Hormonal Communication Flashcards
What is endocrine communication ?
- Specialised glands secrete hormones into bloodstream
- Circulatory system carries hormone to target cell/ tissue
- Lipid-soluble steroid hormones diffuse into the cell & bind to complementary receptor in cytoplasm. Peptide hormones bind to complementary receptor on cell-surface membrane
Describe the structure of the adrenal glands
- Located above the kidneys
- A central medulla and an outer cortex, blood vessels located in the medulla
What hormone does the medulla secrete ?
Adrenaline in response to danger, stress or excitement as part of the fight or flight response
Which hormones does the cortex secrete ?
The cortex produces steroid hormones
Aldosterone - controls concentrations of Na+ & K+ ions in the blood
Cortisol - which stimulates an increase in blood glucose concentration
Why is it important that blood glucose concentration remains stable ?
- Maintains constant blood water potential prevents osmotic lysis/ cremation of cells
- Maintain constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions
Define negative feedback
- Self-regulatory mechanisms return internal environment to optimum when there is a fluctuation
- Receptors detect whether a specific level is too low or too high
- This information is communicated through the hormonal or nervous system to effectors
- Effectors react to counteract the change by bringing the level back to normal
Define glycogenesis, glycogenlysis and glucoseogenesis
- Glycogenesis: liver converts glucose into the storage polymer glycogen
- Glycogenolysis: liver hydrolyses glycogen into glucose which can diffuse into blood
Gluconeogenesis: liver converts glycerol & amino acids into glucose
Outline the role of glucagon when blood glucose concentration decreases
- Alpha cells in islets of Langerhans in pancreas detect decrease & secrete glucagon into blood stream
- Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis
- Glucose diffuses from the liver into the bloodstream
- Alpha cells detect that blood glucose concentration has returned back to optimum & stop producing glucagon (negative feedback)
Use the secondary messenger model to explain how glucagon works
- Hormone-receptor complex forms
- Conformational change to receptors activates G-protein
- Activates enzyme adenylate cyclase, which converts ATP to cyclic AMP (cAMP)
- cAMP activates protein kinase A pathway
- Results in glycogenolysis
Outline what happens when blood glucose concentration increases
- Beta cells in islets of Langerhans in pancreas detect increase & secrete insulin into bloodstream
- Insulin binds to surface receptors on target cells on:
A. Increase cellular glucose uptake (facilitated diffusion)
B. Activate enzymes for glycogenesis (liver & muscles)
C. Stimulate adipose tissue to synthesise fat
Describe how insulin leads to a decrease in blood glucose concentration
- Increase permeability of cells to glucose
- Increases glucose concentration gradient e
- Triggers inhibiton of enzymes for glycogenolysis
How is insulin secretion controlled ?
- Beta cells have K+ & Ca2+ ion channels to maintain p.d. -70mV
- As glucose concentration increases, glucose enters Beta cells via facilitated diffusion
- Respiration of glucose produces ATP. ATP-gated K+ ion channels close, so K+ ions have no longer diffuse out of cell
- P.d. In cells becomes more positive = depolarisation. Ca2+ ion channels open. Ca2+ triggers exocytosis of insulin
Describe the exocrine function of the pancreas
Secretes digestive enzymes e.g. amylase, trypsin & lipase to the duodenum via pancreatic tract
Explain the causes of Type 1 diabetes mellitus and how it can be controlled
Body cannot produce insulin e.g. due to autoimmune response which attacks Beta cells of islets of langerhans
Treat by injecting insulin from animal source or genetically modified bacteria. Possible future treatment: use stem cells to produce new Beta cells
Explain the causes of Type 2 diabetes mellitus and how it can be controlled
- Glycoprotein receptors are damaged or become less responsive to insulin
- Strong positive correlation with poor diet/obesity
- Treat by controlling diet and exercise regime
