B5.1.1

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

Why is homeostasis important for cells and enzymes?

It maintains optimal conditions for enzyme action and all cell functions

What conditions need to be controlled in the human body?

Blood glucose concentration, body temperature and water levels

Does homeostasis involve conscious control?

No, it is controlled automatically

What responses may automatic control systems involve?

Nervous or chemical responses

What do all control systems include?

Receptors, coordination centres and effectors

What are stimuli?

Changes in the environment that are detected by an organism

What are receptors?

Cells which detect stimuli

Where are receptors found?

In our sense organs, such as eyes, skin, nose, mouth and ears

What do coordination centres do?

Receive and process information from receptors

What are examples of coordination centres?

The brain, spinal cord and pancreas

What do effectors do?

Bring about responses which restore optimum levels

What does the nervous system enable animals to do?

React to their surroundings and coordinate their behaviour

What is the nervous system made from?

The central nervous system and the peripheral nervous system

What does the CNS include?

The brain and spinal cord

What does the PNS include?

The nerves that branch out from the brain and spinal cord

What is the sequence of events in the nervous system?

Stimulus --> receptor --> coordinator --> effector --> response

How does information travel from receptors to the CNS?

Along neurones as electrical impulses

What does the CNS do with information from receptors?

Coordinates the response of effectors which may be muscles contracting or glands secreting hormones

What is the nervous system made of?

Nervous tissues

What are nervous tissues made of?

Specialised cells called neurones

What are neurones adapted to do?

Carry electrical impulses from one place in the body to another

What are the parts of a neurone?

Cell body, axon and dendrites

Why are neurones well adapted to their function?

They have long axons insulated by a fatty sheath so electrical impulses can be carried long distances quickly

Why are reflex actions important?

They protect the body from harm

Are reflex actions voluntary or automatic?

They are automatic and rapid

Do reflex actions involve the conscious brain?

No, they do not involve the conscious part of the brain

What are examples of reflex actions?

Pupils constricting in response to bright light, moving in response to touching a hot object

What types of neurones control reflex actions?

Sensory, relay and motor neurones

What do sensory neurones do?

Allow electrical impulses to travel from a receptor to the CNS

Where are relay neurones found?

In the organs of the CNS

What do relay neurones do?

Transfer the electrical impulse from the sensory neurone to the motor neurone

What do motor neurones do?

Allow electrical impulses to travel from the CNS to an effector

What is an effector?

A muscle or gland which brings about a response

What can a muscle do?

Contract and shorten or relax and lengthen

What is a gland?

An organ that secretes a chemical substance

What is a synapse?

A junction between two neurones

What happens when an electrical impulse reaches the end of a neurone?

Chemicals called neurotransmitters are released

What do neurotransmitters do at a synapse?

Diffuse across the synapse

What happens after neurotransmitters cross the synapse?

They trigger an electrical impulse in the next neurone

How do synapses affect nervous transmission?

They slow down the speed of nervous transmission

What happens to reflex speed when there are more synapses?

It becomes slower

How can drugs like alcohol affect impulse transmission?

They can slow down the speed of impulse transmission

What factors affect human reaction time?

Practice, tiredness, alcohol consumption and caffeine consumption

What is the endocrine system composed of?

Glands which secrete hormones directly into the bloodstream

What do hormones do?

They travel in the blood to a target organ and produce an effect

What is a hormone?

A chemical messenger produced by a gland and carried in the bloodstream

What do hormones do?

Alter the activity of specific target organs

How do hormonal effects compare to nervous system effects?

They are slower but act for longer, sent as chemicals to target organs and destroyed by the liver

What is the pituitary gland?

A master gland in the brain that secretes several hormones into the blood

What do pituitary hormones do?

Stimulate other glands to release hormones to bring about effects

When is adrenaline produced?

In times of fear or stress

What does adrenaline do?

Increases heart and breathing rate and boosts delivery of oxygen and glucose to brain and muscles

What is the purpose of adrenaline?

To prepare the body for ‘fight or flight’

What does ADH do?

Helps control water content of the blood by increasing water reabsorption in the kidneys

Where is ADH produced?

In the pituitary gland

What does insulin do?

Controls blood glucose levels by converting excess glucose into glycogen for storage

Where is insulin produced?

In the pancreas

What does thyroxine do?

Stimulates basal metabolic rate and supports growth and development

Where is thyroxine produced?

In the thyroid gland

What other hormones are included in the endocrine system?

Reproductive hormones

What is puberty?

The stage in life where a child's body develops into an adult

When does puberty usually occur?

Between the ages of 10-17

What causes secondary sexual characteristics to appear?

Sex hormones during puberty

What does testosterone do?

Controls the development of male secondary sexual characteristics

Where is testosterone produced?

In the testes

What does oestrogen do?

Controls the development of female secondary sexual characteristics

Where is oestrogen produced?

In the ovaries

Why do cells need glucose?

For respiration to release energy

What monitors and controls blood glucose concentration?

The pancreas and the hormones insulin and glucagon

What type of feedback loop controls blood glucose levels?

A negative feedback loop

What does a negative feedback mechanism do?

Responds when conditions change from the ideal or set point

What happens if a level is too high in the body?

The control system works to reduce it

What happens if a level is too low in the body?

The control system works to increase it

What does insulin do?

Regulates blood glucose concentration

What happens when blood glucose concentration is too high?

The pancreas produces insulin which causes glucose to move into cells and be stored as glycogen

Where is excess glucose stored?

In liver and muscle cells as glycogen

What happens to glycogen when glucose is needed?

It is converted back into glucose

What happens when blood glucose concentration is too low?

The pancreas produces glucagon which causes glycogen to be converted into glucose and released into the blood

What is the role of insulin in glucose regulation?

It signals the liver and muscles to store excess glucose

What is excess glucose stored as?

Glycogen and body fat

What does glucagon do when glucose is low?

Instructs the liver to release stored glucose into the blood

What is diabetes?

A condition where blood glucose levels are too high

How is diabetes treated?

By injecting insulin, which causes glucose to be stored as glycogen, reducing blood glucose levels

How many types of diabetes are there?

Two

What is type 1 diabetes?

A disorder where the pancreas does not produce enough insulin

How is type 1 diabetes treated?

With insulin injections

What is a key feature of type 1 diabetes?

Uncontrolled high blood glucose levels

How often must people with type 1 diabetes monitor glucose levels?

Regularly throughout the day

What affects how much insulin someone with type 1 diabetes needs?

Their diet and level of physical activity

How can people with type 1 diabetes manage blood glucose levels?

By eating a careful diet and exercising regularly

Why does exercise lower blood glucose levels?

Because glucose is used in increased respiration in the muscles

What is type 2 diabetes?

A condition where body cells no longer respond to insulin

Who is more likely to get type 2 diabetes?

Older people

What is a risk factor for type 2 diabetes?

Obesity

How is type 2 diabetes commonly treated?

With a carbohydrate controlled diet and an exercise regime

What does thyroxine do?

Controls the speed at which respiration occurs to release energy for the body to use

Where is thyroxine produced?

In the thyroid gland

How are thyroxine levels controlled?

By negative feedback

What parts of the brain are involved in thyroxine regulation?

The hypothalamus and pituitary gland