• it's the individual pressure exerted independently by a particular gas within a mixture of gasses. The air we breath is a mixture of gasses: primarily nitrogen, oxygen, & carbon dioxide. So, the air you blow into a balloon creates pressure that causes the balloon to expand (& this pressure is generated as all the molecules of nitrogen, oxygen, & carbon dioxide move about & collide with the walls of the balloon). However, the total pressure generated by the air is due in part to nitrogen, in part to oxygen, & in part to carbon dioxide. That part of the total pressure generated by oxygen is the 'partial pressure' of oxygen, while that generated by carbon dioxide is the 'partial pressure' of carbon dioxide. A gas's partial pressure, therefore, is a measure of how much of that gas is present (e.g., in the blood or alveoli). 
   
• the partial pressure exerted by each gas in a mixture equals the total pressure times the fractional composition of the gas in the mixture. So, given that total atmospheric pressure (at sea level) is about 760 mm Hg and, further, that air is about 21% oxygen, then the partial pressure of oxygen in the air is 0.21 times 760 mm Hg or 160 mm Hg.

Characteristics of Facilitated Diffusion & Active Transport - both require the use of carriers that are specific to particular substances (that is, each type of carrier can 'carry' one type of substance) and both can exhibit saturation (movement across a membrane is limited by number of carriers & the speed with which they move materials

Clinical Physiology 

Heart Failure : Heart failure is inability of the heart to pump the enough amount of blood needed to sustain the needs of organism .
It is usually called congestive heart failure ( CHF) .

To understand the pathophysiology  of the heart failure ,  lets compare it with the physiology of the cardiac output :
Cardiac output =Heart rate X stroke volume

Stroke volume is determined by three determinants : Preload ( venous return ) , contractility , and afterload    (peripheral resistance ) . Any disorder of these factors will reduce the ability of the heart to pump blood .

Preload : Any factor that decrease the venous return , either by decreasing the intravenous pressure or increasing the intraatrial pressure will lead to heart failure .

Contractility : Reducing the power of contraction such as in  myocarditis , cardiomyopathy , preicardial tamponade ..etc , will lead to heart failure .

Afterload : Any factor that may increase the peripheral resistance such as hypertension , valvular diseases of the heart may cause heart failure.

Pathophysiology : When the heart needs to contract more to meet the increased demand , compensatory mechanisms start to develope to enhance the power of contractility  . One of these mechanism is increasing heart rate , which will worsen the situation because this will increase the demands of the myocardial cells themselves . The other one is hypertrophy of the cardiac muscle which may compensate the failure temporarily but then the hypertrophy will be an additional load as the fibers became stiff  .

The stroke volume will be reduced , the intraventricular pressure will increase and consequently the intraatrial pressure and then the venous pressure . This will lead to decrease reabsorption of water from the interstitium ( see microcirculation) and then leads to developing of edema ( Pulmonary edema if the failure is left , and systemic edema if the failure is right) .

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.
 

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

Ingestion: Food taken in the mouth is

• ground into finer particles by the teeth,
• moistened and lubricated by saliva (secreted by three pairs of salivary glands)
• small amounts of starch are digested by the amylase present in saliva
• the resulting bolus of food is swallowed into the esophagus and
• carried by peristalsis to the stomach.