P2B - Homeostasis 3

Conditions needed for cells and enzymes

Conditions needed for cells and enzymes

• Very stable conditions in order to work

• Can’t work well if conditions change too much

• Due to this, our bodies have systems to keep internal conditions optimum for cell function = Homeostasis

Homeostasis def and system involved

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

• involves automatic control systems

Endurance athlete homeostasis

• Exercise is a demand on the body so respiration uses glucose to generate energy = blood glucose conc falls

• The athletes body temp will rise and lose water through sweating

• Homeostasis is used to keep the blood glucose conc, body temp and water levels constant

  • basically it consists of automatic control systems making sure that internal conditions stay constant

Automatic control system features and order

1. Stimulus - change to the environment

2. Receptor cells - detect changes in the environment. Pass info to coordination centre.

   • for humans this could mean internal (bloods glucose conc) or external body conditions (skin temp)

3. Coordination centre (brain, spinal cord or pancreas) - receives and processes info from receptor cells. Sends instructions to effector.

4. Effector - muscle or gland that carries out the response, and restore the optimum level.

v1 - homeostasis

Nervous system in homeostasis

• Key part of homeostasis that consists of 2 parts:

  • Central Nervous System (CNS) - brain and spinal cord

  • Other nerves running to/from the CNS

• Enables humans to react to their surroundings and co-ordinate their behaviour

  • one way this is done is through the reflex arc

Automatic control system in the nervous system

1. Receptor detects a stimulus and send electrical impulses down neurones to the CNS

   • neurones is another way of saying nerve cells

2. The CNS is the coordination centre. This sends electrical impulses down other neurones to effectors.

3. Effectors bring about a response

   • usually a muscle which contracts OR gland which secretes a hormone

Reflex arc stages: What happens when you touch a hot object?

1. Stimulus (heat) is detected by a receptor (skin)

2. Electrical impulses pass from receptor along a sensory neurone to the CNS.

3. End of the sensory neurone = junction called a synapse.

4. At synapse a chemical is released. Diffuses across to a relay neurone in the CNS, which it triggers an electrical impulse.

5. Electrical impulse passes across the relay neurone and reaches another synapse. Chemical’s released, triggers an electrical impulse in a motor neurone.

6. Electrical impulse passes down motor neurone to an effector. This case it’s a muscle

7. Muscle contracts and pulls the hand away from the heat = response

Reflexes

• In most cases the brain makes decisions about what action to take, but in reflexes there is no decision making by the conscious part of the brain.

• This makes them automatic and rapid which help to protect us from danger.

v2 - The Nervous system

RP7: Reaction Time

1. Person 1 sits on a stool with upright posture. They place the forearm of their dominant arm across the table with their hand overhanging the edge.

2. Person 2 holds a ruler vertically. 0cm mark should be between P1’s thumb and index.

3. P2 tells P1 to prepare to catch the ruler, and drops it at a random time. P1 must catch as quickly as possible.

4. P2 records the measurement that is level with the top of P1 thumb.

5. P1 has short rest and test is repeated several times and mean is calculated. Convert results to a reaction time using a conversion table (found on the internet).

6. People switch places, allowing us to see if people have different reaction times

RP7: Reaction Time Variables

• Independent - person having reaction time tested

• Dependent - reaction time

• Control

  • starting distance between thumb and index must be constant

  • measure ruler at the top of the thumb

  • keep room conditions the same (lighting and background noise)

  • if any of these change, this could affect the dependent variable

RP7: Reaction Time - several other independent variable we can investigate

• See if reaction time changes depending on the number of tries; may be shorter due to practise (one person catches ruler many times)

• Whether reaction time depends on the hand catching the ruler: test dominant and non-dominant hand of the same person. Dominant may be shorter because we use it more often.

• Whether certain chemicals affect reaction time e.g caffeine: person drinks a measured amount of cola 30mins before experiment. Compare this time with their normal reaction time.

