Biology: Topic 5: Homeostasis and response flashcards

What is homeostasis

The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes

What does homeostasis maintain optimal conditions for?

• Enzyme action

• All cell functions

Why do conditions in your body need to be kept steady?

So that your cells can have the right conditions to function properly

Give three examples of controlling conditions in the body

• blood glucose concentration

• body temperature

• water levels

What type of control systems are these?

Automatic

What might these control systems involve?

Nervous responses or chemical responses

What do all control systems include?

• Receptors

• Effectors

• Coordination centres

What are receptors?

Cells which detect stimuli

What are stimuli?

Changes in the environment

What do coordination centres do?

Receive and process information from receptors

Examples of coordination centres

• brain

• spinal chord

• pancreas

What are effectors?

Muscles or glands which bring about responses which restore optimum levels

What does the nervous system enable humans to do?

React to their surroundings and coordinate their behaviour

How is information relayed in the nervous system?

• Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS)

• The CNS is the brain and spinal cord

• The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones

What does the central nervous system (CNS) consist of?

In vertebrates, only the brain and spinal cord

How is the CNS connected to the body in mammals?

By sensory neurons and motor neurons

What are sensory neurons?

The neurons that carry information as electrical impulses from the receptors to the CNS

What are motor neurons?

The neurons that carry information as electrical impulses from the CNS to effectors 

What is the order of events for a reaction to a stimulus in the nervous system?

stimulus > receptor > coordinator > effector > response

What is a synapse?

The junction between two neurons

What is the gap in a synapse called?

A synaptic cleft

How do synapses work?

• When an impulse reaches the end of the neuron, a chemical (neurotransmitter) is released

• The neurotransmitters diffuse to the next neuron, triggering an electrical impulse to begin

What is a reflex?

A rapid, automatic response to certain stimuli that don’t involve the conscious part of the brain

Why do we have reflexes?

To prevent the chance of being injured

What is a reflex arc?

The passage of information in a reflex (from receptor to effector)

How is the pathway of a reflex arc different from the usual response to stimuli?

The impulse does not pass through the conscious areas of the brain

Describe a reflex arc

• Receptor detects stimulus

• Electrical impulses are sent along a sensory neuron

• In the CNS (spinal cord/ brain) the impulse passes to a relay neuron

• Impulses are then sent along the motor neuron

• There is a synapse between all of these neurons where the neurotransmitters cross the gap by diffusion

• The impulse reaches an effector resulting in the appropriate response

Give 2 examples of reflex arcs

1. pupils getting smaller to avoid damage from bright lights

2. moving your hand from a hot surface to prevent damage

What does the brain do?

Control complex behaviour

Describe the structure of the brain

It is made of billions of interconnected neurons and has different regions that carry out different functions

What are the three components of the brain?

1. Cerebral cortex

2. Cerebellum

3. Medulla

What does the cerebral cortex control?

(cereal and MILC)

• Memory

• Intelligence

• Language

• Consciousness

What part of the brain is the cerebral cortex?

The outer part

What does the cerebellum control?

Fine movement of muscles

What part of the brain is the cerebellum?

The rounded structure towards the bottom/ back

What does the medulla control?

Unconscious actions like breathing and heart rate

What part of the brain is the medulla found in?

The brain stem in front of the cerebellum

Why is it difficult to investigate brain function and treating brain damage and disease?

• It is complex and delicate

• It is easily damaged

• Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it

• It is not fully understood which part of the brain does

What have neuroscientists been able to do?

• Map the regions of the brain to particular functions by:

  • studying patients with brain damage

  • electrically stimulating different parts of the brain

  • using MRI scanning techniques

What is the eye?

A sense organ containing receptors sensitive to light intensity and colour

What is the eye adapted for?

• Accomodation (allowing the eye to change its shape in order to focus on near or distant objects)

• Adaption to dim light

Parts of the eye (7)

• retina

• optic nerve

• sclera

• cornea

• iris

• ciliary muscles

• suspensory ligaments

What is the retina?

A layer of light sensitive cells found at the back of the eye

What does the retina do

• When light hits it, the cells are stimulated

• Impulses are sent to the brain, which interprets the information to create an image

What is the optic nerve?

A nerve that leaves the eye and leads to the brain

What does the optic nerve do?

Carries the impulses from the retina to the brain to create an image

What is the sclera?

The white outer layer which supports the structures inside the eye

What is an adaptation of the sclera?

It is strong to prevent some damage to the eye

What is the cornea?

The see-through layer at the front of the eye

What does the cornea do?

• It allows light through

• The curved surface bends and focuses light onto the retina

What is the iris?

The muscles that surround the pupil

What do the iris muscles do?

Contract or relax to alter the size of the pupil

What do the iris muscles do in bright light?

• Circular muscles contract

• Radial muscles relax to make the pupil smaller

  • this avoids damage to the retina

What do the iris muscles do in dim light?

