bio 5 - homeostasis and response

what is homeostasis?

the regulation of conditions inside your body to maintain a stable internal environment in response to changes in both internal and external condition

how does the body regulate its internal environment?

automatic control systems that regulate temperature, water level and blood glucose ect

what are automatic control systems made up of?

receptor, coordinator and effector

what is the role of a receptor and give an example of one?

receptors detect stimuli (changes in the environment) e.g light receptor cells make up your retinas in your eyes

what is an example of a coordinator and give a example of one?

a coordinator organises a response to the change e.g the brain

what is an effector and give 2 examples?

an effector carries out the change e.g muscles (which react by expanding and contracting) and glands (which respond by secreting hormones)

how does negative feedback work?

negative feedback is used by automatic control systems to regulate your internal environment when the level of something gets too high or low

1) receptor detects stimulus, that the level is too high/low

2) coordination center recives info and organises a response

3) effector carries out the response, restores the optimum level, either decreasing or increasing it

how long will the effectors carry out the response for?

until the receptors der that the level is too high/low and then the cycle of negative feedback begins again

what is the nervous system made up of in invertibrae (animals with a backbone)?

the brain and spinal cord only

do single celled organisms have a nervous system?

no, they can respond directly to the environment

what is the nervous system made up of for multicellular organisms?

CNS (brain, spinal cord, sensory neurones, relay neurones, motor neurones) and effectors (muscles and glands)

what is the different between sensory, relay and motor neurones?

sensory - carry info as electrical impulses from the receptor to the CNS

relay - connect sensory and motor neurones

motor - carry info as electrical impulses from the CNS to the effector

what is a synapse and how do nerve signals travel along the gap in one?

the connection between 2 neurones, the nerve signal is diffused as chemicals across the gap onto the next neurone

what are reflexes?

rapid, automatic responses that don’t involve the conscience part of your brain

what is the passage of info in a reflex called and how does it work?

a reflex arc

1) the receptors detect a stimulus and the info is carried as electrical impulses by a sensory neurone to a relay neurone to the CNS

2) when the nerve signals reach the gap in the synapse between the sensory and relay neurone, the nerve signals are diffused as chemicals across the gap, causing another nerve signal to be carried along the relay neurone, where it meets a synapse again between the relay and motor neurone

3) the motor neurone carries the nerve signal to the effectors, which carry out the response

describe method 1 for investigating reaction time (ruler)

• the person being tested must rest their arm on the edge of the table to stop them moving it randomly

• hold a ruler vertically between their thumb and forefinger, ensuring that their fingers are on the 0cm mark

• let go without warning

• the person will then catch the ruler as soon as it falls, read off of the ruler to see where their fingers catch it, the higher the number the slower their reaction time

• repeate the experiment, using the same person, same hand to catch the ruler and ensuring you drop the ruler form the same height every time

• you can repeat the experiment after the person has drunk caffine

• calculate the mean - this is the average reaction time of the person

describe method 2 for investigating reaction time

• use a simple computer test where the person has to click the mouse or press a key as soon as they see a stimulus on the screen e.g a coloured box

• the reaction time the computer measures will be more accurate as they can measure to the nearest millisecond - has a higher resolution

• it also rules out human error (e.g like the person being able to read the body language of the other so they know when the ruler is going to be dropped)

what is a hormone?

a chemical messenger that has a specific function and travels to a ‘target organ’ to enact it - they control things that need constant adjustment

what is the endocrine system?

the endocrine glands (pancreas, testes, ovaries, thyroid, adrenal and pituitary gland) secrete hormones and make up the endocrine system

what is the function of the pituitary gland?

located in the brain, it secretes hormones that stimulate other glands in the endocrine system to produce their hormones

what is the function of the ovaries?

produces oestrogen which is used in the menstrual cycle to build up the uterus for pregnancy

what is the function of the testes?

produces testosterone which controls puberty in males and sperm production

what is the function of the pancreas?

produces insulin when blood sugar levels are too high and glucagon when they’re too low

what is the function of the adrenal gland?

produces adrenaline which prepares the body for fight or flight

what is the function of the thyroid gland?

produces thyroxine which controls the basal metabollic rate, heart rate and temperature

describe how the body normally gets glucose and how normal metabolism works

• eating carbs puts glucose into the blood from the gut

• the normal metabolism of cells removes glucose from blood

• excercise removes more glucose from the blood

where is excess glucose stored?

in the liver and muscels cells

describe how glucagon works in the body to increase blood glucose levels

• pancreas produces glucagon

• enters the blood stream

• glucagon causes the liver to convert the glycogen it has stored back into glucose

