Chapter 18- The Heart

• Circuits

  1. Pulmonary - deoxygenated blood back to lungs (🫀->🫁 )
  2. Systemic (longest) - send oxygenated blood to body tissues (🫀->🧍‍♀️)
  3. Coronary (shortest) - circuit for heart (🫀<-> 🫁 )
• 3 layers of the heart wall:

  
  

  Cavity

  Visceral Layer- 1. Epicardium

  ET

  Parietal Layer- 2. Myocardium (muscle layer)

  Organ- 3. Endocardium (walls of the chambers)
• 4 Chambers of the Heart:

  • 2 atria - receive blood from the body
  • 2 ventricles - pumps out blood out of the heart
• The Right Atrium (RA) receives blood from 3 veins:

  • Superior Vena Cava
  • Inferior Vena Cava
  • Coronary Sinus (enters from the back of heart)
• 4 Chambers of the Heart Cont.. :

  • The Left Atrium (LA) receives blood from pulmonary veins
  • The Right Ventricle (RV) pumps blood into

  the pulmonary arteries --> lungs

  • The Left Ventricle (LV) pumps blood into

  the aorta --> all body tissues (except lungs)
• Pathway of blood through the pulmonary and systemic circuits:

  RA --(triscupid valve)-> RV --(pulmonary semilunar valve)-> LUNGS --> PULMONARY VEINS --> LA --(biscupid valve)-> LV --> AORTA --> BODY TISSUES --> VENA CAVA --> RA

  Rich Blood - (NGS -> PULMONARY VEINS --> LA --(biscupid valve)-> LV --> AORTA --> BODY)
• Pathway of blood through the coronary circuit (the shortest circuit):

  LV --> AORTA --> CORONARY ARTERIES --> MYOCARDIUM --> CORONARY VEINS --> CORONARY SINUS --> RA
• *REPEAT*

  1. PULMONARY --> LUNGS

  • Deoxy blood
  • Starts in RA
  • IVC + SVC (vena cava)

  or coronary sinus

  --> 3 ways to enter heart

  
  

  2. Systemic --> O2 blood to body

  • O2 blood
  • long circuit
  • LV = pump

  3. Coronary --> O2 blood to heart

  • O2 rich blood
  • short circuit
  • LV = pump
  • Coronary arteries
• Heart Valves

  • Allow for one-way flood of blood through the heart (prevent back flow)
  • Open or close due to pressure differences
• There are 4 heart valves:

  • 2 atrioventricular valves (AV valves) - between the atria and ventricles

  1. triscupid
  2. biscupid

  • 2 semilunar valve (SL valves) - between the ventricles and the arteries carrying blood out of the heart.

  1. aortic
  2. pulmonary
• Heart sounds are heard when the valves close :

  • 1st heard sound - heard when both AV valves close
  • 2nd heard sound - heard when both SL valves close

  (heart sounds are not heard when valves open)
• Pressure differences cause valves to open or close:

  • When atrial pressure > ventricular pressure

  The AV valves open (no sound)

  • When ventricular pressure > atrial pressure

  The AV valves close (1st heart sound)
• Pressure differences cause valves to open or close cont.. :

  1. Blood flowing freely into atria, opening the AV valves

  (atrial pressure > ventricular pressure)

  2. Atrio contract, sending a little more blood to ventricles.

  3. Ventricles fill up w/ blood (ventricular pressure > atrial pressure)

  --> AV closes (1st heart sound)
• Papillary muscles are attached to chordae tendineae (heart strings)
• • No valves between the vena cava and RA
  • No valves between the pulmonary veins and LA

  Blood flows continuously into the 2 atria
• Microscopic Anatomy of Cardiac Muscle Tissue

  Cardiac muscle cells/fibers are :

  • Striated
  • Involuntary
  • Branched
  • Interconnected by intercalated discs
• Intercalated discs contain 2 kinds of cell junctions:

  1. Desmosomes - anchoring junctions

  • adjacent heart cells to adhere to each other

  2. Gap Junctions - communication

  • electrical info b/t heart
  • intercalated disc
  • pacemaker (RA)

  Unit = functional syncytium

  FUNCTIONAL SYNCYTIUM - heart able to beat as 1 unit.
• Cardiac

  • striated
  • involuntary
  • branched short
  • *pacemaker (electrical)
  • heartbeat
  • Intercalated disc

  more mitochondria
• Skeletal

  • striated
  • voluntary
  • t-tubules (extrusive)
  • nervous (electrical)
• RV

  • less muscular
  • blood going RV,

  short destination -> lung

  -> deoxygenated

  LV

  • 3x muscular
  • pump blood
  • t/o body
  • longer path

  -> oxygenated

  *There are NO valves between the vena cava and RA
• There are 2 kinds of cardiac muscle fibers:

