Endocrinology - Week 4 Flashcards
what contributes to calories in
food and absorption
what contributes to calories out
basal metabolic rate, thermogenesis, non purposeful activity, exercise
heritability of obesity
40-70%
what are the efferents of the hypothalamus
pituitary which goes on to: gonads - sex steroids adrenal cortex - cortisol thyroid - thyroxine growth hormone
autonomic NS
parasympathetic - insulin
sympathetic - adrenaline
what are afferents of the hypothalamus
- Conscious control
- Fatty acids, glucose, hormones
- Leptin
- Ghrelin
- Insulin
when is leptin treatment for obesity effective
• Ineffective when leptin is high
o Idiopathic obesity
• Effective when [leptin] is low
o Leptin deficiency (rare)
o Anorexia nervosa
o Lipodystrophy
what are the actions of leptin
• Satiety • Hypothalamic-pituitary-gonadal axis o Puberty o Fertility • Hypothalamic-pituitary-adrenal axis • Hypothalamic-pituitary-thyroid axis
• Peripheral actions??
o Adipocytes, pancreatic islets, immune cells, …
PROBABLY MOST IMPORTANT IN LOW ENERGY STATES
AS SURVIVAL SIGNAL
what are some causes of secondary obesity
- Hypothyroidism
- Cushing’s syndrome - usually iatrogenic
- Hypothalamic disease
• Others o Drugs (oestrogen, beta blockers, tricyclic antidepressants, sodium valproate) o Insulinoma, GH deficiency o Genetic Disorders: e.g. Prader Willi syndrome, Bardet Biedl syndrome, leptin or leptin receptor deficiency, melanocortin 4 receptor defect, POMC deficiency
spotting endocrine disorders in obesity History
• Always obese/age of onset?
o Periods regular/ headache/ thirst, polyuria?
o Diet, eating pattern, alcohol, exercise?
o Drugs?
o Complications and effects on lifestyle
• Examination:
o Features of Cushing’s, hypothyroidism, hypothalamic disease, syndromes
o BP
• Investigations:
o TFTs › Blood glucose
o ?o/n dex suppression test
why is obesity bad for you
- Breathlessness, Sleep apnoea
- Cancers (breast, endometrium, ovary, colon, gallbladder)
- Gallstones, NAFLD
- Incontinence
- Varicose veins
- Arthritis
- Social & Psychological
- Heart attack
- Hypertension
- Diabetes mellitus
- Infertility & hirsutis
describe fat distribution
Fat distribution – Apples and Pears
Central Visceral Android ‘Apple’ HIGH RISK
Peripheral Subcutaneous Gynoid ‘Pear’ LOW RISK
what is important about visceral fat
- different metabolism or secretion
* releases direct to liver
what is lawrence syndrome
“Lipoatrophic” Diabetes
• Generic IR complications o Acanthosis nigricans o Hyperandrogenism o Female subfertility o Precocious puberty o Diabetes mellitus o Soft tissue overgrowth
• Lipotoxic complications o Severe dyslipidaemia o NAFLD, cirrhosis, HCC o Premature atherosclerosis o Diabetes mellitus
describe adipokines
- Secreted from adipocytes or macrophages in adipose tissue
- Manipulations in mice demonstrate potent effects on insulin sensitivity in other tissues
- Correlated with increased insulin sensitivity in other tissues in humans
- Many candidates published – variable importance in subsequent studies
what are the endocrine consequences of obesity
• Altered steroid metabolism in adipose tissue:
o Increased oestrone and oestradiol
Hirsutism and infertility
Hormone-sensitive cancers
o increased reactivation of cortisol from cortisone
• Altered substrate flux and adipose inflammation o Insulin resistance Hyperglycaemia Dyslipidaemia, Fatty Liver Subfertility
• Altered hypothalamic function
o Anovulatory menstrual cycles
Subfertility
describe diabetes and its epidemiology
- Affects 5% of total population
- Affects 10% of people over 65
- Around 3.2 million people are known to have diabetes
- Many people have undiagnosed diabetes
- About 25% require insulin therapy
Diabetes mellitus is a condition associated with an elevated blood glucose. This is a consequence of deficiency of INSULIN, or of its reduced action, or of a combination of both.
