Homeostasis

Definition:

• Maintaining optimal internal body conditions in order for optimum function in response to internal or external changes

Automatic control system:

• Receptor cells detect changes - which are called stimuli - in the environment, either internally or externally

• Receptor cells then pass on electrical impulses through the neurons onto the coordination centre which coordinates a response by receiving and processing the impulses.

  • Examples: Brain, spinal cord, pancreas

• This response is then carried out by the receptor cells which are either a gland or a muscle, in order to restore the optimum level

Nervous system:

• A key role of the nervous system is that it enables humans to react to their surroundings and coordinate their behaviour

• There are 2 parts to the nervous system:

  • Brain, spinal cord and relay neurons

  • Sensory and motor neurons

Reflex arc: ( no decision by the conscious part of the CNS):

• A stimulus is first detected by a receptor which are connected to receptors

• Electrical impulses now pass from the receptor along a sensory neuron to the CNS

• At the end of a sensory neuron, there is a synapse where electrical signals are converted into chemical ones as the form of neurotransmitters, which then diffuses off to a relay neuron in the CNS

• When it reaches the relay neuron, it triggers an electrical impulse, which passes through the relay neuron and to the other end where there is another synapse

• Neurotransmitters are once again released and diffuse to the motor neuron which is connected to the effector.

• Once the electrical impulse is triggered: it then passes along the motor neuron and onto the effector, which will cause a response

  • Due to the reflex arc not involving the conscious part of the brain, this means that reflexes are automatic and rapid, which helps to protect us from danger

The Brain:

There are 3 parts to the brain:

• Cerebral cortex (largest part) - control language, memory and consciousness

• Cerebellum (back of the brain) - controls our balance and co-ordinates muscle contraction and movement

• Medulla (long one) - controls unconscious activities such as breathing rate and heart beat.

Why the brain is difficult to study and treat:

• Protected by the skull and so is hard to access

• The structures of the brain are complex - hard to work out which parts have which function

• Brain is extremely delicate and so is easy to damage

Ways to study the brain:

• Studying patients with brain damage: by looking at where the damage has taken place, they can try to link that part of the brain to it’s function

• Using electrical stimulation: by stimulating different parts of the brain to look at the effects on the person’s behaviour, can be used to narrow down specific regions of the brain to their function

• Using MRI scanning to look at which parts of the brain are most active during different activities

The Eye:

• The eye is a sense organ which contains receptors cells to both light intensity and colour of light

  

Different parts of the eye:

• Cornea: Transparent layer of the front of the eye - function is to start adjusting the focus of light rays

• Pupil: Dark part of the eye, allows light to enter the eye

• Iris: Coloured part of the eye - changes size to accommodate for light intensity

• Lens: To focus light rays onto the retina by changing shape - to allow for focusing on objects from different distances

• Retina: Back of the eye - contains receptor cells for light intensity(Rod cells) and also colour(Cone cells)

• Optical nerve: a nerve which sends electrical impulses to the brain to create an image in the brain

How the iris changes for light intensity(reflex action):

• In bright light, the circular muscles contract whilst the radial muscles relax, which causes the size of the pupil to constrict, which decreases the size of the pupil, so that less light can enter eye and hit the retina which means that the retina gets less damaged

• In dim light, the circular muscles relax and the radial muscles contract which causes the pupil to dilate, which increases the size of the pupil, to allow the maximum amount of light rays to hit the retina so that the eye can create an image in dim lighting

Accommodation:

• Lens is surrounded by a circular muscle called ciliary muscle, which is connected to the lens by suspensory ligaments

  • Lens becoming thicker: When the ciliary muscle contracts, the suspensory ligaments loosen which causes the lens to be thicker and refract light more strongly

  • Lens becoming thinner: When the ciliary muscles relaxes, the suspensory ligaments tighten which causes the lens to be thinner and refracts light less strongly

• Distant object:

  • Light rays from a distant object need to be refracted a small amount and so the lens must be thin, which causes the light rays to refract to focus on the retina on the same point

• Near object:

  • Light rays from a near object need to refracted a larger amount and so the lens must be thicker, which causes the light rays to refract to focus on the retina on the same point

Hyperopia and Myopia:

• Hyperopia is long sightedness: Meaning people can only focus on distant objects and not ones which are near

  • This means that the light rays are focused behind the retina

  • Causes:

    • Age

    • The eyeball being too short

    • The lens being too thin

  • Treatments:

    • Wearing convex shaped lens - to partially focus the light before entering the eye

• Myopia is short sightedness: Meaning people can only focus on near objects and not ones which are distant

  • This means that the light rays are focused in front of the retina

  • Causes:

    • The eye ball being too long

    • The lens is too thick

  • Treatments:

    • By wearing concave shapes lenses - to partially unfocus the light rays before entering the eye

• Treatments to Hyperopia and Myopia:

