Homeostasis Flashcards
Homeostasis
The regulation of conditions to maintain a stable internal environment, in response to internal and external conditions
Stimulus
A change in the environment
Receptor
An organ, tissue or cell that detects a stimulus
Coordination Centre
Receives receptor information, processes it and initiate a response, (brain, spinal cord)
Effector
An organ, tissue or cell that produces a response (either muscles contracting or glands secreting a hormone)
Synapse
A tiny gap between 2 nerve cells which signals must cross
Sensory Neurones
Carry impulses from the receptors to the CNS
Motor Neurones
Carry impulses from the CNS to the effectors
Nervous System Order
Stimulus - Receptors - Sensory Neurones - Coordination Centre (found in CNS) - Motor Neurones - Effector - Response
Reflex Arc
Nerve Pathway that underlies unconscious reflexes
Reflex Action
An automatic, rapid response to a stimulus which minimises any harm to the body
Cerebrum (Cerebral Cortex)
Responsible for:
- Consciousness
- Intelligence
- Memory
- Language
- Senses (sight, hearing, taste, etc)
Cerebellum
Responsible for:
- Balance
- Muscle coordination
Hypothalamus
Responsible for:
- Regulating body temperature
- Sends signals to pituitary gland
Medulla
Responsible for:
- Unconscious activities (e.g. breathing, heart rate)
How do scientists study brain?
- By studying people with brain damage
- By electrically stimulating different parts of the brain
- MRI scans
How do scientists study brain damage?
For example, if someone had a stroke which caused hearing loss, scientists would know the part of the brain responsible for hearing is damaged
How do scientists electrically stimulate different parts of the brain?
- Brain is stimulated using electrodes
- Stimulating certain areas creates certain reactions from the body
- From this scientists can tell what that part of the brain is responsible for
How do MRI scans work?
- Show details of brain structure and function
- Patients are asked to perform various tasks
- By looking at the scan, scientists can see which parts of the brain are active when the task is carried out
Risks of treating the brain
- Brain surgery can cause damage or side effects that can ruin a patient’s quality of life
- Surgery risks (tumours, infection, brain trauma)
- Brain is very complex and fragile so treating brain damage is difficult
Cornea
- Refracts (bends) light as it enters the eye
- Transparent to let light enter
- Contains no blood vessels, O2 diffuses through it
Iris
Controls how much light enters the eye
Pupil
Gap in the centre of the iris that allows light to pass through to the lens
Lens
Changes shape to further refract light so it focuses on the retina
Retina
Contains light receptors that help to see colour
Optic Nerve
Carries impulses between the eye and the brain
Sclera
Tough white outer layer of the eye that protects the eye from injury
Iris Reflex in bright light
- Reflex constricts the pupil (makes it smaller)
- Allows less light to pass through to the lens
- Prevents eye damage
Iris Reflex in low light
- Reflex dilates the pupil (makes it bigger)
- Allows more light to pass through to the lens
- Allows us to see more clearly in the dark
Iris Reflex in low light
- Reflex dilates the pupil (makes it bigger)
- Allows more light to pass through to the lens
- Allows us to see more clearly in the dark
Near Objects
- Ciliary Muscles contract
- Suspensory Ligament
slackens - Lens thickens and strongly refracts light rays
Distant Objects
- Ciliary Muscle relaxes
- Suspensory Ligament pulled taught
- Lens thins and slightly refracts light rays
Hyperopia (Long-Sightedness)
- Light rays don’t refract enough
- Image appears behind the retina
- Can’t focus on nearby objects
- Fixed using a convex lens
Myopia (Short-Sightedness)
- Light rays refract too much
- Image appears in front of the retina
- Can’t focus on distant objects
- Fixed using a concave lens
Other ways to correct vision
- Hard and soft contact lenses
-Laser surgery to change the shape of the cornea - Replacement lens in
the eye
Thermoregulation
The regulation of internal body temperature
Where is the thermoregulatory centre found?
In the hypothalamus
How do our bodies warm us up?
- Vasoconstriction (prevents heat loss through skin)
- Hairs stand up (trap insulating layer of air)
- Shivering (heat energy is released to warm us up)
How do our bodies cool us down?
- Vasodilation (causes heat energy loss)
- Erector muscles relax (hairs lie flat)
- Sweat - a mix of water and urea (evaporates and carries heat energy with it)
Pituitary Gland
Located below the centre of the brain and secretes many hormones
Thyroid
- Produces thyroxine
- Thyroid regulates metabolism
- Found in the neck
Adrenal Glands
- Produce adrenaline (released during fight or flight)
- Increases heart rate
- Above the kidneys
Pancreas
- Produces insulin + glucagon (lowers/raises blood glucose concentration)
- In front of the kidneys
Testes
- Only in males
- Produces testosterone (controls puberty)
- Produces male gametes (sperm)
Ovaries
- Only in females
- Produces oestrogen (controls puberty + menstrual cycle)
- Produces female gametes (eggs)
Differences between Endocrine and Nervous Systems
Endocrine:
- Relies on hormones that travel in the bloodstream
- Slower
- Hormones last longer
- More general
Nervous:
- Relies on electrical impulses that travel through neurones
- Faster
- Don’t last long
- More precise
How does insulin lower
blood glucose levels?
