The Endocrine Pancreas

Question 1

Define body energy

Answer 1

Energy intake minus energy output

Question 2

What hypothalamic centres control energy intake?

Answer 2

Feeding centre- promotes feeling of hunger

Satiety centre- promotes feeling of fullness

Question 3

Describe the glucostatic theory of energy balance

Answer 3

Food intake is determined by blood glucose- as [BG] increases, the drive to eat decreases

Question 4

Describe the lipostatic theory of energy balance

Answer 4

Food intake is determined by fat stores: as fat stores increase, the drive to eat decreases. Leptin is a peptide hormone secreted by fat stores that depresses feeding activity

Question 5

What are the three categories of energy output?

Answer 5

Cellular work
Mechanical work 
Heat loss (associated with cellular and mechanical work- accounts for half of energy output)

Question 6

When in the feeding cycle is the body in an anabolic and a catabolic state?

Answer 6

After eating we enter an anabolic state to store food

Between meals and overnight we enter a catabolic state to break down food to use body stores

Question 7

Through what processes is blood glucose maintained?

Answer 7

Synthesising glucose from glycogen (glycogenesis) or amino acids (gluconeogenesis)

Question 8

What is the given normal range for blood glucose, and what value is considered to be hypoglycaemic?

Answer 8

Normal= 4.2-6.3mM
Hypoglycaemia= <3mM

Question 9

Where are the hormones for the endocrine pancreas produced?

Answer 9

In the islets of Langerhans

Question 10

What are the four types of islet cells and what does each produce?

Answer 10

Alpha cells- glucagon
Beta cells- insulin
Delta cells- somatostatin
F cells- pancreatic polypeptide

Question 11

What two substances control the balance of blood glucose, and in which state is each more prominent?

Answer 11

Insulin and glucagon
Insulin dominates in fed state
Glucagon dominates in fasted state

Question 12

What are the stimuli for insulin secretion?

Answer 12

Blood glucose concentration (most major stimulus)
Glucagon
[Amino acids] plasma
Vargas nerve activity

Question 13

How is excess glucose stored?

Answer 13

As glycogen in the liver and muscle

As triacylglycerols in the liver and adipose tissue

Question 14

Describe the mechanism of control of insulin secretion by [BG]

Answer 14

B cells have a specific type of potassium ion channel that is sensitive to [ATP] within the cell known as the K ATP channel
When glucose is abundant it enters cells through GLUT and metabolism increases, increasing [ATP] within the cell, causing the K ATP channel to close. This leads to a build up of Intracellular [K+], depolarising the cell. Voltage-dependent Ca2+ channels then open and trigger insulin vesicle exocytosis into the circulation.

Question 15

Describe the primary action of insulin

Answer 15

Insulin binds to tyrosine kinase receptors on the cell membrane of insulin-sensitive tissues and stimulates the mobilisation of GLUT-4, which usually resides in the cytoplasm of unstimulated cells. When stimulated, it migrates to the membrane and is able to transport glucose into the cell. When insulin stimulation stops, the GLUT-4 transporters return to the cytoplasm.

Question 16

What types of tissue are sensitive to insulin?

Answer 16

Muscle and fat

Question 17

How does the liver take up insulin?

Answer 17

Through GLUT 2 transporters

Question 18

What are the main additional actions of insulin?

Answer 18

Increases glycogen synthesis in muscle and liver. Stimulates glycogen synthase and inhibits glycogen phosphorylase
Increases amino acid uptake into muscle, promoting protein synthesis
Increases protein synthesis and inhibits proteolysis
Increases triacylglycerol synthesis in adipocytes and liver
Inhibits the enzymes of gluconeogenesis in the liver
Has a permissive effect on growth hormone
Promotes potassium ion entry into cells by stimulating sodium/potassium ATPase

Question 19

What are the stimuli than inhibit insulin release?

Answer 19

Low [BG]
Somatostatin
Sympathetic a2 effects
Stress eg hypoxia

Question 20

What is the function of glucagon and where is its main site of action?

Answer 20

Primary function is to raise blood glucose

Main site of action is liver

Question 21

Describe the main characteristics of glucagon receptors

Answer 21

They are G-protein coupled receptors linked to adenylate cyclase/cAMP system which phosphorylates specific liver enzymes when activated

Question 22

What are the results of activation of glucagon receptors?

Answer 22

Increased glycogenolysis
Increased gluconeogenesis
Formations of ketones from fatty acids

Question 23

What are the effects of amino acids on secretion of insulin and glucagon?

Answer 23

Amino acids in plasma stimulate the release of both insulin and glucagon

Question 24

What stimuli promote glucagon release?

Answer 24

Low [BG]
High [amino acids]
Sympathetic innervation and epinephrine 
Cortisol 
Stress eg exercise

Question 25

What stimuli inhibit glucagon release?

Answer 25

Glucose
Free fatty acids and ketones
Insulin
Somatostatin

Question 26

Describe the parasympathetic innervation of islet cells

Answer 26

Increased parasympathetic activity through the vagus nerve leads to increased insulin secretion and to a lesser extent, increased glucagon secretion. This is in association with the anticipatory phase of digestion

Question 27

Describe the sympathetic activity of islet cells

Answer 27

Increased sympathetic activity promotes glucose metabolisation, leading to increased glucagon and increased epinephrine and inhibition of insulin.

Question 28

What is the main pancreatic function of somatostatin?

Answer 28

To inhibit activity in the GI tract to slow down absorption and prevent exaggerated leaks in plasma concentrations of nutrients

Question 29

How does exercise alter glucose uptake?

Answer 29

In active muscle, GLUT4 transported can migrate to the membrane without insulin being present, so exercise causes uptake of glucose independent of insulin

Question 30

What is the energy source for the brain in periods of prolonged starvation?

Answer 30

Ketones

Question 31

How is energy sourced during periods of starvation?

Answer 31

When nutrients are scarce, the body relies on stores for energy and breaks down adipose tissue into fatty acids. Free fatty acids can be used readily by most tissues to produce energy, and the liver will convert the excess to ketone bodies to provide energy for the brain

Question 32

Describe the effect of poorly controlled insulin-dependent diabetes on ketone absorption

Answer 32

A lack of insulin deceases the rate of uptake of ketones, meaning that they accumulate in the plasma and cause life threatening acidosis due to their acidic nature