  • Contact lenses: Act the same way glasses do

  • Laser surgery: Changing the shape of the cornea, so that it refracts the light rays to greater or lesser extent before hitting the lens

  • Replacement lens surgery: Replacing the lens using an artificial one, so that it can refract the light correctly

The Endocrine system:

• Consists of a series of glands which release hormones

Differences between the endocrine and the nervous system:

• Endocrine uses chemical signals while the nervous system uses electrical impulses

• The effects of the endocrine is very long lasting compared to the nervous system

• The endocrine system uses the blood to carry hormones around the body while the nervous system uses neurons to carry impulses around the body

• The endocrine system reacts much slower than the nervous system

Thyroid gland:

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

Pituitary gland:

• Release hormones which act on other glands in the body - nicknamed the master gland

Diabetes:

• Type 1:

  • When the pancreas is not able to produce sufficient insulin which causes glucose levels in the blood to stay high

  • Treatments:

    • Type 1 diabetes patients monitor their blood glucose concentration and inject insulin is the glucose concentration rises too much

• Type 2:

  • When the body cells stop responding to insulin produced by the pancreas which means less glucose gets converted into glycogen, which causes the glucose concentration in the blood to stay high

  • Treatments:

    • A carbohydrate controlled diet

    • part take in exercise

The Kidneys:

• The body takes in water through food and drink, but also through respiration. There are 3 methods which the body loses water:

  • Breathing: no control over water loss

  • Sweat: water is lost through the skin in sweat which also contains ions and urea - no control

  • Urine: In the kidneys - can control water loss through the kidneys

How the kidneys regulate concentrations of molecules in the blood:

• The blood first passes through the glomerulus which is inside the bowman’s capsule

• Small molecules: water, ions, glucose and urea are all filtered into the bowman’s capsule and into the tubule

• The capillaries near the capsule then undergo selective reabsorption:

  • All the glucose is reabsorbed back into the blood

  • Some water and ions are reabsorbed back into the blood

  • No urea is reabsorbed back into the blood

• The remains then pass through the tubule and into the bladder where they are stored as urine which consists of excess water, excess ions and urea

How the body deals with excess amino acid:

• The amino acids go to the liver where they are then broken down into ammonia (which is called deamination), ammonia is a toxic chemical which is now in the blood but is too large to be filtered through the kidney and so it is further broken down into urea which is also a toxic chemical but is small enough to be filtered by the kidneys

Water regulation:

• When the blood water levels become too low, the pituitary gland releases ADH. ADH then travels to the kidneys where it makes the kidneys more permeable to water, which therefore allows more water to be selectively reabsorbed back into the blood via osmosis and less urine is produced, which leads an increase in blood water levels which stops the release of ADH.

Kidney failure treatments:

• A way to treat kidney failure is by using Kidney dialysis:

  • When a person has kidney failure, their blood will contain a higher concentration of water, ions and urea than is should

  • The patients blood passes over a semi-permeable membrane which allows small molecules such as urea, ions and water to diffuse through but no larger ones such as proteins and blood cells.

  • On the other side of the membrane, there is dialysis fluid but contain any urea which creates a strong concentration gradient for urea which allows diffusion of urea from the blood into the dialysis fluid, which is constantly refreshed to ensure a constant large concentration gradient for urea

  • The dialysis fluid also contains a normal concentration of water and ions, which means that some ions and water molecules can diffuse through into the dialysis fluid which will return the concentration of water and ions to its regular levels

• Another way of treating kidney failure is using a kidney transplant:

  • A diseases kidney is replaced with a healthy one from a doner

• Comparing dialysis and kidney transplants:

  • In dialysis there is no shortage of dialysis machines while there is a shortage in kidney donors

  • In dialysis a patient requires frequent treatment and must have a controlled diet which is inconvenient while with a kidney transplant patients can live a normal life

  • Kidney dialysis is expensive is long term treatment, while kidney transplant is only expensive initially

  • Kidney transplant patients have to take anti-rejection drugs for the rest of their lives while dialysis does not

Human reproduction:

• During puberty, reproductive hormones cause secondary sexual characteristics to develop.

  • These reproductive hormones are testosterone in male testes and in the ovaries it is oestrogen and progesterone

  • Testosterone stimulates the testes to produce sperm

• The menstrual cycle:

  • FSH is first produced by the pituitary gland, which travels to the blood to ovaries where it causes the maturation of an egg and also triggers the release of oestrogen by the ovaries

  • Oestrogen causes the lining of the uterus to thicken, and also stops to release of FSH by the pituitary gland

  • Oestrogen stimulates the release of LH by the pituitary gland, which travels to the ovaries and causes ovulation to occur

  • LH then stimulates the production of progesterone by the ovaries, which stops the pituitary gland from producing FSH and LH, which prevents more eggs from maturing or being released.

