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Homeostasis 2 Flashcards

Endocrine system (blood glucose levels, kidneys, osmoregulation, fertility).

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1
Q

What are hormones?

A

Chemical molecules released directly into the bloodstream.

They are carried into the blood to particular cells in particular organs (target organs) where they produce an effect.

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2
Q

What do hormones control?

A

Things in organs and cells which need constant adjustment.

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3
Q

What is the endocrine system composed of?

A

Endocrine Glands

(which secrete chemicals called hormones directly into the bloodstream.)

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4
Q

Endocrine system in comparison to the nervous system.

A

The effects are slower but act for longer.

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5
Q

Pituitary gland

A

-In the brain

-A ‘master gland’

-Secretes several hormones into the blood in response to body conditions

-These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.

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6
Q

Thyroid gland

A

-Located in the neck

-Produces thyroxine, which is involved in regulating heart rate, temperature, and the rate of metabolism

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7
Q

Adrenal glands

A

-Located above the kidneys

-Produce adrenaline, which is used to prepare the body for a ‘fight or flight’ response

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8
Q

Pancreas

A

-Produces insulin, which is used to regulate blood glucose level

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9
Q

Ovaries

A

-Female only

-Produce oestrogen, which is involved in the menstrual cycle

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10
Q

Testes

A

-Male only

-Produce testosterone, which controls puberty and sperm production in males

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11
Q

Nerves vs hormones

A

-Nerves have very fast action, whereas hormones have slower action

-Nerves act for a very short time, whereas hormones act for a long time

-Nerves act on a very precise area, whereas hormones act more generally across the body

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12
Q

Which organ (gland!) is blood glucose concentration monitored and controlled by?

A

The pancreas

-Using the hormones insulin and glucagon in a negative feedback cycle.

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13
Q

Briefly describe what happens if the blood glucose concentration is too high.

A

-If the blood glucose concentration is too high, the pancreas produces the hormone insulin

-Insulin causes glucose to move from the blood into the cells

-In liver and muscle cells, excess glucose is converted to glycogen for storage

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14
Q

Briefly describe what happens if the blood glucose concentration is too low.

A

-If the blood glucose concentration is too low, the pancreas produces the hormone glucagon

-Glucagon causes glycogen to be converted
into glucose and released into the blood

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15
Q

How does glucose enter the bloodstream?

A

Eating food containing carbohydrates puts glucose (a type of sugar) into the blood.

It’s absorbed from the gut by active transport.

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16
Q

What processes remove glucose from the blood?

A

The normal metabolism of cells (respiration etc.)

Vigorous exercise removes much more glucose from the blood.

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17
Q

How can excess glucose be stored?

A

As glycogen in the liver and in the muscles.

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18
Q

How does insulin control blood glucose
(sugar) levels in the body?

A

-When blood glucose levels get too high, it’s detected by the pancreas.

-This causes the pancreas to release the hormone insulin into the blood stream.

-This hormone then travels around the body, and stimulates the liver and muscles to absorb glucose from the blood.

-In the liver, the glucose is converted to glycogen for storage

-This decreases blood glucose levels so they go back to normal

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19
Q

What does the term ‘high blood glucose concentration’ mean?

A

That there are lots of glucose molecules dissolved in the blood plasma.

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20
Q

What happens if blood glucose concentrations fall too low?

A

There won’t be enough glucose for tissue cells to respire.

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21
Q

How does glucagon work?

A

-When blood glucose levels fall too low, it’s detected by the pancreas.

-This causes the pancreas to release the hormone glucagon into the blood stream.

-This hormone then travels around the body, and binds mainly to cells in the liver.

-This stimulates those liver cells to break down their stored glycogen into glucose and release it into the blood.

-This extra glucose increases blood glucose levels back up to normal.

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22
Q

What is type 1 diabetes?

A

A disorder in which the pancreas fails to produce sufficient insulin.

It is characterised by uncontrolled high blood glucose levels and is normally treated with insulin injections

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23
Q

What is type 2 diabetes?

A

A disorder where the body cells no longer respond to insulin produced by the pancreas.

A carbohydrate controlled diet and an exercise regime (regular exercise) are common treatments.

Obesity is a risk factor for Type 2 diabetes

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24
Q

What is the risk of having diabetes?

A

A person’s blood glucose level can rise to a level that can kill them.

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25
Q

Insulin therapy

A

A highly efficient treatment for type 1 diabetes, whereby a person is injected with insulin several times throughout the day, most likely before mealtimes.

