exam 1: cardiac structure & function

Heart location

The heart is a hollow, muscular organ that lies in the central thoracic cavity slightly to the left of the midline, between the 3rd and 5th intercostal spaces, anterior to the vertebrae, posterior to the sternum & lungs

Pericardium

The great vessels are surrounded by a fibroserous sac called the pericardium. It is a loose, double layer sac of elastic connective tissue. It is surrounded by approximately 10-50ml of serous fluid, which prevents friction as the heart beats.

What does the pericardium surround?

The heart and proximal ends of the aorta, vena cava, and the pulmonary artery

Pericardium function

Helps protect the heart against infection, trauma, and friction. Aids in the function by helping with the free pumping motions. The many attachments around the pericardial sac hold it securely in the thorax (chest), which helps keep the heart in its normal position.

2 layers of pericardium

Fibrous, serous

2 layers of the pericardium’s serous layer

1. The parietal layer lines the inside of the fibrous pericardium

2. The visceral layer (or epicardium) reflects back on itself and lines the outer fibrous layer, forming the parietal pericardium

Pericardial space (cavity)

Located between the visceral and parietal layers & contains a clear fluid that is released the serous membrane. The fluid acts as a lubricant to prevent friction during contraction and relaxation of the heart.

Shape of the heart

The heart is shaped roughly like a cone and consists of four muscular chambers

Which chambers are less muscular? What are their function?

The R and L atria are less muscular than the R and L ventricles. The atria deliver blood to their respective ventricles, and the ventricles are the main pumping chambers.

• ventricles contract harder and that is why they have myocardium.

R side vs L side of the heart (pressure and receiving blood, & circulation)

Right side: low pressure → receives deoxygenated blood from body → pumps to lungs (pulmonary circulation)

Left side: high pressure → receives deoxygenated blood from lungs → pumps to body (systemic circulation)

Where do R sided structures of the heart lie?

Mostly anterior to their left sided counterparts (more toward the front of the body)

Atrial chambers location compared to the ventricles

Atrial chambers are located mostly to the R of their corresponding ventricle (atria sit above and slightly to the right of their ventricles)

Valves

Four major valves in the heart direct blood flow in a forward direction and prevent backward leakage.

• the AV valves (tricuspid & mitral) seperate the atria and ventricles.

• The semilunar valves (pulmonic & aortic) seperate the ventricles from the great arteries

What opens to the right atriums?

• superior vena cava

• Inferior vena cava

• Coronary sinus

  • these structures feed blood to the RA

Venae cavae role in the circulatory system

Return's deoxygenated blood from systemic veins into the RA

Coronary sinus role in the circulatory system

Carries venous return from the coronary arteries

Interatrial septum

Forms the wall of the RA and repeated it from the LA

Describe the right ventricle

• roughly triangular shape

• superior portion forms a cone shaped outflow tract to the pulmonary artery

• outflow tract wall is smooth

• rest of ventricle contains muscular ridges called trabeculae carneae, giving a sponge-like appearance

• Large trabecula crossing the ventricle is called moderator band

Papillary muscles & tricuspid valve (RV)

• 3 papillary muscles attach to the tricuspid valve leaflets via chordae tendineae

• When the ventricle contracts, papillary muscles tighten the chordae. This helps keep valve leaflets aligned and closed.

• Prevents blood from flowing backward into the RA (regurgitation)

Pulmonic valve (RV)

• Located at the apex of the RV → leads to pulmonary artery

• Has 3 cusps attached to a fibrous ring

• Opens when RV contracts

• Closes when ventricle relaxes due to blood pushing back from pulmonary artery

• Prevents blood from flowing backward into into the RV (regurgitation)

Left Atrium - key features

• Receives blood from 4 pulmonary veins (from lungs)

• Blood enters the posterior (back) part of the atrium

• Wall is about 2mm thick, slightly thicker than the RA

• Blood flows through the mitral valve into the left ventricle (below the atrium)

