Homeostasis and Response
A mind map of the whole AQA Homeostasis and Response topic
- Created by: B.B.Revision
- Created on: 19-06-20 12:43
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- Homeostasis and Response
- Homeostasis
- The Human Nervous System
- The Central Nervous System
- Key components of the CNS are the brain, the spinal cord and neurones
- Synapses
- They are gaps between neurones for electrical impulses to travel across
- They can be found at each junction of a reflex arc
- First an electrical impulse reaches the end of the neurone before the synapse
- Then it triggers the release of neurotransmitters that diffuse across the synapse
- At the other end of the synapse, the neurotransmitters bind to receptors and their presence causes the release of more electrical impulses
- Then it triggers the release of neurotransmitters that diffuse across the synapse
- Reflexes
- Reflexes allow us to respond quickly to situations without conscious thought. This means that the impulses go through a reflex arc which doesn’t include the brain
- E.g. blinking, sneezing, dropping hot objects etc
- Components of a reflex arc
- Stimulus - change in the environment
- Receptor - detect stimuli
- Neurones - carry electrical impulses
- Can be sensory neurones (carries impulse to the CNS), relay neurones (really signals from sensory neurone to motor neurone in CNS), or motor neurone (carries impulse from CNS to effector)
- Effector - brings about the response to the stimulus
- Response - an action that helps you avoid a dangerous situation
- Can be tested with the reaction time practical
- One person sits down while the other holds the ruler with 0cm at the top of the person sitting’s hand
- Then the standing person drops the ruler and the sitting person catches it
- Record the measurement at which the person catches it and use a conversion table to find their reaction time. Then repeat the experiment and find the mean reaction time
- Then the standing person drops the ruler and the sitting person catches it
- One person sits down while the other holds the ruler with 0cm at the top of the person sitting’s hand
- Reflexes allow us to respond quickly to situations without conscious thought. This means that the impulses go through a reflex arc which doesn’t include the brain
- The brain
- The brain is a complex organ made of many neurones and split into different sections
- Medulla - responsible for unconscious activities
- Cerebellum - muscle coordination
- Cerebral Cortex - conscious thought
- Lots of studies have been done on the brain and electrical impulses and MRI scans have helped treat brain diseases and increase understanding of the brain
- The brain is a complex organ made of many neurones and split into different sections
- The Eye
- Eye Anatomy
- Link to eye diagram
- Accommodation
- When the lens changes shape in order to refract light at varying distances and focus on objects
- Close up - ciliary muscles contract and suspensory ligaments relax making the lens thicker and rounder causing greater refraction
- Far away - ciliary muscles relax and suspenseful ligaments contract making the lens flatter and thinner causing less light refraction
- When the lens changes shape in order to refract light at varying distances and focus on objects
- Iris causes adaptation to different light levels by changing the size of the pupil to reduce or increase the amount of light that reaches the retina
- Eye Defects
- Myopia - short sightedness
- Light is focused in front of the retina
- Hyperopia - long sightedness
- Light focused behind the retina
- Fixed by using lenses in glasses or contact lenses to refract light better. Laser eye surgery and replacement lenses are also options
- Myopia - short sightedness
- Eye Anatomy
- Control of Body Temperature
- The thermoregulatory centre of the brain monitors temperature as blood flows through it
- Receptors in the skin monitor body surface temperature
- Ideal body temperature is 37 degrees Celsius
- Too cold
- Muscle contractions increase (shivering)
- Requires energy through respiration which produces heat, warming us up
- Hairs stand on end
- Traps an insulating layer of air around the body
- Vasoconstriction
- Less blood goes to your extremities so less can be transferred to the surroundings
- Muscle contractions increase (shivering)
- Too hot
- Sweat
- Goes onto the surface of the skin and holds heat energy. When it has enough energy it evaporates, taking heat with it and cooling us down
- Hairs lie flat
- Vasodilation
- More blood goes to the capillaries at the edge of our skin making more heat to be transferred to the surroundings