  • issue is that there may be some other chemical in the cola that is affecting reaction time

  • to check this, carry the test out again using a caffeine-free cola and compare all reaction times

  • safety - check that the person has no medical issues affected by caffeine (allergy or heart condition)

  • carry out the test in a lab where hazardous chemicals aren’t normally used

v3 - RP7: Reaction Time

Brain’s role, how it does it and why theres different parts

• critical role in CNS - controls complex behaviour (language)

• to do this it contains billions of interconnected neurones

• different parts of the brain carry out different functions

• Cerebral cortex - highly folded, outer part of the brain

• Functions include language, memory, consciousness

• Cerebellum

• Controls balance and co-ordinates our movements

• medulla

• controls heart rate and breathing rate

Issues with investigating the brain

Extremely difficult to study and treat brain damage/diseases since:

• protected by the skull = hard to access

• very complex structures = hard to find out which parts carry out specific functions

• extremely delicate and easy to damage

How to investigate the brain

• look at patients with brain damage

  • wherever damage happened, we can link that part of the brain to its function

• electrically stimulate different parts and look at the effects on the person’s behaviour

  • allows us to narrow down specific regions to their functions

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

  • when person looks at image we see greater activity in the part of the brain responsible for image processing

v4 - the brain

Eye def

• a sense organ

• contains receptors sensitive to light intensity and light colour

Eye parts (in order of how the eye detects light):

1. cornea

2. pupil & iris

3. lens

4. retina

5. optic nerve

• sclera

• ciliary muscles

• suspensory ligaments

Name, Function, stage of how the eye detects light

• Cornea: light rays pass through this transparent front

• Job: start the focussing of the light rays

• stage 1

Name, Function, stage of how the eye detects light

• Top one: Pupil - space in the centre of the iris which light rays pass through

• Bottom one: Iris - coloured part of the eye

• stage 2

Name, Function, key feature, stage of how the eye detects light

• Lens: light rays now pass through this

• Job: focus the rays onto the back of the eye

• Key feature: Can change its shape, allowing us to focus on distant or near objects (accommodation)

• stage 3

Name, Function, stage of how the eye detects light

• Retina: back of the eye where light rays are focussed

• Contains receptor cells for light - these allow us to detect light intensity and light colour

• stage 4

Name, Function, stage of how the eye detects light

• Optic Nerve - receptor cells in the retina send electrical impulses down this to the brain

• stage 5

Name, Function

• Sclera - white part of the eye

• Tough outer structure protects the eye

Name, Function

• Top: ciliary muscles

• Bottom: suspensory ligaments

• Both work with the lens - together they allow us to focus on distant or near objects

Iris job in detailed steps for a dark room

Controls the size of the pupil:

1. Dark room = light amount in your eye is low. Drop in light intensity is sensed by light receptors in the retina.

2. Receptors send electrical impulses to the brain.

3. Brain sends electrical impulses to specific muscles in the iris.

4. Muscles contract, causing the pupil to become larger (dilate). This allows more light to enter the eye.

   • this is a reflex action since it doesn’t involve the conscious part of the brain

   • the opposite effect happens in a bright room, protecting the eye from damage

v5 - the eye

Eye focusing

• A lot is carried out by the cornea, but the cornea is a fixed focus

• The rest is by the lens

  • allows us to focus on near or distant objects by changing its shape

Accommodation

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

Ciliary muscle and suspensory ligaments def

• Ciliary muscle - circular muscle that surrounds the lens

• It’s connected to the lens by fibres called suspensory ligaments

How accommodation takes place

By contracting or relaxing, ciliary muscles can change the lens thickness:

• when ciliary muscle contracts, suspensory ligaments loosen.

  • lens is now thicker and refracts light rays more strongly

• when ciliary muscle relaxes, suspensory ligaments are pulled tight.

