B5: Homeostasis and response Flashcards
what is homeostasis?
- the maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular function.
Give 3 examples of conditions maintained by homeostasis in the body
• Blood glucose concentration
• Body temperature
• Water levels
What two types of responses are used in body control systems?
Nervous and chemical
What three components do all control systems have?
• Receptors
• Coordination centres
• Effectors
What is the function of a receptor?
Receptors detect changes in the environment (stimuli).
What is the function of an effector?
Effectors (muscles or glands) bring about responses to stimuli.
What is the function of a coordination centre?
- obtain and process information from receptors.
- Eg brain and spinal cord
What is the function of the nervous system
- allows the body to react to its surroundings and coordinate an appropriate response.
How does a stimulus lead to a response being carried out by the body?
• Stimulus is converted into an electrical impulse by the receptors.
• The electrical impulse passes along sensory neurones to the central nervous system (CNS).
• The CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response.
Describe the sequence of events on the way the nervous system works
Stimulus— receptor— coordinator— effector—response
Define a ‘reflex action’
- an automatic and rapid response
- which does not involve any conscious input from the brain
Why are reflex actions important ?
- Reflex actions aid survival by preventing harm to the body
Describe how a reflex action occurs via a reflex arc (4 marks)
- the stimulus is detected by a receptor
- an electrical impulse passes along a sensory neurone to the spinal cord (part of the CNS)
- At a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap
- this stimulates a new impulse which passes along the relay neurone
- the same process occurs at a synapse between a relay neurone and a motor neurone
At the effector , an appropriate response is carried out.
Describe the knee jerk reflex (4)
- receptor detects pain and sends electrical impulses along the sensory neurone
- electrical impulses then move to the relay neurone in the spinal cord
- the electrical impulses are then transmitted from relay neurone to the motor neurone
- motor neurone sends impulses to the effector ( the muscle )
- muscle contracts
- so knee jerks away from pain
What is the difference between a reflex pathway and a conscious pathway.
Within a reflex pathway, the coordination centre is a relay neurone found in the spinal cord/ unconscious parts of the brain.
- In a conscious pathway, the coordination centre is in the conscious part of the brain.
What is the function of the cerebral cortex. And where is it found
- the outer layer of the brain which is divided into two hemispheres.
- Is responsible for higher-order processes such as intelligence, memory, consciousness and personality
What is the function of the cerebellum and where is it found
- this is underneath the cerebral cortex
- is responsible for balance, muscle coordination and movement
What is the function of the medulla and where is it found ?
This region controls unconscious activities such as heart rate and breathing
Give 4 reasons why the investigation and treating of the brain difficult
- the brain is a complex and delicate organ
- the brain is easily damaged
- certain membranes prevent drugs from reaching the brain
- the exact function of each part of the brai is not known
What methods are used by scientists to determine brain function?
- studying patients with brain damage
- electrical stimulation of the brain
- MRI scans
delte
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How can we study patients with brain damage?
- observing the changes in an individual following damage on a certai area of the brain
- this can provide information on the role this area has
How can we use electrical stimulation to map out the regions of the brain?
- Tiny electrodes can be pushed into different parts of the brain
- tiny jolts of electricity stimulate these regions and the mental or physical changes in the individual effects can be observed.
How can we use MRI scanning techniques?
- to create an image of the brain.
- it can be used to show which part of the brain is affected by a tumour, or which part is active during a specific task.
- the scanners can detect changes in blood flow
evaluate the benefits and 2 risks of procedures carried out on the brain and nervous system
Risk:
- high level of risk due to the complexity of the brain
- If surgery is undergone more permanent damage or side-effects may be created, which could affect the patients’ quality of life.
Benefits
- improves quality of life and patient health
- treats disorders of some kind
What stimuli are the receptors of the eye sensitive to?
Light intensity and colour
What are the 2 main functions of structures found within the eye?
- accommodation ( focusing on near or distant objects)
- adaptation to dim light
Describe the structure and function of the retina
- the retina is a light-sensitive layer found at the back of the eye
- light stimulates the retinal cells resulting in impulses being sent to the brain
Describe the structure and the function of the optic nerve
- the optic nerve connects the eye and the brain
- it carries impulses to the brain so that an image can be visualised
Describe the structure and function of the sclera
- the scelta is the tough white outer layer of the eye which protects its internal structures
Describe the structure and function of the cornea
- the cornea is the curved transparent layer at the front of the eye
- it lets light into the eye and refracts it
Describe the structure and function of the iris
- The iris is a muscle which controls the size of the pupil by contracting or relaxing.
