Homeostasis and Response Flashcards
What is 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
What are things which require homeostatic processes in the human body?
- Body temperature
- Blood water concentration
- Blood glucose levels
What type of processes are homeostatic processes?
Automatic (not under conscious control)
What do homeostatic processes in humans result from?
Hormonal/endocrine and nervous control systems
Why is it important we maintain body temperature?
To maintain enzyme reactions
Why is it important we maintain blood water concentration?
to prevent osmotic damage to cells and tissues
Why is it important we maintain blood glucose levels?
To provide substrates for respiration
What does the nervous system do?
Allows rapid communication around the body via nerve impulses travelling through nerve cells/neurons.
What are reflexes?
Automatic responses to changes in the internal and external environment that are designed to keep us safe
What nervous systems do reflexes require?
- central
- peripheral
What is the central nervous system made up of?
- brain
- spinal chord
What is the peripheral nervous system made up of?
sensory and motor systems that extend out the central nervous system
What do reflexes rely on?
A receptor detecting a stimulus
What is a stimulus?
A change in the environment
What is the similar pattern which all responses undergo?
Stimulus - receptor - co-ordinator - effector - response
What is a receptor?
The organ or cell that detects the stimulus
What is a co-ordinator?
the brain or the spinal chord
What is an effector?
The tissue/organ that carries out a response
What is a response?
How the body responds to the stimulus, e.g. muscles move and glands secrete hormones
What is a synapse?
A synapse is a gap between nerve cells where the electrical signal is converted to a chemical signal that diffuses across the synapse,initiating the electrical impulse in the next neurone
What enable us to survive without conscious control as a baby?
Innate reflexes
Describe the reflex arc in chronological order:
- stimulus
- receptor
- sensory neurone
- synapse
- relay neurone
- synapse
- motor neurone
- effector
What is the brain made of?
millions of interconnected neurons
What is present at each connection in the brain?
Can be thousands of different neurons which gives an almost infinite number of neural pathways
What are the three main regions of the brain?
- cerebral cortex (covers cerebrum)
- cerebellum
- medulla
What is special about the arrangement of the cerebrum?
it is highly folded to increase surface area
What is the cerebrum involved in?
- consciousness
- intelligence
- memory
- language
What does the cerebellum do?
- coordinates voluntary muscle activity
What does the medulla do?
- coordinates involuntary muscle activity e.g. heart rate, breathing
Why is our knowledge of the brain very limited?
Since the brain has a delicate and complex nature
What was the historical way in which information on the brain was gathered?
Seeing the effects that brain injuries had on the body
What has been used to establish the effect and response of different regions of the brain?
Electrical stimulation applied to the different parts of the brain during surgery
What is the most recent technology used in gathering information on the brain?
Magnetic Resonance Imaging (MRI)
What type of investigation is MRI and what does this mean?
Non-invasive
- reduce the risk of accidental injury and infection
What does MRI use to produce images of the brain?
Magnetic fields and radiowaves
What is the risk of brain surgery?
Infection or a stroke
What is an alternative to brain surgery? WHat does this involve?
gene therapy which uses stem cells to treat brain injury
What can be done to the brain to treat Parkinson’s disease?
Electrical stimulation of the brain can help reduce muscle tremors caused by CNS disorders like Parkinson’s disease
What do MRI scans identify?
WHat areas of the brain are active when people are doing certain activities
What type of organ is the eye an example of?
A sense organ
What is a sense organ?
An organ that contains receptors
What is accomodation?
The process of changing the shape of the lens of the eye to focus on near or distant objects
What kind of receptors does the eye contain?
Those which are sensitive to light intensity and colour
Describe the process by which an eye focusses on a near object:
- the ciliary muscles contract
- the suspensory ligaments loosen
- the lens thickens(more curved) and refracts more light rays
Describe the process by which an eye focusses on a distant object:
- the ciliary muscles relax
- the suspensory ligaments tighten
- the lens becomes thinner and only slightly refracts light rays
What can damage the retina?
Very bright light
What is the sclera?
The tough, supporting wall/outer coat of the eye. It is white.
What is the cornea?
Transparent outer later found at the front of the eye. It refracts light into the eye.
What is the iris?
The coloured part of the eye. It contains muscles that allow it to control the diameter of the pupil and thus how much light enters the eye
What does the lens do?
Focus light onto the retina
What is the retina?
