Menstruation Physiology – This course is designed to understand the care of pregnant women and newborn: antenatal, intra-natal and postnatal; breast feeding, family planning, newborn care and ethical issues, The aim of the course is to acquire knowledge and develop competencies regarding midwifery, complicated labour and newborn care including family planning.
Menstruation Physiology
Concept:
Menstruation, or period, is normal vaginal bleeding that occurs as part of a woman’s monthly cycle. Every month, your body prepares for pregnancy. If no pregnancy occurs, the uterus, or womb, sheds its lining. The menstrual blood is partly blood and partly tissue from inside the uterus. It passes out of the body through the vagina.
Periods usually start between age 11 and 14 and continue until menopause at about age 51. They usually last from three to five days. Besides bleeding from the vagina, you may have,
- Abdominal or pelvic cramping pain
- Lower back pain
- Bloating and sore breasts
- Food cravings
- Mood swings and irritability
- Headache and fatigue
Premenstrual syndrome, or PMS, is a group of symptoms that start before the period. It can include emotional and physical symptoms.
Menstruation:
It is the visible manifestation of cyclic physiologic uterine bleeding due to shedding of the endometrium following invisible interplay of hormones mainly through hypo-thalamo-pituitary- ovarian axis.
Or
It may be defined as a periodic & cyclical shedding of progestational endometrium accompantied by loss of blood.
Menstrual cycle:
The cyclical changes in the female that takes place in the endometrium and results in bleeding per vagina from uterus is called menstrual cycle.
Review of Menstrual cycle
Content:
The female menstrual cycle includes the cycle of regular changes in: the anterior pituitary gland hormones, in the ovaries, and in the uterine endometrial lining. These changes are designed to prepare the woman’s body for possible pregnancy.
The hormonal cycle of hypothalamus and anterior pituitary gland – hormones include: gonadotrophin releasing hormone (GnRH), oestrogen, progesterone, follicle stimulating hormone (FSH) and luteinising. hormone (LH).
- hypothalamus produces GnRH;
- this influences the anterior pituitary gland to secrete FSH and LH;
- gonadotrophic activity of hypothalamus and anterior pituitary gland influenced by feedback mechanisms from ovarian hormones.
- FSH causes Graafian follicles in ovaries to develop and enlarge, and secrete oestrogen;
- LH is produced a few days after FSH, caused by rising oestrogen levels;
- after ovulation, levels of FSH and LH drop rapidly;
- progesterone inhibits any new rise in LH;
- if no pregnancy, corpus luteum degenerates after 14 days;
- Negative feedback mechanism of progesterone stops, so FSH and LH can rise again… and new cycle begins.
The ovarian cycle includes – follicular phase, ovulatory phase, and luteal phase.
- Graafian follicle – under influence of FSH and later LH, this matures, moves to surface of ovary and
- ruptures to release ovum (ovulation);
- the empty follicle is known as corpus luteum, which collapses and atrophies unless pregnancy occurs.
The uterine or endometrial cycle includes – proliferative phase, secretory phase, and menstrual phase.
- following menstruation until ovulation the endometrium regenerates (proliferates) and thickens, under influence of oestrogen;
- secretory phase follows ovulation, under influence of progesterone and oestrogen from corpus luteum; the functional layer of endometrium thickens and becomes spongy because of the numerous glands;
- menstrual phase, where if pregnancy has not occurred, the thickened endometrium is shed as vaginal bleeding
There are also changes in the cervical mucous.
Figure: uterine or endometrial cycle
Endometrial changes in menstrual cycle:
Cycle has been traditionally divided into three phases
1. Menstrual phase: The first 4 days
2. Proliferative phase: 10 days
3. Secretary phase: 14 days
1. Menstrual phase:
As a result of the ovarian cycle the uterus is subjected to the influence first of oestrogen and then of a combination of oestrogen and progesterone. Both are withdrawn when the corpus luteum degenerates and menstruation occurs within a few days. The concentration of the estrogen & progesterone fall leading to changes in local prostaglandin metabolism & concentration.
Many of the arterioles show intense vaso-constriction & some of the called arterioles become kinked, as the endometrium shrinks, there is stasis of blood flow in them. From time to time, some of the arterioles relax & bleeding occurs through the necrosed walls of the vessels in the functional layer of the endometrium leads to its disintegration.
2. Proliferative phase:
(Folicular phase/ oestrogenic phase/ postmenstrual phase/ Preovulatory phase): After menstruation only the stratum basalis is left. Under the influence of oestrogen from the ripening follicle, the cells of the surface epithelium& glands become taller & more comumnar.