This makes sure that glucose is removed from the body quickly once food has been digested, stopping the level from getting too high.

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26
Q

What does the amount of insulin that needs to be injected (type 1 diabetes) into a person depend on?

A

-Their diet

-Their activity level

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27
Q

Other than insulin therapy, what can people with type 1 diabetes do to control blood glucose levels?

A

-Limiting the intake of food rich in simple carbohydrates (like sugars), which cause blood glucose levels to rise rapidly

-Regular exercise, which helps to remove excess glucose from the blood

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28
Q

How does water leave the body?

A

-Via the lungs during exhalation

-Via the skin in sweat

-Excess is removed via the kidneys in the urine

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29
Q

How do ions leave the body?

A

-Via the skin in sweat

-Excess ions are removed via the kidneys in the urine

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30
Q

How does urea leave the body?

A

-Via the skin in sweat

-Excess urea is removed via the kidneys in the urine

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31
Q

We have no control over water, ion or urea loss by what?

A

The lungs or skin.

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32
Q

What happens if body cells lose or gain too much water by osmosis?

A

They do not function efficiently.

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33
Q

What does the digestion of proteins result in?

A

Excess amino acids. (which cannot be stored).

These need to be excreted safely.

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34
Q

How are excess amino acids excreted safely?

A

They are deaminated in the liver to form ammonia. (deamination)

Ammonia is toxic and so it is immediately converted to urea for safe excretion.

Urea is then transported to the kidneys, where it’s filtered out of the blood and excreted from the body in urine.

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35
Q

How do the kidneys produce urine?

A

By filtration of the blood and selective
reabsorption of useful substances such as glucose, some ions and water.

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36
Q

Name some substances that are removed from the body in urine.

A

-Urea
-Ions
-Water

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37
Q

We can’t control the amount of water we lose from the skin in sweat and from the lungs when breathing out.

So, how is the amount of water in the body balanced?

A

-The amount if water we consume

-The amount of water removed by the kidneys in urine

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38
Q

Kidneys are basically…

A

filters to clean the blood (DO NOT WRITE IN EXAM!)

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39
Q

How are ions (e.g. sodium, nitrogen) taken into the body?

A

In food.

They are then absorbed into the bloodstream.

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40
Q

What could happen if the ion content of the body is wrong?

A

This could upset the balance between ions and water, meaning too much or too little water is drawn into the cells by osmosis.

Having the wrong amount of water can damage cells or mean that they don’t work as well as usual.

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41
Q

Why is it the job of the kidneys to maintain the right balance of ions in the body?

A

The amount of ions lost in sweat is not regulated.

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42
Q

What happens to ions in the kidneys?

A

The right amount of ions is reabsorbed into the blood after filtration and the rest is removed from the body in urine.

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43
Q

What happens when the kidneys filter your blood?

A

Glucose, amino acids, mineral ions, urea, and water all move out of your blood and into your kidney. Blood cells and proteins are too large to leave the blood in this filtering process.

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44
Q

What happens to glucose one in the kidney tubules?

A

It is ALL reabsorbed back into the blood by diffusion and active transport.

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45
Q

Hypertonic blood

A

-Too many ions in the blood, not enough water

-Water moves via osmosis out of cells into the blood

-Cells shrink

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46
Q

Hyper

A

Too much (solute in blood)

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47
Q

Hypo

A

Not enough (solute in blood)

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48
Q

Hypotonic blood

A

-Too much water in blood, not enough solutes

-Water moves into cells via osmosis

-Red blood cells swell and burst (as they have no cell membrane)

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49
Q

Isotonic blood

A

-An equal concentration of water in the blood and in the cells

-So, there is no net movement of water

-This is the ‘perfect’ balance (WE’S WANTS IT)

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50
Q

What are tubules?

A

The tube-like structures that filtered fluid flows through once it’s undergone ultrafiltration in the Bowman’s capsule.

They all join to the collecting duct (filtered fluid is now urine) which joins to the ureters.

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51
Q

Where does selective reapsorbtion take place?

A

The proximal convoluted tubule (but you can just say tubules).

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52
Q

Each kidney contains millions of tiny units called what?

A

Nephrons

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53
Q

What surrounds the tubules?

A

Capillaries so that anything useful can be pumped back into the bloodstream by active transport.

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54
Q

Where does fine tuning of the blood water content take place?

