Which change occurs in the uterine lining in response to the normal reproductive hormones to support implantation?

• A. Thickening of the lining
• B. Thinning of the lining
• C. Shrinking of the lining
• D. No change to the lining

Answer: (A)

The uterus prepares a receptive lining by increasing its thickness in response to normal reproductive hormones. Estrogen drives the proliferative phase, rebuilding and thickening the endometrium after menstruation. After ovulation, progesterone from the corpus luteum transforms this thickened lining into a secretory, highly vascular and glandular environment, rich in nutrients to support a developing embryo. This thickening and secretory transformation create the suitable substrate for implantation. If the lining didn’t thicken, or instead thinned or remained unchanged, there wouldn’t be enough tissue and nourishment for an implanted conceptus.