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Homeostasis and Response

AQA Biology topic 5

5.1 Homeostasis 21/11/2017

Homeostasis: An introduction

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Wow it’s hot here! What would happen if I stand here for too long? What would happen if I drank too much water?

Homeostasis means “controlling internal conditions in order to maintain optimum conditions for bodily responses”

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Homeostasis Some examples of homeostasis in our bodies:

Internal conditions that need controlling + how

Temperature

Ion content

Water content

Blood glucose

Increased by shivering, lost by sweating

Increased by eating, lost by sweating + urine

Increased by drinking, lost by sweating + urine

Increased and decreased by hormones

These conditions are controlled by our control systems:

Cells called “receptors” detect a stimulus (change in the environment)

Coordination centres such as the brain coordinate the body’s response

Effectors such as muscles and glands bring about the response

5.2 The Nervous System 21/11/2017

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The Nervous System The NERVOUS SYSTEM enables us to react to our surroundings. It consists mainly of the brain, the spinal chord, nerve cells (“neurones”) and receptors.

Where do we have receptors?

1) Light receptors in the eyes

2) Sound receptors in the ears

3) Taste receptors on the tongue

4) Smell receptors in the nose

5) Touch, pressure and temperature receptors in the skin

6) Changes of position receptors in the ears (balance)

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Nervous Reactions When we react to a stimulus the Central Nervous System (CNS – brain and spinal chord) in our body uses the following pattern:

Stimulus Receptor Coordinator Effector Response

For example, consider a man and a camel: Oh

No!

What are the stimulus, receptor, coordinator, effector and response in this situation?

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Examples of reactions Stimulus Receptor

(i.e. the thing that detects the

stimulus)

Effector

(i.e. the thing that will do the

reaction)

Response

(i.e. action taken)

Bright light

Sour taste

Losing balance

Sit on a drawing pin

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Conscious actions A conscious action is one where the brain makes a considered response. Here’s what happens:

Stimulus Receptor Sensory Neurone Coordinator

Motor Neurone Effector Response

1) Receptors in your skin detect a stimulus

3) Here another sensory neurone carries the electrical signal to the brain

4) The brain decides to move away the hand

5) This electrical impulse is sent by MOTOR NEURONES to the hand muscles (the effectors) via the spinal chord…

2) The impulse is carried as electrical impulses by SENSORY NEURONES to the spinal chord

6) Which then moves the hand away (the response)

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Reflex actions

Sometimes conscious action is too slow to prevent harm, e.g…

In situations like this the body bypasses the brain to produce a quicker response. Here’s how it works…

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Reflex actions

1. Receptor

2. Sensory neurone

3. Relay neurone in the spinal chord

4. Motor neurone

5. Effector

By bypassing the conscious part of the brain, this response is much quicker.

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Types of nerve cell Nucleus Muscle strands

(effector) Cell body

1) Motor neurone 2) Sensory neurone 3) Relay neurone

Impulse Impulse

Nerve cells (neurones) are elongated with branched endings to connect to many muscles fibres.

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Synapses

Neurones never ____ each other – there is a small gap between them called a _____. A signal is sent from one _______ to the next by a _______ transmitter across the synapse. These transmitters are then ________.

Words – chemical, synapse, neurone, touch, destroyed

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The Brain (Biology only)

Cerebral cortex – responsible for thought,

intelligence etc

Medulla – controls automatic actions like

breathing and circulation Cerebellum – coordinates

movement and balance

The brain controls complex behaviour and is made of billions of neurones and different regions:

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Studying the Brain (Bio HT only)

The cerebral cortex is the part of our brain most concerned with intelligence, memory and consciousness. By studying the effects (e.g. memory/sight loss) when different parts of the brain are damaged scientists have been able to identify which parts of the brain control which functions.

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Other techniques of studying the brain

1) An electroencephalogram (EEG) is a visual record of the electrical activity generated by neurons in the brain. It works by amplifying and detecting the electrical signals from the brain.

2) Magnetic resonance imaging (MRI) scanning is a new technique that produces images of different cross sections of the brain and uses colours to represent activity.

What are the risks of these methods?

