Phases of cardiac cycle :

1. Early diastole ( also called the atrial diastole , or complete heart diastole) : During this phase :

- Atria are  relaxed
- Ventricles are relaxed
- Semilunar valves are closed
- Atrioventricular valves are open
During this phase the blood moves passively from the venous system into the ventricles ( about 80 % of blood fills the ventricles during this phase.

2. Atrial systole : During this phase :

- Atria are contracting
- Ventricles are relaxed
- AV valves are open
- Semilunar valves are closed
- Atrial pressure increases.the a wave of atrial pressure appears here.
- P wave of ECG starts here
- intraventricular pressure increases due to the rush of blood then decrease due to continuous relaxation of ventricles.

The remaining 20% of blood is moved to fill the ventricles during this phase , due to atrial contraction.

3. Isovolumetric contraction : During this phase :

- Atria are relaxed
- Ventricles are contracting
- AV valves are closed
- Semilunar valves are closed
- First heart sound
- QRS complex.
The ventricular fibers start to contract during this phase , and the intraventricular pressure increases. This result in closing the AV valves , but the pressure is not yet enough to open the semilunar valves , so the blood volume remain unchanged , and the muscle fibers length also remain unchanged , so we call this phase as isovolumetric contraction ( iso : the same , volu= volume , metric= length).

4. Ejection phase : Blood is ejected from the ventricles into the aorta and pulmonary artery .

During this phase :

- Ventricles are contracting
- Atria are relaxed
- AV valves are closed
- Semilunar valves are open
- First heart sound
- Intraventricular pressure is increased , due to continuous contraction
- increased aortic pressure .
- T wave starts.

5. Isovolumetric relaxation:  This phase due to backflow of blood in aorta and pulmonary system after the ventricular contraction is up and the ventricles relax . This backflow closes the semilunar valves .

During this phase :

- Ventricles are relaxed
- Atrial are relaxed
- Semilunar valves are closed .
- AV valves are closed.
- Ventricular pressure fails rapidly
- Atrial pressure increases due to to continuous venous return. the v wave appears here. 
- Aortic pressure : initial sharp decrease due to sudden closure of the semilunar valve ( diacrotic notch) , followed by secondary rise in pressure , due to elastic recoil of the aorta ( diacrotic wave)  .
- T wave ends in this phase

• Partial Pressures of O₂ and CO₂ in the body (normal, resting conditions):

• Alveoli
  • PO₂ = 100 mm Hg
  • PCO₂ = 40 mm Hg
• Alveolar capillaries
  • Entering the alveolar capillaries
    • PO₂ = 40 mm Hg (relatively low because this blood has just returned from the systemic circulation & has lost much of its oxygen)
    • PCO₂ = 45 mm Hg (relatively high because the blood returning from the systemic circulation has picked up carbon dioxide) 

• While in the alveolar capillaries, the diffusion of gasses occurs: oxygen diffuses from the alveoli into the blood & carbon dioxide from the blood into the alveoli.

• Leaving the alveolar capillaries
  • PO₂ = 100 mm Hg
  • PCO₂ = 40 mm Hg
• Blood leaving the alveolar capillaries returns to the left atrium & is pumped by the left ventricle into the systemic circulation. This blood travels through arteries & arterioles and into the systemic, or body, capillaries. As blood travels through arteries & arterioles, no gas exchange occurs.
• • Entering the systemic capillaries
    • PO₂ = 100 mm Hg
    • PCO₂ = 40 mm Hg
  • Body cells (resting conditions)
    • PO₂ = 40 mm Hg
    • PCO₂ = 45 mm Hg
• Because of the differences in partial pressures of oxygen & carbon dioxide in the systemic capillaries & the body cells, oxygen diffuses from the blood & into the cells, while carbon dioxide diffuses from the cells into the blood.
• • Leaving the systemic capillaries
    • PO₂ = 40 mm Hg
    • PCO₂ = 45 mm Hg
• Blood leaving the systemic capillaries returns to the heart (right atrium) via venules & veins (and no gas exchange occurs while blood is in venules & veins). This blood is then pumped to the lungs (and the alveolar capillaries) by the right ventricle.