describe insulin
- Hormone secreted in pancreas (islets)
- Anabolic hormone
- Essential for fuel storage and cell growth
- Promotes uptake of glucose into cells for energy
- Prevents breakdown of fat and protein
describe pancreatic cells
Alpha cell Glucagon 11%
Beta cell Insulin 85%
Delta cell Somatostatin 3%
F cell Pancreatic polypeptide 1%
describe the structure of insulin
Insulin has an alpha and beta subunit which are linked by disulphide bonds and C-peptide. This is proinsulin. Prior to release by cells, C-peptide is cleaved away to leave insulin and free C-peptide. This is done by b-cell peptidases.
how is Insulin Secretion from Beta Cells is Directly Coupled to Glucose Influx
Beta cells have GLUT 2 transporters which are insulin independent and let in glucose purely based on extracellular glucose concentration. This glucose is metabolised by the cell to give ATP. This ATP will inhibit K channels which then don’t pump K out of the cells. This leads to depolarisation of the membrane which in turn leads to voltage gated Ca channels to open and let Ca into the cell. Ca causes exocytosis of insulin granules into the bloodstream.
describe insulin release
- Pro-insulin is converted to insulin and C-peptide in equimolar amounts
- In response to ingestion of food, stored insulin is released first, followed by newly synthesised insulin
- This gives a biphasic response of insulin secretion
- C-peptide can be used as a measure of endogenous insulin secretion in people with diabetes
INSULIN from pancreas: • Secreted into portal vein • Acts first on LIVER • Passes through liver into systemic circulation • Acts on MUSCLE and FAT
what are the Principal Actions of Insulin
↑ Glucose uptake in FAT and MUSCLE ↑ Glycogen storage in LIVER and MUSCLE ↑ Amino Acid uptake in MUSCLE ↑ Protein Synthesis ↑ Cell proliferation ↑ Lipogenesis in ADIPOSE TISSUE
↓Apoptosis
↓ Gluconeogenesis from 3-Carbon precursors
↓Ketogenesis (in LIVER)
Insulin Causes Translocation of GLUT 4 to Cell Membranes. This allows insulin-dependent glucose uptake into cells
what is the difference between insulin and glucagon
Insulin favours glycogenesis and inhibition of gluconeogenesis
Glucagon favours glycogenolysis and gluconeogenesis
what are some 3-carbon precursors
Alanine (from ingested protein)
Pyruvate (from muscle protein)
Lactate (from muscle glycogen)
Glycerol (from fat)
what are the 4 ways of being diagnosed with diabetes
- Fasting plasma glucose > 7.0 mmol/l
- 2hr plasma glucose in OGTT > 11.1 mmol/l
- Random plasma glucose > 11.1 mmol/l
- HbA1c > 48 mmol/mol
- If the patient is asymptomatic, the same test should be repeated to confirm the diagnosis of diabetes
- Do not delay urgent care waiting for a second test
describe Glycated Haemoglobin (HbA1c)
• Rate of formation of glycated haemoglobin is directly proportional to ambient blood glucose concentration
• Reflects integrated blood glucose (BG) concentrations during lifespan of erythrocyte (120 days)
• Blood sample can be taken at any time of day, irrespective of food consumption
Normal ≤41 mmol/mol
Pre-diabetes 42-47 mmol/mol
Diabetes ≥ 48mmol/mol
Situations where HbA1c should NOT be used as a Diagnostic Test
• Rapid onset of diabetes
– Suspected Type 1 Diabetes
– Children
– Drugs – steroids; antipsychotics
• Pregnancy
– Glucose levels can rise rapidly
– HbA1c is lower
• Conditions where red cell survival may be reduced – Haemoglobinopathy – Haemolytic anaemia – Severe blood loss – Splenomegaly – Antiretroviral drugs
