Anatomy Ch 19: Circulatory System: The Heart

Cardiovascular System

Includes:

• Heart

• Blood vessels

Heart

A muscular pump that keeps blood moving

Blood Vessels

• Deliver blood to organs and tissues

• Return blood back to the heart

Major Divisions of the Cardiovascular System

1. Pulmonary Circuit

2. Systemic Circuit

Pulmonary Circuit

• Caries blood from the heart to the lungs

Purpose: gas exchange

• Blood released CO2

• Blood picks up O2

• Then returns blood back to the heart

• Blood here is mostly deoxygenated going to lungs and oxygenated returning

Systemic Circuit

• Carries blood from the heart to the rest of the body

• Supplies all organs and tissues

→ includes lung tissue and the heart wall itself

• Returns blood back to the heart

• Blood leaving the heart is oxygenated

• Blood returning is deoxygenated

Position, Size, and Shape of the Heart

• Located in the mediastinum

→ thick portion between the lungs

• Shape: roughly triangular

Heart Base

Wide, superior (upper) portion

Apex

Tapered, inferior (lower) end

→ points slightly to the left

Pericardium (Heart Covering)

1. Fibrous Pericardium

2. Serous Pericardium (inner layer)

Fibrous Pericardium

• Outer layer

• Dense connective tissue

• Anchors heart:

→ inferiorly to the diaphragm

→ anteriorly to the sternum

Serous Pericardium (inner layer)

Has two layers:

• Parietal layer

• Visceral layer (Epicardium)

Parietal Layer

Lines the inside of the fibrous pericardium

Visceral layer (Epicardium)

• Sticks directly to the heart surface

• Forms the outermost layer of the heart wall

• Moves as the heart contracts

Pericardial Cavity

• Space between parietal and visceral layers

• Contains 5-30mL of pericardial fluid

Fluid:

• Reduces friction

• Allows smooth heart movement

Inflammation= pericarditis (painful)

Layers of the Heart Wall (Outside → Inside)

1. Epicardium

2. Myocardium

3. Endocardium

Epicardium

• Same as visceral layer of serous pericardium

• Thin serous membrane

• Coronary blood vessels run through it

Myocardium

• Thickest layer

• Made of cardiac muscle

• Responsible for pumping blood

Endocardium

• Smooth inner lining of heart chambers

• Made of simple squamous epithelium

Covers:

• Heart valves

• Continuous with blood vessel lining (endothelium)

Myocardium (Closer Look)

• Thick because it has the greatest workload

• Cardiac muscle arranged in spiraling bundles

• Forms a twisting pattern (vortex) near the apex

• This creates a wringing motion

→ improves efficiency of blood pumping

Fibrous Skeleton of the Heart

• Dense connective tissue framework

• Located between atria and ventricles

• Forms fibrous rings that surround:

→ heart valves

→ major blood vessels

Fibrous Skeleton of the Heart Functions

1. Provides structural support

2. Anchors cardiomyocytes, giving the something to pull against

3. Provides electrical insulation

Internal Anatomy of the Heart

4 Chamber TOTAL

• Atriums (2 upper chambers)

• Ventricles (2 lower chambers)

Atriums (2 upper chambers)

• Right atrium & Left atrium

Function: receive blood returning to heart

• Each atrium has an auricle

→ earlike flap

→ slightly increases volume

• Separated by interatrial septum

Ventricles (2 lower chambers)

• Right ventricle & Left ventricle

Function: pump blood into arteries

• Separated by interventricular septum

• Inner walls have ridges called trabeculae carneae

→ Help prevent wall collapse during contraction

Surface Anatomy - Coronary Sulcus

Separates atria from ventricles

Surface Anatomy - Intraventricular Sulcus

Marks boundary between ventricles

Heart Valves (one-way blood flow)

• Atrioventricular (AV) Valves

• Semilunar Valves

Atrioventricular (AV) Valves

Control blood flow between atria and ventricles

• Right AV Valve (Tricuspid)

-3 cusps (flaps)

• Left AV Valve (Mitral/Bicuspid)

-2 cusps

Chordae Tendineae

• Tendinous cords

• Connect AV valves to papillary muscles

• Prevent valves from:

-Flipping backward

-Bulging into atria during ventricular contraction

Semilunar Valves

• Pulmonary valve

• Aoritc valve

Pulmonary Valve

Between right ventricle and pulmonary trunk

Aoritc Valve

Between left ventricle and aorta

1. Blood enters the right atrium

• From the superior vena cava and inferior vena cava

• Blood is deoxygenated (low O2, high CO2)

