---

Heart and Vascular System - Complete Anatomy Notes

---

STEP 1 - OVERVIEW AND POSITION OF THE HEART

• About the size of a clenched fist
• Weighs approximately 250-350 g in adults

• The base (posterior surface) faces posteriorly and to the right - formed mainly by the left atrium
• The apex points inferiorly, anteriorly, and to the left - formed by the left ventricle
• The apex sits at approximately the 5th intercostal space, midclavicular line

• Right border: Superior vena cava + right atrium + inferior vena cava
• Left border: Arch of aorta + pulmonary trunk + left auricle + left ventricle
• Inferior border: Right ventricle + left ventricle (at apex)

---

STEP 2 - THE PERICARDIUM

2.1 Fibrous Pericardium

• A tough, cone-shaped bag of dense connective tissue
• Base attached to the central tendon of the diaphragm
• Apex is continuous with the adventitia of the great vessels
• Attached anteriorly to the sternum by sternopericardial ligaments
• Limits cardiac distension and holds the heart in position

2.2 Serous Pericardium

• The pericardial cavity is the narrow potential space between these two layers, containing a small amount of serous fluid that allows frictionless cardiac movement
• The two layers are continuous at the roots of the great vessels

2.3 Pericardial Sinuses

• Transverse pericardial sinus: Between the arterial vessels (aorta + pulmonary trunk) anteriorly and the venous vessels (SVC + pulmonary veins) posteriorly - important landmark in cardiac surgery
• Oblique pericardial sinus: Behind the left atrium, between the pulmonary veins

2.4 Pericardial Innervation

• The phrenic nerves (C3-C5) supply the fibrous pericardium
• Pain from pericardial disease can be referred to the shoulder and lateral neck (C3-C5 dermatomes)
• Visceral pericardium (epicardium) has no pain sensation

Clinical Note: In cardiac tamponade, rapid accumulation of fluid in the pericardial cavity compresses the heart and causes biventricular failure. Treatment: pericardiocentesis (needle drainage).

---

STEP 3 - EXTERNAL ANATOMY OF THE HEART

3.1 Surfaces

3.2 External Grooves (Sulci)

• Coronary sulcus (atrioventricular groove): Circles the heart, separating atria from ventricles; contains the right coronary artery, left circumflex artery, coronary sinus, and small cardiac vein
• Anterior interventricular sulcus: On the anterior surface; contains the anterior interventricular artery (LAD) and great cardiac vein
• Posterior interventricular sulcus: On the diaphragmatic surface; contains the posterior interventricular artery and middle cardiac vein

---

STEP 4 - THE FOUR CARDIAC CHAMBERS

• Right pump: Receives deoxygenated blood from the body, sends it to the lungs (pulmonary circulation)
• Left pump: Receives oxygenated blood from the lungs, sends it to the body (systemic circulation)

4.1 Right Atrium

• Forms the right border of the heart
• Receives blood from 3 openings: Superior vena cava (upper posterior wall), Inferior vena cava (lower posterior wall), and Coronary sinus (between IVC and tricuspid valve)
• Interior divided by the crista terminalis (muscular ridge) into:
  • Sinus of venae cavae (posterior) - smooth-walled; embryological origin: right horn of sinus venosus
  • Atrium proper (anterior) - has muscular ridges called musculi pectinati (pectinate muscles)
• Right auricle: Ear-like muscular pouch that overlaps the ascending aorta
• Fossa ovalis: Oval depression on the interatrial septum - remnant of the embryonic foramen ovale
• Tricuspid valve guards the right atrioventricular orifice

4.2 Right Ventricle

• Forms most of the anterior surface of the heart
• Has the thinnest wall of the four chambers (less resistance in pulmonary circulation)
• Interior features:
  • Trabeculae carneae - irregular muscular ridges on inner walls
  • Papillary muscles (anterior, posterior, septal) - attached to valve cusps via chordae tendineae
  • Septomarginal trabecula (moderator band) - muscular band from interventricular septum to anterior papillary muscle; carries the right bundle branch of the conduction system
  • Conus arteriosus (infundibulum) - smooth-walled outflow cone that leads to the pulmonary valve
• Pulmonary (semilunar) valve guards the exit into the pulmonary trunk (3 cusps: anterior, left, right)

4.3 Left Atrium

• Forms most of the base (posterior surface) of the heart
• Receives 4 pulmonary veins (2 from each lung) on its posterior surface
• Has left auricle - narrow, hooked pouch
• Smooth posterior wall (derived from the incorporated pulmonary veins)
• Anterior wall has some pectinate muscles (in the auricle)
• Mitral (bicuspid) valve guards the left atrioventricular orifice - 2 cusps (anterior/aortic + posterior/mural)