A

The distal convoluted tubule.

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55
Q

Loop of Henle

A

The big loop, water is absorbed by osmosis here (not essential but good to know).

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56
Q

Which hormone is responsible for regulating water levels in the body?

A

Antidiuretic hormone (ADH)

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57
Q

Which part of the brain detects the level of water in the body?

A

Hypothalamus

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58
Q

Name the process that controls water levels in the body.

A

Osmoregulation.

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59
Q

Explain how the blood entering a nephron is filtered to remove excess sodium ions and water.

A

-In the glomerulus, the process of ultrafiltration occurs, whereby small molecules (such as sodium ions and water) are passed through into the Bowman’s capsule.

-As blood flows through the tubules, selective reabsorption occurs

-Urine production occurs in the collecting duct, and excess fluid and sodium ions are removed

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60
Q

Explain why a kangaroo rat (lives in the desert) has a longer loop of Henle than most mammals.

A

-There is a lack of water in the desert

-So the kangaroo rat needs to retain as much water as possible

-A longer loop of Henle provides a larger surface area for maximum absorption of water

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61
Q

Which gland secretes ADH?

A

The pituitary gland.

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62
Q

How does the body respond to too low water levels?

A

-Receptors in the hypothalamus detect the low concentration of water in the bloodstream.

-This causes it to send a signal to the pituitary gland, which tells it to release more antidiuretic hormone (ADH).

-The ADH travels around the body in the
bloodstream, and stimulates the kidneys to reabsorb more water from the tubules into the blood.

-This means that less urine will be made, and the concentration of water in the blood rises.

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63
Q

How does the body respond to too high water levels?

A

-Receptors in the hypothalamus detect the high concentration of water in the bloodstream.

-This causes it to send a signal to the pituitary gland, which tells it to release less antidiuretic hormone (ADH).

-The ADH travels around the body in the blood, and stimulates the kidneys to reabsorb less water from the tubules into the blood.

-This means that more urine will be made, and the concentration of water in the blood decreases.

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64
Q

Alcohol supresses the production of ADH. Suggest how this can lead to dehydration.

A

The kidneys will reabsorb less water, so too much water may be lost from the body in urine.

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65
Q

Which structure carries urine from the bladder out of the body?

A

Urethra

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66
Q

How much urea is selectively reabsorbed?

A

None

67
Q

How many ions are selectively reabsorbed?

A

It depends on how many we already have in the blood

68
Q

How much glucose is selectively reabsorbed?

A

Almost all

69
Q

Glomerulus

A

A network of capillaries, where waste products and some water are filtered out from the blood.

Found inside nephrons.

70
Q

Ultrafiltration

A

Some of the liquid part of the blood is forced from the glomerulus into the Bowman’s capsule (the start of the tubules).

Only very small things can be filtered through.

71
Q

Where does selective reabsorption happen?

A

Throughout the nephron.

72
Q

Parts of the nephron. (not required but handy for A level!)

A

-Glomerulus
-Bowman’s capsule
-Proximal convoluted tubule
-Loop of Henle
-Distal convoluted tubule
-Collecting duct

73
Q

Osmoregulation relies on the process of what?

A

negative feedback.

74
Q

How can people who suffer from kidney failure be treated?

A

-Organ transplant (a cure)

-Dialysis (not a cure)

75
Q

What happens if the kidneys don’t work properly?

A

-Waste substances build up in the blood

-You lose your ability to control the levels of ions and water in your body

-Eventually, this results in death

-You can get problems in the heart, bones, nervous system, stomach, mouth, etc.

76
Q

In a dialysis machine, why is it important that the membrane between the blood and dialysis fluid is partially permeable?

A

To only allow some substances (like ions and waste substances) to diffuse across, but not large molecules like proteins.

77
Q

In a dialysis machine, why is it important to continually pump fresh dialysis fluid through the machine?

A

To maintain a concentration gradient for diffusion across the membrane.

78
Q

If a person has too much sodium in their blood, which way will the sodium diffuse during dialysis?

A

From their blood into the dialysis fluid.

79
Q

Dialysis fluid contains _________________ of useful substances as healthy blood.

A

The same concentration.

This means that useful dissolved ions and glucose won’t be lost from the blood during dialysis.

Only waste substances, excess ions and water, diffuse across the membrane.

80
Q

What are the downsides of dialysis?

