Arterioles are referred to as "resistance vessels" because they:

A. To increase systemic blood pressure in response to low oxygen levels: Systemic blood pressure regulation is primarily controlled by the autonomic nervous system and endocrine responses, not by tissue-level autoregulation. Autoregulation acts locally rather than influencing overall systemic pressure.

B. To regulate perfusion through signals from the central nervous system: While the CNS can influence vascular tone via sympathetic output, autoregulation is independent of central input. It relies on local factors within the tissue to adjust blood flow to meet metabolic demands.

C. To adjust blood flow based on local chemical and pressure signals: Autoregulation ensures that tissue perfusion matches local needs by responding to changes in oxygen, carbon dioxide, pH, and local blood pressure. Vasodilation or vasoconstriction occurs directly within the tissue’s arterioles to maintain optimal nutrient and oxygen delivery.

D. To ensure constant blood flow regardless of local metabolic activity: Autoregulation does not override metabolic demands; instead, it fine-tunes blood flow according to local chemical and pressure cues. Constant flow regardless of tissue activity could lead to hypoxia or excess perfusion, which autoregulation prevents.

Axillary Artery: C

Left Subclavian Artery: K

Ulnar Artery: F

Superficial Palmar Arch: H

A. Axillary artery: The axillary artery, presented by letter C is the continuation of the subclavian artery. It courses through the axilla and becomes the brachial artery at the inferior border of the teres major muscle. It gives off key branches including the thoracoacromial, lateral thoracic, subscapular, and anterior and posterior circumflex humeral arteries. It supplies the shoulder joint, lateral thoracic wall, and upper limb.

B. Left Subclavian artery: The left subclavian artery presented as K arises from the arch of the aorta, posterior to the left common carotid artery. It travels laterally toward the upper limb, arching over the apex of the lung and passing between the anterior and middle scalene muscles. It supplies blood to the brain (via the vertebral artery), thoracic wall, and left upper extremity.

C. Ulnar artery: The ulnar artery as F is one of the two terminal branches of the brachial artery, arising in the cubital fossa opposite the neck of the radius. It travels along the medial (ulnar) side of the forearm. It primarily forms the superficial palmar arch and supplies the medial forearm, hand muscles, and digits, particularly the medial three and a half fingers.

D. Superficial palmar arch: The superficial palmar arch as H, is an arterial arcade in the palm primarily formed by the ulnar artery, with contribution from the superficial branch of the radial artery. From this arch arise the common palmar digital arteries, which divide into proper digital arteries supplying the fingers, ensuring collateral circulation within the hand.