYCERIDES AND OTHER LIPIDS FROM THE GASTROINTESTINAL TRACT BY LYMPH
The Chylomicrons
Explain in your own words:
CHYLOMICRON TRIGLYCERIDES ARE HYDROLYZED BY LIPOPROTEIN LIPASE, AND FAT IS STORED IN ADIPOSE TISSUE
Summary of Major Pathways for Metabolism of Chylomicrons
Chylomicron vs. Lipoprotein
composition
Explain in your own words:
USE OF TRIGLYCERIDES FOR ENERGY
Formation of ATP
Explain in your own words:
LARGE AMOUNTS OF ATP ARE FORMED BY OXIDATION OF FATTY ACIDS
(ATP computation for stearic acid)
Explain in your own words:
FORMATION OF ACETOACETIC ACID IN THE LIVER AND ITS TRANSPORT IN THE BLOOD
Enumerate the Ketone Bodies
1) Acetoacetic acid
2) Beta-hydroxybutyric acid
3) Acetone
Hormonal Enhancement of Fatty Acid Hydrolysis from Storage
1) increase glucocorticoids by adrenal cortex
2) increase glucagon secretion by pancreas - release glucose and fatty acid in blood
3) decrease insulin - enhance fatty acid release by depriving cells of glucose
Synthesis of Triglycerides from Carbohydrates
The average person has (1) as much energy stored as fat than as a form of carbohydrate (glycogen)
Each gram of fat has (2) calories of energy by each gram of glycogen
(1) 150 times
(2) 2.5 times
Hormonal Regulation of Fat Utilization
(1) decrease in insulin
(2) release of epinephrine and norepinephrine by the adrenal medulla (during exercise)
(3) release of adrenocorticotropic hormone, ACTH, by the anterior pituitary gland; leads to secretion of glucocorticoids by adrenal cortex
(4) Growth hormone
(5) Thyroid hormone
2 and 3 activates hormone-sensitive triglyceride lipase
Cushing’s Syndrome
Excessive ACTH and glucocorticoids leading to ketosis
Major types of phospholipids
- lecithins
- cephalins
- sphingomyelin
Phospholipid composition
phosphoric acid radical and fatty acid w/ nitrogenous base
Phospholipids are formed in
liver (90%)
intestinal cells and others (10%)
Nitrogenous base of lecithin formation
choline
Nitrogenous base for cephalins
Inositol
SPECIFIC USES FOR PHOSPHOLIPIDS
- constituent of lipoproteins in the blood
- form thromboplastin for clotting process
- for nervous system myelin sheath
- donors of phosphate radicals for chemical reactions
- form cellular structures - cell membrane
Basic structure of cholesterol
sterol nucleus from acetly-CoA
Sterol nucleus can have modified side chains to form….
1) cholesterol
2) cholic acid - for bile acids
3) steroid hormones
FACTORS THAT AFFECT PLASMA CHOLESTEROL CONCENTRATION
Feedback control of body cholesterol
(1) Increase in exogenous cholesterol decreases/inhibits essential enzyme (3-hydroxy-3-methylglutaryl CoA reductase) for endogenous cholesterol synthesis
(2) high saturated fat diet increases fat deposition in liver to create cholesterol
(3) diet in unsaturated fat depresses blood cholesterol conc.
(4) lack of insulin and thyroid hormone increases blood cholesterol
(5) genetic disorders of cholesterol metabolism can increase cholesterol levels