4.4 Left Ventricle

• Has the thickest wall (~3x the right ventricle wall thickness) to generate high systemic pressure
• Produces most of the left pulmonary surface and the apex
• Interior features:
  • Trabeculae carneae (finer than right side)
  • 2 papillary muscles (anterior and posterior) with chordae tendineae to mitral valve cusps
  • Smooth outflow tract (aortic vestibule) leading to the aortic valve
• Aortic (semilunar) valve guards the aortic orifice - 3 cusps: right, left (coronary cusps), and posterior (non-coronary)
• Above the aortic cusps are 3 aortic sinuses (sinuses of Valsalva) - the right and left coronary arteries arise from the right and left sinuses respectively

---

STEP 5 - CARDIAC VALVES IN DETAIL

Cardiac Skeleton

• Dense fibrous connective tissue rings (annuli fibrosi) surrounding all four valve orifices
• Provides attachment for valve cusps and myocardium
• Electrically isolates atria from ventricles - the AV bundle is the only muscular connection through this insulating layer
• Includes: right and left fibrous trigones, and four annuli fibrosi

---

STEP 6 - THE CARDIAC CONDUCTION SYSTEM

6.1 Sinoatrial (SA) Node - "Pacemaker"

• Located at the superior end of the crista terminalis, at the junction of the superior vena cava and right atrium
• Sets the rate of the heartbeat (~60-100 bpm at rest)
• Excitation spreads across both atria causing atrial contraction
• Blood supply: SA nodal branch of the right coronary artery (in ~55-60% of people) or left circumflex artery

6.2 Atrioventricular (AV) Node

• Located near the opening of the coronary sinus, close to the attachment of the septal cusp of the tricuspid valve, within the AV septum
• Receives the atrial excitation wave and delays it (allows atrial contraction to complete before ventricular contraction begins - the "PR interval" on ECG)
• Blood supply: AV nodal branch of the right coronary artery (~90% of cases)

6.3 Atrioventricular Bundle (Bundle of His)

• Direct continuation of the AV node
• Runs along the lower border of the membranous interventricular septum
• Then splits into right bundle branch and left bundle branch
• The right bundle branch: passes down the right side of the septum, enters the septomarginal trabecula, reaches the anterior papillary muscle, then spreads as Purkinje fibers
• The left bundle branch: passes to the left side of the muscular septum, descends to the apex, gives off branches, becomes Purkinje fibers

6.4 Subendocardial Plexus (Purkinje Fibers)

• Network of specialized cells spreading throughout both ventricles
• Contacts increase greatly at the subendocardial level - enables synchronized ventricular contraction from apex upward toward the outflow tracts
• Creates a unidirectional wave of excitation from papillary muscles/apex toward the arterial outflow tracts

---

STEP 7 - CORONARY VASCULATURE

7.1 Coronary Arteries

• Originates from the right aortic sinus
• Descends vertically in the coronary sulcus between the right atrium and right ventricle
• Turns posteriorly at the inferior margin to the diaphragmatic surface
• Key branches:
  • SA nodal branch - to the sinoatrial node (runs posterior to SVC)
  • Right marginal branch - runs along the acute (inferior) margin toward the apex
  • Posterior interventricular (descending) artery - in the posterior interventricular sulcus (in "right-dominant" hearts, ~70% of people)
  • AV nodal branch

• Originates from the left aortic sinus
• Short main stem (left main coronary artery) passes between the pulmonary trunk and left auricle
• Divides into 2 major branches:
  • Anterior interventricular (LAD - Left Anterior Descending) artery: Descends in the anterior interventricular sulcus to the apex; supplies the anterior wall of both ventricles and the anterior 2/3 of the interventricular septum; most commonly occluded artery in MI
  • Circumflex artery: Continues in the coronary sulcus, wraps around the left side to the posterior surface; supplies the left atrium and posterior left ventricle; in "left-dominant" hearts, gives off the posterior interventricular artery

• ~70% right-dominant (RCA gives posterior interventricular artery)
• ~10% left-dominant (circumflex gives posterior interventricular artery)
• ~20% co-dominant

• Flows to the epicardium during both systole and diastole
• Flows to the endocardium predominantly during diastole (endocardium is compressed by LV pressure during systole)
• Flow is regulated by metabolic signals: nitric oxide, adenosine, bradykinins, prostaglandins, CO2

7.2 Cardiac Veins

7.3 Coronary Lymphatics

• Lymphatics follow the coronary arteries
• Drain mainly to brachiocephalic nodes (anterior to brachiocephalic veins) and tracheobronchial nodes (at the inferior end of the trachea)

---

STEP 8 - CARDIAC INNERVATION

• Superficial part: Inferior to the aortic arch, between the aortic arch and pulmonary trunk
• Deep part: Between the aortic arch and the tracheal bifurcation

