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ACCESS HE. Human Biology.

ACCESS HE. Human Biology. REPRODUCTION. Menstruation. Menstruation. Occurs approximately every 28 days. Occurs throughout the childbearing years of the female (approx 35years).

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ACCESS HE. Human Biology.

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  1. ACCESS HE.Human Biology. REPRODUCTION. Menstruation.

  2. Menstruation. • Occurs approximately every 28 days. • Occurs throughout the childbearing years of the female (approx 35years). • Menstrual cycle consists of a series of events that take place in the ovaries and walls of the uterus at the same time.

  3. Control of Menstrual Cycle. • Menstrual cycle is controlled by hormones. • The Pituitary Gland, (anterior lobe), secretes two Gonadotrophins (sex hormones). • - Follicle Stimulating Hormone (FSH). • - Luteinising Hormone (LH).

  4. FSH and LH.. • FSH is responsible for stimulating the development the of the ovary follicle and secretion of oestrogen by the ovaries. • LH is responsible for stimulating the secretion of oestrogen and progesterone. • LH is also responsible for triggering ovulation (the discharge of the mature ovum). • The ovum is the egg.

  5. Follicle Stimulating Hormone (FSH). • The FSH stimulates the ovaries to secrete hormones to which the uterus responds. • Oestrogen. • Progesterone.

  6. Three Phases. • The menstral cycle has three phases. • -The Proliferative Phase (14 days). • - The Secretory Phase (10 days). • - The Menstrual Phase ( 4 days).

  7. The Proliferative Phase. • Proliferative: Reproduction and Growth. • Ovarian follicle becomes mature under the influence of FSH. • Follicles are small sac-like structures on the surface of the ovaries. • The follicle contains an ovum and fluid. • When the follicle is mature it is called a Graafian follicle. • The follicle is producing the hormone oestrogen.

  8. The Proliferative Phase. • Oestrogen stimulates the proliferation (growth) of the endometrium (lining of the uterus) in preparation for the fertilised ovum. • The endometrium becomes much thicker and has a greatly increased supply of blood and mucous membrane. • As soon as the ovum is mature and ready to be fertilised the Graafian follicle ruptures (splits). • This is ovulation. • At the same time as ovulation oestrogen production ceases. • End of Phase !.

  9. The Secretory Phase. • Secretory: Because of all the extra secretions produced. • The released ovum begins its journey through the fallopian tubes towards the uterus. • LH is now secreted by the pituitary gland. • LH develops the corpus luteum. • The corpus luteum is a fatty mass that swells from the empty Graafian follicle. • The corpus luteum is producing progesterone. • Progesterone causes the endometrium to become oedematous (swollen) and large amounts of watery mucus is secreted. The extra thick endometrium provides a cosy bed with a rich nourishing blood supply in readiness for a fertilised ovum. • The extra thick endometrium provides a cosy bed with a rich nourishing blood supply in readiness for a fertilised ovum.

  10. The Secretory Phase. • The watery mucus is thought to help the passage of sperm through the uterus to the Fallopian tube. • Fertilisation of the ovum takes place in the Fallopian tube. • There is also an increase in the secretion of watery mucus in the vagina at this time.The ovum may remain ‘fertilisable’ for just 8 hours after ovulation. • The deposited sperm in the female genital tract may only be capable of fertilising the ovum for 24 hours, however, they may survive for several days. • This means that the ovulation period is very short in each cycle. • It is important to remember that it is impossible to predict ovulation with certainty; even with regular cycles. • If the ovum is fertilised then it is the beginning of pregnancy. • If the ovum is not fertilised then it is the end of the second phase.

  11. The Menstrual Phase. • Menstrual: Derived from the word ‘menses’ • Menses: Latin pleural for ‘month’. • The ovum is not fertilised. • The high level of progesterone in the blood inhibits the activity of the pituitary gland, therefore the production of LH is substantially reduced. • Lack of LH causes the corpus luteum to degenerate. • As the corpus luteum can no longer function effectively the production o progesterone is decreased. • After about 10 days the progesterone in the blood is very low. • This causes the endometrium to break down. • Menstruation begins.

  12. The Menstrual Phase. • The menstrual flow consists of the extra secretions, the lining of the endometrium, blood from the extra supply of capillaries that are broken down and the unfertilised ovum. • This is the end of the third phase. • The first stage (the proliferative phase) begins all over again with another ovarian follicle being stimulated by the FSH.

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