  Contractile : 99%

  • similar to skeletal
  • can't self-depolarize
  • outside electrical
  • stimulation

  ex: autorhythmic fibers

  • stable potential
  • can shorten
• There are 2 kinds of cardiac muscle fibers:

  Autorhythmic : 1%

  • pacemakers
  • self-depolarize
  • unstable potential
  • can't shorten
  • no break between action potentials (APs) due to pacemaker potential
• The Cardiac Conduction System is a group of structures:

  • made of autorhythmic fibers
  • that initiates and transmits electrical impulses (APs) through the heart.
  • results in rhythmic contractions
• Cardiac Conduction System

  1. Sinoatrial Node (SA Node)(Pacemaker), sinus rhythm
  2. Interatrial Septum, Atrioventricular Node (AV Node)
  3. Interventricular Septum, L/R bundle branches, AV branches --> Left Branch or Right Branch --> APEX --> ventricles, purkinje fibers --> ventricular contraction
• Sinus rhythm - the normal rhythm of the heartbeat set by the SA node.
• The action potential of contractile cardiac muscle cells: Depolarization

  1. Depolarization is due to Na+ influx, more positive

  • Na+ open
  • Na+ rushes in
  • (-90 mV to 30 mV)
• The action potential of contractile cardiac muscle cells: Plateau

  2. Plateau

  • Na+ closing
  • Stays (+) due to Ca2+ influx
  • *muscle contract (+30 mV to 0 mV)

  Absolute refractory period : extending the peak of AP long enough to stimulate muscle to contact.
• The action potential of contractile cardiac muscle cells: Repolarization

  3. Repolarization is due to K+ channels opening, more negative

  • (0 mV to -90 mV)
  • K+ leaves
  • more negative
• Electrocardiogram (ECG or EKG) tracing is a recording of the flow of electrical impulses (all APs) produced by the heart.
• There are 3 segments in an EKG tracing:

  • P-Q interval (start of P to starts of QRS)

  -From atria to ventricle

  • Q-T interval (start of QRS to end of T)

  -From ventricular depolarization to repolarization

  • S-T interval (end of S to start of T)

  -Ventricular depolarization allows ventricle to stay contracted long enough.

  -During plateau of cardiac conduction system
• The Cardiac Cycle - all the events associated w/ one heart beat

  • Systole = contraction
  • Diastole = relaxation

  Depolarization causes systole

  Repolarization cause diastole
• Length of cardiac cycle : 0.8 seconds
• There are 3 main periods in the cardiac cycle: atrial systole, ventricular systole and relaxation period
• • Atrial systole, 0.1 sec, atria (systole), ventricles (diastole)
  • Ventricular systole, 0.3 sec, atria (diastole), ventricles (systole)
  • Relaxation period, 0.4 sec, atria (diastole), ventricles (diastole)
• 1. Atrial systole

  • Both ventricles contract shortly after P wave
  • AV valves remain open
  • SL valves remain closed
  • Ventricles fill w/ blood
• 2. Ventricular systole

  • Both ventricles contract shortly after QRS
  • AV valves close (1st heart sound)
  • Isovolumetric contraction period occurs in the beginning
  • SL valves open
  • Blood pumped out of ventricles and into aorta and pulmonary arteries
• 3. Relaxation Period

  • Ventricles relax shortly after T wave
  • SL valves close (2nd heart sound)
  • Isovolumetric relaxation period occurs in the beginning
  • AV valves open in middle of period
  • Blood fills ventricles
• Isovolumetric - constant volume of blood in ventricles;

  all 4 valves closed

  • Isovolumetric contraction (brief period at beginning of ventricular systole) - ventricles contract while valves closed.
  • Isovolumetric relaxation (brief period at beginning of relaxation period) - ventricles relax while valves closed.
• Cardiac Output - amount of blood pumped out of each ventricle per minute.

  CO = HR x SV

  HR - Heart rate

  CO - 75 b/t min * 70ml/bt = 5.25 L/min

  ≈ 5L of blood passes through heart a minute
• Cardiac Output (CO)

  = volume of blood pumped out of ventricle per minute

  • (L/min)

  Stroke Volume (SV)

  • In 1 heartbeat what volume blood pumped out of vent
  • (ml/bt)

  Heart Rate (HR)

  • (bt/min)
  • heartbeat per minute