Human Circulatory System

In arteries the tunica media contains smooth muscle cells & elastic tissue, is thicker than that of veins so it can control and maintain blood pressure.

Capillaries are the smallest of a body's blood vessels, measuring 5-10 μm in diameter, which connect arterioles and venules, and enable the interchange of water, oxygen, carbon dioxide, and many other nutrients and waste chemical substances between blood and surrounding tissues. 

Veins are defined as blood vessels that carry blood toward the heart, whereas arteries carry blood away from the heart.

As blood is pumped by the heart directly into the aorta, the blood travels at 30 cm/sec. From the aorta, blood flows into the arteries and arterioles and, ultimately, to the capillary beds. As it reaches the capillary beds, the rate of flow is dramatically (one-thousand times) slower than the rate of flow in the aorta. 

The blood in the pulmonary artery is under less pressure since it is only being pumped a short distance to the lungs and so does not need a thick wall. The aorta (which transports the blood over greater distances) receives blood under greater pressure from the powerful left ventricle and so needs a thicker wall. The pulmonary valve (pulmonic valve) is the semilunar valve of the heart that lies between the right ventricle and the pulmonary artery. Valves are used to prevent backflow of blood. The pulmonary vein carries oxygenated blood from the lungs to the left side of the heart, from the pulmonary circulation. The heart contraction is enough to keep the blood flowing as the distance between the lungs and back to the heart is minimal compared to the systemic circulation. So, the pressure of the heart exerting is enough to keep the blood in one direction.

Arteries are blood vessels that carry blood away from the heart. While most arteries carry oxygenated blood, there are two exceptions to this, the pulmonary and the umbilical arteries. All veins carry blood towards the heart. 

Visceral pericardium receives blood from coronary artery while parietal and fibrous pericardium get blood supply from internal thoracic (mammary artery).

Pulmonary artery and the Pulmonary vein are a set of blood vessels that are related to the lungs. The Pulmonary artery carries deoxygenated blood from the right ventricle to the lungs for oxygenation, this oxygenated blood is carried back to the heart by the Pulmonary vein for systemic circulation i.e. for ​circulation to different parts of the body.

Veins are less muscular than arteries, contain valves to help keep blood flowing in the right direction, towards the heart. They carry deoxygenated blood from tissues back to the heart. 

• Materials, including oxygen, carbon dioxide, amino acids, sugars, and water, are exchanged between the blood and tissue fluid within blood vessels known as capillaries.
  
• Blood pressure and osmotic pressure control the pressure in a capillary. Blood pressure, caused by the heart’s beating, is higher at the arterial end of the capillary and causes water to exit at that point.
  
• On the other hand, blood pressure is weak by the time blood reaches the venous end of the capillary, and osmotic pressure becomes higher, causing water to enter at that end.
  

Aorta is the largest artery present in the body. It originates from the left ventricle and extends down to the abdomen. The aorta distributes oxygenated blood to all parts of the body.

Circulatory system or cardiovascular system is the organ system that helps to transport oxygen, nutrients, hormones etc to all the cell of the body. It consists of heart, veins, arteries, capillaries. Thus, the correct answer is option D.

The circulatory system transports gases, nutrients, and hormones. Nerve impulses are transmitted through the nervous system, not the circulatory system.