5) Homeostasis and Response

What is homeostasis?

the regulation of an internal environment to maintain optimum conditions for cell/enzyme function in response to internal and external changes.

What 3 things does homeostasis control?

Blood glucose concentration
Body temperature
Water levels

What 3 things do all automatic control systems have?

- Receptors
- Coordination centres
- Effectors

What are receptors?

Cells that detect stimuli (changes in the environment)

What are coordination centres?

process the information received from the receptors, e.g. brain, spinal cord and pancreas

What are effectors?

bring about responses to bring conditions in the body back to optimum levels (muscles or glands)

What is the purpose of the nervous system?

enables humans to react to their surroundings and to coordinate their behaviour

What is the CNS comprised of?

brain and spinal cord

What is the order of the reflex arc?

stimulus,
receptor,
sensory neurone,
relay neurone,
motor neurone,
effector,
response

Describe the usual response to stimuli (4)

1) Receptor cells convert a stimulus into an electrical impulse

2) The impulse travels along sensory neurones to the CNS

3) Information is process and response is coordinated - electrical impulse is sent along motor neurones to effectors.

4) Effectors carry out the response (muscles contract, glands secrete hormones)

What are reflexes and why are they important?

Reflexes are rapid, automatic responses that do not involve the conscious part of the brain

They're important to prevent harm

Describe the reflex arc (5)

1) Stimulus detected by receptors

2) Impulses sent along sensory neurone

3) In the CNS - impulse passes to relay neurone

4) Impulses sent along motor neurone

5) Impulse reaches effector - results in a reponse.

What are 2 examples of reflex arcs?

Pupils getting smaller to avoid retinal damage (bright lights)

Moving your hand from a hot surface to prevent damage

What is a synapse?

Gap between neurons

Describe how impulses cross synapses (3)

1) Impulse reaches end of neuron - chemical is released into synapse.

2) Chemical diffuses across the synapse.

3) When the chemical reaches the second neuron, it triggers the impulse to begin again in the next neuron.

What is reaction time and how is it measured?

How long it takes you to react to a stimulus.

It can be measured with the ruler drop test.

What is the brain's function and what is it made of?

The brain controls complex behaviour.

It is made of billions of interconnected neurones and has different regions that carry out different functions.

Describe the function and location of the cerebral cortex (cerebrum)

Top/outer part of the brain

Controls consciousness, intelligence, memory and language

Describe the function and location of the cerebellum

Rounded structure at bottom/back of the brain

Controls movement of muscles + balance.

Describe the function and location of the medulla

Found in the brain stem in front of the cerebellum

Controls unconscious actions such as breathing and heart rate

Why is studying/treating the brain difficult? (4)

1) It is complex/delicate

2) It is easily damaged

3) It's not fully understood which part of the brain does what

4) Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it

How do neuroscientists study the brain?

1) Studying patients with brain damage - can provide info on the role a certain area of the brain has.

2) Electrically stimulating parts of the brain - stimulation may result in mental/physical change.

3) MRI Scans - creates an image of the brain - shows which part is active during a task or affected by a tumour.

What is the retina? (2-3)

Layer of light sensitive cells (rods and cones) found at the back of the eye.

When light hits, the cells are stimulated. Impulses are sent to the brain, which interprets info to create an image.

What is the optic nerve? (2)

A nerve that leaves the eye and leads to the brain.

It carries impulses from the retina to the brain to create an image.

What is the sclera?

White outer layer which supports internal eye structures - strong to prevent some damage

What is the cornea? (2)

Transparent layer at the front of the eye.

Allows light through and it's curved surfave bends/focuses light onto retina.

What is the iris?

Muscles that surround the pupil.

They contract or relax to alter the size of the pupil (accomodation)

What is the eye?

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

What are the ciliary muscles?

muscles which relax or contract to alter the shape and focal length of the lens

What are suspensory ligaments?

Ligaments connecting ciliary muscle to the lens, control accommodation (focusing).

What is accomodation?

the process of changing the shape of the lens to focus on near or distant objects.

Describe accomodation for a near object (3)

the ciliary muscles contract

• the suspensory ligaments loosen

• the lens is then thicker and refracts light rays strongly.

Describe accommodation for a distant object (3)

• the ciliary muscles relax

• the suspensory ligaments are pulled tight

• the lens is then pulled thin and only slightly refracts light rays.

What is myopia? (3-4)

short-sightedness

light focuses in front of retina

lens is too curved (eye too long) - distant objects appear blurry

What is hyperopia? (4-5)

long-sightedness

light is focused behind the retina

Lens is too flat (eyeball too short) - cannot refract light enough

(near objects are out of focus)

List the 4 ways eye disorders can be treated

1) Spectacle lenses (Glasses)
2) Contact lenses
3) Laser eye surgery
4) Replacement lens

Describe how glasses (spectacle lenses) can treat myopia

Concave lenses

Spread out light rays (corrects)

Describe how glasses (spectacle lenses) can treat hyperopia

convex lenses

bring light rays together (refracts)

Describe contact lenses (3)

- sit on surface of the eye, almost invisible (ideal for sports)

- Hard + soft lenses

- Soft lenses are more comfortable, but have a higher infection risk.

