What is the primary function of capillaries?

A. E (Brachiocephalic vein): The brachiocephalic veins are large veins formed by the union of the internal jugular and subclavian veins on each side of the body. The left and right brachiocephalic veins converge to form the superior vena cava. They serve as major conduits for venous blood returning from the head, neck, upper limbs, and thorax to the heart.

B. A (Vertebral vein): The vertebral veins accompany the vertebral arteries within the transverse foramina of the cervical vertebrae. They drain the cervical spinal cord, vertebrae, deep neck muscles, and portions of the posterior brain. These veins empty into the brachiocephalic veins, providing a deep venous return pathway from the neck and posterior cranial structures.

C. C (Internal jugular vein): The internal jugular veins are the principal veins that drain blood from the brain, superficial face, and neck. They originate from the dural venous sinuses at the base of the skull and descend within the carotid sheath lateral to the internal carotid artery and common carotid artery. They join the subclavian veins to form the brachiocephalic veins.

D. F (Superior vena cava): The superior vena cava is a large, short vein that carries deoxygenated blood from the head, neck, upper limbs, and thoracic structures into the right atrium. It is formed by the convergence of the left and right brachiocephalic veins and lies in the superior mediastinum, anterior to the trachea and to the right of the ascending aorta.

A. Warm and flushed skin: Warm, flushed skin typically indicates vasodilation and increased blood flow rather than impaired perfusion. It is often seen in fever, inflammation, or early sepsis and generally reflects adequate tissue oxygenation, not compromise.

B. Elevated oxygen saturation levels: High oxygen saturation (SpO₂) usually indicates sufficient oxygen delivery to the tissues. While oxygen saturation measures arterial oxygenation, it does not reflect impaired microcirculatory perfusion; tissues can still be hypoperfused despite normal SpO₂ in certain shock states.

C. Bluish discoloration of the skin (cyanosis): Cyanosis occurs when there is an increased amount of deoxygenated hemoglobin in the blood or inadequate oxygen delivery to tissues. It is a direct clinical sign of compromised tissue perfusion and impaired oxygenation, often first visible in lips, nail beds, or earlobes, signaling urgent need for assessment.

D. Increased capillary refill speed: Normally, capillary refill is under 2 seconds. A faster-than-normal refill usually indicates vasodilation or hyperdynamic circulation rather than compromised perfusion. Sluggish or delayed capillary refill is a more reliable indicator of reduced peripheral perfusion.