homeostasis and response Flashcards
define homeostasis
the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
why must the body regulate the core body temperature of 37ºC
because this is the optimum temperature for enzyme action and all cell functions
what happens if body temperature falls too high or above optimum
enzymes will denature and metabolic processes can’t take place, so cells will die
what does homeostasis control
blood glucose concentration, body temperature and water levels
what two types of response can control systems have
chemical or electrical
what do all control systems include
receptors, coordination centres and (effectors, muscles or glands)
function of receptors
they detect stimuli
define stimuli
changes in the environment
function of coordination centres e.g. brain, spinal cord, pancreas
they receive and process information from receptors
function of effectors, muscles or glands
they bring about responses which restore optimum levels
what does the nervous system enable
it enables humans to react to their surroundings and to coordinate their behaviour
how does information get from receptors to the CNS
the information from receptors passes along neurones as electrical impulses to the CNS.
function of the CNS and what it is made up of
our CNS is made up of our brain and spinal cord; the brain coordinates the response of effectors to the stimulus, which may be muscles contracting or glands secreting hormones
order of stimulus to response
stimulus -> receptor -> coordinator -> effector -> response
examples of stimuli
temperature, light, position, sound, touch, etc.
sensory neurone function
they transmit messages from sense receptors e.g. eye or nose, to the brain or spinal cord
motor neurone function
they transmit messages from the brain and spinal cord to the muscles and organs, which are effectors
define a reflex arc
the nervous pathway that a nerve impulse takes during a reflex action
relay neurone function
they connect motor neurones to sensory neurones
what is a synapse
gap between two neurones
function of a synapse
allows the nerve cells to pass on their electrical impulse to another cell; also controls the direction in which impulses travel, as they can only travel one way through a synapse.
function of neurotransmitters
they carry chemical signals from one neuron (nerve cell) to the next target cell; this can be another nerve cell, a muscle cell or a gland
why are reflex actions important
because reflex actions are automatic and rapid (they do not involve the conscious part of the brain), meaning they protect our body from danger
what is the brain
an organ that controls complex behaviour; it’s made of billions of interconnected neurones and has different regions that carry out different functions
what does the cerebral cortex control
it’s responsible for higher-order processes such as intelligence, memory, consciousness and personality
what does the cerebellum control
it’s responsible for balance, muscle coordination and movement
what does the medulla control
it controls unconscious activities such as heart rate and breathing
why is treating brain disorders very difficult
because the brain is very complex and delicate
how have neuroscientists been able to map the regions of the brain to particular functions
by studying patients with brain damage, electrically stimulating different parts of the brain, and using MRI scans
pros and cons of electrically stimulating different parts of the brain
PROS:
- helps control your movement symptoms when your medications aren’t working as well as they used to
- doesn’t damage brain tissue
CONS:
- could cause stroke
- temporary pain and swelling at the implantation site
pros and cons of MRI scans
PROS:
- non-invasive and doesn’t use radiation
- no side-effects
CONS:
- very expensive
- may cause peripheral muscle or nerve stimulation
what is the eye
a sense organ containing receptors sensitive to light intensity and colour
define accommodation
the process of changing the shape of the lens to focus on near or distant objects
function of retina
contains light-sensitive cells which convert light that enters your eye into electrical signals your optic nerve sends to your brain which creates the images you see
function of optic nerve
a nerve composed of many sensory neurones carrying impulses from the retina to the brain which creates the images you see
function of sclera
tough white protective outer layer
function of cornea
refracts light through the pupil as it enters the eye
function of iris
alters the size of the pupil, controlling the amount of light entering the eye
function of ciliary muscles
they control the thickness of the lens to allow focussing
function of suspensory ligaments
attach the ciliary muscles to the lens
how does the eye focus on near objects
the ciliary muscles contract, the suspensory ligaments loosen, therefore the lens is then thicker and refracts light rays strongly
how does the eye focus on distant objects
the ciliary muscles relax, the suspensory ligaments are pulled tight, therefore the lens is then pulled thin and only slightly refracts light rays
why does myopia (short sightedness) and hyperopia (one sightedness) occur
rays of light do not focus on the retina
how is myopia and hyperopia treated
they’re generally treated with spectacle lenses which refract the light rays so that they do focus on the retina. MYOPIA - treated using a concave lens, HYPEROPIA - treated using a convex lens
- new technologies now include hard and soft contact lenses, laser surgery to change the shape of the cornea and a replacement lens in the eye
what does the thermoregulatory centre do, how does it work and where is it found
it is found in the hypothalamus; it monitors and controls body temperature; the thermoregulatory centre contains receptors sensitive to the temperature of the blood. the skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre
what happens if body temperature is too high
blood vessels dilate (vasodilation) and sweat is produced from the sweat glands. both these mechanisms cause a transfer of energy from the skin to the environment
what happens if body temperature is too low
blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).
