Homeostasis & Feedback Mechanisms Flashcards
Define: homeostasis
The maintenance of a constant internal environment
Why is homeostasis important?
In general:
- It makes an organism more independent from its environment
Temperature/pH:
- Prevents denaturing of proteins (especially enzymes)
- Ensures reactions occur at predictable rates
Water potential:
- Prevents cells bursting or shrinking due to osmosis
What are the types of feedback mechanism? What do they do?
- Positive feedback: where a mechanism amplifies a change
- The feedback causes a corrective measure to remain turned on
- Negative feedback: where a mechanism restores a level to normal
- The feedback causes a corrective measure to be turned off
What is the purpose of each type of feedback mechanism?
Positive: rapidly activate something - not used in homeostasis
Negative: homeostatis - multiple used for a factor to give more control and make a response faster
What are the two categories of organisms for thermoregulation?
- Endotherms - have physiological mechanisms for regulating temperature
- Ectotherms - don’t have physiological mechanisms so rely on the environment for warmth they regulate body temperature using behavioural responses
What are the receptors for detecting temperature?
Thermoreceptors found in the skin and the hypothalamus
What mechanisms are in place for when body temperature is below normal?
- Shivering - produce more heat from respiration
- Less sweating - less heat lost
- Hairs stand up - traps insulating layer of air
- Vasoconstriction - less heat lost to the skin
- Hormones - adrenaline and thyroxine increase metabolic rate
What mechanisms are in place for when body temperature is above normal?
- Sweating - heat lost from the skin to the sweat to evaporate the water
- Hairs lie flat - less insulation
- Vasodialation - more heat lost from the skin
What blood vessels contract/dialate to regulate blood flow?
Arterioles
What organ is involved in the regulation of blood glucose?
Pancreas - specifically the islets of Langerhans
Which hormones are involved in blood glucose regulation?
- Insulin
- Glucagon
- Adrenaline
What happens when blood glucose levels are high?
- Detected by the beta cells in the islets of Langerhaans
- They secrete insulin which binds to receptors on the surface of cells
- Consequently:
- The permeability of cells to glucose increases (the cells take up glucose)
- In liver cells: glucose → glycogen
- In adipose cells: glucose → glycerol
- In muscle cells: increased rate of respiration
What happens when blood glucose levels are low?
- Detected by alpha cells in the islets of Langerhaans
- They secrete glucagon which binds to receptors on liver cells
- Consequently:
- The permeability of liver cells to glucose increases (the liver cells release glucose into the blood)
- Glycogen → glucose
- Non carbohydrates → glucose
- Rate of respiration decreases
What is the effect of adrenaline on blood glucose levels?
- Secreted by the adrenal glands
- Binds to receptors on the surface of liver cells causing:
- Secretion of glucagon
- Glycogen → glucose
- Inhibits glucose → glycogen
- This happens because, in binding, adrenaline activates an enzyme
- This converts ATP → cAMP which acts as a signalling molecule a begins a cascade (chain of reactions)
What is glyogenesis?
Conversion of glucose to glycogen
How does the thickness of the uterus lining change during the menstrual cycle?
How do the levels of oestrogen and progesterone vary during the menstrual cycle?
How do the levels of FSH and LH vary during the menstrual cycle?