Tissue lining at the back of the eyeball which contains receptor cells sensitive to light and colour. Sends electrical impulses to the brain
What is the optic nerve?
Bundle of over a million nerve fibres that carries impulses from the receptors on the retina to the brain
What do ciliary muscles and suspensory ligaments do?
Control the shape of the lens
How does the eye adjust to bright light?
- reflex triggered that makes the pupil smaller
- circular muscles in the iris contract
- radial muscles relax
- reduces amount of light that can enter the eye
How does the eye adjust to dim light?
- reflex triggered that makes the pupil wider
- circular muscles in the iris relax
- radial muscles contract
- increases amount of light that can enter the eye
Why do older people often have to wear reading glasses?
- as you get older, your lens loses flexibility
- this means it can’t easily spring back to a round shape
- this means light can’t be focused well for near viewing
What is the medical term for long-sightedness?
hyperopia
What is the medical term for short-sightedness?
myopia
What causes hyperopia?
- when the lens is the wrong shape and doesn’t refract light enough
- or the eyeball is too short
- images of near objects are brought into focus behind the retina
What can be used to correct long-sightedness?
- glasses with a convex lens (curves outwards)
- lens refracts rays so they focus on the retina
What causes myopia?
- when the lens is the wrong shape and refracts too much light
- or the eyeball is too long
- images of distant objects are brought into focus in front of the retina
What can be used to correct short-sightedness?
- glasses with a concave lens (curved inwards)
- lens refracts rays so they focus on the retina
What are the alternatives to glasses to correct vision defects?
- contact lenses
- laser eye surgery
- replacement lens surgery
What is the difference between a hard and soft contact lense?
- hard contact lenses are made of relatively rigid material and last a long time
- they have to be removed overnight and kept sterile
- soft lenses are made of more flexible materials which are more comfortable but do not last as long and carry a higher risk of infection
How does laser eye surgery to treat eye defects?
- a laser is used to vaporise tissue, changing the shape of the cornea
- slimming the cornea down makes it less powerful and can improve short sight
- changing the shape so that it is more powerful will improve long sight
- since the cornea refracts light into the eye
What occurs during replacement lens surgery to treat eye defects?
- natural lens of the eye is removed
- artificial lens, made of clear plastic, is inserted in its place
What must be kept at a stable level in the body for enzymes to function properly?
core body temperature at around 37 degrees centigrade
What part of the body is responsible for monitoring core body temperature?
the thermoregulatory centre in the hypothalamus of the brain
How does the thermoregulatory centre monitor the core body temperature?
- contains receptors that are sensitive to the temperature of the blood flowing through the brain
- receives impulses from temperature receptors in the skin
What does the thermoregulatory centre trigger from effectors to cool the body down?
- more sweat is produced in sweat glands on the skin. this extra sweat evaporates from the skin, transferring energy to the environment
- blood vessels supplying capillaries on the skin surface dilate so more blood flows through the capillaries. The skin flushes so more energy is transferred by radiation from your skin
What is vasodilation?
When blood vessels supplying surface skin capillaries dilate to let more blood through the capillaries
Why is it harder to keep cool in humid weather?
The water in the sweat produced by your sweat glands does not evaporate
What does the thermoregulatory centre trigger from effectors to warm the body up?
- sweat production is reduced so less less energy is transferred to the environment as water evaporates
- skeletal muscles contract and relax rapidly (shiver) which requires lots of respiration. The energy transferred from these exothermic reactions raises the body temperature
- hairs on skin are pulled erect by contracting erector pili muscles to trap an insulating later of air
- blood vessels supplying skin capillaries constrict and reduce bloodflow through capillaries so less energy is transferred from radiation out the body through the skin
What is vasoconstriction?
When blood vessels supplying skin capillaries contract to reduce the bloodflow going through those capillaries
What is the endocrine system?
Many different glands which each produce a hormone or hormones
How do glands release hormones into the blood?
By secretion
What are hormones made from?
Protein (although may have additional groups added)
Compare the response between nerve cells and hormones:
Hormones cause slower responses than nerves but the effects last longer
What is the ‘master gland’ and what does it do?
- Pituitary gland located just below brain
- makes many hormones that affect other glands
What hormone does the thyroid produce? What does it do?
- thyroxine
- involved in basal cell metabolism and controls growth and development
What hormones does the pancreas produce? What do they do?
