Anatomy of Heart

Location of Heart on Surface

• Located in the thorax → the heart is inside the thoracic (chest) cavity.

• Extending to the 5th intercostal space → the bottom of the heart reaches around the 5th space between the ribs.

• To the left of the sternum mainly

Location of Heart in Mediastinum

• Mediastinum = the central region of the thoracic cavity (entire space of chest), between vertebrae & sternum.

  • Contains the heart, great vessels, trachea, esophagus, etc.

  • Does NOT contain the lungs (the lungs are in the pleural cavities).

• Middle portion of the mediastinum = the middle mediastinum, which is occupied mainly by the heart.

Mediastinum Portions

• The transverse thoracic plane runs from: Sternal angle anteriorly to T4–T5 intervertebral disc posteriorly

Purpose: to divide the mediastinum into superior & inferior parts.

• The inferior mediastinum is divided into 3 parts

From front → back:

Anterior → Middle → Posterior

And the heart is in the middle mediastinum

Surfaces of Heart

• Base → the back/posterior part of the heart. Mostly formed by the left atrium, with some right atrium. It’s where the major vessels attach.

• Apex → the pointed bottom of the heart. Formed by the left ventricle and points down, forward, and to the left.

• Diaphragmatic surface → the bottom surface resting on the diaphragm. Mostly formed by the left ventricle, with some right ventricle.

• Sternocostal (anterior) surface → the front surface, facing the sternum/ribs. Mostly the right ventricle.

• Pulmonary surfaces → the sides facing the lungs:

  • Right pulmonary surface → mainly right atrium

  • Left pulmonary surface → mainly left ventricle

Anterior Heart Features

How each part works step by step:

Superior Vena Cava

• Large vein that brings deoxygenated blood from the upper body to the right atrium.

Right Atrium

• Receives deoxygenated blood coming from the SVC.

• Has an auricle (small pouch) attached to allow it to hold more blood

Right Ventricle

• Pumps deoxygenated blood to the pulmonary trunk..

Pulmonary Trunk

• Carries deoxygenated blood to the pulmonary arteries then lungs to pick up oxygen.

Left Atrium

• Receives oxygenated blood from the lungs.

• Has an auricle (small pouch) attached to allow it to hold more blood.

Left Ventricle

• Pumps oxygenated blood to the aorta

• Has the thickest myocardium because it has to generate high pressure.

Aorta

• The body’s largest artery.

• Carries oxygenated blood to entire body.

The aorta then gives off three major branches:

Brachiocephalic trunk
→ supplies the right side of the head/neck and right upper limb

Left common carotid artery
→ supplies the left side of the head and neck

Left subclavian artery
→ supplies the left upper limb

Posterior Heart Features

How each part works step by step:

Superior Vena Cava

• Large vein that brings deoxygenated blood from the upper body to the right atrium.

Inferior Vena Cava

• Brings deoxygenated blood from the lower body to the right atrium.

Right Atrium

• Receives deoxygenated blood coming from the SVC & IVC.

• Has an auricle (small pouch) attached to allow it to hold more blood

Right Ventricle

• Pumps deoxygenated blood to the pulmonary trunk.

Pulmonary Trunk

• Carries deoxygenated blood to the pulmonary arteries then lungs to pick up oxygen.

Left Atrium

• Receives oxygenated blood from the lungs.

• Has an auricle (small pouch) attached to allow it to hold more blood.

Left Ventricle

• Pumps oxygenated blood to the aorta

• Has the thickest myocardium because it has to generate high pressure.

Aorta

• The body’s largest artery.

• Carries oxygenated blood to entire body.

The aorta then gives off three major branches:

Brachiocephalic trunk (contains right subclavian artery & right common carotid artery)

→ supplies the right side of the head/neck and right upper limb

Left common carotid artery

→ supplies the left side of the head and neck

Left subclavian artery

→ supplies the left upper limb

Posterior & Anterior Sulcus

Coronary Sulcus

• Groove between the surface of right atria and the ventricles for anterior view (left atria and ventricles for posterior view)

• contains right & left coronary arteries

• What it does: pathway for the coronary arteries and veins that supply/drain the heart muscle.

Anterior/Posterior Interventricular Sulcus

• Grooves between the surface of right & left ventricles (depends on anterior or posterior surface)

• Contains right & left coronary arteries

• What it does: pathway for coronary blood vessels that supply the myocardium.

Pericardium

2 layers of the pericardium:

Fibrous pericardium

• Fibrous outer layer that helps anchor heart in place inferiorly to diaphragm

• Comes superiorly to surround great vessels

Parietal layer of serous pericardium (wall of body cavity)

• 2 layers (visceral & parietal)

• Parietal layer: sticks directly to the fibrous pericardium

• Visceral layer: epicardium

Pericardial Cavity: the space between the parietal & visceral layers of serous pericardium. Has fluids to prevents friction.

Layers of the Heart

Layers of the heart

1. Pericardium - surrounds/encloses the heart and the roots of great vessels (like the protective sac)

2. Epicardium (visceral) - directly on heart surface (membrane that protects the muscle heart’s surface to reduce friction)

3. Myocardium - muscle of the heart (helps contraction and pumping out blood)

4. Endocardium - linings of chambers of heart (makes inside of heart’s surface smooth to reduce friction)

Coronary Arteries

Brings oxygenated blood TO the heart muscle.