4 things that cool us down on a hot day
1) vasodilation - capillaries get wider so a larger amount of blood can flow near the skins surface, heat is lost to the environment
2) hairs and hair erector muscles are relaxed
3) evaporation of sweat from the sweat glands which takes heat energy away from the body
4) no shivering
4 things that heat us up on a cold day
1) vasoconstriction - capillaries get thinner so less blood can flow near the skin surface, heat is kept near to the body
2) no sweat is produced, which reduces the amount of heat energy taken away from the body
3) body starts to shiver to produce heat for the body
4) hairs and hair erector muscles stand on end to trap a layer of air
function of the endocrine system
it secrets hormones directly into the bloodstream; the blood carries the hormone to a target organ where it produces an effect
function of the pituitary gland and where it’s found
it is found in the brain and secretes several hormones into the blood in response to body conditions; these hormones in turn act on other glands to stimulate other hormones to be released, to bring about effects
what does the pancreas secrete and why
it secretes insulin and glucagon to regulate blood glucose concentration
what hormone does the thyroid produce and why
it produces thyroxine which controls the basal metabolic rate and plays a role in growth and development
what hormone do the adrenal glands release and why
they release adrenaline in times of stress or fear by increasing heart rate and boosting delivery of oxygen and glucose to the brain and muscles in order to activate fight or flight
what hormone do the ovaries produce and why
they produce oestrogen to control female reproduction
what hormone do the testes produce and why
they produce testosterone to control male reproduction
name all the endocrine glands
pituitary gland, pancreas, thyroid, adrenal gland, ovary, testes
difference between the endocrine system and the nervous system
the endocrine system relies on hormones while the nervous system relies on electrical impulses. the hormones are transported by the blood whilst impulses are carried along hormones
similarity between the endocrine system and the nervous system
they both send information around the body in order to carry out homeostasis
which sends information faster out of the endocrine system and the nervous system
compared to the nervous system, the endocrine system transports hormones slower than the nervous system sends electrical impulses, but hormones act for longer
what happens if blood glucose concentration is too high
- increase in blood glucose concentration is detected by pancreas cells
- the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells
- in the liver and muscle cells, excess glucose is converted to glycogen for storage
what happens if blood glucose concentration is too low
- decrease in blood glucose concentration is detected by the pancreas cells
- the pancreas produces the hormone glucagon which binds to liver and muscle cells
- in the liver and muscle cells, glycogen is converted back into glucose and released into the blood
why must glucose levels be kept at a constant level by homeostasis
because glucose is needed by every cell to carry out respiration and release energy to stay alive
what happens to cells if there is too little glucose
too little glucose could cause cells to die due to a lack of respiration and energy
what happens to cells if there is too much glucose
too much glucose will affect solute concentration outside cells, affecting osmosis, and causing too much water to be drawn out of cells; this causes them to shrivel up and die
when does blood glucose concentration rise
after a carb-rich meal
what is type 1 diabetes
a disorder in which the pancreas fails to produce sufficient insulin
what is type 1 diabetes characterised by and how is it treated
uncontrolled high blood glucose levels and is normally treated with insulin injections after meals to reduce blood glucose concentration when it rises
what is type 2 diabetes
where the body cells no longer respond to insulin produced by the pancreas
why should you get injections in type 1 diabetes and not pills
because insulin is a protein (like all hormones) that would be destroyed by enzymes
treatment for type 2 diabetes
a carbohydrate controlled diet and a regular exercise regime to keep blood glucose levels at a minimum
why can people with type 2 diabetes not get insulin injections
because the cells stop responding to the insulin
risk factors for type 2 diabetes
- MAIN RISK FACTOR: obesity; as obesity levels increase, more people are getting type 2 diabetes
- age: >40
- genetics: having a close relative with the condition
- ethnicity: South Asian, Chinese, African-Carribean or black African
other treatment options for diabetes
TYPE 1 DIABETES:
- pancreas transplants so that they don’t have to reject insulin (immune rejection
