Cardiovascular/Heart (ch.18) Pt1

Notes (Part 1)

18.1 Heart Anatomy

The Pulmonary and Systemic Circuits

• Heart is a transport system consisting of two side-by-side pumps

  • Right side receives OXYGEN-POOR blood from tissues

    • Pumps blood to lungs to get rid of CO2, pick up O2, via PULMONARY CIRCUIT

  • Left side receives oxygenated blood from LUNGS

    • Pumps blood to body tissues via SYSTEMIC CIRCUIT

• Receiving chambers of heart

  • Right atrium

    • Receives blood returning from SYSTEMIC circuit

  • Left atrium

    • Receives blood returning from PULMONARY circuit

• Pumping chambers of heart

  • RIGHT VENTRICLE

    • Pumps blood through pulmonary circuit

  • LEFT VENTRICLE

    • Pumps blood through systemic circuit

Size, Location, and Orientation of Heart

• Approximately the size of a FIST

  • Weighs less than 1LB

• Location

  • In mediastinum between SECOND rib and FIFTH intercostal space

  • On superior surface of DIAPHRAGM

  • Two-thirds of heart to left of midsternal line

  • Anterior to vertebral column, posterior to sternum

• Base (posterior surface) leans toward RIGHT SHOULDER

• Apex points toward LEFT HIP

• Apical impulse palpated between fifth and sixth ribs, just below left nipple

Coverings of the Heart

• PERICARDIUM: double-walled sac that surrounds heart; made up of two layers

  • Superficial fibrous pericardium: functions to protect, anchor heart to surrounding structures, and prevent overfilling

  • Deep two-layered serous pericardium

    • PARIETAL LAYER lines internal surface of fibrous pericardium

    • VISCERAL LAYER (EPICARDIUM) on external surface of heart

    • Two layers separated by fluid-filled pericardial cavity (DECREASES FRICTION)

Clinical – Homeostatic Imbalance 18.1

• PERICARDITIS

  • Inflammation of pericardium

  • Roughens membrane surfaces, causing pericardial friction rub (creaking sound) heard with STETHOSCOPE (auscultation)

  • Cardiac tamponade

    • Excess fluid that leaks into pericardial space

    • Can compress heart’s pumping ability

    • Treatment: fluid is drawn out of cavity (usually with syringe)zx

Chambers and Associated Great Vessels

• Internal features

  • FOUR chambers:

    • Two superior ATRIA

    • Two inferior VENTRICLES

  • INTERATRIAL SEPTUM: separates atria

  • INTERVENTRICULAR SEPTUM: separates ventricles

• Atria: the receiving chambers

  • Small, thin-walled chambers; contribute little to propulsion of blood

  • Right atrium: receives DEOXYGENATED blood from body

    • Three veins empty into right atrium:

1. SUPERIOR VENA CAVA – returns blood from body regions above diaphragm

2. INFERIOR VENA CAVA – returns blood from body regions below the diaphragm / lower extremities

3. CORONARY SINUS – returns blood from CORONARY VEINS

• Left atrium: receives oxygenated blood from LUNGS

  • FOUR pulmonary veins return blood from lungs

Ventricles: the discharging chambers

• Make up most of the volume of heart

• RIGHT VENTRICLE: most of anterior surface

• LEFT VENTRICLE: posteroinferior surface

• TRABECULAE CARNEAE: irregular ridges of muscle on ventricular walls

• PAPILLARY MUSCLES: project into ventricular cavity

  • Anchor chordae tendineae that are attached to HEART VALVES

• THICKER WALLS walls than atria

Actual pumps of heart:

• Right ventricle

  • Pumps blood into PULMONARY TRUNK

• Left ventricle

  • Pumps blood into AORTA (largest artery in body)

