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)