4. Robbins: Endocrine Pancreas Flashcards
Endocrine pancreas is made up of ________.
Islet of langerhans, located in the neck and tail of the pancreas.
What cells make up the islet of langerhans?
[4 major cell types and 2 minor cell types]
-
4 major cell types
- Alpha cells
- Beta cells
- Delta cells (ς)
- PP cells
-
2 minor cell types
- D1 cells
- Enterochromaffin cells
Function of alpha and beta cells
- Alpha cells: secrete glucagon => ↑ glycogenolysis in liver => [↑ blood sugar/glucose]
- Beta cells: secrete insulin => [regulates glucose utilization] & [↓ blood sugar/glucose]
Function of delta and PP cells
- Delta cells: secrete somatostatin => [suppress release of insulin and glucagon_]_
- PP cells: secrete pancreatic polypeptide => [GI effects: ↑ secretion of GI enzymes & inhibits intestinal motility]
Function of D1 cells and enterochromaffin cells
-
D1 cells: secrete VIP (vasoactive intestinal polypeptide) =>
- [glycogenolysis and hyperglycemia]
- stimulates [GI secretion => diarrhea]
- Enterochromaffin cells: make serotonin & source of pancreatic tumors that cause from carcinoid syndrome.
D1 cells of the endocrine pancreas secrete what; what is the effect of this secretory product?
- VIP
- Induces glycogenolysis and hyperglycemia
- Stimulates GI secretions –> secretory diarrhea
What is the main job of the islet of langerhans?
Glucose homeostasis: regulated by
- release of glucose from liver
- utilization of glucose by tissue
- Insulin and glucagon
How is insulin release regulated?
- GLUT-2 (glucose transporter) to move to takes glucose into B-cells.
- Glucose is metabolized => makes ATP
- ATP inhibits membrane K+ channel
- Membrane is depolarized => Ca2+ influx
- Ca2+ influx => insulin release.
- Insulin causes GLUT-4 to move into the plasma membrane and promote glucose uptake in target cell.
How is insulin processed?
Proinsulin => cleaved in B-cell to [insulin & C-peptide]
How can we measure if insulin was administered by meds or made by the body?
Measure C-peptide, a marker of endogenous insulin.
Insulin and glucagon effects during fasting vs feeding stages
-
Fasting
- [↓ insulin and ↑ glucagon] => hepatic gluconeogenesis and glycogenolysis & ↓ glycogen synthesis => ↑ blood glucose (mainly by liver) prevent hypoglycemia
-
Meal
- ↑ glucose load causes [↑ insulin and ↓ glucagon] => glucose uptake and utilization to prevent hyperglycemia
What is the major insulin responsive site for postprandial glucose utilization and critical to prevent hyperglycemia?
Skeletal muscle
Insulin effects on adipose tissue
- ↑ glucose uptake
- ↑ lipogenesis
- ↓ lipolysis
Insulin effects on liver
- ↑ Glycogen synthesis
- ↑ Lipogenesis
- ↓ Gluconeogenesis
Insulin effects on striated muscle
- ↑ glucose uptake
- ↑ glycogen synthesis
- ↑ protein synthesis
Main job in insulin
MOST potent anabolic hormone:
- Growth- promoting effects
- Tell body how to utilize glucose
What cell?
B-cells (insulin): => dark reaction
What cell?
D cells (somatostatin)
What cell?
a cells (glucagon)
What cell?
EM of B-cell with membrane-bound granules, dense rectangular core and halo.
What cell?
Left: a-cell with dense, round center
Right: delta cells
The most important stimulus for insulin synthesis and release is ______.
Glucose
What are incretins?
Hormones released from cells in GI after a meal (oral glucose) that help to promote insulin release
What are 2 incretins?
- Glucagon-like-peptide 1 (GLP-1)
- Glucose-dependent insulin-releasing polypeptide (GIP)
MOA of incretins
- GLP-1 and GIP act on B cells in pancrease => ↑ insulin release
- GLP-1 acts on a-cells and suppresses glucagon release => ↓ blood glucose (↓ glucose release from liver )
- Inactivated by DPP-4 (dipeptidyl peptidase-4)
What 2 classes of drugs have been created for pt’s with T2DM based on the incretin effect?
