The correct option is 1 and 3 only.
Explanation
Oxytocin is a peptide hormone synthesized by the hypothalamus and released by the posterior pituitary gland (neurohypophysis). It acts primarily on smooth muscles within the body and stimulates their contraction. It plays a critical role in female reproductive physiology, specifically during childbirth and lactation.
Statement-wise Analysis
- Statement 1 is Correct: Oxytocin acts on the smooth muscles of the uterus. During the later stages of pregnancy, it stimulates vigorous contractions of the uterine smooth muscles, which is essential for the expulsion of the foetus. This process is known as parturition (childbirth).
- Statement 2 is Incorrect: Oxytocin does not inhibit milk ejection; rather, it stimulates it. While Prolactin is responsible for the synthesis and production of milk, Oxytocin acts on the myoepithelial cells of the mammary glands to cause contraction. This contraction forces milk from the alveoli into the ducts, a process known as the "milk let-down" or milk ejection reflex.
- Statement 3 is Correct: The primary physiological mechanism of oxytocin is the stimulation of smooth muscle contraction. This applies to both the uterine muscles during labor and the smooth muscle-like myoepithelial cells in the mammary glands during lactation.
Key Takeaway: Oxytocin is known as the "birth hormone" and the "milk-ejecting hormone." It stimulates smooth muscle contraction to facilitate parturition and the milk let-down reflex, whereas Prolactin is responsible for milk synthesis.