Blood Vessels

Question 1

Why is the axillary artery divided into three parts?

Answer 1

The axillary artery is divided into three parts based on its relation to the pectoralis minor muscle, which acts as a landmark. This division has clinical significance for understanding the vascular supply to the upper limb and for surgical procedures. Here’s a breakdown:

1. First Part (Proximal to Pectoralis Minor)
   • Location: The first part of the axillary artery is located medial to the pectoralis minor.
   • Branches: It gives off the superior thoracic artery, which supplies the upper thoracic wall and the first two intercostal spaces.
2. Second Part (Posterior to Pectoralis Minor)
   • Location: The second part is located posterior to the pectoralis minor muscle.
   • Branches: It gives off two major branches:
   • Thoracoacromial artery: Supplies the shoulder and pectoral region.
   • Lateral thoracic artery: Supplies the lateral chest wall and the breast.
3. Third Part (Distal to Pectoralis Minor)
   • Location: The third part is located lateral to the pectoralis minor.
   • Branches: It gives off three main branches:
   • Subscapular artery: Supplies the subscapularis muscle, the latissimus dorsi, and parts of the scapular region.
   • Anterior circumflex humeral artery: Supplies the deltoid and the shoulder joint.
   • Posterior circumflex humeral artery: Supplies the deltoid, teres minor, and the shoulder joint.

Clinical Relevance:
• The division helps in identifying and understanding the blood supply to the shoulder and upper arm. It also aids in surgical interventions like vascular access and in cases of trauma, where knowledge of these divisions is essential for managing hemorrhage or arterial injuries.

Question 2

How does the collateral circulation around the elbow ensure blood flow during arterial blockage?

Answer 2

The collateral circulation around the elbow ensures continuous blood flow to the forearm and hand, even in the event of arterial blockage or narrowing, such as in cases of subclavian or brachial artery obstruction. This network of blood vessels provides alternative pathways for blood to reach the distal parts of the arm. Here’s how it works:

1. Key Arteries Involved:
   • Brachial artery: The main artery supplying blood to the arm.
   • Radial and Ulnar arteries: These are the two main branches of the brachial artery that supply the forearm and hand.
2. Collateral Circulation Pathways:

Several collateral arteries form anastomoses (connections) around the elbow, allowing blood to bypass any blockages in the main arteries:
• Radial recurrent artery: This artery arises from the radial artery and anastomoses with branches of the brachial artery.
• Ulnar recurrent arteries: These arise from the ulnar artery and connect with branches of the brachial artery.
• Interosseous recurrent artery: It comes from the posterior interosseous artery (a branch of the ulnar artery) and forms anastomoses with branches of the brachial artery.
• Profunda brachii artery: The deep brachial artery also contributes to collateral circulation via its branches, which form anastomoses with the radial recurrent artery and the ulnar recurrent arteries.

3. Function of Collateral Circulation:
   • In the case of blockage of the main brachial artery, blood can still reach the forearm and hand through the anastomotic vessels.
   • This collateral circulation helps prevent ischemia (lack of blood flow) and ensures the continued supply of oxygen and nutrients to the tissues, even when there is obstruction in the main arterial pathway.
4. Clinical Relevance:
   • In cases like arterial occlusion, vascular surgery, or trauma, collateral circulation helps maintain perfusion to the lower parts of the arm.
   • This system is also important in diagnosing arterial blockages as the presence of collateral circulation may delay symptoms of ischemia.

Question 3

Why is the radial artery commonly used for coronary artery bypass grafting?l

Answer 3

The radial artery is commonly used for coronary artery bypass grafting (CABG) due to several reasons:
1. Long-term Patency: Studies show that the radial artery has a good long-term success rate in maintaining open blood flow (patency) after CABG, making it a reliable graft choice.
2. Easy Accessibility: The radial artery is easily accessible through a small incision at the wrist, making it simpler to harvest compared to other vessels like the internal thoracic artery.
3. Sufficient Size: The radial artery has an appropriate diameter and length for use as a graft, allowing it to be easily connected to the coronary arteries.
4. Minimal Impact on Function: The radial artery can be safely harvested without significantly affecting the function of the forearm, as the ulnar artery provides adequate blood supply to the hand.
5. Reduced Risk of Infection: Since the radial artery is a superficial vessel, harvesting it carries a lower risk of complications like deep vein thrombosis or infection, compared to deeper vessels like the internal thoracic artery.