• Increased red cell survival
– Splenectomy
• Renal dialysis
– Reduced HbA1c, especially if treated with erythropoietin
• Iron and vitamin B12 deficiency
– Small effects on HbA1c
what is the glucose tolerance test
- Used to assess state of glucose tolerance
- 75g oral glucose load
- No restriction or modification of carbohydrate intake for preceding three days
- Fast overnight
- Test is performed in morning – seated; no smoking
- Blood samples for plasma glucose taken at 0hrs and 2 hrs
describe impaired glucose tolerance
Fasting plasma glucose: <7.0 mmol/l
2 hours after 75g oral glucose load: 7.8-11.0 mmol/l
• Affects 20% of population aged 40-65 years (UK)
• Increased mortality from cardiovascular disease (doubled)
• Natural history - 15% develop diabetes in 5 years, 15% return to normal
• Check fasting plasma glucose annually
what is impaired fasting glucose
(Fasting Hyperglycaemia)
Fasting plasma glucose: 6.0 – 6.9 mmol/l
• Intermediate state between normal glucose metabolism and diabetes
• Impaired glucose tolerance often present also (but not always)
• Found in 5% of population and prevalence increases with age
• Increased risk of vascular complications
what classes as a prediabetic state
- Fasting blood glucose 6.0-6.9 mmol/l
- 2 hr OGTT blood glucose 7.8-11.0 mmol/l
- HbA1c 42-47 mmol/mol
- Fasting hyperglycaemia and Impaired Glucose Tolerance often co-exist
what are risk factors for type 2
• Genetics – Race • Increasing age • Central obesity • Low birth weight
what is the extent of genetic risk for type 2
2x for one parent
5x for two parents
37x for two siblings
- Genome-wide association studies have identified >400 gene variants associated with an increased risk of Type 2 diabetes
- Most relate to beta cell function or mass, rather than obesity/insulin resistance
- 40% of the overall risk of Type 2 diabetes is determined by genetic factors
what is type 2 diabetes
Type II diabetes is a combination of insulin resistance and beta cell dysfunction
why does diabetes incidence increase with age
- Beta cell function reduces with age
* Obesity increases with age
what is the classical presentation of type 2
- Asymptomatic – found on routine screening
- Thirst, polyuria (osmotic symptoms)
- Malaise, chronic fatigue
- Infections, e.g. thrush (candidiasis); boils
- Blurred vision
- Complication as presenting problem (e.g. retinopathy, neuropathy)
describe metabolic syndrome
linked to diabetes - very high cardiovascular disease risk • Central obesity • High BP • Fairly high triglycerides • Low HDL-cholesterol • Insulin resistance
what other disorders are linked to type 2
- Obstructive Sleep Apnoea
- Polycystic Ovarian Disease
- Hypogonadotrophic Hypogonadism in men
- Non-Alcoholic Fatty Liver Disease
what is the classical presentation of type 1
- Polyuria, thirst
- Fatigue, malaise
- Weight loss
- Blurred vision
- Nausea, vomiting
- Usual presentation is in childhood, adolescence or young adulthood
- Can present at any age
- Short history (weeks) of florid osmotic symptoms and rapid weight loss; Ketonuria/ketonaemia is usually present
- High risk of metabolic decompensation – ketoacidosis
what is the pathogenesis of type 1
- Genetic predisposition – HLA haplotypes (HLA-DR and HLA-DQ) as risk alleles
- Environmental trigger
- ? viral infection
- ? chemical toxin
- Autoimmune mechanism activated – can detect antibodies in blood to GAD, IA2 and/or ZnT8
- Destruction of pancreatic beta cells - once 80% are destroyed you start having symptoms of hypoglycaemia
