5.3 HOMEOSTASIS Flashcards
What is the coordination of cells?
The coordination of cells:
- evolution of organisms has given rise to multicellular life
- multicellular organisms must coordinate the function of different cells and systems to operate effectively
- very few body cells can work in isolation
What is homeostasis?
Homeostasis is the maintenance of a stable equilibrium in the conditions inside the body.
What is the role of cell signalling in homeostasis?
Cell signalling is the communication of cells. The nervous and endocrine systems are coordinated by cell signalling. One cell releases a chemical which then has an effect on another cell (target cell).
What is signal initiation?
Signal initiation:
- sensory receptors detect changes in the bodies internal and external environments
- information from the receptors is transmitted to the brain via sensory neurones
What are the types of signal transfer?
Types of signal transfer:
- locally (e.g neurotransmitters across synapse)
- long distances = using hormones (e.g ADH secretion)
What is signal response?
Signal response:
- impulses are sent along motor neurones to effectors which bring about changes to restore equilibrium
- effectors are the muscles or glands that respond to the stimuli
How do plants respond to cell signalling?
Plants response:
- don’t have nervous systems but need to respond to internal and external changes
- use plant hormones to achieve a response
- stems grow towards a light source to maximise their rate of photosynthesis (due to auxin)
What is negative feedback?
Negative feedback is the reversing of a change in the internal environment.
What is positive feedback?
Positive feedback is where a change in the internal environment is detected and then reinforced by effectors to reinforce the change.
- not common
- usually harmful (e.g body temp decreases, enzymes less active, decreased heat)
- blood clotting cascade and role of oxytocin in childbirth
What is sensitivity?
Sensitivity is the ability to response to internal and external changes.
What is a stimulus?
A stimulus is a detectable change in external or internal environment of an organism.
What are receptors?
Receptors are extrinsic glycoproteins that bind to chemical signals, triggering a response by the cell.
What are effectors?
Effectors are a muscle or gland which carries out the bodies response to a stimulus
What is an example of positive feedback?
An example of positive feedback is labour, where the cervix opens and oxytocin is released. Oxytocin increases contractions which causes the cervix to stretch more.
What are ectotherms?
Ectotherms are animals that use their surroundings to warm their bodies, so their core temperature is heavily dependant on the environment (e.g reptiles, fish).
What are endotherms?
Endotherms are animals that rely on their metabolic processes to warm their bodies and maintain core temperature (e.g birds, mammals).
How is temperature change detected?
Temperature change is detected by:
- peripheral receptors in the skin
- temperature receptors in the hypothalamus detect the temperature of the blood deep in the body
- gives the body greater sensitivity
What is the hypothalamus?
The hypothalamus:
- temperature receptors in the hypothalamus act as a thermostat for the body = it controls the responses that a core body temperature of 37 degrees C
- within the hypothalamus there is the heat loss centre and heat gain centre
What is vasodilation?
Vasodilation:
- cooling down when core body temp increases
- arterioles near surface of skin dilate when temp increases
- vessels that provide a direct connection between arterioles and venules (arteriovenous shunt vessels) constrict
- forces blood through capillary networks close to the surface of the skin
- skin flushes and cools as a result of increased radiation
- if skin is pressed against cool surfaces then cooling happens from conduction
- as core temp increases, rate of sweating also increases
- sweat evaporates, heat is lost, blood cooled below surface
- in some animals sweat glands are covered by hair, so they pant when they get hot
- erector pilli muscles in the skin collapse, avoids trapping an insulating layer of air
What is vasoconstriction?
Vasoconstriction:
- warming up when core body temp decreases
- arterioles near surface of skin constrict when temp decreases
- skin pales, little radiation takes place
- warm blood kept well below surface
- rates of sweating decreases, decreases cooling from skin, evaporation in lungs still occurs
- erector pilli muscles contract, hairs on skin stand up, reduces heat loss, creates insulating layer of air
- shivering occurs
What is shivering?
Shivering:
- rapid involuntary contracting and relaxing of the large voluntary muscles in the body
- metabolic heat from the exothermic reactions warm up the body instead of moving = effective way of raising the core temperature
- endotherms living in cold climates have adaptations that minimise their SA:V ratio to reduce cooling (e.g small ears)
What are the behavioural mechanisms for warming up in ecotherms?
Behavioural mechanisms - warming up:
- basking in the sun (lizards, locusts, butterflies)
- conduction = press bodies against warm group
- ectothermic metabolic reactions = vibration of muscles/wings
What are the behavioural mechanisms for cooling down in ecotherms?
Behavioural mechanisms - cooling down:
(important to cool down to stop enzymes denaturing)
- shelter from sun
- press bodies against cool earth or stone
- wallow in water or mud
What are physiological responses in ecotherms?
Physiological responses:
- dark colours absorb thermal radiation faster
- alteration of heart rate to increase or decrease metabolic rate