1. PATHOPHYSIOLOGY OF THE CONDUCTION SYSTEM


2. Cardiac arrhythmias = deviation from normal rate, rhythm

    

   1. Heart block (types) = conduction system damage
      1. Complete Heart Block = 3rd degree block
         1. idioventricular beat (35-45/min)
         2. Atria at normal sinus rhythm
         3. Periods of asystole (dizziness, fainting)
         4. Causes = myocardial infarction of ventricular septum, surgical correction of interseptal defects, drugs
      2. Incomplete Heart Block = 2nd degree block
         1. Not all atrial beats reach ventricle
         2. Ventricular beat every 2nd, 3rd, etc. atrial beat, (2:1 block, 3:1 block)
      3. Incomplete Heart Block = 1st degree block
         1. All atrial beats reach ventricle
         2. PR interval abnormally long = slower conduction
      4. Bundle branch blocks (right or left)
         1. Impulses travel down one side and cross over
         2. Ventricular rate normal, QRS prolonged or abnormal
   2. Fibrillation
      1. Asynchronous contractions = twitching movements
      2. Loss of synchrony = little to No output
      3. Atrial Fibrillation
         1. Irregular ventricular beat & depressed pumping efficiency
         2. Atrial beat = 125 - 150/min, pulse feeble = 60 - 70/min
         3. Treatment = Digitalis - reduces rate of ventricular contraction, reduces pulse deficit
      4. Ventricular Fibrillation
         1. Almost no blood pumped to systemic system
         2. ECG = extremely bizarre
         3. Several minutes = fatal
         4. Treatment = defibrillation, cardiac massage can maintain some cardiac output

4.    Emphysema
1. Permanent enlargement of airways with distension of alveolar walls
 
    Thickened Bronchial Submucosa, Edema & Cellular Infiltration (loss of elasticity), Dilation of Air spaces, due to destruction of alveolar walls (Air trapped by obstruction)

2.    Lower Respiratory tree destruction

    Respiratory Bronchioles, Alveolar ducts, & Alveolar sacs

Types of Emphysema:
    
    1.    Centrilobular (Centriacinar) = Respiratory Bronchioles
    Rarely seen in non Smokers, More in Men than Women, Found in Smokers with Bronchitis

    2.    Panlobular (Panacinar) 

    Hereditary, Single autosomal recessive gene. Deficient in 1-globulin (1-antitrypsin), Protects respiratory tract from neutrophil elastase (Enzyme that distroys lung connective tissue) , Aged persons, Results from Bronchi or Bronchiolar constriction

    NOTE: Smoking = Leading cause of Bronchitis, Emphysema
 

Surface Tension

1.    Maintains stability of alveolus, preventing collapse

2.    Surfactant (Type II pneumocytes) = dipalmityl lecithin

3.    Type II pneumocyte appears at 24 weeks of gestation;
    1.    Surfactant production, 28-32 weeks;
    2.    Surfactant in amniotic fluid, 35 weeks.
    3.    Laplace equation for thin walled spheres P = 2T
        a.    P = alveolar internal pressure r
        b.    T = tension in the walls r = radius of alveolus
        
4.    During normal tidal respiration

    1.    Some alveoli do collapse (Tidal pressure can't open)
    2.    Higher than normal pressure needed (Coughing)
    3.    Deep breaths & sighs promote re-expansion
    4.    After surgery/Other conditions, Coughing, deep breathing, sustained maximal respiration

Heart sounds

Heart sounds are a result of beating heart and resultant blood flow . that could be detected by a stethoscope during auscultation . Auscultation is a part of physical examination that doctors have to practice them perfectly.
Before discussion the origin and nature of the heart sounds we have to distinguish between the heart sounds and hurt murmurs. Heart murmurs are pathological noises that results from abnormal blood flow in the heart or blood vessels.
Physiologically , blood flow has a laminar pattern , which means that blood flows in form of layers , where the central layer is the most rapid . Laminar blood flow could be turned into turbulent one .

Turbulent blood flow is a result of stenotic ( narrowed ) valves or blood vessels , insufficient valves , roughened vessels` wall or endocardium ,  and many diseases . The turbulent blood flow causes noisy murmurs inside or outside the heart.

Heart sounds ( especially first and second sounds ) are mainly a result of closure of the valves of the heart . While the third sound is a result of vibration of ventricular wall and the leaflets of the opened AV valves after rapid inflow of blood from the atria to ventricles . 

Third heart sound is physiologic in children but pathological in adults.

The four heart sound is a result of the atrial systole and vibration of the AV valves , due to blood rush during atrial systole . It is inaudible neither in adults nor in children . It is just detectable by the phonocardiogram .

Characteristic of heart sounds :

1. First heart sound  (S1 , lub ) : a soft and low pitch sound, caused by closure of AV valves.Usually has two components ( M1( mitral ) and T1 ( tricuspid ). Normally M1 preceads T1.

2. Second heart sound ( S2 , dub) : sharp and high pitch sound . caused by closure of semilunar valves. It also has two components A2 ( aortic) and P2 ( pulmonary) . A2 preceads P2.

3. Third heart sound (S3) : low pitched sound.

4. Fourth heart sound ( S4) very low pitched sound.

As we notice : the first three sounds are related to ventricular activity , while the fourth heart sound is related to atrial activity.
Closure of valves is not the direct cause for heart sounds , but sharp blocking of blood of backward returning of blood by the closing valve is the direct cause.
 

Chemical Controls of Respiration

A.    Chemoreceptors (CO2, O2, H+)

1.    central chemoreceptors - located in the medulla
2.    peripheral chemoreceptors - large vessels of neck

B.    Carbon Dioxide Effects

1.    a powerful chemical regulator of breathing by increasing H+ (lowering pH)
    
a. hypercapnia            Carbon Dioxide increases -> 
                        Carbonic Acid increases ->
                        pH of CSF decreases (higher H+)- >
                        
DEPTH & RATE increase (hyperventilation)

b. hypocapnia - abnormally low Carbon Dioxide levels which can be produced by excessive hyperventilation; breathing into paper bag increases blood Carbon Dioxide levels

C.     Oxygen Effects

1.    aortic and carotid bodies - oxygen chemoreceptors

2.    slight Ox decrease - modulate Carb Diox receptors
3.    large Ox decrease - stimulate increase ventilation
4.    hypoxic drive - chronic elevation of Carb Diox (due to disease) causes Oxygen levels to have greater effect on regulation of breathing

D.    pH Effects (H+ ion)

1.    acidosis - acid buildup (H+) in blood, leads to increased RATE and DEPTH (lactic acid)

E.    Overview of Chemical Effects

 Chemical                             Breathing Effect

increased Carbon Dioxide (more H+)     increase
decreased Carbon Dioxide (less H+)     decrease

slight decrease in Oxygen             effect CO2 system
large decrease in Oxygen             increase ventilation

decreased pH (more H+)                 increase
increased pH (less H+)                 decrease

AdenosineTriphosphate (ATP)

• Animal cells cannot directly use most forms of energy
  • Most cellular processes require energy stored in the bonds of a molecule, adenosine triphosphate (ATP)
  • ATP is referred to as the energy currency of the cell

It is a nucleotide, formed from:

• the base adenine (the structure with 2 rings),
• the 5 carbon sugar deoxyribose (one ring)
• 3 phosphates

Energy is stored in the bonds between the phosphates and is released when the bonds are broken