Lecture 3 (Heart)

Mediastinum

The midline visceral compartment in the thorax between the sternum anteriorly, the bodies of the thoracic vertebrae T1-T12 posteriorly, the diaphragm inferiorly, and the thoracic inlet superiorly

Thoracic Inlet

Bounded by T1 vertebra, first ribs (L + R), and manubrium

Subdivisions of the mediastinum

The main reference landmark for dividing the mediastinum is the sternal angle. A plane drawn between the sternal angle and the inferior edge of the fourth thoracic vertebra (T4) separates the superior and inferior mediastinum

Contents of the superior mediastinum

-Superior vena cava

-Brachiocephalic veins (L+R)

-Arch of aorta

-Brachiocephalic artery

-Left common carotid artery

-Left subclavian artery

-Trachea and primary bronchii (L+R)

-Esophagus

-Vagus and phrenic nerve (L+R)

-Sympathetic chain (L+R)

What is the superficial to deep order of the structures in the throat?

Vein, artery, trachea, esophagus

What are the three parts of the anterior mediastinum?

Anterior, middle, and posterior

Anterior inferior mediastinum

It is located posteriorly to the sternum and anterior to the heart, contains mostly lymph nodes and fat

What is the biggest structure in the mediastinum?

The heart

Where does the right pulmonary trunk run?

Under the aorta

What structures are found inside the middle inferior mediastinum?

-Heart in the pericardial sac

-Part of the superior vena cava

-Ascending aorta

-Pulmonary trunk with L + R pulmonary arteries

-Pulmonary veins (L+R)

-Phrenic nerves

-Lymph nodes

Where is the posterior inferior mediastinum located?

Posterior to the heart and anterior to the bodies of vertebrae T5 to T12

What structures are found in the posterior inferior mediastinum?

-Descending aorta

-Esophagus

-Vagal plexuses (branches of L and R vagus nerves)

-Sympathetic chain (L+R)

Where does the heart sit

The pericardium, also called the pericardial sac

What are the layers of the pericardium?

The outer fibrous layer, and the inner serous layer (broken into two parts- the parietal serous and the visceral serous)

Pericardial Cavity

The space between the parietal serous and visceral serous layers, which contains a layer of pericardial fluid (decreases friction)

Parietal serous pericardium

Lines the interior of the pericardial sac and is inseparable from the fibrous pericardium

Visceral serous pericardium

Covers the surface of the heart

Heart valves found between chambers:

Tricuspid valve and bicuspid (mitral) valve

Heart valves found within blood vessels:

Semilunar valves: aortic valve and pulmonary valve

Tricuspid valve

Situated between the right atrium and right ventricle

Bicuspid Valve

Situated between the left atrium and the left ventricle

Parts of the heart valves

Cusps, chordae tendineae, and papillary muscles

Aortic Valve

In the base of the aorta

Pulmonary Valve

In the base of the pulmonary trunk

Which ventricle is stronger, why?

The left ventricle because it pumps oxygenated blood into the aorta which goes to the rest of the body

What are the branches of the ascending aorta, and what is their roles?

Right and left coronary arteries, and they supply oxygenated blood to the heart

What structures come off the right coronary artery?

The marginal artery and the posterior interventricular artery

What structures come off the left coronary artery?

Anterior interventricular artery and the circumflex artery

What are the main veins of the heart?

Great cardiac vein, middle cardiac vein, and small cardiac vein

Coronary sinus

All veins draining (deoxygenated blood) the heart muscle ultimately drain into the largest vein of the heart. Which then delivers blood to the right atrium

What is the nerve supply for the heart?

Parasympathetic and sympathetic, as well as its own intrinsic nerve supply

Effect of parasympathetic innervation on the heart?

Decreases heart rate, the “rest and digest” response, the vagus nerve (CN X) is the source of parasympathetic fibers to the heart

Effect of sympathetic innervation on the heart?

Increases the heart rate, the “fight or flight response”

Components of the hearts intrinsic nerve supply

Sinoatrial node (SA node) and the atrioventricular node (AV node)

Sinoatrial (SA) node

In the right atrium, is part of the intrinsic nerve supply of the heart and is regulated by sympathetic and parasympathetic nervous systems (the vagus nerve and the sympathetic chain are in contact)

Atrioventricular (AV) node

The SA node regulates this node that is situated in the interatrial septum, which then regulates the contraction of most of the heart, it causes a slight delays

Where does a pace maker wire go?

In the right atrium through the superior vena cava then the brachiocephalic vein, to the SA node

What are the conducting cells of the heart?

Not neurons, but modified cardiac cells called Purkinje fibers, they distribute the impulses to the ventricular muscles

Venous Blood

Deoxygenated blood

Arterial Blood

Oxygenated blood

Pulmonary arteries

Only arteries to carry deoxygenated blood

Pulmonary veins

Only veins to carry oxygenated blood

Veins normally carry

Deoxygenated blood towards the heart

Arteries normally carry

Oxygenated blood away from the heart