5.1.4 Hormonal Communication Flashcards
What is endocrine communication ?
•Specialised glands secrete hormones into bloodstream
•Circulatory system carries hormone to target cell / tissue.
What hormones do the adrenal cortex secrete ?
•Mineralocorticoids that target kidneys and control Na+ / K+ concentration in blood
•Glucocorticoids (cortisol) that stimulate an increase in blood glucose concentration .
Why is it important that blood glucose concentration remains stable ?
•Maintain constant blood water potential, preventing osmotic lysis
•Maintain constant concentrations of respiratory substrates: organism maintains constant level of activity regardless of environmental conditions.
Define negative feedback
•Self regulatory mechanisms return internal conditions to optimum when there is a fluctuation
•Different mechanisms are responsible for dealing with an increase / decrease.
Define glycogenesis
When the liver converts glucose into the storage polymer glycogen
Define glycogenolysis
When the liver hydrolyses glycogen into glucose which can diffuse into the blood
Define gluconeogenesis
When the liver converts glycerol and amino acids into glucose
Outline the role of glucagon in blood blood glucose concentration falls [4]
• Alpha cells in the Islets of Langerhans of pancreas detect decrease and secrete glucagon into blood
•Glucagon binds to surface receptors on liver cells and activates enzymes for glycogenolysis and glyconeogenesis
•Glucose then diffuses from liver to blood
•Alpha cells detect the blood glucose increase and stop producing glucagon.
Use the secondary messenger model to explain how glucagon works [5]
•Hormone receptor complex forms
•Conformational change to receptor activates G-Protein
•This activates adenylate cyclase which converts ATP into cyclic AMP (cAMP)
•cAMP activates protein kinase A pathway
•This results in glycogenolysis.
Outline what happens when blood glucose concentration increases
•Beta cells in the Islets of Langerhans of pancreas detect increase and secrete insulin into bloodstream
•Insulin binds to surface receptors (liver/skeletal muscle) to:
a) increase cellular glucose uptake
b) activate enzymes for glycogenesis
c) stimulate adipose tissue to synthesise fat.
Describe how insulin leads to a decrease in blood glucose concentration
•Increases permeability of cells to glucose
•Increases glucose concentration gradient (glycogen forms)
•Triggers inhibition of enzymes for glycogenolysis.
How is insulin secretion controlled ?
•Beta cells have K+ and Ca2+ ion channels to maintain p.d. of -70mV
•As glucose concentration increases, glucose enters cells via facilitated diffusion
•Respiration of glucose produces ATP. ATP gated K+ channels close so K+ no longer diffuses out of cell
•P.d. of cell increases, depolarisation. Ca2+ voltage gated channels open, Ca2+ causes exocytosis of insulin.
Describe the exocrine function of the pancreas
Secretes digestive enzymes eg amylase and lipase to the duodenum via the pancreatic tract.
Explain the causes of type 1 diabetes and how it can be controlled
•The body cannot produce insulin due to autoimmune response which attacks beta cells of Islets of Langerhans
•It is treated by injecting insulin from animals or genetically modified bacteria.
•In the future stem cells may be used to make new beta cells.
Explain the causes of type 2 diabetes and how it can be controlled
•Gluvoprotein receptors are damaged or become less positive to insulin
•Strong positive correlation between poor diet / obesity
•Treat by controlling diet and exercise regime.
