1050
UNIT 5
Continuity
27
(a) Fluctuation of gonadotropin levels:
Fluctuating
levels of pituitary gonadotropins (follicle-stimulating
hormone and luteinizing hormone) in the blood
regulate the events of the ovarian cycle.
(b) Ovarian cycle:
Structural changes in the ovarian
follicles during the ovarian cycle are correlated with
(d) changes in the endometrium of the uterus during
the uterine cycle.
(c) Fluctuation of ovarian hormone levels:
Fluctuating levels of ovarian hormones (estrogens
and progesterone) cause the endometrial changes
of the uterine cycle. The high estrogen levels are
also responsible for the LH/FSH surge in (a).
(d) The three phases of the uterine cycle:
• Menstrual: The functional layer of the
endometrium is shed.
• Proliferative: The functional layer of the
endometrium is rebuilt.
• Secretory: Begins immediately after ovulation.
Enrichment of the blood supply and glandular
secretion of nutrients prepare the endometrium
to receive an embryo.
Both the menstrual and proliferative phases occur
before ovulation, and together they correspond to the
follicular phase of the ovarian cycle. The secretory
phase corresponds in time to the luteal phase of the
ovarian cycle.
(a) Fluc
leve
horm
regu
(c) Fluc
Fluc
and
of th
also
(d) c
the u
(b) Ova
follic
end
• Pr
o
end
Se
En
sec
to r
Both the
before o
follicular
phase c
ovarian
(d) The
±
Me
en
Menstrual
phase
Menstrual
flow
Endometrial
glands
Blood vessels
Functional
layer
Basal layer
Proliferative
phase
Secretory
phase
1
5
10
15
20
25
Days
28
FSH
LH
Plasma hormone level
Progesterone
Estrogens
Plasma hormone level
Primary
follicle
Secondary
follicle
Vesicular
follicle
Ovulation
Corpus
luteum
Degenerating
corpus luteum
Follicular
phase
Ovulation
(Day 14)
Luteal
phase
Figure 27.22
Correlation of anterior pituitary and ovarian hormones with structural
changes of the ovary and uterus.
The time bar at the bottom of the figure, reading Days
1 to 28, applies to all four parts of this figure. (For a related image, see
A Brief Atlas of the
Human Body
, Plate 53.)
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