Lipids: Functions, Structure, and Metabolism

Vocabulary flashcards covering the types, functions, structures, digestion, and recommendations for lipids based on lecture notes.

Triglycerides

The most common type of lipid, making up $95\%$ of dietary lipids; they are composed of glycerol and three fatty acid chains and do not dissolve in water.

Phospholipids

Lipids that make up about $2\%$ of dietary lipids, are water-soluble, and are synthesized in the body to form cell and organelle membranes.

Sterols

The least common type of lipid with a multi-ring structure; cholesterol is the most well-known example and is used to synthesize sex hormones and bile salts.

Adipose tissue

Specialized body tissue where excessive energy is stored as fat; these cells can expand almost indefinitely in size.

Visceral fat

The layer of fat that protects vital organs.

Subcutaneous fat

A fat layer underneath the skin that protects from falls, prevents friction, and helps regulate body temperature.

Bioavailability

The degree to which nutrients, such as vitamins $A$, $D$, $E$, and $K$, or phytochemicals, are absorbed and used by the body, often increased when paired with lipids.

Satiety

The feeling of fullness provided by dietary fats due to their calorie-dense nature.

Carboxylic acid group

The $-COOH$ group located on one end of a fatty acid carbon chain.

Methyl group

The $-CH_{3}$ group located on one end of a fatty acid carbon chain.

Saturated fats

Fatty acids with no double bonds between carbon atoms; they are typically solid at room temperature.

Monounsaturated fats

Fatty acids that contain exactly one double bond in their carbon chain.

Polyunsaturated fats

Fatty acids that contain two or more double bonds in their carbon chain.

Cis fatty acid

An unsaturated fat structure where hydrogen atoms are bonded to the same side of the carbon chain.

Trans fatty acid

An unsaturated fat structure where hydrogen atoms are bonded to opposite sides of the carbon chain, typically resulting from hydrogenation.

Essential fatty acids

Fatty acids that the body cannot synthesize and must be obtained from food; they include Omega-3 and Omega-6 fatty acids.

Eicosanoids

Powerful hormones derived from Omega-3 and Omega-6 fatty acids that control functions such as the central nervous system, immune response, and blood pressure.

Docosahexaenoic acid (DHA)

An omega-3 essential fatty acid that plays an important role in synaptic transmission in the brain during fetal development.

Amphiphilic

A molecule, such as a phospholipid, that has both a hydrophobic (water-disliking) fatty-acid side and a hydrophilic (water-liking) phosphate group.

Lecithin

A phospholipid used as an emulsifier; it composes $28\%$ of brain matter and $66\%$ of the fat in the liver.

Lingual lipase

An enzyme in the mouth that, along with saliva and chewing, initiates the process of lipid digestion.

Gastric lipase

A stomach enzyme that begins breaking down triglycerides into diglycerides and fatty acids.

Bile

A substance produced by the liver and stored in the gallbladder that acts as an emulsifier, containing bile salts, lecithin, and cholesterol derivatives.

Pancreatic lipase

An enzyme that enters the small intestine to break down fats into free fatty acids and monoglycerides.

Micelles

Structures formed when bile salts envelop fatty acids and monoglycerides, featuring a water-soluble exterior for transport to the intestinal microvillus.

Chylomicron

A large lipoprotein formed in the intestinal cells that transports food fats through the lymphatic system into the bloodstream via the jugular vein.

Steatorrhea

A condition characterized by fat malabsorption where fats are excreted in the stool; can result from Crohn's disease or cystic fibrosis.

VLDL (Very low-density lipoproteins)

Lipoproteins made in the liver that transport triglycerides to various body tissues.

LDL (Low-density lipoproteins)

Often called 'bad cholesterol,' these carry cholesterol to tissues; high levels can lead to heart disease or atherosclerosis as they house over $50\%$ cholesterol.

HDL (High-density lipoproteins)

Often called 'good cholesterol,' these carry cholesterol out of the bloodstream and back to the liver for reuse or removal.

Total cholesterol goal

The recommended lab range for total cholesterol is under $200\,mg/dL$.

Acceptable Macronutrient Distribution Range (AMDR) for fat

Fat calories should be limited to $20-35\%$ of total daily calories.