In summary, the radial artery is favored in CABG due to its reliable patency, easy access, and minimal functional impact.

Question 4

What is the clinical significance of the Allen’s test for arterial patency?

Answer 4

The Allen’s test is used to assess the patency of the radial and ulnar arteries and their ability to supply the hand with blood. It is clinically significant for ensuring adequate collateral circulation, particularly before procedures like arterial cannulation or harvesting the radial artery for coronary artery bypass grafting (CABG). Here’s why it’s important:

1. Purpose of the Test:
   • The test checks the blood supply to the hand through the radial and ulnar arteries.
   • It ensures that if one artery (e.g., the radial artery) is compromised, the other (e.g., the ulnar artery) can still supply sufficient blood to the hand.
2. How the Test Is Done:
   • The patient is asked to make a fist while pressure is applied to both the radial and ulnar arteries.
   • The patient then opens the hand, which should appear pale.
   • Pressure on the ulnar artery is released, and if the hand reperfusion occurs (i.e., the hand flushes with blood), the ulnar artery is patent and compensates for the radial artery.
   • The test is repeated by releasing pressure on the radial artery to check ulnar patency.
3. Clinical Significance:
   • For radial artery harvesting: Before using the radial artery for CABG, it’s important to confirm that the ulnar artery is providing sufficient blood flow to the hand.
   • For arterial cannulation: Ensures that there is an adequate collateral supply to the hand if the radial artery is used for cannulation or other procedures.
   • Arterial insufficiency: A positive Allen’s test (failure of the hand to reperfuse) indicates insufficient collateral circulation, which could increase the risk of complications in surgeries involving the radial artery.

Question 5

Why is the cephalic vein preferred for intravenous cannulation?

Answer 5

The cephalic vein is preferred for intravenous cannulation due to several reasons:
1. Superficial Location: The cephalic vein is located just beneath the skin, making it easily accessible for insertion of an intravenous (IV) line.
2. Large Size: It is relatively large in diameter, which allows for the easy passage of cannulas and makes it ideal for delivering fluids, medications, or drawing blood.
3. Easily Palpable: In most people, the cephalic vein can be easily felt and located, especially in the lateral aspect of the forearm or upper arm, providing a straightforward access point.
4. Low Risk of Complications: The cephalic vein is less likely to be in close proximity to major nerves or arteries compared to other veins like the basilic vein, reducing the risk of complications during cannulation.
5. Reliable Access: It is a consistent vein with reliable access, even in cases of difficult venous access, making it a good choice for emergency or repeated access.

Question 6

How does the venous drainage of the upper limb ensure efficient circulation?

Answer 6

The venous drainage of the upper limb ensures efficient circulation through a network of superficial and deep veins that work together to return blood to the heart. Key aspects of this system include:

1. Superficial Veins:
   • Cephalic vein: Drains the lateral side of the upper limb and drains into the axillary vein.
   • Basilic vein: Drains the medial side and joins the brachial veins to form the axillary vein.
   • Median cubital vein: A common site for venipuncture, it connects the cephalic and basilic veins at the elbow, allowing easy venous access.
2. Deep Veins:
   • Brachial veins: These accompany the brachial artery and drain the deep tissues of the upper limb, joining the basilic vein to form the axillary vein.
   • Axillary vein: Drains blood from the upper limb into the subclavian vein, which then joins the internal jugular vein to form the brachiocephalic vein, eventually leading to the superior vena cava.
3. Valves in Veins:
   • The venous valves in both superficial and deep veins prevent backflow and promote unidirectional flow of blood toward the heart, especially during activities like arm movement or when standing.
4. Connection Between Superficial and Deep Systems:
   • Perforating veins connect the superficial veins to the deep veins, allowing efficient blood transfer between the two systems. This helps in maintaining pressure balance and promoting proper venous return to the heart.
5. Muscle Pump:
   • Muscle contractions during movement help to push blood from the veins in the upper limb toward the heart, aiding circulation and preventing blood stasis.

