B3.2 The Endocrine system

Question 1

State the function of a hormone

Answer 1

• hormones are chemical messengers, made in endocrine glands and secreted into blood
• blood transports hormones in plasma around body
• hormones cause a response in specific cells that are found in target organs
• they regulate functions of many cells and organs
• normally, hormonal responses are fairly slow and long lasting, however some can act more quickly (adrenaline)
• hormones also control boy processes that need constant adjustment e.g. body temperature (keeping body conditions constant is called homeostasis)

Question 2

Explain the role played by target cells

Answer 2

• hormones travel al over body in bloodstream
• but, only target organs respond
• hormones diffuse out of blood and bind to specific receptors for that hormone, found on membranes / in cytoplasm if cells in target organs, known as target cells
• once bound to their receptors, hormones stimulate target cells to produce a response

Question 3

Explain the role of the endocrine system

Answer 3

• it’s the name given to all endocrine glands + the hormones that they produce
• endocrine system controls + coordinates body processes with the nervous system
• sends messages around body to provide info about any changes in your internal and external environment
• also send info on how the body should respond

Question 4

Explain how the messaging system in nerves and hormones differ

Answer 4

Messaging system - speed of communication - method of transport/transmission - duration of response - area targeted

Nerves - very fast - electrical impulse along axon of a neurone - short acting - very precise area

Hormones - slower - in the blood- longer acting - larger area

Question 5

Name the endocrine glands and the hormones that they produce

Answer 5

Hypothalamus + pituitary gland: produce hormones that regulate production of other hormones
Thyroid gland: thyroxine
Adrenal glands: adrenaline
Pancreas: insulin
Ovaries (in females): produce progesterone and oestrogen
Testes (in males): produce testosterone

Question 6

Describe and explain the function of testosterone in males

Answer 6

• responsible for changes during puberty
• stimulates sperm production
• it’s rising levels during puberty also cause an increase in heights body and pubic hair growth, and enlargement of penis and testes

Question 7

Explain the role of thyroxine in the body

Answer 7

• hormone produced in thyroid gland
• plays vital role in body’s metabolic rate (speed at which body transfers energy from its chemical stores in order to perform its functions)
• function of thyroid gland is to take iodine, convert it into thyroxine by combining it with amino acid tyrosine.

Thyroxine controls how much energy is available to cells.

• when body requires more energy, hypothalamus causes pituitary gland to release TSH
• TSB stimulates thyroid gland to release thyroxine which increases metabolic rate, allowing cells to transfer additional energy
• when cells have required amount of energy, hypothalamus inhibits production of TSH so the thyroid gland stops releasing thyroxine

Question 8

Explain the purpose of negative feedback

Answer 8

• it is important to keep internal conditions constant - negative feedback is an important type of control that is used in homeostasis
• conditions inn body change from set point
• change detected by receptor
• correct mechanisms activated by an effector
• conditions returned to set point
• corrective mechanisms switched off

Question 9

Explain the role of adrenaline in the body

Answer 9

• adrenal glands near kidney
• in times of stress they release adrenaline which immediately prepares body for intensive action (flight or flight response)

When you feel threatened or scared, brain signals adrenal glands to secrete adrenaline, causing body to respond by:
- respiring more quickly to increases rate of ATP production
- increasing rate of breathing to cope with extra demand for oxygen
- increasing heart rate
- diverting blood away from areas like digestive system towards muscles
When stress is removed, signals to adrenal gland stop, so they stop producing adrenaline - the affected body systems return to their previous state
- quick response unlike normal hormones

Question 10

Describe and explain the purpose of the menstrual cycle

Answer 10

• monthly cycle during which a women’s body gets ready for pregnancy
• around 28 days
• each month lining of uterus starts to thicken ready to receive a fertilised egg
• at the same time an egg starts to mature in an ovary
• approx 14 days later, egg is released from ovary (ovulation)
• lining of uterus remains thick
• if egg is fertilised, it may implant in uterus lining, and then it will receive nutrients + oxygen from mother - pregnancy
• if egg isn’t fertilised, uterus lining + egg are removed from body (period/menstruation)