8.1 Parasympathetic Supply (Vagus Nerve - CN X)

• Preganglionic fibers: cardiac branches of right and left vagus nerves
• Synapse in ganglia within the plexus or walls of the atria
• Effects:
  • Decreases heart rate
  • Reduces force of contraction
  • Constricts coronary arteries

8.2 Sympathetic Supply

• Preganglionic fibers: upper 4-5 thoracic spinal cord segments (T1-T5)
• Synapse in cervical and upper thoracic sympathetic ganglia
• Postganglionic fibers: bilateral cardiac nerves to cardiac plexus
• Effects:
  • Increases heart rate
  • Increases force of contraction
  • Dilates coronary arteries

8.3 Visceral Afferents (Pain Fibers)

• Travel with sympathetic trunk fibers
• Enter spinal cord at T1-T5
• Referred pain: Cardiac ischemia pain is referred to the chest, left arm, jaw, and neck because these share the same spinal cord levels (T1-T5)
• Vagal afferents sense blood pressure and chemistry (reflex functions, not pain)

---

STEP 9 - GREAT VESSELS

9.1 Pulmonary Trunk

• Arises from the conus arteriosus of the right ventricle
• Contained within the pericardial sac
• Associated with the ascending aorta in a common sheath
• Bifurcates at the level of the T4/T5 intervertebral disc into:
  • Right pulmonary artery: Passes right, posterior to ascending aorta and SVC
  • Left pulmonary artery: Passes inferior to the aortic arch, anterior to descending aorta

9.2 Ascending Aorta

• Contained within the pericardial sac
• Above the aortic valve are 3 aortic sinuses (left, right, posterior)
• Right and left coronary arteries originate from the right and left sinuses

9.3 Arch of Aorta

• Gives off 3 branches (left to right in the superior mediastinum):
  1. Brachiocephalic trunk - divides into right subclavian + right common carotid
  2. Left common carotid artery
  3. Left subclavian artery

9.4 Superior Vena Cava

• Formed by union of left and right brachiocephalic veins
• Inferior half lies within the pericardial sac
• Enters right atrium at approximately the 3rd right costal cartilage

9.5 Inferior Vena Cava

• Passes through the diaphragm at vertebra T8
• Enters the fibrous pericardium; short segment within pericardial sac before entering right atrium

9.6 Pulmonary Veins

• Usually 2 from each lung (4 total)
• Enter the posterior surface of the left atrium
• Short segment of each within the pericardial sac

---

STEP 10 - BLOOD FLOW THROUGH THE HEART (Complete Circuit)

BODY (deoxygenated blood)
     |
     v
Superior Vena Cava / Inferior Vena Cava / Coronary Sinus
     |
     v
RIGHT ATRIUM
     |  (tricuspid valve opens)
     v
RIGHT VENTRICLE
     |  (pulmonary valve opens)
     v
PULMONARY TRUNK --> Right & Left Pulmonary Arteries
     |
     v
LUNGS (gas exchange - CO2 released, O2 absorbed)
     |
     v
4 Pulmonary Veins (oxygenated blood)
     |
     v
LEFT ATRIUM
     |  (mitral valve opens)
     v
LEFT VENTRICLE
     |  (aortic valve opens)
     v
AORTA --> SYSTEMIC CIRCULATION (body)

---

STEP 11 - VASCULAR SYSTEM (Systemic Vessels)

11.1 Vessel Wall Layers (Tunica Structure)

11.2 Types of Blood Vessels

11.3 Major Systemic Arteries

1. Ascending aorta - coronary arteries
2. Aortic arch - brachiocephalic, left common carotid, left subclavian
3. Descending thoracic aorta - bronchial, esophageal, posterior intercostal arteries
4. Abdominal aorta - celiac trunk, SMA, suprarenal, renal, gonadal, IMA, common iliac arteries
5. Bifurcates into common iliac arteries at L4

11.4 Major Systemic Veins

• Superior vena cava (SVC): Drains head, neck, upper limbs, and upper thorax
• Inferior vena cava (IVC): Drains lower limbs, pelvis, abdomen
• Azygos system: Drains thoracic wall, posterior mediastinum
• Portal vein: Drains GI tract and spleen to liver before returning to IVC (via hepatic veins)

---

STEP 12 - WALL OF THE HEART (Histology)

• Striated, branching, uninucleate cells
• Connected end-to-end by intercalated discs (containing gap junctions - allow electrical coupling, and desmosomes - mechanical coupling)
• ~60-70% of heart cells are actually cardiac fibroblasts (not muscle), which produce the extracellular collagen matrix

• Cardiac fibroblasts produce the collagen scaffold
• In pathological states (hypertension, MI, heart failure), fibroblasts produce excess extracellular matrix leading to cardiac fibrosis
• Therapies including statins, ACE inhibitors, beta-blockers, and ARBs reduce fibrosis (favorable "reverse remodeling")

---

QUICK REFERENCE SUMMARY TABLE

---