topic 1 homeostasis

what is homeostasis

the process of keeping the internal condition stable despite changes inside or outside the body

negative feedback

opposes the original change restoring the body to normal

what does a positive feedback do and give example

pushes the body further from normal until a specific outcome is reached, e.g labour, or blood clotting

list the 5 components of the stimulus response model in order

A stimulus is detected by a receptor, processed by a modulator (control centre), acted on by an effector, producing a response.

In high blood glucose, which pancreatic cells detect the change and what hormone is released?

Beta cells; insulin

In low blood glucose, what happens?

Alpha cells release glucagon, liver breaks down glycogen into glucose

Which sensory receptor detects light?

Photoreceptor

Which receptor detects pain or harmful stimuli?

Nociceptor

What part of a neuron receives signals from other neurons?

Dendrites

What is the function of the myelin sheath?

Insulates the axon and speeds up impulse transmission

What do sensory neurons do?

Carry impulses from receptors to the central nervous system

Where are interneurons found?

Only in the brain, spinal cord and visual system

What is the resting potential of a neuron and what maintains it?

Resting potential is about -70mV, maintained by the sodium-potassium pump moving 3 Na+ out for every 2 K+ in.

What happens during depolarisation?

Na+ rushes into the cell, membrane reversing the charge to positive +30mV

What happens during repolarisation?

K+ leaves the cell, making the inside negative again.

In synaptic transmission, what triggers vesicles to release neurotransmitter?

An arriving action potential opens calcium channels; Ca2+ influx causes vesicles to fuse with the membrane and release neurotransmitter (exocytosis).

What are the three steps of signal transduction?

Reception (hormone binds receptor) → Transduction (triggers internal reactions) → Response (cell responds).

What is upregulation?

More receptors are produced, increasing the cell's response to a hormone

What is kleptothermy?

Sharing another animal's metabolic heat, e.g. huddling

What is the difference between hibernation and torpor?

Hibernation is long-term (often winter), torpor is short-term

What does vasodilation do for thermoregulation?

Widens blood vessels near the skin, increasing blood flow and releasing heat

Where is ADH produced and released from?

Produced in the hypothalamus, released by the pituitary gland

What happens when ADH levels are high (dehydration)?

Collecting ducts become more permeable, more water reabsorbed, urine is concentrated

What is abscisic acid and what does it do?

The 'stress hormone' in plants that inhibits growth to conserve resources under stress

Why do closed stomata reduce photosynthesis?

Closing stops CO2/O2 gas exchange needed for photosynthesis