Cardiovascular System

• Midsternal line: A line drawn from the midpoint of the sternum to the midpoint of the clavicle.

  A) midsternal line

  B) 2nd rib

  C) sternum

  D) diaphragm

  E) Point of maximal intensity (PMI)

  
• Parietal Pleura: Outer layer of the lung that lines the thoracic cavity.

  A) superior vena cava

  B) left lung

  C) aorta

  D) parietal pleura (cut)

  E) pulmonary trunk

  F) parietal pericardium (cut)

  G) apex of heart

  H) diaphragm

  
• Parietal Pericardium: A thin layer of connective tissue that lines the pericardial cavity and provides a layer of insulation to the heart.
• Arteries:

  • Thick walled tubes
  • Elastic Fibres
  • Circular Smooth Muscle
• •Pulmonary circulation: between the heart and lungs
• •Systemic circulation: between the heart and all body systems
• •The heart is positioned in the middle of the mediastinum behind the breastbone in the chest, slightly offset to the left.
• •Atria: upper chambers

  Ventricles: lower chambers
• Parts of the heart (right side);

  A) superior vena cava

  B) right pulmonary veins

  C) pulmonary semilunar valves

  D) right atrium

  E) right atrioventricular valve

  F) right ventricle

  G) inferior vena cava
• Parts of the heart (left side):
• systemic:

  Left heart to all body except lungs.

  oxygenated blood

  Systemic veins: deoxygenated blood
• Right heart to lungs (pulmonary),

  Pulmonary arteries: deoxygenated blood

  Pulmonary veins: oxygenated blood
• Atria: receive blood from veins

  Ventricles: pump blood to arteries
• •The heart walls are composed of spirally arranged cardiac muscle fibres:

  Endothelium, myocardium, and epicardium
• •Cardiac muscle fibres are interconnected by intercalated discs to form functional syncytia:

  •Desmosomes and gap junctions
• •Heart is enclosed by the pericardial sac:

  Consists of a fibrous covering and secretory lining
• •Valves are Fastened to papillary muscles by chordae tendinea.

  
• •Autorhythmic cells:

  •Do not contract

  •Initiate and conduct APs

  •No resting potential; neural input not necessary to initiate an AP

  •Pacemaker activity instead: Slow depolarization, drift to threshold, then firing
• heart tissue structure:
• Cardiomyocytes:

  Narrower and much shorter than skeletal muscle cells (20nm wide, 100nm long)

  May be branched, contain many mitochondria
• Innervation from the brain to the heart:

  
• •Contractile cells: 99% of the cardiac muscle cells do the mechanical work of pumping

  •Auto rhythmic cells: initiate and conduct the action potentials responsible for contraction of working cells
• AP generation in heart:

  
• Atrial and Ventricular Excitation and Conduction;

  •Atrial excitation

  •Interatrial pathway

  •Internodal pathway

  •Conduction between the atria and the ventricles

  •AV nodal delay

  •Ventricular excitation

  •Ventricular conduction system is crucial for hastening spread of excitation in ventricles
• Electrical parts of the Heart:

  A) sinoatrial node

  B) purkinje fibres

  C) bundle of his

  D) atrioventricular node

  
• SA node is the pacemaker of the heart:

  •The SA node is located in the right atrium (right upper chamber) of the heart

  .•It spontaneously generates an electrical impulse causing the heart to contract

  .•the rate of the impulses is set by the nerves innervating the sinoatrial node.
• The Atrioventricular Node:

  •The link between atrial depolarization and ventricular depolarization

  •Located at the base of the right atrium.

  •The action potential is conducted rapidly from the SA node to the AV node through internodal pathways .

  •The propagation of action potentials through the AV node is relatively slow (requiring approximately 0.1 sec).

  •This delay allows atrial contraction to be completed before ventricular excitation occurs.
• The Bundle of His:

  • The bundle of His is a collection of cardiomyocytes specialised for electrical conduction
  • These cells transmit the electrical impulses from the AV node to the point of the apex of the fascicular branches via the bundle branches.
  • The branches then separate at the apex of the heart and enter the ventricle walls.
  • It takes less than 40 milliseconds for the impulse

       to travel from the bundle of His to the ventricular

       muscle
• The Purkinje Fibres:

  •The Purkinje fibres are located in the inner ventricular walls of the heart, just beneath than any other cells in the heart.

  •Purkinje fibres allow synchronized contractions

  •Specialised conducting fibres larger than cardiomyocytes with fewer myofibrils and a large number of mitochondria

  •Able to conduct action potentials more quickly and efficiently than of ventricles
• Cardiac excitation:

  
• •The action potential of contractile cardiomyocytes shows a characteristic ‘plateau’

  •Plateau phase: membrane potential is maintained close to this peak positive level for several hundred milliseconds

  •Calcium entry from the ECF Induces a much larger Ca2+ release from the sarcoplasmic recticulum
• Pericardial sac


  Encloses the heart and consists of a fibrous covering and a secretory lining that produces lubricating fluid.
• Pleural cavity


  Encloses the lungs and consists of parietal and visceral pleura with lubricating fluid in between.