Much more likely to get type I diabetes in northern areas than southern Europe for example theory that certain viruses which trigger it live better in northern climates
what is the genetic risk of type 1
Relative with Type 1 diabetes Relative Risk
Father 9
Mother 3
Both parents 30
Non-HLA-identical Sibling 3
HLA-identical Sibling 16
Non-identical twin 20
Identical twin 35
what Autoimmune Disorders are Associated with Diabetes
- Thyroid disease
- Pernicious anaemia
- Coeliac disease
- Addison’s disease
- Vitiligo
what effects on daily life does type 1 have
• Hypoglycaemia – Driving – Employment • Risks of Diabetic Ketoacidosis • Pregnancy • Childhood and adolescence • Complications
what are the causes of secondary diabetes
• Exocrine Pancreas Disorders
o Pancreatectomy
o Trauma
o Tumours
• Endocrinopathies
o Acromegaly
o Cushing’s
o Pheochromocytoma
• Drugs
o Steroid treatment
Can often tip someone over the edge if they are susceptible to diabetes type II
describe monogenic diabetes
- Big function altering mutations which lead to diabetes
- Early-onset diabetes
- Not insulin-dependent diabetes
- Autosomal dominant inheritance
- Obesity unusual
- Caused by a single gene defect altering beta-cell function
- 1-2% of ‘Type 2’ diabetes
what is home glucose monitoring
• Demonstrates glucose control throughout day (and night)
• Identifies hypoglycaemia (especially when asymptomatic)
• Provides information to adjust insulin dose
• Allows manipulation of insulin dose during
- intercurrent illness
- travel, sport, other activities
• Assists self-control of diabetes – improves glycaemic control
what is CGMS – Continuous Glucose Monitoring System
- Wireless sensor and monitor communication
- Hypo and hyperglycaemia alarms
- “real time” glucose values
Freestyle Libre Flash Glucose Monitoring System
describe HbA1c as a monitoring tool
• Checked at the time of a visit to a diabetes clinic or GP surgery
• Allows evaluation of :
- efficacy of therapeutic regimen
- patient’s adherence to treatment
- risk of developing diabetic complications
• Enhances clinical decision-making if available at time of clinical consultation
what type of monitoring should type 1 do
HBGM - yes
CGMS/Libre - yes
HbA1c - yes
blood ketones - yes
what type of monitoring should type 2 insulin do
HBGM - yes
CGMS/Libre - no
HbA1c - yes
blood ketones - no
what type of monitoring should type 2 sulphonyurea do
HBGM - ?
CGMS/Libre - no
HbA1c - yes
blood ketones - no
what type of monitoring should other treatments do
HBGM - ?
CGMS/Libre - no
HbA1c - yes
blood ketones - no
what type of monitoring should gestational diabetes do
HBGM - yes
CGMS/Libre - no
HbA1c - no
blood ketones - no
what are the aims of Dietary Management in Diabetes
- To achieve good glycaemic control
- To reduce hyperglycaemia and avoid hypoglycaemia
- To ensure adequate nutritional intake
- To assist with weight management
- To avoid aggravating diabetic complications
Reduce/eliminate refined carbohydrates and saturated fat
Restrict TOTAL caloric intake (portion size)
In order to
Increase insulin sensitivity
Lower blood glucose
Lower triglycerides/ LDL-cholesterol
what is a “healthy” diet in diabetes
CARBOHYDRATE: 45-60% (unrefined, complex)
FAT: <35% (monounsaturated 10-20%)
PROTEIN: 10-15% (do not exceed 1g/kg body wt)
High intake of dietary fibre (fruit, vegetables); low intake of salt
what is the dietary treatment in type 1 diabetes
- At diagnosis insulin should be started immediately!
