homeostasis

homeostasis

homeostasis is 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

Homeostasis maintains optimal conditions for enzyme action and all cell functions.

In the human body, these include control of:

• blood glucose concentration

• body temperature

• water levels.

what do automatic control systems may involve

These automatic control systems may involve nervous responses or chemical responses

0. All control systems include:

• cells called receptors, which detect stimuli (changes in the environment)

• coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors

• effectors, muscles or glands, which bring about responses which restore optimum levels.

what do nervous systems enable humans to do

The nervous system enables humans to react to their surroundings and to coordinate their behaviour.

what 2 parts make up the nervous system

CNS (brain and spinal cord)

-other nerves running to and from the central nervous system

describe a pathway through nervous system

a stimuli will be detected by the receptors and this will send electrical impulses down neurones to CNS (coordination centre) and this now sends electrical impulses down other neurones to effectors and they will bring about a response

stimulus receptor coordinator effector response

what do effectors tend to be

which may be muscles contracting or glands secreting hormones.

the CNS

The CNS is the brain and spinal cord. The CNS coordinates the response of effectors

reflex arc of when you touch a hot object

-stimulus (heat) is detected by a receptor

-electrical impulses now pass from the receptor along a sensory neurone to the CNS

-reach a synapse where a chemical is released and diffused to a relay neurone where it triggers an electrical impulse

-the electrical impulse passes across the relay neurone and reaches another synapse. Once again, a chemical is released

-this chemical triggers an electrical impulse in a motor neurone

and the electrical neurone will pass down the effector (in this muscle

-muscle now contracts and pull hand away from heat

reflex actons

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.

what is reaction time

• Reaction time is the time taken to respond to a stimulus; reactions are usually very quick responses typically taking less than a second to occur

what factors can affect reaction time

age, stress or use of drugs

outline method to investigate reaction time

1. sit down on the chair and place your forearm of your weaker/non-dominant hand on the table with your hand hanging over the end of the table

2. have your partner hold a ruler with the bottom end in between your fingers so you can practise holding the ruler with 2 fingers

3. have your partner hold the ruler and remove your finger

4. have your partner hold the ruler in line so that the 0 mark is level with the top of your thumb

5. your partner will drop the ruler without telling you beforehand, and you will catch the ruler as quickly as possible

6. note and record the number level with the top of your thumb after you have caught ruler in a table

7. repeat test at least 5 times

8. find reaction times by using a conversion table to convert the ruler measurements

9. The process is then repeated after a condition is changed (the person drinks a can of caffeinated drink or has to repeat the experiment when loud background music is playing)

   • Remember to only change one factor (independent variable) in your investigation

independent variable

dependent variable

control variable

• amount of energy

• reaction time

• same hand, same ruler, same height which is being dropped from

sources of error

-participants may have different experiences in performing a similar task previously i.e some participants may already be practiced in this task

-samples size may be too small to make a valid conclusion

why is using computer program to measure reaction times likely to be more valid tan the method using a dropped ruler

1. removes human errors from measurements

2. reaction time can be measured in milliseconds which is more accurate than seconds

brain

The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.

cerebral cortex

-outer part

-function include language, memory and consciousness

cerebellum

controls balance and co-ordinates movements

medulla

controls our heart rate and breathing rate

 explain some of the difficulties of investigating brain function and treating brain damage and disease.

-brain is protected by skull so it is very tricky to access

-the structure of the brain are extremely complex meaning it is difficult to work out which parts of the brain carry out specific functions

-very delicate and easy to damage

3 ways that scientists use to investigate the brain

1. Many scientists look at patients who have suffered brain damage by looking to see where the damage has taken place they can try to link that part of the brain to its function

2. we can electrically stimulate different paarts of the brain and look at the effects on the person’s behavioiur and that allows us to narrow down specific regions to their functions

3. we can use MRI scanning to loook at which parts of the brain are most active during different activities

eye

The eye is a sense organ containing receptors sensitive to light intensity and colour.

