B3.2 - The endocrine system

• Hormones


  -A hormone is a chemical messenger produced by a gland and carried by the blood, which alters the activity of one or more specific target organs i.e. they are chemicals which transmit information from one part of the organism to another and bring about a change.

  -The glands that produce hormones in animals are known collectively as the endocrine system.
• Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response.
• Hormones only affect cells with target receptors that the hormone can bind to. These are either found on the cell membrane, or inside cells. Receptors have to be complementary to hormones for there to be an effect.
• The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess.
• Difference in nervous and endocrine system:

  A) nerves, brain, spinal cord

  B) glands

  C) electrical impulse

  D) chemical hormone

  E) fast

  F) slower

  G) short- until nerve impulses stop

  H) longer - until hormone is broken down

  
• Thyroxine

  -Thyroxine is a hormone that is released from the thyroid gland (which is located in the neck).

  -It stimulates the metabolic rate; this is the speed at which chemical reactions occur in the body when it is at rest.
• Thyroxine is an example of negative feedback:


  -Thyroxine levels are controlled by negative feedback; with levels of TSH (thyroid-stimulating hormone) released from the pituitary gland responsible for maintaining normal levels in the bloodstream.

  -If the level of thyroxine is too high, the release of TSH is inhibited, so less thyroxine is released from the thyroid gland.

  -If the level of thyroxine falls below a normal level, the release of TSH from the pituitary gland is increased, which stimulates the thyroid to release more thyroxine.
• Adrenaline

  The adrenaline glands lie near your kidneys. In times of stress they secrete the hormone adrenaline. Adrenaline immediately prepares the body for the fight or flight response.
• Adrenaline is produced in situations where the body may be in danger
• Effects of adrenaline

  1. Increasing blood glucose concentration

  2. Increasing heart rate and breathing rates

  3. Increasing blood pressure

  4. Diverting blood flow towards muscles and away from non-essential parts of the body

  5. Dilating pupils
• Increasing blood glucose concentration

  For increased respiration in muscle cells
• Increasing heart rate and breathing rates


  So glucose and oxygen can be delivered to muscle cells, and carbon dioxide taken away from muscle cells more quickly
• Diverting blood flow towards muscles and away from non-essential parts of the body e.g. the digestive system


  To ensure the reactants of respiration are as available as possible
• Dilating pupils


  To allow as much light as possible to reach the retina so more information can be sent to the brain
• Breaking down of stored glycogen to glucose


  1. In the liver and muscle cells

  2. To ensure a higher blood glucose concentration for increased respiration in muscle cells
• Negative Feedback


  -Negative feedback mechanisms in homeostasis helps to maintain conditions in the body within an optimal range; any movement away from ideal conditions results in changes occurring which bring them back.

  -This involves detecting that the level of a substance or a condition has gone above or below normal levels, which triggers a response to bring the level back to normal again.
• Testosterone


  -main male sex hormone

  -produced in the testes

  -Stimulates sperm production

  -Important for the development of the male reproductive system
• Oestrogen


  -Main female sex hormone

  -produced in ovaries

  -Involved in menstrual cycle

  -Promotes female sexual characteristics e.g. breast development
• Progesterone


  -produced in ovaries

  -Supports pregnancy

  -Involved in menstrual cycle
• FSH and LH


  -released from pituitary gland

  -Help control the menstrual cycle
• the menstrual cycle

  The average menstrual cycle is 28 days long and there are four main stages:

  1. Day 1 is when menstruation starts. The uterus lining breaks down and is released.
  2. Lining of the uterus builds up again (day 4 to 14), into a thick spongy layer full of blood vessels.
  3. Ovulation (the release of an egg) occurs on around day 14, about halfway through the cycle, and the egg then travels down the oviduct to the uterus.
  4. Maintenance of the uterus lining ready to accept a fertilised egg.
• The menstrual cycle

  A) menstruation

  B) maintained

  C) builds up

  D) lining breaks down

  
• Follicle-stimulating hormone (FSH) 


  Produced by the pituitary gland - causes an egg to mature in the ovary and stimulates the ovaries to produce oestrogen.
• Luteinising hormone (LH)


  Produced by the pituitary gland and stimulates ovulation (the release of the egg) and indirectly stimulates progesterone production.
• Oestrogen

  Produced by the ovaries - causes the lining of the uterus to thicken and grow and stimulates the production of LH and inhibits the production of FSH so that only one egg is released in each cycle.
• Progesterone

  -Produced specifically by an empty egg follicle called the corpus luteum and is required to maintain the lining of the uterus so when the level of progesterone falls and there's a low oestrogen level, the lining breaks down.