18.2 Heart Valves

• Ensure UNIDIRECTIONAL blood flow through heart

• Open and close in response to PRESSURE changes

• Two major types of valves

  • ATRIOVENTRICULAR VALVES located between atria and VENTRICLES

  • SEMILUNAR VALVES located between ventricles and MAJOR ARTERIES

• No valves are found between major veins and atria; not a problem because:

  • INERTIA of incoming blood prevents backflow

  • Heart contractions compress VENOUS OPENINGS

Atrioventricular (AV) Valves

• Two atrioventricular (AV) valves prevent backflow into atria when ventricles contract

  • tricuspid valve (RIGHT AV VALVE): made up of three cusps and lies between right atria and ventricle

  • mitral valve (LEFT AV VALVE) bicuspid valve: made up of two cusps and lies between left atria and ventricle

  • Chordae tendineae: anchor cusps of AV valves to papillary muscles that function to:

    • Hold valve flaps in closed position

    • Prevent flaps from everting back into atria

Semilunar (SL) Valves

• Two SEMILUNAR (SL) VALVES prevent backflow from major arteries back into VENTRICLES

  • Open and close in response to pressure changes

  • Each valve consists of three cusps that roughly resemble a half moon

  • Pulmonary semilunar valve: located between right ventricle and pulmonary trunk

  • Aortic semilunar valve: located between left ventricle and aorta

Clinical – Homeostatic Imbalance 18.2

• Two conditions severely weaken heart:

  • INCOMPETENT VALVE

    • Blood backflows so heart re-pumps same blood over and over

  • VALVULAR STENOSIS

    • Stiff flaps that constrict opening

    • Heart needs to exert more force to pump blood

• Defective valve can be replaced with mechanical, animal, or cadaver valve

18.3 Pathway of Blood Through Heart

Right side of the heart

• Superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus →

• Right ATRIUM →

• Tricuspid / RIGHT AV VALVE →

• RIGHT VENTRICLE →

• PULMONARY SEMILUNAR VALVE →

• PULMONARY TRUNK →

• Pulmonary ARTERIES→

• LUNGS

Left side of the heart

• FOUR pulmonary veins →

• LEFT ATRIUM →

• LEFT AV VALVE →

• LEFT VENTRICLE →

• AORTIC SEMILUNAR VALVE →

• SYSTEMIC CIRCULATION →

• DOUBLE PUMP circulation

The Heart is a Double Pump, Each Side Supplying its Own Circuit

• Equal volumes of blood are pumped to pulmonary and systemic circuits

• Pulmonary circuit is SHORT, low-pressure circulation

• Systemic circuit is LONG, high-friction circulation

  • BLOOD PRESSURE HAPPENS IN ARTERIES

• Anatomy of ventricles reflects differences

  • Left ventricle walls are 3X thicker than right

    • Pumps with greater pressure

Coronary Circulation

• Functional blood supply to heart muscle itself

• SHORTEST circulation in body

• Delivered when heart is RELAXED

• LEFT VENTRICLE receives most of coronary blood supply

Coronary arteries

Leaves the aorta (oxygenated blood) → heart

• Both left and right coronary arteries arise from base of aorta and supply arterial blood to heart

• Both encircle heart in CORONARY SULCUS

• Branching of coronary arteries varies among individuals

• Arteries contain many anastomoses (JUNCTIONS)

  • Provide additional routes for blood delivery

  • Cannot compensate for coronary artery OCCLUSION (blockage)

  • Coronary artery occlusion → widowmaker

• Heart receives 1/20^th of body’s blood supply

LEFT CORONARY ARTERIES supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle; has two branches:

• ANTERIOR INTERVENTRICULAR ARTERY

• CIRCUMFLEX ARTERY

RIGHT CORONARY ARTERIES supplies right atrium and most of right ventricle; has two branches:

• RIGHT MARGINAL ARTERY

• POSTERIOR INTERVENTRICULAR ARTERY

Coronary veins

• CARDIAC VEINS collect blood from CAPILLARY BEDS

• SVC, IVC, CORONARY SINUS empties into RIGHT ATRIUM; formed by merging cardiac veins

