Cardiovascular system

• cardiovascular system:

  result of several types of tissue
• main structures of the heart:

  pericardium

  pericardial fluid

  fibrous pericardium

  myocardium

  endocardium
• main structures of heart: pericardium

  pericardium = double walled sac that hearts enclosed in
• main structures if heart: pericardial fluid

  pericardial fluid = provides lubrication, reducing friction between heart and intrathoracic structures during heartbeats
• main structures of heart: Fibrous pericardium

  fibrous pericardium = protects heart and anchors cardiac structures
• main structures of heart: myocardium

  myocardium = cardiac muscle, form walls for heart chambers
• main structures of heart: endocardium

  endocardium =

  layer of simple squamous endothelial cells that line chambers of heart

  covers valves

  continuous with blood vessel lining
• blood vessels:

  provide continuous route for blood leaving heart to return to heart
• arteries:

  • carry blood away from heart
  • several layers of muscle
  • elastic and fibrous tissue
• arterioles:

  • carry blood to capillaries
  • several layers of muscle
  • less elastic
• capillaries:

  • site of exchange between blood and interstitial fluid
  • smallest vessel
  • layer of endothelium
• venules:

  • receive blood from capillaries
• veins:

  • carry blood to atria
  • thinner wall
  • larger diameter than arteries
• venous valves:

  • allow blood to flow in one direction and prevent backflow
  • arteries dont need valves = arterial system is high pressure which pushes the blood along network of arteries
• pressure decreases along venous system?

  • resistance offered by the vessels
  • friction between blood cells
• elastic recoil in arteries:

  • elastic properties of arterial walls allow recoil
  • propagates pressure produced by heart in the form of pressure waves
  • propels blood forward into smaller arteries and arterioles
• pericytes:

  • present in micro - vessels
  • induce vasoconstriction and vasodilation in capillary beds
  • regulate vascular diameter and capillary blood flow
• blood circulation:

  • pulmonary circulation
  • systemic circulation
• pulmonary circulation:

  • carries deoxygenated blood to lungs to become oxygenated by gas exchange
  • returns oxygenated blood to heart
  • pressure for this comes from right ventricle
• systemic circulation:

  • carries oxygenated blood from heart to all areas of body
  • returns deoxygenated blood
  • pressure for this comes from left ventricle
• heart receives blood:

  through coronary circulatory system

  made of: coronary arteries, veins, and capillaries
• venous blood from myocardium is returned directly into right atrium by coronary sinus, adjacent to opening of caudal vena cava
• portal system:

  a vessel divides into capillaries

  recombines to form another vessel

  re- divides into second capillary bed
• Primary function of cardiovascular system

  The transport of substances to and from all parts of the body
• Substances transported

  • Nutrients
  • Water
  • Gases that enter the body from the external environment
  • Materials that move from cell to cell within the body
  • Waste products that cells eliminate
• Cardiac cycle

  Period between the start of one heartbeat and the beginning of the next
• Cardiac cycle includes

  • Diastole = period of relaxation
  • Systole = period of contraction
• Cardiac cycle phases

  • Atrial systole
  • Atrial diastole
  • Ventricular systole
  • Ventricular diastole
• Cardiac conduction system

  Specialised muscle cells that generate and conduct electrical impulses (AP)
• Contraction of heart = result of spontaneous depolarisation
• Automaticity / auto-rhythmicity


  Spontaneous depolarisation of cardiac muscle cells
• cardiac cycle:

  • atrial systole begins: atrial contraction - force blood into ventricles
  • ventricular systole (1st phase) - ventricular contraction pushes AV valves closed
  • ventricular systole (2nd phase) - pressure rises, exceeds pressure in arteries - semilunar valves open - blood leaves
  • ventricles relax - pressure drops - blood flows back against semilunar valves - they close - blood flows into atria
  • all chamber's are relaxed, ventricles fill passively
• cardiac conductive system:

  Cardiac conductive system:

  
• why don's arteries need valves?

  arterial system is high pressure so pushes blood along
• cardiac contractility:

  1. Action potential initiated at SA node
  2. stimulus spreads across atrial surface + reaches AV node
  3. 100 msec delay at AV node, atrial contraction begins
  4. impulse travels along interventricular septum within AV bundle which branches to purkinje fibres and travels to papillary muscles of the right ventricle via the moderator band
  5. impulse is distributed by purkinje fibers and relayed throughout ventricular myocardium
  6. atrial contraction is complete and ventricular contraction begins
• efficient cardiac contraction:

  • atrial excitation and contraction need to be completed before ventricular contraction\
• efficient cardiac contraction


  excitation of cardiac muscle fibres should be coordinated - each chamber contracts as a unit
• efficient cardiac contraction

  • pair of atria and pair of ventricles should be coordinated so that both members of the pair contract simulatenously
• action potential in cardiac muscle:

  • pacemakers have unstable membrane potentials = never rest at constant value
• the funny current:

  the pace making current in sinoatrial node: funny current channels open when cell membrane is -60 mV inducing a depolarisation that reaches threshold at - 40 mV