  • Progesterone also maintains the lining of the uterus in case of a fertilised egg implanting, if there is not fertilised egg, the level of progesterone falls, which causes the egg and uterus lining to shed, and the woman has a period.

Contraception:

Hormonal contraception:

• Oral contraception:

  • contain hormones which prevent the production of FSH, which means that the egg does not mature

  • Advantages:

    • Is highly effective if taken correctly

  • Disadvantages:

    • Must be taken everyday, so if forgotten a woman is at a risk of pregnancy

    • Have side effects such as increased risk of breast cancer or blot clots

    • Don’t protect against STIs

• Implant, skin patch or an injection:

  • Contain progesterone, which stops the production of FSH and LH, meaning that the egg can not be released nor released

  • Advantages:

    • More convenient than taking daily pills (implant lasts for 3 years, injection about 13 weeks and the patch lasts around 1 week

  • Disadvantages:

    • Can have side effects

    • Don’t protect against STIs

Barrier contraception:

• Condom or diaphragm:

  • Stop a sperm from reaching an egg

  • Advantages:

    • Effective form of contraception

    • No side effects due to them not using hormones

    • Reduced risk of STIs

    • More effective if a spermicide is used - kills or disable sperm

  • Disadvantages:

    • May break or slip off, leading to pregnancy

• IUD(intrauterine device):

  • called a coil. Prevent an embryo from implanting. Can also release hormones which reduce the chances of fertilisation

  • Advantages:

    • Highly effective

    • Can prevent pregnancy for up to 10 years

    • have very few side effects

  • Disadvantages:

    • Do not protect against STIs

Surgical contraception:

• Sterilisation:

  • This prevents the egg from reaching the uterus or the sperm from leaving the penis

  • Advantages:

    • Highly effective

  • Disadvantages:

    • Very difficult to reverse

    • Do not prevent against STIs

Treating Infertility:

Hormone treatment:

• FSH and LH are given to women, through an injection which causes an egg to mature and to be released, and so increases ovulation, which therefore increases the chances of becoming pregnant through sexual intercourse.

In-vitro fertilisation(IVF):

• The mother is first treated with FSH and LH to release eggs, which is then collected from the mother.

• The sperm is then collected from the father, which is used to fertilise to eggs on a petri dish in a laboratory

• These fertilised eggs then develop into embryos.

• Once there are enough embryos, they are then inserted into the mothers uterus

• These embryos can then develop normally inside in the uterus

  • Advantages:

    • Gives a chance to have children in infertile women

  • Disadvantages:

    • The success rates are low

    • High costs

    • Chance of having multiple children

    • Embryos will be destroyed, which is unethical

Thyroxine:

• Thyroid releases thyroxine:

  • Stimulates the bodies basal metabolic rate, meaning metabolic reactions take place at a faster rate

  • Playing an important role in growth and development

Regulating thyroxine:

• When the thyroxine levels fall in the blood, it is detected by the brain and the pituitary gland release TSH.

• This stimulates the thyroid to produce more thyroxine into the blood

• When the thyroxine levels are high, it is detected by the brain, which causes the pituitary glad to stop releasing TSH

• As TSH levels falls, the thyroid produces less thyroxine into the blood

Plant Hormones:

Investigating effects of light on a plant shoot:

• shoots which have light shining on them from 1 side, the shoots then grow towards the light

• Shoots which their tips have been cut off do not grow towards the light, helping to show that the tips produce a hormone called auxin

• When the shoot tips are covered, the shoot does not grow towards the light, which helps to show that the tip is sensitive light

• When the bottom of the shoots where covered, the shoots tips grew normally towards the light, which helps to show that the bottom of the shoots are not sensitive to light

Phototropism:

• The hormone auxin is concentrated in the tip of the shoot

• When light is shined on one side of the shoot, the auxin concentrates onto the dark side of the shoot

• Because auxin promotes growth in shoots, then that will mean that the side which is dark with more auxin will grow faster than the side with light

• This then causes the plant to begin to bend towards the direction of the light source

Gravitropism:

• Auxin is also produced in the roots, but gravity causes it to concentrate to the bottom side of the root.

• In a root auxin inhibits growth of cells and so that means that the side with no auxin will grow faster than the side with auxin

• This then causes the horizontal root to point towards the ground as it grows, which is towards gravity

Other plant hormones:

• Gibberellins:

  • Important in the germination of seeds

• Ethene:

  • Controls cell division

  • Ripening of fruits

Uses of plant hormones:

• Auxins:

  • Used as weed killers in gardens

  • They are used as rooting powders

  • Used to promote growth in plant tissue culture

• Gibberellins:

  • End seed dormancy - force earlier germination

  • Used to encourage plants to flower

  • To make fruit grow larger

• Ethene:

  • Ethene is used to ripen fruit such as bananas, before they are sold