- This allows the eye to adjust to bright and dim lighting
Describe the structure and function of the ciliary muscles and suspensory ligaments
The ciliary muscles and suspensory ligaments hold the lens in place and control its shape
Describe how the iris alters the size of the pupil in both bright and dim light
Bright light: circular muscles contract and radial muscles relax - makes pupil smaller to avoid retinal damage
Dim light: circular muscles relax and radial muscles contract- makes pupil larger so more light can enter the eye
How does the eye focus on a nearby object
- ciliary muscles contract
- suspensory ligaments loosen
- lens becomes thicker and more curved- light rays are refracted strongly
How does the eye focus on distant objects?
Ciliary muscles relax
Suspensory ligaments tighten
Lens becomes thinner - light rays are refracted weakly
How can myopia be treated?
Myopia can be treated using glasses with a concave lens, which spreads out light rays so they can be focused on the retina
What is hyperopia?
- long-sightedness
- occurs when the lens of the eye is too flat or short. As a result , light is focused behind the retina so images appear out of focus.
How can hyperopia be treated?
- treated using glasses with a convex lens , which brings the light rays together so they can be focused on the retina.
What are two types of contact lenses?
- hard- rigid material, last a long time , must be kept sterile
- soft- flexible material, last for a shorter time, more comfortable
What is laser eye surgery and how does it treat myopia and hyperopia
- the use of lasers to fix visual defects in adults
- to treat myopia, lasers reduce the thickness of the cornea so light is refracted less strongly.
- to treat hyperopia, lasers alter the curvature of the cornea so light is refracted correctly
How can replacement lenses be used to treat visual defects?
A replacement lens can either be implanted into the eye along with the natural lens
Give three risks of lens replacement
- retinal damage
- cataracts
- infections
Where is body temperature controlled in the body?
- the thermoregulatory centre in the hypothalamus of the brain
How is temperature monitored by the body?
- thermoregulatory centre has receptors sensitive to blood temperature
- skin has receptors sensitive to skin temperature - sends impulses to thermoregulatory centre
What physiological changes occur when the body temperature is too high.
Vasodilation- blood vessels near the surface of the skin dilate - more heat is radiated away as more blood flows closer to the surface of the skin
Sweating- sweat evaporates from skin surface resulting in increased heat energy transfer away from the body
What physiological changes occur when the body temperature is too low?
Vasoconstriction- blood vessels near the surface of the skin constrict so less heat is radiated away
Shivering- respiration allows muscles to contract as it is an exothermic reaction so heat energy is released
Sweating stops
Give the name of the body’s coordination system which involves hormones
The endocrine system
What is a hormone ?
- A hormone is a chemical messenger secreted by a gland.
- It travels in the blood to a target organ , where it causes a response
What type of organ secretes hormones?
Glands
Which gland controls many other glands in the body?
The pituitary gland
Why is the pituitary gland considered a ‘master gland’
It secretes a wide range of hormones, some of which may stimulate other endocrine glands
What is the role of the pituitary gland in the endocrine system?
- secretes human growth hormone. Controls growth
- stimulates the thyroid gland
- stimulates ovulation and the production of oestrogen in the ovaries
- stimulates the production of sperm and testosterone in the testes
What is the role of the thyroid gland in the endocrine system?
Secretes the hormone thyroxine - controls basal metabolic rate , heart rate and body temperature
What is the role of the pancreas in the endocrine system?
controls blood glucose concentration
What is the role of the adrenal gland i the endocrine system?
Secretes adrenaline - controls the body’s ‘fight or flight’ response
What is the role of the ovaries in the endocrine system?
Secrete oestrogen , which coordinates the menstrual cycle and the development of female secondary sexual characteristics
What is the role of the testes in the endocrine system ?
Secrete testosterone , which coordinates the production of sperm and the development of male secondary sexual characteristics
Which organ monitors and controls blood glucose concentration?
The pancreas
How does the pancreas respond when blood glucose levels are too high?
- The pancreas secretes the hormone insulin.
- insulin binds to receptors on the liver and muscles , causing excess glucose to be converted into glycogen and stored
How does the pancreas respond when blood glucose levels are too low?
- The pancreas secretes the hormone glucagon.
- Glucagon binds to liver cells, causing glycogen to be converted into glucose and released into the blood.
How is blood glucose concentration controlled using a negative feedback loop?
- when the blood glucose concentration rises or falls below the optimum , a hormone is secreted by the pancreas
- the action of either hormone (insulin or glucagon) helps bring back the concentration to the correct level.
What is type 1 diabetes ?
- an auto immune disorder in which the pancreas does not produce sufficient insulin to control the blood glucose concentration
- as a result, blood glucose levels are often very high, leading to excessive urination, tiredness and weight loss.