- - GLP-1 receptor AGO
- - DPP-4 inhibitors (↓ breakdown of incretins)
How is the incretin-effect affect in T2DM?
Blunted:
Diabetes Mellitis
- What is it?
- Leading cause of what in the US:
- More common in:
- Lease common in:
- Problem with NL glucose homeostasis => hyperglycemia
- 1. Defective insulin secretion
- 2. Defective insulin effect
- ESRD, adult-onset blindness, non-traumatic LE amputation due to atherosclerosis
- MC = american indian/alaska native > Black and hispanic
- LC: Asian and white
NL blood glucose
70- 120 mg/dL
Fasting plasma glucose for DB Diagnosis
- Fasting plasma glucose > 126 mg/dL
Which value of HbA1C is considered diagnositc for diabetes?
> 6.5 %
A random plasma glucose ≥ ______ mg/dL is considered diagnostic for diabetes.
≥ 200 mg/dL
What are 4 genetic syndromes associated w/ diabetes?
- - Down syndrome
- - Klinefelter syndrome
- - Turner syndrome
- - Prader-Willi syndrome
What are T1DM and T2DM?
T1DM: AI disease that causes immune-mediated destruction of pancreatic B-cells => absolute deficiency of insulin.
- T- cells lose self-tolerance against antigens on B- cells
T2DM: Caused by combination of resistance to insulin & inadequate secretory response by B-cells => relative insulin deficiency.
T1DM
- Onset:
- AutoAB:
- Pathology:
-
Onset
- Usually childhood & adolesnce
-
AutoAB
- Anti-insulin ab
- Anti-GAD ab
- anti-ICA512 ab
-
Pathology
- Insulitis (inflammtory infiltrate of T-cells and MO)
- B-cell depletion
- Islet atrophy
T1DM
- Genetics:
-
Clinical:
- Weight
- Insulin levels
- DKA?
-
Genetics
- MHC class II; HLA-DR3 or DR4 with DQ8.
-
Clinical
- NL or WL
- Progressive ↓ in insulin
- Severe and w/o insulin therapy: DKA
T2DM
- Onset:
- AutoAB:
- Pathology:
-
Onset:
- Adult, but increasing incidence in childhood and adolescence
-
AutoAB:
- None
-
Pathology:
- No insulitis
- Amyloid deposits
- Mild B-cell deposition
T2DM
- Genetics:
-
Clinical:
- Weight
- Insulin levels
- DKA?
Genetics:
- Genetics AND environment are important
- Strong familial predisposition: majority have a 1st degree relative with T2DM
- Obesity (esp central) = major RF
Clinical:
- 80% are obese
- Early = ↑ in blood insulin bc of B-cell compensation; Later = NL/moderate ↓ in insulin bc B-cell exhaustion
- Severe => hyperglycemic hyperosmotic syndrome (HHS)
Pancreas must be ___ destroyed to give overt T1DM symptoms (Hyperglycemia + ketosis)
>90%
Which type of diabetes (T1DM or T2DM) has a stronger genetic component?
T2DM —> disease concordance >90% in monozygotic twins
What are the 2 cardinal metabolic defects that characterize T2DM?
- - ↓ response of peripheral tissues, especially skeletal m., adipose, and liver to insulin = insulin resistance
- - Inadequate insulin secretion in the face of insulin resistance and hyperglycemia = β-cell dysfunction
What causes insulin resistance in T2DM?
Obesity and excess adipocytes cause:
- ↑ in bad adipokines => promote hyperglucemia and
- ↓ in toxic FFA => release cytoines => + inflammasome => secretion of IL-1β => release of pro-inflammatory cytokines =>
- Inflammation: damages B cells and end organs => ↓ response to insulin
Insulin resistance in T2DM results in what?
- Liver = no gluconeogenesis: high fasting blood glucose levels
- Skeletal muscle = failure of glucose uptake and glycogen synthesis after a meal => high post-prandial blood glucose levels
- Adipose tissue = activation of “hormone-sensitive” lipase is NOT inhibited => excess TAG breakdown and FFA.