1. Homeostasis and Response
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23/11/2018
Homeostasis and Response
AQA 2016 Biology topic 5
W Richards
The Weald School

2. 5.1 Homeostasis
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3. Homeostasis: An introduction
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Homeostasis: An introduction
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”

4. Internal conditions that need controlling + how
Homeostasis
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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. 5.2 The Nervous System
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6. The Nervous System
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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?
Light receptors in the eyes
Sound receptors in the ears
Taste receptors on the tongue
Smell receptors in the nose
Touch, pressure and temperature receptors in the skin
Changes of position receptors in the ears (balance)

7. Stimulus Receptor Coordinator Effector Response
Nervous Reactions
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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?

8. Examples of reactions Stimulus Receptor
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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

9. Conscious actions
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A conscious action is one where the brain makes a considered response. Here’s what happens:
4) The brain decides to move away the hand
3) Here another sensory neurone carries the electrical signal to the brain
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
1) Receptors in your skin detect a stimulus
6) Which then moves the hand away (the response)
Stimulus Receptor Sensory Neurone Coordinator
Motor Neurone Effector Response

10. Reflex actions
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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…

11. Reflex actions 3. Relay neurone in the spinal chord 2. Sensory neurone
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3. Relay neurone in the spinal chord
2. Sensory neurone
4. Motor neurone
5. Effector
1. Receptor
By bypassing the conscious part of the brain, this response is much quicker.

12. Muscle strands (effector)
Types of nerve cell
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Nucleus
Muscle strands (effector)
Cell body
Nerve cells (neurones) are elongated with branched endings to connect to many muscles fibres.
1) Motor neurone
2) Sensory neurone
3) Relay neurone
Impulse
Impulse

13. Words – chemical, synapse, neurone, touch, destroyed
Synapses
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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

14. The Brain (Biology only)
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The brain controls complex behaviour and is made of billions of neurones and different regions:
Cerebral cortex – responsible for thought, intelligence etc
Cerebellum – coordinates movement and balance
Medulla – controls automatic actions like breathing and circulation

15. Studying the Brain (Bio HT only)
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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.

16. Other techniques of studying the brain
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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.
What are the risks of these methods?
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.

17. The Eye (Bio HT only) Iris Sclera Lens Retina Pupil Cornea Optic nerve
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Iris
Sclera
Lens
Retina
Pupil
Cornea
Optic nerve
Optic nerve
Suspensory ligaments
Suspensory ligaments
Ciliary muscles

18. Seeing things
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The eye is a sense organ containing receptors sensitive to light intensity and colour. How do they work?
Rays of light are refracted (bent) first by the cornea and then by the lens. They focus on the retina.

19. Focussing on different distances (“accommodation”)
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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.

20. The Iris Reflex Q. How does the eye respond to light?
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Q. How does the eye respond to light?
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.

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

22. 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?

23. Controlling Body Temperature (Bio only)
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Wow it’s hot!
The thermoregulatory centre in the brain detects “warm blood”.
Also, temperature sensors in the skin detect the heat and send information to the brain.
When the brain detects the high temperature it takes two main steps....

24. Body Temperature (Bio only)
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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
Effectors (muscles and sweat glands) carry out the response

25. Maintaining Body Temperature
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Cold
Hot
Vasodilation
Vasoconstriction

26. 5.3 Hormonal Condition in Humans
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5.3 Hormonal Condition in Humans

27. Hormones
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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 adrenal gland
The pancreas produces _______
The adrenal gland produce ________
The pituitary gland produces FSH and LH
Testes produce __________
Ovaries produce progesterone
Words – testosterone, glands, bloodstream, insulin, adrenaline

28. The Endocrine System
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Where are the following glands and organs in our body?
Adrenal
Kidney
Thyroid
Pituitary
Hypothalamus
Testes
Ovaries
Pancreas 1.
Pituitary 2.
Hypothalamus 3.
Thyroid 4.
Adrenal 5.
Kidney 6.
Pancreas 7.
Ovaries 8.
Testes

29. The Pituitary Gland in more detail
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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

30. Controlling Blood Sugar levels
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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

31. Diabetes What is diabetes? What do the pens (above right) do?
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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?

