Glucose Homeostasis

Question 1

Importance of glucose

Answer 1

Glucose is an important energy substrate

Particularly imp for CNS

Question 2

Threshold leaves for glucose

Answer 2

If glucose level falls below normal levels of 4-5 mmol/L ( hypoglycaemia) , then cerebral function is increasingly impaired

If blood glucose concentration is less than 2 mmol/L , unconsciousness, coma and ultimately death can occur

Question 3

Persistent hyperglycaemia results in

Answer 3

Diabetes mellitus

Question 4

Hormone that is hypoglycaemia

Answer 4

Insulin

Question 5

Hormones that are hyperglycaemic

Answer 5

Glucagon
GH
Cortisol
Catecholamines

Question 6

Which is the more prevalent form of diabetes

Answer 6

Type 2 Diabetes

Question 7

What kind of structure is the pancreas gland

Answer 7

Retroperitoneal structure

Question 8

What are the two types of cells in the pancreas

Answer 8

Exocrine acinar cells

Islet of Langerhans

Question 9

Pancreas

Answer 9

Most of pancreas generates exocrine secretions via duct to small intestine via the acinar cells - 98% of secretions including protease, amylase and lipas

Other clumps of cells are islets of langerhans but receive 10-15% of blood supply

Question 10

Types of cells in the islets of langerhans

Answer 10

Alpha cells (20%) which secretes glucagon 
Beta cells (60%) insulin 
Delta cells (10%) somatostatin

Question 11

Two types of junctions in the islets of langerhans

Answer 11

Gap junctions and tight junctions
Gap junctions allow small molecules to pass directly between cells
Tight junctions create small intercellular spaces

Paracrine and endocrine communication between islet cells

Question 12

What does insulin do

Answer 12

Stimulates growth and development and reduces blood glucose ( stimulates growth via IGF )

Question 13

What does glucagon do

Answer 13

Increases blood glucose

Question 14

What does somatostatin do

Answer 14

It inhibits both insulin and glucagon - negative feedback

Question 15

What happens when there is an increase in blood glucose on Beta cells

Answer 15

Glucagon +
GI hormones +
Increased plasma glucose +
Amino acids +
Sympathetic nervous system inhibits via a2 adrenoreceptors -
Somatostatin -
Parasympathetic stimulate toon enhances rate of insulin release

All act on B cells to release insulin

Question 16

What does insulin then do

Answer 16

Causes
Build up of glycogen stores
Breakdown of glucose
Increased uptake of glucose into cells by GLUT4

Increased protein synthesis
Reduction of breakdown of fat

Question 17

Reduction in blood glucose on alpha cells

Answer 17

What stimulates alpha cell secretion;

Parasympathetic nerve activity 
Amino acids
Decreased plasma glucose 
Some GI hormones
CCK
SNS activity 
PNS activity 

What inhibits the alpha cells secretion

Insulin
Somatostatin

Question 18

Effects of glucagon release

Answer 18

Increased gluconeogenesis by liver from amino acids
Increased glycogenolysis by liver
Increased lipolysis for gluconeogenesis

Question 19

Glucokinase and the stimulation of insulin release

Answer 19

Glucose binds to glut 2

Glucose phosphorylated to Glucose 6-P by glucokinase which is then used to produce ATP

ATP inhibits voltage gated potassium channel and so depolarisation occurs and calcium enters the beta cells and this stimulates insulin release

Question 20

Insulin and C peptide

Answer 20

Insulin is stored as pro insulin and when proteolytically cleaved, it forms C peptide and insulin

Question 21

What is the incretin effect

Answer 21

Gut hormones 
Secreted in response to nutrients in gut
Stimulates insulin and suppresses glucagon 
Increases satiety 
Useful in treatment of diabetes

Question 22

Insulin receptor

Answer 22

2 extra cellular alpha subunits
2 intra cellular beta subunit

Once insulin binds to alpha subunit there is a conformational change in the tyrosine kinase domains of beta subunits which undergo auto phosphorylation together with cellular proteins. This leads to the insertion of GLUT4 into the plasma membrane in the intracellular vesicles