Anatomy - Lecture 13: Mediastinum subdivisions, anterior & middle mediastinum (heart)

What is the mediastinum?

central portion between 2 pleural sacs limited on either sides by the mediastinal pleura

What are the boundaries of the mediastinum?

• front → sternum

• behind → T1-T12 vertebrae

• above → thoracic inlet

• below → diaphragm

• on each side → mediastinal pleura

At which level does the imaginary horizontal plane extend and divide the mediastinum into superior and inferior?

sternal angle to the lower border of T4

How is the mediastinum divided?

• mediastinum

  • superior

  • inferior

    • anterior

    • middle

    • posterior

What are the boundaries of the anterior mediastinum?

• front → body of the sternum

• behind → pericardium

• above → imaginary horizontal plane extending from sternal angle to the lower border of T4

• below → diaphragm

• on each side → mediastinal pleura

What are the contents of the anterior mediastinum?

• superior and inferior sterno-pericardial ligaments

• thymus gland

• loose areolar tissue

• retrosternal lymph nodes

Where is the thymus gland located?

behind manubrium and partly behind body of the sternum (both superior and inferior mediastinum)

What are the contents of the middle mediastinum?

• heart enclosed in the pericardium

• nerves

  • phrenic

  • deep cardiac plexus

• lymph nodes (tracheobronchial nodes)

• arteries

  • ascending aorta and pulmonary trunk dividing into right and left pulmonary arteries

• veins

  • lower part of the superior vena cava

  • arch of azygos

  • 4 pulmonary veins

• tubes

  • bifurcation of trachea

What are the properties of the pericardium?

• conical fibroserous sac

• encloses the heart and roots of great vessels

• consists of two layers

  • fibrous pericardium

  • serous pericardium

What are the relations of the fibrous pericardium?

• apex → continuous with tunica adventitia of great vessels

• base → blends with central tendon of diaphragm

• anteriorly → attached to sternum by sterno-pericardial ligaments

• behind → related to the posterior mediastinum

• on each side → related to the mediastinal pleura

through these attachments, pericardium maintains the thoracic position of heart

What are the properties of the serous pericardium?

• closed sac lies within fibrous pericardium

• lined by mesothelium

• consists of visceral and parietal layers

  • parietal layer lines the fibrous pericardium

  • visceral layer (epicardium) covers the heart and roots of great vessels

• pericardial cavity → between 2 layers

  • filled with pericardial fluid

  • allows free movement of the heart

  • fluid provides lubrication

What is inflammation of the serous pericardium called?

pericarditis, causes chest pain

What is the nerve supply of the pericardium?

• parietal is pain sensitive and visceral is insensitive

• pain of pericarditis originates in parietal pericardium alone and transmitted by the phrenic nerve

• cardiac pain (angina) originates in cardiac muscle or vessels and transmitted by sympathetic nerves

What is the arterial supply of the pericardium?

branches from the the thoracic, musculophrenic artery and descending thoracic arteries

What is the drainage of fluid from the pericardial cavity called?

• pericardiocentesis

• relieve cardiac tamponade

• wide bore needle inserted through the left 5th or 6th intercostal space near sternum

What are the properties of the heart?

• muscular organ

• placed obliquely behind body of sternum and costal cartilages

• has 4 chambers

  • 2 atria

  • 2 ventricles

• heart presents

  • apex

  • base

  • three surfaces

    • sternocostal (anterior)

    • diaphragmatic (inferior)

    • left

  • four borders

    • superior → two atria

    • inferior → two ventricles

    • right → right atrium

    • left → left ventricle and left auricle

  • grooves/sulci (sulci are occupied by vessels)

    • atrioventricular groove (coronary sulcus) → between atria and ventricles

    • interventricular sulcus → between two ventricles

    • interatrial sulcus → between two atria

  • auricles → extensions of atrium

What are the properties of the apex?

• formed by the left ventricle

• located in the left 5th intercostal space

• lies just medial to the midclavicular line

What are the properties of the base/posterior surface of the heart?

• formed by two atria

• openings of four pulmonary veins and superior & inferior vena cava

What are the properties of the sternocostal surface of the heart?

• formed by the right atrium and ventricle, left ventricle and auricle

• has anterior interventricular sulcus & right part of the coronary sulcus

What are the properties of the diaphragmatic surface of the heart?

• formed by the right & left ventricles

• rests on the central tendon of the diaphragm

• has posterior interventricular sulcus

How does the blood flow through the heart?

What separates the right and left atriums?

inter-atrial septum

What separates right and left ventricles?

inter ventricular septum

What are the valves of the heart?

• right atrioventricular → tricuspid valve

• left atrioventricular → bicuspid (Mitral) valve

• pulmonary valve

• aortic valve

How are the cuspid valves attached to papillary muscle?

chordae tendineae

Where are the 2 great vessels valves (semilunar) valves?

What is the blood supply of the heart?

supplied by two coronary arteries

• right coronary artery

• left coronary artery

drained by cardiac veins and coronary sinus

How is the heart innervated?

• sympathetic and parasympathetic nerves which form cardiac plexus (superficial and deep cardiac plexus)