Question

What is the correct order of occurrence of 4 phases of oestrus cycle?

• A. Proestrus -- Oestrus -- Dioestrus -- Metestrus
• B. Oestrus -- Metestrus -- Proestrus -- Dioestrus
• C. Proestrus -- Oestrus -- Metestrus -- Dioestrus
• D. Dioestrus -- Metestrus -- Proestrus -- Oestrus

Hint:

Use the sequential logic of the ovarian structures to remember the order:
Developing Follicle (Proestrus) \(\rightarrow\) Mature Follicle (Estrus) \(\rightarrow\) Developing CL (Metestrus) \(\rightarrow\) Mature CL (Diestrus).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The estrous cycle is a rhythmic physiological process in female mammals regulated by the endocrine system.
The cycle is divided into four distinct phases based on behavioral changes, hormonal dominance, and ovarian structures.
Detailed Explanation:
The chronological sequence of the estrous cycle starting from the follicular development phase is as follows:
1. Proestrus: This is the follicular phase preceding heat.
Under the influence of follicle-stimulating hormone (FSH), ovarian follicles grow rapidly and secrete estrogen.
2. Estrus: This is the period of sexual receptivity (heat).
High estrogen levels trigger the release of luteinizing hormone (LH), leading to ovulation in most species.
3. Metestrus: This is the post-ovulatory transition phase.
Estrogen levels fall, and the cells of the ruptured follicle begin to luteinize, forming the early corpus luteum (CL).
Progesterone production starts to increase.
4. Diestrus: This is the mature luteal phase.
The corpus luteum is fully functional and produces high levels of progesterone.
If pregnancy does not occur, luteolysis takes place, and the cycle repeats starting with proestrus.
Therefore, the correct order is: Proestrus \(\rightarrow\) Estrus \(\rightarrow\) Metestrus \(\rightarrow\) Diestrus.

Step 2: Final Answer:
The correct order of occurrence is Proestrus -- Oestrus -- Metestrus -- Dioestrus.