  • lens is now pulled thin and only slightly refracts light rays

Focusing on distant objects

Light from distant objects needs to be focused only a relatively small amount:

• ciliary muscle relaxes, suspensory ligaments pulled tight = thin lens

• because the lens is thin, light rays are only slightly refracted

• light rays are now focused to a point on the retina

Focusing on near objects

Light from near objects needs to be focused a large amount:

• ciliary muscle contracts, suspensory ligaments loosen = thick lens

• because the lens is thicker, light rays are refracted more strongly

• light rays are now focused to a point on the retina

Hyperopia, different cases/causes and treatments

• Long sightedness = can focus on distant, not on nearby objects

• Many cases the eyeball is too short so the light is focused at a point behind the retina

• OR Some cases (elderly) the lens becomes less elastic = lens can’t become thick enough to focus on near objects

• treated by using convex lensed glasses = partially focus the light before it enters the eye

Myopia, different cases/causes and treatments

• Short sightedness = can focus on nearby, not on distant objects

• Eyeball is too long so the light is focused at a point in front of retina

• OR Lens is too thick and light is focused in front of retina

• treated by using concave lensed glasses = partially unfocus the light before it enters the eye

Alternative to glasses

• Hard or soft contact lenses

• Sit on the eyeball and refract light same way as glasses

• New treatments:

  • laser surgery changes cornea shape to refract light to a greater or lesser extent

  • lenses inside the eye can be replaced using an artificial lens

v6 - how the eye focuses

Thermoregulatory centre (TC), job, how it does the job, location

• body temp (37C) is monitored and controlled by this part of the brain = homeostasis

• contains receptors that are sensitive to blood temp

• skin also contains these receptors

• these receptors send electrical impulses down the sensory neurones to the TC

Body’s response to restore normal body temp if someone exercised

Body temp too high (e.g from exercise):

• Sweat glands release sweat onto skin surface.

  • Sweat evaporates and takes energy from the body, cooling it down.

• Flushing - Network of capillaries under the skins surface are supplied with blood by blood vessels deeper in the skin.

  • Vessels supplying the capillaries dilate (get wider) = vasodilation.

  • More blood flows through the capillaries. .Heat can now transfer out of the blood so body temp is back to normal

Body’s response to restore normal body temp if it’s too low

• Vasoconstriction: Blood vessels supplying capillaries constrict (narrow).

  • less blood flows through the capillaries and less heat is lost from body

• Shivering: skeletal muscles contract

  • to generate energy for this, out muscles cells increase respiration rate

  • this releases heat which warms the body

• Stop sweating

v7 - thermoregulation

Endocrine system

• Consists of a number of glands

• These glands secret hormones directly into the bloodstream

• Blood carries the hormones around the body

• Each hormone only acts and binds on specific target organs where it triggers an effect

Endocrine system vs nervous system

• nervous:

  • uses electrical impulses that travel down neurones

  • signalling is extremely fast and effects of it is very short lived (brief)

• endocrine:

  • uses hormones which are chemicals that are carried in the bloodstream

  • produces much slower effect thats more longer lasting

Key endocrine system glands

• Pancreas

• Ovaries & testes

• Thyroid gland

• Adrenal glands

• Pituitary gland

Name, function

• Pancreas

  • digestion

  • releases hormones involved in controlling blood glucose conc

Name, function

• Ovaries and testes

  • release hormones involved in puberty and reproduction

Name, function

• Thyroid gland

  • produces hormones involved in growth and regulating the body’s basal metabolic rate (how rapidly the body’s reactions take place)

Name, function

• Adrenal glands

  • release adrenaline hormone which is produced in times of fear or stress

Name, function

• Pituitary gland in the brain:

  • Extremely important - called the master gland

• Releases a number of different hormones into the blood depending on the conditions

• Pituitary hormones act on other glands and they cause other hormones to be released = trigger a range of different effects in the body

v8 - Endocrine system

Endocrine system controlling blood glucose conc if too high

• Glucose used by all cells to release energy by respiration = very important that blood glucose conc is constant as possible

• Conc is monitored by pancreas

• Homeostasis taking place:

  • after a carb-rich meal, blood glucose conc can rise

  • pancreas senses this and produces insulin hormone

  • it travels in blood and triggers body cells to take up glucose from the blood

  • also trigger liver and muscle cells to store excess glucose as glycogen

  • since glucose is taken out of blood and stored, conc returns to normal

Type 1 Diabetes

• When the pancreas doesn’t produce enough insulin

• Graph:

