LECTURE 9 (Insulin & Glucagon) Flashcards
Which 2 parts does the Pancreas consist of?
Exocrine & Endocrine
Describe the Endocrine part of the pancreas
- Secretes hormones
- Made up of “Islets of Langerhans”
- Include Beta cells, Alpha cells and Delta cells
What are the different cell types in the endocrine part of the pancreas?
- Beta cells = secrete insulin (most abundant) & is centrally located
- Alpha cells = secrete glucagon
- Delta cells = secrete somatostatin
What differentiates insulin from glucose?
Unlike glucose, insulin does not cross the placenta
What are the properties of Insulin?
- Protein hormone
- Insulin + C-peptide are increased insulinoma, whereas exogenous insulin lacks C-peptide
- Insulin structure: alpha chain, beta chain, disulphide bridges & C-peptide
What is C-peptide?
“connecting” peptide which has a long half-life and is an indicator of INSULIN PRODUCTION
Describe how insulin in formed
1) Synthesised as “PREPROINSULIN” made by ribosomes of the RER and is then cleaved into “PROINSULIN”
2) Proinsulin is transported to the Golgi apparatus and packaged into secretory granules
3) Proinsulin is cleaved -> exocytosis of INSULIN + C-PEPTIDE equally
Describe Insulin secretion by pancreatic B cells
Glucose enters B cells -> Increased ATP generated from glucose metabolism closes K+ channels (target of SULFONYLUREAS) and depolarises B cell membrane -> Voltage-gated Ca2+ channels open -> Ca2+ influx and stimulation of insulin exocytosis
[more glucose -> more insulin release]
What is insulin also release in response to apart from glucose?
Amino acids
[especially when glucose + amino acids]
Production of insulin is inhibited by ______________
Epinephrine
What increases and decreases insulin release?
- Beta-2-receptors = increase insulin release
- Alpha-2-receptors = decrease insulin release
[alpha effect is the dominant effect in the pancreas]
What is the result of the Fight or flight response?
Increased plasma glucose
Explanation: If you’re feeling stressed, your body releases stress hormones like cortisol and adrenaline. This should give you an energy boost for a ‘fight or flight’ response. But the hormones actually make it harder for insulin to work properly, known as insulin resistance -> decrease use of glucose for insulin release -> increased plasma glucose
Describe GLUT 1
Insulin-dependent
FOUND IN:
- Blood
- Blood-brain barrier
- Heart (lesser extent)
Describe GLUT 2
- Insulin-dependent
- High Km
- Low affinity
FOUND IN:
- Liver
- Pancreas
- Small intestine
Describe GLUT 3
- Insulin-dependent
- Low Km
- High affinity
FOUND IN:
- Brain
- Neurons
- Sperm