human reproduction I

male reproductive system

female reproductive system

gametes and fertilization

• Fertilization: The fusion of the nuclei from a male gamete and a female one.
• For humans, fertilization occurs in the oviduct.
• Gametes have adaptations, as follows:

human sex hormones

• Primary sexual characteristics: are present during the development of a fetus in a uterus, basically the differences between female or male reproductive organs.
• Secondary sexual characteristics: changes that occur during puberty and are controlled by the release of hormones (testosterone for males and estrogen for females).
  • For both, growth of sexual organs and body hair, emotional changes due to the increased levels of hormones, more interest in sex, and increased mood swings.

the menstrual cycle

starts in the early adolescence of females and is mainly controlled by sex hormones.

• Average duration: 28 days per cycle.
• Ovulation occurs normally halfway through the cycle, around day 14 when the egg travels through the oviduct.
• when an egg is not fertilized it causes menstruation, due to the breakdown of the thickened lining of the uterus (endometrium)
• Average menstruation: 5-7 days, when it starts a new menstrual cycle begins too.
• After menstruation, the lining of the uterus (endometrium) starts to thicken again in preparation for possible implantation during the next cycle.

hormones

• The hormones that regulate the menstrual cycle are secreted by the ovary and the pituitary gland.
• Estrogen levels rise from day 1, with their peak before ovulation (day 14).
  • Estrogen stimulates endometrium development after menstruation and after ovulation inhibits LH and FSH production.
• Progesterone stays low until ovulation has occurred, causing the endometrium to thicken further. Progesterone levels are lower when fertilization does not occur, and therefore cause menstruation.
  • Progesterone also inhibits FSH and LH production.
• FSH stimulates egg maturation in the follicles of the ovary and stimulates estrogen secretion.
• LH stimulates ovulation and results in the formation of “holes” in the ovary called corpus luteum.

interaction between hormones

1. The pituitary gland produces FSH, stimulating the development of a follicle in the ovary.
2. An egg develops on the inside of the follicle, which produces estrogen.
3. Estrogen causes the development and repair of the endometrium while inhibiting FSH production, just so that no more egg cells are matured.
4. When estrogen levels rise, it stimulates the release of LH from the pituitary gland too. This causes ovulation.
5. The follicle becomes the corpus luteum, which produces progesterone.
6. Progesterone maintains the uterus lining, but if the egg cell isn’t fertilized corpus luteum breaks down and progesterone levels drop causing menstruation.
7. endometrium breaks and is removed through the vagina.
8. If the egg IS fertilized the corpus luteum keeps producing progesterone preventing abortions due to the uterus lining breaking.
9. Until the placenta has developed when it starts secreting progesterone throughout the pregnancy.

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