Give three ways Type 1 diabetes can be treated.
- insulin injections before meals - allows glucose to be converted into glycogen
- limiting carbohydrate intake
- using pancreas and pancreatic cell transplants
What is type 2 diabetes?
- a disorder in which the body’s cells stop responding to insulin , leading to an uncontrolled blood glucose concentration .
- It’s onset is linked with increasing age and obesity
Give 4 ways type 2 diabetes can be treated
- following a carefully- controlled diet
- doing regular exercise
- losing weight
- use of drugs which increase insulin production and effectiveness
define osmosis
The movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane
In what ways is water lost from the body?
- During exhalation via the lungs
- sweating
- urine ( some reabsorbed in the kidney)
In what ways are ions lost from the body
- sweating
- urine ( some reabsorbed in the kidney)
How are excess amino acids excreted from the body?
- excess amino acids are delaminated in the liver to form ammonia
- ammonia is toxic , therefore it is converted into urea
- urea is excreted from the body via sweat and urine
How do the kidneys maintain the balance of water and other substances in the body
- filter blood in order to remove waste products via urea
- selectively reabsorbed useful molecules eg glucose, water, ions
What does the hormone ‘ ADH’ stand for
Anti-diuretic hormone
Where is ADH secreted in the body?
The pituitary gland of the brain
How does ADH affect the reabsorption of water in the kidneys
- When the blood is too concentrated, the pituitary gland secretes more ADH
- ADH travels in the bloodstream to the kidney making kidney tubule more permeable to water
- more water is reabsorbed in the kidneys, resulting in a smaller volume of more concentrated urine.
Why is kidney failure dangerous?
unable to filter the blood properly leading to:
- a build up of toxic molecules (eg urea) in the body
- cell damage due to uncontrolled balance of ions
Give the 2 main ways of treating kidney failure?
- dialysis
- transplant
What is kidney dialysis?
- use of a specialist machine to carry out the function of kidneys.
- the persons blood flows through a partially permeable membrane surrounded by dialysis fluid
- the fluid has the same concentration of dissolved ions and glucose as healthy blood
- only waste substances eg urea will diffuse across barrier from blood
What is the main male reproductive hormone and their function
- testosterone
- produces by the testes
- which controls sperm production
What is the main female reproductive hormone?
- Oestrogen,
- produced in the ovaries
What is the menstrual cycle?
- monthly cycle of physiological changes that occur in females , involving menstruation and ovulation
Describe the events of the menstrual cycle
- uterus lining thickens and eggs begin to mature in the ovaries
- a egg is released from one of the ovaries( ovulation )
- uterus lining remains thick
- if egg is fertilised , pregnancy may occur .
- If not both the egg and the uterus lining are shed during menstruation
What is ovulation?
- release of a mature egg from the ovaries, which occurs approximately every 28 days
Name the 4 main hormones involved in the menstrual cycle
- oestrogen
- progesterone
- follicle-stimulating hormone (FSH)
- luteinizing hormone (LH)
what is the role of FSH in the menstrual cycle?
.- controls the maturation of eggs within the ovaries ( inside a follicle )
- triggers the production of oestrogen in the ovaries
what is the role of oestrogen in the menstrual cycle?
- produced by the ovaries and released due to the action of FSH
- it causes the regrowth and repair of the uterus lining
- it triggers the production of LH and restricts the release of more FSH
what is the role of LH in the menstrual cycle
- LH is produced in the pituitary gland as a result of oestrogen. it triggers ovulation
what is the role of progesterone in the menstrual cycle?
- it is secreted from the follicle of the ovary. it sustains the uterus lining and inhibits FSH and LH
What is contraception?
contraception refers to any method of preventing pregnancy
what are the two types of oral contraceptives ? And a pro and con
- combined contraceptive pill ( contains oestrogen and progesterone)
- mini pill ( contains only progesterone)
adv:
- highly effective if taken correctly
disadvantage:
- must be taken every day and side effects
Give four ways the contraceptive pill prevent pregnancy?
- inhibits FSH - eggs do not mature
- prevents the development of the uterus lining - eggs cannot implant
- increases the thickness of cervical mucus - immobilises sperm cells
what is the contraceptive patch and an adv and disadv
- contains progesterone
- it is a patch that is placed onto the skin for 7 days at a time
adv
: more convenient then taking a pill
con : - lasts only 7 days
what is the contraceptive implant?
- a small rod inserted under the skin which continuously releases the hormone progesterone
- lasts for 3 years
adv :
- more convenient
- lasts for a long period of time
disadv:
- side effects such as blood clots
what is the contraceptive injection?
an injection containing the hormone progesterone - lasts for approximately 3 months
what is the IUS?
