Blood Vessel Lab Lecture Review-slides

Pulmonary Circulation

  • Pathway of deoxygenated blood
    • Leaves right ventricle → pulmonary trunk → left & right pulmonary arteries.
    • In the lungs, blood passes through pulmonary arterioles → pulmonary capillaries → pulmonary venules (gas exchange occurs here).
  • Return of oxygenated blood
    • Oxygen-rich blood exits pulmonary venules → left & right pulmonary veins → empties into left atrium.
  • Key vessels to locate on models/images
    • Pulmonary trunk
    • Left pulmonary artery & right pulmonary artery
    • Left pulmonary vein & right pulmonary vein
  • Functional significance
    • Only circuit where arteries carry deoxygenated blood and veins carry oxygenated blood.
    • Low-pressure, short-length circuit protects delicate pulmonary capillaries.

Circulation to / from the Head & Neck

  • Arterial supply (branches of aorta)
    • Aorta
    • Ascending aorta → Aortic arch.
    • Brachiocephalic trunk (right-side only)
    • Splits into:
      • Right common carotid a. (supplies right head/neck).
      • Right subclavian a. (supplies right upper limb & thorax).
    • Left common carotid a. (direct branch of aortic arch ➔ supplies left head/neck).
  • Common carotid aa. (left & right)
    • Course: parallel to trachea.
    • Bifurcate near level of thyroid cartilage into:
    • External carotid a. – supplies superficial structures external to skull (face, scalp, neck).
    • Internal carotid a. – supplies internal skull structures; contributes about 75\% of cerebral blood flow.
      • After entering skull, branches help form Cerebral arterial circle (Circle of Willis).
  • Vertebral → Basilar pathway
    • Vertebral aa. (branches of subclavian aa.) ascend via transverse foramina of cervical vertebrae → enter skull through foramen magnum.
    • Merge to form unpaired Basilar a. (lies on ventral pons) → divides into branches forming part of Circle of Willis.
  • Circle of Willis
    • Arterial anastomosis encircling sella turcica; equalizes cerebral BP & provides collateral flow if one vessel occludes.
  • Venous drainage
    • Vertebral vv. (only on images) → drain cervical spinal cord & deep neck → empty into subclavian v.
    • External jugular vv. – drain superficial head/neck → subclavian v.
    • Internal jugular vv. – drain cranial cavity (dural venous sinuses).
    • Junctions
    • Left internal jugular + left subclavian → Left brachiocephalic v.
    • Right internal jugular + right subclavian → Right brachiocephalic v.
    • Left & right brachiocephalic vv. → Superior vena cava (SVC) → right atrium.
  • Clinical pearls
    • Jugular venous distension can indicate elevated right atrial pressure.
    • Carotid pulse palpation assesses perfusion to brain.

Circulation to / from the Upper Limbs

  • Arterial pathway
    • Subclavian a. (R: branch of brachiocephalic trunk; L: direct branch of aortic arch).
    • Renamed Axillary a. beyond 1st rib → supplies axilla, shoulder, chest wall, proximal humerus.
    • Renamed Brachial a. beyond teres major.
    • In antecubital fossa, brachial splits → Radial a. (lateral forearm) & Ulnar a. (medial forearm).
    • Superficial palmar arch (primarily ulnar contribution) forms arterial anastomosis in palm.
  • Venous drainage—two systems
    1. Superficial system
    • Cephalic v. (lateral arm) & Basilic v. (medial arm) drain hand.
    • Connected by Median cubital v. at elbow (common phlebotomy site).
    • Both empty into Axillary v.
    1. Deep system
    • Digital vv. → Superficial palmar venous arch → paired Radial vv. & Ulnar vv.
    • Merge → Brachial vv. (in antecubital region).
    • Brachial vv. + Basilic v. → Axillary v.
  • Proximal continuation
    • Axillary v. becomes Subclavian v. at lateral border of 1st rib.
    • Subclavian v. + Internal jugular v. → Brachiocephalic v.
    • Confluence of L & R brachiocephalic vv. → SVC.