Question 11

Describe the role of FSH in controlling the menstrual cycle and explain interactions with other hormones

Answer 11

• Follicle-stimulating hormone
• secreted by pituitary gland
• travels to ovaries where it causes an egg to mature
• also stimulates ovaries to produce oestrogen

Question 12

Describe the role of Oestrogen in controlling the menstrual cycle and explain interactions with other hormones

Answer 12

• made and secreted by ovaries
• causes lining of uterus to build up
• as oestrogen levels rise they inhibit production of FSH
• this usually prevents more than 1 egg maturing
• also stimulates pituitary gland to release LH

Question 13

Describe the role of LH in controlling the menstrual cycle

Answer 13

• secreted by pituitary gland and goes to ovaries

- when LH reaches a peak in middle of cycle, ovulation is triggered

Question 14

Describe the role of Progesterone in controlling the menstrual cycle and explain interactions with other hormones

Answer 14

• maintains uterus lining
• levels of this hormone remain high throughout pregnancy
• also inhibits LH (so inhibits ovulation)

Question 15

Explain the use of hormones in contraception

Answer 15

• contraception is any technique used to prevent pregnancy
  2 groups:
• non-hormonal + barrier methods that prevent sperm contacting egg or physical devices that release chemical compounds which also kill sperm cells or prevent implantation of fertilised eggs
• hormonal - use hormones to disrupt normal female reproductive cycle

Question 16

Evaluate non-hormonal methods of contraception

Answer 16

Non-hormonal methods

Condom

• over penis or vagina
• prevents sperm entering vagina
• can also prevent spread of STIs
• male = 98% female = 95%

Diaphragm/ cervical cap

• inserted in vagina to cover cervix
• removed 6 or more hours after sex
• prevents sperm cells from entering uterus
• not effective unless used in combo with spermicide
• 92-96% effective

Intrauterine device (IUD,coil)

• inserted into uterus, releasing copper which prevents sperm surviving in uterus and fallopian tubes
• can also prevent implantation of fertilised ovum
• remains effective for 5-10 years
• over 99% effective

Question 17

Evaluate hormonal methods of contraception

Answer 17

Oestrogen + progesterone pill (combined pill)

• prevents ovulation - prevents implantation of fertilised egg into uterus wall
• thicker mucus from cervix, stopping sperm reaching ovum
• taken daily for 21 days on menstrual cycle

Progesterone pill

• thins lining of uterus, presenting implantation an maybe also ovulation
• thickens mucus from cervix, stopping sperm reaching ovum
• must be taken around same time everyday

Intrauterine system (IUS, hormonal coil)

• inserted into uterus
• has same effect on body as progesterone-only pill
• remains effective for 3 - 5 years

All hormonal methods are over 99% effective

Question 18

State some causes of infertility

Answer 18

• blocked Fallopian tubes
• blocked sperm ducts
• not enough sperm being produced in the testes
• a lack of mature eggs produced in the ovaries
• a failure of the ovaries to release an egg

Question 19

Explain how hormones can be used to treat infertility

Answer 19

Fertility treatment - using hormones to treat some conditions

• FSH - when woman takes this artificial fertility drug it stimulated eggs to mature in her ovaries + triggers oestrogen production
• this significantly increases her chances of getting pregnant as it increases likelihood of 1 or more eggs being released

Question 20

Explain how IVF works?