Describe laser eye surgery (3-4)

- lasers used to change the shape of the cornea (risk of cateracts, retinal damage or infections)

Myopia - cornea is slimmed down, reducing refraction

Hyperopia - cornea shape (curvature) is changed, refraction is increased

Describe replacement lens surgery (2)

Hyperopia - replacing the lens with an artificial one or adding it on top of natural lens.

Risk of retinal damage, cataracts and blindness.

What is the pupil reflex?

carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light

Describe how the eye adapts to dim light

Circular muscles relax
Radial muscles contract
Pupil is dilated (more light enters eye)

Describe how the eye adapts to bright light

Circular muscles contract
Radial muscles relax
Pupil is constricted (less light enters eye)

What controls body temperature?

Thermoregulatory centre (hypothalamus)

How does the thermoregulatory centre monitor body temperature? (2)

- Contains receptors that monitor the temperature of the blood

- Thermoreceptors in the skin send impulses to the thermoregulatory centre

What is the optimum human body temperature?

37°C

What happens when body temperature is too high? (4)

- Sweat is produced from sweat glands (evaporates from skin surface, increased energy transfer away from body)

- Vasodilation - more blood flows closer to surface of skin, increased energy transfer away from body.

(Arterioles dilate, shunt vessel constricts)

- Hairs lie flat - reduces insulation as air can freely circulate, increases heat loss.

What happens when body temperature is too low? (5)

- sweating stops

- Shivering (skeletal muscles contract rapidly) to generate heat from respiration (exothermic)

- Hairs stand on end, creates insulating layer, traps warm air

- Vasoconstriction - blood doesn't flow close to the surface, less heat lost

(Arterioles constrict, shunt vessel dilates)

What are the two communication systems?

nervous system and endocrine system

What is the endocrine system?

composed of glands which secrete chemicals called hormones directly into the bloodstream

What are hormones?

Chemical messengers (secreted by glands) that travel through the bloodstream to act upon a target organ to produce an effect

Compare nervous/chemical responses

Nervous are quicker, chemical last longer

What is the pituitary gland? (3-4)

The master gland

Secretes several hormones to have an effect on the body or act on other glands to stimulate them to produce different hormones

Secretes FSH, LH, TSH, ADH, GH, etc.

What is the pancreas? (2)

Secretes insulin
Controls blood glucose levels

What is the thyroid gland? (2)

Secretes thyroxine (stimulated by TSH)

Controls metabolic rate, heart rate and temperature

What is the adrenal gland? (2)

Secretes adrenaline

Involved in the fight or flight response (in times of stress)

What is the ovary? (2)

Secretes oestrogen

Involved in the menstrual cycle + development of female secondary sexual characteristics

What are the testes? (2)

Secretes testosterone

Involved in sperm production and development of secondary sexual characteristics

How is blood glucose concentration controlled?

By the pancreas - must be kept within a certain limit as glucose is needed by cells for respiration.

What happens when blood glucose levels are too high? (5)

1) Pancreas secretes insulin

2) Insulin binds to muscle/liver cells

3) Glucose moves from the blood into muscle cells for respiration

4) Excess glucose is converted to glycogen and stored in the liver

5) Blood glucose concentration is reduced.

What happens when blood glucose levels are too low? (5)

1) Pancreas secretes glucagon

2) Glucagon binds to liver cells

3) Causes glycogen to be broken down into glucose

4) Glucose is released into bloodstream

5) Blood glucose concentration is increased.

How is blood glucose concentration controlled by negative feedback? (2)

- When blood glucose levels increase/decrease, a hormone is secreted to counteract the change

- Action of this hormone cannot occur continually as when the blood reaches a certain glucose concentration the other hormone is produced, resulting in the opposite effect.

What is Type 1 diabetes?

1) The pancreas cannot produce enough insulin

2) Blood glucose level can rise to a fatal amount

3) Glucose is excreted in urine, lots of urine is produced - leaving individual thirsty.

How is Type 1 diabetes treated? (3)

1) Insulin injections at meal times - results in glucose being taken up from the bloodstream

2) Limit simple carbohydrates (have a balanced diet, get exercise)

3) Attempts to use pancreas and pancreatic cell transplants + genetically engineering pancreatic cells from mice to make insulin.

What is type 2 diabetes?

1) The body cells no longer respond to insulin

2) Blood glucose levels can rise to a fatal amount

3) Obesity is a risk factor

How is type 2 diabetes treated? (3)

1) Reduce number of simple carbs

2) Lose weight, increase exercise

3) Drugs to make insulin more effective on body cells - help the pancreas make more insulin or reduce amount of glucose absorbed from gut

What is osmosis?

Diffusion of water molecules/particles from a dilute solution (high concentration) to a concentrated solution (low concentration) across a semi-permeable membrane.

How is water/liquids lost from the body? (4)

1) Via lungs during exhalation

2) Water, ions and urea are lost from the skin during sweat

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

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

What happens to cells as they gain water? (3)

1) Water concentration of blood increases - body cells take up water.