  • Great cardiac vein of anterior interventricular sulcus

  • Middle cardiac vein in posterior interventricular sulcus

  • Small cardiac vein from inferior margin

• Several anterior cardiac veins empty directly into right atrium anteriorly

Clinical – Homeostatic Imbalance 18.3

• ANGINA (pain) pectoris

  • Thoracic pain caused by fleeting deficiency in blood delivery to myocardium

  • Cells are WEAKENED

• MYOCARDIAL INFARCTION (heart attack)

  • Prolonged coronary blockage

  • Areas of cell death are repaired with NONCONTRACTILE scar tissue

18.4 Cardiac Muscle Fibers

• Cardiac muscle cells: striated, short, branched, fat, interconnected

  • One central nucleus (at most, 2 nuclei)

  • Contain numerous large mitochondria (25–35% of cell volume) that afford resistance to FATIGUE

  • Rest of volume composed of sarcomeres

    • Z discs, A bands, and I bands all present

  • T tubules are wider, but less numerous

    • Enter cell only once at Z disc

• SR SIMPLER than in skeletal muscle; no triads

INTERCALATED DISCS → are connecting junctions between cardiac cells that contain:

• DESMOSOMES: hold cells together; prevent cells from separating during contraction

• GAP JUNCTIONS: allow ions to pass from cell to cell; electrically couple adjacent cells

  • Allows heart to be a functional syncytium, a single coordinated unit

• Intercellular space between cells has connective tissue matrix (endomysium)

  • Contains numerous capillaries

  • Connects cardiac muscle to cardiac skeleton, giving cells something to pull against

How Does the Physiology of Skeletal and Cardiac Muscle Differ?

Similarities with skeletal muscle

1. Muscle contraction is preceded by depolarizing ACTION POTENTIAL

2. Depolarization wave travels down T tubules; causes sarcoplasmic reticulum (SR) to release Ca2+

3. Excitation-contraction coupling occurs

   1. Ca²⁺ binds TROPONIN causing filaments to slide

Differences between cardiac and skeletal muscle

1. Some cardiac muscle cells are self-excitable

   1. Two kinds of myocytes

      1. CONTRACTILE CELLS: responsible for contraction

      2. PACEMAKER CELLS: noncontractile cells that spontaneously depolarize

         1. Initiate depolarization of entire heart

         2. Do not need nervous system stimulation, in contrast to skeletal muscle fibers (INVOLUNTARY)

2. Heart contracts as a UNIT

   1. All cardiomyocytes contract as unit (functional syncytium), or none contract

   2. Contraction of all cardiac myocytes ensures effective pumping action

   3. Skeletal muscles contract INDEPENDENTLY

3. Influx of Ca²⁺ from extracellular fluid triggers Ca²⁺ release from SR

   1. Depolarization opens slow Ca²⁺ channels in sarcolemma, allowing Ca²⁺ to enter cell

   2. Extracellular Ca²⁺ then causes SR to release its intracellular Ca²⁺

   3. Skeletal muscles do not use EXTRACELLULAR Ca²⁺

4. Tetanic contractions cannot occur in cardiac muscles

• Cardiac muscle fibers have LONGER REFRACTORY PERIODS than skeletal muscle fibers

  • Absolute refractory period is almost as long as contraction itself

  • Prevents TETANIC contractions

  • Allows heart to relax and CONTRACT / FILL UP as needed to be an efficient pump

5. The heart relies almost exclusively on aerobic respiration

   1. Cardiac muscle has more mitochondria than skeletal muscle so has greater dependence on OXYGEN

      1. Cannot function without OXYGEN

   2. Both types of tissues can use other fuel sources

      1. Cardiac is more adaptable to other fuels, including lactic acid, but must have oxygen

Summary on Table 18.1