Major Blood Vessels

Why This Matters

Blood vessels aren't just anatomical tubes to memorize—they're the body's highway system, and understanding their organization reveals how the cardiovascular system maintains life. You're being tested on your ability to trace blood flow through both systemic and pulmonary circuits, identify where vessels branch and merge, and explain why certain vessels carry oxygenated versus deoxygenated blood. Exams frequently ask you to follow blood from a specific organ back to the heart, or to explain clinical applications like where to check a pulse or measure blood pressure.

The key concepts you need to master include systemic versus pulmonary circulation, arterial branching patterns, venous drainage and return, and portal circulation. Don't just memorize vessel names—know what circuit each vessel belongs to, what structures it supplies or drains, and how it connects to neighboring vessels. When you understand the logic of vascular organization, tracing any pathway becomes straightforward.

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Pulmonary Circuit Vessels

The pulmonary circuit is short but conceptually tricky because it reverses the usual oxygen rules. Arteries carry blood away from the heart (regardless of oxygen content), and veins carry blood toward the heart. In the pulmonary circuit, this means arteries carry deoxygenated blood and veins carry oxygenated blood.

Pulmonary Arteries

• Only arteries carrying deoxygenated blood—this is the most commonly tested exception to the "arteries = oxygenated" rule
• Originate from the right ventricle and bifurcate into left and right branches, each entering its respective lung
• Enable gas exchange by delivering blood to pulmonary capillaries where $CO_2$ is released and $O_2$ is absorbed

Pulmonary Veins

• Only veins carrying oxygenated blood—four total, two from each lung, draining into the left atrium
• Complete the pulmonary circuit by returning freshly oxygenated blood to the heart's systemic pump
• No valves present—unlike most veins, pulmonary veins rely on pressure gradients rather than valves for flow

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Great Vessels of the Heart

These are the major highways connecting the heart to systemic and pulmonary circulation. Understanding their positions and functions is essential for tracing any blood flow pathway.

Aorta

• Largest artery in the body—originates from the left ventricle and distributes oxygenated blood to the entire systemic circuit
• Four anatomical regions: ascending aorta, aortic arch (gives off brachiocephalic, left common carotid, and left subclavian arteries), descending thoracic aorta, and abdominal aorta
• Elastic artery structure allows it to expand during systole and recoil during diastole, maintaining continuous blood flow

Superior Vena Cava

• Drains the upper body—head, neck, arms, and upper thorax return deoxygenated blood through this vessel to the right atrium
• Formed by merger of left and right brachiocephalic veins posterior to the first right costal cartilage
• No valves present—blood flow depends on pressure gradients and respiratory pump action

Inferior Vena Cava

• Largest vein in the body—returns deoxygenated blood from everything below the diaphragm to the right atrium
• Formed by union of left and right common iliac veins at approximately vertebral level L5
• Receives hepatic veins carrying processed blood from the liver before entering the heart

Coronary Arteries

• Supply the myocardium itself—branch from the ascending aorta immediately above the aortic valve
• Left coronary artery divides into the left anterior descending (supplies anterior heart) and circumflex (supplies lateral/posterior left ventricle) branches
• Right coronary artery supplies the right atrium, right ventricle, and typically the SA and AV nodes—blockage here causes most heart attacks

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Head and Neck Vessels

These vessels are clinically significant for pulse assessment, blood pressure in the brain, and understanding stroke pathophysiology.

Common Carotid Arteries

• Primary blood supply to the head—bifurcate at approximately C4 into internal and external carotid arteries
• Internal carotid supplies the brain (anterior circulation); external carotid supplies the face, scalp, and neck structures
• Carotid sinus at the bifurcation contains baroreceptors that monitor blood pressure—this is why pressure on the neck can cause fainting

Jugular Veins

• Internal jugular veins are the primary drainage for the brain, running deep alongside the internal carotid arteries
• External jugular veins drain superficial head and neck structures and are visible when distended
• Jugular venous distension (JVD) indicates elevated right atrial pressure—a key clinical sign of heart failure

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Upper Limb Arterial Pathway

Arteries follow a logical branching pattern from proximal to distal. Memorize this sequence: subclavian → axillary → brachial → radial/ulnar.