2) Concentration of water in bloodstream is higher than that in cells - water moves into cells by osmosis.

3) Cells expand - may eventually result in damge or may burst. (If too much water)

What happens to cells as they lose water?

1) Water concentration of blood decreases, body cells lose water.

2) Concentration of water in bloodstream is lower than that in cells - water moves out of cells by osmosis.

3) Cells shrink as they lose water - won't function properly.

What is the function of 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 kidney make urine?

1) Filtering out waste products

2) Selectively reabsorbing useful substances (glucose, ions and water)

Describe deamination (3)

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 is ADH?

anti-diuretic hormone

controls loss of water as urine

Describe how ADH controls water loss (6)

1) Released by pituitary gland - when receptor detects that blood is too concentrated.

2) Travels in bloodstream to kidney tubules

3) Increased amount of ADH increases tubules permeability

4) More water moves out of the tubules and back into the bloodstream

5) Results in a smaller volume of more concentrated urine + less concentrated blood due to water

6) Example of negative feedback (if conc. of blood increases/decreases, more/less ADH is secreted to counteract the change?

What is kidney failure? (2)

When your kidneys stop working.

Means waste products build up, harmful to the body and eventually results in death.

How can kidney failure be treated?

Dialysis
Kidney Transplant

What is kidney dialysis?

where the function of the kidneys is carried out using an artificial membrane

Describe kidney dialysis (3)

1) Blood moves between partially permeable membranes surrounded by dialysis fluid

2) Fluid has same conc. of ions and glucose as healthy blood

3) Because of this, only excess ions/water diffuse across the membrane (useful ions/glucose remain)

Positives of kidney dialysis (2)

Acts as an artificial kidney

Keeps people alive while waiting for a transplant

Negatives of kidney dialysis (7)

1) Time consuming (3 times a week, for 3-4 hours)

2) Blood clots form

3) Follow a strict diet

4) Build up of waste products between sessions can leave you feeling ill

5) Unpleasant experience

6) May have to travel to a hospital (time consuming)

7) Expensive

What are kidney transplants? (3)

- Provides individual with a healthy kidney

- Currently the only cure

- Transplanted from people who have died suddenly, or from people who are still alive

Positives of a kidney transplant (4)

1) Cure

2) Person doesn't need to visit hospital as regularly as dialysis

3) Cheaper than overall cost of dialysis

4) Can reduce risk of rejection with immunosupressants

Negatives of kidney transplants

1) Body may reject organ as the immune system recognises antigens as foreign.

2) Immunosupressants leave a person vulnerable to other diseases

3) Transplanted kidneys don't last forever

4) Expensive if repeated

What is puberty?

reproductive hormones cause secondary sex characteristics to develop.

Name the 4 hormones involved in the menstrual cycle

1) Oestrogen
2) Progesterone
3) FSH (Follicle stimulating hormone)
4) LH (Luteinising hormone)

Describe testosterone (3)

Main male reproductive hormone

Produced by testes

Stimulates sperm production

Describe the menstrual cycle (4)

- Uterus lining breaks down, woman has period

- Layer builds up again until ovulation (Day14) occurs

- Egg is released from ovary and moves to uterus via fallopian tube

- If a fertilised egg is not embedded in the lining after 28 days, it begins to break down (egg + lining) and the cycle continues

What is oestrogen? (6)

Main female reproductive hormone

Causes lining of the uterus to grow again

Produced in ovary

Stimulated by FSH

Produces secondary sexual characteristics

Stimulates LH, inhibits FSH

What is FSH? (4)

follicle-stimulating hormone

causes egg maturation in ovary, within the follicle

produced in pituitary gland

stimulates oestrogen production

What is LH? (4)

Luteinising hormone

Produced in pituitary gland

Stimulated by oestrogen

Causes ovulation (release of an egg)

What is progesterone? (3)

Prduced in ovaries - secreted from egg follicle

Maintains uterus lining - supports pregnancy is egg is fertilised

Inhibits release of FSH + LH

What is contraception?

Methods used to prevent a woman from becoming pregnant during or following sexual intercourse

What are the two types of contraception?

hormonal and non-hormonal

Why must the contraceptive pill be taken regularly?

Otherwise, the bodies own hormones will be released, leading to egg maturation

What is the combined pill? (4) (5 side effects)

Contains oestrogen and progesterone

Both levels are high, inhibits FSH so eggs don't mature

Lining stops developing - mucus in cervix thickens to immobilise sperm

Side effects - mood swings, depression, breast pain, breast enlargement, increased blood pressure

What is the mini pill? (2)

Progesterone only

Has less side effects in comparison to the mixed pill

What is the contraceptive patch? (3)

Contains oestrogen + progesterone

Small, stuck on skin

Lasts for 7 days

What is the contraceptive implant? (4)

Continuous amount of progesterone

Prevents ovaries from releasing egg

Thickens mucus in cervix, immobilises sperm and stops fertilised eggs from embedding in uterus

Lasts for 3 years