cornea

transparent layer in front t of the eye where light passes through and its function is to start the focussing of the light rays

iris

the muscle surrounding the pupil - the coloured part of the eye

pupil

the space in the centre of the iris which light passes through

lens

the light rays will through it after going through the pupil and its job is to focus the light rays onto the back of the eye

-it can change its shape allowing us to focus on distant or near objects (accommodation)

retina

where the image is formed at the back of the eye and the retina will contain receptor cells for light which allow us to detect light intensity and light colour

optic nerve

the receptor cells in the retina now send electrical impulses down the optic nerve to the brain

sclera

the white part of the eye surrounding the eye-this tough outer structure protects the eye

ciliary muscles and suspensory ligaments

work with the lens to allow focus on distant or near objects

what happens to the size of the pupil when you enter a dark room

the light entering is low and this drop in light intensity is sensed by light receptors in the retina and these send electrical impulses to the brain. the brain then sends electrical impulses to specific muscles in the iris and these muscles contract causing pupil to become larger -circular muscles relax and radial muscles contract

what happens to the size of the pupil when you enter a bright room

the light entering is high and this increase in light intensity is sensed by light receptors in the retina and these send electrical impulses to the brain. the brain then sends electrical impulses to specific muscles in the iris and they causing pupil to become smaller -circular muscles contract and radial muscles relax

accommodation

the ability to change the shape of the lens to focus on near or distant objects

focusing on distant objects

the light only needs to be focused by a small amount

-the ciliary muscle relaxes and the suspensory ligaments are pulled tight and the lens will be pulled thin meaning that light rays will only be slightly refracted

focusing near objects

light from near objects need to be focused a large amount meaning that ciliary muscles contract (so ciliary muscles have a) smaller diameter and suspensory ligaments loosen. the lens is thicker and refracts the light rays more strongly (lens is more convergent) and the light rays will focus on the retina to form an image

long sightedness

-hyperopia

-cannot focus on nearby objects

-many cases eyeball is too short meaning that the light is focused at the point behind the retina

-in other cases, especially in the elderly the lens becomes less elastic meaning that lens cannot become thick enough to focus on near objects

how can longsightednesses be treated

by using glasses with convex lenses which partially focus the light before they enter the eye and it is potruding outwards

short sightedness

-myopia

-cannot focus on distant objects

-eyeball can be too long and so the light is focused at a point in front of the retina

-can also be caused when the lens is too thick meaning that again the light is focused infront of the retina

how can shortsightedness be treated

can use concave lens (going inwards) to partially unfocused the light before it enters the eye

instead of using glasses what can we use

• New technologies now include hard and soft contact lenses, laser surgery to change the shape of the cornea and a replacement lens in the eye.

how can body temperature is measured

Body temperature is monitored and controlled by the thermoregulatory centre in the brain.

the thermoregulatory centre in the brain

The thermoregulatory centre contains receptors sensitive to the temperature of the blood.

what does the skin contain

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

what happens if temperature is too high

If the body temperature is too high, blood vessels dilate (vasodilation) meaning that more blood flows through the capillaries meaning that heat can transfer out of blood and sweat is produced from the sweat glands.the sweat will evaporate and this takes energy from the body, cooling the body down. Both these mechanisms cause a transfer of energy from the skin to the environment.

what happens if body temperature is too low

If the body temperature is too low, blood vessels constrict (vasoconstriction),-les blood flows through and less heat lost from the body sweating stops and skeletal muscles contract (shiver)- to generate energy for this contraction the muscle cells increase their rate of respiration and this releases heat

the endocrine system

The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream.

how are hormones transported

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

difference between endocrine and nervous systems

Compared to the nervous system the effects are slower but act for longer

the pituitary gland

The pituitary gland in the brain is 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.

