Download MENSTRUAL CYCLE

MENSTRUAL CYCLE
Learning Objectives
At the end of the tutorial, the student should be able to :
• Define menstrual cycle.
• Tell us the duration of menstrual cycle.
• Describe the physiologic changes that occur in the female
reproductive organs during the menstrual cycle.
• Explain the regulation of menstrual cycle.
• Express the applied physiology
Menstrual Cycle
Definition:
Periodic vaginal bleeding that occurs with the shedding of the
uterine mucosa (menstruation).
Menstruation
• Indicate periodic shedding of the stratum functionale of the
endometrium, which becomes thickened prior to
menstruation under the stimulation of ovarian steroid
hormones.
A : Functional Layer.
B: Basal layer.
Duration of the cycle
• Variable,
• an average figure is 28 days from the start of one menstrual
period to the start of the next.
• First day of menstruation “day one “ of the cycle.
Timing events in the menstrual cycle.
1. Onset of menstruation
0
4
8
12
16
20
24
28
Phases of the menstrual Cycle
Changes in ovary :
– THE FOLLICULAR PHASE:
From first day of menstruation until day of ovulation.
– LUTEAL PHASE:
After ovulation is luteal phase until first day of menstruation
Phases of the menstrual Cycle
• Changes in the endometrium:
– Menstrual ,
– Proliferative and
– Secretory Phase
Ovarian Cycle
• Follicular Phase ( Day 1 to Day 13 ):
– Menstruation lasts from 1 to day 4 or 5 of the
average cycle.
– Secretion of Ovarian steroid hormones are at
their lowest.
– Ovaries contain only primary follicles.
• Follicular Phase ( Day 1 to Day 13 ):
– Some primary follicles grow, and become secondary
follicles.
– Towards the end , one follicle in one ovary reaches
maturity and reaches graffian follicle.
– As follicles grow, the granulosa cells secrete estradiol
( the principal estrogen), which reaches its highest
concentration in the blood at about day 12 of the cycle,
2 days before ovulation.
Growth of follicles:
Antral follicle
Graafian
follicle
Primordial
follicle
Oocyte
Granulos
a cells
Antrum
(fluid filled
space)
Thecal
cells
Ovulation
Key events in the ovarian
cycle
LH
2. Ovulation
0
4
1. Follicular
Day growth
1
8
12
16
Menstruation
•
20
24
3. Luteal
function
28
Oestradi
ol
4. Luteal
regressi
on
Progesterone
(and
OVULATION
oestradiol)
Follicular Phase ( Day 1 to Day 13 ):
– Growth of follicles and secretion of estradiol are stimulated by FSH.
– FSH in early follicular phase is slightly greater then in late follicular phase.
– Towards the end , FSH and estradiol also stimulate the production of LH
receptors in the graffian follicle.
– Graafian follicle is prepared for the next major event.
LH Surge
• Begins about 24 hours before ovulation.
• Reaches its peak 16 hours before ovulation.
• LH surge acts to trigger ovulation.
 Positive feedback effect of estradiol on the pituitary , an
increase in LH secretion in late follicular phase
culminates in an LH s.
Timing events in the menstrual cycle.
2. LH surge
LH
Ovulation
• LH Surge causes graafian follicle to rupture at about
day 14.
• Secondary oocyte arrested at metaphase II of meiosis , is
released from ovary into the uterine tube.
• Ovulation occurs
Luteal phase
• After Ovulation, the empty follicle is stimulated by LH to
become corpus luteum.
• Corpus luteum secretes both estradiol an progesterone.
• Progesterone levels in the blood are negligible before
ovulation but rise rapidly to a peak level during the luteal
phase, approximately one week after ovulation
• Progesterone with estradiol during the luteal phase
exert an inhibitory, or negative feedback effect on
FSH n LH secretion.
• Corpus luteum produces inhibin which may help to
suppress FSH secretion.
• This retards the development of new follicles.
• Further ovulation does not occur.
• Multiple ovulations and possible pregnancies on
succeeding days of cycle are prevented.
• New follicles develop towards the end of one cycle in
preparation for the next.
• Inhibin production is decreased at the end of luteal phase.
• Estrogen and progesterone levels also fall during the late
luteal phase ( starting about day 22) because corpus luteum
regresses and stops functioning.
• With the declining function of corpus luteum, esterogen and
progesterone fall to very low levels by day 28 of the cycle.
