Human Circulatory System

The renal vein carries blood AWAY from the kidneys after urea has been filtered out and excreted in urine, so it has the lowest urea concentration. The renal artery brings blood TO the kidneys with high urea content that needs to be removed. The dorsal aorta and posterior vena cava carry systemic blood with intermediate urea levels. Since the kidneys' job is to remove urea from blood, the blood leaving them (renal vein) has the least amount of it.

Arterial blood has a higher pH (more alkaline, ~7.45) than venous blood (~7.35) because arterial blood carries oxygen and has less carbon dioxide. Venous blood returning from tissues has accumulated CO2 and metabolic waste, making it slightly more acidic. The pH difference is small but physiologically significant. They are not the same, and the difference is definite and consistent in healthy circulation.

Elastic arteries like the aorta need to stretch and recoil with each heartbeat to maintain continuous blood flow. Their tunica media (middle layer) is rich in elastic fibers, primarily elastin, which provide this essential elasticity. Smooth muscle fibers are present but are more prominent in muscular arteries that regulate blood flow through vasoconstriction. Collagen provides strength but not stretch. Loose alveolar tissue is not a major component of arterial walls.

Pulmonary veins are the ONLY veins in the body that carry oxygenated blood. They transport freshly oxygenated blood from the lungs back to the left atrium of the heart. Arteries normally carry oxygenated blood away from the heart (except for pulmonary arteries), and veins normally carry deoxygenated blood toward the heart. Pulmonary veins are the exceptional case - they're veins that carry 'pure' (oxygenated) blood.

Blood capillaries consist of a single layer of endothelial cells resting on a basement membrane, which allows for efficient exchange of gases, nutrients, and wastes between blood and surrounding tissues. They lack connective tissue and smooth muscle in their walls.

A portal vein system is characterized by a vein that originates from capillaries in one organ (e.g., capillaries in the gastrointestinal tract), travels to another organ without first returning to the heart, and then breaks into a second capillary network (e.g., in the liver). The hepatic portal system is the classic example.

Arteries are thick-walled vessels that carry blood away from the heart under high pressure generated by ventricular contraction. Their walls contain smooth muscle and elastic tissue to withstand and maintain this pressure, ensuring efficient distribution of oxygenated blood throughout the body.

The aorta descends from the thoracic cavity through the aortic hiatus in the diaphragm at vertebral level T12, but this is more of a passage behind the diaphragm rather than a true penetration. In contrast, the inferior vena cava passes through the vena caval hiatus, and the esophagus passes through the esophageal hiatus: both are true openings in the diaphragm. The aorta's relationship is different; it passes posteriorly without actually going through an opening in the diaphragmatic muscle.

The pulmonary artery is the exception among arteries, carrying deoxygenated blood from the heart to the lungs. Conversely, the pulmonary vein is the exception among veins, carrying oxygenated blood from the lungs back to the heart.

Hypotension is the medical term for abnormally low blood pressure, typically defined as systolic pressure below 90 mmHg. It can cause dizziness, fainting, and inadequate blood flow to organs.

Veins carry blood towards the heart. Superior and inferior vena cava perform this function.

The renal vein carries deoxygenated blood away from the kidney toward the inferior vena cava. The afferent arteriole brings blood TO the glomerulus, and efferent arteriole carries blood away FROM the glomerulus (but still within kidney). Renal portal veins are found in lower vertebrates like birds and reptiles, not mammals. Renal vein is the correct answer for the vessel that 'takes away blood from the kidney.'

Yes, it is correct. The pulmonary vein carries the impure blood from the heart to the lungs. It carries carbon di oxide rich blood to the lungs.

Yes, it is correct. The valves present in the veins allow blood to flow only towards the heart.

This is the correct option as this statement is false. Plasma is a viscous fluid that constitutes nearly 55 percent of the blood.