32. Diabetes
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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

33. Diabetes and Obesity What conclusions can you draw from this data?
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What conclusions can you draw from this data?
% obesity of US population
No. of people (in millions) with Diabetes

34. More interesting statistics…
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No. of fast food outlets
No. of people (in millions) with Diabetes

35. Glucogen and “Negative Feedback” (HT only)
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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.

36. Words – membrane, concentrated, dilute, diffusion, gradient
Osmosis recap
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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.

37. Excreting Products (Bio only)
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Our bodies need to get rid of surplus amounts of:
Water – removed by the lungs during exhalation and through sweating.
Urea – produced when excess amino acids are broken down in the liver and is transferred to the bladder. Also lost via sweating.
Ions – excreted through the skin via sweating.
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.
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?

38. Amino Acids in Digestion (HT only)
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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

39. Kidneys (Bio only)
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Kidneys are responsible for controlling ion, urea and water content.
Blood in
Kidneys are made up of two important tissues – BLOOD VESSELS and TUBULES.
Blood out
Ureter (tube that takes urine down to bladder)

40. Kidneys work in 3 stages:
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Kidneys work in 3 stages:
Blood vessel
Tubule
1. ULTRAFILTRATION - Lots of water and products of digestion are squeezed out of the blood and into tubules under pressure.
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.
3. WASTE – excess water, excess ions and any urea are now removed through the ureter

41. Controlling Water Content (Bio only)
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Another example of a “negative feedback” mechanism:
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.

42. Controlling Water Content 2 (Bio only)
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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.

43. Partially permeable membranes
Dialysis (Bio only)
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Sometimes kidneys can fail due to infections, toxic substances or genetic reasons. One possible answer is to use a dialysis machine:
Dialysis fluid
Blood
Partially permeable membranes
Urea
Sugar
Sugar
Urea
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.

44. Kidney transplants (Bio only)
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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

45. Hormones in Human Reproduction
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During puberty reproductive hormones cause the development of secondary sex characteristics.
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”)

46. Hormones in the Menstrual Cycle
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Several hormones are also involved in the menstrual cycle, where hormones can...
…cause an egg to mature (the hormone FSH)
…stimulate the release of eggs (the hormone LH)
…maintain the lining of the uterus (oestrogen and progesterone)
FSH and LH are produced by the pituitary gland whereas oestrogen and progesterone are produced by the ovaries.

47. Fertility (HT only)
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Four hormones are involved in the menstrual cycle: oestrogen, LH, FSH and progesterone. Here’s how:
Step 1: FSH produced by the pituitary gland causes both an egg to mature and the ovaries to start producing oestrogen
Step 3: LH stimulates the release of the mature egg in day 14 of the menstrual cycle (“ovulation”).
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.

48. The 4 stages of the menstrual cycle:
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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.

49. The Menstrual Cycle Thickness of uterus lining Day 0 Day 7 Day 14
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Thickness of uterus lining
Day 0
Day 7
Day 14
Day 21
Day 28
Day 4
Hormone concentration
FSH LH
Oestrogen
Progesterone

50. Methods of Contraception
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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.

51. Evaluating Contraceptive Methods
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The Pill
Implants
Barriers
Spermicides
Sterilisation
operations
Planning by
calendar
Intrauterine
devices
Pros and cons
of different methods

52. Fertility Drugs and IVF (HT only)
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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

53. Evaluating fertility treatment
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Risks:
Stress
Low success rates
Risk of multiple births
Benefits: New babies!
Fertility
treatment
Moral issues:
What happens to unused embryos
Storage time of frozen embryos
The use of sperm or embryos after the death of a partner

54. Adrenaline and Thyroxine (HT only)
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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.

55. 5.4 Plant Hormones (Bio only)
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56. Plant Hormones
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The growth of roots and shoots is controlled by hormones:
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.
In the roots hormones slow down growth of the cells in the lower region, which makes the root bend down.

57. Some Definitions
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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).
Two more important plant hormones:
Ethene is a hormone that helps fruit to ripen
Gibberellins are important in starting seed germination

58. More on Plant Hormones (HT only)
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1) Auxin
2) Ethene
Auxins are used as _____ killers, rooting powders and tissue ______
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