Pulmonary Trunk, Aorta, Carotid & Subclavian Systems – Comprehensive Notes

Pulmonary Trunk

  • Contained within the pericardial sac and covered by visceral serous pericardium (shares common sheath with ascending aorta).

  • Originates at the conus arteriosus of the right ventricle:

    • Opening lies slightly anterior to the aortic orifice.

  • Course:

    • Ascends while moving posteriorly and to the left.

    • Initially anterior, then left of the ascending aorta.

  • Termination / Bifurcation (level of TV–TVI intervertebral disc; posterior to 3rd left costal cartilage, left sternal border):

    • Right pulmonary artery ➜ passes right, posterior to ascending aorta & SVC, enters right lung.

    • Left pulmonary artery ➜ passes inferior to aortic arch & anterior to descending aorta, enters left lung.

Ascending Aorta

  • Within pericardial sac; enveloped by visceral serous pericardium (common sheath with pulmonary trunk).

  • Origin: aortic orifice at base of left ventricle (lower edge of 3rd left costal cartilage, posterior to left sternum).

  • Course: ascends superiorly, slightly forward & rightward to level of 2nd right costal cartilage ➜ enters superior mediastinum to become arch of aorta.

  • Aortic sinuses (immediately above valve): posterior, right, left.

    • Right & left coronary arteries arise from corresponding sinuses.

Other Intrapericardial Vessels

  • Superior vena cava (SVC):

    • Inferior half lies in pericardial sac.

    • Traverses fibrous pericardium at level of 2nd costal cartilage; enters RA at lower border of 3rd costal cartilage.

    • Covered by serous pericardium except small posterior area.

  • Inferior vena cava (IVC):

    • Pierces diaphragm at T8T8 level; short intrapericardial segment before entering RA.

    • Covered by serous pericardium except small posterior area.

  • Pulmonary veins (2 per lung):

    • Very short intrapericardial segments entering superior posterior LA.

    • Posterior surfaces partially uncovered by serous pericardium.

    • Oblique pericardial sinus lies between R & L pulmonary veins.

Arch of Aorta

  • Thoracic aorta segments: 1) ascending, 2) arch, 3) descending (thoracic) aorta.

  • Only the arch resides in superior mediastinum.

  • Begins as ascending aorta exits pericardial sac; course: upward, backward, leftward; ends left of vertebral level T4/T5T4/T5.

  • Maximal height: mid-manubrium.

  • Relation to trachea: initially anterior ➜ then lateral (left) to trachea.

Branches of Arch (crossed anteriorly by left brachiocephalic vein)

  1. Brachiocephalic trunk (largest; origin behind manubrium; slightly anterior to other branches)

    • Ascends posteriorly & rightward.

    • Terminates at upper edge of right sternoclavicular joint → divides into:

      • Right common carotid artery (supplies right head & neck).

      • Right subclavian artery (supplies right upper limb).

    • Occasional thyroid ima artery branch to thyroid gland.

  2. Left common carotid artery

    • Origin just left & posterior to brachiocephalic trunk.

    • Ascends along left tracheal margin; supplies left head & neck.

  3. Left subclavian artery

    • Origin left & posterior to left common carotid.

    • Ascends along left tracheal margin; principal supply to left upper limb.

Ligamentum Arteriosum / Ductus Arteriosus

  • Embryonic patent vessel connecting pulmonary trunk to arch of aorta ➜ shunts blood past non-functional fetal lungs.

  • Closes soon after birth, forming fibrous ligamentum arteriosum (situated in superior mediastinum).

Clinical Correlations (Thoracic Aorta & Arch)

  • Coarctation of aorta: congenital narrowing distal to left subclavian origin → diminished lower-body flow; collateral intercostal vessels enlarge causing inferior rib notching; ↑ afterload on heart → potential failure.

  • Fixed attachment points predisposed to traumatic rupture: aortic valve, ligamentum arteriosum, diaphragmatic hiatus (median arcuate ligament).

  • Aortic dissection: intima/media separation forming false lumen; proximal dissections endanger coronary/cerebral flow; distal may compromise visceral supply.

  • Right-sided aortic arch: rare; may accompany dextrocardia/situs inversus; can coexist with aberrant branching (e.g.
    left subclavian from distal arch looping behind esophagus) → dysphagia.

  • Abnormal origins: common brachiocephalic + left CCA trunk, left vertebral from arch, right subclavian from distal arch behind esophagus (vascular ring).

Carotid System (Anterior Triangle of Neck)

  • Arterial supply: common, external, internal carotid arteries.

  • Venous drainage: internal jugular vein & tributaries.

Common Carotid Arteries

  • Right CCA: branch of brachiocephalic trunk posterior to right sternoclavicular joint; entirely cervical.

  • Left CCA: direct from aortic arch in thorax → enters neck near left sternoclavicular joint.

  • Course: ascend within carotid sheath (lateral to trachea & esophagus); give no branches in neck.

