homeostasis (new) Flashcards
define homeostasis
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
State the purpose of Homeostasis
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
What type of response is involved in automatic control systems?
These automatic control systems may involve nervous responses or chemical responses.
What do all control systems include?
All control systems include:
- cells called receptors, which detect stimuli (changes in the environment).
- Coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors.
- Effectors, muscles or glands, which bring about responses which restore optimum levels.
State the purpose of the nervous system.
The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
Where is information passed in the nervous system?
Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS).
How does the central nervous system coordinate the response of effectors?
The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.
Recall the reflex arc.
Stimulus –> receptor –> coordinator –> effector –> response
Recall the 3 types of neurones found in the reflex arc.
Sensory neurone, Relay neurone and Motor neurone.
what are reflex actions.
Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
Describe the function of the brain.
The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.
What have neuroscientists so far achieved?
Neuroscientists have 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 scanning techniques.
Why is the brain difficult to study?
The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult.
what is the eye.
The eye is a sense organ containing receptors sensitive to light intensity and colour.
Define Accommodation
Accommodation is the process of changing the shape of the lens to focus on near or distant objects.
Describe the actions of the eye when it focuses on a near object.
To focus on a near object: * the ciliary muscles contract * the suspensory ligaments loosen * the lens is then thicker and refracts light rays strongly.
Describe the actions of the eye when it focuses on a distant object.
To focus on a distant object: * the ciliary muscles relax * the suspensory ligaments are pulled tight * the lens is then pulled thin and only slightly refracts light rays.
sclera
the tough white supporting wall of the eye
cornea
transparent outer layer at the front of the eye that refracts light
pupil
hole at center of eye where light enters
iris
contains muscles that allow it to control the diameter of the pupil affecting how much light can enter
(circular and radial muscles)
retina
layer at back of eye that contains both types light receptor cells (light intensity and colour)
lens
focuses light on the retina
cilliary muscles and suspensory ligaments
control the shape of the lens
optic nerve
carries carries impulses from receptors on the retina to the brain
Explain the 2 common defects of the eye.
Two common defects of the eyes are myopia (short sightedness) and hyperopia (long sightedness) in which rays of light do not focus on the retina.
How are defects of the eye treated?
Generally these defects are treated with spectacle lenses which refract the light rays so that they do focus on the retina.
How are defects of the eye treated using new technology?
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.
iris reflexin response too dim light
the circular muscles relax and the radial muscles contract causing the pupil to become wider
iris reflex in response to bright light
circular muscles contract and radial muscles relax causing pupil to become smaller
contact lenses
- lenses that sit on surface of the eye and are shaped to compensate for fault in focasing
- lightweight and almost invisible
- more convinient than glasses for certain activities
laser eye surgery
- laser used to vaporise tissue changing the shape of the cornea
- slimming cornea down makes it less powerful improving short sight
- changing shape so its more powerful improves long sight
- risk of complications
reeplacement lense surgery
- sometimes may be more effective for longsightedness than other treatments
- natural lense removed and artificial plastic lense replaces it
- higher risk than laser - possible damage to the retina
Recall how body temperature is monitored and controlled?
Body temperature is monitored and controlled by the thermoregulatory centre in the brain.
Explain how body temperature is monitored and controlled?
The thermoregulatory centre contains receptors sensitive to the temperature of the blood.
Explain how the skin reacts when body temperature is too high.
If the body temperature is too high,
- blood vessels dilate (vasodilation) - closer to surface
- sweat is produced from the sweat glands
- Both these mechanisms cause a transfer of energy from the skin to the environment.
- hairs on skin lie flat -less air trapped near surface of skin so no insulating layer so heat transfered more easily
Explain how the skin reacts when body temperature is too low.
If the body temperature is too low,
- blood vessels constrict (vasoconstriction),
- sweating stops
- skeletal muscles contract (shiver).
- hairs on skin stand up - traps insulating layer of air
endocrine system
The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream.
Explain how hormones travel to organs in the body.
The blood carries the hormone to a target organ where it produces an effect.
How is blood glucose monitored and controlled?
Blood glucose concentration is monitored and controlled by the pancreas.
