Week 11 Diabetes Flashcards
What are normal blood glucose levels?
80-90mg/100ml
4-6 mmol.
What is the major endocrine organ responsible for glucose homeostasis?
Pancreas (Islets of Langerhans)
What two hormones does the pancreas produce and what is their function?
Insulin: promotes glucose uptake form the blood and storage in tissues.
Glucagon: promotes glucose metabolism from tissues to increase blood glucose levels.
What are the clinical manifestations of hypoglycemia?
Early:
Palpitations
Tachycardia
Diaphoresis
Anxiety
Weakness, hunger, nausea
Prolonged:
Hypothermia
Confusion, hallucinations, seizures
Coma
What are the clinical manifestations of hyperglycemia?
Early:
Polydipsia
Polyuria
Altered vision
Weight loss, mild dehydration
Prolonged:
Cardiac arrythmias
Coma
How much of the pancreas is exocrine?/endocrine?
Exocrine: 97-99 by weight%
Endocrine: 1-3 by weight%
What are the Islet endocrine cell types?
a-cells (15-20%): secrete glucagon.
B-cell (65-80%): secrete insulin and Islet Amyloid PolyPeptide (IAPP/amylin)
d-cell (3-10%): secrete somatostatin
PP cell (3-5%): secrete pancreatic polypeptide
The amounts of each cell type varies from person to person.
What is the function of IAPP/amylin?
Decreases gastric emptying, suppresses glucagon secretion, stimulates satiety center.
Controls blood gluces in an insulin sparing fashion.
What is the function of pancreatic polypeptide (PP)?
Delays gastric emptying and reduces acute food intake.
Reduces appetite and food intake.
Discuss Islet blood flow
Rich vascular supply to Islets.
B, a, and d cells are aligned along blood vessels.
This allows communication for constant blood glucose regulation. “Very good neighbourhood to be in”
Discuss Islet innervation
Richly innervated by ANS.
PNS: Vagus nerve (CNX), Ach stimulates insulin secretion.
SNS: Post-ganglionic fibers originate in celiac ganglion. Norepi inhibits insulin secretion. Epi also plays a part.
Discuss proinsulin synthesis
A&B chains and a C peptide
Synthesized in the RER, transits through GA, packaged into secretory vesicles and can be stored in granules for hours or days.
In the mature secretory granule insulin forms a dense crystal with zinc in center, C-peptide in granule halo.
Glucose stimulates proinsulin synthesis.
Discuss proinsulin processing
Processed in granules by prohormone convertase enzymes PC1/3 and PC2.
Cleavage by PC1/3 and PC2 followed by removal of basic residues by carboxypeptidase E.
This results in equimolar amounts of Insulin and C-peptide.
C-peptide has no established biological action and is excreted in urine. Can be used to assess a person’s insulin secretory capability.
Proinsulin cleavage is efficient, only 2-5% of total insulin is secreted as proinsulin in normal folks.
What is the major stimulus for insulin secretion?
Glucose.
GLUCOSE-DEPENDENT: protects against inappropriate secretion of insulin.
Discuss neural regulation of insulin secretion
PNS: Vagus nerve, Ach: Simulates islets
SNS: Norepi/epi: Inhibit islets
GLUCOSE-DEPENDENT
Discuss hormonal regulation of insulin secretion
STIMULATORY HORMONES:
Incretins (GIP, GLP-1) enhance glucose stimulated insulin secretion.
Released in intestines after a meal.
GLP-1 suppresses glucagon release, delays gastric emptying, inhibits food intake
INHIBITORY HORMONES:
Somatostatin from gut inhibits adenylyl cyclase and PKA: inhibits both insulin and glucagon secretion.
GLUCOSE-DEPENDENT
What other nutrients play a stimulatory role other than glucose?
Arg, Lys: potentiate the GLUCOSE stimulus for insulin secretion.
GLUCOSE-DEPENDENT
List the stimulatory and inhibitory mechanisms of insulin secretion.