• the glucose is added to the bloodstream

describe how insulin decreases blood glucose levels

• pancreas secrets insulin

• insulin goes into the bloodstream

• transfers glucose into liver and muscle cells

• insulin makes this glucose be stored as glycogen

how does type 1 diabetes work?

the pancreas doesn’t secerete enough or any insulin, so the body’s blood glucose level becomes too high and can’t be regulated

how does type 2 diabetes work?

the body no longer responds to the insulin produced by the pancreas

how is type 1 and 2 diabetes treated?

type 1 - insulin therapy, regular injections with insulin around mealtimes, amount of insulin needed is based on person’s diet and how active they are , regular excercise and controlled carb diet

type 2 - excercise and controlled carb diet

describe what happens each day if the menstrual cycle

day 1 - lining breaks down

day 4 - lining builds back up again, ready for egg to be released

day 14 - egg is released (ovulation)

day 14 - 28 - uterus lining is maintained

day 28 - begins to break down again (period begins)

what is the function of FSH?

produced by pituitary gland - matures an egg in an ovary in a structure called a follicle - stimulates oestrogen

what is the function of oestrogen?

produced by the ovaries - causes the lining of the uterus to build up ready for an egg to be released on ovulation - inhibits FSH and stimulates LH

what is the function of LH?

produced by the pituitary gland - stimulates the release of an egg on day 14 (ovulation) - doesn’t stimulate or inhibit anything

what is the function of progesterone?

produced by the ovaries - maintains the lining of the uterus for pregnancy - inhibits LH and FSH

describe how the combined contraceptive pill works

• contains progesterone and oestrogen

• oestrogen inhibits FSH, will slow and eventually stop egg development and production

• progesterone creates a thick mucus which prevents sperm reaching an egg

• 99% effective

• has some side effects - headaches and nausea

• doesn’t protect against stds

evaluate the other 5 hormone contraceptives

• progesterone only pill - just as effective as the combined - fewer side effects

• IUD (copper and plastic) - plastic release progestrone and copper kills sperm - inserted in the uterus

• injection - progesterone - each dose lasts 2-3 months

• patch - worn on the skin - oestrogen and progesterone - alsts one week

• implant - under skin of arm - releases continuous progesterone - lasts 3 years

evaluate the 3 barrier/non-hormone contraceptives

• condom - stops sperm meeting egg - protect against stds

• diaphram - worn over the cervix - used with spermicide

• spermicide - a substance that kills/disables sperm - 70/80% effective when used on its own

what hormones are given to women to increase fertility?

FSH and LH

what are the pros and cons of the fertility drug?

pros -0 help women get pregnant

cons - some react badly to the hormone

• may not always work

• can be expensive after afew tries

• too many eggs could be stimulated, resultinbg in multiple unplanned pregnancies

describe the process of IVF

• FSH and LH are given to stimulate egg production , then eggs are taken from the mother and places in a petri dish in an lab incubator

• the eggs are then fertilised with the father’s sperm, ICIS can be used if the father has a low sperm count, this is when the sperm is injected directly into the eggs

• ICIS = intra-cytoplasmic sperm injection

• the eggs are grown into embryos in the lab incubator

• when they are tiny balls of cells, one or two are transferred into the mother’s uterus

how do ,microcopes help IVF?

genetic testing - check if the embryos or healthy and if they have genetic diaseses from the parents - help them decide wether to go through with IVF

time lapse imaging - the growth of the embryos can be continuously monitored

what are the pros and cons of IVF?

pros - can help women get pregnant

cons - expensive - success rate in UK is around 26% - mentally and physically challenging - women may react badly to hormones (abdominal pain, vomiting and dehydration) - may lead to multiple births and increased risk or miscarriage and still birth

why do some people disagree with IVF?

as the other embryos are destroyed, some see this as murder of potential human life, some believe the genetic testing used in IVF will lead to allowing parents to chose children with their desired characteristics e.g eye colours and gender

how does adrenaline prepare the body for fight or flight response?

trigerring mechanisms that increase the supply of oxygen and glucose in the cells of the brain and muscles, also increases heart rate

how does the thyroid gland use negative feedback to regulate the body’s temperature, metabollic rate and heart rate?

• the pituitary gland detects a stimulus, a change in the metabollic rate for example, and produces TSH (thyroid stimulating hormone)

• TSH causes the thyroid gland to produce thyroxine, which is made from iodine and amino acids

• thyroxine regulates the metabollic rate until it is too high, then the pituitary gland will detect the change and inhibit TSH, so that the thyroid gland stops producing thyroxine, making the metabollic rate slow down to normal