Lipids:

• about 40% of the dry mass of a typical cell
• composed largely of carbon & hydrogen
• generally insoluble in water
• involved mainly with long-term energy storage; other functions are as structural components (as in the case of phospholipids that are the major building block in cell membranes) and as "messengers" (hormones) that play roles in communications within and between cells
• Subclasses include:
  • Triglycerides - consist of one glycerol molecule + 3 fatty acids (e.g., stearic acid in the diagram below). Fatty acids typically consist of chains of 16 or 18 carbons (plus lots of hydrogens).
  • phospholipids - Composed of 2 fatty acids, glycerol, phosphate and polar groups , phosphate group (-PO⁴) substitutes for one fatty acid & these lipids are an important component of cell membranes

steroids - have 4 rings- cholesterol, some hormones, found in membranes include testosterone, estrogen, & cholesterol

Concentration versus diluting urine 

Kidney is a major route for eliminating fluid from the body to accomplish water balance. Urine excretion is the last step in urine formation. Everyday both kidneys excrete about 1.5 liters of urine.
Depending on the hydrated status of the body, kidney either excretes concentrated urine ( if the plasma is hypertonic like in dehydrated status ) or diluted urine ( if the plasma is hypotonic) .
This occurs thankful to what is known as countercurrent multiplying system, which functions thankfully to establishing large vertical osmotic gradient .
To understand this system, lets review the following facts:
1. Descending limb of loop of Henle is avidly permeable to water.
2. Ascending limb of loop of Henly is permeable to electrolytes , but impermeable to water. So fluid will not folow electrolytes by osmosis.and thus Ascending limb creates hypertonic interstitium that will attract water from descending limb.
Pumping of electrolytes
3. So: There is a countercurrent flow produced by the close proximity of the two limbs.                   
                                                   
Juxtamedullary nephrons have long loop of Henle that dips deep in the medulla , so the counter-current system is more obvious and the medullary interstitium is always hypertonic . In addition, peritubular capillaries in the medulla are straigh ( vasa recta) in which flow is rapid and rapidly reabsorb water maintaining hypertonic medullary interstitium.

In distal tubules water is diluted. If plasma is hypertonic, this will lead to release of ADH by hypothalamus, which will cause reabsorption of water in collecting tubules and thus excrete concentrated urine.

If plasma is hypotonic ADH will be inhibited and the diluted urine in distal  tubules will be excreted as diluted urine.

Urea  contributes to concentrating and diluting of urine as follows:

Urea is totally filtered and then 50% of filtrated urea will be reabsorbed to the interstitium, this will increase the osmolarity of medullary interstitium ( becomes hypertonic ). Those 50% will be secreted in ascending limb of loop of Henle back to tubular fluid to maintain osmolarity of tubular fluid. 55% of urea in distal nephron will be reabsorbed in collecting ducts back to the interstitium ( under the effect of ADH too) . This urea cycle additionally maintain hypertonic interstitium.

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

HEART DISORDERS

1. Pump failure => Alters pressure (flow) =>alters oxygen carrying capacity.
   1. Renin release (Juxtaglomerular cells) Kidney
   2. Converts Angiotensinogen => Angiotensin I
   3. In lungs Angiotensin I Converted => Angiotensin II
   4. Angiotensin II = powerful vasoconstrictor (raises pressure, increases afterload)
      1. stimulates thirst
      2. stimulates adrenal cortex to release Aldosterone
         (Sodium retention, potassium loss)
      3. stimulates kidney directly to reabsorb Sodium
      4. releases ADH from Posterior Pituitary
2. Myocardial Infarction

    

   1. Myocardial Cells die from lack of Oxygen
   2. Adjacent vessels (collateral) dilate to compensate
   3. Intracellular Enzymes leak from dying cells (Necrosis)
      1. Creatine Kinase CK (Creatine Phosphokinase) 3 forms
         1. One isoenzyme = exclusively Heart (MB)
         2. CK-MB blood levels found 2-5 hrs, peak in 24 hrs
         3. Lactic Dehydrogenase found 6-10 hours after. points less clearly to infarction
      2. Serum glutamic oxaloacetic transaminase (SGOT)
         1. Found 6 hrs after infarction, peaks 24-48 hrs at 2 to 15 times normal,
         2. SGOT returns to normal after 3-4 days
   4. Myocardium weakens = Decreased CO & SV (severe - death)
   5. Infarct heal by fibrous repair
   6. Hypertrophy of undamaged myocardial cells
      1. Increased contractility to restore normal CO
      2. Improved by exercise program
   7. Prognosis
      1. 10% uncomplicated recovery
      2. 20% Suddenly fatal
      3. Rest MI not fatal immediately, 15% will die from related causes
3. Congenital heart disease (Affect oxygenation of blood)
   1. Septal defects
   2. Ductus arteriosus
   3. Valvular heart disease
      1. Stenosis = cusps, fibrotic & thickened, Sometimes fused, can not open
      2. Regurgitation = cusps, retracted, Do not close, blood moves backwards