Human Circulatory System

These are the two large veins, which carry deoxygenated blood to the right atrium.

Squamous epithelium forms the outermost layer of skin, and lines the body's cavities and other parts. These include the heart, alveoli, the blood and lymph vessels and the oesophagus.

Yes, it is the correct answer. Statements a and d are incorrect. 

The increase in the supply of blood to skin by widening the blood vessels is called vasodilation. This results in greater loss of heat from body.

Aneurysm represents a blood-containing tumor connected directly with the lumen of an artery.

Tumor vasculature originates through the process of angiogenesis in which existing blood vessels are recruited and remodelled to provide increased hyper blood flow to avascular tumor tissues.

After birth, the ductus arteriosus (a fetal shunt between pulmonary artery and aorta) closes and becomes the ligamentum arteriosum, a fibrous connective tissue remnant. The fossa ovalis is the remnant of the foramen ovale (atrial septal defect).

Venae cavae are the two largest veins in the body that carry deoxygenated blood from various regions of the body to the right atrium of the heart. The superior vena cava located in the upper chest region is formed by the joining of the brachiocephalic veins and the inferior vena cava is formed by the joining of the common iliac veins, which meet a little below the small of the neck.

It is the largest artery in the body originating from the left ventricle of the heart and extending down to the abdomen, where it bifurcates into two smaller arteries. The aorta distributes oxygenated blood to all parts of the body through the systemic circulation. Damage to the aorta can threaten vital functions and can even cause death.

A venule is a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to the larger blood vessels called veins. Venules are blood vessels that drain blood directly from the capillary beds. Many venules unite to form a vein.

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.