Topic 7 - Endocrine Regulation: Insuline Secretion

Question 1

Learning Objectives

Answer 1

1. Describe the mechanisms that regulate insulin secretion in the pancreas
2. Outline the disease of diabetes and understand the differences between type 1 and 2 diabetes

Question 2

Pancreas

Answer 2

Contains islets
- Dense compactment of approx. 200 cells
- Islets contain Alpha, Beta and exocrine cells

Question 3

Principles of Beta cell function

Answer 3

Beta cells respond to multiple inputs to secrete insulin:
- Glucose
- Amino acids
- Hormones
- etc.

Beta cells adjust its output based on its inputs

Question 4

Process of Beta cells ‘sensing’ glucose to release insulin

Answer 4

1. Beta cells of the pancreas contain GLUT-2 Transporters
2. Glucose entres the beta cell through the GLUT-2 Transporter and is metabolised by the mitochondria, producing ATP from ADP
3. This leads to an increase of ATP in the cytosol, ATP then interacts with K-ATP Channels, closing them.
4. This causes the membrane potential to become more positive and depolarisation occurs.
5. As depolarisation occurs, Voltage dependant clacium channels open allowing for Ca2+ ions to entre the cell.
6. The Ca2+ concentration then builds up in the cell and promotes the release of insulin containing granules for exocytosis.
7. The insulin containing granules undergo exocytosis of the beta cell and the insulin is released into the blood stream.

Question 5

Type 1 Diabetes symtoms

Answer 5

• Urinating frequently
• Fatigue
• Weight loss
• Exessive thirst

Question 6

Type 1 Diabetes

Answer 6

• Autoimmune disease
• Early onset

1. Antigen presenting cells present to the immune system
2. The immune system responds
3. ‘B’ cells produce antibodies against presented beta cells
4. Once multiple antibodies start being produced, Type 1 diabetes occurs
5. Antibodies trigger the release of T cells which kill the presented beta cells
6. Eventually the T cells kill manu Islets and beta cells of the pancreas. Leading to uncontrolled blood glucose levels as the body struggles to produce sufficient insulin.

Question 7

Type 1 Diabetes treatment

Answer 7

The body has to rely on insulin pumps and/or injections as it cannot create its own.

Question 8

Type 2 Diabetes Symptoms

Answer 8

• Constant Hunger
• Slow wound healing
• Blurred vision
• Frequent urination
• Skin itching/ fungal & genetals
• Unexplained weight loss
• Numb hands and feet

Question 9

Type 2 Diabetes

Answer 9

• Late onset
• Body can still secrete insulin with beta cells. However the body becomes resistent to insulin
• Insulin will travel to skeletal muscle and fat cells, but will not react and not lead to the creation of more GLUT-4 Transporters
• Leading to elevated glucose levels over a long period of time
• Having constant high blood glucose leads to the symptoms of type 2 diabetes over time

Question 10

Pancreas Anatomy

(Not in outcomes)

Answer 10

1. Pancreatic Islets (Alpha, Beta, Exocrine)
2. Spleen
3. Acinar cells
4. Pancreatic Duct
5. Duodenum of small intestine
6. Common bile duct
7. Bile duct (from gall bladder)
8. Pancreas
9. Splenic artery

Question 11

Process of insulin on GLUT-4 Production

Answer 11

1. Insulin reaches an insulin receptor on a target cell (skeletal muscle or adipose) and triggers ‘GLUT-4 containing vessicles’ to fuse with the cell membrane
2. The vessicles begin to fuse with the cell membrane, releasing the GLUT-4 Transporters into the membrane
3. The vessicle has then dissapered and fully fused with the membrane, leaving its GLUT-4 transporters
4. More and more vessicles continue to fuse with the membrane, creating many GLUT-4 Transporters, leading to higher intake and diffusion levels of glucose.
5. The vessicles maintain a cycle of fission and fusion on the membrane.