Physiology 2 - Endocrine Pancreas

Question 1

The energy of the body is the energy input - the energy output. What determines our food intake?

Answer 1

Glucostatic Theory - Feeding centres suppressed/satiety centres promoted as blood [Glc] rises.

Lipostatic Theory - Fat stores decrease the drive to eat.

Question 2

How does increasing fat stores reduce the urge to eat?

Answer 2

Leptin (a peptide hormone) is released from fat stores and depresses the feeding centre.

Disruption of this hormone can lead to obesity

Question 3

What are the categories of energy output?

Answer 3

Cellular Work
Mechanical Work (Both muscular and intracellular)
Heat Loss

Question 4

Define Anabolic vs Catabolic Pathways?

Answer 4

Anabolic refers to synthesis of large molecules, largely for storage

Catabolic refers to breakdown of large molecules, largely for energy

Question 5

Define the absorptive & Post-absorptive state?

Answer 5

Absorptive State occurs after eating, ingested nutrients supply energy and the excess is stored.

Post-Absorptive (Fasting) occurs between meals where body stores are used for energy

Question 6

Describe and give examples of obligatory Glucose utilisers?

Answer 6

The Brain is the major Obligatory Glucose Utiliser.

It means it can’t use fats, carbs or protein for energy, hence why we require a constant blood Glucose level.

Question 7

What is the normal range of Blood Glucose?

Answer 7

Around 5mmol

(4.2-6.3ish)

Hypoglycaemia is considered below 3mM

Question 8

What hormones are responsible for regulating Blood glucose and where are they made?

Answer 8

Insulin & Glucagon are the major ones.

Made in Islets of Langerhans of the pancreas

Question 9

Describe the 4 cell types of the Islets of Langerhans?

Answer 9

Alpha cells - make glucagon
Beta cells - Make insulin
Delta cells - Make Somatostatin (GHIH)
F cells make Pancreatic Polypeptide

Question 10

What class of hormone are insulin/glucagon?

Answer 10

Peptide Hormones

Question 11

In short what is the function of insulin vs glucagon?

Answer 11

Insulin reduces Blood Glucose

Glucagon Increases Blood Glucose

Therefore they are both stimulated by the opposite level of blood glucose.

Question 12

How does Glucose trigger Insulin secretion by Beta Cells?

Answer 12

B cells contain ATP sensitive K+ channels.

1) High blood glucose enters cell
2) Metabolises to ATP
3) ATP closes K+ Channels, causing cell to depolarise
4) Voltage Dependant Ca2+ channels open & Ca2+ triggers Insulin-Vesicle Exocytosis

Question 13

Other than high blood [Glc] what else triggers insulin release?

Answer 13

• Increased plasma [amino acids]
• Glucagon
• Incretin Hormones e.g. CCK, Secretin, GIP & Gastrin
• Vagal Activity

Question 14

Glucagon has the opposite effect to insulin so why would it trigger insulin release?

Answer 14

Glucagon creates more glucose in the blood. Insulin is required for glucose uptake by cells so is needed for the new glucose to be used.

Question 15

Why do incretin hormones trigger insulin release?

Answer 15

So that the glucose being absorped from the gut doesn’t trigger a dangerous spike in blood [Glc]

Question 16

What are the 8 actions of insulin?

Answer 16

Glucose effects:

1) Increased Glc uptake in muscle/adipose
2) Increased Glycogenesis
3) Inhibits Gluconeogenesis
4) Increased TAG synthesis in adipose/liver

Protein:

5) Increased Amino acid uptake in muscle
6) ) Increased protein synthesis in muscle

Other:

7) Promotes K+ entry to cells
8) permissive effect on growth hormone

Question 17

How does insulin cause increased Glc uptake?

Answer 17

Insulin-Sensitive Tissues (muscle/adipose) have specific Tyrosine Kinase Receptors for insulin.
These stimulate GLUT-4 transporters to take up Glc

Question 18

The liver isn’t an Insulin-sensitive tissue, but it’s Glc uptake is still affected by insulin, how?

Answer 18

Insulin activates Hexokinase within the liver, this turns Glc to Glc-6-phosphate, creating a conc. gradient for Glc to enter the cell.

Question 19

What trigger’s release of Glucagon?

Answer 19

1) Low blood Glucose
2) High blood [amino acids]
3) Sympathetic innervation/Epinephrine on B2 receptors
4) Cortisol
5) Stress e.g. Exercise

Question 20

Why does a rise in blood amino acids trigger a release of both insulin & Glucagon?

Answer 20

Amino acids cause insulin release because it makes muscles take up more amino acids and form more proteins.

They also trigger glucagon release to counter the insulin so that it doesn’t cause hypoglycaemia

Question 21

How does Glucagon raise Blood Glc?

Answer 21

Triggers phosphorylation of enzymes responsible for:

1) Glycogenolysis
2) Gluconeogenesis
3) Lipolysis

Question 22

How is the ANS involved in the Islet cells?

Answer 22

Parasympathetic activity (via Vagus) during the anticipatory stage of digestion triggers insulin (and some glucagon) release.

Sympathetic innervation promotes glucagon & epinephrine while inhibiting insulin as part of the fight/flight response

Question 23

4 hormones are involved in the Glucose Counter-Regulation, what are they and how do they regulate glucose?

Answer 23

Glucagon - Liver glycogenolysis, Lipolysis and Gluconeogenesis

Epinephrine - Muscle/liver glycogenolysis, Gluconeogenesis & Lipolysis

Cortisol - Gluconeogensis, inhibits Glc uptake, lipolysis & Protein Catabolism

GH - Gluconeogenesis, Inhibition of Glc uptake & Lipolysis

Question 24

What is somatostatin?

Answer 24

A peptide hormone produced by delta cells in the pancreas and hypothalaus (aka GHIH)

Question 25

What does somatostatin do?

Answer 25

1) Slows absorption of nutrients in the gut to reduce blood Glc spikes
2) Suppresses insulin/glucagon in a paracrine fashion
3) Inhibits secretion of GH from Ant Pituitary

Question 26

We have described how blood glucose is controlled in the steady state, what happens during exercise?

Answer 26

Exercise does 2 things:

1) increases insulin sensitivty of muscle
2) Induces insulin-independant increase in GLUT-4 transporters

This effect lasts hours and regular exercise can cause prolonged increases in insulin sensitivity

Question 27

We have described how blood glucose is controlled in the steady state, what happens during starvation?

Answer 27

During starvation glucose drops.
In response the body breaks down adipose tissue to Fatty acids.
The liver converts FAs to Ketone bodies which the brain can adapt to use for energy.

Question 28

Summary of Insulin

Answer 28

Reduces Glucose levels in the blood as well as promoting Amino acid uptake and protein synthesis.
A peptide hormone produced in B cells in the pancreas

Question 29

Summary of Glucagon

Answer 29

Raises blood glucose and stimulates lipolysis.

A peptide hormone produced in a cells in the pancreas