blood glucose concentrations - HOMEOSTASIS

what type of cells does the Isle of Langerhans consist of?

Beta and Alpha cells

what cells detect an increase in blood glucose concentration?

Beta cells in the Isle of Langerhans

What cells detect a decrease in blood glucose concentration?

Alpha cell in the Isle of Langerhans

Define glycogenisis

conversion of glucose to glycogen

Define glyconeogenesis

the creation of new glucose from amino acids and lipids

Define homeostasis

maintaining a constant internal environment for cells in the body despite changes in the external environment

What is the function of B- cells in the isle of Langerhans?

Secrete insulin into the blood

Define negative feedback

a process in which a change in some parameter such as blood glucose concentration brings about processes which move its levels back towards normal again

What are insulin’s 2 main target organs?

Liver and skeletal muscle

Function of insulin

Increases uptake of glucose and increased conversion of glucose to glycogen

Function of Alpha cells in the isle of Langerhans?

stimulated to secrete a hormone called glucagon

What do beta cells do in response to blood glucose concentration falling?

stop secreting insulin

Define glycogenolysis?

Hydrolysis of glycogen into glucose

Function of adrenaline (blood glucose context)

(same effect as glucagon) converts stored glycogen to glucose by binding to a different receptor initially and causing enzyme activation and cascade

what types of proteins are adrenaline and glucagon?

peptide hormones - cannot pass through membrane

Can glucose diffuse through the phospholipid bilayer?

No - as it is polar

Difference between GLUT4 and GLUT2 proteins

GLUT4 is stored in vesicles within the cell whilst GLUT2 are lodged in the CSM

What type of proteins do Liver cells have that allow glucose passing through CSM?

GLUT2

Will insulin affect the concentration of GLUT2 proteins in liver cells?

No, as they are always in the CSM

Explain the effect of insulin on liver cells (5 marker)

• Insulin stimulates the activation of the enzyme glucokinase which phosphorylates glucose

• This traps glucose inside the cell

• insulin also stimulate phsophofructokinase and glycogen synthase

• this decreases blood glucose concentration to normal and this is detected by B cells and insulin secretion is stopped

• insulin still circulating in the blood is excreted by the kidneys

What is glucagon and how does it attach to cells?

Glucagon is a peptide hormone which binds to receptors in the CSM

define kinases

Enzymes that transfer phosphate group from ATP to an acceptor

define phosphorylase’s

enzymes that break down glycogen to glucose - 1 - phosphate

Explain the effect on glucagon in cell signalling

• glucagon receptor activates another protein embedded in the membrane known as G-protein

• G-protein activates adenylyl cyclase

• activated adenylyl cyclase catalyses the formation of cAMP from ATP in the cell cytoplasm

• cAMP is a second messenger

• cAMP activates protein kinase A enzymes by binding to them

• protein kinase A enzymes activate other kinase enzymes by phosphorylating them which activates other enzymes such as glycogen phosphorylase

• this is an enzyme cascade and acts to amplify the original hormone signal

• glycogen in liver is hydrolyses to glucose - 1 phosphate by glycogen phosphorylase

• Glucose-1-phosphate is converted to glucose

• GLUT2 transportes in CSM allow glucose to diffuse out of the cell into the blood

• blood glucose concentration increases.

What is cAMP and its function?

a second messenger that activates protein kinase A enzymes by binding to them

what is the function of adenylyl cyclase?

It is activated to catalyse the formation of cAMP from ATP in cell cytoplasm

where is cAMP made?

cell cytoplasm

what is the purpose of an enzyme cascade?

to amplify the original hormone signal