Metabolism

Question 1

Insulin

Answer 1

Synthesized and released by the pancreas

Islets of Langerhans

β-cells

Secretion increases during the absorptive state

Most important regulator of metabolism

Question 2

Plasma Glucose Control Over Insulin Secretion

Answer 2

1. High plasma glucose stimulates insulin secretion from pancreatic islet beta cells
2. Plasma insulin increases
3. Insulin stimulates adipocytes (fat cells) and muscle cells (skeletal & cardiac) to take up glucose
4. Insulin also inhibits glucose release from the liver
5. Plasma glucose level drops

Question 3

Insulin Secretion Stimulated by:

Answer 3

1. Plasma glucose
2. Plasma amino acids
3. Incretins: hormones secreted from small intestine
   - GLP-1 (Glucagon-Like Peptide-1) &
   -GIP (Glucose-Dependent Insulinotropic Polypeptide)
4. Parasympathetic activity

Question 4

Insulin Secretion Inhibited by:

Answer 4

Sympathetic activity
1. Directly via SNS neurons
2. Increased plasma epinephrine

Question 5

Responses of Target Cells to Insulin

Answer 5

Muscle cells
* Take up glucose
* Direct use in aerobic respiration
* Storage as glycogen
* Take up amino acids
* Synthesize proteins

Adipocytes (fat cells)
* Take up glucose
* Synthesize fatty acids
* Make fatty acids in the plasma
* Fat cells take up and store

Liver cells
* Synthesize glycogen
* Synthesize fatty acids

Question 6

Glycogenolysis

Answer 6

The process where the body breaks down glycogen, a stored form of carbohydrates, into glucose to provide energy

Question 7

Gluconeogenesis

Answer 7

A metabolic process where glucose is synthesized from non-carbohydrate sources like lactate, certain amino acids, and glycerol.

Question 8

1- Glucagon

Answer 8

Synthesized and released by the α-cells

Secretion increases during the post-
absorptive state

Maintains blood glucose during fasting

Question 9

Plasma Glucose Control Over Glucagon Secretion

Answer 9

1. Low plasma glucose stimulates glucagon secretion from pancreatic islet alpha cells
2. Plasma glucagon increases
3. Glucagon stimulates liver cells to:
4. Break down glycogen into free glucose (glycogenolysis)
   & release it
5. Make new glucose & release it
6. Make new ketones & release them
7. Plasma glucose & ketone levels increase

Question 10

2- (catecholamines)

Answer 10

Stimulated by:
* Low plasma glucose
* Glucose receptors sense levels
Increases in:
* Plasma epinephrine
* SNS activity to liver & adipose tissue
* Glycogenolysis
* Gluconeogenesis
* Lipolysis