• Circular muscles relax

• Radial muscles contract to make the pupil larger

  • so more light can enter to create a better image

What do the ciliary muscles and suspensory ligaments do?

• Hold the lens in place

• Control its shape

What is accomodation?

The process of changing the shape of the lens to focus on near or distant objects

How does the eye focus on a near object?

• the ciliary muscles contract

• the suspensory ligaments loosen

• the lens is then thicker and refracts light rays strongly

How does the eye focus on a distant object?

• the ciliary muscles relax

• the suspensory ligaments are pulled tight

• the lens is then pulled thin and only slightly refracts light rays

When do eye defects occur?

When light cannot focus on the retina

What are two common defects of the eyes?

• myopia (short sightedness)

• hyperopia (long sightedness)

What is myopia?

When the lens is too curved, so distant objects appear blurry

What is hyperopia?

When the lens is too flat, so it cannot refract light enough

How are these eye defects treated generally?

With spectacle lenses which refract the light rays so they do focus on the retina

What new technologies are there to correct myopia and hyperopia?

• hard and soft contact lenses

• laser surgery to change the shape of the cornea

• a replacement lens in the eye

How is body temperature monitored and controlled?

By the thermoregulatory centre in the brain

What does the thermoregulatory centre contain?

Receptors sensitive to the temperature of the blood

What part does skin play in the control of body temperature?

It skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre

What is human body temperature?

37.5 degrees celsius

What happens if your body temperature is too high?

• Blood vessels dilate (vasodilation)

• Sweat is produced from the sweat glands

What does vasodilation mean?

More blood flows closer to the surface of the skin, resulting in increased energy transfer from the body

What does sweat do?

Evaporates from skin surface resulting in increased energy transfer away from body

What happens if your body temperature is too low?

• Blood vessels constrict (vasoconstriction)

• Sweating stops

• Skeletal muscles contract (shiver)

• Hairs stand on end

What does vasoconstriction mean?

Blood does not flow so close to the surface, resulting in less heat lost

What does shivering do?

Generate heat from respiration

What do hairs standing on end do?

Create an insulating layer, trapping warm air

What are the two communication systems of the human body?

• the endocrine system

• the nervous system

What is the endocrine system composed of?

• glands which secrete chemicals called hormones directly into the bloodstream

• the blood carries the hormone to a target organ where it produces an effect

What are hormones?

Chemical messenger made by the endocrine system which affects a specific target organ and is released and carried by the blood

What are hormones caarried in?

The blood plasma

How does the endocrine system compare to the nervous system

• chemical messengers rather than nervous impulses

• effects are slower

• effects last longer

• act more generally

Where is the pituitary gland?

The brain

What is the pituitary gland?

• A ‘master gland’ which secretes several hormones into the blood in response to body conditions

• These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects

Why does your blood glucose level need to be kept within a certain limit?

Glucose is needed by cells for respiration

How can you increase blood glucose levels?

Eating foods that contain carbohydrates

What does the pancreas do?

Monitor and control blood glucose concentration

What happens if the blood glucose concentration is too high?

• pancreas secretes hormone insulin

• this causes glucose to move from blood into cells

• in liver and muscle cells, excess glucose is converted to glycogen for storage

What happens if the blood glucose concentration is too low?

• the pancreas secretes the hormone glucagon

• this causes glycogen to be converted into glucose and released into the blood

What is Type 1 diabetes?

• A disorder in which the pancreas fails to produce sufficient insulin

• It is characterised by uncontrolled high blood glucose levels

• It is normally treated with insulin injections

What is Type 2 diabetes?

• When the body cells no longer respond to insulin produced by the pancreas

• A carbohydrate controlled diet and an exercise regime are common treatments

What is a risk factor for Type 2 diabetes?

Obesity

What can high blood glucose be fatal? - osmosis

• there will be water movement out of cells

• dilute to concentrated solution of water

• across partially permeable membrane

• causes cells to shrink

What is negative feedback?

How your automatic control systems keep your internal environment stable

How your body decreases the level of something with negative feedback

• Receptor detects a stimulus - level is too high

• The coordination centre receives and processes the information, then organises a response 

• Effector produces a response which counteracts the change and restores the optimum - the level decreases

What is osmosis?

The net movement of water particles across a partially permeable membrane from an area of high water concentration (dilute) to an area of low water concentration (concentrated) down the concentration gradient

What happens if the water concentration of the blood increases?

• Cells in the body take up water by osmosis

• This is because the conc. of water in the blood is lower than the conc. in cells

• Cells expand as they take up more water

• They may burst

What happens if the water concentration of the blood decreases?

• Cells lose water

• Causing them to shrink

How does water leave the body?

• Sweating

• Via the lungs during exhalation

• In urine - depending in the conc. of water in the blood

What leaves the body in sweat?

• Water

• Urea

• Ions

Is there control over the water, ions and urea that leaves the body via the lungs and sweat?

No

What happens if body cells lose or gain too much water?

They do not function efficiently