A

-It is time consuming (3-4 hr session, 3 x a week)

-There is a risk of blood clots or infection

-It is expensive to run

81
Q

Why can a living person donate a kidney?

A

We are all born with two but can survive with one.

82
Q

If a patient has a kidney transplant, what type of drugs are they required to take for the rest of their lives?

A

Immunosuppressants

83
Q

Rejection of a transplanted organ.

A

The main risk with kidney transplants is that the organ will be rejected.

This can happen because the body’s immune system treats the transplanted organ as a foreign object, and so tries to destroy it.

We can reduce the risk of this happening by using immunosuppressants to suppress the immune system.

84
Q

Why is dialysis more expensive than a kidney transplant in the long run?

A

Dialysis is more expensive because it involves continued treatment every week for the rest of the person’s life.

In contrast, transplants just involve an initial surgery and then continued taking of medicines (which are relatively cheap).

85
Q

What happens in a dialysis machine?

A

A person’s blood flows between partially permeable membranes surrounded by dialysis fluid.

86
Q

Positives of dialysis

A

Can buy a patient with kidney failure valuable time until a donor organ is found.

87
Q

Where are healthy kidneys usually transplanted from?

A

People who have died suddenly, but they have to be on the organ donor register or carry a donor card.

88
Q

There is are long waiting lists for…

A

…kidneys.

89
Q

testosterone

A

The main reproductive hormone in men.

It is produced by the testes and stimulates sperm production.

90
Q

Oestrogen

A

The main reproductive hormone in women.

It is produced by the ovaries.

It brings about physical changes and is involved in the menstrual cycle.

91
Q

What happens during puberty?

A

Your body starts releasing reproductive hormones which trigger off secondary sexual characteristics (such as the development of facial hair in men and breasts in women) and cause eggs to mature in women.

92
Q

Ovulation

A

The release of one egg from the ovaries approximately every 28 days.

93
Q

Describe the 4 stages of the menstrual cycle. (Stages 1 and 2)

A

Stg 1 - On day 1, menstruation starts. The uterus lining breaks down for about four days (this can differ)

Stg 2 - The uterus lining builds up again from day 4 to 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg.

94
Q

Describe the 4 stages of the menstrual cycle. (Stages 3 and 4)

A

Stg 3 - An egg develops and is released from the ovary at day 14 (ovulation)

Stg 4 - The uterus lining is then maintained for about 14 days until day 28. If no fertilised egg has landed on the uterus lining by this time, it starts to break down and the cycle starts again.

95
Q

Which hormones are involved in the menstrual cycle of a woman?

A

-Follicle stimulating hormone (FSH)

-Luteinising hormone (LH)

-Oestrogen

_progesterone

96
Q

Where is FSH produced?

A

The pituitary gland.

97
Q

What is the role of FSH?

A

-FSH causes an egg to mature in one of the ovaries. (in a structure called a follicle)

-FSH stimulates the ovaries to produce oestrogen

(this is why we see higher levels of FSH before oestrogen starts to increase on that funky looking graph)

98
Q

What is the role of LH?

A

-LH stimulates the release of an egg (ovulation)

99
Q

Where is LH produced?

A

The pituitary gland.

100
Q

What is the role of oestrogen?

A

-Oestrogen stimulates the lining of the uterus to grow

-Oestrogen stimulates the release of LH and inhibits the release of FSH

101
Q

Where is progesterone produced?

A

The ovaries by the remains of the follicle after ovulation.

102
Q

What is the role of progesterone?

A

-Progesterone maintains the lining of the uterus (during the second half of the menstrual cycle)

-Progesterone inhibits the release of LH and FSH

103
Q

What happens when the level of progesterone falls?

A

The uterus lining breaks down.

104
Q

What happens if an egg is fertilised?

A

An embryo would implant into the uterus lining and slowly develop into a foetus.

The menstrual cycle would stop.

105
Q

Explain the interactions of FSH, oestrogen, LH and progesterone in the control of the menstrual cycle.

A

-FSH stimulates the ovaries to produce oestrogen.

-As oestrogen levels increase, they start to inhibit FSH (an example of negative feedback).

-When oestrogen levels get too high, they stimulate the release of LH, causing an ‘LH spike. This results in ovulation.

-Progesterone inhibits both LH and FSH

106
Q

Why does a pregnant woman keep her uterus lining?

A

High levels of progesterone, which inhibits the production of both LH and FSH.

107
Q

What are the hormonal methods of contraception?

