B5 - Homeostasis And Response 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.
How does homeostasis maintain optimal conditions in the human body?
It is used to keep blood glucose concentration, body temperature and water levels constant
Describe the key features of automatic control systems in the body
Receptor cells - detect changes in the environment (stimulus).
Coordination centre (brain, spinal cord, pancreas) - receives and processes information from receptor cells.
Effectors - Muscles or glands which bring about responses which restore optimum levels.
What is the function of the nervous system?
The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
Describe how the structure of the nervous system is adapted to its functions
Receptors detect a stimulus and send electrical impulses down neurones to the central nervous system.
The central nervous system coordinates the response of effectors which may be muscles contracting or glands secreting hormones.
Describe the structure of the reflex arc (1,2,3,4)
- First, the stimulus is detected by a receptor
- Electrical impulses now pass from the receptor along a sensory neurone to the central nervous system.
- When the electrical impulses reach the synapse, a chemical is released.
- This chemical now diffuses across a relay neurone in the central nervous system where it triggers an electrical impulse.
Describe the structure of the reflex arc (5,6,7,8)
- The electrical impulse now passes across the relay neurone and reaches another synapse.
- Again a chemical is released which triggers an electrical impulse in a motor neurone.
- The electrical impulse now passes down the motor neurone to an effector (muscle or gland)
- The effector brings about a response (e.g. muscle contracting to pull hand away from heat)
Why are reflex actions important?
Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
Because they are rapid, reflexes help to protect us from danger.
Functions of the cerebral cortex
Language, memory and consciousness
Functions of the Cerebellum
Controls balance and co-ordinates movement
Functions of the Medulla
Controls heart rate and breathing rate
Explain the difficulties of investigating brain function and treating brain damage & disease
The brain is protected by the skull, so it is difficult to access.
Structures of the brain are extremely complex.
The brain is extremely delicate and easy to damage.
What 3 ways do scientists use to investigate the brain?
Look to see where brain damage has taken place and link that part of the brain to its function.
Electrically stimulate the brain and look at the effects on the persons behaviour. (to narrow down specific regions to their functions).
MRI scanning to see what parts of the brain are most active during different activities.
Function of the Cornea
To start the focussing of light rays onto the retina.
Function of the Retina
Contains receptor cells for light which allow us to Detect light intensity and light colour.
Function of the sclera
A tough outer structure to protect the eye.
Function of the iris
Control the size of the pupil.
To focus on a near object:
The ciliary muscles contract.
The dispensary ligaments loosen.
The lens is then thicker and refracts light rays strongly.
To focus on a distant object:
The ciliary muscles relax.
The dispensary ligaments are pulled tight.
The lens is then pulled thin and only slightly refracts light rays.
Describe how myopia (short sightedness) & hyperopia (long sightedness) are treated
With spectacle lenses which refract light rays so they focus on the retina.
Hard or soft contact lenses, laser surgery to change the shape of the cornea & replacement lens in the eye.
Where is body temperature controlled in the body?
The thermoregulatory centre in 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 changes occur when body temperature is too high?
• Vasodilation - blood vessels get wider so more blood flows through the capillaries - heat transfers out of blood
• Sweating - evaporation of water takes energy from the body, cooling it down
What changes occur when body temperature is too low?
• Vasoconstriction - less blood flows through the capillaries & less heat is lost
• Shivering - Skeletal muscles contract - energy required through respiration - releases heat & warms the body
• Sweating stops
Name the coordination system which involves hormones
Endocrine system
What is a hormone?
A chemical messenger secreted by a gland.
Travels in the blood to a target organ, where it causes a response,
Why is the pituitary gland considered a “master gland” ?
Secretes a wide range of hormones, some of which may stimulate other endocrine glands.
Where is blood glucose concentration monitored & controlled?
The Pancreas
What happens if blood glucose concentration is too high?
Pancreas produces insulin that causes glucose to move from the blood into the cells.
What happens if blood glucose concentration is too low?
Pancreas produces glucagon that causes glycogen to be converted into glucose & releases into the blood
What is type 1 diabetes & how is it treated?
• Pancreas fails to produce sufficient insulin
• Treated with insulin injections
What is type 2 diabetes & how is it treated?
What is the risk factor?
• Body cells no longer respond to insulin
• Treated with carbohydrate controller diet & exercise.
