homeostasis 6C Flashcards
What is homeostasis?
The maintenance of a stable internal environment within narrow limits.
Why is homeostasis important?
Keeps enzymes working at optimum conditions and prevents damage to cells or organs.
What is the normal blood glucose concentration in humans?
Around 90 mg per 100 cm³ of blood.
What are the hormones involved in blood glucose regulation?
Insulin (lowers blood glucose) and glucagon (raises blood glucose), both secreted by the pancreas.
What cells in the pancreas secrete insulin and glucagon?
Beta cells secrete insulin
Alpha cells secrete glucagon
How does insulin lower blood glucose concentration?
Binds to receptors on liver/muscle cells
Increases permeability to glucose by inserting GLUT4 transporters
Activates enzymes that convert glucose to glycogen (glycogenesis)
Increases rate of respiration of glucose
How does glucagon raise blood glucose levels?
Binds to receptors on liver cells
Activates enzymes for glycogenolysis (glycogen → glucose)
Promotes gluconeogenesis (amino acids/fats → glucose)
Decreases glucose uptake by cells
Which hormone uses the second messenger model and how?
Glucagon:
Activates an enzyme that converts ATP to cyclic AMP (cAMP)
cAMP activates protein kinase A → triggers glycogen breakdown
What is diabetes?
A condition where the body cannot regulate blood glucose properly.
What is Type 1 diabetes?
Autoimmune destruction of beta cells → little/no insulin made → blood glucose stays high.
How is Type 1 diabetes treated?
Insulin injections or pumps; regular blood sugar monitoring.
What is Type 2 diabetes?
Receptors become unresponsive to insulin; usually due to poor diet and inactivity.
How is Type 2 diabetes treated?
Healthy diet, weight loss, regular exercise, sometimes medication.
What method is used to detect glucose in urine?
Benedict’s test:
Add Benedict’s reagent and heat
If glucose is present, solution turns brick red
Use colorimetry for quantitative results
Why must body temperature be controlled?
To maintain enzyme activity — too high and enzymes denature; too low and enzyme activity slows.
Where is body temperature regulated?
In the hypothalamus.
How is temperature detected?
Thermoreceptors in the skin and hypothalamus detect changes and send nerve impulses to effectors.
What happens when body temperature is too high?
Sweating: increases heat loss by evaporation
Vasodilation: arterioles near skin surface widen → more heat lost
Hair erector muscles relax: hair lies flat → less insulation
What happens when body temperature is too low?
Shivering: muscles contract → heat produced by respiration
Vasoconstriction: arterioles constrict → less blood to skin
Hair erector muscles contract: hair stands up → traps insulating air
What is osmoregulation?
The control of water and salt concentrations in the blood.
What organ controls water reabsorption?
The kidney, specifically in the nephron.
What hormone regulates water reabsorption?
ADH (antidiuretic hormone)
Where is ADH produced and released?
Produced by the hypothalamus, released by the posterior pituitary.
How does ADH increase water reabsorption?
Binds to receptors in distal convoluted tubule and collecting duct
Triggers insertion of aquaporins into membranes
Makes the membrane more permeable to water → more water reabsorbed into blood
What triggers ADH release?
Osmoreceptors in hypothalamus detect low water potential → ADH is released.
What is negative feedback?
A mechanism that restores conditions to their normal level after a change.
Why is negative feedback important?
It keeps conditions like blood glucose and temperature stable despite external changes.
Can negative feedback involve multiple effectors?
Yes – having multiple effectors gives more control and allows finer regulation.
