Sexual Hormones in Humans | Biology for GCSE/IGCSE - Year 11 PDF Download

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 girls and testosterone in boys

Human secondary sexual characteristics

Female secondary sexual characteristics:

Male Secondary Sexual Characteristics:

Common Changes:

• Both boys and girls experience growth of sexual organs and body hair.
• Emotional changes occur due to increased hormone levels in the body, leading to more interest in sex and mood swings.

The Menstrual Cycle

•  Begins during early teenage years in females, typically around age 12, under the influence of hormones. 
• The standard length of a menstrual cycle is 28 days. 
• Ovulation, where an egg is released, usually happens around the midpoint of the cycle, approximately on day 14. The egg then moves from the ovary through the fallopian tube to the uterus. 
• If the egg remains unfertilized, menstruation occurs, commonly known as a period. This process results from the shedding of the thickened uterine lining. 
• Menstruation typically lasts for about 5 to 7 days, marking the commencement of a new cycle. 
• Following menstruation, the uterine lining readies itself by thickening once more, preparing for a potential implantation in the subsequent cycle. 

Hormones of the Menstrual Cycle

• The menstrual cycle is regulated by hormones released from the ovary and the pituitary gland in the brain.
  • Ovary: Plays a crucial role in hormone regulation.
  • Pituitary Gland: Releases essential hormones for the menstrual cycle.

Roles of FSH and LH

• FSH (follicle-stimulating hormone) is released by the pituitary gland and initiates the maturation of an egg in the ovary.
• FSH also stimulates the ovaries to start releasing oestrogen.
• The pituitary gland is prompted to release luteinising hormone (LH) when oestrogen levels peak.
• LH triggers ovulation and stimulates the ovary to produce progesterone.

The roles of oestrogen and progesterone

• Oestrogen levels rise from day 1, reaching a peak just before day 14.
• This rise in oestrogen causes the uterine wall to thicken and the egg to mature.
• The peak in oestrogen occurs just before the egg is released.
• Progesterone levels remain low from day 1 to 14, then start to rise once ovulation has occurred.
• The increasing progesterone levels cause the uterine lining to thicken further; a drop in progesterone levels leads to the breakdown of the uterine lining, resulting in menstruation (a 'period').

Interaction between all four of the menstrual cycle hormones

During the menstrual cycle, various hormones work together in a carefully orchestrated dance to prepare the body for pregnancy.

• Pituitary Gland and FSH: The pituitary gland secretes Follicle-Stimulating Hormone (FSH), which kickstarts the development of a follicle in the ovary.
• Egg Development and Oestrogen: Within the follicle, an egg matures, and the follicle itself starts producing the hormone oestrogen.
• Oestrogen's Role: Oestrogen promotes the growth and repair of the uterine lining while also inhibiting further FSH production.
• LH Surge and Ovulation: When oestrogen levels peak, it triggers the pituitary gland to release Luteinizing Hormone (LH), leading to ovulation around day 14 of the cycle.
• Corpus Luteum and Progesterone: The now-empty follicle transforms into the corpus luteum, which starts producing progesterone.
• Progesterone's Function: Progesterone is crucial for maintaining the thickness of the uterine lining, preparing it for potential implantation of a fertilized egg.
• Menstruation Process: If fertilization does not occur, the corpus luteum breaks down, progesterone levels decrease, leading to the shedding of the uterine lining and menstruation.
• Pregnancy and Progesterone: If pregnancy happens, the corpus luteum continues to produce progesterone, preventing the shedding of the uterine lining until the placenta fully develops and takes over this function.