1 / 13

Reproduction in Humans (part 2): Menstrual cycle

Students will learn about:<br>- briefly describe the menstrual cycle with reference to the alternation of menstruation and ovulation, <br>the natural variation in its length, and the fertile and infertile phases of the cycle with reference to <br>the effects of progesterone and estrogen only <br>- describe fertilisation and early development of the zygote simply in terms of the formation of a ball <br>of cells which becomes implanted in the wall of the uterus

Joshua21
Download Presentation

Reproduction in Humans (part 2): Menstrual cycle

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Menstrual cycle

  2. Menstruation • First sign of puberty for girls • Monthly discharge of blood/menses from the uterus via the vagina • Length of menstrual period (22-33 days) + amt. of blood lost varies with individuals • Periods could be delayed/stopped due to i) emotional disturbances ii) mental fatigue iii) stress iv) illness v) unbalanced diet/malnutrition

  3. Menstrual (oestrous) cycle • Many developing follicles in the ovary • Young follicles = primary follicles • Consists of potential egg cell surrounded by a layer of follicle cells

  4. Menstrual (oestrous) cycle • Maturation of primary follicles = Graafian follicle (matured primary follicle) • Contains an egg surrounded by follicle cells and a fluid-filled space • Egg has haploid number of chromosomes due to meiosis • Egg is ready to be released by the ovary Graafian follicle primary follicle

  5. Menstrual (oestrous) cycle • At about 14th day from the beginning of menstruation, Graafian follicle ruptures and releases egg into the oviduct funnel (ovulation) • After ovulation, follicle develops into corpus luteum (secretes progesterone + some oestrogen) • Progesterone causes uterine lining to remain thick and soft and to become well supplied with blood vessels • Uterine lining is now ready for embryo to be implanted

  6. Menstrual (oestrous) cycle • If no fertilization occurs, the corpus luteum will persist for some time • Eventually it breaks down and stops producing hormones (progesterone + oestrogen) • This is the start of menstruation (~28th day from onset of previous menstruation) Graafian follicle primary follicle (secretes progesterone + oestrogen)

  7. Follicle developement

  8. Hormonal control of menstrual cycle Onset of menstruation • Anterior pituitary lobe secretes FSH (follicle stimulating hormone) • FSH stimulates i) development of follicles in ovaries (usually one egg ripens to become Graafian follicle in one of the ovaries during each cycle) ii) stimulates follicles in the ovary to secrete oestrogen

  9. Hormonal control of menstrual cycle Effects of oestrogen 1) After menstruation, it causes the repair and growth of the uterine lining (endometrium) 2) A high concentration of oestrogen in blood inhibits FSH production, preventing the ripening and growth of more follicles 3) It stimulates the pituitary gland to secrete LH (luteinising hormone)

  10. Hormonal control of menstrual cycle Effects of LH 1) causes ovulation 2) causes the formation of corpus luteum Functions of progesterone (secreted by corpus luteum) 1) keeps the uterine lining thick and well supplied with blood, preparing it for implantation of the embryo 2) inhibits both FSH and LH production

  11. 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 The Menstrual Cycle FSH stimulates development of follicles in ovaries + follicles in the ovary to secrete oestrogen (causes ovulation + formation of corpus luteum) oestrogen (keeps the uterine lining thick and well supplied with blood, preparing it for implantation of the embryo + inhibits both FSH and LH production) Graafian follicle primary follicle (secretes progesterone + oestrogen)

  12. If fertilization Does not take place… • Menstruation occurs (drop in LH → corpus luteum degenerates → progesterone production stops → uterine lining breaks down → menstruation)

  13. Qn: From your knowledge of the menstrual cycle, how do you think oral contraceptives work? • Oral contraceptives prevent pregnancy by • inhibiting FSH and LH production • hence preventing ovulation (as no follicles develop in ovaries)

More Related