ACCESS HE.

Human Biology.REPRODUCTION.

Menstruation.

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.

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).

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.

Follicle Stimulating Hormone (FSH).

• The FSH stimulates the ovaries to secrete hormones to which the uterus responds.

• Oestrogen.• Progesterone.

Three Phases.

• The menstral cycle has three phases.

– -The Proliferative Phase (14 days).– - The Secretory Phase (10 days).– - The Menstrual Phase ( 4 days).

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.

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 !.

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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.

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.

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.

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.