Unit 5 - Homeostasis & Response Flashcards
What is homeostasis?
Homeostasis is the maintenance of a
constant internal environment in order to
maintain optimum conditions for enzyme
and cellular function.
Give examples of conditions maintained
by homeostasis in the body
● Blood glucose concentration
● Body temperature
● Water levels
What two types of responses are used in
body control systems?
Nervous and chemical
What three components do all control
systems have?
● Receptors
● Coordination centres
● Effectors
What is the function of a receptor?
Receptors detect changes in the
environment (stimuli).
What is the function of a coordination centre?
Coordination centres obtain and process
information from receptors.
What is the function of an effector?
Effectors (muscles or glands) bring about
responses to stimuli.
What is the function of the nervous system?
The nervous system allows the body to
react to its surroundings and coordinate an
appropriate response.
How does a stimulus lead to a response
being carried out by the body?
● Stimulus is converted into an electrical impulse by the
receptors.
● The electrical impulse passes along sensory neurones to
the central nervous system (CNS).
● The CNS coordinates an appropriate response and an
electrical impulse is sent along motor neurones to the
effector, which carries out the response.
What sequence of events describes how
the nervous system works?
Stimulus → receptor → coordinator →
effector → response
What is a reflex action?
A reflex action is an automatic and rapid
response which does not involve any
conscious input from the brain.
Why are reflex actions important?
Reflex actions aid survival by preventing
harm to the body.
Describe how a reflex action occurs via a
reflex arc
● The stimulus is detected by a receptor.
● An electrical impulse passes along a sensory neurone to the spinal cord
(part of the CNS).
● At a synapse between a sensory neurone and a relay neurone, a
chemical diffuses across the gap and stimulates a new impulse which
passes along the relay neurone.
● The same process occurs at a synapse between a relay neurone and a
motor neurone.
● At the effector, an appropriate response is carried out.
What is the difference between a reflex pathway
and a conscious pathway?
Within a reflex pathway, the coordination centre
is a relay neurone found in the spinal
cord/unconscious parts of the brain. In a
conscious pathway, the coordination centre is in
the conscious part of the brain.
Give the name of the body’s coordination
system which involves hormones
The endocrine system
What is a hormone?
A hormone is a chemical messenger
secreted by a gland. It travels in the blood to
a target organ, where it causes a response.
What type of organ secretes hormones?
Glands
Which gland controls many other glands
in the body?
The pituitary gland
Why is the pituitary gland considered a
‘master gland’?
It secretes a wide range of hormones,
some of which may stimulate other
endocrine glands.
What is the role of the pituitary gland in
the endocrine system?
● Secretes human growth hormone - controls human
growth.
● Stimulates the thyroid gland.
● Stimulates ovulation and the production of oestrogen in
the ovaries.
● Stimulates the production of sperm and testosterone in
the testes.
What is the role of the thyroid gland in
the endocrine system?
Secretes the hormone thyroxine - controls
metabolism, heart rate and body
temperature.
What is the role of the pancreas in the
endocrine system?
Secretes the hormone insulin - controls
blood glucose levels.
What is the role of the adrenal gland in
the endocrine system?
Secretes adrenaline - controls the body’s
‘fight or flight’ response.
What is the role of the ovaries in the
endocrine system?
Secrete oestrogen, which coordinates the
menstrual cycle and the development of
female secondary sexual characteristics.
What is the role of the testes in the
endocrine system?
Secrete testosterone, which coordinates the
production of sperm and the development of
male secondary sexual characteristics.
Which organ monitors and controls blood
glucose concentration?
The pancreas
How does the pancreas respond when
blood glucose levels are too high?
The pancreas secretes the hormone insulin.
Insulin binds to receptors on the liver and
muscles, causing excess glucose to be
converted into glycogen and stored.
How does the pancreas respond when blood
glucose levels are too low?
The pancreas secretes the hormone
glucagon. Glucagon binds to liver cells,
causing glycogen to be converted into
glucose and released into the blood.
How is blood glucose concentration controlled
using a negative feedback loop?
● When the blood glucose concentration rises or falls
below the optimum, a hormone is secreted by the
pancreas.
● The action of either hormone (insulin or glucagon)
helps bring back the concentration to the correct
level.