• The risk factor is Obesity
Describe the different ways that water can leave the human body
• Water leaves body via the lungs during exhalation
• Water, ions & urea are lost from the skin in sweat
• Excess water, ions & urea are removed via the kidneys in the urine
Explain the role of the kidney in maintaining the concentration of substances in the blood
• Blood passes through capillaries & small molecules filtered out of blood (Urea, ions, water, glucose)
• All of the glucose, some of the ions & some of the water is reabsorbed back into the blood (selective reabsorption)
Explain how the body deals with excess amino acids
• Excess amino acids are deaminated in the liver to form ammonia
• Ammonia is toxic, so it is converted into urea
• Urea is excreted from the body via sweat & urine
ADH is secreted in the:
Pituitary gland of the brain
Describe how the Hormone ADH is used to control the water level in the blood
(Concentrated)
• Pituitary gland releases ADH into bloodstream
• ADH travels to kidneys and causes the tubules to become more permeable to water
• More water is reabsorbed back into the blood
• Less urine produced & water level in blood rises back to normal level
• ADH stopped being released
Describe how the hormone ADH is used to control the water level in the blood
(Dilute)
• Concentration of water in blood rises & ADH is no longer released
• Kidneys reabsorb less water into the blood
• More urine produced & concentration of water in blood returns back to normal
Describe how kidney dialysis works
• Blood passed over a semi-permeable membrane
• Urea, ions & water pass through but larger molecules such as proteins won’t pass through
• Dialysis fluid contains normal concentrations of water & ions so only urea & excess waste molecules diffuse from blood into the dialysis fluid
Advantages & disadvantages of Kidney transplants
• Allows patient to lead a normal life
• Only expensive initially
• Shortage of kidney donors
• Patients have to take anti-rejection drugs for rest of life
Advantages & disadvantages of Kidney dialysis
• No shortage of dialysis machines
• Expensive long term
• Requires frequent treatments & a controlled diet
Name the main male reproductive hormone & its function
• Testorone - Stimulates sperm production
Function of FSH
Causes an egg to mature in the ovary
Function of LH
Causes the egg to be released
(Ovulation)
Functions of Oestrogen & Progesterone
• Maintain Uterus lining incase the egg is fertilised & implants
Oral contraceptives are:
Hormones to inhibit FSH production so the eggs don’t mature
Injection of slow release progesterone:
Inhibits maturation & release of eggs for months/years
Barrier methods:
Prevent sperm reaching the egg
E.g. Condoms
Intrauterine devices:
Prevent implantation of an embryo or release a hormone
Spermicidal agents are used to:
Kill/ disable sperm
Surgical methods for contraception:
Male or female sterilisation
Explain why issues around contraception cannot be answered by science alone
• Ethics - Catholic Church teaches that contraception is unethical.
• Other people believe that it’s a persons right to choose what form of contraception is best for them
Describe IVF
• Mother is given FSH & LH to stimulate maturation of several eggs
• Eggs are collected from the mother & fertilised by sperm from father
• Fertilised eggs develop into embryos
• At the stage when they are tiny balls of cells, 1 or 2 embryos are inserted into the mothers uterus
Describe the problems & issues around IVF
• Emotionally & physically stressful
• Success rates are not high
• Can lead to multiple births which is a risk to the babies & the mother
Explain the role of adrenaline in the body
•Increases heart rate - more oxygen & glucose are delivered in the blood to the brain & muscles
• Oxygen & glucose needed for respiration - prepares the body to fight or run away
Explain the role of thyroxine in the body
• Stimulates the body’s basal metabolic rate - chemical reactions take place at a faster rate
• Plays an important role in growth & development
Explain how thyroxine levels are controlled by negative feedback
• Level of thyroxine in blood monitored by the brain
• When thyroxine level falls, pituitary gland releases TSH into the bloodstream
• TSH triggers the thyroid gland to release more thyroxine into the blood
• Increased level of thyroxine detected by the brain - now prevents the pituitary gland releasing TSH
• As TSH level falls, the thyroid gland releases less thyroxine
What is phototropism?
Response of a plant’s shoot or root to light
What is Geotropism?
The response of a plant’s root or shoot to gravity
What is auxin?
•A hormone which controls the growth of a plants roots & shoots.
•When unevenly distributed in a growing plant, the rate of growth will be unequal
How do plant shoots show positive phototropism?
• One side of the shoot is in light, causing auxin to move to the shaded side
• At shaded side, cells are stimulated to grow - shoot bends toward the light
• As a result, photosynthesis can occur at a faster rate
How do plant shoots show negative geotropism?
• In a horizontal shoot, auxin accumulates in lower side due to gravity
• Cells on lower side of shoot grow more, causing shoot to bend away from direction of gravity
• As a result, more light is available for photosynthesis
How do plant roots show positive geotropism?
• In a horizontal root, auxin accumulates in lower side, causing cells to grow less
• Root bends in direction of gravity
• As a result, more water & nutrients are available to the plant roots
Roles of gibberellins
Seed germination
Roles of ethene
• Cell division
• Ripening of fruits
Uses of auxins
• Weedkillers
• Rooting powders
• Promoting growth in tissue culture
Uses of ethene
• Food industry for ripening of fruit during storage & transport
Uses of Gibberellins
• End seed dormancy
• Promote flowering
• Increase fruit size