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Suspensory ligaments

Optic nerve

The Eye (Bio HT only)

Retina

Pupil

Cornea

Ciliary muscles Suspensory ligaments

Optic nerve

Lens

Iris Sclera

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Seeing things

Rays of light are refracted (bent) first by the cornea and then by the lens. They focus on the retina.

The eye is a sense organ containing receptors sensitive to light intensity and colour. How do they work?

21/11/2017 Focussing on different distances (“accommodation”)

For distant objects the ciliary muscles relax and the suspensory ligaments pull tight making the lens pull

thin – the light doesn’t refract as much.

For close objects the ciliary muscles contract allowing the lens to go fat, thus bending the

light more.

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The Iris Reflex

When the light is bright the radial muscles relax, the circular muscles contract and the pupil increases in size.

When the light is bright the radial muscles _____, the circular muscles _______ and the pupil ________ in size.

Q. How does the eye respond to light?

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Using lenses to correct vision Short sighted – “myopia” Long sighted – “hyperopia”

Using Lasers in Surgery Lasers are being increasingly used in laser eye surgery:

What are the advantages and disadvantages of this treatment compared to using glasses or contact lenses?

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Controlling Body Temperature (Bio only)

Wow it’s hot!

Also, temperature sensors in the skin detect the heat and send information to the brain.

The thermoregulatory centre in the brain detects “warm blood”.

When the brain detects the high temperature it takes two main steps....

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Body Temperature (Bio only)

Effectors (muscles and sweat glands) carry out the response

Nerve endings in the skin (receptors) detect the external temperature

Temperature detectors in the brain detect the blood temperature

The brain coordinates a response using hormones

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Maintaining Body Temperature

Cold Hot

Vasodilation

Vasoconstriction

5.3 Hormonal Condition in Humans

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Hormones Hormones are “chemical messengers” produced by endocrine _____. They control the way in which parts of the body work and are transported to their target organs in the _______. The effects are slower compared to the nervous system but last for longer. Some examples...

• The pancreas produces _______

• The adrenal gland produce ________

• The pituitary gland produces FSH and LH

• Testes produce __________

• Ovaries produce progesterone The adrenal gland

Words – testosterone, glands, bloodstream, insulin, adrenaline

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The Endocrine System

1. 2.

3.

4.

5.

6.

7.

8.

Pituitary Hypothalamus

Thyroid

Adrenal

Kidney

Pancreas

Ovaries

Testes

Where are the following glands and organs in our body?

Adrenal

Kidney

Thyroid

Pituitary

Hypothalamus

Testes

Ovaries

Pancreas

The Pituitary Gland in more detail 21/11/2017

The pituitary gland is a “______ gland” which secretes several ______ into the ______ in response to body conditions. These hormones act in turn on other ______ in order to cause different hormones to be ________ and bring about other responses.

Words – secreted, glands, hormones, master, blood

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Controlling Blood Sugar levels We need glucose in our bodies to help our cells to respire and produce energy. The amount of it in our blood is controlled by the pancreas. What happens if we have too much glucose?

If blood sugar is too high the pancreas releases insulin,

which causes glucose to move from the blood into cells

The liver then converts glucose into insoluble

glycogen and is removed from the blood

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Diabetes

What is diabetes?

What do the pens (above right) do?

What does an insulin injection (above left) do?

What is the difference between Type 1 and Type 2 Diabetes?

How does physical activity affect Type 1 and Type 2 Diabetics?

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Diabetes Diabetes is a ________ in which a person’s blood sugar (i.e. glucose) level may rise to a _______ level. Type 1 diabetes is when the ______ doesn’t produce enough _________, whereas type 2 diabetes is when the body no longer responds to its own insulin or doesn’t make enough of it.

Type 1 diabetes can be controlled using insulin ________ whereas type 2 diabetes can be controlled by careful _______ and exercise. Diabetics have to test their blood sugar level before they decide how much insulin to _______ themselves with. Diets high in fibre and complex carbohydrates can help to maintain a healthy sugar level.

Words – insulin, disease, inject, dangerous, eating, pancreas, injections

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Diabetes and Obesity

% obesity of US population

No. of people (in millions)

with Diabetes

What conclusions can you draw from this data?

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More interesting statistics…

No. of fast food outlets

No. of people (in millions)

with Diabetes

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Glucogen and “Negative Feedback” (HT only) What happens if we don’t have enough glucose?