Students should be able to identify the position of the following on a diagram of the human body:

• pituitary gland

• pancreas

• thyroid

• adrenal gland

• ovary

• testes.

okay

pancreas

involve in controlling the concentration of glucose

the ovaries and testes

release hormones involved in puberty and in reproduction

thyroid gland

produces hormones which are involved in growth and in regulating the body’s basal metabolic rate

adrenal glands

releases the hormone adrenaline which is produced in times of fear or stress

how is blood glucose levels monitored by

Blood glucose concentration is monitored and controlled by the pancreas.

what happens if blood glucose level too high

If the blood glucose concentration is too high, the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells. In liver and muscle cells excess glucose is converted to glycogen for storage.

what is type 1 diabetes

Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels

how is type 1 diabetes normally treated

is normally treated with insulin injections.

type 2 diabetes

In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas

some treatments for type 2 diabetes

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

risk factor for type 2 diabetes

Obesity is a risk factor for Type 2 diabetes.

what happens if blood glucose concentration falls

If the blood glucose concentration is too low, the pancreas produces the hormone glucagon that causes glycogen to be converted into glucose and released into the blood.

explain the effect on cells of osmotic changes in body fluids.

if the blood becomes too dilute then water moves into cells by osmosis and if blood becomes too concentrated then water moves by osmosis out of cells. if body cells gain or lose too much water by osmosis then they don’t work efficiently

ways water leaves body

Water leaves the body via the lungs during exhalation.

Water, ions and urea are lost from the skin in sweat.

There is no control over water, ion or urea loss by the lungs or skin.

Excess water, ions and urea are removed via the kidneys in the urine.

deamination

The digestion of proteins from the diet results in excess amino acids which need to be excreted safely. In the liver these amino acids are deaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion.

what are the kidneys

The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water.

how does the kidneys adjust the level of molecules in the blood

-first the blood passes through capillaries

-here small molecules are filtered out of the blood, these include urea, ions and water as well as sugar glucose which will pass into a tube

-all of the glucose, some ions and some water reabsorbed back into blood-selective reabsorption

-no urea reabsorbed

-urea, excess ions and excess water are released as urine

what happens if blood becomes too concentrated( level of water in blood falls)

the pituitary glands will release the hormone ADH in the bloodstream

ADH will travel to the kidneys and cause the kidney tubules to become more permeable to water meaning that more water can now pass out of the kidney tubules. this means that more water is reabosorbed from the tubules back into the blood -less urine is produced and the amount of water in the blood rises back to its normal level

-as the level of water in the blood returns to normal, the pituitary gland stops releasing ADH

what happens if blood becomes too dilute

pituitary gland will stop releasing ADH meaning that kidneys will reabsorb less water into blood

-now more urine is produced and the concentration of water returns back to normal

what happens if the kidneys fail

the levels of water, ions and urea need to be adjusted using a machine -kidney dialysis

how does kidney dialysis works

when a person has kidney failure, their blood will contain a higher concentration of water, ions and urea than usual

-in kindey dialysis, the patient’s blood passes over a semi permeable membrane which allows urea, ions and water through but will not allow larger molecules such as proteins to pass through -blood cells are also too large

-on the other side of the membrane we have dialysis fluid, the dialysis fluid contains normal concentration of water and ions but it does not contain any urea. we have a concentration gradient for the urea so the urea diffuses from the blood into the dialysis fluid

-the dialysis fluid is constantly refreshed which ensures that there is always a large concentration gradient for urea. the dialysis fluid will also contain the normal concentrations of water and ions, which means that some of the water and ions will diffuse from the blood into the dialysis fluid which will mean that the concentrations of water and ions in the patient’s blood will return to normal

disadvantages of kidney dialysis

-patients have to visit a hospital several times a week

-have to eat a controlled diet so they do not produce too much urea

kidney transplant

the diseased kidney is replaced by a healthy kidney from donor but may be rejected by patient’s immune system

compare the disadvantages and advantages of dialysis and kidney transplant

in dialysis no shortage of dialysis machines but shortage of kidney donors

-dialysis requires frequent treatment and a controlled diet but tranplant allows patient to lead a normal life