- Sweat
- The Central Nervous System
- Homeostasis is all the processes within a cell or body that help to maintain optimal conditions
- The conditions that need to be regulated
- Water
- Blood Sugar
- Internal body temperature
- CO2 levels
- Urea concentration (in urine)
- Control systems
- They are made up of effectors, receptors and control centres
- Effectors are muscles or glands that carry out the responses to stimuli in order to maintain optimum levels
- Receptors detect changes in the external or internal environment
- Coordination centres receive and process information from receptors
- They can be either nervous or chemical
- They use a negative feedback loop
- They are made up of effectors, receptors and control centres
- The Human Nervous System
- Hormonal Coordination in Humans
- The Endocrine System
- Coordinates the body’s response to changes in the environment using hormones
- Hormones are chemical messengers released into the blood to be sent to organs
- There are lots of different endocrine glands
- Thyroid - in the neck and releases thyroxine which controls metabolism, heart rate and temperature
- Ovaries - female only, produce oestrogen and controls puberty an the menstrual cycle
- Testes - male only, helps control puberty and sperm release
- Pancreas - produces glucagon and insulin and help regulate blood sugar
- Pituitary gland - master gland, produces hormones in response to changes in the hypothalamus, triggers other glands to release hormones
- Adrenal Glands - above each kidney, produce adrenaline for fight or flight response
- Different to nervous system in many ways...
- Slower response
- Uses chemical messengers in the blood
- Response can be long lasting
- Can act on large areas of the body
- Coordinates the body’s response to changes in the environment using hormones
- Blood Glucose
- It is important to keep glucose levels within a range because too little can cause tiredness as glucose is needed for respiration which provides energy and too much can damage osmosis
- As blood flows through the pancreas, the body detects the glucose concentration and releases hormones in a negative feedback loop if it is too high or too low
- If too high, the pancreas releases insulin to bring it down
- Insulin converts excess glucose into glycogen to be stored in the liver
- If too low, the pancreas produces glucagon to bring it up
- When glucagon is detected, the liver turns glycogen back into glucose and sends it into the blood
- If too high, the pancreas releases insulin to bring it down
- Some people have a condition called diabetes which means they are unable to regulate their blood sugar
- Type 1 - a person doesn’t produce enough insulin, probably caused by the body attacking pancreas cells, develops in childhood
- Treated by regulating diet and injecting insulin
- Type 2 - a person’s body no longer responds to insulin, this is usually caused by being overweight or old age, develops in adulthood
- Treated by regulating diet and exercise
- Type 1 - a person doesn’t produce enough insulin, probably caused by the body attacking pancreas cells, develops in childhood
- Kidneys
- Control of water balance
- It is important to control the amount of water and ions diffusing in and out of cells
- Balance can be disrupted by: sweating, illness, exhaling and eating too much salt
- Ion levels must be kept constant to keep normal diffusion between cells
- Water volume is monitoring by the hypothalamus
- If there is too much water, the hypothalamus inhibits the release of ADH which means less water is reabsorbed
- It is important to control the amount of water and ions diffusing in and out of cells
- Main functions to filter blood and produce urine to get rid of urea and excess water
- Urea is toxic to cells and is formed by: excess amino acids and ammonia produced by deamination
- Kidneys contain nephrons in which the two stages of urine production take place
- Ultrafiltration - the blood is filtered and all urea, water and salts move into a nephron tubule as the blood cells and proteins are too big
- Selective Reabsorption - useful substances are reabsorbed into the blood . This leaves urea and excess salts and water to form urine which is collected be the kidneys and travels to the bladder to be excreted
- If there is too little water, the hypothalamus triggers ADH to be released which increases the permeability of the tubules to more water is reabsorbed
- Some people’s kidneys don’t filter blood properly so they need to have kidney dialysis which replicates what the tubules do
