Lipid Metabolism - Structure, Digestion, Transport, and Clinical Correlations

Vocabulary practice flashcards created from the lecture notes on lipid metabolism, covering lipid structure, digestion, transport, beta-oxidation, cholesterol biosynthesis, ketone body production, and clinical manifestations in oral and ocular health.

Triacylglycerol (TAG)

The primary storage and transport form of fatty acids contained in adipocytes, composed of a glycerol backbone attached to three fatty acids via ester bonds.

Ester Bond

A chemical bond formed between an acid (such as a fatty acid) and an alcohol (such as glycerol or cholesterol) in lipid biochemistry.

Cholesterol Ester

A highly hydrophobic storage or transport form of cholesterol formed by joining cholesterol to a fatty acid via an ester bond.

Lingual Lipase

An enzyme secreted from Von Ebner's glands in the tongue that hydrolyzes ester bonds in triacylglycerols, remaining active in the acidic environment of the stomach.

Von Ebner's Glands

Exocrine glands located in the tongue papillae that secrete lingual lipase into the oral cavity to initiate lipid digestion.

Gastric Lipase

An enzyme secreted in the stomach that works alongside lingual lipase to degrade triacylglycerols, together releasing $10\text{--}30\%$ of total dietary fatty acids.

Bile Salts

Amphipathic detergent-like molecules synthesized in the liver from cholesterol that emulsify dietary lipids into microscopic droplets in the small intestine.

Emulsification

The physical and chemical process of dispersing unmixable dietary lipid droplets into stable, microscopic droplets suspended in water, dramatically increasing surface area for enzymatic breakdown.

Enterohepatic Circulation

The recycling pathway in which approximately $95\%$ of bile salts are reabsorbed in the terminal small intestine and returned to the liver via the portal vein.

Pancreatic Lipase

A digestive enzyme secreted by the pancreas into the small intestine that cleaves triacylglycerols into free fatty acids and 2-monoacylglycerol.

Cholesteryl Esterase

A pancreatic enzyme that hydrolyzes cholesterol esters into free cholesterol and a free fatty acid.

Cholecystokinin (CCK)

A peptide hormone secreted by intestinal cells in response to dietary lipids entering the duodenum; it causes gallbladder contraction to release bile and stimulates pancreatic enzyme secretion.

Secretin

A hormone released by intestinal cells in response to low pH in the intestine that stimulates the pancreas to secrete bicarbonate to buffer intestinal contents.

Mixed Micelles

Microscopic spherical aggregates of digested free fatty acids, monoacylglycerols, cholesterol, fat-soluble vitamins, and amphipathic bile salts that allow lipids to cross the unstirred water layer of intestinal brush border cells.

Steatorrhea

A pathological condition characterized by increased undigested dietary lipids in the feces, resulting from lipid malabsorption and causing abdominal pain, cramping, bloating, and foul-smelling stools.

Lipoprotein

A macromolecular sphere consisting of a phospholipid/cholesterol outer shell, apolipoproteins, and an inner core of triacylglycerols and cholesterol esters used to transport hydrophobic lipids through the bloodstream.

Apolipoprotein

Surface proteins on lipoproteins that provide structural integrity, improve water solubility, and act as ligands for tissue-specific cellular receptors during lipid transport.

Chylomicrons

Lipoproteins synthesized in intestinal enterocytes that carry exogenous (dietary) triacylglycerols to adipose, skeletal, and cardiac muscle tissues.

Very Low Density Lipoprotein (VLDL)

Lipoproteins synthesized in the liver that carry endogenous triacylglycerols to systemic tissues during fasting, shrinking as they deliver fatty acids to eventually become LDL.

Low Density Lipoprotein (LDL)

The primary cholesterol delivery vehicle in the bloodstream that carries cholesterol esters to peripheral tissues via LDL-receptor endocytosis.

High Density Lipoprotein (HDL)

Lipoproteins originating from the liver and intestine that perform reverse cholesterol transport by collecting excess cholesterol from peripheral tissues and returning it to the liver.

$\beta$-Oxidation

A mitochondrial pathway consisting of four repeating reaction steps that shorten fatty acids by two carbon units per cycle, yielding $1 \times \text{FADH}_2$, $1 \times \text{NADH}$, and one acetyl-CoA for ATP production.

HMG-CoA Reductase

The rate-limiting and committed enzyme in cholesterol biosynthesis that converts HMG-CoA to mevalonate in the cytosol and endoplasmic reticulum.

Statins

A class of lipid-lowering drugs (e.g., atorvastatin, simvastatin) that act as competitive inhibitors of HMG-CoA reductase, halting mevalonate production and upregulating cell surface LDL receptors.

Xanthomas

Cholesterol-rich lipid deposits that form in body tissues (often subcutaneous) as a result of disorders of lipid metabolism.

Xanthelasmas

Cholesterol-rich subcutaneous lipid deposits specifically localized around the eyelids and eye region.

Arcus Corneae

Opaque white, gray, or blue ring-shaped extracellular deposits of cholesterol and phospholipids formed within the corneal stroma around the corneal periphery.

Hollenhorst Plaque

An embolized cholesterol plaque lodged within small retinal arteries, originating from an upstream arterial plaque and posing a severe risk of retinal damage.

Evaporative Dry Eye Disease

An ocular condition resulting from Meibomian gland dysfunction where altered systemic lipid composition leads to plugged eyelid glands and deficient tear film lipid layers.

Ketogenesis

The hepatic process occurring during starvation or low insulin states where excess mitochondrial acetyl-CoA is converted into acetoacetate and $\beta$-hydroxybutyrate.

Ketolysis

The conversion of $\beta$-hydroxybutyrate and acetoacetate back into acetyl-CoA within the mitochondria of peripheral tissues (including the brain) for energy production via the citric acid cycle.

Ketoacidosis

A potentially fatal metabolic imbalance caused by excessive accumulation of ketone bodies in the blood, lowering blood pH and causing dehydration and a characteristic fruity breath odor due to acetone.