-dialysis is expensive in the long term but transplant only expensive intially

-if transplant then have to take anti-rejection drugs for rest of life

what happens during puberty

During puberty reproductive hormones cause secondary sex characteristics to develop.

oestrogen

Oestrogen is the main female reproductive hormone produced in the ovary.

ovulation

At puberty eggs begin to mature and one is released approximately every 28 days. This is called ovulation.

testosterone

Testosterone is the main male reproductive hormone produced by the testes and it stimulates sperm production.

how does the uterus prepare for ovulation

the uterus lining becomes thick and spongy.

the 4 hormones involved in the menstrual cycle

Follicle stimulating hormone (FSH)

Luteinising hormone (LH)

Oestrogen

progesterone

Follicle stimulating hormone (FSH)

causes maturation of an egg in the ovary.

Luteinising hormone (LH)

stimulates the release of the egg.

Oestrogen and progesterone

are involved in maintaining the uterus lining incase the egg is fertilised and implants

how do the hormones interact with each other

-in the first stage, FSH is released by the pituitary gland

-FSH travels in the blood to the ovaries where it causes an egg to mature

-at the same time, FSH triggers the ovaries to make oestrogen

-oestrogen will cause the lining of the uterus to become thick

-oestrogen also stops the pituitary gland from releasing any more FSH

-instead pituitary gland will release LH

-LH trigger ovulation in other words the mature egg is released

-once the ovary has released its egg, the ovary now produces the hormone progesterone

-the progesterone stops the pituitary gland from releasing FSH and LH -that is to prevent any more eggs from maturing or being released

-progesterone will also keep the lining of the uterus thick incase a fertilised egg implants

-if fertilisation does not take plae, the level of progesterone falls and so the uterus lining and egg are now released and woman has her period

hormonal contraception

rely on releasing oestrogen, progesterone or a combination of the two

-if oestogen is released steadily everyday, it will inhibit FSH meaning that no egg will be developed or released

-progesterone stimulates production of thick mucus and so prevents the sperm from reaching the egg

Fertility can be controlled by a variety of hormonal and non-hormonal methods of contraception.

These include:

• oral contraceptives that contain hormones to inhibit FSH production so that no eggs mature

• injection, implant or skin patch of slow release progesterone to inhibit the maturation and release of eggs for a number of months or years

• barrier methods such as condoms and diaphragms which prevent the sperm reaching an egg

• intrauterine devices which prevent the implantation of an embryo or release a hormone

• spermicidal agents which kill or disable sperm

• abstaining from intercourse when an egg may be in the oviduct

• surgical methods of male and female sterilisation.

combined oral contraceptive pill

contains both oestrogen and progesterone

-99% effective but side effects such as headaches

progesterone only pill

99% effective

fewer side effects

advantage of condom

protect against sexually transmitted diseases

he use of hormones to treat infertility

This includes giving FSH and LH in a 'fertility drug' to a woman. She may then become pregnant in the normal way.

In Vitro Fertilisation (IVF) treatment process

• IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs.

• The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.

• The fertilised eggs develop into embryos.

• At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus (womb).

benefits and drawbacks of IVF

Although fertility treatment gives a woman the chance to have a baby of her own:

• it is very emotionally and physically stressful

• the success rates are not high

• it can lead to multiple births which are a risk to both the babies and the mother.

• expensive

• not all embryos inserted into womb and so destroyed-unethical

adrenaline

Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.

thyroxine

Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development.

negative feedback of thyroxine

-level of thyroxine in blood is monitored by the brain

when thyroxine level falls, pituitary gland releases hormone TSSH into bloodstream

-this triggers the thyroid gland to release more thyroxine into blood

-the increased level of thyroxine is now detected by brain

-this now prevents the pituitary gland from releasing TSH

-as TSH level falls, the thyroid gland releases less thyroxine

what do plants produce hormones for

Plants produce hormones to coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism)

what does unequal distribution of auxin lead to

Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.