- Insulin and glucogen
- regulate blood sugar levels
What hormone does the adrenal gland produced? What does it do?
- Adrenaline
- Raises the heart rate to provide cells with more oxygen and glucsoe to prepare for fight or flight
What hormone do the ovaries and testes produce?
reproductive hormones
What organ monitors blood sugar levels?
Pancreas
What is produced when blood sugar levels are too high?
Insulin
What is produced when blood sugar levels are too low?
glucagon
What does insulin do?
Tells muscle cells and the liver to take up glucose and covert it to glycogen
Why is glycogen effective?
Does not dissolve so it doesn’t diffuse back out of the cells (stored in muscle cells) or affect osmosis (so cells don’t lyse)
What does glucagon do?
Tells muscle cells and the liver to convert glycogen into glucose and release it into the blood
What principle is the effect of glucagon?
Negative feedback
What is negative feedback?
A mechanism where a stimulus generates a response that reverses the stimulus
Describe type 1 diabetes:
- occurs when the pancreas is unable to produce insulin
- generally diagnosed in children and young adults
- treated by the injection of insulin
What kind of diets to type 1 diabetics eat?
low sugar diets to help prevent high glucose levels
Describe type 2 diabetes:
- occurs when the body’s cells become resistanct to the insulin produced by the pancreas
- risk factors are obesity and lack of exercise
- treatment tends to be diet or medication to release more sugar in the urine
How does the body gain water?
- drinking
- respiration
- eating
How does the body lose water?
- sweating
- breathing
- urination
What removes excess water, ions and urea in urine?
Kidneys
How is urea made?
In the liver by the removal of the amine group from amino acids. Excess amino acids are deaminated forming ammonia which is toxic, the liver immediately converts this to urea for safe excretion
What is the kidney made up of?
millions of tiny tubules called nephrons
Describe the parts involved in the controlling of water balance:
- kidneys
- ureters
- renal artery
- renal vein
- bladder
- urethra
- sphincter muscle
What is at the part at the top of the ureter called?
Collecting duct
What happens to the blood before being pushed into the nephron?
It is filtered
What are forced into the nephron from the blood?
Most of the water, dissolved ions and glucose
Why do large proteins and cells remain in the blood and don’t go into the nephrons?
Since they are too large in size to fit through the filters
Where is the glucose reabsorbed back into the nephron ?
At the start
By which process and why does glucose get reabsorbed into the blood from the nephrons?
Active transport since it will be moved against the concentration gradient
Are the water and ions reabsorbed into the blood or go to the collectiong duct?
Some water and ions are absorbed according to the body’s needs but the rest go to the collecting duct
What hormone is released in the brain when we are dehydrated?
Anti Diuretic Hormone
What does the Anti Diuretic Hormone do?
Increases the permeability of the kidney tubule to allow more water to be reabsorbed into the blood so we produce small volumes of concentrated urine
How is ADH an example of negative feedback?
If we need to excrete more water, we need to produce less ADH
What are the two treatments for kidney failure?
- Dialysis
- Transplant
How does dialysis work?
- Dialysis patient has their blood redirected through a machine for several hours a few times a week
- Within the machine is dialysis fluid.
- This fluid contains glucose and ions etc. at the correct concentration to prevent diffusion of these out of the blood
- However, it contains no urea so that the urea diffuses out the blood, and into the dialysis fluid
What does a kidney transplant rely on?
A suitable donor being available
The kidney not being rejected by the body’s immune system
What are the benefits of a kidney transplant?
It is a cure rather than just a treatment
Cheaper in the long run than dialysis and less time consuming
What are secondary sexual characteristics in women?
- menstrual cycle
- uterus grows
- development of breasts
- fat deposits on hips, buttocks and thighs
What is the male reproductive hormone? Where is it produced? What does it stimulate?
- testosterone
- testes
- sperm production
What is the female reproductive hormone? Where is it produced? What does it stimulate?
- oestrogen
- overies
- physical changes and involved in menstrual cycle
What are the four stages to menstruation?
- breaking down of the uterus lining in a period (day 0-4)
- development of an egg cell in the ovaries and rebuilding of the uterus lining (4-14)
- ovulation at around day 14
- maintaining of the uterus lining until day 28 and if no egg is fertilised, process starts again
What are the four hormones controlling menstruation?
- FSH (follicle stimulating hormone)
- Oestrogen
- LH (luteinising hormone)
- progesterone
What does FSH do?
