EC

Dissection 3.1 - Heart and Lungs

Dissection Guide

Removal of the Ribcage

  • Costal parietal pleura: Thin serous membrane immediately under endothracic fascia and rib

    • Loosely adhered to the inner surface of the ribcage

  • Transverse thoracis muscles: adjacent to the lower end of the sternum

    • Innermost layer of the intercostal m.

    • Can see on reflected ribcage

  • Internal mammary (thoracic) a.: On the innerside of the removed ribcage

    • Course vertically adjacent to sternum

    • Branch off subclavian a

    • Branches into superior epigastric a. and musculophrenic a. near xiphisternal junction

      • Superior epigastric a. anastamoses with inferior epigastric a.

  • Within each intercostal space is an anterior intercostal a

    • Arises from the internal thoracic a.

    • In each space, an anterior intercostal a. and posterior intercostal a. anastomoses at level of costocervical junctions

    • Provides collateral pathway

Dissection of Pleural Sacs

  • Layer 1: Pleural sac

  • Layer 2: Parietal pleyra

  • Layer 3: Percardium sac

  • Layer 4: Mediastrinal pleura

    • Phrenic n. descends vertically through mediastinum between layer 3 and 4

    • Course just anterior to root of the lung

  • Diaphragm: Located just below each lung

Dissection of Superior Mediastinum

  • Contains roots of great vessels (aortic arch, R brachiocephalic trunk and a., LCCA, L subclavian)

  • L and R brachiocephalic v. + Azygous v. → SVC

    • Azygous v. on posteriolateral side of SVC (arches over root of the lungs)

      • Joins outside pericardial sac

    • Internal jugular + subclavian veins → L brachiocephalic v.

      • Runs obliquely

    • R braciocephalic is vertical

  • Aortic arch → Brachiocephalic trunk, L CCA and L subclavian a.

    • External of pericardial sac

    • Ascending aorta is posterior to the sac

  • Brachiocephalic a. → R CCA and R subclavian a.

  • Trachea: immediately posterior to brachiocephalic trunk and L CCA

    • Esophagus lies deep to trachea

  • Phrenic n. ascends behind the subclavian v. then crosses 1st rib and anterior scalene m.

  • Vagus n.: enters thorax

    • R side: Crosses right subclavian b/w brachiocephalic trunk and R braciocephalic v.

      • R Recurrent laryngeal n.: Arises around lower border of R subclavian a. and then turns superiorly (ascend between trachea and esophagus)

    • L side: Between L CCA and L subclavian a.

      • Crosses aortic arch

      • L Recurrent laryngeal n.: Turns medially under ligamentum arteriosum (around aortic arch)

Heart

  • Within pericardial sac

  • Note that the L atrium is located posteriorly

    • Apex points inferolaterally

  • Pulmonary veins (4 of them) are located on the posterior aspect of the pericardial sac

    • Enter L atrium


Bolded Terms

1st intercostal space

  • Space between the 1st and 2nd ribs

Anterior intercostal artery

  • Small artery that arises from the internal thoracic artery

  • Located in each intercostal space

  • Anastomoses with posterior intercostal artery at the level of the costochondral junctions

Anterior scalene muscle

  • Deep to phrenic nerve (after they ascend behind the subclavian v. and cross the 1st rib)

Aortic arch

  • Transition between ascending and descending aorta

  • Branches off of the aortic arch: Brachicocephalic trunk, L CCA, L Subclavian)

Apex of the heart

  • Tip of the left ventricle pointing inferolaterally

Ascending aorta

  • Arises from the left ventricle

Azygous vein

  • Arches over the root of the lung to join with the SVC outside the pericardial sac

Brachiocephalic trunk

  • The right-most branch of the aortic arch

  • R subclavian and R CCA arises from the brachiocephalic trunk

Brachiocephalic veins

  • Formed by the convergence of the R/L internal jugular and subclavian veins

  • R brachiocephalic v. is nearly vertical

  • L brachiocephalic v. passes obliquely from L to R

  • Join to form the SVC

Common Carotid artery

  • L CCA is a branch off the aorta

  • R CCA is a branch off the brachiocephalic trunk

  • Each split into an internal and external carotid artery

Diaphragm

  • Dome-shaped muscle inferior to the lungs

  • Contraction flattens and expands lung volume

Esophagus

  • Located immediately posterior to the trachea

Inferior vena cava

  • Join with the right atrium (along with the superior vena cava)

Innermost intercostal muscle

  • Transverse thoracis muscles adjacent to the lower end of the sternum

Intercostal nerve

  • Located near the upper border of an intercostal space (within the costal groove)

Internal jugular vein

  • Joins with subclavian v. to form the brachiocephalic veins

  • Drains blood from the brain, face, and neck

Internal mammary/thoracic artery

  • Vessels that course vertically adjacent to the sternum between the internal intercostal muscles and transversus thoracis muscle

  • Divides into 2 terminal branches near the xiphisternal junction (superior epigastric a. and musculophrenic a.)

Left atrium

  • Receives oxygenated blood from pulmonary veins (2 L and 2 R)

Left ventricle

  • Pumps blood into ascending aorta

  • Located posteriorly

Ligamentum arteriosum

  • Adult remnant of ductus arteriosus (shunt during fetal circulation)

Musculophrenic artery

  • One of the terminal branches of the mammary artery

Parietal pleura

  • External layer covering lungs

  • Space between parietal and visceral pleura = pleural cavity

Phrenic nerve

  • Arises in the neck from the ventral rami of C3, 4, 5

  • Descend vertically through mediastinum between mediastinal parietal pleura and pericardium

  • Course just anterior to root of the lung

  • Have sensory and motor components

Pleural sac

  • Consist of outer parietal pleura and inner visceral pleura that encloses the lungs

Pulmonary veins

  • Veins that travel to the left atrium from the lungs

  • Carry oxygenated blood

Recurrent laryngeal nerve

  • Arises from the vagus nerve

  • R recurrent laryngeal n. at the lower border of the right subclavian artery and turns superiorly to ascend in the neck between the trachea and esophagus

Right atrium

  • Receives deoxygenated blood from coronary sinus, SVC, and IVC

Right ventricle

  • Receives deoxygenated blood from the right atrium

  • Pumps to R and L lungs through pulmonary arteries (1 R and 1 L)

Subclavian artery

  • L subclavian branches directly off aortic arch

  • R subclavian branches off brachiocephalic trunk

Subclavian vein

  • Converge with internal jugular v. to form brachiocephalic veins

Superior epigastric artery

  • Terminal branch of mammary artery that anastamoses with the inferior epigastric artery

Superior vena cava

  • Drains into right atrium

Trachea

  • Located immediately posterior to the brachiocephalic trunk and L CCA

  • Can palpate the cartilaginous rings

Transverse thoracis

  • Innermost intercostal muscles (just adjacent to the sternum)

Vagus nerve (CN X)

  • R vagus crosses R subclavian artery between the brachiocephalic trunk and R brachiocephalic vein

  • L vagus is located between the L CCA and L subclavian a.

    • Descends on the L side of the aortic arch angling downward to pass behind the root of the lung

    • Giving rise to the L recurrent laryngeal n. (turns medially under ligamentum arteriosum)