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The Menstrual Cycle The menstrual cycle is a monthly cycle, process of maturing and release of an egg. If sexual intercourse has occurred, this can result in pregnancy. Key hormones • The menstrual cycle is controlled by four hormones from the endocrine system: o Follicle Stimulating Hormone (FSH) o Oestrogen o Luteinising Hormone (LH) o Progesterone Stages • The menstrual cycle can be divided into four stages depending on the levels of the hormones. Eggs • A female is born with all of her eggs ready, but only one egg will mature each month once the female reaches puberty. FSH • FSH stands for Follicle Stimulating Hormone. • It is released by the pituitary gland and causes an egg in the ovary to mature. Oestrogen • Oestrogen is produced in the ovaries and causes the development of the thick, spongy uterus lining. LH • LH stands for Luteinising Hormone. • LH is produced by the pituitary gland and stimulates the release of a mature egg on Day 14 of the menstrual cycle. • This release is called ovulation. Progesterone • Progesterone is produced in the ovaries after ovulation. • It is responsible for maintaining the lining of the uterus during days 14-28. • When progesterone levels drop, this triggers the breakdown of the lining. This marks day 1 of the next menstrual cycle. • The release of an egg during the menstrual cycle is called Ovulation. Controlling Fertility - The Contraceptive Pill Pharmaceutical companies have designed contraceptive pills. They reduce a woman’s fertility to reduce the likelihood of pregnancy. There are two main types of contraceptive pill: Combined pill • Contains both oestrogen and progesterone. • By taking it every day, enough oestrogen builds up in the female body to inhibit the production of FSH so that no eggs mature. Progesterone-only pill • Stimulates the production of thick, sticky mucus, which is very difficult for any sperm to penetrate. • Inhibits the release of FSH, so that eggs don’t mature. • Just as effective as the combined pill but with fewer side effects. Controlling Fertility - Other Contraception Options Research and developments in technology have led to more contraceptive methods. These contraceptives don't have to be taken daily: Contraceptive injection • The contraceptive injection contains progesterone and can last up to three months. Contraceptive implant • The contraceptive implant, which can last for 3 years, is inserted under the skin (normally in an arm) and continuously releases a small amount of progesterone. daily: Contraceptive injection Contraceptive implant Contraceptive patch • The woman places the small contraceptive patch onto the skin, which only has to be changed once a week. • This steadily releases progesterone. Condoms Condoms are effective in protecting against sexually transmitted infections (STIs), such as chlamydia, gonorrhoea, and HIV. Use • Condoms can be worn by the male on his penis during sexual intercourse. Prevention • Condoms prevent the sperm from entering the female during ejaculation. Spermicide • Condoms often contain a spermicide, which kills the sperm on release. Sterilisation Women and men can control fertility to prevent themselves from getting pregnant. If they choose to have a permanent procedure to remove any chance of getting pregnant, they undergo a sterilisation: Men • For a man, this involves having the sperm ducts (the tubes between the testes and the penis) cut so that the sperm are not released on ejaculation. Women • For a woman, this involves having the fallopian tubes (ducts which connect the ovaries to the uterus) cut so that an egg cannot reach the uterus. • • Sterilisation is a permanent procedure to remove any chance of getting pregnant. Natural methods’ Some women prefer to use ‘natural methods’ of contraception. Whatever the choice of contraception, it is essential that people protect themselves against unwanted pregnancies as well as sexually transmitted diseases. Timing • Since a female’s body temperature usually rises during ovulation, some women choose to avoid sexual intercourse on days when they know (or feel) that they are ovulating. • However, sperm can last up to six days inside the woman’s body, so this is not a very reliable or effective method of contraception. Abstinence • The only truly effective way (apart from sterilisation) to avoid pregnancy is abstinence. • This simply means that a couple chooses to not have sexual intercourse unless they are ready for a baby. • • Whatever the choice of contraception, it is essential that people protect themselves against unwanted pregnancy as well as sexually transmitted diseases. Tropisms Tropisms are controlled by auxins. They are groups of responses that can be split into: Phototropisms • These involve growth either towards (positively phototropic) or away from (negatively phototropic) a light source. Gravitotropisms (or geotropisms) • Growth either towards (positively gravitropic) or away from (negatively geotropic) the direction of gravity. • One side of the shoot is exposed to more light. • Auxin is redistributed within the shoot so that the concentration is greater on the shaded side. • This unequal auxin distribution will result in increased cell elongation (grows longer) on the shaded side. • In shoots, auxins promote the elongation of cells. • However, in roots, auxins prevent the elongation of cells.