- Disadvantages: takes 3-4 hours, three times a week, increased risk of blood clots and infections, expensive
- Advantages: lifesaving process, gives the patient more time to find a kidney donor
- Some people get transplants if one becomes available. People usually choose to get one from a family member as their body is less likely to reject it but they will still need to take immunosuppressants
- Advantages: cheaper than dialysis, patient doesn’t need dialysis anymore
- Disadvantages: need to take immunosuppressants, kidney may be rejected by the body, long waiting list
- Control of water balance
- Puberty and hormones
- In girls it stimulates the production of oestrogen and the menstrual cycle as well as breast development and pubic hair growth
- In boys the hormone testosterone rises causing sperm production, facial and pubic hair grows, voice deepens
- The menstrual cycle is the process in women which involves the maturation and release of an egg. If sexual intercourse occurs then pregnancy may occur
- One egg matures each month once a female reaches puberty. There are many hormones involved in menstruation
- They are: FSH, LH, oestrogen and progesterone
- FSH: causes the eggs to mature and stimulates the production of oestrogen
- LH: released by pituitary gland and stimulates ovulation
- Oestrogen: produced in ovaries, builds up the uterus lining, inhibits the release FSH and stimulates the production of LH
- Progesterone: produced in the ovaries, maintains uterus lining (days 14-28) and inhibits the production of LH and FSH
- They are: FSH, LH, oestrogen and progesterone
- One egg matures each month once a female reaches puberty. There are many hormones involved in menstruation
- Contraception
- Pharmaceutical companies have designed contraceptive methods to reduce the likelihood of a pregnancy
- progesterone only pill, stimulates production of thick mucus that stops sperm getting through, stops FSH which means eggs don’t mature
- Combined pill, contains progesterone and oestrogen and taken daily, produces enough FSH to stop eggs maturing. It has more side-effects than the progesterone only pill
- Contraceptive implant - lasts for three years, placed under the skin, slowly releases progesterone
- Contraceptive injection - lasts up to three months, contains progesterone
- Intrauterine devices - inserted into the uterus, stop implantation, some release progesterone
- Diaphragms - shallow plastic cups, sit at entrance to uterus, prevent sperm coming past, sometimes covered in spermicide
- Condoms - worn by the male on his penis during sexual intercourse which prevents sperm entering the female, has spermicide to kill sperm
- Sterilisation - permanent, for a woman means having fallopian tubes cut, for a man means having the sperm duct cut
- There are also natural methods such as avoiding sexual intercourse when the woman is ovulating or abstinence
- Contraceptive patch - only changed once a week, worn on skin, slowly releases progesterone
- Pharmaceutical companies have designed contraceptive methods to reduce the likelihood of a pregnancy
- Treating infertility
- Some people have low hormone levels which means that they are unable to have children
- This can be treated by prescribed fertility drugs or IVF
- Fertility drugs - contain FSH and LH to stimulate the growth of more eggs
- IVF - patients are given fertility drugs, the eggs are collected and so are some of the male’s sperm before being fertilised in a laboratory. It grows into an embryo and is then implanted into the uterus
- This can be treated by prescribed fertility drugs or IVF
- Some people have low hormone levels which means that they are unable to have children
- The Endocrine System
- Plant Hormones
- Gibberellins are important in starting of the germination process of plants
- Used to increase flower and fruit size and initiate germination
- Auxins change growth patterns to allow plants to grow away fro m or towards a stimulus (tropisms)
- Tropisms can be split into phototropismsand gravitropisms which are either positive or negative
- A positive phototropism grows towards the light, a negative grows away from the light
- A positive gravitropism grows in the direction of gravity and a negative away
- Used in weed killers
- Tropisms can be split into phototropismsand gravitropisms which are either positive or negative
- Ethene - controls cell division and ripening of fruits
- It is used in the food industry to control the ripening of fruit
- Gibberellins are important in starting of the germination process of plants
- Homeostasis
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