  • 2 people ate same meal w carbs - blood glucose conc rises

  • No diabetes - conc rapidly returns to normal levels due to insulin

  • Type 1 - conc rises and then stays at high level due to pancreas no producing sufficient insulin

Type 1 Diabetes treatments

• Monitor blood glucose conc

• Insulin injection if conc rises too much (after carb-rich meal) = blood glucose conc falls

Type 2 diabetes, treatment and risk factors

• Body cells stop responding to insulin produced by the pancreas = blood glucose conc can rise too high

• Treatment:

  • diet containing a controlled carb level- aim is to prevent conc from rising too high

  • advised to exercise

• Risk factor:

  • obesity - as these levels rise in the UK, more people are developing t2

Endocrine system controlling blood glucose conc if too low

• In between meals if conc is too low then:

  • pancreas releases glucagon hormone into bloodstream

  • glucagon triggers liver cells to convert glycogen stores back to glucose

  • this glucose is released into the blood = normal conc returns

Blood glucose conc in a normal person

• Rises and falls slightly during the day

• Conc is controlled by a balance between insulin and glucagon

• If conc rises then pancreas releases insulin = conc falls

• When conc falls to certain level, pancreas releases glucagon = conc rise

• Insulin and glucagon have opposite effects on conc = they form a negative feedback cycle

v9 - control of blood glucose concentration

Importance of constant water levels

• Very important - if body cells gain or lose too much water by osmosis then they don’t work efficiently

• If blood is too dilute then water moves into cells by osmosis

• If blood is too concentrated with water, then water moves out of cells by osmosis

• Body has a system in place to maintain water balance = part of homeostasis

How body takes in water

• food and drink

How body loses water

• Via lungs when exhaling - no way to control

• Sweating = water through skin (also contains ions like sodium and waste product urea) - no way to control this since it’s a part of the body temps control system

• Via kidneys in urine - can control water loss. If blood is too dilute, kidneys remove excess water and produce more urine (urea and excess ions are also lost)

How kidneys remove waste product urea

1. Blood containing urea enters the kidney (x2) through an artery.

2. Kidney removes urea, excess ions/water.

3. These leave the kidney as urine - stored in the bladder.

4. Blood leaves the kidney through a vein = blood contains no urea.

5. Homeostasis has been carried out by removing all urea

How kidneys adjust the level of molecules in the blood

1. Blood passes through capillaries. Small molecules are filtered out of blood (urea, ions, water, glucose). These pass into tubules (means very small tube).

2. Selective reabsorption: All of the glucose, some of the ions/water are reabsorbed back into the blood

3. Urea, excess ions/water are released as urine.

4. Homeostasis has been carried out by adjusting water and ion conc in blood

Graph of concs of glucose, ions and urea in the blood before and after passing the kidneys

• glucose = no change since kidneys filter glucose out of blood and then reabsorb it all back into blood

• ions = conc decreased since kidneys filter ions out, but reabsorb a certain amount back into the blood depending on the bodies needs

• urea = conc falls to virtually 0 since kidneys filter all of it out and don’t reabsorb it

How body deals with excess amino acids

When digesting proteins, amino acids pass into the blood. We often eat more protein than the body needs

• Deamination: liver breaks down the excess amino acids and produces the chemical ammonia

• Ammonia is a very toxic chemical so liver immediately converts it to urea

• Urea is safely excreted by the kidneys

v10 - The Kidneys

How blood water level is controlled when too concentrated

Exercising on a hot day leads to sweating which is losing water. If blood is too concentrated, in other words the water level falls:

1. Pituitary gland releases the hormone ADH into the bloodstream.

2. ADH travels to the kidneys and it causes the kidney tubules to become more permeable to water (more water can pass out).

