Edexcel IGCSE Biology: Double Science 复习笔记 3.1.7 Human Sex Hormones

Edexcel IGCSE Biology: Double Science 复习笔记 3.1.7 Human Sex Hormones

Secondary Sexual Characteristics

 

  • Primary sexual characteristics are present during development in the uterus and are the differences in reproductive organs etc between males and females
  • Secondary sexual characteristics are the changes that occur during puberty as children become adolescents
  • They are controlled by the release of hormones
    • Oestrogen in females
    • Testosterone in males

     

 

 

 

Human secondary sexual characteristics

 

Female Secondary Sexual Characteristics Table16.6-Female-secondary-sexual-characteristics-table-1

 

 

 

Male Secondary Sexual Characteristics Table

Male-secondary-sexual-characteristics-table_1.png

 

 

  • Some changes occur to both males and females, including the growth of sexual organs and growth of body hair
  • Emotional changes also occur due to the increased levels of hormones in the body
  • These include more interest in sex and increased mood swings

 

The Menstrual Cycle

 

  • Starts in early adolescence in females (around age 12) and is controlled by hormones
  • The average menstrual cycle is 28 days long
  • Ovulation (the release of an egg) occurs about halfway through the cycle (day 14) and the egg then travels down the oviduct to the uterus
  • Failure to fertilise the egg causes menstruation (commonly called a period) to occur - this is caused by the breakdown of the thickened lining of the uterus
  • Menstruation lasts around 5 - 7 days and signals the beginning of the next cycle
  • After menstruation finishes, the lining of the uterus starts to thicken again in preparation for possible implantation in the next cycle

 

 

 

Changes-in-the-lining-of-the-uterus-during-the-menstrual-cycle

 

Changes in the lining of the uterus during the menstrual cycle

 

 

 

Hormonal control of the menstrual cycle

  • The menstrual cycle is controlled by hormones released from the ovary and the pituitary gland in the brain
  • Oestrogen levels rise from day 1 to peak just before day 14
  • This causes the uterine wall to start thickening and the egg to mature
  • The peak in oestrogen occurs just before the egg is released
  • Progesterone stays low from day 1 – 14 and starts to rise once ovulation has occurred
  • The increasing levels cause the uterine lining to thicken further; a fall in progesterone levels causes the uterine lining to break down (menstruation / ‘period’)

 

 

The roles of FSH and LH

  • FSH (follicle-stimulating hormone) is released by the pituitary gland and causes an egg to start maturing in the ovary
  • It also stimulates the ovaries to start releasing oestrogen
  • The pituitary gland is stimulated to release luteinising hormone (LH) when oestrogen levels have reached their peak
  • LH causes ovulation to occur and also stimulates the ovary to produce progesterone

 

 

Pituitary-hormones_1

 

Changes in the levels of the pituitary hormones FSH and LH in the blood during the menstrual cycle

 

 

 

The roles of oestrogen and progesterone

  • Oestrogen levels rise from day 1 to peak just before day 14
  • This causes the uterine wall to start thickening and the egg to mature
  • The peak in oestrogen occurs just before the egg is released
  • Progesterone stays low from day 1 – 14 and starts to rise once ovulation has occurred
  • The increasing levels cause the uterine lining to thicken further; a fall in progesterone levels causes the uterine lining to break down (menstruation / ‘period’)

 

 

 

Ovarian-hormones

 

Changes in the levels of oestrogen and progesterone in the blood during the menstrual cycle

 

 

 

Interaction between all four of the menstrual cycle hormones

  • The pituitary gland produces FSH which stimulates the development of a follicle in the ovary
  • An egg develops inside the follicle and the follicle produces the hormone oestrogen
  • Oestrogen causes growth and repair of the lining of the uterus wall and inhibits production of FSH
  • When oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (usually around day 14 of the cycle)
  • The follicle becomes the corpus luteum and starts producing progesterone
  • Progesterone maintains the uterus lining (the thickness of the uterus wall)
  • If the ovum is not fertilised, the corpus luteum breaks down and progesterone levels drop
  • This causes menstruation, where the uterus lining breaks down and is removed through the vagina - commonly known as having a period
  • If pregnancy does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down and aborting the pregnancy
  • It does this until the placenta has developed, at which point it starts secreting progesterone and continues to do so throughout the pregnancy

 

 

Hormones-in-the-menstrual-cycle

 

Diagram showing where hormones involved in the menstrual cycle are made and act

转载自savemyexams

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