and immunosuppressants)
OR
- stem cell research/artificial pancreases
TYPE 2 DIABETES:
- eating balanced diet
- lose weight
- regular exercise
- drugs to help insulin work better
explain the negative feedback loop of blood glucose concentration
- blood glucose concentration of a normal person rises slightly and falls slightly over the course of the day; this is because the blood glucose concentration is controlled by a balance between insulin and glucagon
- so, when blood glucose levels fall, glucagon is released and when the blood glucose levels are too high, insulin is released – forming a negative feedback loop
why is it important that the body keeps the blood water concentration relatively constant
if the blood becomes too dilute, water will move into cells by osmosis, causing them to burst – and, if blood becomes too concentrated, water will move out of cells by osmosis, causing them to shrivel. in both scenarios, if body cells gain or lose too much water by osmosis, they will not work efficiently
what three ways do we lose water. state whether they’re controlled or uncontrolled
1) water leaves the body via the lungs during exhalation (uncontrolled)
2) sweating, as the sweat glands produce sweat on the skin and it evaporates (uncontrolled)
3) through urine which is produced by the kidney. if blood is too dilute, kidney will remove this water and produce a greater volume of dilute urine (controlled)
what is removed via the kidneys in the urine
water, ions and urea
what is removed via the sweat glands in sweat
water, ions and urea
what does the digestion of protein from the diet cause
it 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 happens when there is a low blood water concentration
1) the brain detects the low water levels and pituitary gland releases the hormone ADH as a result
2) ADH then travels through the blood and triggers kidney tubules to become more permeable
3) as the kidney tubules become more permeable, more water is reabsorbed back into the blood during selective reabsorption
4) this increases blood water levels back to normal and produces a small amount of concentrated urine
what is the function of ADH
to increase permeability of kidney tubule
what happens when there is a high blood water concentration
1) pituitary gland detects high blood water levels and stops releasing ADH
2) this means that kidney tubules are less permeable so that less water is reabsorbed into the bloodstream during selective reabsorption
3) this decreases blood water levels back to normal because lots of dilute urine is produced that takes water away from the body
how do the kidneys produce urine
by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water
describe filtration
as the blood enters the kidney, all small molecules are filtered out of the blood and into the kidney (filtration) - these include water, urea, mineral ions, amino acids and glucose
why can proteins and blood cells not be filtered
proteins and blood cells are too large to diffuse through and remain in the capillaries
what does the release of more ADH cause
it causes more water to be reabsorbed back into the blood from the kidney tubules; this is controlled by negative feedback
what happens after filtration takes place
selective reabsorption takes place; this is where useful substances are reabsorbed back into the bloodstream i.e. all of the glucose (and all amino acids) some of the ions and some of the water is reabsorbed back into the blood through kidney tubules
what happens to the molecules not reabsorbed into the blood
they are released as urine and this includes urea, excess ions and excess water
why do glucose levels not change after the kidney filters it
because although it is filtered out of the blood, it is all reabsorbed
why does the concentration of ions decrease after the kidney filters it
because excess ions are not reabsorbed
why is there no urea in the blood after the kidney filters it
because urea is a waste product, none is reabsorbed back into the blood because we don’t need it
how can kidney failure be treated
kidney transplants or dialysis
what happens during dialysis
during dialysis, the patient’s ‘impure’ blood with excess water, mineral ions and urea is passed through a dialysis machine which contains a semi-permeable membrane that separates the blood and the dialysis fluid; this membrane will only allow smaller molecules like water, ions and urea through but will not allow larger molecules like blood cells and proteins through
what does dialysis fluid contain
it contains the concentrations of water, ions and urea of healthy blood – meaning it contains no urea, some water and some ions
why does the dialysis fluid need to have specific amounts of each substance
because it forms a concentration gradient between the patient’s blood and the dialysis fluid, causing all the urea to diffuse from patient’s blood into fluid, some ions to diffuse from blood to fluid and some water to move by osmosis into the fluid across the semi-permeable membrane
