organogenesis

1. Menstrual cycle
The Menstrual cycle is characteristic of primates
(Man & Monkey).It does not occur in other
vertebrates.
In mammals other than primates the sexual cycle
is known as Oestrous cycle.
The rhythmic changes undergone by the sexual
organs at an interval of 20 days is called
Menstrual cycle.
It takes its name from elaborate process called
menstruation or menses or bleeding.

2. • Menstruation is the periodic discharge of
blood mucus and cellular debris from the
uterus through the vagina at about four weeks
interval.
• This bleeding occurs at the end of each
menstrual cycle in the absence of pregnancy.

3. Duration of Menstrual cycle
• The length of menstrual cycle in an ideal woman is
about 28 days (four weeks).
• This duration is found only in 10% to 15% of women.
• In all other women the duration varies from 21 days to
35 days i.e., from 3 weeks to 5 weeks.
• No womwn is absolutely regular in the duration of the
cycle.
• All women who have kept accurate records for 10 years
or more have noted unexpected changes in the cycle
length; a period of 35 days may follow a period of 21
days.
• In Chimpanzees te length of the cycle is 35 days.

4. Phases of Menstrual cycle (Start from
here)
• The cycle is divided in to 3 phases:
1) Proliferative phase
2) Premenstrual phase or secretory phase
3) Destructive phase or menses

5. Proliferative phase
• This period begins from 6th day of mestruation and lasts for 9 days.
• On 6th day, damage of uterus caused by menstrution is repaired
completely.
• After the repair the proliferative phase begins.
• At the beginning the uterine epithelium remains extremely thin.
During this phase the following changes occur:
1) The uterine epithelium receives more blood.It increases in
thickness.
2) In the ovary Graffian follicle grow and matures.
3) On 14th day ovulation occurs. The Graffian follicle ruptures and the
egg is released. In some women during ovulation slight bleeding
occurs .Since this bleeding occurs in the middle of the menstrual
cycle, it is called intermenstrual bleeding or Hartman’s sign.

6. Secretory phase or
Premenstrual cycle
(15th day to 28th day)
• This phase lasts for 14 days. During secretory phase the following changes occur:
1) The uterine epithelium progressively increases in thickness. The uterus becomes
highly vascular.
2) The uterine glands become elongated and much coiled. The glands secrete more
and more mucus. The mucus is called uterine milk. Uterine milk accumulates in
the depressions found in uterus. The uterine milk is nutritive in function .It is
utilized by embryo later for its early stages of development.
3) The ruptured follicle is soon filled with blood. This blood filled ruptured follicle is
known as corpus haemorrhagiam. The follicle cells multiply rapidly and they are
deposited with an yellow carotenoid substance. These yellow cells replace the
clotted blood of corpus haemorrhagicum.The corpus haemorrhagicum is now
yellow in colour .This yellow body is called as corpus luteum.
If pregnancy occurs, corpus luteum persists, but if not,it degenerates 4 days
before menstuation. The degenerated corpus luteum is replaced by a connective
tissue sap called corpus albicans. It has no functional significance.

7. Destructive phase or Menses
(1st day to 5th day)
• This phase lasts for 4 or 5 days. It occurs in the
absence of pregnancy. This phase is characterised
by menses or menstrual discharge. The discharge
contains mucous, cellular debris and blood shed
from the internal lining of the uterus.
The total loss of blood in normal women
in one menstrual period varies from 50 to 400 ml.
This discharge often begins gradually becomes
more profuse for a day or two, then gradually
diminishes. The average duration of the flow is 4
days, but it may continue for a week.

8. Factors affecting menstrual cycle
• The length of the menstrual cycle is affected by many
factors.
• Abrupt changes in climate, serious emotional disturbance,
age, diet, general health and similar other factors may
shorten or lengthen a cycle.
• In young girls the cycle is usually irregular.
• The irregularity is noted in the early years after menarche (
first menses).Similarly irregular cycles usually occur during
menopause (Menopause is the period of life when
menstruation naturally ceases).It naturally occurs between
the ages of 45 and 50,although it may set in earlier or later.
• Menopause is associated with marked changes in ovaries.
The ovary becomes smaller and graffian follicles disappear.