📖 Physiology
Phases of cardiac cycle
PhysiologyPhases 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
SENSORY PATHWAYS
PhysiologySensory pathways include only those routes which conduct information to the conscious cortex of the brain. However, we will use the term in its more loosely and commonly applied context to include input from all receptors, whether their signals reach the conscious level or not.
Plasma
PhysiologyPlasma: is the straw-colored liquid in which the blood cells are suspended.
|
Composition of blood plasma |
|
|
Component |
Percent |
|
Water |
~92 |
|
Proteins |
6–8 |
|
Salts |
0.8 |
|
Lipids |
0.6 |
|
Glucose (blood sugar) |
0.1 |
Plasma transports materials needed by cells and materials that must be removed from cells:
- various ions (Na+, Ca2+, HCO3−, etc.
- glucose and traces of other sugars
- amino acids
- other organic acids
- cholesterol and other lipids
- hormones
- urea and other wastes
Most of these materials are in transit from a place where they are added to the blood
- exchange organs like the intestine
- depots of materials like the liver
to places where they will be removed from the blood.
- every cell
- exchange organs like the kidney, and skin.
COMPONENTS OF THE CELLULAR ENVIRONMENT
PhysiologyWater: comprises 60 - 90% of most living organisms (and cells) important because it serves as an excellent solvent & enters into many metabolic reactions
- Intracellular (inside cells) = ~ 34 liters
- Interstitial (outside cells) = ~ 13 liters
- Blood plasma = ~3 liters
40% of blood is red blood cells (RBCs)
plasma is similar to interstitial fluid, but contains plasma proteins
serum = plasma with clotting proteins removed
intracellular fluid is very different from interstitial fluid (high K concentration instead of high Na concentration, for example)
- Capillary walls (1 cell thick) separate blood from interstitial fluid
- Cell membranes separate intracellular and interstitial fluids
- Loss of about 30% of body water is fatal
Ions = atoms or molecules with unequal numbers of electrons and protons:
- found in both intra- & extracellular fluid
- examples of important ions include sodium, potassium, calcium, and chloride
Ions (Charged Atoms or Molecules) Can Conduct Electricity
- Giving up electron leaves a + charge (cation)
- Taking on electron produces a - charge (anion)
- Ions conduct electricity
- Without ions there can be no nerves or excitability
- Na+ and K+ cations
- Ca2+ and Mg2+ cations control metabolism and trigger muscle contraction and secretion of hormones and transmitters
Na+ & K+ are the Major Cations in Biological Fluids
- High K+ in cells, high Na+ outside
- Ion gradients maintained by Na pump (1/3 of basal metabolism)
- Think of Na+ gradient as a Na+ battery- stored electrical energy
- K+ gradient forms a K+ battery
- Energy stored in Na+ and K+ batteries can be tapped when ions flow
- Na+ and K+ produce action potential of excitable cells