- produced in pituitary gland
- causes an egg cell to devlop from an immuture cell in the ovaries (follicle to be procise)
- stimulates ovaries to produce oestrogen
How does oestrogen reach the uterus from the ovaries?
via the bloodstream
What does oestrogen do?
- produced in the ovaries
- stimulates rebuilding of the lining of the uterus
- inhibits FSH release
- stimulates LH release
What does LH do?
- produced in the pituitary gland
- causes egg to be released from ovary to the uterus in ovulation
What does progesterone do?
- produced in ovaries by the remains of the follicle after ovulation
- maintains lining of the uterus
- when production falls, lining breaks down
- inhibits the release of FSH and LH
Why does a woman’s placenta keep producing progesterone when she is pregnant?
- maintains lining of the uterus to protect the embryo/foetus (acts as a cushion)
- inhibits LH and FSH production
- which stops the woman producing more egg cells so another egg cell isn’t released
- so she can’t get pregnant again
What is the natural or ‘rhytmn method’ contraceptive method?
Only having intercourse when there is no egg in the oviduct (ie. avoiding the 14th day of cycle)
What is the advantage of the natural contraceptive method?
Accepted by religious groups opposed to contraception
What is the disadvantage of the natural contraceptive method?
Unreliable, as both sperm and eggs can live for several days and the cycle can be irregular
No protection from STIs
What are the barrier contraceptive methods?
Condom or diaphragm which prevent sperm cells from reaching an egg cell
What is the chemical contraceptive method?
Spermicides which kill or disable sperm
What is the advantage of a barrier method contraceptive?
Can prevent the spread of many STIs
Effective temporary measure
What is an intrauterine device?
A copper or plastic device insterted into the uterus to prevent the implantation of an embryo. Some contain progesterone to increase effectiveness
What is the advantage of an intrauterine device?
Can be in place for up to 10 years and is >99% effective
What is the disadvanatge of an intrauterine device?
No protection from STIs
Uncomfortable during menstruation
How does the oral contraceptive work?
Prevents the production of FSH so eggs can’t mature by introducing oestrogen and progesterone
What is the advantage of an oral contraceptive?
can help regulate periods
is >99% effective
What is the disadvantge of an oral contraceptive?
Must be taken daily otherwise increased risk of pregnancy
Many side effects
Does not protect against STIs
How does an injection, implant or skin patch contraceptive work?
slowlt releases progesterone straight into the blood stream to inhibit the maturation and release of eggs for a number of months or years
What are the advanatages of implant contraceptives?
- Removes the need to remember to take the pill
- Can now be controlled by an app to switch off if desired
WHat are the disadvantages of implant contraceptives?
- older implants cannot be removed
- will prevent pregnancy for several years
- does not protect against STIs
How does surgery to prevent pregnancy work?
Tubes that carry sperm or eggs are tyed or severed
WHat is the advantage of surgerical contraception?
- permanent solution normally
WHat is the disadvantage of surgical contraception?
- can be a permanent solution
- does not protect against STIs
Describe the process for In vitro fertilisation:
- mother is given FSH and LH to stimulate the maturation of several eggs.
- The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.
- The fertilised eggs develop into embryos.
- At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb).
What’s glycogen?
A storage of carbohydrate found in the muscles and liver
How does negative feedback help keep the levels of thyroxine in the body relatively constant?
- if thyroxine levels increase, the hormone inhibits the production of TSH, so the release of thyroxine is stopped
- this is negative feedback
- if thyroxine levels fall, release of TSH is no longer inhibited so it is released and then stimulates the release of thyroxine from the thyroid gland
What changes in the body does adrenaline stimulate
- heart and breathing rate increase which increases the delivery of oxygen and glucose to the muscles and brain
- stored glycagon in the liver is converted to glucose
- blood is diverted from the digestive system to the muscles
- more respiration in the muscles
- pupils dilate
- increased mental awareness
What is an ethical issue with IVF?
Unwanted embryos may be destroyed
What is an economic issue with IVF?
Expensive to the couple or NHS
What is a social issue with IVF?
Can be emotionally or physically stressful to the couple
Large numbers of kids waiting to be fostered or adopted
What steps are taken to prevent the immune system of a patient attacking the donor organ?
- having a donor with a matching blood and siilar tissue type with the recipient
- immunosupressant drugs taken
