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Biology Part 1- Human Biology > Homeostasis > Flashcards

Flashcards in Homeostasis Deck (43):

what is homeostasis?

maintaining a constant internal environment to be able to respond to changes in the external environment


what needs controlling in the body?

- water
- pH
- urea
- temperature
- CO2
- blood sugar


what is a stimulus?

a change in the environment of an organism


how does an organism respond to a stimulus?

an animal's response to a stimulus is coordinated by their central nervous system. The CNS consists of the brain and spinal cord. It gathers information about, and responds to, changes in the environment. Receptors respond to a stimulus and send impulses along sensory neurons to the CNS. The CNS coordinates the info and sends impulses along motor neurons to the effectors, which bring out a response


what is osmoregulation?

controlling water content in the body


what is thermoregulation?

control of an optimum temperature for the body (allowing enzymes to work in an optimum environment)


how does the body control temperature (too hot)?

- sweat glands (in skin) release more sweat which evaporates, removing heat energy from the skin
- blood vessels (leading to the skin capillaries) dilate (become wider) to allow more blood to flow through the skin, and so more heat is lost (and the body can cool down)
- hair muscles relax; by lying flat, so heat can escape


how does the body control temperature (too cold)?

- muscles contract rapidly, resulting in shivering; these contractions need energy from respiration, so some of it is released as heat
- blood vessels constrict (become narrower) to conserve more heat in the body by letting less blood flow through the skin
- hair muscles pull hair on its end; it traps a layer of air above skin, to help insulate the skin against heat loss


how does the pancreas monitor and control the blood glucose concentration (too high)?

- the pancreas secrete insulin which enters the blood
- insulin allows glucose to be absorbed by body cells
- blood glucose is reduced


how does the pancreas monitor and control the blood glucose concentration (too low)?

- pancreas doesn't produce insulin
- less glucose is absorbed by body cells
- blood glucose increased


what does a coordinated response require?

- a stimulus
- a receptor
- an effector


what is a receptor?

receptors are a group of cells that detect an external stimuli, they are situated in all the sense organs


what are effectors?

effectors, for example muscle cells and cells found in glands, are cells that coordinate a response to the stimuli. They can react in different ways depending on the stimuli, for example, glands can secrete hormones whereas muscles can contract.


what is the difference between nervous and hormonal communication?

the nervous and hormonal system both coordinate responses within the body. The nervous does this by electrical impulses so is very fast. Hormones do this with chemicals which travel, a little slower at the speed of the bloodstream


how does the nervous communication system work?

- stimulation of receptors in sense organs sends electrical impulses
- messages are carried by electrical impulses along nerves and neurons
- fast impulses
- short-lived


how does the hormonal communication system work?

- endocrine glands produce hormones
- hormones are carried by the plasma to target hormones to stimulate change
- slow as it is carried by plasma
- long-lived


what is the role and source of ADH?

a lack of water is detected by the hypothalamus in the brain, it causes the pituitary gland to produce ADH. This makes the kidneys reabsorb more water-so less is lost from the body. (Control water levels)


what is the role and source of adrenaline?

adrenaline is produced in the adrenal gland and prepares the body for 'fight' of 'flee/flight'. Heart rate quickens to increase the flow of blood to muscles- this means that they can respire more (as there is more oxygen available) to provide energy.


what is the role and source of testosterone?

produced in ovaries in girls and testicles in boys. Plays a key role in puberty, developing sex organs and inspiring hair growth


what is the role and source of progesterone?

produced in the ovaries it maintains the lining ready for pregnancy, and continues to do so if the egg is fertilised


what is the role and source of insulin?

located in the pancreas and it lowers blood glucose


wha is the role and source of oestrogen?

produced in the ovaries, is controls other hormones to regulate the menstrual cycle. It stops the production of FSH and starts the production of LH


what does the central nervous system consist of?

- the central nervous system decides the response for a stimulus which is detected by a receptor
- sensory neurons will carry these messages (impulses) to the central nervous system (brain and spinal cord) to be passed on to the effector by motor neurons
- effector will carry out the response


what are the different types of nerve/neurons?

- sensory neuron- connect the sense cells to the CNS
- motor neurons- connect the CNS to the effectors
- relay neurons- connect the sensory neuron to the motor neurons in the CNS


how are rapid responses created?

- stimuli is detected by receptors and will stimulate sensory neurons to send electrical impulses to the CNS
- CNS will pass on impulses to the relay neurons across the synapse (gap) by chemicals
- the relay neurons will pass on impulses to the motor neurons which is carried to the effector
- the effector will carry out the response rapidly


how do synapses work?

- an electrical impulse travels along an axon
- this triggers the nerve-ending of a neuron to release chemical messages called neurotransmitters
- these chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the next neuron
- the receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse


what are neurotransmitters?

a chemical substance that is released at the end of a nerve fibre by the arrival of a nerve impulse and, by diffusing across the synapse of junction, causes the transfer of the impulse to another nerve fibre, a muscle fibre of another structure


reflex arc



what happens in a reflex arc?

- heat (stimuli) is detected by the finger (receptor) and will stimulate sensory nuerons to carry electrical impulses to the CNS (brain and spinal cord)
- electrical impulses will be passed on to relay neurons which will carry impulses through the CNS where a response is decided and is passed on to the motor neurone
- motor neurons will carry electrical impulses to the biceps (effector)
- biceps will contract and will withdraw the finger away from the hot object (response)


what is a reflex action?

when the safety of an organism demands a very quick response, the signals may be passed directly from a sensory neuron, via a relay neuron, to a motor neurone for instant, unthinking action. This is a reflex action


diagram of the eye



what is the cornea?

front part of the tough outer coat, the sclera. It is convex and transparent


what is the function of the cornea?

refracts light- bends it as it enters the eye


what is the iris?

pigmented- decides the colour of your eyes- so light cannot pass through. Its muscles contract and relax to alter the size of its central hole or pupil


what is the function of the iris?

controls how much light enters the pupil


what is the lens?

transparent, bi-convex, flexible disc behind the iris attached by the suspensory ligaments to the ciliary muscles


what is the function of the lens?

focuses light onto the retina


what is the retina?

the lining of the back of the eye containing two types of photoreceptor cells- rods- sensitive to dim light and black and white- and cones- sensitive to colour. A small area called the fovea in the middle of the retina has many more cones than rods


what is the function of the retina?

contains the light receptors


what is the optic nerve?

bundle of sensory neurones at the back of the eye


what is the function of the optic nerve?

carries impulses from the eye to the brain


what is the function of the conjunctiva?

this lubricates and protects the surface of the eye


what happens when the eye detects light?

the eye detects when light is strong/little and enlarges/shrinks when necessary (shrinking in bright light and enlarging in dim light)