Homeostasis Flashcards
Negative feedback
Returns a condition to its set point when it increases above or below it
Positive feedback
Change in conditions moves further from set point
Homeostasis
Maintenance of a constant internal environment
Why is homeostasis necessary?
- Maintain water potential
- Maintain temperature
- Maintain blood-glucose levels
Endotherms
Maintain body temperature at a set point
Ectotherms
Rely on external heat energy
What controls body temperature in humans?
The thermostat in the hypothalamus
Second messenger action
- adrenaline approaches receptor site
- adrenaline fuses to receptor site, activates enzyme inside membrane
- enzyme converts ATP to cAMP which acts as the second messenger
- cAMP activates other enzymes which carry out glycogenolysis
Where are the hormones secreted from?
Islets of Langerhans
Alpha cells
Secrete glucagon
Beta cells
Secrete insulin
Rise in blood-glucose
- Detected by B cells in Islets of Langerhans
- Secrete insulin into blood plasma
- Insulin bonds to receptors on muscle and liver cells
- Produces a signal, increasing number of glucose transporter proteins (more glucose uptake)
- Enzymes that convert glucose to glycogen activated
- Glucose removed from blood
Decrease in blood-glucose
- Detected by A cells
- Secrete glucagon
- Binds to receptors
- Adenylate cyclase activated and converts ATP to cAMP
- Activates protein kinase enzymes which cause glycogenolysis
Type I diabetes
Immune system attacks beta cells so insulin cant be produced. Controlled by injections. Cannot be taken orally because stomach enzymes will break it down.
Type II diabetes
Receptors on cells lose responsiveness to insulin. Controlled by diet and exercise.
What does the kidney do?
Excretes waste products such as urea from the body, as well as controlling blood water and ion concentration
Ultrafiltration
- Glomerulus surrounded by Bowman’s Capsule.
- Blood leaves glomerulus in efferent arteriole which has a small diameter so is under high pressure.
- Filtrate is therefore forced out.
- Passes through pores in epithelial cells and into Bowman’s capsule.
Selective reabsorbtion
- Filtrate from glomerulus passes firstly through the PCT.
- Glucose is reabsorbed by facilitated diffusion and then by active transport.
- Water also reabsorbed by osmosis.
- PCT has microvilli to increase surface area.
- Also has mitochondria which provide ATP for active transport.
Counter-current multiplier
- Na+ actively transported out ascending limb using ATP
- Low WP in medulla in interstitial space, but walls of ascending limb impermeable
- Water passes out descending limb by osmosis into interstitial space which enters blood
- Filtrate loses water, lowering WP
- At bottom of loop, Na+ diffuses out and as it goes higher, moves out by active transport. WP increases
- Gradient of WP. Higher in loop, lower in space
- Collecting duct permeable and as filtrate moves down, passes out by osmosis into blood
- WP lowers, also in space, so water constantly lost across collecting duct. Always WP gradient.
Water reabsorption in collecting duct
- Osmoreceptors in hypothalamus monitor blood WP
- If decreases, water moves out osmoreceptors
- Signal sent to pituitary gland, which releases ADH
- ADH moves through blood and causes walls of collecting duct to become more permeable
- More water reabsorbed so urine more concentrated
