Which of the following is not an important step in the event of parturition ?

Options

A. High levels of estrogen , prostaglandins and oxytocin cause the smooth muscles of the uterus to contract.
B. The estrogen/ Progesterone ratio increase .
C. Increase in oxytocin levels due to the positive feedback effect.
D. Release of prolactin.

Answer

To solve the question "Which of the following is not an important step in the event of parturition?", we will analyze the process of parturition and identify the steps involved.

### Step-by-Step Solution:

**Step 1: Understand Parturition**
- Parturition, or childbirth, is the process of delivering a fully developed fetus from the uterus through the birth canal.

**Step 2: Identify Key Steps in Parturition**
- The process of parturition is initiated by a complex neuroendocrine mechanism, primarily involving signals from the fully developed fetus.
- The placenta plays a crucial role by inducing uterine contractions, which is referred to as the fetal ejection reflex.
- The release of the hormone oxytocin from the maternal pituitary gland is triggered, which further stimulates stronger uterine contractions.
- Prostaglandins are also released in response to oxytocin, contributing to uterine contractions.
- The balance of estrogen and progesterone shifts, with an increase in estrogen indicating the initiation of parturition.

**Step 3: Identify the Hormones Involved**
- Key hormones involved in the process of parturition include:
- Oxytocin: stimulates uterine contractions.
- Prostaglandins: enhance uterine contractions.
- Estrogen: increases to facilitate the process.
- Progesterone: decreases to allow contractions.

**Step 4: Determine the Role of Prolactin**
- Prolactin is a hormone that is released after parturition and is responsible for milk production in the mammary glands.
- Since prolactin is not directly involved in the actual process of childbirth but rather in the post-partum phase, it is not considered an important step in parturition.

**Step 5: Conclusion**
- Based on the analysis, the hormone prolactin is not an important step in the event of parturition. Therefore, the correct answer is the option that refers to prolactin.

### Final Answer:
The correct option is **Prolactin** (4th option).

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