The Menstrual Cycle • Releasing of one egg (ovulation) every month from the ovaries • 4 steps: • Preparing the egg • Releasing egg • Preparing the endometrium • Shedding endometrium if egg is not fertilized • Takes about 28 days
Hormonal Control of the Menstrual Cycle There are four principal hormones involved in the control of the human menstrual cycle Pre-Ovulation Hormones FSH – Follicle Stimulating Hormone – secreted into the blood from the pituitary gland LH – Luteinising Hormone – secreted into the blood from the pituitary gland Post-Ovulation Hormones OESTROGEN– secreted by the developing follicles (ball of cells around ova) in the ovary PROGESTERONE – secreted by the yellow body (corpus luteum) in the ovary
Hormones of the Pituitary Gland Anterior lobe of the pituitary gland Hypothalamus FSH – Follicle Stimulating Hormone LH – Luteinising Hormone
Follicle Stimulating Hormone = FSH • Causes follicles (ball of cells that help develop ova) to develop in the ovary. • Stimulates follicular cells of the ovary to secrete oestrogen & small amounts of progesterone.
Luteinising Hormone = LH • Causes ovulation • Causes a follicle after ovulationto develop into a Yellow body (corpus luteum)which produces oestrogen and progesterone.
LH FSH oestrogens • 28 Day Cycle: • 1-5: • Menstruation; endometrium is shed • FSHincreases • 6-12: • Follicles develop and oestrogenincreases • 12-14: • Oestrogen at peak; LH and FSHspike • 14: • Ovulation
LH FSH progesterone oestrogens • 28 Day Cycle: • 14-25: LH causes follicle to change to yellow body (corpus luteum) which raisesprogesterone levels • Endometrium thickens and FSHinhibited
LH FSH progesterone oestrogens • 28 Day Cycle: • No feritilization • 25-28: High progesterone levels inhibitLH(negative feedback) • Yellow body (corpus luteum) degrades so progesteronedrops • FSH increases and endometrium is lost(menstruation)
Spiral arteries Progesterone thickens the endometrium Progesterone stimulates glands in the endometrium to increase in size Oestrogen secreted by the developing follicles repairs the endometrium Endometriumis being shed during menstruation Endometrial Changes • The events occurring in the ovary during the menstrual cycle are accompanied by changes in the endometrial lining of the uterus
LH FSH progesterone oestrogens • 28 Day Cycle: • Fertilization • Endometriumstays due to progesterone from yellow body • Placenta forms and keeps oestrogen levels high • LH is inhibited so ovulation does not start again