Homeostasis and Response Flashcards
Homeostasis
Regulation of internal conditions of a cell or organism to maintain optimum conditions for function in response to internal + external changes
What does homeostasis maintain optimal conditions for
- enzyme action
- all cell functions
What do automatic control systems maintain in body
- body temperature
- blood glucose level
- water content
Main components of automatic control systems
- receptor cells
- coordination centres
- effectors
Receptor cells
Detect stimuli - changes in environment
Coordination centres
Receive + process information from receptors - to organise response
Examples coordination centres
- brain
- spinal cord
- pancreas
Effectors
Muscles/glands which bring about responses which restore optimum levels when stimulated by coordination centre
Function of nervous system
Enables humans to react to surroundings and coordinate behaviour
Parts of nervous system
- central nervous system
- sensory neurons
- motor neurons
- effectors
Sensory neurons
Carry electrical impulses from receptors to CNS
Motor neurons
Carry electrical impulses from CNS to effectors
Examples of receptors
- taste receptors on tongue
- sound receptors in ears
What can receptors form part of
Larger, complex organs
Function of effectors in nervous system
Muscles/glands which respond to nervous impulses - muscles may contract, glands may secrete hormones
How does CNS coordinate response
- receptor stimulated
- sensory neurons carry information from receptors to CNS
- CNS decides what to do - coordinates response
- CNS sends info to effectors along motor neurons and response happens
Synapse
Connection between 2 neurons
How do nerve signals move between neurons
- chemical diffusion
- chemicals set off new electrical signal to next neuron
Reflexes
Rapid, automatic responses to certain stimuli, don’t involve conscious part of brain - can reduce chance of being injured
Reflex arc
Passage of information in a reflex from receptor to effector
Order of reflex arc
- stimulus
- receptor
- sensory neuron
- CNS
- relay neuron
- motor neuron
- effector
- response
Reflex arc
- receptors detect stimulus
- impulse sent along sensory neuron to relay neuron in CNS
- impulse reaches synapse between sensory/relay neuron - they trigger chemical release causing impulse to be sent along relay neuron
- impulses reach synapse between relay/moror neuron - chemicals released to send impulse along motor neuron to effector
Reaction time
Time it takes to respond to a stimulus - often less than a second
Factors affecting reaction time
- age
- gender
- drugs
Reaction time PRACTICAL
- person sits with arm resting on edge of table
- tester holds ruler vertically with 0 end level between person’s thumb/forefinger
- tester lets go of ruler without warning - person tries to catch ruler as fast as they can
- reaction time - number on ruler above thumb where it was caught
- repeat several times - mean time
- CVs - same person + hand + ruler height
More accurate way of measuring reaction time
Computer tests - e.g- click mouse when see stimulus on screen
Benefits of using computer reaction time tests
- more precise - no human errors in measurement
- more accurate - time in milliseconds
- remove possibility of person predicting when ruler will drop for example using body language
Hormones
Chemical messengers sent in blood
Where do hormones go
- released directly into blood
- carried in blood to target organs
Target organs
Particular organs which hormones only affect
Why are hormones needed
To control things in organs/cells that need constant adjustment
Endocrine glands
- various glands which produce + secrete hormones
- make up endocrine system
Endocrine glands in body
- pituitary glands
- pancreas
- thyroid
- adrenal gland
- ovary
- testes
Pituitary gland
- in brain
- ‘master gland’
- secretes several hormones into the blood in response to body conditions
- the hormones act on other glands to stimulate other
hormones to be released to bring about effects
Pituitary gland hormone
- FSH
- LH
FSH/LH target organ
Ovaries
Pancreas hormone
- insulin
- glucagon
Insulin/glucagon target organ