  • Termination: bifurcate at superior border of thyroid cartilage (carotid triangle) → external & internal carotids.

  • Special sensory structures at bifurcation:

    • Carotid sinus (dilated proximal ICA + distal CCA): baroreceptors; innervation – glossopharyngeal nerve [IX].

    • Carotid body (2–6 mm chemoreceptor): monitors O$_2$; innervation – glossopharyngeal [IX] & vagus [X].

Internal Carotid Arteries (ICA)

  • No cervical branches; enter skull via carotid canal (petrous temporal bone).

  • Intracranial course through cavernous sinus, then give off:

    • Ophthalmic artery (orbit).

    • Posterior communicating artery (Circle of Willis).

    • Anterior choroidal artery (motor/visual pathways).

    • Anterior cerebral artery.

    • Terminal continuation: middle cerebral artery (lateral cerebrum).

  • Supply: cerebral hemispheres, eyes, orbits, forehead.

External Carotid Arteries (ECA)

  • Begin immediately after CCA bifurcation; numerous cervical & facial branches.

  1. Superior thyroid a. – thyroid gland, larynx, SCM, cricothyroid, thyrohyoid.

  2. Ascending pharyngeal a. – pharynx, palate, tonsil, pharyngotympanic tube, meninges.

  3. Lingual a. – tongue muscles, floor of mouth, palatine tonsil, soft palate, sublingual gland, epiglottis.

  4. Facial a. – face from mandible up to medial eye corner; also palate, tonsil, pharyngotympanic tube, submandibular gland.

  5. Occipital a. – posterior scalp, meninges, SCM, mastoid cells, deep back muscles.

  6. Posterior auricular a. – parotid, auricle, scalp posterior to ear, middle/inner ear.

  7. Superficial temporal a. (terminal) – parotid, masseter, face, auricle, temporalis, temporal/parietal fossae.

  8. Maxillary a. (terminal, larger) – extensive deep facial supply: EAM, TMJ, dura, teeth, nasal cavity, palate, infratemporal & pterygopalatine fossae, infra-orbital skin.

Internal Jugular Vein (IJV)

  • Origin: continuation of sigmoid sinus (superior bulb) + receives inferior petrosal sinus within jugular foramen.

  • Traverses carotid sheath: initially posterior to ICA, later lateral to CCA; vagus nerve [X] posterior between artery & vein.

  • Joins subclavian vein posterior to sternal clavicular end → forms brachiocephalic vein.

  • Major tributaries: inferior petrosal sinus, facial, lingual, pharyngeal, occipital, superior & middle thyroid veins.

  • Jugular venous pulse: clinical window into right heart hemodynamics.

Subclavian Arteries

  • Arch out of thorax into root of neck.

  • Right: terminal branch of brachiocephalic trunk (posterior to right SC joint).

  • Left: direct branch of aortic arch (posterior to left CCA, lateral to trachea).

  • Both pass anterior to pleural dome & posterior to anterior scalene; cross lateral border of rib I → become axillary artery.

Division by Anterior Scalene Muscle

  1. First part – origin → medial border of anterior scalene.

  2. Second part – posterior to anterior scalene.

  3. Third part – lateral to anterior scalene → lateral border rib I.

Branches (arise mostly from first part)

  1. Vertebral artery

    • Origin: first part, medial to anterior scalene.

    • Ascends through transverse foramina C6→C1C6 \to C1, loops medially over posterior arch of atlas, enters cranial cavity via foramen magnum.

    • Supplies posterior brain (joins opposite vertebral to form basilar artery).

  2. Thyrocervical trunk – divides into:

    • Inferior thyroid a. → thyroid gland; gives ascending cervical a. (prevertebral muscles & spinal branches).

    • Transverse cervical a. → trunk crosses posterior triangle, terminates as:

      • Superficial branch (trapezius).

      • Deep branch / dorsal scapular a. (rhomboids, levator scapulae).

    • Suprascapular a. → crosses over superior transverse scapular ligament to supraspinatus fossa.

  3. Internal thoracic (internal mammary) artery

    • Descends posterior to clavicle & ribs, anterior to pleura & transversus thoracis; multiple thoracic wall branches (used in CABG).

  4. Costocervical trunk

    • Origin: first part (left) or second part (right).

    • Gives:

      • Deep cervical a. → posterior neck, anastomoses with occipital.

      • Supreme intercostal a. → posterior intercostal aa. for 1st & 2nd spaces.

Summary Table – Subclavian Branches vs Supplies

  • Vertebral ➜ posterior brain, spinal cord.

  • Thyrocervical trunk ➜ inferior thyroid (thyroid), transverse cervical (trapezius/rhomboids), suprascapular (scapular region).

  • Internal thoracic ➜ anterior thoracic wall, pericardium, diaphragm.

  • Costocervical trunk ➜ deep cervical musculature, 1st–2nd intercostal spaces.

End