Homeostasis and Response

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Homeostasis

Conditions inside the body need to be steady

Cells need to be at the right conditions to function

Homeostasis - regulation of conditions inside body (and cells) to maintain stable internal environmental

Automatic control systems - regulate internal environment

Include both nervous and hormonal communication

All automatic control systems are made up of three components which work together to maintain steady conditions

Automatic control systems keep internal conditions stable using negative feedback

When level of something gets too high or too low - body uses negative feedback to bring it back to normal

1. Receptor detects a stimulus - level is too low

2. Co-ordination centre receives and processes information, then organises a response

3. Effector produces response - counteracts change and restores optimum level - level increases

1. Receptor detects a stimulus - level is too high

2. Co-ordination centre receives and processes information, then organises a response

3. Effector produces a response - counteracts change and restores optimum level - level decreases

Effectors will carry on producing responses for as long as they're stimulated by co-ordination centre - causes opposite problem

Receptor detects if level becomes too different - negative feedback starts again

Process is all automatic

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Nervous System

Nervous system means that humans can react to their surroundings and co-ordinate their behaviour

Central Nervous System - in vertebrates this consists of brain and spinal cord only

CNS is connected to the body by sensory neurones and motor neurones

Motor neurones - neurones that carry electrical impulses from the CNS to effectors

Effectors - all muscles and glands - respond to nervous impulses

Receptors are cells that detect stimuli

Many different types of receptors

Can form part of larger, complex organs

Effectors respond to nervous impulses and bring about change

Muscles and glands are effectors

Muscles contract in response to a nervous impulse whereas glands secrete hormones

CNS is a co-ordination centre

Receives information from receptors

Coordinates a response - carried out by effector

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Synapses and Reflexes

Connection between two neurones is called a synapse

Nerve signal is transferred by chemicals - diffuse across the gap

Chemicals then set off a new electrical signal in the next neurone

Reflexes are rapid, automatic responses to certain stimuli - don't involve conscious part of the brain

Reduce chances of being injured

Passage of information in a reflex is called a reflex arc

Neurones in reflex arcs go through spinal cord

When a stimulus is detected - impulses are sent along a sensory neurone to a relay neurone in CNS

Impulses reach a synapse between sensory neurone and relay neurone, trigger chemicals to be released

Cause impulses to be sent along the relay neurone

Impulse reach a synapse between relay neurone and motor neurone, same thing happens - chemicals are released

Cause impulses to be sent along motor neurone

Impulses then travels along motor neurone to effector (usually a muscle)

Muscle then contracts - don't have to think about response, it's quicker than normal response

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Endocrine System

Hormones are chemical messengers released directly into blood

Only affect particular organs

Control things in organs and cells that need constant adjustment

Produced in (and secreted by) various glands - endocrine glands

Tend to have long-lasting effects

Pituitary Gland

Produces many hormones that regulate body conditions

"master gland" - hormones act on other glands, directing them to release hormones

Thyroid

Produces thyroxine

Involved in regulating things

Adrenal Gland

Produces adrenaline

Use to prepare body for a "fight or flight" response

Ovaries - females only

Produces oestrogen - menstrual cycle

Pancreas

Produces insulin - regulate blood glucose

Testes - males only

Produces testosterone - controls puberty and sperm production

Hormones and Nerves have differences

Nerves:

Very FAST action

Act for SHORT TIME

Act on very PRECISE AREA

Hormones:

SLOWER action

Act for LONG TIME

Act in a more GENERAL way

If response is very quick - probably nervous

Some information needs to be passed to effectors quickly, no good using hormones to carry the message - too slow

If response lasts for a long time - probably hormonal

You may feel a bit wobbly for a while afterwards

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Controlling Blood Glucose

Eating foods containing carbohydrates puts glucose into the blood

Normal metabolism of cells removes glucose from the blood

Vigorous exercise removes much more glucose

Excess glucose can be stored as glycogen in liver and muscles

Level of glucose in blood must be kept steady

Changes are monitored and controlled by pancreas, using insulin and glucagon, in a negative feedback cycle

Blood Glucose level TOO HIGH - insulin is added

Blood with too much glucose

Insulin is secreted by pancreas

Glucose moves from blood into liver and muscles cells

Insulin makes liver turn glucose into glycogen

Blood glucose reduced

Blood Glucose level TOO LOW - glucagon is added

Blood with too little glucose

Glucagon secreted by pancreas

Glucose is released into blood by liver

Glucagon makes liver turn glycogen into glucose

Blood glucose increased

Diabetes - can't control blood sugar level

Diabetes is a condition that affects ability to control blood sugar level

Type 1

Where pancreas produces little or no insulin

Means person's blood glucose level can rise to a deadly level

Insulin therapy

Usually involves several injections throughout the day

Glucose is removed from blood quickly

Stopping level getting too high

Amount of insulin depends on person's diet and how active they are

Need to think about limiting intake of carbohydrates

Type 2

Person becomes resistant to insulin

Body produces insulin but doesn't respond properly

Cause a person's blood sugar to rise to a dangerous level

Being overweight can increase your chance of developing it

Controlled by eating a carbohydrate-controlled diet and getting regular exercise

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Puberty and Menstrual Cycle

At puberty, body starts releasing sex hormones that trigger off secondary sexual characteristics and cause eggs to mature in women

