**Question:** All the following are tributaries of Superior vena cava except

A. Right subclavian artery
B. Right hepatic vein
C. Right renal vein
D. Right testicular vein

**Correct Answer: D. Right testicular vein**

**Core Concept:**
The Superior vena cava (SVC) is the main trunk of the venous system in the upper body, returning deoxygenated blood to the right atrium of the heart. It receives blood from various tributaries or veins, which are the smaller vessels that join the SVC.

**Why the Correct Answer is Right:**
The correct answer, "Right testicular vein," is not a tributary of the Superior vena cava because it is a drainage vein for the testicle in the male reproductive system. The right testicular vein, along with its counterpart on the left side, collects blood from the testis and epididymis and transports it to the pampiniform plexus, which further drains into the internal iliac veins and eventually joins the inferior vena cava. This process is specific to the male reproductive system and does not contribute to the blood flow in the Superior vena cava.

**Why Each Wrong Option is Incorrect:**
A. Right subclavian artery (Option A) is incorrect because it is an artery, not a vein. Arteries carry oxygenated blood away from the heart, while veins carry deoxygenated blood towards the heart.

B. Right hepatic vein (Option B) is incorrect because it is a tributary of the inferior vena cava (IVC), not the superior vena cava (SVC). The IVC receives blood from the liver and lower body, while the SVC collects blood from the head, neck, upper limbs, and thoracic organs.

C. Right renal vein (Option C) is incorrect because it is a tributary of the inferior vena cava (IVC), not the superior vena cava (SVC). The IVC receives blood from the kidneys, while the SVC collects blood from the head, neck, upper limbs, and thoracic organs.

**Core Concept:**
The Superior vena cava (SVC) is an essential part of the venous system in the human body, responsible for returning blood from the head, neck, upper limbs, and thoracic organs to the right atrium of the heart, where it is pumped to the rest of the body. Understanding the anatomy of the venous system helps students understand how blood returns to the heart and ultimately circulates throughout the body.

**Why Each Wrong Option is Incorrect:**
Option A (Right subclavian artery) and Option B (Right hepatic vein) are arteries and not veins, which are responsible for returning blood to the heart. Option C (Right renal vein) is a tributary of the inferior vena cava, not the superior vena cava. The inferior vena cava receives blood from the kidneys, while the superior vena cava collects blood from the head, neck, upper limbs, and thoracic organs.