2.16
Diabète de type II II : physiopathologie
Physiopathologie
Le diabète de type 2 (DT2DM) est un trouble métabolique chronique caractérisé par une résistance à l’insuline et un dysfonctionnement…
Le diabète sucré de type 2 est un trouble métabolique chronique progressif caractérisé par une résistance à l’insuline et un dysfonctionnement progressif des cellules bêta-cellules pancréatiques, entraînant une altération de la régulation du glucose.
La résistance à l’insuline se développe initialement dans le muscle squelettique, le foie et le tissu adipeux.
Le muscle squelettique, principal site d’absorption du glucose après le prandial, devient moins réactif à l’insuline, réduisant ainsi l’élimination du glucose.
Parallèlement, la résistance hépatique à l’insuline entraîne une production continue de glucose même après les repas.
Une signalisation insulinique altérée et des cellules alpha dérégulées augmentent les niveaux de glucagon, augmentant encore la production de glucose hépatique.
En réponse, les cellules bêta compensent initialement en augmentant la sécrétion d’insuline ; cependant, une exposition prolongée à l’hyperglycémie et au stress métabolique altère progressivement la fonction des cellules bêta.
Dans le tissu adipeux, la résistance à l’insuline augmente la lipolyse, élevant les acides gras libres circulants, qui aggravent la résistance à l’insuline par des effets lipotoxiques.
Ces troubles métaboliques interconnectés alimentent collectivement une hyperglycémie chronique.
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Q1: What causes insulin resistance in type 2 diabetes?
Insulin resistance develops initially in skeletal muscle, liver, and adipose tissue. Skeletal muscle becomes less responsive to insulin, reducing glucose clearance despite normal or high insulin levels. The liver fails to suppress gluconeogenesis, causing excess glucose production. In adipose tissue, insulin resistance increases lipolysis, elevating free fatty acids that worsen insulin resistance through lipotoxic effects.
Q2: How does hepatic glucose output increase in type 2 diabetes?
Hepatic insulin resistance prevents the liver from suppressing glucose production after meals. Additionally, impaired insulin signaling and dysregulated alpha cells elevate glucagon levels, further increasing hepatic glucose output. This dual mechanism sustains chronic hyperglycemia by maintaining elevated fasting and postprandial glucose levels despite the body's attempt to regulate blood sugar.
Q3: What happens to pancreatic beta cells over time in type 2 diabetes?
Beta cells initially compensate for insulin resistance by increasing insulin secretion. However, prolonged exposure to hyperglycemia and metabolic stress progressively impairs beta-cell function. Glucotoxicity, lipotoxicity, oxidative stress, and inflammation reduce beta-cell mass through apoptosis, leading to inadequate insulin secretion and worsening glucose control.
Q4: How do free fatty acids contribute to type 2 diabetes progression?
Elevated free fatty acids from increased adipose tissue lipolysis worsen hepatic insulin resistance and directly damage beta cells through lipotoxic effects. Reduced lipoprotein lipase activity contributes to diabetic dyslipidemia, characterized by high triglycerides, low HDL, and small dense LDL particles, further perpetuating metabolic dysfunction.
Q5: What role does skeletal muscle play in glucose regulation in type 2 diabetes?
Skeletal muscle is the primary site of postprandial glucose uptake. In type 2 diabetes, muscle insulin resistance reduces glucose clearance despite normal or elevated insulin levels. Additionally, muscle insulin resistance alters protein metabolism, increasing amino acid release that fuels gluconeogenesis, further elevating blood glucose.
Q6: How can type 2 diabetes lead to serious acute complications?
Stress hormones including cortisol and catecholamines worsen hyperglycemia and may trigger hyperosmolar hyperglycemic state or, rarely, diabetic ketoacidosis. Chronic hyperglycemia causes protein glycation, oxidative stress, and inflammation, leading to macrovascular complications such as coronary artery disease and stroke, as well as microvascular complications.
Q7: What are the long-term microvascular complications of type 2 diabetes?
Chronic hyperglycemia causes microvascular complications including diabetic neuropathy, diabetic nephropathy, and diabetic retinopathy. These result from protein glycation, oxidative stress, and inflammation affecting small blood vessels and nerves. Understanding these complications is essential for recognizing clinical manifestations and diagnosis in affected patients.