WITHDRAWL OF OVARIAN STEROIDS CAUSES MENSTRUATION AND
PERMETS A NEW CYCLE OF FOLLICLE DEVELOPMENT TO PROGRESS
Cyclic changes in the Endometrium
• Development of the endometrium is timed by the cyclic
changes in the secretion of estradiol and progesterone from
the ovarian follicles.
• Three phases can be identified:
– The proliferative phase.
– The secretory phase.
– The menstrual phase
The proliferative Phase
• occurs while the ovary is in follicular phase.
• Increasing amounts of estradiol stimulate proliferation of
stratum functionale of the endometrium.
• Spiral arteries develop in the endometrium.
• Estradiol stimulates the production of receptor proteins for
progesterone at this time, in preparation for the next phase of
the cycle.
The secretory phase
• Occurs when ovary is in its luteal phase.
• Increased progesterone secretion stimulates the development
of uterine glands.
• Endometrium becomes thick, vascular and ‘ spongy’ in
appearance.
• Uterine glands becomes engorged with glycogen during the
phase following ovulation.
• Endometrium is well prepared to accept and nourish an
embryo
.
Uterine changes in the menstrual cycle.
Endometrial depth
More secretion from the
glands – hence the
term “secretory phase”
Oestradiol
causes an
increase in
thickness (the
“proliferative
phase”)
0
4
8
12
Menstruation
16
20
24
28
OVULATION
The menstrual Phase
• Occurs as a result of fall in ovarian hormone secretion
during the late luteal phase .
• Necrosis and sloughing of the stratum functionale may
be produced by constriction of spiral arteries.
• It seems spiral arteries are responsible for menstrual
bleeding
Terminal differentiation of
stromal cells –
“decidualisation”
Characteristic “spiral arteries”
0
4
8
12
16
Menstruation
20
24
28
Optimal time for
implantation
Cyclic changes in the female reproductive tract
• High levels of estradiol secretion cause cornification of
vaginal epithelium. ( the upper cells die and become filled
with keratin.
• During luteal phase, high levels of progesterone cause the
cervical mucus to thicken and become sticky after ovulation
has occured.
CLINICAL
ABNORMAL MENSTRUATION :
Most common disorders of female reproductive tract.
•
•
•
Amenorrhea: Absence of Menstruation.
Dysmenorrhea : Painful menstruation which may be marked
by severe cramping.
Menorhagia: Excessively profuse or prolonged
bleeding.
Hormone involve in Pregnancy and Parturition
Normal Pregnancy
• Pregnancy
The course that the embryo and the fetus grow in the
maternal body
• Stages of pregnancy
Early pregnancy: ≤12 weeks
Mid pregnancy: ≥13 weeks,≤27 weeks
Late pregnancy:≥28 weeks
Term pregnancy:≥37 weeks,<42 weeks
Human Chorionic Gonadotropin Functions
• Prevents degeneration of corpus luteum
• Stimulates corpus luteum to secrete E + P which, in turn,
stimulate continual growth of endometrium.
• hCG stimulates leydig cells of male fetus to produce
testosterone in conjunction with fetal pituitary
gonadotrophins.Thus indirectly involved in development of
external genitalia.
• Suppresses maternal immune function & reduces possibility of
fetus immunorejection
• Stimulates maternal thyroid gland and development of fetal
adrenal glands.
Human Chorionic
Somatomammotropin
• effect on latation (HPL) ?
•growth hormone effects
•decreases insulin sensitivity - more
glucose for the fetus
• low levels - placental insuf.
Estrogen (E)
• FORMS-estriol,estradiol &estrone .
• Estriol most important .
• Levels increase throughout pregnancy
• 90% produced by placenta.(syncytiotrophoblast)
• Placental production is transferred to both maternal and fetal
compartments
• Main effects are:
• Stimulate growth of the myometrium and antagonize the
myometrial-suppressing activity of progesterone. In many
species, the high levels of estrogen in late gestation induces
myometrial oxytocin receptors, thereby preparing the uterus for
parturition.
• Stimulate mammary gland development. Estrogens are one
in a battery of hormones necessary for both ductal and alveolar
growth in the mammary gland.
• Inhibition of Prolactin secretion
Progesterone (P)
•
Levels increase throughout pregnancy
•
80-90% is produced by placenta and secreted to both fetus and mother
•
•
Progestins, including progesterone, have two major roles during pregnancy:
Support of the endometrium to provide an environment conducive to fetal
survival. If the endometrium is deprived of progestins, the pregnancy will
inevitably be terminated.