Liver
Insulin/glucagon effect
Monitors/controls changes of glucose levels in blood
Thyroid hormones
Thyroxine
Thyroxine target organ
Heart
Adrenal gland hormone
Adrenaline
Adrenaline target organ
- heart
- muscles
Oestrogen target organ
Uterus
Testes hormone
Testosterone
Testosterone target organ
Testes
Testosterone effect
- controls male puberty
- stimulates sperm production
Difference between nerves/hormones
- nerves act fast, hormones act slower
- nerves act for short time, hormones act for long time
- nerves act on precise area, hormones act in more general way
When are nerves needed
For when you need a quick response - e.g- reflex
Why are hormones needed
For when you need a long lasting effect - e.g- adrenaline in ‘fight/flight’
How does glucose get into blood
Eating foods containing carbohydrates puts glucose into blood from gut
How is glucose removed from blood
- normal metabolism removes it
- vigorous exercise removes much more
What happens to excess glucose
Stored as glycogen in liver/muscles
What happens if blood glucose too high
- insulin released into blood
- this makes liver turn glucose into glycogen
What happens if blood glucose too low
- glucagon released
- glucose moves from blood into cells
- liver turn glycogen into glucose
Type 1 diabetes
Pancreas produces too little or no insulin - blood glucose level can rise to death
Type 1 diabetes treatment
- insulin therapy - several insulin injections throughout day to ensure glucose is removed
- usually at mealtimes
- very effective
- amount of insulin depends on diet + activity
Type 2 diabetes
- person becomes resistant to own insulin - still produced but body cells don’t respond to hormone
- blood sugar can rise to dangerous level
Type 2 diabetes control
- obesity risk factor
- carbohydrate controlled diet
- regular exercise
What do hormones do at puberty
Release sex hormones that trigger off secondary sexual characteristics + cause eggs to mature in women
Male secondary sex characteristic
Facial hair
Female secondary sex characteristic
Breasts
Menstrual cycle STAGE 1
- day 1 - menstruation
- uterus lining breaks down for about 4 days
Menstrual cycle STAGE 2
- days 4-14 - uterus lining builds up again
- builds up into thick spongy layer full of blood vessels, ready to receive fertilised egg
Menstrual cycle STAGE 3
- day 14 - ovulation
- egg develops + released
Menstrual cycle STAGE 4
- days 14-28 - wall maintained
- if no fertilised egg has landed on uterus wall by day 28, spongy lining breaks down, cycle restarts
Hormones controlling menstrual cycle
- FSH
- oestrogen
- LH
- progesterone
FSH
- produced in pituitary gland
- causes egg to mature in one of the ovaries in a follicle
- stimulates ovaries to produce oestrogen
What does FSH stand for
Follicle Stimulating Hormone
Oestrogen
- produced in ovaries
- causing lining of uterus to grow
- stimulates release of LH + inhibits release of FSH
LH
- produced by pituitary gland
- stimulates release of egg at ovulation (day 14)
What does LH stand for
Luteinising hormone
Progesterone
- produced in ovaries by remains of follicle after ovulation
- maintains uterus lining in 2nd half of cycle
- progesterone levels fall - lining breaks down
Hormonal contraceptions
- oestrogen
- progesterone
How is oestrogen a contraception
- prevents release of egg
- taken everyday - keeps level permanently high, inhibits production of FSH, egg development/production eventually stop
How is progesterone a contraception
Stimulates production of thick mucus, preventing sperm getting through and reaching egg
The pill
- combined oral contraceptive pill
- contains oestrogen + progesterone
Effectiveness of the pill
Over 99%
Downsides of the pill
- side effects - headaches + nausea
- doesn’t protect against STDs
Benefits of progesterone-only pill
- fewer side effects than the pill
- just as effective
Contraceptive patch
- contains oestrogen + progesterone
- small 5cmx5cm patch stuck to skin
- lasts 1 week
Contraceptive implant
- inserted under skin of arm
- continuously releases progesterone - makes it hard for sperm to swim to egg
- lasts up to 3 years
Intrauterine device (IUD)
