**Question:** First organ to attain functional maturity is:

A. Liver
B. Kidney
C. Lung
D. Heart

**Core Concept:** In human development, the organs reach functional maturity in a specific sequence, which is essential for understanding organ interactions and ensuring proper organogenesis.

**Why the Correct Answer is Right:** The correct answer is **D. Heart**. The heart is considered the first organ to attain functional maturity during fetal development. This is due to the heart being a vital organ with specific functions that need to be performed early on.

**Why Each Wrong Option is Incorrect:**

A. Liver (Answer C): While liver development is vital, it usually attains functional maturity after the cardiovascular system, around the 9th week of gestation.

B. Kidney (Answer B): Kidney development occurs later than the cardiovascular system, but it does not reach full maturity until after birth.

C. Lung (Answer C): Lung development is crucial, but it attains functional maturity after the cardiovascular system, around the 26th week of gestation.

**Clinical Pearl / High-Yield Fact:** Understanding organ maturation sequences helps in diagnosing congenital anomalies, such as those affecting the cardiovascular or respiratory systems. For example, respiratory distress syndrome (RDS) is related to immature lungs, while congenital heart defects often manifest due to developmental abnormalities in the cardiovascular system.

**Correct Answer:** D. Heart