STIMULATORY:
GIP, GLP-1 (incretins)
Glucagon - yes glucagon (thats all you need to know right now)
Ach (PNS CN X)
Glucose
Arg, Lys
Free fatty acid exposure
INHIBITORY:
Somatostatin (Gut and d-cells)
Norepi/epi (SNS post ganglionic fibers from celiac ganglion)
What does prolonged exposure to glucose or free fatty acids lead to?
Glucotoxicity and lipotoxicity
Apoptosis of B-cells
Discuss the simplified mechanism of glucose-induced insulin secretion
- Glucose enters B-cell via GLUT-2 transporter.
- Glucokinase phosphorylates Glucose to G6P.
- Glycolysis produces ATP.
- ATP sensitive K channels (with sulfonylurea receptors) close.
- B-cell depolarizes.
- Voltage gated Ca channels open and Ca enters cell.
- Exocytosis of insulin secretory granules.
What is the rate limiting step of glucose induced insulin secretion?
Glucokinase phosporylation.
Considered the GLUCOSE SENSOR of the B-cell.
What is the general mechanism of sulfonylurea treatment?
Sulfonylurea receptor is part of ATP sensitive K channels.
Binding of sulfonylureas could lead to closure of K channel and stimulate insulin secretion by a glucose-INdependent mechanism.
What are the major target tissues of insulin?
Muscle
Fat
Liver
**Promotes energy storage = Anabolic
What effects does insulin have on carbohydrate metabolism?
Overall: increased glucose storage and utilization
Myocytes & adipocytes:
Stimulates glucose uptake by upregulating GLUT4 on cell surface.
In mm glucose is used as energy or stored as glycogen.
In fat glucose is stored at G3P+FFAs = triglycerides.
Liver:
Activation of glycogen synthase = increased glucose storage.
Activation of glucokinase, phosphofructokinase and pyruvateK = increased glucose utilization.
Inhibits glycogenolysis via inactivation of liver glycogen phosphorylase.
Inhibits gluconeogenesis via inhibition of pyruvate carboxylase, PEPCK and fructose 1,6 diphsphatase.
What effects does insulin have on fat metabolism?
Overall: Increased fat storage in adipose tissue.
Increased FA and Triglyceride synthesis by stimulation of lipoprotein lipase = breaks down lipoproteins to FFAs so they can enter adipocytes.
Simulates FA synthesis from glucose.
Inhibits lipolysis in adipocytes.
What effects does insulin have on protein and aa metabolism?
Overall: Increased protein synthesis.
MM: stimulates aa uptake
LIVER and MM: increased rate of protein synthesis, inhibits protein catabolism. Inhibition of gluconeogenesis.
What are the chronic metabolic effects of insulin?
Changes the expression of many metabolic enzymes:
Increased expression of anabolic enzymes, decreased catabolic enzymes.
What are the effects of insulin on cell growth?
Stimulates cell growth and DNA synthesis (mitogen - links to cancer).
What type of receptor is the insulin receptor?
Tyrosine Kinase enzyme.
What is the precursor to glucagon and where is it made?
Proglucagon (LARGE precursor)
a-cells in pancreas
L-cells in intestine
Processing of proglucagon ends up giving Glucagon (a-cells), GLP-1 and GLP-2 (intestinal)
What is the major site of glucagon action?
Liver.
Increases liver glucose release to increase blood glucose levels.
Increased glycogenolysis (Glycogen phosphorylase)
Increase gluconeogenesis (Increase uptake of glycogenic aa’s).
Discuss regulation of glucagon secretion
STIMULATION:
Neural: PNS (CNX Ach) & SNS (epi/norepi)
Hormonal: GIP, CCK (also stimulates gallbladder contraction and pancreatic enzyme secretion, slows gastric emptying)
Nutrients: Low glucose, aa (ala, arginine)
INHIBITION:
Hormonal: GLP-1, somatostatin, insulin
Nutrients: High glucose.
Discuss somatostatin
The major form in islet cells is SS-14, but found in many tissues.
