biology topic 5- homeostasis Flashcards
What is homeostasis?
The maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular function
What 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 a receptor?
Receptors detect changes in the environment (stimuli)
What is the function of a coordination centre?
Coordination centres obtain and process information from receptors
What is the function of an effector
Effectors(muscles or glands) bring about responses to stimuli
What is the function of the nervous system?
Allows the body to react to its surroundings and coordinate an appropiate response
How does a stimulus lead to a response being carried out by the body?
-stimulus is converted into an electrical impulse by 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
What sequence of events describes how the nervous system works?
Stimulus-receptors-coordinator-effector-response
What is a reflex action?
An automatic and rapid response which does not involve any conscious input from the brain
Why are reflex actions important?
Aid survival by preventing harm to the body
Describe how a reflex action occurs via a reflex arc
-stimulus is detected by a receptor
-an electrical impulse passes along a sensory neurone to the spinal cord
-at a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap and 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
What is the function of the cerebral cortex?
Controls consciousness, intelligence, memory and language
What is the function of the cerebellum?
Controls muscular coordination
What is the function of the medulla?
Controls unconscious activities e.g. breathing
Why is the investigation and treatment of the brain difficult?
-the brain is a complex and delicate organ
-the brain is easily damaged and destroyed
-certain membranes prevent drugs from reaching the brain
-the exact function of each part of the brain 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
What stimuli are the receptors of the eye sensitive to?
Light intensity and colour
What are the two main functions of structures found within the eye?
-focusing on near or distant objects-accommodation
-adaption to dim light
Describe the function and function of the retina
-The light sensitive layer found a the back of the eye
-light stimulates the retinal cells, resulting in impulses being sent to the brain
Describe the function and structure of the optic nerve
-The optic nerve connects the eye and the brain
-it carries impulses so that an image can be visualised
Describe the function of the sclera
The sclera is a tough outer layer of the eye which protects its internal structures
Describe the function of the cornea
-the curved transparent layer at the front of the eye
-it lets light into the eye and allows light to be focused onto the retina
Describe the structure 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 sensory ligaments
The ciliary muscles and suspenders 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 pupils smaller to avoid retinal damage
-dim light — circular muscles relax and radial muscles contract— makes pupils larger so more light can enter the eye
What is accommodation?
Accommodation is the alteration of the lens’ shape in order to focus on near or distant objects
How does the eye focus on nearby objects?
-ciliary muscles contract
-suspenseful ligaments loosen
-lens becomes thicker and more curved-light rays are refracted strongly
How does the eye focus on a far away object?
-ciliary muscles relax
-suspensory ligaments tighten
-lens becomes thinner-light rays refracted weakly
What is myopia?
-(Short-sightedness) usually occurs when the lens of the eye is too curved
-as a result, light is focused in front of the retina so images appear blurry
How can myopia be treated?
-Can be treated using glasses with a concave lenses
-spreads out light rays so they can be focused don’t the retina
What is hyperopia?
-(long-sighted) usually occurs when the lens of the eye is too flat
-as a result light is focused behind the retina so images appear out of focus
How can hyperopia be treated?
Can be treated using glasses with a convex lens , which brings the light rays together so they can be focused on the retina
what is laser eye surgery?
-the use of lasers to fix visual defects in adults
-treat myopia—lasers reduce the thickness of the cornea so light is refracted less strongly
-hyperopia—lasers alter the curvature of the cornea so that light is refracted correctly
Where is body temperature controlled in the body?
Body temperature is controlled by the thermoregulatory centre in the hypothalamus of the brain
How is temperature measured by the body?
-thermoregulatory centre has receptors sensitive to blood temperature
-skin has receptors sensitive to skin temperature-sends impulses to thermoreregulatory 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
-sweating-evaporation of water takes away heat energy from the surface of the skin
What physiological changes occur when the body temperature is too low?
-vasoconstriction-blood vessels near the surface of the skin contradict-less heat radiated away
-shivering-respiration allows muscles to contract .it is an exothermic process, 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 chemical messenger secreted by a gland. It travels in the 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 human 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 endocrine system?
Secretes the hormones thyroxine - controls metabolism, heart rate and body temperature
what is the role of the pancreas in the endocrine system?
Secretes the hormones insulin - controls blood glucose levels
What is the role of the adrenal gland in the endocrine system?
Secretes adrenaline - control’s the body’s ’fight or flight’ response
What is the role of the ovaries in the endocrine system?
Secretes 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?
Secretes 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 hormones 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 high?
-the pancreas secretes the hormones 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 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 helps bring back the concentration to the correct level
What is type 1 diabetes?
-autoimmune 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
How can type 1 diabetes be treated?
-insulin injections before meals-allows glucose to be converted into glycogen
-limiting carbohydrate intake
-attempts using pancreas and pancreatic cell transplants; investigations into genetic engineering of pancreatic cells
What is type 2 diabetes?
A disorder in which the body’s cells stop responding to insulin, leading to an uncontrolled blood glucose concentration
-its onset is linked with increasing age and obesity
How can type 2 diabetes be treated?
-following a carefully controlled diet
-doing regular exercise
-losing weight
-use of drugs which increase insulin production and effectiveness
What is osmosis?
The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
In what way is water lost form the body?
-during exhalation via the lungs
-sweating
-urine
In what ways are ions lost from the body?
-sweating
-urine
How are excess amino acids excreted form the body?
-excess amino acids are delaminated in the liver to form ammonia
-ammonia is toxic, therefore it is covered into urea
-urea is excreted form the body via sweat and urine
How do kidneys maintain the balance of water and other substances in the body?
-filter blood in order to remove waste products
-selectively re absorb useful molecules
Where is ADH secreted in the body?
