Final answer:
At puberty, estrogen levels lead to the growth of the uterus, ovaries, and breasts, which are directly involved in the reproductive cycle and the development of secondary sexual characteristics.
Step-by-step explanation:
The organs/tissues/structures that increase in size in response to increasing estrogen levels at puberty are the uterus, ovaries, and breasts. Estrogen, which is produced by the ovaries during puberty, stimulates these structures to grow and develop as part of the maturation process. Specifically, the uterus and ovaries grow to facilitate the reproductive cycle, and the breasts develop as one of the female secondary sexual characteristics. The fallopian tubes also mature in response to estrogen, contributing to the reproductive system's preparedness for potential pregnancy. Unlike these, other listed structures such as the brain, adrenal glands, kidneys, long bones, and heart are not prominently affected by estrogen in regards to increasing in size during puberty.