- Insulin binds to receptors on muscle + liver cells
- Those cells take in glucose and store it as glycogen
- This lowers BGC back to normal
How does glucagon raise blood glucose levels?
- Insulin binds to liver receptor cells
- Those cells break down glycogen into glucose and release it into the bloodstream
- This raises BGC back to normal
Type 1 Diabetes
- Starts at and early age but affects are lifelong
- The pancreas stops producing insulin so BGC becomes to high and isn’t lowered
Type 2 Diabetes
- Happens at older age
- The body stops responding to insulin so cells don’t take in glucose
Type 1 Diabetes Treatment
Insulin injections into the abdomen/thigh
Type 2 Diabetes Treatment
- Healthy, low sugar diet
- Lots of exercise
Role of the kidneys
- Filter the blood and remove any waste products from it
- Regulate levels of ions + water
Deamination
- Where excess amino acids are converted into fats and carbohydrates for storage
- Takes place in the liver
Where is urea made?
In the liver during deamination
How does water leave the body?
- Sweat
- Through the lungs when breathing
- Through urine
Why is water regulation important?
- Cells lose/gain water depending on how much water is in the body
- An excess of water means it enters the cells through osmosis and damages them or causes them to burst
- A lack of water means water leaves the cell making it flaccid
How do the kidneys filter the blood?
- Selective reabsorption
- As blood passes through the kidney, tubules absorb all small molecules
- Things that are good for the blood (all glucose and some water) are reabsorbed back into the blood
- Urea isn’t reabsorbed but excreted
What happens when there is too little water in the bloodstream?
- The hypothalamus signals the pituitary gland to release more ADH
- ADH enters the kidneys and alerts the tubules to reabsorb more water
- Less urine is produced
What happens when there is too much water in the bloodstream?
- The hypothalamus doesn’t signal the pituitary gland to release ADH
- Less ADH enters the kidneys so less water is reabsorbed
- More urine is produce
Kidney system
- Blood enters through renal artery and exits through renal vein
- Kidneys produce urine
- Urine passes though the ureters and is stored in bladder
- Excreted through urethra
Consequences of kidney failure
- Waste substance aren’t removed from the body
- Ion and water levels aren’t regulated
- Causes illness and death if untreated
Dialysis
Medical treatment where blood is removed, filtered and put back in the body
How does dialysis work?
- Blood passes through dialysis machine and makes contact with dialysis fluid
- Blood and fluid separated by partially permeable membrane
- Ions, water and glucose diffuse in and out of the blood so a good concentration of all is created in the blood
Why is dialysis fluid constantly replaced?
- To created a constant concentration gradient
- Without one, eventually the molecules wouldn’t diffuse in and out of the blood
Disadvantages of dialysis
- Treatment is time consuming
- Dialysis can cause blood clots and infection
- Dialysis is a life process (has to be done regularly for life)
Kidney transplant
Surgical procedure where the kidney is replaced
Disadvantages of kidney transplants
- Organ may be rejected by recipient’s immune system
- Drugs are given to stop this but it weakens the immune system and increases chance of illness
- Surgical risks (surgery could go wrong)
- Lack or organ donors
Puberty
Period where adolescents start to develop secondary sexual characteristics
What are the 4 stages of the menstrual cycle?
