Homeostasis and Feedback Systems

Define homeostasis

The body’s ability to maintain a stable internal environment despite variable external conditions

Occurs through the constant interactions of the body’s regulatory processes

Define equilibrium

The body’s constant state of balance

What systems regulate homeostasis

Nervous - through nerve impulses to organs that can counter the change (targeted and rapid responses but short lasting)

Endocrine - secretes hormones from glands into the blood (slower but wide-spread and longer-lasting)

Define feedback systems

Cycle of events in which body conditions are monitored, evaluated and maintained/changed and then re-evaluated

State components of feedback systems

Controlled condition (variable that is monitored)

Stimulus (any disruption to the controlled condition)

Receptor (detects the change and notified control centre)

Control centre (receives info from receptor)

Effector (receives commands from control centre and produces response)

Response (effect that changes controlled condition to return to homeostasis)

Define negative feedback

The response opposes the initial stimulus to reverse the change

Used in conditions that need frequent adjustments

Describe negative feedback system for thermoregulation (hot)

Stimulus = hot day

Controlled condition = body temp

Receptor = thermoreceptors

Control centre = hypothalamus

Effector = blood vessels and sweat glands

Responses = blood vessels dilate and move to surface of skin to release heat, sweat glands produce sweat and release heat through evaporative cooling

Describe negative feedback system for thermoregulation (cold)

Stimulus = cold day

Controlled condition = body temp

Receptors = thermoreceptors

Control centre = hypothalamus

Effectors = blood vessels and skeletal muscles

Responses = blood vessels constrict and move away from surface of skin to preserve heat, skeletal muscle contract to produce shivering to produce heat

Define positive feedback

The response strengthens/enhances stimulus to produce an amplified change

Describe the positive feedback system during childbirth

Stimulus = contractions of uterus wall push baby’s head onto cervix

Controlled condition = stretching of cervix

Receptor = stretch sensitive nerve cells in cervix

Control centre = pituitary gland releases oxytocin into blood

Effector = muscle cells on uterus wall

Response = uterus wall contracts more forcefully → causes baby to further stretch the cervix

Birth decreases stretching → breaks positive cycle