A

-The combined oral contraceptive pill

-Contraceptive patch

-Contraceptive injection

-Contraceptive implant

-IUD (intra uterine device)

108
Q

How does the combined pill work?

A

Releases oestrogen and progesterone to inhibit FSH and LH production so that no eggs mature.

109
Q

How does oestrogen reduce fertility?

A

If taken every day, levels of oestrogen remain permanently high, so it starts to inhibit the production of FSH.

After a while, egg development and productions stop and stay stopped.

110
Q

How does progesterone reduce fertility?

A

Progesterone inhibits LH and FSH.

It also stimulates the production of a thick mucus in the cervix, which acts as a physical barrier to prevent any sperm getting through and reaching an egg.

111
Q

How effective is the combined oral contraceptive pill?

A

Over 99%

112
Q

Negatives of the combined oral contraceptive pill.

A

-Can cause side effects such as headaches and nausea

-Doesn’t protect against STDs

-Has to be taken every day (could forget)

113
Q

Progesterone-only pill

A

-Just as effective as combined oral contraceptive pill

-Fewer side effects

114
Q

What does an injection, implant or skin patch of slow release progesterone do?

A

Inhibit the maturation and release of eggs for a number of months or years.

115
Q

Contraceptive patch

A

-Contains oestrogen and progesterone
-Small and is stuck to the skin
-Each patch lasts 1 week

116
Q

How long does a contraceptive implant last?

A

Up to 3 years

117
Q

Contraceptive implant

A

-Inserted under the skin of the arm

-Releases a continuous amount of progesterone

-This stops the ovaries releasing eggs, makes it hard for the sperm to swim to the egg, and stops any fertilised egg implanting in the uterus

118
Q

Which hormone does the contraceptive injection contain?

A

Progesterone

119
Q

How effective is the contraceptive patch?

A

99.8%

120
Q

How long does a contraceptive injection last?

A

2-3 months

121
Q

Contraceptive patch evaluation

A

-Easy
-Effective

-Only lasts a week
-Side effects

122
Q

Contraceptive injection evaluation

A

-Effective

-Painful
-Side effects
-Requires a specialist

123
Q

Contraceptive implant evaluation

A

-Effective

-Side effects
-Requires a specialist

124
Q

IUD evaluation

A

-Effective

-Painful
-side effects
-requires a specialist

125
Q

IUS evaluation

A

-Effective

-invasive
-Requires a specialist
-Copper degrades over time (for copper coil)

126
Q

Condoms evaluation

A

-Are the only contraceptive method that prevents STIs

127
Q

Diaphragm evaluation

A

-Has to be used with a spermicide (kills sperm) which is only 70-80% effective.

128
Q

Sterilisation evaluation

A

-Requires a specialist

-A permanent procedure which can be good or bad

-There’s a small chance that the fallopian tubes can re-join (females)

129
Q

Natural methods evaluation

A

-Popular with those who think hormonal and barrier methods are unnatural

-Unreliable/risky
-Not very effective

130
Q

What is the only way to be completely sure that sperm and egg don’t meet.

A

Abstinence (not having sexual intercourse).

131
Q

Natural methods (calendar methods)

A

Avoiding sexual intercourse on the days a woman is most fertile. (when an egg may be in the oviduct).

132
Q

Sterilisation (surgical method)

A

-Cutting or tying the fallopian tubes (which connect the ovaries to the uterus) in a female.

-Cutting or tying the sperm duct (the tube between the testes and the penis) in a male.

133
Q

Spermicidal agents

A

Kill or disable sperm

-Standalone method -70% effective :(
-With a diaphragm

134
Q

IUD (intrauterine device)

A

-A T-shaped device that is inserted into the uterus to kill sperm and prevent implantation of an embryo (fertilised egg)

-There are two main types: plastic IUDs that release progesterone and copper IUDs that prevent the sperm surviving in the uterus (copper coil)

135
Q

What are non-hormonal forms of contraception designed for?

A

To stop the sperm from getting to the egg (includes barrier methods - condom, diaphragm).

136
Q

How long do IUS’ and IUDs last for?

A

Over 3 years

137
Q

Why might a woman be infertile?

A

-Some women have levels of FSH that are too low for their eggs to mature

-This means that no eggs can be released and a woman can’t get pregnant

138
Q

Explain the use of hormones in modern
reproductive technologies to treat infertility.

A

-Women with low levels of FSH can be given a fertility drug containing FSH and LH to stimulate ovulation.