- intrauterine system
- a small plastic device that is inserted into the uterus .
- it releases progesterone which thickens cervical mucus and prevents uterine lining from thickening
what is the IUD?
- a small copper-containing device inserted into the uterus which prevents the implantation of embryos
what is a spermicide and give a disadvantage ?
- a chemical that kills or immobilises sperm cells - however they are not effective and work better when combined with barrier methods.
Define a barrier method of contraception?
- a physical separation between the sperm and the egg
Give and describe a barrier method of contraception
condoms: thin sheath worn on the penis or the inside of the vagina - protects against STIs but may tear/break
diaphragms: a thin cap placed over the cervix - prevent entry of sperm
what surgical methods of contraception are available ?
sterilisation:
- in males, the sperm ducts are tied ( vasectomy )
in females, the oviducts are tied
define abstinence
- practice of not having sex which also avoids pregnancy
- some people abstain from sex around the time of ovulation - this is known as the rhythm method, but is quite unreliable
how do fertility drugs increase the chance of pregnancy?
- many contain FSH which stimulates oestrogen production and the maturation of eggs in the ovary
- they also contain LH which triggers ovulation
What is IVF?
- in vitro fertilisation is a type of fertility treatment
- mother is given FSH and LH stimulates maturation of eggs and ovulation
- eggs are fertilised using sperm in a laboratory where they develop into embryos
- 1 or 2 embryos are inserted into a mother’s womb
give 2 advantages of fertility treatment?
- allows infertile couples to have children
- can store a woman’s egg for later
give 4 disadvantages of fertility treatment
- it can be a very expensive process
- it has a low success rate - especially for older couples
- increases chance of multiple pregnancies - dangerous for mother and babies
- side effects of fertility drugs
what is negative feedback?
- a type of control where the body responds to an increase or decrease in a factor by returning it to the optimum level
how is this release of thyroxine controlled by negative feedback
- levels of blood thyroxine falls - detected by receptors in the brain
- pituitary gland releases more TSH
- more thyroxine produced and released by the thyroid gland
- blood thyroxine level returns to normal
define adrenaline
a hormone secreted by the adrenal gland in times of stress. it is responsible for the ‘ fight or flight response’
give 5 effects of adrenaline
- increase in heart and breathing rate - delivers oxygen and glucose to the body
- stored glycogen converted to glucose
- dilation of pupils
- blood diverted away from digestive system to muscles
- increased mental awareness
what is a tropism
- the response of a plant to a specific stimulus
what is a phototropism?
- the response of a plant’s shoot or root to light
what is gravitropism?
- the response of a plant’s shoot or root to gravity
what is auxin?
- a hormone which controls the growth of a plant’s shoots and roots.
- when auxin is unevenly distributed in a growing plant, the rate of growth will also be unequal
how do plants shoots show positive phototropism?
- one side of the shoot is in the light , causing auxin to move to the shaded side
- at the shaded side, the cells are stimulated to grow - the shoot bends towards the light
- as a result, photosynthesis can occur at a faster rate
how do plants shoots show negative gravitropism
- in a horizontal shoot, auxin accumulates in the lower side due to gravity
- cells on the lower side of shoot grow more , causing the shoot to bend away from direction of gravity
- as a result, more light is usually available for photosynthesis
how do plant roots show positive gravitropism
- in a horizontal root, auxin accumulates in the lower side, causing cells to grow less
- the root bends in the direction of gravity
- as a result, more water and nutrients are available to the plant roots.
what are gibberellins?
- a type of plant hormone involved in seed germination
what is ethene?
- a type of plant hormone involved in cell division and ripening of fruit
what are the three uses of auxins?
- weedkillers - auxin causes cells to grow at a rapid rate, causing plant death
- rooting powder - auxin causes new plant to grow very quickly
- tissue culture - auxin promotes growth of roots and shoots
what are the uses of ethene?
- control of food ripening in the food industry
- allows fruit to be ripened just before they are sold
give three uses of giberellins?
- termination of seed dormancy
- promotion of flowering
- increase of fruit size
what is a kidney transplant ?
- the diseased kidney is replaced with a healthy kidney from a donor
Compare the use of dialysis and kidney transplant
dialysis :
- no shortage of dialysis machines
- requires frequent treatments and controlled diets
- expensive in long term
transplant
- shortage of kidney donors
- allows patient to lead normal life
- only expensive initially
- have to take anti rejection drugs
compare how auxin works in roots and shoots
roots:
auxin inhibits cell growth
shoots:
auxin stimulates cell growth