Answer 20

• used when treatment with hormones alone isn’t successful
  1- Fertility drugs (FSH and LH) are used to make lots of eggs mature at the same time for collection
  2- The eggs are collected and placed in a special solution in a Petri dish
  3- A sample of semen is collected and the sperm and eggs are mixed in the Petri dish
  4- The eggs are checked to make sure they have been fertilised and that early embryos are developing properly
  5- When the fertilised eggs have formed tiny balls of cells, 1 or 2 of the tiny embryos are placed in womb of mother. Then, if all goes well, at least one baby will grow and develop successfully

Question 21

Describe the issues surrounding fertility treatments

Answer 21

• it’s not a natural process
• it allows parents to conceive who wouldn’t otherwise be able to have a baby
• enables older parents to have children
• many IVF treatments result in multiple births. This can be dangerous for both mother and unborn babies
• can result in no pregnancy which would be distressing
• IVF is very expensive and there is only limited availability through NHS
• it allows younger women to focus on their careers, and choose to have a baby later in life

Question 22

Explain how plant hormones are important in the control and coordination of plant growth and development

Answer 22

• auxin is made near tips of plant shoots and roots
• the response to a stimulus occurs as of an uneven distribution of auxin
• this causes an unequal growth rate, which results in the shoot or root bending
• auxin stimulates shoot cells to grow more, but inhibits the growth of root cells

Question 23

Explain the role of auxin in phototropism

Answer 23

1 - when light hits 1 side of shoot tip, auxin moves to the opposite side, causing the concentration of auxin to build up in the unlit side
2 - cells respond by elongating, increasing the length of the side of the shoot, so the shoot bends towards the light
3- When light falls evenly on the shoot the level of auxin is evenly distributed throughout the tip, so all cells in the tip grow at the same rate so the shoot grows straight

The stem growing towards the light means it can photosynthesise more meaning more food is produced for the plant, so it can grow faster - increases plant’s chances of survival

Question 24

Explain the role of auxin in gravitropism

Answer 24

• in roots, the shaded side also contains more auxin, but these cells elongate less so the roots bend away from light
  1- A normal young (bean) plant is laid on its side in the dark. Auxin is equally spread through tissues
  2- Both in the shoot and in the root, more auxin gathers on the lower side
  3- The root grows more on the side with least auxin, making it bend and grow down towards the force of gravity. When it has grown down, the law in becomes evenly spread again
  4- The shoot grows more on the side with the most auxin, making it bend and grow up away from the force of gravity. When it has grown up, the auxin becomes evenly spread again

Question 25

Describe the function and effects of 3 plant hormones

Answer 25

Plant hormones are produced by cells in 1 area of plant and then transported to a different area to produce a response.

Auxins - stimulate growth by causing cell elongation. They also help to regulate fruit development. Without auxins, fruits are often too small.

Ethene - causes plant fruits to ripen by stimulating the conversion of starch into sugar. This is why a ripe fruit tastes sweeter than an unripe one. It is the only plant hormone existing as a gas.

Gibberellins - promote growth, particularly stem elongation. They can also end dormancy period of seeds and buds. This leads to shoots and flowers opening

Question 26

Describe some of the different ways in which people use plant hormones to control plant growth

Answer 26

Killing weeds
- weed killers are selective herbicides that contain auxin, which makes weeds grow too fast and so the rapid uncontrolled growth kills the plant

Promoting root growth

• rooting powder contains auxin
• people use auxin good produce identical plants from cuttings
• they cut off a plant shoot, dip it into rooting powder and plant it
• after a few days roots develop from the cut stem and they anchor into soil to take up water + minerals

Delaying ripening
- auxin sprayed on fruit trees to delay ripening so that harvest can be collected all at same time and can prevent fruit dropping off trees early

Ripening fruit
- Ethene sprayed on fruit trees so that their fruits risen quicker and can be ready earlier in the growing season

Producing seedless fruit
- apply auxin to unpollinated flowers the plant produces seedless fruit as seeds are produced after a plant is pollinated by insects or the wind

Controlling dormancy
- spray seeds with gibberellins or auxins so that they can germinate (otherwise they wait until ideal conditions for growth which normally prevents them germinating at the end of summer so that they can survive winter)