Release from d-cells is stimulated by glucose, sulfonylureas, aa’s, CCK, cAMP.
Release from d-cells is inhibited by cholinergic stimulation.
d-cells provide (-) feedback by inhibiting both insulin and glucagon. This ensures islet endocrine output is reset when blood glucose gets back to set point.
Ensures timely reduction of insulin secretion.
Discuss IAPP/amylin
Cosecreted with insulin from B-cells.
Slows gastric emptying.
Slows glucagon secretion.
Regulates blood glucose in an INSULIN SPARING fashion.
Discuss pancreatic polypeptide (PP)
Secreted postprandially.
Delays gastric emptying.
Reduces acute food intake.
Discuss ghrelin
Expressed in islet during development.
Secreted by endocrine cells in gastric fundus.
Stimulates growth hormone from pituitary (GH inhibits insulin action).
Important in appetite regulation, increases appetite.
What is the major clearance site for glucagon?
Renal capillary bed.
Discuss the role of glucocorticoids (cortisol) in carbohydrate metabolism.
Counter-regulatory to insulin action.
Important for blood glucose during fasting.
Increases liver gluconeogenesis.
At what mM levels do the following mechanisms take action:
1. Insulin release
2. Glucagon release
3. Epinephrin release
4. Growth hormone release
5. Cortisol release
- 4.6
- 3.8
- 3.8
- 3.7
- 3.2 (dangerous level)
What type of dysfunction is central to both T1D and T2D?
Islet dysfunction.
T1D: Beta-cell-specific AUTOIMMUNITY, involves both genes and environmment.
T2D: Diabetogenic environment (obesity/insulin resistance) - B cell stressors
What can be used to predict T1D in an individual?
Autoantibodies that are markers of immune response.
What type of disease is T1D classified as?
Autoimmune.
Associated with other autoimmune diseases.
Strong genetic association with HLA loci.
Islet cell antibodies (ICAs) to B cell granule proteins (insulin, GAD)
Specific T lymphocyte attack on B cells.
Disease concordance for T1D in identical twins
> 50% (suggests environmental component is necessary)
Polygenetic.
Discuss the environmental component of T1D
Disease SUSCEPTIBILITY is inherited, disease is not.
Environmental triggers:
*Viruses (enteroviruses-coxsackie)
Diet/nutrition (Vit D deficiency)
Stress (B cell stress, insulin resistance)
Diabetes Mellitus definition
A chronic incurable disease characterized by elevated blood glucose, resulting from defective insulin production and/or action.
***need B cell dysfunction
Discuss the epidemiology of T1D
Most common in children, but also found in adults.
Incidence: 1:400
Increasing at 3%/year
Approximately 300,000 Canadians
Therapeutic interventions for T1D
Replace B cells via stem cell or donor islet transplantation.
Replace insulin with pumps.
Other potential sources for islet transplant
Human organ donors
Xenotransplant (pigs)
Embryonic stem cells (genetic engineering for better B cells)
Immunotherapy in T1D prevention and recent-onset T1D
Has alot of promise:
Peptide antigen therapy (insulin)
Abatacept
Ustekinemab
Golimumab
Teplizumab - $200k/yr, only delays disease by 2 years.
Target different parts of immune pathway.
Carry risk.
Delay but do not prevent.
T2D epidemiology
Usually occurs in >45 years but now seen in children.
90% of all diabetes.
6.4% prevalence worldwide
12-14% prevalence US
>90% concordance in identical twins
Frequent in certain ethnic groups.
Associated with sedentary lifestyle and western diet.
Progression of T2D
Early:
Impaired glucose tolerance (IGT)
Normal fasting glucose w/abnormal
Treated w/diet and exercise.
Overt but mild:
Moderate fasting hyperglycemia (7mM)
Insulin resistance present
Insufficient insulin secretion
Treated with diet/exercise, oral agents.
Advanced:
Severe fasting hyperglycemia (>9mM)
Insulin secretion greatly impaired or absent
Often requires insulin for treatment.