why are both the dialysis fluid and the blood of the patient constantly replenished and replaced
to maintain a steep concentration gradient for urea to diffuse across; this causes the patient’s blood to contain no urea and to contain normal levels of ions and water
pros and cons of dialysis
PROS:
- no need to wait for donor
- no risk of immune rejection
- no immunosuppressants
CONS:
- it is expensive
- you have to eat a controlled diet (to not produce too much urea)
- inconvenient and time consuming; need to visit a hospital several times a week for several hours
- there is a risk that excess ions, water and urea will build up between sessions which can be dangerous
pros and cons of kidney transplants
PROS:
- allows patient to lead normal life with little inconvenience
- cheaper than dialysis in the long-run
CONS:
- risk of immune rejection
- immunosuppressants; could forget to take AND increases risk of other infections
- shortage of kidney donors, so long waiting list; some could die before even getting a transplant
problems with the kidneys that require dialysis or transplants
- damaged due to injury
- polycystic kidneys (genetic)
- bacterial infections
- kidney failure
what happens during puberty
reproductive hormones cause secondary sex characteristics to develop
what is the main male reproductive hormone
testosterone produced by the testes and it stimulates sperm production
what is ovulation
eggs beginning to mature and one being released approximately every 28 days
what does FSH cause
maturation of an egg in the ovary, and also stimulates ovaries to produce oestrogen
what is FSH secreted by
the pituitary gland
what does LH cause
stimulates the release of the egg from the ovary, triggering ovulation
what is LH secreted by
the pituitary gland
what is oestrogen secreted by
the ovaries
what does oestrogen cause
it stimulates the uterus lining to grow again after menstruation; also inhibits the release of FSH; also stimulates the release of LH
what is progesterone secreted by
an empty egg follicle
what does progesterone cause
it helps maintain a pregnancy if the egg is fertilised; also inhibits the release of both FSH and LH
what is progesterone’s secondary role
it maintains the uterus lining in the second half of the cycle so it’s ready to receive a developing embryo if the egg is fertilised
describe the trend in blood oestrogen level
it increases to prepare for ovulation and decreases when ovulation begins
how do oral contraceptives work
they contain hormones to inhibit FSH production so that no eggs mature
how do injections, implants and skin patches work
they slow release progesterone to inhibit the maturation and release of eggs for a number of months or years
how do barrier methods work
barrier methods such as condoms and diaphragms which prevent the sperm reaching an egg
how do intrauterine devices
they prevent the implantation of an embryo or release a hormone
how do spermicidal agents work
they kill or disable sperm
when would you abstain from intercourse (as a method of contraception)
when an egg may be in the oviduct
surgical process for males and females as a contraceptive
sterilisation
what is IVF
IVF is a treatment that involves giving a mother FSH and LH to stimulate the maturation of several eggs
how does IVF work
1) mother is given FSH and LH to stimulate maturation of several eggs
2) the eggs are collected from the mother and fertilised by sperm from the father in the laboratory
3) the fertilised eggs develop into embryos
4) at the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb)
cons of IVF
- it is very emotionally and physically stressful
- the success rates are not high
- it can lead to multiple births which are a risk to both the babies and the mother
why do plants produce hormones
to coordinate and control growth and responses to light (phototropism) and gravity (geotropism)
what happens to a plant when there are unequal distributions of auxin
this causes unequal growth rates in plant roots and shoots
why are gibberellins important
they initiate seed germination
why is ethene important
it controls cell division and ripening of fruits
how do negative feedback systems work
they work to maintain a steady state; if a factor in the internal environment increases, changes take place to reduce it and restore the original level; if a factor in the internal environment decreases, changes take place to increase it and restore the original level
what are plant growth hormones used in
agriculture and horticulture
what are auxins used as
- as weed killers
- as rooting powders
- for promoting growth in tissue culture
what are ethenes used for
they’re used in the food industry to control ripening of fruit during storage and transport
what can gibberellins be used to
- end seed dormancy
- promote flowering
- increase fruit size
