1. The Endocrine System Pancreatic Islets

2. Pancreatic Islets
The pancreas is a mixed gland and has both endocrine and exocrine functions
The pancreatic islets produce hormones
Insulin —allows glucose to cross plasma membranes into cells from beta cells
Glucagon —allows glucose to enter the blood from alpha cells
These hormones are antagonists that maintain blood sugar homeostasis

3. Pancreatic Islets
Insulin —allows glucose to cross plasma membranes into cells from beta cells
Glucagon —allows glucose to enter the blood from alpha cells
Figure 9.14a–b

4. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood
Uptake of glucose from blood is en- hanced in most body cells
Blood glucose levels decline to set point; stimulus for insulin release diminishes
Elevated blood sugar levels
Liver takes up glucose and stores it as glycogen
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Imbalance
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Stimulus: declining blood glucose levels (e.g., after skipping a meal)
Imbalance
Low blood sugar levels
Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes
Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver
Liver breaks down glycogen stores and releases glucose to the blood
Figure 9.15

5. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Figure 9.15, step 1

6. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Elevated blood sugar levels
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Imbalance
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Figure 9.15, step 3

7. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood
Elevated blood sugar levels
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Imbalance
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Figure 9.15, step 4

8. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood
Uptake of glucose from blood is en- hanced in most body cells
Elevated blood sugar levels
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Imbalance
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Figure 9.15, step 5

9. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood
Uptake of glucose from blood is en- hanced in most body cells
Elevated blood sugar levels
Liver takes up glucose and stores it as glycogen
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Imbalance
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Figure 9.15, step 6

10. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood
Uptake of glucose from blood is en- hanced in most body cells
Blood glucose levels decline to set point; stimulus for insulin release diminishes
Elevated blood sugar levels
Liver takes up glucose and stores it as glycogen
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Figure 9.15, step 7

11. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Stimulus: declining blood glucose levels (e.g., after skipping a meal)
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Low blood sugar levels
Figure 9.15, step 9

12. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Stimulus: declining blood glucose levels (e.g., after skipping a meal)
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Low blood sugar levels
Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver
Figure 9.15, step 10

13. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Stimulus: declining blood glucose levels (e.g., after skipping a meal)
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Imbalance
Low blood sugar levels
Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver
Liver breaks down glycogen stores and releases glucose to the blood
Figure 9.15, step 11

14. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Stimulus: declining blood glucose levels (e.g., after skipping a meal)
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Low blood sugar levels
Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes
Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver
Liver breaks down glycogen stores and releases glucose to the blood
Figure 9.15, step 12

15. Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood
Uptake of glucose from blood is en- hanced in most body cells
Blood glucose levels decline to set point; stimulus for insulin release diminishes
Elevated blood sugar levels
Liver takes up glucose and stores it as glycogen
Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts)
Imbalance
Homeostasis: Normal blood glucose levels (90 mg/100ml)
Stimulus: declining blood glucose levels (e.g., after skipping a meal)
Imbalance
Low blood sugar levels
Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes
Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver
Liver breaks down glycogen stores and releases glucose to the blood
Figure 9.15, step 13