  -Inhibits the production of FSH and LH

  -A low progesterone level allows FSH to increase and then the whole cycle starts again.
• Stages of the menstrual cycle

  1. Pituitary gland produces FSH

  2. FSH stimulates development of new follicle in ovary

  3. Egg matures inside follicle

  4. Follicle produces oestrogen

  5. Oestrogen causes growth and repair of uterus lining

  6. Oestrogen inhibits production of FSH

  7. High oestrogen stimulates release of LH

  8. LH causes ovulation

  9. Follicle becomes corpus luteum

  10. Corpus luteum produces progesterone

  11. Progesterone maintains uterus lining

  12. If egg not fertilised, corpus luteum breaks down, progesterone drops, menstruation occurs

  13. If fertilisation occurs, corpus luteum continues producing progesterone, preventing uterus lining breakdown

  14. Placenta develops, secretes progesterone to maintain lining throughout pregnancy
• Menstruation:

  A) Ovulation

  B) FSH

  C) LH

  
• Menstruation:

  A) Ovulation

  B) Oestrogen

  C) Progesterone

  
• Oral contraceptives:

  -Contain hormones to inhibit FSH production so that no eggs mature. There are two types:

  1. The combined pill:

  • Contains oestrogen and progesterone, which is over 99% effective at preventing pregnancy.
  • High levels of oestrogen inhibit FSH production, preventing the maturation and release of eggs.
  • Progesterone also plays a role in inhibiting the release of mature eggs and stimulates the production of a thick mucus, which prevents sperm from reaching any eggs that are released.

  1. The mini-pill:

  • A progesterone-only pill, which has fewer side effects.
• Injection, implant, or skin patch:

  -They slowly release progesterone to inhibit the maturation and release of eggs for a number of months or years.

  -Benefits of implants reduce the chance of someone forgetting to take the pill.
• Intrauterine devices (IUD):

  -Inserted into the uterus to prevent the implantation of an embryo or release of a hormone.

  -A plastic IUD produces progesterone, which stimulates the production of a thick mucus lining, preventing sperm from reaching any eggs.

  -A copper IUD works by releasing low levels of copper ions, which disable sperm cells
• Barrier methods:

  Work by preventing sperm from reaching the egg:

  Condom:

  • Latex sheath worn over the penis to prevents sperm from entering the vagina.

  Female Condom:

  • Latex sheath worn inside the vagina and prevents entry of sperm

  Diaphragm:

  • A rubber cap that fits over the entrance to the cervix
  • Prevents entry of sperm into the uterus
• Natural methods:

  Natural planning:

  • Avoiding sexual intercourse during the fertile period of the menstrual cycle when ovulation occurs.
• Surgical methods:

  1. Vasectomy:

  • The sperm ducts are cut, so prevents sperm from being ejaculated.
  • Very effective but difficult to reverse.

  1. Female sterilisation (tubal ligation):

  • The oviducts are cut or tied off, preventing eggs from reaching the uterus or sperm from reaching the eggs.
  • Very effective but difficult to reverse.
• Different Methods of Contraception Table:

  A) 99

  B) every day

  C) fewer side effects

  D) weeks or months

  E) hormonal

  F) STI's

  G) medical professional

  H) STI's

  I) applied

  J) break

  K) combined pill and minipill

  L) injection, implant or skin patch

  M) condom, femidom and diaphram

  N) natural planning

  O) sterilisation and vasectomy

  P) 99

  Q) 98

  R) 95

  S) 94

  T) chemical

  U) control

  V) menstrual cycle

  W) illness

  X) lifestyle

  Y) 99

  Z) permanent

  [) surgery

  \) STI's

  ]) 99

  
• hormones to promote natural pregnancy:


  Sometimes, women may have low levels of FSH so low numbers of eggs maturing in their ovaries or no eggs being released during ovulation. Hormones can be given to promote egg production:

  1. FSH (Follicle-stimulating hormone) is given to stimulate eggs to mature.
  2. LH (Luteinising hormone) is given to stimulate ovulation.

  This method carries the risk that several eggs may be released at once, which would increase the chance of multiple births.
• In Vitro Fertilisation (IVF)


  A method of assisted reproduction where eggs are fertilised by sperm outside the body, in glass
• When is IVF is use?

  • If the female cannot conceive naturally even after taking fertility drugs
  • If there are issues with both male and female fertility in a couple
• IVF procedure


  1. FSH and LH given to female to stimulate egg production

  2. Eggs harvested from ovary

  3. Eggs fertilised in petri dish with male sperm

  4. Embryos formed and placed back into female uterus

  5. Several embryos implanted to increase chance of pregnancy