Diabetes Flashcards
What is diabetes?
Chronic hyperglycemia due to insulin dysfunction/deficiency/resistance
- random (>11.1mmol/L)
- fasting (>7 mmol/L)
What are the common acute presentations of diabetes (4)?
Triad
1) Polyuria
2) Polydipsia
3) Weight loss
4) Polyphagia
What are the common chronic presentations of diabetes (5)?
1) Fatigue
2) Poor wound healing
3) ↑infection
4) Blurry vision (vascular changes)
5) ↓peripheral sensation (Neuropathy)
How is glucose sensed by ß-cells of the pancreas?
Glucose → GLUT2
→ Glycolysis → ATP → closes ATP dependent K+ channel
→ ↓K+ efflux → membrane depolarise
→ open voltage-dependent Ca2+ channel → Ca2+ influx
→ exocytosis of insulin from vesicles
How is insulin produced?
1) Produced as preproinsulin
2) Signal peptide cleaved → Disulfide bonds between A and B chain → Proinsulin
3) Cleavage of C-peptides → Mature Insulin
What are the 3 cell signaling pathways and 2 other intracellular effects of insulin?
Insulin → RTK → P-ed IRS:
1) SREBP → Lipid synthesis
2) MAPK pathway → Cell growth
3) PI3K pathway
a) → inhibit lipolysis and gluconeogenesis
b) → mTOR pathway
i) → protein synthesis
ii) →PP I → Glycogen synthesis
c) inhibit GSK3ß → ↓inhibition of glycogen synthesis
Others:
1) ↑exocytosis of GLUT4 (muscle and adipocytes)
2) K+ influx
Is type 1 or 2 DM more common?
Type 2 (90%)
True or false:
Type 1 DM is the most common metabolic condition in children.
True
What is the pathogenesis of type 1 DM?
Insult during childhood/development
→ Activate T cells
→ Immune-mediated destruction of ß-cells
→ progressive loss of pancreatic secretory capacity until < min. insulin requirement
Genetic predisposition:
Twins (~30-50% chance if one is affected)
What are the autoantibodies detected to diagnose type 1 DM?
1) Glutamic acid decarboxylase autoantibodies (GAD)
2) Islet cell autoantibodies (ICA)
What are the effects of insulin deficiency on carbohydrate metabolism in type 1 DM (3)?
Insulin deficiency → unopposed glucagon action:
1) ↑Glycogenolysis (only liver)
2) ↑Gluconeogenesis (Liver from muscle ↑proteolysis and adipocyte ↑lipolysis)
3) ↓GLUT4 uptake (muscle and adipocytes)
What are the effects of insulin deficiency on lipid metabolism in type 1 DM (3)?
Insulin deficiency → unopposed glucagon action:
1) ↑ß-oxidation (only liver from lipolysis by HSL)
2) ↑TG synthesis → ↑VLDL export (Liver)
3) ↓LPL → ↓chylomicron uptake
4) ß-oxidation and ketolysis for energy (muscle)
What is the pathogenesis of the acute-subacute clinical presentation of DM?
1) ↑Glucose → Osmotic diuresis (> renal threshold) → Polyuria + dehydrations
2) ↑Ketogenesis
i) → ketoacidosis
ii) ↑Respiration → acetone in breath (sweet breath)
3) ↑ Lipolysis and proteolysis
i) → WL
ii) → Δmental state
iii) → ↓appetite
iv) → hyperlipidemia
What are 6 biochemical changes and their pathogenesis in type 1 DM?
Diabetic ketoacidosis:
1) ↑glucose + ↑osmolarity (Dehydration)
2) ↑urea (proteolysis and dehydration)
3) ↓pH + ↓HCO3- (ketoacidosis)
4) ↓pCO2 (compensatory respi alkalosis)
5) ↑Na+ (but appears falsely normal coz ↑blood glucose pulls water → dilute)
6) ↓K+ (but appears normal coz acidotic displacement from cells)
What are 2 significant abnormal urine finding in poorly controlled type I DM?
1) ↑glucose (blood glucose > renal threshold)
2) ↑ketones
What are the 5 management principals for diabetic ketoacidosis?
1) Attend to (i) airway (ii) breathing (iii) circulation
2) Replace fluid/Na+/K+
3) Start insulin replacement (be wary of inward K+ shift)
4) Treat any precipitating cause of presentation (eg. antibiotic)
5) Prevent complication (eg. heparin to ↓clotting due to hypercoagulable state)
How is type 1 DM treated chronically?
Provide insulin in similar pattern as healthy individuals
1) Continuous infusion
2) Intermittent dosing via subcut
How is glucose monitoring done in DM patients?
Short term:
Home glucose monitoring (finger prick)
Long term:
HbA1C (average blood glucose over 100-120 days)
- 4-6.1% (ideal <7%)
Why is central obesity linked to type 2 DM?
Central fat: ↑Visceral fat
1) linked to metabolic syndrome → impaired fasting glucose
2) visceral fat (hypertrophy) → M2 to M1 → FFA + Cytokines → inflammation:
a) TNFα pathway (cytokines)
b) NFκB pathway (cytokines) + FFA → ↑lipid metabolism
bi) → DAG → activate PKC
bii) → Ceramides
TNFα and PKC (via IRS), Ceramides (via PI3K pathway) inhibit insulin signaling
→ risk factor for type 2 DM
How does visceral obesity lead to insulin resistance?
Visceral fat (hypertrophy) → M2 to M1→ FFA + Cytokines → inflammation:
a) TNFα pathway (cytokines)
b) NFκB pathway (cytokines) + FFA → ↑lipid metabolism
bi) → DAG → activate PKC
bii) → Ceramides
TNFα and PKC (via IRS), Ceramides (via PI3K pathway) inhibit insulin signaling
With px with metabolic syndrome and thus at risk of type 2 DM, compared to a normal individual:
Glucose levels during fast (↑/↓)
Glucose levels after meals (↑/↓)
Insulin levels after meals (↑/↓)
Glucose levels during fast ↑
Glucose levels after meals ↑
Insulin levels after meals 2/3x ↑
Describe the pathogenesis of type 2 DM.
Combination of genetic predisposition (twin concordance >50%) and diet/lifestyle:
1) Insulin R → compensatory ↑ in insulin secretion (but fasting blood glucose still normal)
2) ↑glucose/FFA → ß cell toxicity → ↓ß cells → ↓insulin secreting capacity → ↓ability to compensate by ↑insulin → chronic hyperglycemia
What is the metabolic difference between type 1 and 2 DM?
Type 1: Absolute insulin deficiency → ketoacidosis
Type 2: Insulin R → (partial insulin response→ sufficient to prevent ketoacidosis
What are the pathogenesis of 4 chronic presentations of type 2 DM?
↑glucose → ↑ROS → microvascular pathology via inflammation/proliferation:
a) Polyol pathway (glucose → aldose reductase → sorbitol
b) Glycation → AGE
c) PKC activation
1) Sorbitol → osmotic damage → cataracts → microvascular pathology → loss of vision
2) microvascular pathology → neuropathy
i) Sensory → pain, tingling, loss of sensation
ii) Motor → weakness, muscle wasting
iii) Autonomic → erectile dysfunction
3) Damage to glomerular capillaries → nephropathy → microalbuminuria → HTN → renal failure
