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).