Hormonal Communication Flashcards
What is an endocrine system?
A communication system using hormones as signalling molecules
Distinguish between endocrine glands and exocrine glands
Endocrine: release hormones directly into the blood; which travel through blood to target cells
Exocrine gland: secrete products (not hormones) into ducts which carry them straight to target cells on the epithelium of body surfaces. Eg. Mammary glands secrete milk onto breast surface
Explain how the pancreas can be described as an exocrine gland?
Small groups of cells called Acini surrounding tubules at their centre, which connect to form the pancreatic duct
Cells of the acini synthesise & secrete the following enzymes:
- amylase (digests amylose to maltose)
- trypsinogen (inactive protease converted to trypsin when enters duodenum)
- lipase (digests lipids)
- sodium hydrogencarbonate (alkali to neutralise contents of digestive system that have just left the stomach)
Explain how the pancreas can be described as an endocrine gland?
Alpha cells in islets of langerhans release glucagon hormone directly into blood
Beta cells in islets of langerhans release insulin directly into blood
Explain how insulin is secreted from the beta cells
- Normally K+ channels are open and Ca2+ channels closed; K+ diffuses out making inside negative compared with outside (-60mV)
- When glucose conc. outside cell is high, glucokinase detects & increases glucose metabolism to produce ATP
- extra ATP causes K+ channels to close
- K+ no longer diffuses out; inside gets less negative, opening the voltage gated Ca2+ channels
- Ca2+ enters cell & binds to insulin vesicles, causing them to move to cell membrane & fuse with it, releasing insulin into blood by exocytosis.
Describe the structure of pancreatic tissue
Islet of langerhans at centre = group of alpha & beta cells with a capillary network within it
Dispersed around the islet of langerhans are acini; small groups of exocrine cells with a tubule in the middle - eventually all tubules join to form pancreatic duct leading to duodenum
Define gluconeogenesis, glycogenolysis, & glycogenesis
Gluconeogenesis: generation of glucose molecules from non-carbohydrate biomolecules; amino acids & fats
Glucogenolysis: glycogen converted to glucose
Glycogenesis: glucose converted to glycogen for storage
Distiguish between hypoglycaemia & hyperglycaemia and what are their effects? inconsciousness
Hypo: low glucose conc. for long periods of time - inadequate delivery of glucose to cells causing fatigue, impaired brain function (unconsciousness), seizures
Hyper: high glucose conc. for long periods of time - organ damage
If consistently high - diagnosed with diabetes mellitus
What is diabetes mellitus, and distinguish between type 1 & type 2
A condition in which blood glucose concentrations can’t be controlled
Type 1: autoimmune response in which immune system attacks beta cells - NO INSULIN PRODUCED (juvenile)
Type 2: late onset; insulin is produced but receptors not responsive to insulin - linked to obesity, lack of exercise, afro-carribean origin, family history, high sugar diet
State the 2 classes of hormones, giving 2 examples for each and how they impact target cells
Protein and peptide hormones: adrenaline, insulin, glucagon- insoluble in phospholipid bilayer so bind to receptors on membrane, releasing a second messenger inside the cell.
Steroid hormones: oestrogen, testosterone- can pass through plasma membrane & enter nucleus to have a direct on DNA
Why are non-steroid hormones known as first messengers?
& describe how cAMP acts as a second messenger
They bind to receptors on plasma membrane & releasing a second messenger molecule, which initiates the effect inside the cell
Usually act via the G protein in the plasma membrane- it is activated when the hormone binds- which then activates the enzyme adenyl cyclade to convert ATP to cAMP; cAMP is the 2nd messenger, which will then have an effect by either acting directly on a protein- eg ion channel, or initiating a cascade of reactions that alter cell activity
