Hormones

• A hormone is a chemical substance 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.
• Major endocrine glands of the body (part 1):

  
• Major endocrine glands of the body (part 2):

  
• Table of endocrine hormones:

  
• 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.
• Only cells with complementary receptors can bind with and respond to the hormone:

  
• Table to compare responses of the nervous and endocrine system:

  
• Hormones play a key role in human reproduction.

  • During puberty, reproductive hormones cause secondary sex characteristics to develop.
• Male reproductive hormones:

  • The main male reproductive hormone is testosterone which is produced by the testes;
  • Testosterone stimulates...
  • Sperm production
  • Growth of body hair
  • Growth of penis and testes
  • Muscle development
  • Deepening of the voice
• Male secondary sexual characteristics:

  
• Female reproductive hormones:

  • The main female reproductive hormone is oestrogen which is produced by the ovaries
  • Oestrogen plays an important role in the menstrual cycle which begins at puberty,
  • It also causes physical changes to occur in the body...
  • Breast development
  • Widening of hips
  • Growth of body hair
• Other key female reproductive hormones include:

  • Progesterone which is responsible for maintaining the lining of the uterus
  • Follicle stimulating hormone (FSH) that is responsible for stimulating the maturation of an egg in the ovary
  • Luteinising hormone (LH) which is responsible for ovulation of the egg once matured
• Female secondary sexual characteristics:

  
• Hormonal contraception:

  Oral contraceptives

  • Contain hormones to inhibit FSH production so that no eggs mature; there are two types:
  • 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
  • The mini-pill
  • A progesterone-only pill, which has fewer side effects
• Injection, implant or skin patch

  • 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 (which should be taken at the same time every day to be most effective)
• Intrauterine devices (IUD)

  • Inserted into the uterus to prevent the implantation of an embryo or release a hormone 
  • A plastic IUD
  • Produces progesterone which stimulates the production of a thick mucus lining preventing sperm from reaching any eggs
• Non-Hormonal contraception:

  Barrier methods

  • These all work by preventing sperm from reaching the egg
  • Condom
  • Latex sheath worn over the penis
  • Prevents sperm entering the vagina as ejaculate remains in condom
  • Protects against STIs
• Femidom (Non-Hormonal contraception)

  • Latex sheath inserted into the vagina
  • Prevents entry of sperm into the vagina
  • Diaphragm
  • A rubber cap that fits over the entrance to the cervix
  • Prevents entry of sperm into uterus
  • Often used with a spermicide (cream which kills sperm)