Diabetes Flashcards
(100 cards)
Define Diabetes Mellitus
Syndrome of chronic hyperglycaemia due to relative insulin deficiency, resistance or both
What types of complications are associated with diabetes?
Hyperglycaemia results in serious microvascular (retinopathy, nephropathy, neuropathy) or macrovascular (strokes, renovascular disease, limb ischaemia and heart disease) problems
What are normal levels of blood glucose?
Blood glucose levels should be between 3.5-8.0mmol/L under all conditions
What is the main organ involved in glucose homeostasis and what is its role?
The liver is the principal organ of glucose homeostasis:
- Stores & absorbs glucose as glycogen - in post-absorptive state
- Performs gluconeogenesis from fat, protein and glycogen
- If blood glucose is HIGH then the liver will make glycogen (convert
glucose to glycogen) in a process called glycogenesis - in the long term
the liver will make triglycerides (lipogenesis) - If blood glucose is LOW then the liver will split glycogen (convert
glycogen to glucose) in process called glycogenolysis - in the longer
term the liver will make glucose (gluconeogenesis) from amino acids/
lactate
How much glucose is produced daily?
200g is produced and utilised each day with more than 90% derived from liver glycogen and hepatic gluconeogenesis and the remainder from renal gluconeogenesis
Where is glucose utilised?
- The brain is the MAJOR CONSUMER of glucose and its function depends on
an uninterrupted supply of this substrate - Tissues such as muscle and fat have insulin-responsive glucose
transporters and absorb glucose in response to postprandial (post-meal)
peaks in glucose and insulin
Why is the brain so reliant on just glucose and no other energy forms?
- fatty acids (which can be turned into ketones and then acetyl-CoA for Krebs) cannot cross the blood brain barrier
How is glucose utilised in muscles?
Either stored as glycogen or metabolised to lactate or CO2 and H2O
How is glucose utilised in adipose tissue?
Fat uses glucose as a substrate for triglyceride synthesis. Lipolysis of triglyceride releases FA and glycerol which is used in hepatic gluconeogenesis
What are some of the roles of insulin?
- Suppresses hepatic glucose output - decreases glycogenolysis &
gluconeogenesis - Increases glucose uptake into insulin-sensitive tissues:
- Muscle - glycogen & protein synthesis
- Fat - fatty acid synthesis
- Suppresses:
- Lipolysis
- Breakdown of muscles (decreased ketogenesis)
What is meant by biphasic insulin release?
B-cells can sense the rising glucose levels and aim to metabolise it
by releasing insulin - glucose levels are the major controlling factor
in insulin release!
- First phase response is the RAPID RELEASE of stored insulin
- If glucose levels remain high then the second phase is initiated. This
takes longer than the first phase due to the fact that more insulin
must be synthesised.
What are some of the roles of glucagon?
- Increases hepatic glucose output - increases glycogenolysis & gluconeogenesis
- Reduces peripheral glucose uptake
- Stimulates peripheral release of gluconeogenic precursors e.g. glycerol & amino acids
- Stimulates:
- Muscle glycogenolysis & breakdown (increased ketogenesis)
- Lipolysis
What are some other counter-regulatory hormones that are involved in diabetes?
Adrenaline, Cortisol, and GH which increase glucose production in the liver and reduce the utilisation in fat and muscle
How is insulin formed and explain C peptides
- Insulin is coded for on CHROMOSOME 11 produced in the BETA CELLS of
the ISLETS of LANGERHANS of the PANCREAS:- Proinsulin is the precursor of insulin
- It contains the Alpha & Beta chains of insulin which are joined together
by a C PEPTIDE - When insulin is being produced, the proinsulin is cleaved from its C
peptide and is then used to make insulin which is then packaged into
insulin secretory granules - Thus when there is insulin release there will also be a high level of C
peptide in the blood from the cleavage of the proinsulin from it - Synthetic insulin DOES NOT have C peptide - thus the presence of C
peptide in the blood determines whether release is natural (then C peptide
will be present) or synthetic (then C peptide will not be present) - After secretion, insulin enters the portal circulation and is carried to the
liver, its prime target organ
What are the main roles of insulin in the fed and fasting state?
- In the fasting state - its main action is to regulate glucose release by the liver
- In the post-prandial state - its main action is to promote glucose uptake by fat and muscle
How does glucose get into cells?
A family of specialised glucose-transporter (GLUT) proteins carry glucose
through the membrane and into cells.
Explain GLUT-1 transporters
- Enables basal NON-INSULIN-STIMULATED glucose uptake into many cells
Explain GLUT-2 transporters
Found in BETA-CELLS of the pancreas
Transports glucose into the beta-cell - enables these cells to SENSE GLUCOSE LEVELS
It is a low-affinity transporter, that is, it only allows glucose in when there is a high concentration of glucose i.e. when glucose levels are high and thus WANT insulin release
In this way, via GLUT2, beta-cells are able to detect high glucose levels and thus release INSULIN in response
Also found in the renal tubules and hepatocytes
Explain GLUT-3 transporters
Enables NON-INSULIN-MEDIATED glucose uptake into BRAIN, NEURONS & PLACENTA
Explain GLUT-4 transporters
Mediates much of the PERIPHERAL ACTION of INSULIN
It is the channel through which glucose is taken up into MUSCLE and ADIPOSE TISSUE cells following stimulation of the insulin receptor by INSULIN binding to it
What is the role of the insulin receptor in glucose transport?
- This is a glycoprotein, coded for on the short arm of chromosome 19, which
straddles the cell membranes of many cells - When insulin binds to the receptor it results in the activation of tyrosine
kinase and initiation of a cascade response - one consequence of which is
the migration of the GLUT-4 transporter to the cell surface and increased
transport of glucose into the cell
What conditions might diabetes be secondary to?
- Pancreatic pathology e.g. total pancreatectomy, chronic pancreatitis, haemochromatosis
- Endocrine disease e.g. Acromegaly and Cushing’s disease
- Drug induced commonly by thiazide diuretics and corticosteroids
- Maturity onset diabetes of youth (MODY):
- Autosomal dominant form of type 2 diabetes - single gene defect altering beta cell function
- Tends to present <25 yrs with a positive family history
Brief description of Type 1 DM
The type 1 diabetic is young, has insulin deficiency with no resistance and immunogenic markers
Brief description of Type 2 DM
Common in all populations enjoying an affluent lifestyle and is also increasing in frequency - particularly in adolescents - resistance to insulin