Question 7

Why is the brachial artery used for blood pressure measurement?

Answer 7

The brachial artery is used for blood pressure measurement due to the following reasons:
1. Accessibility: The brachial artery is easily accessible at the antecubital fossa (the bend of the elbow), making it convenient for clinicians to place the sphygmomanometer cuff and stethoscope to measure blood pressure.
2. Size: The brachial artery is a relatively large vessel, ensuring a clear and consistent reading when measuring blood pressure, especially in adult patients.
3. Appropriate Pressure Point: The brachial artery is at a level close to the heart, providing an accurate reflection of central arterial pressure, which is used to assess overall cardiovascular health.
4. Stable and Reliable: The brachial artery is less influenced by muscle activity or external movement, providing more stable and reliable measurements than arteries in other locations, such as the radial or femoral arteries.

Question 8

How does the anastomosis at the hand ensure adequate blood supply despite injuries?

Answer 8

The anastomosis at the hand ensures adequate blood supply despite injuries through a network of interconnected arteries that provide alternative routes for blood flow. This system allows the hand to continue receiving oxygenated blood even if one or more arteries are damaged. Key features include:

1. Arterial Anastomoses:
   • Radial and ulnar arteries: The radial and ulnar arteries are the main blood supply to the hand. They form anastomoses with each other through smaller vessels.
   • Deep and superficial palmar arches: These are formed by the radial and ulnar arteries. The deep palmar arch is primarily supplied by the radial artery, while the superficial palmar arch is mostly supplied by the ulnar artery. These arches connect the major arteries, ensuring continued blood flow to the hand.
2. Collateral Circulation:
   • In case of an injury or obstruction in one of the main arteries (e.g., radial or ulnar), blood can be diverted through the collateral circulation, which includes branches from the palmar arches and digital arteries.
3. Flexibility in Blood Supply:
   • If one artery is blocked or injured (for example, due to trauma or surgery), the anastomoses between the arteries allow the other artery to take over the blood supply, maintaining perfusion to the fingers and hand.
4. Function of Digital Arteries:
   • The digital arteries supply the fingers and receive blood from both the superficial and deep palmar arches, further contributing to the hand’s ability to compensate for injuries.

Question 9

Why is the superficial palmar arch more prone to the injury than the deep palmar arch?

Answer 9

The superficial palmar arch is more prone to injury than the deep palmar arch due to its anatomical location and structure:

1. Closer to the Surface:
   • The superficial palmar arch is located just beneath the skin, making it more exposed and vulnerable to cuts, lacerations, or trauma, especially in the palm of the hand.
   • In contrast, the deep palmar arch is situated deeper in the hand, beneath muscles and tendons, which provides more protection from external injuries.
2. Position in the Hand:
   • The superficial palmar arch lies just above the flexor tendons and closer to the skin, whereas the deep palmar arch is located closer to the bones and is shielded by the surrounding structures.
3. Anatomical Variation:
   • The superficial palmar arch is mainly formed by the ulnar artery, which is more superficial compared to the radial artery that contributes to the deep palmar arch. The ulnar artery is more vulnerable to injury, particularly in the palm and wrist areas.
4. Function of the Arteries:
   • The deep palmar arch provides the main blood supply to the hand, while the superficial palmar arch is more involved in supplying blood to the fingers. Despite the superficial arch being more prone to injury, the deep arch and collateral circulation can often compensate for the loss of the superficial arch.

Question 10

What is the clinical relevance of the venae comitantes accompanying the brachial artery?

Answer 10

The venae comitantes accompanying the brachial artery have several clinical significances:
1. Aid in Venous Return: They help return blood from deeper tissues in the arm.
2. Venous Access: Used in IV cannulation or arterial access when other veins are not available.
3. Hemodialysis: Can be used in creating fistulas for dialysis.
4. Pressure Regulation: Help maintain proper circulation and prevent venous stasis.
5. Protection: Provide some protection to the brachial artery and assist with temperature regulation.
6. Trauma Management: Serve as collateral circulation if the main artery is injured.