3. This means more water is reabsorbed from the tubules back into the blood.

4. Because of this less urine is produced and the amount of water in blood rises back to its normal level.

5. As the blood water level returns to normal, the pituitary gland stops releasing ADH.

   This is a negative feedback cycle

How blood water level is controlled when too dilute

Drinking a large amount of water means the blood water conc rises:

1. Pituitary gland stops releasing ADH

2. This means the kidneys reabsorb less water into the blood

3. Now more urine is produced and blood water conc return to normal

Kidney failure and treatment

• Kidney failure means their blood has a higher conc of water, ions and urea than it should

• Kidney dialysis machine: these concs need to be adjusted using this machine

How kidney dialysis machine works

1. Patients blood passes over a semi-permeable membrane. This allows urea, ions and water through but not larger molecules like proteins or blood cells to pass.

2. On the other side of the membrane there is dialysis fluid - containing normal concs of water/ions but doesn’t contain any urea.

3. We have a conc gradient for urea so it diffuses from the blood into the fluid.

   • fluid is constantly refreshed so theres always a large conc gradient

4. Since it contains normal concs of water/ions, this means some of the water/ions will diffuse from the blood into the fluid.

   • due to this, the conc of ions/water will return back to normal in the patient

Cons of kidney dialysis

• inconvenient - visit hospital several times a week

• controlled diet so they don’t produce too much urea

Alternative of kidney dialysis and its issues

Kidney transplant:

• diseased kidney is replaced with a healthy kidney from a donor

Issues:

• donated kidney may be rejected by patients immune system

Dialysis vs Kidney transplant

Dialysis:

• no shortage of machines

• requires frequent treatments and controlled diet

• expensive in long term

Transplant:

• Shortage of kidney donors

• Patient can lead normal life

• Only expensive initially, less in the long term

• Patients must take anti-rejection drugs for lifetime

v11 - Maintaining the body’s water balance

Human reproduction, puberty and hormones released by organs

• endocrine system is very important in human reproduction since during puberty, reproductive hormones cause secondary sexual characteristics to develop (pubic hair)

• in men the testes produce testosterone hormone which stimulates the testes to produce sperm

• in women the ovaries produce oestrogen hormone

Ovulation def, process and steps

• Puberty begins: eggs (in ovaries) start maturing and every 28 days one’s released - part of the menstrual cycle

• In preparation, the uterus lining becomes thick and spongy

• Egg makes its way down to the uterus

  • if sperm is present then the egg can be fertilised

  • it’ll implant into the uterus wall and develop into a baby

• Period: If not fertilised, then both the egg and the uterus lining are released

Menstrual cycle key hormones functions

• Follicle stimulating hormone (FSH) causes an egg to mature in the ovary

• Luteinising hormone (LH) causes this egg to be released (ovulation)

• Oestrogen and progesterone are involved in maintaining uterus lining in case the egg is fertilised and implants

Menstrual cycle key hormones interactions and stages

1. FSH is released by the pituitary gland. It travels in the blood to the ovaries where it matures an egg.

2. At the same time, FSH triggers the ovaries to make oestrogen which causes uterus lining to thicken. Oestrogen also stops pituitary gland from releasing anymore FSH

3. Instead the pituitary gland now releases LH which triggers ovulation (mature egg is released into the uterus).

4. Once ovary releases it, ovaries now produces progesterone. This stops the pituitary gland from releasing FSH and LH to prevent any more eggs from maturing or being released. Progesterone also keeps the uterus lining thick in case a fertilised egg implants.

5. If fertilisation doesn’t happen then progesterone level falls. Uterus lining and egg are now released = period.

Menstrual cycle graph interpretations

• FSH level rises and this triggers ovaries to release oestrogen

• As oestrogen level increases, this inhibits (stops) FSH production = FSH falls

• Oestrogen triggers LH release so LH level rises to a peak around day 14

• LH triggers ovulation and once this happens the ovary releases progesterone = progesterone levels rise

• If fertilisation doesn’t happen then progesterone levels fall and woman has period

v12 - menstrual cycle

Contraception and all types

Ways to prevent fertilisation:

• Contraceptive pill, Implant, skin patch or injection - Hormonal

• Condom, diaphragm - Barrier method

• Intrauterine device/IUD (coil)

• Surgical forms (sterillisation)

