The document summarizes reproductive cycles in mammals. It describes the estrous cycle found in most non-primate mammals, characterized by a brief period of fertility called estrus. The estrous cycle has four phases: proestrus, estrus, metestrus, and anestrus. It also describes the human menstrual cycle, which repeats monthly and is characterized by changes in the uterine lining and maturation and ovulation of follicles. If fertilization does not occur, the thickened uterine lining is shed as menstrual flow. Both cycles are regulated by hormones from the pituitary gland and ovaries.

1. Reproductive Cycles in
Mammals
Md Ekramuddin

2. What is reproductive Cycle
• Periodic changes in ovary and uterine
endometrium reproductively matured females
in most mammals to become capable of
breeding and to give birth of young is called
reproductive cycle.
• This is finely regulated by a set of hormones
from pituitary and ovary.

3. Types
Reproductive cycle
Estrous cycle Menstrual cycle

4. Estrous Cycle
• Found in most mammals except primates
• Derived from Latin oestrus meaning "frenzy“.
• There is a brief period of reproduction called
heat period or estrus
• 4 phases- proestrus, estrus, metestrus or
diestrus and anestrus

5. Features of proestrus
• One or several follicles of the ovary start to grow.
• Their number is species-specific.
• Typically this phase can last as little as one day or as long as three
weeks, depending on the species.
• Under the influence of estrogen, the lining of the uterus
(endometrium) starts to develop. Some animals may experience
vaginal secretions that could be bloody.
• The female is not yet sexually receptive; the old corpus
luteum degenerates; the uterus and the vagina distend and fill with
fluid, become contractile and secrete a sanguinous fluid; the vaginal
epithelium proliferates and the vaginal cytology shows a large
number of non-cornified nucleated epithelial cells.
• Variant terms for proestrus include pro-oestrus, proestrum, and pro-
oestrum.

6. Estrus
• Estrus or oestrus refers to the phase when the female
is sexually receptive ("in heat").
• Under regulation by gonadotropic hormones, ovarian
follicles mature and estrogen secretions exert their
biggest influence.
• The female then exhibits sexually receptive behavior, a
situation that may be signaled by visible physiologic
changes.
• In some species, the labia are reddened. Ovulation may
occur spontaneously in others.
• Especially among quadrupeds, a signal trait of estrus is
the lordosis reflex, in which the animal spontaneously
elevates her hindquarters.

7. Metestrus
• This phase is characterized by the activity of
the corpus luteum, which produces progesterone.
• The signs of estrogen stimulation subside and
the corpus luteum starts to form.
• The uterine lining begins to appear.
• In the absence of pregnancy the diestrus phase
(also termed pseudo-pregnancy) terminates with
the regression of the corpus luteum.
• The lining in the uterus is not shed, but is
reorganized for the next cycle.

8. Anestrus
• Anestrus refers to the phase when the sexual cycle rests.
• This is typically a seasonal event and controlled by light
exposure through the pineal gland that
releases melatonin.
• Melatonin may repress stimulation of reproduction in
long-day breeders and stimulate reproduction in short-
day breeders. Melatonin is thought to act by regulating
the hypothalamic pulse activity of the gonadotropin-
releasing hormone.
• After completion (or abortion) of a pregnancy, some
species have postpartum estrus, which is ovulation and
corpus luteum production that occurs immediately
following the birth of the young. For example,
the mouse has a fertile postpartum estrus that occurs 14
to 24 hours following parturition.

9. Menstrual cycle
• Repeats in every month (Gr. mensa=month)
• Found in primates
• Characterised by change in uterine endometrium
and maturation of an ovarian follicle and its
ovulation in every cycle.
• Uterine endometrium is made ready to receive
the embryo for implantation
• If no fertilization the thick endometrium is
released along with blood called menstrual flow

10. Ovarian Changes
Morphology of the
normal ovary changes dramatically during
the menstrual cycle.
The cyclic changes including maturation of the
follicles, ovulation, and progression and
regression of the luteal body are repeated in the
normal ovaries during the reproductive age
influenced by hormonal changes.
Phases of the menstrual cycle are menstruation,
the follicular phase, ovulation and the luteal
phase.

11. Ovarian changes

12. Ovarian phase and endometrial phase

13. More image

14. Uterine endometrial changes

15. Uterine change and hormones

16. Pituitary and ovarian hormones

17. Some terms
• Menarche- start of first menstrual flow in life
• Menopause- stop of menstrual flow for rest of
life
• Amenorrhoea- stop of menstrual flow for 3-4
cycles in reproductive life(not menopause)
• Dysmenorrhoea- painful and abnormal
menstrual flow
• LH surge- sudden increase(10-12 fold) of LH
secretion prior to ovulation

18. Thank you