Mediastinum

Anatomy & Physiology PA 481 C

Tony Serino, Ph.D.

Biology Department

Misericordia Univ.

Mediastinum

Anterior

Superior

Middle

Posterior

Superior and anterior are continuous with each other; both may bereferred to as the superior mediastinum

Superior Mediastinum

Great Vessels of the Heart

Aortic arch

Transverse thoracic plane

Remnant of Ductus arteriosus

Ligamentumarteriosum

Usual Aortic Arch Pattern

65% of all people

RS

BT

LS

LCRC

Aortic Arch Variations

27% one BT withboth CC exiting 5%

1.2% two BT

left vert. a.

SVC

BC BC

SVC

Vagus

Phrenic

Pulmonary Arteries and Veins

Trachea and Primary bronchi

Structure Order

BC

Aorta PA

Trachea

Esophagus• Function: Deglutition• Two sphincters: upper

and lower esophageal sphincters (lower is physiological only)

• Retropleural position (therefore, covered by adventitia)

• Mucosa: stratified squamous with many mucus glands (esophageal glands)

• Muscularis: changes from skeletal to smooth muscle

Esophagus Histology

Thymus Gland• Bilobed organ that is largest in children, but begins to regress sharply at the onset of puberty (around age 11)

• It is the site of T-cell lymphocyte production and produces hormones (such as, thymosin) that modifies their physiology

General Circulatory System

1. Cardiovascular– Consists of a closed

system of vessels which transport blood

– Two circuits: Systemic and Pulmonary

– Arteries move blood away from the heart

– Veins move blood toward the heart

General Circulatory System2. Lymphvascular –

moves lymph– Consist of blind end

tubes which collect interstitial fluid (now called lymph) and returns it to circulation

– The lymph is cleaned before returned to the blood vessels

Heart Development

Fetal Circulation

Selected Heart Defects

Heart as a Dual Pump

• Cardiac muscle arranged as whorls that squeeze the blood

• Twin pumps: systemic and pulmonary

• Four chambers: 2 atria and 2 ventricles

Cardiac Muscle Cells

Cardiac Muscle Depolarization

Conductance of Ions during Depolarization

Heart: Location

Heart in Relation to other Organs

Layers of the Heart and Pericardium

Heart: Anterior ViewTransverse Pericardial sinus

Heart: Posterior View

Oblique Pericardial sinus

Heart: Internal Anatomy

Differences in Ventricular Wall

Coronary Artery Schematic

(LAD)

Most Common Coronary Arterial Pattern

Fig. 1.51

Ant. Desc. a. (LAD)

Post. Desc. a.

R. Marginal a.

L. Marginal a.

Circumflex a.

Coronary Variation

15% LCA dominant

Single CA

Most people right dominant.

Circumflex from right aortic sinus

(4% have an accessory coronary artery)

(note: which branch gives rise to posterior descending a.determines dominance)

Fig. 12.66b

Fig. 12.66c

Fig. 12.66d

Coronary Vein Schematic

Coronary Veins

Fig. 1.52

Coronary sinus

Great Cardiac v.

Small Cardiac v. Middle Cardiac v.

Ant. Cardiac veins

Major Cardiac Valves

aortic valve (SL)AV (tricuspid)

Heart Valves

sinus

Nodule (corpara aranti)

cusps

Fig. 12.07b

Diastole: Period of Ventricular Filling

Systole: Isovolumetric Contraction

Systole: Ventricular Ejection

Diastole: Isovolumetric Relaxation

Conduction System of Heart

Pacemaker Potential

ECG and electrical changes

Normal ECG

ECG

Normal Sinus Rhythm

Junctional Rhythm (AV node rhythm)

Second Degree Heart Block

Ventricular Fibrillation (V-fib)

Heart Sounds

• “Lub-dub”• Sound associated with

valve closing producing turbulent blood flow

Cardiac Cycle

(ml/min)

Factors Affecting SV• Stroke Volume (SV) =

End Diastolic Volume – End Systolic Volume• SV = EDV – ESV (ml/beat)• EDV affected by:

– Venous return which is dependent on venous tone, skeletal muscle pumps, etc.

• ESV– As the heart fills it is stretched which allows for better overlap of

the contractile proteins which will affect the force of contraction and the ESV (Starling’s Law of the Heart)

– Increasing the force of contraction at any EDV will decrease the ESV and increase the SV (sympathetic stimulation and epinephrine)

Sympathetic Stimulation

• Leads to increase HR• Increases in Ca++

release from SR, increase Ca++ through membrane and increase myosin crossbridge cycling

• Increases force of contraction

Heart Rate Control• Sinus Rhythm = normal SA node control• Autonomic Activity

– Sympathetic (thoracic trunk) = accelerator (induces tachycardia)

– Parasympathetic (vagus n.)= brake (induces bradycardia)

• Hormones– epinephrine

• Drugs-caffeine, nicotine, atropine, etc.

Posterior Mediastinum

Thoracic aorta

Sympathetic trunk

Vagus n.

Azygous v.

Trachea

Esophagus

Phrenic n.

Intercostal a., v., & n.

Hemiazygous v.

Lung root

Thoracic duct

Small Aortic Branches

Bronchial a.

Intercostals

Coronary

Esophageal

Azygous vein

Hemiazygous v.

Nerves of Post. Mediastinum

Thoracic Duct