2. Right atrium → Right ventricle

Blood flows through the right AV (tricuspid) valve

3. Right Ventricle Contracts

Contraction forces the pulmonary valve open

4. Blood enters the pulmonary trunk

Passes through pulmonary valve into the pulmonary trunk

5. Pulmonary arteries → lungs

• Right and left pulmonary arteries deliver blood to lungs

• Blood unloads CO2 and loads O2

6. Blood returns to hear from lungs

• Via pulmonary veins

• Enters the left atrium

• Blood is now oxygenated

7. Left atrium → left ventricle

Blood flows through left AV (mitral) valve

8. Left ventricle contracts

• (occurs simultaneously with right ventricular contraction)

• Forces aortic valve open

9. Blood enters the aorta

Through aortic valve into ascending aorta

10. Systemic circulation

• Blood distributed to all body organs

• Unloads O2 and loads CO2

11. Return to right atrium

• Blood returns via venae cavae

• Cycle repeats

Coronary Circulation

• blood vessels that supply the heart wall

• Includes:

  • Coronary arteries → deliver oxygen & nutrients

  • Capillaries → extremely dense

  • Coronary veins → return blood to heart

Why Coronary Circulation is Necessary

• Over an 80-year lifespan:

  • Heart beats > 3 billion times

  • Each ventricle pumps > 200 million liters of blood

• The myocardium (heart muscle) has extremely high energy demands

• Blood inside heart chambers cannot nourish heart tissue

Left Coronary Artery (LCA)

Branches off the ascending aorta

1. Anterior interventricular artery

2. Circumflex artery

Anterior Interventricular Artery

Supplies:

• Both ventricles

• Anterior 2/3 of interventricular septum

Circumflex Artery

• Runs in coronary sulcus on left side

• Gives off left marginal branch

• Ends on posterior heart surface

• Supplies:

  • Left atrium

  • Posterior wall of left ventricle

Right Coronary Artery (RCA)

Branches off the ascending aorta

Supplies:

• Right atrium

• Sinoatrial (SA) node (pacemakers)

1. Right marginal artery

2. Posterior interventricular artery

Right Marginal Artery

Supplies lateral right atrium and ventricle

Posterior Interventricular Artery

Supplies posterior walls of ventricles

Coronary Venous Return (How Blood Leaves the Heart Wall)

• Minor Route (5-10%)

• Major Route (Most Blood)

Minor Route (5-10%)

• Drains directly into heart chambers (mostly right ventricle)

• Via small cardiac veins

Major Route (Most Blood)

• Drains into coronary sinus

• Coronary sinus empties into right atrium

Main Veins Feeding the Coronary Sinus

1. Great Cardiac Vein- anterior heart

2. Middle (posterior interventricular) cardiac vein- posterior heart

3. Left marginal vein- empties in coronary sinus

Angia Pectoris

• Chest pain due to partial coronary blockage

• Caused by:

  • Blood clots or fatty deposits

• Results in temporary ischemia (low blood flow)

• Myocardium switches to anaerobic metabolism

• Produces lactate, which stimulates pain

• Is reversible

Myocardial Infarction (MI)

• Results from long-term or complete obstruction

• Causes death of myocardium downstream

• Can lead to:

  • Fibrillation

  • Cardiac arrest

• Responsible for 27% of deaths in the U.S. annually

Treatments for Coronary Artery Obstruction

• Coronary bypass surgery

• Gene therapy

• Angioplasty

Coronary Bypass Surgery

Vein (often from leg) used to bypass blocked artery

Gene Therapy

• Injection of VEGF gene

• Stimulates growth of new blood vessel

• May eliminate need to bypass surgery

Angioplasty

• Ballon opens artery

• Stent (mesh tube) inserted to keep it open

• Stents often drug-coated to dissolve blockages

Collateral Circulation

• Helps protect against heart attack

• Some coronary arteries converge

• Connection points= arterial anastomoses

• Provide alternate routes of blood flow

• Protect heart tissue if a primary vessel is blocked

• Reduces severity of heart attacks

Cardiomyoctes

• Striated muscle cells

• Short and branched

• Contain one central nucleus

• Nucleus is surrounded by a light-staining region of glycogen

Functional Significance of Branching

• Allows each cell to contact multiple neighboring cells

• Cells from a network

• This network allows cardiac cells to:

  • Communicate efficiently

  • Coordinate contraction

  • Enables the heart to be autorhythmic (able to generate its own rhythm)

Intercalated Discs: Three Key Features

1. Interdigitating Folds

2. Mechanical Junctions

3. Electrical Junctions (Gap Junctions)

Interdigitating Folds

• Cell membranes fold together like fingers

• Increase surface area of contact

• Help cells interlock securely

Mechanical Junctions

Physically hold cells together during contraction

• Fascia Adherens

• Desmosomes

Fascia Adherens

• Broad anchoring junction

• Thin (actin) filaments attach to the plasma membrane

• Acts like velcro, anchoring muscle fibers

Desmosomes

• Strong mechanical links

• Prevent cardiomyocytes from being pulled apart during contraction

Electrical Junctions (Gap Junctions)