* Right Coronary A. → supplies (to bring) much of the general right side (RV & RA) of the heart

* Right Marginal A. → supplies the right margin/right ventricle

* Left Coronary A. → supplies much of the left side (LV & LA) of the heart

* Left Marginal A. → supplies the left margin/left ventricle

* Circumflex A. → supplies the left margin and ventricles parts of the heart

* Anterior Interventricular A. (Runs in anterior sulcus) → supplies the front of the ventricles

* Posterior Interventricular A. (Runs in posterior sulcus) → supplies the back of the ventricles

• Coronary Veins

- Take deoxygenated blood AWAY FROM the heart muscle.

• Small cardiac vein → drains (to collect and carry blood away) the right side of the heart

• Right marginal vein → drains the right margin

• Great cardiac vein → drains much of the anterior heart

• Middle cardiac vein → drains the posterior heart

• Left marginal vein → drains the left margin

• Left Atrium Oblique Vein - drains the left atrium

• Left posterior ventricular vein → drains the posterior of the left ventricle

• Anterior cardiac veins → drains the anterior right ventricle, directly into the right atrium

• Coronary sinus → large collecting vein that receives blood from several cardiac veins and empties into the right atrium

Cusps, Trabeculae Carnae, Chordae Tendinae

Cusps

→ The flaps that form AV valves.
→ Open to let blood move forward and close to stop blood from flowing backward.

Chordae tendineae

→ fibrous cords attached to the cusps to the papillary muscles of the AV valves
→ Holds the valve cusps in place when the ventricle contracts

Trabeculae carneae

→ Irregular muscular elevations projecting on the inside walls of the ventricles.
→ Helps the ventricles contract effectively

Papillary Muscles

• A special type of trabeculae carnae attached to the ventricular wall and the chordae tendinae

• Pulls on chordae tendineae & prevents AV valve from flipping inside out when ventricles contract

How the Mitral Valves works

1. Ventricles relax
   → pressure in ventricles is low
   → mitral valve opens
   → blood flows left atrium → left ventricle

2. Ventricles contract
→ pressure in the left ventricle rises
→ blood wants to push back toward the left atrium

3. Mitral/Bicuspid valve closes
→ the cusps come together and seal the opening
→ prevents blood from flowing back into the atrium

4. Papillary muscles contract
→ they pull on the chordae tendineae
→ this helps stop the valve cusps from flipping inside-out/prolapsing into the atrium

Transverse Section of Heart (the

Tricuspid Valve — AV valve

• Between the right atrium and right ventricle

• Opens: blood moves RA → RV

• Closes: prevents blood from going back into the right atrium

Bicuspid/Mitral Valve — AV valve

• Between the left atrium and left ventricle

• Opens: blood moves LA → LV

• Closes: prevents blood from going back into the left atrium

Pulmonary Valve — semilunar valve

• Between the right ventricle and pulmonary trunk

• Opens: blood moves RV → pulmonary trunk

• Closes: prevents blood from going back into the right ventricle

Aortic Valve — semilunar valve

• Between the left ventricle and aorta

• Opens: blood moves LV → aorta

• Closes: prevents blood from going back into the left ventricle

• Conducting System of Heart

• Atria = rooms that receive blood

• Ventricles = rooms that pump blood

• Valves = doors that control which direction blood can move

Phase 1: Atrial systole (Both atria are in systole (contracted), while ventricles are in diastole (relaxed))

• The blood enters the ventricles (bc they’re relaxed) through the AV valves (between the atrium & ventricles)

• ends when the AV valves slam shut

• Produces a lub sound

Phase 2: Ventricular systole (Ventricles are in systole (contract), while the atria are in diastole (relaxed))

• Blood in the right ventricle exits through the pulmonary artery trunk to the pulmonary arteries due to ventricle pushing blood out

• Blood in the left ventricle exits into the aorta

• ends as the ventricles complete their pumping job

Phase 3: Atrial and ventricular diastole

• Blood starts filling the heart again.

• Blood returning to the heart fills the atria and passively into the ventricles

• Semilunar valves closes for the dub sound

Heart Nodes

SA node — starts the signal

• SA = sinoatrial node

• Located in the right atrium

• Creates the electrical signal that makes the both atria contract

2. AV node — briefly delays the signal

• AV = atrioventricular node

• Located between the atria and ventricles (interatrial septum)

• Receives the signal from the SA node.

• Delays it briefly so the atria have time to finish contracting and empty blood into the ventricles.

3. AV bundle — carries the signal downward

• Carries the electrical signal from the AV node into the ventricles.

4. Right & left bundle branches — split the signal

The AV bundle divides into:

• Right bundle branch → right ventricle

• Left bundle branch → left ventricle

They carry the signal down toward the bottom of the heart.

5. Subendocardial branches — spread the signal

Also called Purkinje fibres.

• Spread the electrical signal throughout the ventricular walls.

• This causes the ventricles to contract, pushing blood out.

• They travel through the interventricular septum (wall between the ventricles).