Left Ventricle - structure

• Cone shaped and longer than the right ventricle

• Wall is 9-22 mm thick (about 3x thicker than RV)

• Contains trabeculae carneae (muscular ridges)

• These ridges are finer and more numerous than in the RV

Left ventricle - papillary muscles & mitral valve

• Has 2 large papillary muscles (bigger than RV)

• Connected to the mitral valve by chordae tendinae

• Chordae are thicker but fewer than in the RV

• Each papillary muscle attaches to both mitral valve leaflets

• When the ventricle contracts, chordae tighten to keep the valve aligned

• Prevents blood from leaking backward into the LA (regurgitation)

Aortic Valve (LV)

• Separated the LV from the aorta

• Has 3 cusps attached to a fibrous ring Opens

• Opens when the LV contracts and closes when it relaxes

• Prevents blood from flowing back into the LV

• R and L coronary arteries originate just above the valve cusps in the aorta

Interventricular (IV) Septum

• Thick wall between the R and L ventricles

• Large muscular part bulged toward the RV

• Small membranous part is thin & oval shaped, located just inferior (below) the aortic valve cusps

Path of blood flow through the heart

SVC/IVC → RA → tricuspid valve → RV → pulmonic valve → pulmonary artery → lungs (co2 out, o2 in) → lungs → pulmonary veins → LA (oxygenated blood) → mitral (bicuspid) valve → LV → aortic valve → aorta → body

Impulse conduction system: Bundle of His (AV bundle) & branches

• Located distal to the AV node

• Passes through the IV septum

• Bifurcates into 2 branches

  • R bundle branch → compact, carries signals to RV

  • L bundle branch → broader, spreads across the left septum

• Helps conduct electrical impulses to ventricles for contraction

Impulse conduction system: R bundle branch pathway

• Runs through the IV septum toward the apex

• Becomes subendocardial (closer to inner heart surface) near the RV wall

• Bifurcates into 2 branches

  • One travels through the moderator band

  • Another continues toward the apex of the RV

• Forms a network of fibers that spreads throughout the RV to coordinate contraction

Impulse conduction system: L bundle branch pathway

• Splits into 3 main parts:

  • Anterior fascicle → goes to apex and anterior papillary muscle

  • Posterior fascicle → goes to posterior papillary muscle

  • Septal branch → supplies the septum

• All branches form a network (plexus) under the inner lining of the heart

• This network spreads electrical signals across the entire LV to coordinate contraction

Impulse conduction system: Purkinje fibers & ventricular activation

• Subendocardial networks send Purkinje fibers into ventricular muscle

• Electrical signal spreads in order:

  • Papillary muscles first

  • Then ventricular walls

• Papillary muscles contract slightly before the ventricles

• Keeps AV valve leaflets stable during contractions

• Prevents blood from flowing backward (regurgitation)

Coronary arteries - function & origin

• Supply the heart muscle with oxygen and nutrients

• Arise from the aorta just above the aortic valve cusps

Cardiac Vessels - what are they?

• Include:

  • Coronary arteries → Oxygen rich blood to muscles we need

  • Coronary veins → Take same pathway as arteries. Delivers oxygen poor blood to body.

  • Lymphatic vessels

• Located mainly in epicardial fat (fat on the hearts surface) within loose connective tissue

Left Main Coronary Artery (LMCA)

• Runs between the LA and pulmonary trunk

• Splits into 2 main branches:

  • Left Anterior Descending (LAD) artery

  • Circumflex artery

• Supplies blood to major areas of the left side of the heart

Right Coronary Artery (RCA) - distribution

• Travels in the right AV groove between RA and RV

• Branches include:

  • Acute marginal branches → supply RV

  • Posterior descending artery (PDA) → supplies inferior/posterior ventricles + posterior 1/3 of IV septum

  • AV nodal artery → supplies the AV node

Coronary veins

• Follow a similar path to the coronary arteries

• Drain blood from the myocardium (heart muscle)

• Carry deoxygenated blood back to the RA

• Blood returns through coronary sinus