Bio Menstrual Cycle

What is the menstrual cycle

Monthly cycle of events consisting of

• The ovarian cycle, the monthly preparation and shedding of an egg cell from an ovary

• The uterine cycle, the buildup of the endometrium

Define menstruation

The process from which blood from the uterus is discharged through the vagina monthly

Why does menstruation occur or not occur

• Menstruation = sign that pregnancy has not occurred the previous cycle

  • Uterine bleeding caused by the breakdown and shedding of the endometrium

• No menstruation = embryo implants in endometrium and obtains nutrients from it, hence endometrium is not broken down

*Endometrium regrows after menstruation

What does menstrual discharge consist of

Blood and clusters of cells and mucus from the broken down endometrium

Define ovulation

The release of matured eggs from an ovary into the oviduct

Define hormones

Chemical messengers produced in minute quantities by an endocrine gland (It is transported in the bloodstream to target organ(s) where it exerts its functions. After performing its functions, they are eventually destroyed by the liver)

What is the luteinising hormone (LH)

A hormone secreted by the anterior pituitary which

• stimulates ovulation

• stimulates the conversion of remaining follicle tissues to the corpus luteum

What is the follicle-stimulating hormone (FSH)

A hormone secreted by the anterior pituitary which

• stimulates the growth of ovarian follicles (when ruptured, they fill with cells to become corpus luteum)

What is oestrogen

A hormone secreted by the ovaries which

• aids in the thickening and maintenance of endometrium

• inhibits further secretion of FSH and LH

What is progesterone

A hormone secreted by the ovaries which

• inhibits further secretion of FSH and LH

• aids in the thickening and maintenance of endometrium

What happens at the start of homeostasis during the menstrual cycle

1. Anterior pituitary gland releases FSH which stimulates the growth of ovarian follicles

2. Developing follicle secretes oestrogen which stimulates repair and buildup of endometrium

3. High and sudden peak levels of oestrogen stimulate the secretion of LH

4. Surge in LH stimulates

   1. Ovulation

   2. The conversion of remaining follicle tissue to corpus luteum

What is the negative feedback that occurs during the menstrual cycle after the formation of corpus luteum

• Corpus luteum secretes progesterone & oestrogen which

  • Continue with thickening and maintenance of endometrium which fills with blood capillaries

  • Inhibit further secretion of LH & FSH

• Falling levels of LH & FSH cause corpus luteum to degenerate

  • Progesterone & oestrogen levels eventually decrease

  • Menstrual cycle starts from the beginning as endometrium breaks down