Download - Control of the oestrous cycle
CONTROL OF THE OESTROUS CYCLEDaniel Laverick| Andrew Westgarth |Andrew Watkis
DEFINITION The Oestrus Cycle : The regular
pattern of changes that takes place in the reproductive system of female mammals, which is controlled through the interaction of a number of hormones!
The Menstrual Cycle : In humans and some other primates, the lining of the uterus is shed along with some blood between each cycle.
HORMONAL CONTROL OF THE MENSTRUAL CYCLE
• There are four main hormones that control the human oestrous cycle:
• Follicle-stimulating hormone (FSH): Stimulates the development of follicles. Stimulates production of oestrogen.
• Luteinising hormone (LH): Causes ovulation to occur. Stimulates production of progesterone.
• Oestrogen: Causes rebuilding of uterus lining. Stimulates production of LH.
• Progesterone: Maintains uterus lining. Inhibits production of FSH.
• Oestrogen and progesterone are produced in the ovaries, while FSH and LH are produced in the pituitary gland of the brain.
THE CYCLEThe menstrual cycle
begins when the uterus lining is shed (along with blood)
DAY 1-5
The pituitary gland releases into the blood
which stimulates follicles in the ovary to
grow and mature. Each follicle contains
an egg
DAY 1
The growing follicles secrete small amounts of oestrogen into the blood. This low level of oestrogen causes the
uterus lining to build up, and also inhibits(stops) the release of FSH and LH.
This is Negative Feedback.
As the follicles grow, more oestrogen is produced. The level of
oestrogen increases until, it reaches it’s critical point. This then inhibits the production of more FSH
and stimulate production of LH, which is Positive Feedback
DAY 10
The LH then causes one of the
follicles in the ovary to release its egg. (Ovulation)
DAY 14
THE CYCLE CONTINUEDAfter Ovulation, LH stimulates the
now empty follicle to develop into a structure known as the Corpus
Luteum, which secretes progesterone.
Progesterone maintains the thick lining of the
uterus, and also inhibits release of FSH and LH (Negative Feedback)
If the egg is not fertilised, the corpus luteum
degenerates and so no longer produces progesterone.
With less progesterone, the lining of the uterus is no longer
maintained and so breaks down (menstruation). Less
progesterone also means that FSH release is no longer inhibited.
FSH release therefore resumes and the cycle repeats.
MENSTRUAL PHASE• It lasts for about 3 – 5 days.• If the ovum is not fertilized, corpus luteum
regresses from 24th day of the cycle. • This causes a decrease in estrogen and
progesterone levels. • It results in shrinkage of endometrium,
coiling and spasm of arteries leading to breakage of the endometrium.
• The necrosed endometrium is shed along with blood and other secretions.
28-11
MENSTRUAL CYCLE
DIAGRAM