Subclavian Arteries

• Supply the upper limb, chest, shoulders, and part of the brain via the vertebral artery branch
• Asymmetric origin: left subclavian branches directly from the aortic arch; right subclavian branches from the brachiocephalic trunk
• Become axillary arteries at the lateral border of the first rib

Brachial Arteries

• Main artery of the upper arm—continuation of the axillary artery at the lower border of teres major
• Blood pressure measurement site—stethoscope placed over brachial artery in the antecubital fossa during sphygmomanometry
• Bifurcates into radial and ulnar arteries just distal to the elbow

Radial Arteries

• Supply the lateral forearm and hand—run along the radius bone
• Primary pulse check site—easily palpated at the wrist (radial pulse) due to superficial position against the radius
• Commonly used for arterial blood gas sampling and arterial line placement

Ulnar Arteries

• Supply the medial forearm and hand—run along the ulna bone
• Larger than the radial artery and contributes more to the superficial palmar arch
• Allen test assesses patency of both radial and ulnar arteries before radial artery procedures

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Lower Limb Arterial Pathway

Similar to the upper limb, lower limb arteries follow a predictable sequence: external iliac → femoral → popliteal → anterior/posterior tibial.

Femoral Arteries

• Major blood supply to the lower limb—continuation of the external iliac artery after passing under the inguinal ligament
• Femoral pulse palpated in the femoral triangle (midpoint between ASIS and pubic symphysis)—used in emergencies when peripheral pulses are absent
• Gives off profunda femoris (deep femoral artery), which supplies the thigh muscles

Popliteal Arteries

• Located in the popliteal fossa (behind the knee)—continuation of the femoral artery after passing through the adductor hiatus
• Popliteal pulse is difficult to palpate due to deep position—requires knee flexion and firm pressure
• Bifurcates into anterior and posterior tibial arteries at the lower border of popliteus muscle

Anterior Tibial Arteries

• Supply the anterior leg compartment—pass through the interosseous membrane to reach the anterior leg
• Become the dorsalis pedis artery at the ankle—palpated on the dorsum of the foot between the first and second metatarsals
• Dorsalis pedis pulse assesses peripheral circulation, especially important in diabetic patients

Posterior Tibial Arteries

• Supply the posterior leg compartment and plantar foot—run deep to the soleus muscle
• Posterior tibial pulse palpated posterior to the medial malleolus—another key peripheral pulse site
• Divide into medial and lateral plantar arteries that supply the sole of the foot

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Visceral Vessels

These vessels supply and drain the abdominal organs. The portal system is especially high-yield because it's a unique circulatory arrangement.

Renal Arteries

• Supply the kidneys directly from the abdominal aorta—branch at approximately L1-L2 vertebral level
• Receive 20-25% of cardiac output—kidneys filter approximately 180 liters of blood daily
• Right renal artery is longer because it must cross behind the IVC to reach the right kidney

Mesenteric Arteries

• Superior mesenteric artery (SMA) supplies the midgut: small intestine, cecum, ascending colon, and most of transverse colon
• Inferior mesenteric artery (IMA) supplies the hindgut: distal transverse colon, descending colon, sigmoid colon, and rectum
• Mesenteric ischemia from blockage causes severe abdominal pain—"pain out of proportion to exam" is a classic presentation

Hepatic Portal Vein

• Carries nutrient-rich blood from GI tract to the liver—not directly to the heart like other veins
• Formed by merger of superior mesenteric and splenic veins behind the neck of the pancreas
• Portal system allows the liver to process absorbed nutrients and detoxify substances before they enter systemic circulation—first-pass metabolism occurs here

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Venous Return Vessels

Veins return blood to the heart, often working against gravity. Understanding their structure (valves, muscle pump) explains clinical conditions like varicose veins.

Saphenous Veins

• Great saphenous vein is the longest vein in the body—runs from the medial foot to the femoral vein in the groin
• Small saphenous vein runs along the posterior calf and drains into the popliteal vein
• Commonly harvested for coronary artery bypass grafts due to length and accessibility—also prone to varicose veins due to superficial position

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Quick Reference Table

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Self-Check Questions

1. Trace the pathway of a red blood cell from the right ventricle through the pulmonary circuit and back to the left atrium. Which vessels carry deoxygenated blood in this circuit?

2. Compare the superior and inferior vena cava: what regions does each drain, and where do they both terminate?

3. A patient has weak peripheral pulses. Which four pulse points would you check in the lower extremity, and where exactly is each located?

4. Explain why the hepatic portal vein is classified as a vein even though it doesn't drain directly into the heart. What is the clinical significance of portal circulation?

5. If an FRQ asks you to trace blood flow from the left ventricle to the right kidney and back to the right atrium, which vessels would you include in your pathway?