Homeostasis Flashcards
(53 cards)
What is homeostasis?
The maintenance of internal environment within set limits around an optimum
Why is it important that core temperature remains stable?
- maintain stable rate of enzyme-controlled reactions & prevent damage to membranes
- temperature too low = enzyme & substrate molecules have insufficient kinetic energy
- temperature too high = enzymes denature
Why is it important that blood pH remains stable?
- maintain stable rate of enzyme-controlled reactions
- acidic pH = H+ ions interact with H-bonds & ionic bonds in tertiary structure of enzymes - shape of active site changes so no ES complexes form
Why is it important that blood glucose concentration remains stable?
- maintain constant blood water potential: prevent osmotic lysis/crenation 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
Define positive feedback
A fluctuation triggers changes that result in an even greater deviation from the normal level
Outline the general stages involved in negative feedback
Receptors detect deviation -> coordinator -> corrective mechanism by effector -> receptors detect that conditions have returned to normal
Suggest why separate negative feedback mechanisms control fluctuations in different directions
Provides more control especially in case of ‘overcorrection’ which would lead to a deviation in the opposite direction from the original one
Suggest why coordinators analyse inputs from several receptors before sending an impulse to effectors
- receptors may send conflicting information
- optimum response may require multiple types of effector
Why is there a time lag between hormone production and response by an effector
Takes time to:
- produce hormone
- transport hormone in the blood
- cause required change to the target protein
Name the factors that affect blood glucose concentration
- amount of carbohydrate digested from diet
- rate of glycogenolysis
- rate of gluconeogenesis
Define glycogenesis
Liver converts glucose into the storage polymer glycogen
Define glycogenolysis
Liver hydrolyses glycogen into glucose which can diffuse into blood
Define gluconeogenesis
Liver converts glycerol & amino acids into glucose
Define the role of glucagon when blood concentration decreases
- alpha cells in islets of Langerhans in pancreas detect decrease & secrete glucagon into bloodstream
- glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis
- glucose diffuses from liver into bloodstream
Outline the role of adrenaline when blood glucose concentration decreases
- Adrenal glands produce adrenaline which binds to surface receptors on liver cells & activates enzymes for glycogenolysis
- Glucose diffuses from liver into bloodstream
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 to:
a) increase cellular glucose uptake
b) activate enzymes for glycogenesis (liver & muscles)
c) stimulate adipose tissue to synthesise fat
Define how insulin leads to a decrease in blood concentration
- increases permeability of cells to glucose
- increases glucose concentration gradient
- triggers inhibition of enzymes for glycogenolysis
How does insulin increase permeability of cells to glucose?
- increases number of glucose carrier proteins
- triggers conformational change which opens glucose carrier proteins
How does insulin increase the glucose concentration gradient?
- activates enzymes for glycogenesis in liver & muscles
- stimulates fat synthesis in adipose tissue
Use the secondary messenger model to explain how glucagon and adrenaline work
- Hormone-receptor complex forms
- Conformational change to receptor activates G-protein
- Activates adenylate cyclase, which converts ATP to cAMP
- cAMP activates protein kinase A pathway
- Results in glycogenolysis
Explain the causes of type 1 diabetes and how it can be controlled
Body cannot produce insulin e.g due to auto immune responses which attacks beta cells of islets of langerhans
Treat by injecting insulin
Explain the causes of type 2 diabetes 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
Name some signs and symptoms of diabetes
- high blood glucose concentration
- glucose in urine
- polyuria
- polyphagia
- polydipsia
- blurred vision
- sudden weight loss