The glands which are at first straight, narrow and tubular gradually wiongate and winden becoming slightly tortuous. The stromal cells hypertrophy.
Two types of blood vessels are seen in the endometrium: Short straight in the basal layer and long coileled areeroles into the functional layer; Endometrium measures 2-3 mm
3. Secretary phase: (Luteal phase, progesteronic or post ovulatory or premenstrual phase)
After ovulation the corpus luteum seretes both estrogen & progesterone. Under influence of these hormones glands become extremely tortuous & their epithelium projects into their lumina Hypertrophy of the stromal cells continues until they resemble the decidual cells or pregnancy. The endrometrium becomes 5-7 mm thick and shows three layers: In the stratum compactum, the stromal cells are closely packed and the necks of the glands are straight.
In the stratum spongiosum convoluted glands coiled arterioles & comparatively few stromal cells An inactive basal layer which shows little secretory response. This is not shed during
menstruation.
Mechanism of menstruation
Unfertilized mature ovum and no implantation
↓
Degeneration of corpus luteum
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Withdrawn of hormonal influence(progesterone & oestrogen) on the progestational
↓
endometrium
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Shrinkage of endometrium
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Shortening of vessels by increasing & tightening their coils
↓
Arteriolar vasoconstriction and some of the coiled arterioles become kinked
↓
Stasis of blood flow
↓
Ischaemic necrosis of the area of endometrium
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Bleeding from the necrosed area of endometrium
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all layers of the endometrium except stratum basale is sloughed out.
[Flow chart of mechanism of menstruation]
Importance of LMP:
LMP means “last menstrual period”. For clinicians LMP is very much important because the expected date of delivery is calculating traditionally and roughly by the LMP. This calculation is as follows:
EDD = LMP +9 calendar months ± 7 days.
This becomes extreme important for those areas where USG facilities is not available.
Define EDD.
The estimated date of delivery (EDD), also known as expected date of confinement, and estimated due date or simply due date, is a term describing the estimated delivery date for a pregnantwoman. Normal pregnancies last between 37 and 42 weeks.
EDD = LMP + 9 calendar months ± 7 days.
This becomes extreme important for those areas where USG facilities is not available.
Calculation of estimated due date
Content:
The duration of pregnancy is given as 280 days. Understanding when ovulation occurs in the menstrual cycle, that knowledge is used to calculate the estimated due date (EDD) of when the pregnancy would be full term. Ovulation occurs 14 days after the 1st day of the last period if the woman has a regular 28 day menstrual cycle. Therefore:
- an accurate menstrual history needs to be taken, including date of first day of last menstrual period (LMP), and usual length and regularity of menstrual cycle;
- EDD is then calculated by adding 7 days + 9 calendar months to LMP;
- Midwife must explain to the woman that EDD is only one day within a timeframe of when baby is due, though, not the actual date of birth!
- Midwife must check if LMP was normal, to distinguish true LMP from a small ovulation bleed;
- Midwife must check length of menstrual cycle: the average cycle is 28 days, but this is individual; if it is a regular 35 day cycle, then another 7 days needs to be added to EDD; if less than 28 day cycle, then the appropriate number of days must be subtracted from EDD.
[Ref-DMW, Lesson Plan volume 1/page 9]
Patterns of abdominal uterine bleeding / menstrual abnormality
1. Menorrhagia/ hypermenorrhoea
2. Polymenorrhoea
3. Polymenorrhagia
4. Metrorrhagia/intermenstrual bleeding
5. Menometrorrhagia
6. Hypomenorrhoea
7. Cryptomenrrohoea/Oligomenorrhoea
8. Contact bleeding /postciotal bleeding.
Abnormal uterine bleeding:
Abnormal uterine bleeding includes abnormal menstrual bleeding due to other causes such as pregnancy, systemic disease or cancer.
Clinical types of abnormal uterine bleeding:
- Menorrhagia (hypermenorrhoea)
- Polymenorrhoea
- Polymerrhoea
- Metrorrhagia
Patterns of abdominal uterine bleeding / menstrual abnormality:
- Menorrhagia/hypermenorrhoea
- Polymenorrhoea
- Polymenorrhagia
- Metrorrhagia / intermenstrual bleeding
- Menometrorrhagia
- Hypomenorrhoea
- Cryptomenrrohoea/Oligomenorrhoea
- Contact bleeding /postciotal bleeding
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