Suppression of contractility in uterine smooth muscle, which, if unchecked,
would clearly be a disaster. This is often called the "progesterone block" on the
myometrium. Toward the end of gestation, this myometrial-quieting effect is
antagonized by rising levels of estrogens, thereby facilitating parturition.
•
• Progesterone and other progestins also potently inhibit
secretion of the pituitary gonadotropins luteinizing hormone and
follicle stimulating hormone. This effect almost always prevents
ovulation from occurring during pregnancy
• Stimulates development of alveolar tissue of the
mammary gland
Placental hormones:
During early
pregnancy, HCG is
secreted by the
syncitial
trophoblasts.
Later, the placenta
secretes estradiol,
progesterone,
relaxin and somatomammotropin.
Function of placental hormones: (summary)
•
•
•
•
•
HCG is similar to LH and maintains the corpus luteum in a functional state for 34 months.
– This keeps progesterone levels high and they maintain the functional
endometrium.
Relaxin increases flexibility in the pelvic joints, as well as suppressing release of
oxytocin.
Placental progesterone keeps the uterine wall intact.
Somatomammotropin acts like prolactin and triggers the mammary glands to
develop.
Estrogen increases the sensitivity of the myometrium to mechanical irritation, as
well as oxytocin stimulation.
Parturition
Hormones and parturition
• Stimulants
– oxytocin
– PGF2a
– PGE2
•
Relaxants
–
–

–
PGE2
relaxin
-adrenergic
nitric oxide
• Endocrine
– sex steroids, oxytocin
• Paracrine
– amnion-chorion-decidua-myometrium
– sex steroids, oxytocin, prostaglandins, etc.
• Autocrine
–
–
–
–
–
thrombin
endothelin
AT II
a-adrenergic
vasopressin
Parturition
•
•
•
Parturition
–
Process by which a
baby is born
•
Labor
–
In mother
–
–
Estrogens overcome
inhibitory influence of
progesterone
–
Oxytocin is released
First stage
•
Second stage
•
In fetus
–
Adrenal gland is
enlarged prior
–
Onset of regular uterine
contraction until cervix
dilates to fetal head
diameter
From maximum cervical
dilation until baby exits
vagina
Third stage
•
Expulsion of placenta
from uterus
• Estrogen in late pregnancy:
– Stimulates production of oxytocin receptors in
myometrium.
– Produces receptors for prostaglandins.
– Produces gap junctions between myometrium cells in
uterus.
• Factors responsible for initiation of labor are incompletely
understood.
Factors Influencing Parturition
Regulators of Parturition
Parturition: The Process of Childbirth
• The mechanisms signaling the onset of labor are not clearly
understood, although several theories exist.
• Potential role of progesterone?:
- decreasing progesterone prior to labor would allow uterine
contractions to occur
- however, there is no decline in progesterone before labor in
humans
- some studies suggest there is a decline in uterine
progesterone receptors, resulting in decreased progesterone action,
leading to labor
Potential Role of Oxytocin in Parturition?
• Oxytocin causes uterine contraction.
• However, oxytocin levels do not increase until after labor
starts, according to more recent studies.
• Oxytocin may play a role in uterine contraction following
labor, resulting in decreased blood loss.
Potential Role of Relaxin in Parturition?
• Relaxin acts on the cervix, causing dilatation and softening.
• In some animals relaxin increases before labor starts.
• In humans, relaxin is high beginning early in pregnancy and stays
elevated until labor.
• Relaxin does act to soften connective tissues, such as the ligaments
connecting the pelvic bones, to allow increase in size of the birth
canal.
• Relaxin also decreases uterine contractility during pregnancy.
Potential Role of Prostaglandins in Parturition
Parturition
(continued)
• Prostaglandins cause dilation and softening of the cervix.
• Prostaglandins also cause uterine contractions.
• The levels of prostaglandins increase in fetal membranes before the
onset of labor.
• It is believed that some (unknown) signal from the fetus causes
increased prostaglandin production from fetal membranes, which then
act on the uterus and cervix to initiate labor.
• Fetal adrenal cortex:
– Chain of events may be set in motion through CRH
production.
– Fetal adrenal zone secretes DHEAS, which travel from
fetus and placenta.
• Uterine contractions:
– Oxytocin.
–
Prostaglandins.
Thank you for
attention