• Abstinence from sex during time after ovulation - natural contraception

Contraceptive pill, how it works and pros/cons

• very common

• contains hormones that prevent FSH production. FSH causes egg to mature = pill stops egg maturing

• Advantage

  • highly effective if taken correctly

• Disadvantage

  • must be taken daily

  • certain pills have side-effects: increase in breast cancer or blood clot risks

  • doesn’t protect against STIs (HIV)

Implant, skin patch or injection, how it works and pros/cons

• Hormonal contraception: contains progesterone - stops eggs from maturing/releasing

• Advantage

  • more convenient than a daily pill - e.g implant last for 3 years, injection 13 weeks and patch 1 week

• Disadvantage

  • side-effects

  • doesn’t protect against STIs (HIV)

Condom, diaphragm, how it works and pros/cons

Barrier method: prevent sperm from reaching an egg.

Both condoms/diaphragm are more effective w spermicide gel that kills/disables sperm and reduces fertilisation chances.

• Advantage:

  • effective if used correctly

  • no hormones used = no side-effects

  • reduce STI risk

• Disadvantage:

  • can break or slip off

Intrauterine device/IUD (coil), how it works and pros/cons

• Prevent an embryo from implanting

• Some coils release hormones to reduce fertilisation chances

• Advantage:

  • IUD is highly effective and can prevent pregnancy for up to 10 years

  • very few side effects

• Disadvantage:

  • doesn’t protect against STI

Surgical contraception, how it works and pros/cons

• Called sterilisation

• Women - prevents egg from reaching the uterus

• Men - prevents sperm from leaving the penis

• Advantage:

  • both are highly effective

• Disadvantage:

  • very hard to reverse so patient must be certain of never having a child

  • don’t protect against STIs

Abstinence, how it works and pros/cons

• abstaining from sex during time after ovulation

• natural contraception

• catholic church says all contraception is unethical except natural contraception

• Disadvantage:

  • very hard to tell when a woman has ovulated

  • doesn’t protect from STIs

v13 - Contraception

Infertility

• Men - reduced sperm count

• Women - difficult to conceive

Fertility treatment in women - “Fertility Drug”

• FSH and LH are given - causing more ovulation than usual therefore increasing pregnancy chances through sex

Fertility treatment in women - “In-vitro fertilisation (IVF)”

1. Mother is treated with the fertility drug - causes several eggs to mature and eggs are collected

2. Sperm are collected and used to fertilise eggs in a lab, which turn into embryos

3. Once embryos are tiny balls of cells, these are inserted into uterus

4. They develop inside mother in the usual way

IVF pros/cons

Advantage:

• gives woman chance to have her own baby

Disadvantages:

• success rates aren’t high

• emotionally stressful for both parents

• physically demanding on mother - fertility drug and egg collection

• can lead to multiple births - risky for babies and the mother

• not all embryos created will be transferred into mother = destroying can be unethical

• expensive - some think money could be spent on other medical issues (cancer)

v14 - hormones to treat infertility

Adrenal glands location and main effects

• Top of the kidneys and releases adrenaline

• Increase heart rate = more oxygen and glucose delivered in blood to brain and muscles. Both are needed for aerobic respiration.

• Prepares the body to either fight or run away - fight or flight

Thyroid gland location and main effects

• base of the neck and releases thyroxine

• stimulates body’s basal metabolic rate - makes chemical reactions happen at a faster rate

• important in growth and development

• thyroxine level in blood is controlled by negative feedback

Negative feedback with thyroxine example and other non-detailed examples in the body

1. Blood thyroxine level is monitored by the brain. Level falls = pituitary gland releases TSH into bloodstream.

2. TSH triggers thyroid gland to release more thyroxine into blood

3. Increased thyroxine level is detected by brain. This prevents the pituitary gland from releasing TSH.

4. As TSH level falls, thyroid gland releases less thyroxine.

• Negative feedback cycle= As thyroxine level falls, events are triggered which cause thyroxine levels to increase. If levels are too high, events are triggered to bring it back down.

• Other examples: control of blood glucose, or in the menstrual cycle