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Menstrual cycle
Menstruation <ul><li>First sign of puberty for girls </li></ul><ul><li>Monthly discharge of blood/menses from the uterus v...
Menstrual (oestrous) cycle <ul><li>Many developing follicles in the ovary </li></ul><ul><li>Young follicles =  primary fol...
Menstrual (oestrous) cycle <ul><li>Maturation of primary follicles =  Graafian follicle  (matured primary follicle) </li><...
Menstrual (oestrous) cycle <ul><li>At about 14 th  day from the beginning of menstruation, Graafian follicle ruptures and ...
Menstrual (oestrous) cycle <ul><li>If no fertilization occurs, the corpus luteum will persist for some time </li></ul><ul>...
Follicle developement
Hormonal control of menstrual cycle <ul><li>Onset of menstruation </li></ul><ul><li>Anterior pituitary lobe  secretes FSH ...
Hormonal control of menstrual cycle <ul><li>Effects of oestrogen </li></ul><ul><li>1) After menstruation, it causes the re...
Hormonal control of menstrual cycle <ul><li>Effects of LH </li></ul><ul><li>1) causes ovulation </li></ul><ul><li>2) cause...
The Menstrual Cycle primary follicle Graafian follicle (secretes progesterone + oestrogen) (causes ovulation + formation o...
If fertilization <ul><li>Does not take place… </li></ul><ul><li>Menstruation occurs (drop in LH  -> corpus luteum degenera...
Qn: From your knowledge of the menstrual cycle, how do you think oral contraceptives work?  <ul><li>Oral contraceptives pr...
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Chapter 17 Reproduction in Humans Lesson 2 - The Menstrual Cycle

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Chapter 17 Reproduction in Humans Lesson 2 - The Menstrual Cycle

  1. 1. Menstrual cycle
  2. 2. Menstruation <ul><li>First sign of puberty for girls </li></ul><ul><li>Monthly discharge of blood/menses from the uterus via the vagina </li></ul><ul><li>Length of menstrual period (22-33 days) + amt. of blood lost varies with individuals </li></ul><ul><li>Periods could be delayed/stopped due to </li></ul><ul><li>i) emotional disturbances </li></ul><ul><li>ii) mental fatigue </li></ul><ul><li>iii) stress </li></ul><ul><li>iv) illness </li></ul><ul><li>v) unbalanced diet/malnutrition </li></ul>
  3. 3. Menstrual (oestrous) cycle <ul><li>Many developing follicles in the ovary </li></ul><ul><li>Young follicles = primary follicles </li></ul><ul><li>Consists of potential egg cell surrounded by a layer of follicle cells </li></ul>
  4. 4. Menstrual (oestrous) cycle <ul><li>Maturation of primary follicles = Graafian follicle (matured primary follicle) </li></ul><ul><li>Contains an egg surrounded by follicle cells and a fluid-filled space </li></ul><ul><li>Egg has haploid number of chromosomes due to meiosis </li></ul><ul><li>Egg is ready to be released by the ovary </li></ul>primary follicle Graafian follicle
  5. 5. Menstrual (oestrous) cycle <ul><li>At about 14 th day from the beginning of menstruation, Graafian follicle ruptures and releases egg into the oviduct funnel ( ovulation ) </li></ul><ul><li>After ovulation, follicle develops into corpus luteum (secretes progesterone + some oestrogen ) </li></ul><ul><li>Progesterone causes uterine lining to remain thick and soft and to become well supplied with blood vessels </li></ul><ul><li>Uterine lining is now ready for embryo to be implanted </li></ul>
  6. 6. Menstrual (oestrous) cycle <ul><li>If no fertilization occurs, the corpus luteum will persist for some time </li></ul><ul><li>Eventually it breaks down and stops producing hormones (progesterone + oestrogen) </li></ul><ul><li>This is the start of menstruation (~28 th day from onset of previous menstruation) </li></ul>primary follicle Graafian follicle (secretes progesterone + oestrogen)
  7. 7. Follicle developement
  8. 8. Hormonal control of menstrual cycle <ul><li>Onset of menstruation </li></ul><ul><li>Anterior pituitary lobe secretes FSH ( follicle stimulating hormone ) </li></ul><ul><li>FSH stimulates </li></ul><ul><li>i) development of follicles in ovaries (usually one egg ripens to become Graafian follicle in one of the ovaries during each cycle) </li></ul><ul><li>ii) stimulates follicles in the ovary to secrete oestrogen </li></ul>
  9. 9. Hormonal control of menstrual cycle <ul><li>Effects of oestrogen </li></ul><ul><li>1) After menstruation, it causes the repair and growth of the uterine lining ( endometrium ) </li></ul><ul><li>2) A high concentration of oestrogen in blood inhibits FSH production , preventing the ripening and growth of more follicles </li></ul><ul><li>3) It stimulates the pituitary gland to secrete LH ( luteinising hormone ) </li></ul>
  10. 10. Hormonal control of menstrual cycle <ul><li>Effects of LH </li></ul><ul><li>1) causes ovulation </li></ul><ul><li>2) causes the formation of corpus luteum </li></ul><ul><li>Functions of progesterone (secreted by corpus luteum) </li></ul><ul><li>1) keeps the uterine lining thick and well supplied with blood, preparing it for implantation of the embryo </li></ul><ul><li>2) inhibits both FSH and LH production </li></ul>
  11. 11. The Menstrual Cycle primary follicle Graafian follicle (secretes progesterone + oestrogen) (causes ovulation + formation of corpus luteum) (keeps the uterine lining thick and well supplied with blood, preparing it for implantation of the embryo + inhibits both FSH and LH production) Ostrogen causes the repair and growth of the uterine lining + stimulates the pituitary gland to secrete LH + high concentration of oestrogen in blood inhibits FSH production FSH stimulates development of follicles in ovaries + follicles in the ovary to secrete oestrogen oestrogen
  12. 12. If fertilization <ul><li>Does not take place… </li></ul><ul><li>Menstruation occurs (drop in LH -> corpus luteum degenerates -> progesterone production stops -> uterine lining breaks down -> menstruation) </li></ul>
  13. 13. Qn: From your knowledge of the menstrual cycle, how do you think oral contraceptives work? <ul><li>Oral contraceptives prevent pregnancy by </li></ul><ul><ul><li>inhibiting FSH and LH production </li></ul></ul><ul><ul><li>hence preventing ovulation (as no follicles develop in ovaries) </li></ul></ul>

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