Circulation to / from the Lower Limbs

  • Aortic route
    • Left ventricle → Ascending aorta → Aortic arch → Descending thoracic aorta.
    • After passing through diaphragm (at T12), becomes Descending abdominal aorta.
    • At L4, splits into Left & Right common iliac aa.
  • Iliac split
    • Each common iliac a. divides into:
    • Internal iliac a. – pelvic organs, gluteal region.
    • External iliac a. – primary supply to lower limb.
  • Femoral & distal branches
    • External iliac a. passes under inguinal ligament → renamed Femoral a.
    • Posterior to knee → Popliteal a. → branches:
    • Anterior tibial a. (anterior compartment leg) → crosses ankle → Dorsalis pedis a.
    • Posterior tibial a. (posterior compartment) → gives off Fibular a. (lateral leg).
  • Venous drainage – superficial vs deep
    1. Superficial
    • Dorsal venous arch on foot drains to:
      • Great saphenous v. (medial ankle → groin) → empties into femoral v.
      • (Small saphenous v. not required.)
    1. Deep
    • Foot → Dorsalis pedis v. → renamed Anterior tibial v.
    • Fibular v. drains lateral leg → joins Posterior tibial v.
    • Anterior & Posterior tibial vv. merge → Popliteal v.
    • Superiorly → Femoral v. → becomes External iliac v. above inguinal ligament.
  • Proximal convergence
    • External + Internal iliac vv. → Common iliac v.
    • L & R common iliac vv. → Inferior vena cava (IVC) (lies right of abdominal aorta).

Blood Vessel Structure

  • General organization
    • All vessels (except capillaries) possess three concentric tunics surrounding the lumen.
  • Tunica intima
    • Innermost; simple squamous endothelium + thin areolar CT.
    • Smooth, friction-reducing surface for laminar flow.
  • Tunica media
    • Middle; concentric smooth muscle + elastic fibers.
    • Functions: vasoconstriction (smooth muscle contraction → ↓ diameter) & vasodilation (relaxation → ↑ diameter).
    • Thickness greatest in arteries (esp. muscular & elastic types).
  • Tunica externa (adventitia)
    • Outermost; areolar CT with collagen & elastin.
    • Anchors vessel; houses vasa vasorum ("vessels of vessels" supplying outer wall of large arteries/veins).
  • Lumen differences
    • Arteries: smaller, rounder lumen; thick media → resists high pressure.
    • Veins: larger, often flattened lumen; thick externa; contain valves (not shown in histology slides) preventing backflow.

Histology Comparisons

  • Muscular artery vs medium-sized vein (LM 100×)
    • Artery exhibits thicker tunica media and wavy internal elastic lamina; lumen typically circular.
    • Vein shows thinner media, thicker externa, more irregular/flattened lumen.
  • Elastic artery tunica intima
    • Appears wavy due to recoil of abundant elastic lamellae in media.
    • Veins lack this wavy morphology—intima remains smooth.
  • Practical applications
    • Recognition of vessel type in histological sections helps pathologists diagnose arteriosclerosis, thrombosis, etc.

Fetal Circulation

  • Structures to identify
    • Umbilical cord, Umbilical vein, Umbilical arteries
    • Four heart chambers + Foramen ovale (interatrial shunt) & Ductus arteriosus (pulmonary trunk ↔ aorta shunt)
    • Ductus venosus (umbilical v. → IVC bypassing liver)
    • Major great vessels (IVC, aorta, pulmonary trunk/aa./vv.)
  • Hemodynamic principles
    • Placenta supplies O$_2$ & nutrients; fetal lungs are non-functional → pulmonary circulation has high resistance.
    • Therefore, right-sided heart pressures > left-sided.
  • Step-by-step fetal route
    1. Oxygenated blood from placenta → fetus via Umbilical vein.
    2. Through Ductus venosus to IVC (mixes with deoxygenated systemic blood).
    3. IVC + SVC blood enters Right atrium.
    4. Majority shunted RA → LA via Foramen ovale → Left ventricle → systemic aorta → body.
    5. Small portion RA → RV → Pulmonary trunk; most of this diverted to aorta via Ductus arteriosus (bypassing lungs).
    6. Mixed blood returns to placenta via paired Umbilical arteries for re-oxygenation.
  • Comparative summary
    • Shunts prioritize perfusion of developing brain & heart while bypassing lungs & partially liver.

Postnatal Changes

  • At birth (first breaths & clamping of cord)
    • Umbilical vein & arteries constrict → become ligamentum teres (round ligament of liver) & medial umbilical ligaments respectively.
    • Ductus venosus collapses → ligamentum venosum within liver.
    • Foramen ovale closes as LA pressure exceeds RA (forms fossa ovalis).
    • Ductus arteriosus constricts within 10\text{–}15\,\text{h} → ligamentum arteriosum.
  • Failure of closure leads to congenital defects (e.g., patent ductus arteriosus causing mixing of oxygenated/deoxygenated blood).

Blood Vessel Lab Checklist (Study Tips)

  • Be able to trace blood flow from heart to any named region & back.
  • Accurately identify each listed artery & vein on:
    • Plastic torso models
    • Cadaver prosections
    • Photographic slides / textbook images
  • Recall tunic composition differences on histology slides.
  • Explain functional significance of Circle of Willis, fetal shunts, superficial vs deep venous systems.
  • Memorize vessel name changes at anatomical landmarks (e.g., subclavian → axillary at first rib).