- Menstruation
- Uterus lining develops
- Ovulation
- Uterus lining maintained
Menstruation
- Between days 0-7
- Uterus lining breaks down
- Bleeding as a result
Lining builds up
- Between days 7-14
- Lining becomes a thick spongy layer with lots of blood vessels in it
- This prepares the lining for a fertilised egg
Ovulaltion
- On day 14
- Egg is released from the ovary
Lining is maintained
- 14-28 days
- If no egg has been fertilised by day 28, menstruation occurs (cycle repeats until fertilised egg)
- If an egg has been fertilised before day 28, it implants itself into the womb to develop into a foetus
Follicle Stimulating Hormone
- Causes egg to mature in ovary
- Stimulates oestrogen
- Produced in pituitary gland
Oestrogen
- Repairs, thickens and maintains uterus lining
- Stimulates LH
- Inhibits FSH
Luteinising Hormone (LH)
- Triggers ovulation
- Produced in the pituitary gland
Progesterone
- Maintains uterus lining
- Produces mucus in the cervix
- Inhibits LH and FSH
Contraception
Any method used to prevent pregnancy
Hormonal Methods
Rely on the release of oestrogen/progesterone to prevent the release of an egg
Oestrogen Pill
- Taken everyday to inhibit FSH
- Inhibiting FSH means no egg is matured or released
Progesterone Pill
- Releases progesterone
- This produces a thick mucus in the cervix
- Sperm can’t reach the egg
Combined Pill
- Contains progesterone and oestrogen
- Very effective but has side effects
- E.g. headaches, nausea
Contraceptive Patch
- Placed on the upper arm
- Releases progesterone and oestrogen
- Lasts 1 week
Contraceptive injection
- Progesterone is injected in the upper arm
- Lasts 2-3 months
Contraceptive Implant
- Placed under the skin in the arm
- Slowly releases progesterone
- Lasts 3 years
IUD (Intrauterine Device)
- Placed inside the uterus
- Releases progesterone
- Lasts over 3 years
Non-Hormonal Devices
Prevents the sperm from reaching the egg and fertilising it
Copper IUD (Copper Coil)
- Prevents sperm from surviving in the uterus by killing them
- Lasts over 3 years
Condoms
- Acts a barrier and traps sperm
- Only form of contraception that protects against STD’s as well
Diaphragm
- Fits over the cervix
- Blocks sperm from entering the uterus
- Unreliable so is used with spermicides
Sterilisation
- Cutting the fallopian tubes (women)
- Cutting the sperm ducts (men)
Natural methods
- Intercourse only at certain times of the month
- Withdrawing before ejaculation
Abstinence
- Refraining from intercourse
- Only method that has a 100% success rate
Infertility Problem
- Low production of FSH so egg doesn’t mature properly or at all
- FSH and LH are given in pill form to mature and release eggs
How IVF (In Vitro Fertility) works
- FSH and LH are given in pill form to mature and release eggs
- Eggs are collected and fertilised with father’s sperm in a lab
- Fertilised eggs are placed in an incubator and grow into embryos
- One or more embryos are inserted into the uterus to grow into foetuses
Pro of IVF
- Allows infertile couples to have children
Cons of IVF
- Doesn’t always work (low success rate)
- Side effects (e.g. abdominal pains, vomiting)
- Multiple embryos can lead to multiple unwanted pregnancies
- Leads to higher risks of complications (stillbirths, miscarriage)
Ethical issues
- IVF leads to destruction of unused embryos that had potential of life
- Could lead to designer babies
Adrenaline
- Produced in the adrenal glands during ‘fight or flight’ response, when you’re scared, stressed or are about to exercise
- Prepares the body for physical activity
Adrenaline Impacts
- Increased heart rate
- Increased blood flow
- Increased blood flow to the muscles
- Increases glucose breakdown by stimulating the liver to breakdown glycogen
Thyroxine
- Produced y the adrenal glands in the neck
- Main role is to increase metabolic rate
- Pituitary gland produces TSH which stimulates the thyroid to produce thyroxine
What happens if thyroxine levels are too low?
- The pituitary gland produces more TSH
- This stimulates the thyroid to produce more thyroxine so levels increase to normal
What happens if thyroxine levels are too high?
- Thyroxine inhibits the production of TSH form the pituitary gland
- Less TSH means less thyroxine is being produced from the thyroid
- Levels fall to normal
Phototropism
Plant response to the stimulus of light
Geotropism/Gravitropism
Plant response to the stimulus of gravity
Auxins
- Control growth at the ends of shoots and roots of a plant
- Stimulates growth in the shoots
- Inhibits growth in the roots
Shoots
- Positively phototropic (grow towards the light)
- Negatively geotropic (grow away from the ground against gravity)
Direction of growth in plant shoot
- Towards the sun
- Auxin accumulates in the shaded side of a plant
- Auxin stimulates growth in shoots so shaded side will grow at a faster rate - towards the light
Roots
- Negatively phototropic (grow away from light)
- Positively geotropic (grow towards the ground)
Direction of growth in plant roots
- Constantly curves upwards and downwards
- Auxin accumulates on the lower side of root
- Auxin inhibits growth in roots so lower side grows at a slower rate and curves downwards
- Now there is more auxin in the upper side of the root so that side grows slower
- Root curves upwards
- Cycle repeats
Uses of Auxin
- Growing plant clones in tissue cultures
- Used in rooting powder to grow plant cuttings
- Used to kill weed by disrupting their growth pattern
Gibberellin
Initiates seed germination
Uses of Gibberellin
- Controlling dormancy by inducing germination to produce multiple crops
- Induced flowering
- Used to grow larger fruit
Ethene
Controls cell division and ripening of fruits
Use of Ethene
Ripens fruit after it has been transported from different countries so it’s fresh
