Q.Write difference between estrus cycle and menstrual cycle.

The human menstrual cycle proceeds: menstrual (bleeding) phase → follicular (proliferative) phase → ovulatory phase (ovulation ~day 14) → luteal (secretory) phase.

Phases of the ~28-day menstrual cycle:

1. Bleeding / menstrual phase (days 1–5): breakdown and shedding of the endometrium.
2. Follicular (proliferative) phase: FSH drives Graafian-follicle growth; oestrogen regenerates the endometrium.
3. Ovulatory phase: an LH surge triggers ovulation (release of the secondary oocyte, ~day 14). …

After ovulation, the remaining follicular tissue transforms into the corpus luteum, which acts as a temporary endocrine gland and secretes progesterone to maintain the endometrium for implantation.

After the Graafian follicle ruptures and releases the ovum (ovulation), the leftover follicular cells reorganise into the corpus luteum. This yellowish body functions as a temporary endocrine gland and secretes large amounts of progesterone, which prepares and maintains the uterine endometrium for possible implantation and pregnancy. If fertilization does not occur, the corpus luteum degenerates.

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In an idealised 28-day human menstrual cycle, ovulation (release of the ovum from the Graafian follicle) occurs around day 14, triggered by the mid-cycle LH surge.

The ovarian/menstrual cycle can be divided into phases:

• Menstrual phase (~day 1–5): shedding of the uterine lining.
• Follicular phase (~day 1–13): a follicle matures into the Graafian follicle under FSH/LH influence; oestrogen rises. …

Progesterone from the corpus luteum maintains the endometrium, which is essential for implantation and pregnancy.

Menarche marks the onset of puberty in females — the first menstrual bleeding, signalling the start of reproductive capability.

At puberty, rising levels of gonadotropins (FSH and LH) stimulate the ovaries to begin producing oestrogen, which triggers maturation of the reproductive system and the start of the menstrual cycle. The very first such menstrual flow a girl experiences, typically between the ages of 11-13 years, is termed menarche. It is distinct from menopause (the permanent c …

(d) Corpus albicans.

Without fertilization, the corpus luteum degenerates into a small fibrous scar called the corpus albicans.

After ovulation, the ruptured Graafian follicle transforms into the corpus luteum, which secretes progesterone to maintain the uterine lining in case of pregnancy. If fertilization does not occur, the corpus luteum degenerates (about day 24-26 of the cycle) into a small, white, fibrous mass called the corpus albicans, progesterone secretion falls, and menstruation follows. Tunica albuginea is the fibrou …

The corpus luteum is the ovarian structure that secretes progesterone, the hormone that maintains the uterine lining for pregnancy.

After ovulation, the ruptured Graafian follicle is transformed by LH (the mid-cycle LH surge) into the corpus luteum, a temporary endocrine structure in the ovary.

• Its main secretion is progesterone, along with small amounts of estrogen and relaxin.
• Progesterone maintains the secretory endometrium, preparing it for implantation, and suppresses further follicular development (and hence FSH/LH release) during the luteal phase.
• If fertilisation does not occur, the corpus luteum degenerates (into the corpus albicans) after about 10-14 days, progesterone levels fall, and menstruation follows.

Why the other options are wrong: …

The menstrual cycle in women is on average about 28–29 days — option (b).

Concept: The menstrual cycle is the cyclic reproductive change in the human female, counted from the first day of one menses to the first day of the next. It is driven by pituitary hormones (FSH, LH) and ovarian hormones (estrogen, progesterone).

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In a typical 28-day menstrual cycle, ovulation (release of the secondary oocyte from the ovary) occurs near the midpoint of the cycle, around day 14 — within the 12–16 day range.

The menstrual cycle has three main phases: the menstrual phase (days 1–5, shedding of the endometrium), the follicular/proliferative phase (up to around day 13–14, during which a follicle matures under FSH and the endometrium regenerates under rising oestrogen), ovulation (a surge of LH around day 14 triggers release of the secondary oocyte from the Graafian follicle), and …

Menarche = the very first menstrual period; it starts the repeating menstrual cycle at puberty.

At puberty, rising levels of gonadotropins (FSH, LH) trigger ovarian and uterine changes that culminate in the first menstrual bleeding, called menarche. This event marks the beginning of the cyclic (roughly 28-day) menstrual cycle that continues until menopause.

• (b) Menses is the monthly bleeding phase of each cycle (not specifically the first one). …

The corpus luteum, formed from the ruptured follicle after ovulation, mainly secretes progesterone, the hormone that maintains the uterine lining for pregnancy.

Formation and role of the corpus luteum

• After ovulation, the remnants of the Graafian follicle in the ovary develop into a temporary endocrine structure called the corpus luteum.
• The corpus luteum secretes large quantities of progesterone, which is essential for maintaining the endometrium (uterine lining) so that it can support implantation of the embryo, should fertilization occur. …

Menarche = the first menstruation, marking the beginning of a female's reproductive years.

At puberty, hormonal changes (rise in GnRH, FSH, LH, and ovarian oestrogen) trigger the maturation of the reproductive system. In a human female this is marked by menarche — the first occurrence of the menstrual cycle. It signals that the ovaries and uterus have become functional and that cyclical ovulation and menstruation have begun, continu …