The pituitary gland of the brain
What is the full name of the hormone ADH?
Anti-diuretic hormone
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 and increases the permeability of kidney tubules to water.
-more water is reabsorbed in the kidneys, resulting in a smaller volume of more concentrated urine
Why is kidney failure dangerous?
When the kidneys are damaged, they may be unable to filter the blood properly. This may lead to:
-a build-up of toxic molecules int he body
-an uncontrolled ion and water balance and cells being damaged as a result of osmosis
What are the two main ways of treating kidney failure?
-dialysis
-transplant
What is kidney analysis?
-The use of a specialist machine to carry out the function of kidneys
-dialysis fluid contains the Same concentration of glucose and ions as healthy blood
-as a result, only excess and waste molecules are lost from the blood, and glucose and ions remain
What5 is the function of reproductive hormones during puberty?
-males:cause the development of secondary sexual characteristics
-females:cause the development of secondary characteristics and the maturation of eggs
What is the main male reproductive hormone?
Testosterone, which is produced by the testes and controls sperm production
What is the main female reproductive hormone?
Oestrogen, produced by the ovaries and is involved in the menstrual cycle
What is the menstrual cycle?
The monthly cycle of physiological changes that occur in females, involving the shedding of the uterus lining and ovulation
Describe the events of the menstrual cycle
-uterus lining thickens and eggs begin to mature in the ovaries
-an egg is released from one of the ovaries (uterus lining remains thick)
-if the egg is fertilised, pregnancy may occur. If not both the egg and the uterus lining are shed during menstruation
What is ovulation?
The 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)
-luteinising hormone (LH)
What is the role of FSH in the menstrual cycle?
-FSH is secreted by the pituitary gland.
-It controls the maturation of eggs within the ovaries and triggers the production of oestrogen by 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 re growth of the uterus lining
-triggers the production of LH and restricts the release of more FSH
What is the role of LH in the menstrual cycle?
-produced in the pituitary gland as a result of oestrogen
-its release triggers ovulation
What is the role of progesterone in the menstrual cycle?
-secreted from the follicle of the ovary
-sustains the uterus lining and inhibits FSH and LSH
What is contraception?
Refers to any method of preventing pregnancy
What are the two types of oral contraceptives?
-combined contraceptive pill
-mini pill
How does the contraceptive pill prevent pregnancy?
-inhibits FSH - eggs do not mature
-prevents development of the uterus lining - eggs cannot implant
-increase the thickness of cervical mucus - immobilises sperm cells
What is the contraceptive patch?
-contains both oestrogen and progesterone
-it is a patch that is placed onto the skin for 7 days at a time
What is the contraceptive implant?
A small rod inserted under the skin which continuously releases the hormone progesterone - lasts for 3 years
What is the contraceptive injection?
An injection containing the hormone progesterone - lasts for approximately 3 months
What is a spermicide?
A spermicide is a chemical that kills or immobilises sperm cells
What is a barrier method of contraception?
Involves a physical separation between the sperm and the egg. They include:
-condoms
-diaphragms- a thin cap placed over the cervix
How do fertility drugs increase the chance of pregnancy?
Many fertility drugs contain FSH - which stimulates oestrogen production and the maturation of eggs in the ovary as well as LH which triggers ovulation
What is IVF?
A type of fertility treatment:
-mother is given FSH + LH
-eggs fertilised using sperm in a lab
-1 or 2 embryos inserted into mother’s womb
What are the advantages of fertility treatment?
-allows infertile couples to have children
-can store a women’s egg for later
What are the advantages of fertility treatment?
-can be expensive
-low success rate
-can be dangerous for mother and child
-side effects of drugs
What is negative feedback?
A type of control where the body responds to an increase or decrease in a factor by returning to the optimum level
What is thyroxine?
A hormone released by the thyroid gland
-triggered by the thyroid stimulating hormone (TSH)
-thyroxine controls the body’s metabolic rate , growth and development
How is the release of thyroxine controlled by negative feedback?
-levels of blood thyroxine fall-detected by receptors in the brain
-pituitary gland released by the thyroid gland
-blood thyroxine level returns to normal
What is adrenaline?
A hormone secreted by the adrenal gland in times of stress. It is responsible for the ‘fight or flight response’
What are the effects of adrenaline?
-increase in heart and breathing rate- delivers oxygen and glucose to the body
-stored glycogen converted to glucose
-dilation of the pupils
-increase mental awareness
-blood diverted away from digestive system to muscles
What is tropism?
Th response of a plant to a specific stimulus
What is phototropism?
The response of a plants shoot or root to light
What is gravitropism?
The response of a plant shoot or root to gravity
What is auxin?
A hormone which controls the growth of a plants shoots and roots
-when auxin is unevenly distributed in a growing plant, the rate of growth will also be unequal
How do plant shoots show positive phototropism?
-one side of the shoot is in the light, causing auxin to move to the shaded side
-on shaded side, the cells are stimulated to grow -shoot bends towards light
-as a result, photosynthesis can occur at a faster rate
How do plant shoots show negative gravitropism?
-in a horizontal shoot, auxin accumulates in the lower side due to gravity
-cells on lower side of shoot grow more, causing the shoot to bend away form the direction of gravity
-as a result, more light is usually available for photosynthesis
What are gibberellins?
A type of plant hormone involved in seed germenation
What is ethane?
A type of plant hormone involved in cell division and ripening
What are the uses of auxins?
-weed killers
-rooting powder
-tissue culture-promote growth
What are the uses of ethene?
Control of food ripening in food industry-allows fruit to be ripened just before sold
What are the uses of gibberellins?
-termination of seed dormancy
-promotion of flowering
-increase of fruit size
