Homeostasis Part 1

What is homeostasis?

is the regulation of the conditions inside your body (and cells) to maintain a stable internal environment, in response to changes in both internal and external conditions

internal condtions that are controlled include

- body temperature

-blood sugar levels

-water content of the body

blood sugar is needed to

to provide the cells with a constant supply of energy

Water content of the body

water leaves the body via the lung when we breathe out and via the skin when we sweat to cool us down, excess water is also lost via the kidney in the urine

What does the body do if temperature is too high/low? What controls it?

too high- sweating

too low- shivering, goosebumps

the brain controls it

What does the body do if water is too high/low? What controls it?

too high- urinate

too low- urine is concentrated

the kidneys control it

What does the body do if sugar is too high/low? What controls it?

too high- produces insulin

too low- produces glucagon

pancreas controls it

stimulus

an environmental change

response

a reaction to a stimulus

effector

a muscle or gland the causes the response

receptors

a cell that detects a change in the environment

Coordination centre

organs the receive and process information from the receptors

e.g.(brains, spinal cord, pancreas)

nerve cell

long connections on each end to create a network of connections

How does information pass along a neuron (nerve cell)?

through electrical impulses

what is a reflex response?

a fast and automatic response to a stimlus

which part of the CNS (central nervous system) is responsible for a reflex reaction?

the spinal cord

describe a reflex action

1) receptor detects the stimulus

2)receptor generates an electrical impulse in the sensory neurone

3) at the end of the sensory neurone chemical transmission of neurotransmitters occurs across the synapse by diffusion

4)this triggers an electrical impulse in the relay neurone, located in the spinal cord

5) this triggers an electrical impulse in the motor neurone

6) which triggers the effector to carry out a response. This could be a muscle or a gland

reaction time

Time taken to respond to a stimulus.

factors affecting reaction time

• age

• weight

• medical history

• under the influence of a stimulant/ depressant

• fatigue

stimulant

a drug that increases reactions

depressant

a drug that decreases reactions

brain

an organ inside your skull, that is made up of billions of interconnected neurones that form different regions

functions of the cerebrum cortex

controls consciousness, intelligence, memory and language

Functions of the medulla (oblongata)

controls unconscious activity e.g.

• heart beat,

• the movement of the gut and

• breathing and

• sneezing

Functions of the cerebellum

controls muscular activity and balence

Give 3 ways scientists can study the brain

• Study people with brain damage

• Electrically stimulate different parts of the brain

• Scan the brain, using CT, PET, MRI, or fMRI scanners

Why are patients often awake during brain surgery?

To provide doctors with feedback about parts of the brain being operated on and to prevent damage done to the brain

sclera

the tough, supporting wall of the eye

cornea

the transparent outer layer found at the front of the eye. It refracts light into the eye

pupil

the pupil in the centre of the eye, through which light enters

iris

contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye

retina

the layer at the back of the eye that contains two types of light receptor cells. One is sensitive to light intensity and the other is sensitive to colour

lens

focuses the light onto the retina

ciliary muscles

control the shape of the lens

optic nerve

carries impulses from the receptors on the retina to the brain

dilated is when

the pupil widens, allowing more light to enter the eye

pupil constricts…

• radial muscles contract

• circular muscles relax

explain how the eye reacts to dim light

• pupils dilates

• this allows the eye to let more light in

• the radial muscles contract

• the circular muscles relaxes

explain how the eye reacts to bright light

• pupil constricts

• let less light in

• the radial muscles relaxes

• the circular muscles contract

focusing the light

• light reflects off an object towards the eye

• when passing through the cornea, jelly within the eye the light is refracted

• the refracted light is focused on the light sensitive cells of the retina

• depending of the light intensity, the pupil can change size to allow more or less light in

How do the circular and radial muscles work together to control the size of the pupil?

The circular muscles relax and radial muscles contract making the pupil larger and when the radial muscles relax and the circular muscles contract and the pupil becomes smaller

Describe how the brain receives information about light entering the eye.

You should include the names of structures in your answer. 3 marks

The retina has light sensitive receptor cell which stimulates to the sensory neutron which is the optic nerve which connects to the brain

accommodation

is the movement of the lens to allow you to see object near and far equally well

accommodation for near objects

to focus on near objects

the ciliary muscles contracts

loosening the suspensory ligaments

which thickens and curves the lens

light lays are strongly refracted onto the retina

accommodation for far objects

to focuse on distant objects

the ciliary muscles relax

pulling the suspensory ligaments tight

which flattens and thins the lens

light rays are only slightly refracted and focused onto the retina

define mypoia

short sighted

define hyperopia

long-sighted - unable to focus on near objects

problems with myopia

• distant objects look blurred because

• the light is being focused in front of the retina

• causing the image to appear blurred

• caused by a lens that is too curved or a long eyeball

solution to myopia

Wearing glasses with a concave lens this refocuses that rays onto the retina

problems with hyperopia

Closer objects looked blurred

The light is being focused behind the retina

Causing the image to appear blurred

Caused by a lens that is too flat and thin or a short eyeball

solution for hyperopia

Wearing glasses with a convex lens

pros and cons of contact lenses

pros

Thin light weight, almost invisible, more convenient for sport

cons

Risk of infection from finger to eye

pros and cons of laser eye surgery

pros

• Permanent change to the shape of the cornea

cons

• Risk of complication with surgery, infection or eye reacting poorly to the surgery- vision becomes worse

pros and cons of replacement lens surgery

pros

• permenant change

cons

• Much higher risk than laser eye surgery- possible damage to the retina- could lead to loss of sight

How are changes in temperature detected?

Temperature receptors in the skin send impulses to brain

The Thermoregulatory centre of the brain is sensitive to the temperature of blood

3 ways to reduce core body temperature

• hair on skin lie flat

• sweat is produced by sweat glands

• vasodailation

vasodilation

Blood vessels supplying the skin capillaries dilate so more blood flows close to the surface of the skin - increasing transfer of energy to the surrounding

3 ways to increase core body temp

hairs stand up

no sweat

shiver

vasoconstriction

vasoconstriction

Blood vessels supplying the skin constrict. Reduces the blood supply to the skin so less energy transfer from the skin to the environment.

Why is it hard to cool down in humid countries?

Humidity can reduce the rate of sweat evaporation making it difficult to regulate the body's temperature. Water moves from an area of high concentration to an area of low concentration so it will not evaporate from the skin as there is already lots of water in the air. There is also a lack of wind flow so the water is not moves.