Metabolismo De Lipideos (FAST ›)

Inside the cell, FFAs are activated to fatty acyl-CoA by acyl-CoA synthetase. The critical entry step into the mitochondria, where β-oxidation occurs, is mediated by the carnitine shuttle. The enzyme carnitine palmitoyltransferase I (CPT1) is the rate-limiting, regulated step; it converts fatty acyl-CoA to acylcarnitine, which is transported across the inner mitochondrial membrane by translocase and then reconverted to acyl-CoA by CPT2. Malonyl-CoA, the first intermediate in fatty acid synthesis, allosterically inhibits CPT1—a prime example of reciprocal regulation between catabolism and anabolism.

Once inside the mitochondrial matrix, β-oxidation proceeds as a four-step cycle (dehydrogenation, hydration, dehydrogenation, thiolysis) that shortens the fatty acid chain by two carbons (acetyl-CoA) per turn. For a saturated 16-carbon palmitate, this yields 8 acetyl-CoA, 7 FADH2, and 7 NADH. The acetyl-CoA enters the TCA cycle for complete oxidation to CO2 and water, generating substantial ATP via oxidative phosphorylation. In times of prolonged fasting or uncontrolled diabetes, however, the liver produces acetyl-CoA in excess of the TCA cycle’s capacity. This surplus is channeled into —the synthesis of ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone). Ketone bodies serve as a water-soluble, alternative fuel for the brain, heart, and muscle, preserving glucose for obligate users like red blood cells. Pathological overproduction leads to ketoacidosis, a life-threatening condition. metabolismo de lipideos

Lipids, broadly defined as hydrophobic or amphipathic biological molecules, are far more than mere passive energy reserves. The term "metabolismo de lípidos" encompasses a complex, highly regulated network of catabolic and anabolic pathways that are fundamental to cellular life. These pathways govern the breakdown of dietary fats for energy (β-oxidation), the synthesis of fatty acids and complex lipids (lipogenesis), and the formation and clearance of lipoproteins for transport. Disruptions in lipid metabolism are central to the pathogenesis of prevalent metabolic diseases, including obesity, atherosclerosis, type 2 diabetes, and non-alcoholic fatty liver disease (NAFLD). This essay will provide a detailed examination of the core pathways of lipid metabolism—digestion and absorption, transport, catabolism (β-oxidation and ketogenesis), and anabolism (lipogenesis and lipogenesis)—highlighting their biochemical mechanisms, regulatory logic, and physiological integration. Inside the cell, FFAs are activated to fatty

Introduction

When energy demands rise or glucose is scarce (e.g., fasting, exercise), fatty acids become the primary fuel. Hormone-sensitive lipase (HSL) in adipose tissue is activated by glucagon and epinephrine, liberating FFAs into the bloodstream. FFAs, bound to serum albumin, are transported to oxidative tissues like heart, skeletal muscle, and liver. Malonyl-CoA, the first intermediate in fatty acid synthesis,

Dysregulation of these pathways underlies major diseases. results from chronic positive energy balance, with hypertrophied adipocytes becoming insulin-resistant and releasing excess FFAs (lipotoxicity). Atherosclerosis is driven by retention of apoB-containing lipoproteins (LDL) in artery walls, where they become oxidized, triggering inflammation and plaque formation. NAFLD arises from ectopic TAG accumulation in the liver due to increased lipogenesis and reduced VLDL export, often in the context of insulin resistance. The carnitine shuttle defects cause hypoketotic hypoglycemia and cardiomyopathy in infants. Understanding these pathways has led to effective therapies: statins (HMG-CoA reductase inhibitors), fibrates (PPAR-α activators that enhance fatty acid oxidation), and emerging inhibitors of ACC or SCD1 for NAFLD.