B5- homeostasis and response

homeostasis

The process by which living organisms regulate their internal environment to maintain stable, constant conditions despite external changes.

negative feedback

when the level of something gets too high or too low, the body initiates processes to counteract this change and bring the level back to its set point.

describe what happens when an internal condition is too high or low

• receptor detects a stimulus ( level is too high or low)

• the coordination center receives the info and organises a response

• effector produces a response which counteracts the change and restores the optimum level

Central Nervous System (CNS)

The part of the nervous system consisting of the brain and spinal cord, responsible for processing information and coordinating responses.

sensory neurones

the neurones that carry information as electrical impulses from the receptors to the central nervous system.

Motor neurones

the neurones that carry electrical impulses from the central nervous system to effectors.

effectors

The organs or cells that act in response to signals from the nervous system, such as muscles or glands.

receptors

the cells that detect stimuli from the environment and convert them into electrical impulses to send to sensory neurones.

what is the order the body takes to respond to a stimuli

The order is: stimulus, receptor, sensory neurone, central nervous system, motor neurone, effector, response.

synapse

the connection between two neurones. the nerve signal is transferred by chemicals which diffuse across the gap and set off a new electrical signal in the next neurone

reflexes

reflexes are rapid automatic responses to a certain stimuli that don’t involve the conscious part of the brain

relay neurones

connect sensory neurones to motor neurones

what is the practical for investigating reaction time

• ruler drop

• computer tests e.g click the mouse

why are computer tests better than the ruler drop

• more precise - measure time to a millisecond

• remove possibility of human error

• unpredictable timing

hormones

chemical molecules released directly into the blood. they control things in organs and cells that need constant adjustment

Pituitary gland

produces many hormones which act on other glands directing them to release hormones. found at the base of the brain

thyroid

produces thyroxine which regulates rate of metabolism, HR and temperature

ovaries

(females) produce oestrogen which is involved in the menstrual cycle

adrenal gland

produces adrenaline which prepares the body for ‘flight or fight’ response. found above the kidneys

testes

(male) produce testosterone, which controls puberty and sperm production in males

pancreas

produces insulin, which is used to regulate the blood glucose levels

difference between nerves and hormones

nerves :

• fast action

• short time

• precise area

  hormones:

• slower action

• act for long time

• general way

what happens when blood glucose levels are too high

• insulin is secreated into the blood from the pancreas

• the glucose moves from the blood into the liver

• insulin makes the liver turn glucose into glycogen

• blood glucose is reduced

what happens when blood glucose levels are too low

• glucagon secreted by pancreas

• enters the liver

• glucagon makes liver turn glycogen into glucose

• glucose released into blood

Type 1 diabetes

• the pancreas produces little or no insulin meaning their blood glucose can rise to levels that can kill them

• insulin therapy- injections throughout the day, making sure glucose is removed quickly

type 2 diabetes

• a person becomes resistant to their own insulin

• being overweight increases chances

• carb controlled diet and regular exercise controls it

4 stages of the mensural cycle

• stage 1: mensuration starts - lining of the uterus breaks down for about 4 days (period)

• stage 2 : uterus lining builds up again ( day 4-14)

• stage 3 : an egg develops and is released from the ovary

• stage 4 : the wall is maintained until about day 28

the four hormones of the menstrual cycle

1. FSH

2. Oestrogen

3. LH

4. Progesterone

what does FSH do?

• produced in the pituitary gland

• causes an egg to mature in one of the ovaries in a follicle

• stimulates ovaries to produce oestrogen

what does oestrogen do

• produced in the ovaries

• causes the lining of the uterus to grow

• stimulates release of LH

what does LH do

• produced in the pituitary gland

• stimulates the release of an egg

what does progesterone do

• produced in the ovaries

• maintains lining of uterus during the second half of the cycle

• inhibits the release of LH and FSH

methods of contraception using hormones

1. contraceptive patch - contains oestrogen and progesterone(1 week)

2. contraceptive implant - releases a continuous amount of progesterone, which stops the ovaries releasing an egg (3 years)

3. contraceptive injection- progesterone (2-3 months)

4. intrauterine devise (IUD)- inserted into the uterus to kill sperm

non hormonal forms of contraception

1. condom- also prevents STD

2. diaphragm- shallow plastic cup that fits over the cervix

3. spermicide

other ways to avoid pregnancy

• sterilisation - involves cutting or tying the fallopian tube or the sperm duct

• natural methods - avoiding sexual intercouse when a woman is fertile

• abstinence- no intercourse

pros and cons of fertility drugs

pros :

• it helps a lot of women to get pregnant

  Cons :

• it doesnt always work- some women have to do it multiple times and it becomes expensive

• too many eggs could be stimulated resulting in twins, triplets …

what is IVF

• involves collecting eggs and fertalising them in a lab using the mans sperm

• the sperm is injected directly into the egg

• the fertalised eggs are then grown into embryos in an incubator

• they are then transferred into the womens uterus to improve the chance of pregnancy

pros and cons of IVF

Pros :

• can give an infertile couple a child

  Cons:

• multiple births

• success rate is low

• emotional and physical stress on the woman

• side effects- abdominal pain, vomiting, dehydration

why are some people against IVF

• often reults in unused embryos - unethical because of wasted potential life

• genetic testing of embryos before use - people think it could lead to the selection of desired characteristics

how does adrenaline prepare the body for ‘flight or fight’

it triggers mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles - increases heart rate

how is the level of thyroxine controlled

negative feedback