Characteristics of insulin secretion in T2D
Impaired glucose-induced insulin secretion.
Impaired proinsulin processing (hyperproinsulinemia).
Inability to adapt to increasing insulin resistance.
Progressive decline in insulin secretion.
Causes of loss of insulin secretion in T2D
- Glucolipotoxicity: prolonged exposure to high glucose and FFAs is toxic to B cells.
- Pro-inflammatory cytokines: increased # of islet macrophages making pro-inflammatory cytokines.
- Islet amyloid deposits: toxic amyloid deposits composed of IAPP/amylin
**Includes both B cell dysfunction and death. B cell exhaustion/stress/failure.
Discuss insulin resistance in T2D
Involved genetic and/or acquired post-receptor defects in insulin action.
Associated w/obesity, *Visceral obesity. BMI:insulin resistance.
Can arise with other syndromes (polycystic ovaries) or rare gene mutations.
Associated with inflammation in adipose tissue.
What is the best prevention for T2D?
Lifestyle (58% risk reduction).
Genes associated with T2D
Most are related to B cell function
HHEX/IDE
Zinc transporter
TCF7L2
PAM
Usually confer risk of disease: disease is POLYGENIC.
Monogenic forms of diabetes
MODY Mature Onset Diabetes of the Young
Usually occurs before age 30.
Not associated with obesity.
Familial.
14 different types of genetic mutations.
Neonatal Diabetes Mellitus
Rare.
Sulfonylurea receptor mutation.
Gestational Diabetes Mellitus
Appears during pregnancy and resolves after birth.
Risk for infant: increased size, difficult birth.
>50% later develop T2D.
Pregnancy may unmask genetic impairments in B cell function.
Insulin resistance d/t protective factor that makes sure baby gets the nutrients preferentially.
How is diabetes classified?
By the pathogenic process leading to hyperglycemia.
1. T1D
2. T2D
3. GDM
4. MODY
5. Secondary diabetes: medication/drug related, exocrine pancreas related, endocrinopathy (Cushings), infection, other.
Etiology of T1D
Autoimmune or non-autoimmune-mediated destruction of B cells.
What lab investigations can be used to help diagnose T1D?
C-peptide
anti-GAD Ab
anti-ICA Ab
Type 1a vs Type 1b
Type 1a: immune-mediated B cell destruction (95%)
Type 1b: idiopathic B cell destruction (5%)
T2D etiology
Insulin resistance due to obesity, abnormal insulin receptors, adipokines, inflammation, B cell defects, and metabolic syndrome.
Risk factors for T2D
Genetic!!
Family hx
Ethnicity
Obesity
Diet
Sedentary lifestyle
Smoking
What lab investigations can be used to help diagnose T2D?
Cr/eGFR
UACR
Lipid panel
Diabetic eye exam
What are the 4 ways BG is monitored?
- A1c
- CBG: capillary blood glucose
- isCGM: intermittently-scanned continuous glucose monitoring
- trCGM: real-time continous glucose monitoring
List the benefits and limitations of the 4 ways of BC monitoring.
Discuss a structured educational program to facilitate behaviour change results in patients.
Teach patients:
How and when to perform CBG
How to record the results
Meaning of various BG levels
How behaviour and actions affect BG results
Discuss frequency of CBG monitoring with:
Dietary/Lifestyle or Oral medication
Basal insulin once daily
Twice daily insulin
Basal bolus insulin QID or insulin pump
Dietary/Lifestyle or Oral Medication:
Glucose in target - test 1-2 times/week.
Glucose not in target - before and 2 hours after a different meal each day OR 7/day for 1 day/week AND before and after exercise.
Basal insulin 1/day:
Glucose in target - test before breakfast daily.
Glucose not in target - test before breakfast daily and alternate before supper/hs daily.
Twice daily insulin:
Glucose in target - test before breakfast and before supper.
Glucose not in target - test QID acmeals and hs until in target.