If blood sugar levels fall then the pancreas produces glucagon instead, which causes glycogen to be converted back into glucose and released back into the blood.

This is an example of a “negative feedback system” – where an output (in this case, the production of insulin or glucagon) controls the level of glucose in the blood.

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Osmosis recap Osmosis is a “special kind of ___________”. It’s when water diffuses from a __________ area to a less concentrated area through a partially permeable _________ (i.e. one that allows water to move through but not anything else):

Water Sugar solution In this example the water molecules will move from left to right (along the concentration ______) and gradually _____ the sugar solution.

Words – membrane, concentrated, dilute, diffusion, gradient

If body cells lose too much water by osmosis they do not function efficiently.

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Excreting Products (Bio only) Our bodies need to get rid of surplus amounts of:

1) Water – removed by the lungs during exhalation and through sweating.

2) Urea – produced when excess amino acids are broken down in the liver and is transferred to the bladder. Also lost via sweating.

3) Ions – excreted through the skin via sweating.

Q. How is the removal of these products affected by:

- The amount of water we drink

- The outside temperature

- The amount of exercise we do?

There is no control over water, ion or urea loss by the lungs or skin. Excess water, ions and urea are removed by the kidneys via urine instead.

Amino Acids in Digestion (HT only) 21/11/2017

Mmmm that’s a nice steak. What happens if I eat too

much protein?

The digestion of proteins causes excess amino acids. In the liver, these amino acids are “deaminated” to form ammonia, which is toxic, so it is immediately converted into urea for safe excretion.

Amino acids Ammonia Urea

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Kidneys (Bio only)

Blood in

Blood out

Ureter (tube that takes urine down to bladder)

Kidneys are made up of two important tissues – BLOOD VESSELS and TUBULES.

Kidneys are responsible for controlling ion, urea and water content.

21/11/2017 Kidneys Kidneys work in 3 stages:

1. ULTRAFILTRATION - Lots of water and products of digestion are squeezed out of the blood and into tubules under pressure.

3. WASTE – excess water, excess ions and any urea are now removed through the ureter

2. SELECTIVE REABSORPTION – the blood takes back the things it wants (e.g. glucose and ions) even though this means going against a concentration gradient.

Blood vessel Tubule

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Controlling Water Content (Bio only)

Low blood water level causes a high salt concentration

Receptors in the brain detect the high salt content

More ADH is secreted by the kidneys into the blood

The kidney tubules becomes less permeable to water so more is

absorbed into the blood.

The bladder fills with a smaller quantity of urine

Normal blood water level is achieved.

Another example of a “negative feedback” mechanism:

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High blood water level causes a low salt concentration

Receptors in the brain detect the low salt content

Less ADH is secreted into the blood

The kidney becomes more permeable to water so more is reabsorbed.

The bladder fills with a large quantity of urine

Normal blood water level is achieved.

Controlling Water Content 2 (Bio only)

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Dialysis (Bio only) Sometimes kidneys can fail due to infections, toxic substances or genetic reasons. One possible answer is to use a dialysis machine:

Dia

lysi

s fl

uid

Blo

od

Dia

lysi

s fl

uid

Partially permeable membranes

Urea and salt diffuse out of the blood into the dialysis fluid. Also, the dialysis fluid contains the same concentration of sugar and minerals as the blood so these don’t diffuse.

Urea

Urea

Sugar

Sugar

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Kidney transplants (Bio only) Instead of dialysis a kidney could be transplanted into the patient.

This option is cheaper than dialysis but it requires a _______ (a normal person can still function with one kidney). This donor must have a similar ______ type to the patient. Also, the new kidney might be rejected by the body’s ______ system which will try to destroy the new organ. To work around this problem the patient can take “immunosuppresant ___” which suppress the immune system. Transplanted kidneys only work for around nine years and then the patient has to return to _______.

Words – dialysis, donor, immune, tissue, drugs

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Hormones in Human Reproduction

The testes make the hormone testosterone. This hormone stimulates sperm

production.

The ovaries produce the hormone oestrogen. At

puberty eggs begin to mature and one is releases every 28

days (“ovulation”)

During puberty reproductive hormones cause the development of secondary sex characteristics.

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Hormones in the Menstrual Cycle

FSH and LH are produced by the pituitary gland whereas oestrogen and progesterone are produced by the ovaries.