• Allows ions to flow directly between cells

• Electrical signals spread rapidly from cell to cell:

• Causes:

  • both atria to act as one functional unit

  • both ventricles to act as one functional unit

Cardiac Muscle Energy Production

• Relies almost entirely on aerobic respiration to make ATP

• Requires a constant supply of oxygen

Cardiac Muscle Cellular Features Supporting Metabolism

• Rich in myoglobin (stores oxygen)

• Contains glycogen (energy reserve)

• Very large mitochondria

  • occupy about 25% of cell volume

Cardiac Muscle Fuel Flexibility

Can use multiple fuels:

• Fatty acids: 60%

• Glucose: 35%

• Ketones, lactate, amino acids: 5%

• Cardiac muscle is more vulnerable to oxygen deficiency

• Less sensitive to shortages of any one fuel type

Cardiac Conduction System (coordinates the heartbeat)

• Made of:

  • Specialized cardiomyocytes

  • Nerve-like conduction pathways

• Generates and conducts rhythmic electrical signals

• Ensures chambers contract in the correct sequence

1. Sinoatrial (SA) Node

• Patch of modified cardiomyocytes

• Located in the right atrium

• Acts as the pacemaker

• Indicated each heartbeat

• Determines heart rate

2. Atrial Myocardium

• Electrical signal spread through:

  • right atrium

  • left atrium

• Causes atrial contraction

3. Atrioventricular (AV) Node

• Acts as the electrical gateway to ventricles

• Located at atrioventricular junction

• Fibrous skeleton:

  • prevents electrical signals from reaching ventricles any other way

• Creates a slight delay so ventricles fill before contractiong

4. Atrioventricular (AV) Bundle (Bundle of His)

• Only electrical connection between atria and ventricles

• Travels though interventicular septum

• Splits into:

  • right bundle branch

  • left bundle branch

• Conductions signal toward the apex

5. Subendothelial Conducting Network (Purkinje Fibers)

• Nerve-like fibers spread throughout ventricular myocardium

• Distribute signal rapidly to ventricular muscle

Final Signal Transmission

• Cardiomyocytes pass the electrical signal:

  • Cell to cell

  • Through gap junctions

SA Node Activity- Pacemaker Potential

Na+ slowly and constantly leaks into SA node cells

SA Node Activity- Depolarization

• At -40mV (threshold), Ca2+ channels open

• Ca2+ enters the cell, causing depolarization

SA Node Activity- Repolarization

• K+ channels open

• K+ leaves the cell

SA Node Activity- Reset

• K+ channels close

• Na+ leakage begins again → cycle repeats (pacemaker potential)

SA Node Activity- Key points

• Each depolarization of the SA node triggers one heartbeat

• When the SA node fires, it stimulates the rest of the conduction system

Skeletal Muscle Electrical Behavior

• Action potential lasts about 2 milliseconds

• Muscle contraction is brief ( a twitch)

Cardiac Muscle Electrical Behavior

• Action potential lasts 200-250 milliseconds

• Has a prolonged plateau phase

• Prevents rapid re-stimulation

• Produces a longer, sustained contraction

Cardiac Muscle Action Potential (Non-Pacemaker Cells) - Depolarization

• Voltage-gated Na+ channels open

• Rapid Na+ influx

• Membrane potential rises quickly

Cardiac Muscle Action Potential (Non-Pacemaker Cells) - Plateau Phase

• Ca2+ enters through slow Ca2+ channels

• Prolong depolarization

• Most K+ channels remain closed

• Small K+ leakage causes slight downward slope

Cardiac Muscle Action Potential (Non-Pacemaker Cells) - Repolarization

• Ca2+ channels close

• K+ channels open

• Rapid K+ efflux returns membrane to resting potential

ECG/EKG

• A recording of the hearts electrical activity

• Detected by electrodes (leads) placed on the skin

• Signals are amplified by an electrocardiograph

• Displayed on a moving paper or digital chart

What ECG/EKG are used for

• Detect normal vs. abnormal rhythms

• Diagnose:

  • Conduction defects

  • Myocardial infarction

  • Heart enlargement

  • Electrolyte or hormone imbalances

P Wave

Atrial depolarization

QRS Complex

Ventricular depolarization

→ atrial depolarization occurs here but is hidden

T Wave

Ventricular repolarization

PR Interval

• Conduction from SA node through AV node

• Before ventricles activate

PQ Segment

• Conduction from SA node to AV node

• Atrial systole begins

QRS Interval

Ventricular depolarization

ST Segment

• Ventricular systole and blood ejection

• Corresponds to plateau phase of cardiac AP