- Dietary modification requires restriction of refined sugars and saturated fats
- Diet is weight-maintaining for most people
- Insulin dosage adjustment is based on carbohydrate content of meals
- Structured education programmes are available, e.g. DAFNE (Dose Adjustment For Normal Eating)
- Other lifestyle changes (regular exercise) are supplementary
describe indications and contraindications of oral hypoglycaemic drugs
- Indications: Type 2 diabetes (if diet alone inadequate)
- Insulin sensitisers in combination with insulin in Type 1 diabetes
• Contraindications:
o Ketoacidosis
o Severe intercurrent illness
describe sulphonyureas
(e.g. glipizide, gliclazide)
• stimulate secretion of endogenous insulin in beta cells
• used in non-obese patients (may be insulin-deficient)
• used as monotherapy or in combination with metformin, glitazone or insulin
• choice of sulfonylurea is based on duration of action and method of elimination
• promote weight gain
• main adverse effect is hypoglycaemia
describe biguanide
(metformin)
• decreases hepatic glucose production
• increases insulin sensitivity in muscle
• encourages weight loss
• effective as monotherapy or in combination with sulfonylurea, glitazone or insulin
• side-effects include nausea and diarrhoea
• contraindicated in renal impairment (risk of lactic acidosis)
describe glucose prandial regulators
(Glinides)
• Repaglinide (MEGLITINIDE)
• Nateglinide (AMINO ACID DERIVATIVE)
• Insulin secretagogues – direct effect on beta cells
• Stimulate rapid endogenous insulin release when given with meals
• Side-effects include weight gain and hypoglycaemia
• Lower risk of hypoglycaemia than sulfonylureas
describe alpha glucosidase inhibitors
(e.g. Acarbose; Miglitol)
• Delay digestion of carbohydrate and slow down postprandial absorption of glucose
• Do not cause weight gain
• Limited efficacy; can be used in combination
• Gastrointestinal side-effects are common, including bloating and flatulence
describe PPAR gamma activation in fat
Reduces Insulin Resistance in Liver and Muscle
Small insulin sensitive adipocytes
Lipolysis reduced
lowers plasma Free fatty acids
Adiponectin production raised
reduces glucose output and increases glucose uptake
Normoglycaemia
describe thiazolidinediones
(e.g. Pioglitazone) PPAR gamma agonist
• Slow onset of action - take 2-3 months to achieve maximal effect
• Promote weight gain - but redistribute body fat to reduce visceral depot
• Contraindicated in congestive cardiac failure; hepatic impairment May cause fractures
what is the incretin effect
Secretion of insulin is greater in response to oral glucose
Promoted by release of GI hormones “incretins”
describe glucagon-like peptide 1 (GLP-1)
- Potent insulinotropic hormone (incretin) is released in response to meals
- Rapidly degraded in plasma by enzyme Dipeptidyl Peptidase 4 (DPP- 4)
- Plasma GLP-1 is lower in people with impaired glucose tolerance (IGT) and type 2 diabetes compared to healthy non-diabetic subjects
what are the GLP-1 physiological effects
• Upon ingestion of food…
• GLP-1 is secreted from the L-cells in the intestine
o Stimulates glucose-dependent insulin secretion
o Suppresses glucagon secretion
o Slows gastric emptying
o Reduces food intake
o Improves insulin sensitivity
what are the therapeutic forms of GLP-1
Incretin mimetic, synthetic exendin-4 (Exenatide)
GLP-1 analogue (Liraglutide)
DPP- 4 inhibitors (Gliptins)
EXENATIDE: synthetic form of Exendin-4. This was isolated from the salivary secretions of the lizard Heloderma suspectum
(Gila monster), and found to circulate as a meal-related peptide, with GLP-1 actions.
what are incretin mimetics
(e.g. Exenatide, Liraglutide
• Act like a GLP-1 peptide
• Have to be given by injection
• Promote weight loss
• Given in combination with either metformin or sulfonylurea
• Main side-effect is nausea
• Hypoglycaemia rare except when given with SU
what are gliptins
(e.g. sitagliptin; vildagliptin)
• DPP-4 inhibitors – inhibit degradation of incretin hormones and enhance their actions
• Oral route of administration
• Taken in combination with metformin
• Produce modest reduction in HbA1c
• Weight neutral
• Few side-effects, with minimal hypoglycaemia
what are Sodium-glucose Cotransporter-2 (SGLT2) Inhibitors
A class of FDA-approved drugs to lower blood sugar in type 2 diabetes. SGLT2 inhibitors include canagliflozin, dapagliflozin, and empagliflozin.