1) …cause an egg to mature (the hormone FSH)

2) …stimulate the release of eggs (the hormone LH)

3) …maintain the lining of the uterus (oestrogen and progesterone)

Several hormones are also involved in the menstrual cycle, where hormones can...

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Fertility (HT only) Four hormones are involved in the menstrual cycle: oestrogen, LH, FSH and progesterone. Here’s how:

Step 3: LH stimulates the release of the mature egg in day 14 of the menstrual cycle (“ovulation”).

Step 1: FSH produced by the pituitary gland causes both an egg to mature and the ovaries to start producing oestrogen

Step 2: The rising levels of oestrogen cause the pituitary gland to stop producing FSH and produce LH instead

Step 4: Progesterone: This is produced in the ovaries by the remains of the follicle after ovulation. It maintains the lining of the uterus during the second half of the cycle and inhibits the release of FSH and LH.

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The 4 stages of the menstrual cycle:

Day 1: Bleeding starts when the lining of the uterus breaks down and passes out the vagina – “Having a period”

Day 4: The lining starts to build up again and thickens into a spongy layer of blood cells

Day 14 (approx): An egg is released and lasts for around 3 days

Day 28: The lining stays thick awaiting the arrival of a fertilised egg. If one doesn’t come then the lining breaks down again.

21/11/2017 The Menstrual Cycle Thickness of uterus lining

Day 0 Day 7 Day 14 Day 21 Day 28 Day 4

Hormone concentration

Oestrogen Progesterone

FSH LH

Methods of Contraception 21/11/2017

Oral contraceptives that contain hormones to inhibit FSH production so that eggs can’t mature.

Implants that slowly release progesterone to inhibit the maturation and release of eggs.

Barrier methods such as condoms, that prevent sperm reaching the egg.

Intrauterine devices which prevent the implantation of an egg.

Spermicidal agents that kill sperm.

Surgical methods of sterilisation.

Or planning when to abstain from sexual intercourse.

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Evaluating Contraceptive Methods

The Pill

Implants Barriers

Spermicides

Sterilisation operations

Planning by calendar

Intrauterine devices

Pros and cons of different methods

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Fertility Drugs and IVF (HT only) Women may be able to boost fertility with drugs, which contain FSH and LH. If that doesn’t work then IVF is another option. Here’s how it works:

1. FSH and LH are given to the mother to stimulate the release of mature eggs. They are removed from the womb and placed in a solution of oxygen and water to keep them alive

2. Sperm is added

3. The fertlised egg is allowed to grow into an embryo (a group of 4-8 cells)

4. Usually 3 of these embryos are transferred back into the uterus

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Evaluating fertility treatment

Fertility treatment

Risks: 1) Stress 2) Low success rates 3) Risk of multiple births Benefits: New babies!

Moral issues: 1) What happens to unused embryos 2) Storage time of frozen embryos 3) The use of sperm or embryos after the death of a partner

Adrenaline and Thyroxine (HT only) 21/11/2017

Thyroxine from the thyroid gland stimulates the basal metabolic rate and plays an important role in growth and development. Its levels are another example of negative feedback.

Adrenaline is produces by the adrenal glands in times of fear or stress. It increases the heart rate and delivery of oxygen and glucose ready for a “fight or flight” response.

5.4 Plant Hormones (Bio only) 21/11/2017

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Plant Hormones The growth of roots and shoots is controlled by hormones:

In the roots hormones slow down growth of the cells in the lower region, which makes the root bend down.

In the shoots the hormone auxin is “destroyed” by light, so the shoot will bend towards the light as the cells on the shaded side grow quickest.

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Some Definitions Shoots grow towards light (positive phototropism) and against gravity (negative geotropism).

Roots grow away from light (negative phototropism) and in the direction of gravity (positive geotropism).

Ethene is a hormone that helps fruit to ripen

Gibberellins are important in starting seed germination

Two more important plant hormones:

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More on Plant Hormones (HT only) 1) Auxin

Auxins are used as _____ killers, rooting powders and tissue ______

2) Ethene

Controlled use of this hormone can help control the _____ of fruit during transport to ____

3) Gibberellins can be used to end seed _______, promote flowering and increase _____ size

Words – fruit, dormancy, weed, growth, shops, ripening