In men, the main reproductive hormone is testosterone - produced by testes and stimulates sperm production

In women, the main reproductive hormone is oestrogen - produced by ovaries and is involved in menstrual cycle

Menstrual cycle has 4 stages

Stage 1

Day 1 - menstruation starts. Uterus ling breaks down

Stage 2

Uterus lining build up again, from day 4 to 14

Thick spongy layer full of blood vessels, ready to receive a fertilised egg

Stage 3

Egg develops and is released from ovary at day 14 - ovulation

Stage 4

Wall is maintained for about 14 days

If no fertilised egg has landed on uterus wall, spongy lining starts to break down and whole cycle starts again

Menstrual Cycle - controlled by four hormone

FSH

Follice Stimulating Hormone

Produced in pituitary gland

Causes egg to mature

Stimulates ovaries to produce oestrogen

Oestrogen

Produced in ovaries

Causes lining of uterus to grow

Stimulates release of LH - release of an egg and inhibits release of FSH

LH

Luteinising Hormone

Produced in pituitary gland

Stimulates release of an egg at day 14 (ovulation)

Progesterone

Produced in ovaries by remains of follicle after ovulation

Maintains lining of uterus

When level of progesterone falls, lining breaks down

Inhibits release of LH and FSH

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Controlling Fertility

Oestrogen can be used to prevent release of an egg

If it is taken every day, it keeps level permanently high, inhibits production of FSH

Egg development and production stop and stay stopped

Progesterone also reduces fertility

Stimulates production of thick mucus which prevents any sperm getting through and reaching an egg

The Pill - oral contraceptive containing estrogen and progesterone

Over 99% effective

Has side effects like headaches and nausea

Doesn't protect against STIs

Progesterone-only pill

Fewer side effects than the pill

Contraceptive patch contains oestrogen and progesterone

Lasts one week

Contraceptive implant

Under skin of the arm

Releases continuous amount of progesterone

Stops ovaries releasing eggs, making it hard for sperm to swim and stops any fertilised egg implanting in uterus

Last for three years

Injection - contains progesterone

Each dose lasts 2-3 months

IUD

Inserted into uterus to kill sperm and prevent implantation of fertilised egg

Plastic IUDs - release progesterone

Copper IUDs - prevent sperm surviving in uterus

Non-hormonal contraception - designed to stop sperm getting to egg

Condoms - barrier method

Will protect against STIs

Diaphragm - shallow plastic cup that fits over the cervix to form barrier

Used with spermicide

Spermicide - can be used alone

Not as effective (only 70-80%)

Some women have low levels of FSH

Means no egg are released and women can't get pregnant

Hormones FSH and LH

Given to women in a fertility drug to stimulate ovulation

PROS:

Helps lots of women to get pregnant

CONS:

Doesn't always work

Can be expensive

Too many eggs could be stimulated - resulting in unexpected multiple pregnancies

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In Vitro Fertilisation

Involves collecting eggs from woman's ovaries and fertilising them in a lab

Can involve technique called Intro-Cytoplasmic Sperm Injection where sperm is injected directly into an egg

Fertilised eggs are then grown into embryos in an incubator

Once embryos are tiny balls of cells, one or two of them are transferred into uterus

Improve chance of pregnancy

FSH and LH are given before egg collection to stimulate several eggs to mature

So more than one egg can be collected

Pros:

Give an infertile couple a child

Cons:

Multiple births can happen if more than one embryo grows into a baby

Risky for mothers and babies

Success rate is low (26%)

Emotionally and physically stressful

Some have strong reactions to hormones

Process of IVF often results in unused embryos

Eventually destroyed - some say this is unethical

Genetic testing of embryos before implantation - raises ethical issues

Could lead to selection of preferred characteristics

Page 9

Adrenaline and Thyroxine

Hormone released by adrenal glands

Released in response to stressful or scary situations

Brain detects fear or stress

Sends nervous impulses

Gets body ready for "fight or flight"

Increases supply of oxygen and glucose to cells in the brain and muscles

Body can control levels of hormones - using negative feedback

When body detects level of substance has gone above or below normal level, it triggers response to bring level back to normal

Thyroxine

Hormone released by thyroid gland

Important role in regulating basal metabolic rate

Important for loads of processes in the body - such as protein synthesis

Released in response to thyroid stimulating hormone

Released from pituitary gland

Negative feedback system keeps amount of thyroxine inn blood at the right level

Secretion of TSH is inhibited

Reduces amount of thyroxine released