AB

Week 3: Systemic Circulation

Systemic Circulation Essentials

  • Arteries: carry blood away from heart; veins: toward heart; capillaries: exchange materials; lymphatics: return excess tissue fluid.
  • Aorta = largest artery; veins hold ≈ (60\%) of blood (reservoir function).

Aorta & Major Branches

  • Regions: ascending aorta, aortic arch, descending (thoracic ➔ abdominal) aorta.
  • Ascending: gives off left & right coronary arteries.
  • Aortic arch branches (right-to-left):
    • Brachiocephalic trunk ➔ right common carotid + right subclavian.
    • Left common carotid.
    • Left subclavian.
  • Descending thoracic ➔ passes diaphragm ➔ abdominal aorta.

Head & Neck Vasculature

  • Common carotids ➔ internal carotid (to Circle of Willis) + external carotid (face/scalp).
  • Vertebral arteries (from subclavians) also feed Circle of Willis.
  • Circle of Willis ensures collateral cerebral flow; middle cerebral artery = most frequent CVA site (hemiplegia).
  • Venous drainage: internal jugular (brain), external jugular (superficial face/neck), vertebral veins.
  • Flow to heart: jugulars & vertebral ➔ subclavian ➔ brachiocephalic veins (right & left) ➔ superior vena cava (SVC) ➔ right atrium.

Upper Limb Vessels

  • Arterial path (both sides):
    • Subclavian ➔ axillary ➔ brachial ➔ radial & ulnar ➔ hand.
  • Key uses: brachial artery for BP; radial artery for pulse.
  • Deep venous return: palmar veins ➔ radial/ulnar ➔ brachial ➔ axillary ➔ subclavian ➔ brachiocephalic ➔ SVC.
  • Superficial veins: cephalic (lateral), basilic (medial), median cubital (common venipuncture).

Thoracic Cavity Branches

  • Visceral: pericardial, bronchial, esophageal, mediastinal arteries.
  • Parietal: posterior intercostal, subcostal, superior phrenic.
  • Corresponding veins drain mainly into azygos vein ➔ SVC.

Abdominopelvic Arteries

  • Abdominal aorta paired branches: inferior phrenic, suprarenal, renal, lumbar, gonadal (5 pairs).
  • Unpaired: celiac trunk, superior mesenteric, inferior mesenteric (3).
  • Celiac trunk branches: left gastric, splenic, common hepatic.
  • Abdominal aorta terminates as right & left common iliac arteries.

Hepatic Portal System

  • Digestive veins (splenic, gastric, superior mesenteric) ➔ hepatic portal vein ➔ liver (detox/storage) ➔ hepatic veins ➔ IVC ➔ right atrium.
  • Kidneys & liver are the only abdominal organs draining directly into IVC.

Lower Limb Vessels

  • Common iliac ➔ external (lower limb) & internal (pelvis) iliac arteries.
  • External iliac ➔ femoral ➔ popliteal ➔ anterior/posterior tibial + fibular ➔ foot.
  • Superficial venous return: dorsal venous arch ➔ great saphenous (medial) ➔ external iliac; lesser saphenous (lateral) ➔ popliteal.
  • Deep veins: plantar veins ➔ fibular/tibial ➔ popliteal ➔ femoral ➔ external iliac ➔ common iliac ➔ IVC.

Key Clinical & Review Points

  • Brachial artery: BP measurement.
  • Radial artery: pulse assessment.
  • Right subclavian from brachiocephalic; left subclavian direct from aortic arch.
  • Superior mesenteric artery supplies small intestine + proximal colon.
  • Correct right-upper-limb arterial sequence: Aorta ➔ brachiocephalic trunk ➔ right subclavian ➔ right axillary ➔ right brachial ➔ radial & ulnar.
  • Circle of Willis formed by internal carotids + vertebral (via basilar) arteries.