-They may become pregnant in the normal way or then have IVF treatment.

139
Q

Pros of fertility drugs

A

It helps a lot of women to get pregnant when they previously couldn’t.

140
Q

Cons of fertility drugs

A

-They don’t always work

-So, can be done multiple times which can be expensive

-Too many eggs could be stimulated, resulting in unexpected multiple pregnancies (twins, triplets, etc.)

141
Q

Describe the process of In Vitro Fertilisation (IVF) treatment.

A
  • A mother is given FSH and LH to stimulate the maturation of several eggs (often in the form of a fertility drug)
  • The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.
  • The fertilised eggs develop into embryos.
  • At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb).
142
Q

What does Intra-Cytoplasmic Sperm injection (ICSI) involve?

A

The sperm is injected directly into an egg using a tiny needle.

This is helpful in IVF when a man has a particularly low sperm count.

143
Q

IVF pros

A

Can give an infertile couple a child.

144
Q

Fertility treatment (IVF) cons

A
  • it is very emotionally and physically stressful (if multiple failures, reaction to the hormones)
  • the success rates are not high (26% in UK)
  • it can lead to multiple births which are a risk to both the babies and the mother. (e.g. higher risk of miscarriage)
145
Q

Why might IVF be physically stressful for a woman?

A

Some women have a strong reaction to the hormones e.g. abdominal pain, vomiting, dehydration.

146
Q

Give examples of how developments of
microscopy techniques have enabled IVF
treatments to develop.

A

-The improvements have helped to improve the techniques used (and hence the success rate)

-Specialised micro-tools have been developed to use on egg and sperm cells under a microscope

-These can also be used to remove single cells from the embryo for genetic testing (to check it’s healthy)

-More recently, the development of time-lapse imaging (using a microscope and a camera built into the incubator) means the growth of embryos can be continually monitored to identify those more likely to result in a successful pregnancy

147
Q

Why might people be against IVF?

A

-Often results in unused embryos which are eventually destroyed.

-This is thought to be unethical because each embryo has the potential for human life

-The genetic testing of embryos before use also raises ethical issues as some believe this could lead to the selection of preferred characteristics (gender, eye colour).

148
Q

What are thyroxine levels controlled by?

A

Negative feedback.

149
Q

What does adrenaline do?

A

It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.

150
Q

What is adrenaline?

A

Adrenaline is a hormone produced by the adrenal glands in times of fear or stress.

(or exercise as it prepares the body for activity)

151
Q

What stimulates the secretion of adrenaline?

A

The brain detects fear or stress and sends nervous impulses to the adrenal glands, which respond by secreting adrenaline?

152
Q

Where is thyroxine made?

A

Thyroxine is made in the thyroid gland from iodine and amino acids.

153
Q

What is thyroxine?

A

A hormone that stimulates the basal metabolic rate and plays an important role in growth and development.

154
Q

What is the ‘basal metabolic rate’?

A

The speed at which chemical reactions in the body occur when the body is at rest.

155
Q

What role does thyroxine have in growth and development?

A

It stimulates protein synthesis for growth and development.

156
Q

How does adrenaline lead to increased blood flow?

A

By increasing heart rate and blood pressure

157
Q

How does adrenaline increase blood glucose levels?

A

By stimulating the liver to break down glycogen into glucose.

158
Q

Briefly describe how the production of thyroxine is regulated.

A

The pituitary gland produces Thyroid Stimulating Hormone (TSH), which stimulates the thyroid gland to produce thyroxine.

Thyroxine then inhibits the production of TSH from the pituitary gland.

159
Q

What happens if thyroxine levels are too low?

A

The pituitary gland will release TSH.

This stimulates the thyroid gland to release more thyroxine.

So thyroxine levels in the blood increase back up to normal.

160
Q

What happens if thyroxine levels are too high?

A

The thyroxine will inhibit the pituitary gland from producing TSH.

Less TSH means that the thyroid gland won’t release as much thyroxine.

So thyroxine levels in the blood fall back to normal.

161
Q

The control of thyroxine levels by the hypothalamus and pituitary gland is an example of what?

A

Negative feedback.

If levels of thyroxine rise too high, it will bring about changes to lower the levels, and if they fall too low, it brings about changes to raise them back up.

162
Q

Which organ is TSH released from?

A

Pituitary gland

163
Q

Which organ is thyroxine released from?

A

Thyroid gland

Biology (18 decks)

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