hormonal communication

the role of endocrine glands in the pancreas 

they secrete insulin and glucagon directly into the blood

role of exocrine glands in the pancreas 

they secrete digestive enzymes and sodium hydrogen carbonate into the pancreatic duct which travels to the small intestine 

where is adrenaline released from

the adrenal medulla in the adrenal glands

name some effects of adrenaline

• responsible for ‘fight or flight’

• increase stroke volume and heart rate - more blood pumped around the body faster

• general vasoconstriction - increases blood flow to skeletal muscles, making them contract faster

• dilates pupils - more light can enter the eye

• inhibited activity of the gut - blood is sent to more essential places like the muscles

what are the three stages of communication by chemical messengers 

• reception - a chemical message binds (complementary shape) to a receptor (glycoprotein) on the cell surface

• transduction - the binding of the signal molecule alters the receptor molecule. the signal usually starts a cascade of reactions

• response - the transduction pathway finally triggers a response which can vary from ‘turning on’ a gene, activating an enzyme etc

describe the action of adrenaline

• adrenaline binds to it’s receptor on the CSM of the target cell, creating an adrenaline-receptor complex

• the receptor activates a G protein on the inside of the membrane

• the G protein activates adenylate cyclase (an enzyme in the membrane)

• adenylate cyclase converts ATP into cyclic AMP (cAMP) - this is the second messenger 

• cAMP activates protein kinase A (PKA) 

• PKA activates phosphorylase kinase 

• this converts inactive phosphorylase into active phosphorylase 

• active phosphorylase catalyses the conversion of glycogen into glucose 

• glucose is used in respiration

describe a first messenger

• e.g. adrenaline

• a hormone/chemical messenger that transmits a signal around the body

• cannot enter cells 

describe a second messenger

• e.g. cAMP

• a molecule which transmits a signal inside the cell, usually activates other enzymes

describe the response to a rise in blood glucose levels

• high blood glucose detected by beta cells of the islets of Langerhans 

• beta cells in pancreas stimulated to release insulin into the blood

• most body cells take up more glucose and the liver takes up glucose and stores it as glycogen

• blood glucose level declines to a set point; stimulus for insulin release diminishes and body returns to homeostasis

describe the response to a decline in blood glucose levels

• low blood glucose level detected by alpha cells of islets of Langerhans

• alpha cells in pancreas stimulated to release glucagon into the blood; target is the liver

• liver breaks down glycogen stores and releases glucose into the blood

• blood glucose levels rise to a set point; stimulus for glucagon release diminishes and body returns to homeostasis

describe glycogenesis

a process where glucose is converted into glycogen for storage

describe glycogenolysis

the breakdown of glycogen into glucose for energy

what is gluconeogenesis

the formation of glucose from alternative sources e.g. amino acids and glycerol