Empaglifozin acts as a glucuretic to remove glucose that would otherwise be reabsorbed
which drugs augment supply of insulin from pancreatic beta cells
sulphonyureas
prandial glucose regulators (glinides)
incretin mimetics
which drugs enhance insulin action and reduce resistance
metformin and thiazolidinediones
what drugs delay carbohydrate absorption
alpha glucosidase inhibitors
incretin mimetics
what are the indications for insulin therapy
- Persistently elevated blood glucose and HbA1c on maximum doses of anti-diabetic drugs
- Symptoms of hyperglycaemia and/or infections (e.g. candidiasis)
- Non-fasting ketonuria
- TYPE 1 DIABETES (ketosis-prone)
- TYPE 2 DIABETES
- Secondary failure to anti-diabetes drugs
- Severe intercurrent illness
- Metabolic complications (hyperosmolar states)
what is the problem with insulin therapy
- Insulin has to be given by injection
- Biological action is variable as insulin absorption is influenced by many factors (site of injection, ambient temperature, exercise, etc.)
- Insulin has to be given several times daily
- Insulin regimens are often complicated
what are the Types and Formulations of Insulin
• Short-acting Soluble
(Actrapid; Humulin-S)
• Intermediate-acting Isophane (NPH)
(Insulatard; Humulin-I)
Fixed mixtures are available containing combinations of soluble and isophane insulins e.g. 30% soluble with 70% isophane (Humulin M3)
what are insulin analogues
Substitution of single amino acid in insulin chain
Alters absorption characteristics of insulin
Time-action profile is modified by minor changes in amino acid sequence of insulin molecule
Fast-acting: insulin lispro (Humalog) insulin aspart (Novorapid) insulin glulisine (Apidra)
Long-acting: insulin glargine (Lantus) insulin detemir (Levemir)
Fixed mixtures include Humalog Mix 25 (25% fast-acting) and Novomix 30 (30% fast-acting)
what is the time-action characteristics of soluble insulin
onset of action - 30 mins
peak effect - 1-2 hours
duration of action - 7 hours
what is the time-action characteristics of fast acting analogue
onset of action - 5-10 mins
peak effect - 30-60 mins
duration of action - 3 hours
what is the time-action characteristics of isophane
onset of action - 3 hours
peak effect - 7 hours
duration of action - 12-14 hours
what is the time-action characteristics of long-acting analogue
onset of action - 1 hour
peak effect - none
duration of action - 19-32 hours
what does the choice between insulin regimens depend on
- Targets for glycaemic control
- Time-action profile of insulins
- Ease and convenience of administration
- Flexibility of regimen
- Practical issues (e.g. disability, supply, species preference)
what insulin regimens are there
BASAL-BOLUS (Multiple injection): Short-acting or fast-acting insulin before meals; intermediate-acting or long-acting insulin once daily
TWICE DAILY: Soluble or fast-acting and isophane (NPH) insulins combined; free-mixing or fixed mixture
ONCE DAILY: Intermediate-acting or long-acting insulin, combined with anti-diabetic drugs (Type 2 diabetes)
what are the routes of adminitration for insulin
- SUBCUTANEOUS - syringes, pens, pumps
- intrapulmonary - inhaler (historical)
- intravenous, intramuscular - injection (emergency use)
- intraperitoneal - dialysate (renal failure)
- transplanted islets - pancreatic islets
describe lipohypertrophy at insulin injection site
- unsightly
- slows insulin absorption
- resolves if site avoided
what are the side effects of insulin therapy
- HYPOGLYCAEMIA
- WEIGHT GAIN
- lipodystrophy at injection sites
- peripheral oedema (salt & water retention)
- insulin antibody formation (animal insulins)
- local allergy (rare)