Basal bolus insulin QID or insulin pump:
Glucose is stable/in target - test QID acmeals and hs
Glucose not in target - test 7 times/day.
What is important to remember about CGM?
Monitors BG in interstitium ea 1-5 minutes.
5-15 minute lag = may not helpful for hypoglycemic events.
BG should be confirmed with CBG before changing treatment.
Alarms can be programmed for highs/lows.
What is advantage of an ambulatory glucose profile?
Makes it easier to visualize glycemic patterns by taking 14 days and superimposing them over a 24 hour pattern.
Shows median, quartiles and 10/90th percentiles.
What glucose metric is becoming the Gold standard.
Time In Range (TIR)
% of values between 3.9-10.0mM/L
70% TIR equates to approx A1c of 7.0% with each 10% of TIR equating to about 0.5% change in A1c.
Glucose Management Indicator (GMI)
Glucose metric that shows approximate A1c based on avg CGM readings for 14+ days.
May differ from measured A1c because it is from 14ish days, not 8-12 weeks.
What questions help with interpretation of AGP graphics?
- Are there patterns of hypoglycemia?
- Are the readings within the target range?
- What is the shape of the median curve?
- What is the degree of variability?
What are shown benefits of CGM for those on basal-bolus insulin therapy?
Reduce A1c (~0.5%)
Increase TIR
Reduce hypoglycemic events
Improve QOL and hypoglycemic distress
Diabetes Canada guidelines for BG monitoring
A1c ea 3 months
T2D not on insulin: CBG individualized depending on meds, A1c level, and risk of hypoglycemia.
Increased testing at QID and/or overnight when A1c not in target or episodes of hypoglycemia.
T1D w/basal bolus or CSII: rtCGM
T2D w/basal-bolus and not in A1c target: rtCGM or isCGM
Discuss the basal/bolus concept of insulin secretion
Bolus: Facilitates glucose uptake after meals.
Basal: Suppresses glucose production between meals and overnight.
Discuss insulin pumps
AKA CSII Continuous Subcutaneous Insulin Infusion
Contains rapid acting analogue insulin
Delivers basal rate through the day, rates can be adjusted for different times.
Bolus released prior to meals, adjusted for carb intake and current BG.
Insertion site changed ea 2-3 days.
Advantages of insulin pumps
More precise dosing
Multiple basal rates
More reliable insulin absorption
Improved BG control and A1c w/out hypoglycemia
Flexibility in lifestyle
Stabilizes BG
Improved QOL/satisfaction
Disadvantages of insulin pumps
Mechanical failure more likely (educate patients on trouble shooting)
DKA may develop more rapidly if pump fails
Skin probs/infections
Expensive
Complex
Psychological factors/body image
Must be supervised by specialist/experienced team.
Indications for insulin pumps
Insulin treated diabetes
Need to normalize glucose
Need for flexibility
Hectic lifestyle (shift work/excercise)
Motivated, responsible, and considers safety (carries emergency supply)
Discuss establishing basal and bolus pump doses.
Start by calculating 80% of prepump total daily dose.
Of this amount 50% is basal and 50% is allocated to bolus.
Divide basal by 24 hours for hourly basal dose.
Calculate average daily carb intake and divide by total bolus amount (eg 1:10 means 1 unit insulin for ea 10 g carbs) OR 500/TDI = carb ratio
Discuss Insulin Sensitivity or Correction Factor
How much do we think 1 unit of insulin will lower BG.
100/TDD of insulin.
eg TDD = 40 U
100/40 = 2.5; 1 unit of insulin will lower BG by 2.5 mM/L
Closed-Loop syher stems
CGM connected to pump
Allows for automated insulin delivery (AID).
Still need to tell the pump when and how much you are eating.
Improve A1c and TIR more than other systems.
Free downloadable software algorithms available:
Loop, iAPS, AndroidAPS
Smart insulin pens
Reusable insulin pen that connects via bluetooth.
Records and tracks doses.
Helps calculate dose for a meal.