How does the pancreas react to high glucose concentrations in the blood?
If the blood glucose concentration is too high, the pancreas produces the hormone insulin that causes glucose to move from the blood into the muscle and liver cells to be stored as glycogen)
what happens when blood glucose is too low
pancreas secretes glucagon which causes glycogen to be converted back to glucose
Describe type 1 diabetes.
Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels and is normally treated with insulin injections.
treatment for type 1 diabetes
- insulin therapy - injecting insulin likely at mealtimes several times throughout the day stopping glucose getting too high
- limit carbohydrate intake - as it causes glucose to rise rapidly
- regular exercise - lowers glucose due to increased metabolism of cells
Describe type 2 diabetes.
In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas. A carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk factor for Type 2 diabetes.
type 2 diabetes treatment
- limit carbohydrate intake
- regular exercise
new treatment of diabetes
- pancreas transplant
- pancreas stem cell research
how do you test for diabetes
looking for glucose level in urine sample or blood test (more accurate)
How does water leave the body ?
- Water leaves the body via the lungs during exhalation.
- Water, ions and urea are lost from the skin in sweat.
How are excess substances removed from the body?
Excess water, ions and urea are removed via the kidneys in the urine.
Describe what happens to body cells if there is an inbalance of water.
If body cells lose or gain too much water by osmosis they do not function efficiently.
What is the result of the digestion of proteins?
The digestion of proteins from the diet results in excess amino acids which need to be excreted safely.
Describe how amino acids are removed in the body.
In the liver these amino acids are deaminated to form ammonia.
Describe how ammonia is removed in the body.
Ammonia is toxic and so it is immediately converted to urea for safe excretion.
Describe the function of the kidneys.
The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water.
How are water levels controlled in the body?
The water level in the body is controlled by the hormone ADH which acts on the kidney tubules.
Explain the action of ADH in the body.
ADH is released by the pituitary gland when the blood is too concentrated and it causes more water to be reabsorbed back into the blood from the kidney tubules. This is controlled by negative feedback.
what happens when the water content is too high
- pituitary gland releases less adh
- kidney tubules become less permeable
- less water absorbed
what happens when water content is to low
- pituitary gland releases more adh
- kidney tubles are more permeable
- more water is selectivley reabsorbed
how does dialysis work
- blood flows along a partially permeable membrane alongside dialysis fluid
- membrane allows ions and waste products throgh but not big substances like proteins (like the kidneys)
- fluid has same concentration of ions and glucose as healthy blood so they wont be lost during dialysis
Recall the function of reproductive hormones.
During puberty reproductive hormones cause secondary sex characteristics to develop.
Describe Oestrogen.
Oestrogen is the main female reproductive hormone produced in the ovary.
Describe Testosterone.
Testosterone is the main male reproductive hormone produced by the testes and it stimulates sperm production.
menstural cycle
- stage 1 uterus lining breaks down fsh released from pituitary gland causing egg to mature (days 1-4)
- stage 2 uterus lining built up again by oestrogen released by ovaries and stimulated by fsh and stimulates release of Lh (days 4 - 14)
- stage 3 egg released (ovulation) (day 14)
- stage 4 follical remains after ovulation trigger release of progesterone from ovaries which maintain uterous lining and inhibits fsh and LH (day 14-28)
Explain IVF.
In Vitro Fertilisation (IVF) treatment.
* IVF involves giving a mother 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).
Recall the disadvantages of IVF.
Although fertility treatment gives a woman the chance to have a baby of her own:
* it is very emotionally and physically stressful
* the success rates are not high (26%)
* it can lead to multiple births which are a risk to both the babies and the mother.
Describe Adrenaline.
Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.
Describe Thyroxine.
Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development. Thyroxine levels are controlled by negative feedback.
Why do plants produce hormones?
Plants produce hormones to coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism).
State a disadvantage of unequal distribution of auxin.
Unequal distributions of auxin cause unequal growth rates in plant roots and shoots.
Describe the importance of Gibberellins.
Gibberellins are important in initiating seed germination.
Describe the importance of Ethene.
Ethene controls cell division and ripening of fruits.