- T-shaped device inserted into uterus to kill sperm + prevent implantation of fertilised egg
Types of IUD
- plastic
- copper
Plastic IUD
Releases progesterone
Copper IUD
Prevent sperm surviving in uterus
How do barrier methods work as contraception
Stop sperm getting to egg
Barrier contraceptive methods
- condoms
- diaphragm
- spermicide
Condoms
- worn over penis during vaginal intercourse to stop prevent sperm entering vagina
- only form of contraception to protect against STIs
Diaphragm
- shallow plastic cup fit over cervix
- must be used with spermicide
Spermicide
- substance that disables/kills sperm
- 70-80% effective
Sterilisation
- cutting/tying fallopian tubes in female OR sperm duct in male
- permanent procedure
Natural contraceptive method
- finding when in menstrual cycle woman is most fertile, avoiding having sexual intercourse those days
- not very effective
Abstinence
- not having sexual intercourse
- only way to be completely sure sperm and egg don’t meet
Cause of female not being able to get pregnant
- levels of FSH too low to cause eggs to mature
- no eggs are released and woman can’t get pregnant
Methods of helping fertile women have babies
- fertility drug
- IVF
What does a fertility drug contain
- FSH
- LH
How do fertility drugs work
They stimulate ovulation
Pros of fertility drugs
Help many women get pregnant when they previously couldn’t
Cons of fertility drugs
- doesn’t always work - some women have to do it many times, can be expensive
- too many eggs could be stimulated - unexpected multiple multiple pregnancies
What does IVF stand for
In Vitro Fertilisation
How does IVF work
- FHS + LH given to stimulate eggs to mature
- collect eggs from woman’s ovaries
- fertilise them in lab with man’s sperm
- fertilised eggs grow into embryos in laboratory incubator
- 1/2 embryos transferred into woman’s uterus
What does ICSI stand for
Intra-Cytoplasmic Sperm Injection
How is ICSI used with IVF
Sperm injected directly into egg
When is ICSI often used
When man has low sperm count
Pros of IVF
Can give infertile couple a child
Cons of IVF
- may be multiple births - more than 1 embryo may grow into baby, risky for mother/babies (higher risk of miscarriage)
- low success rate - about 26% in UK, can be stressful/upsetting
- physically stressful for woman - may be reactions to hormones - vomiting, dehydration
Developments in IVF
- advances in microscopes
- specialised micro-tools
- time-lapse imaging
How can specialised micro-tools help IVF
- can be used on eggs/sperm under microscope
- can remove single cells from embryo for genetic testing to check it’s health
Time-lapse imaging
Using microscope + camera built into incubaor
How can time-lapse imaging help IVF
- use microscope + camera built into incubator
- growth of embryos can be continuously monitored to help identify those more likely to result in pregnancy
Ethical issues with IVF
- unused embryos usually destroyed, this is potential human life
- people think genetic testing before implantation can lead to selection of preferred characteristic (gender, age, ect.)
When is adrenaline released
When brain detects fear/stress and sends nervous impulses to adrenal glands, secreting adrenaline
Effect adrenaline on body
- prepares body for ‘fight/flight’
- triggers mechanisms that increase supply of oxygen/glucose to cells in brain/muscles - e.g- increases heart rate
Negative feedback systems
- body detects level of substance has gone above/below normal level
- it triggers response to bring level back to normal again
What is thyroxine made of
- iodine
- amino acids
Thyroxine function
- plays in regulating basal metabolic rate - speed at which chemical reactions occur in body while at rest
- also stimulates protein synthesis for growth + development
When is thyroxine released
In response to thyroid stimulating hormone (TSH) being released from pituitary gland
How is thyroxine in blood kept at right level
negative feedback system
How does thyroxine use negative feedback system
When level of thyroxine in blood higher than nomal, secretion of TSH from pituitary gland inhibited - reduces amount of thyroxine released
