Cardiovascular system - part 2

Pulmonary circuit 

Deoxygenated blood comes back from the body through viens and into the vena cava, where it travels throught the reight atrium and ventricle and out the pulmonary artery were it is trnasporrted to the lungs via arterioles and capilleries. In the lungs gaseous sxchange occurs and oxygen is attched to haemaglobin in the red blood cells.

Systemic circuit

newly oxygenated blood from the lungs goes through venules and into the pulmonary vein of the heart where is passes through the left atrium and ventricle is is pumped out of the aorta, through arterioles and to cappileries in the body for gaseous exchange within mucles or organs.

Oxygenated blood id high in o2 content and low in co2 content

Deoxygenated blood is low in o2 content and high in co2 content

The veins role is to carry blood back to the heart (venous return), they have thin muscle and elastic tissue layers, valves and a wide lumen.

There is very low blood pressure in veins as they are far from the heart, becasue of this a large lumen is needed to easily allow blood flow, the low pressure also means a thick wall is not needed. The valves prevent backflow of blood as the pressure is low so is not pumping one way with great force.

The arteries job is to carry blood away from the heart and to the body, it has a small lumen, and thick walls and endothelium layer. 

Arteries are close to the heart and so there is high pressure in them thick walls are essential as well as this due to the pressure being so igh a large lumen is not needed to allow easy blood flow.

The role of capillaries is to allow gaseous exchange, there structure is small with a lument hat only allows a single cells to pass through at one time.

Capillaries with stand very low blood pressure and so can have thin walls, the lumen is single cell sized to slow down blood flow allowing time for gaseous exchange of oxygen and carbon dioxide.The thin walls aid this gaseous exchange.

Blood is redirected around the body depending on which body parts require it, this redirection is caled "shunting". shunting is done by 2 methods:

• vasocontriction and vasodilation
• open and close pre capillary sphincters

vascualr shunt occurs when receptors in the body detect changes in:

• o2 and co2 levels - chemoreceptors
• blood acidity - chemoreceptors
• joint and tendon movement - proprioreceptors 

Blood vessels then vasodilate and pre capillary sphinters open to increase blood flow.

BP= Blood Velocity x Resistance 

Systolic pressure - Contraction

Diastolic pressure - Relaxing

Blood pressure decreases the further away the blood gets from the heart, the Baroreceptors detect this change in blood pressure. As blood pressure is low in the veins far from the heart , not enough blood will return to the heart, however there are mechanisms to counter this:

• skeletal muscle pump
• pocket valves
• respiratory pump

some other things aid venous return such as:

• smooth muscle tissue 
• gravity

• skeletal muscle pump                                                                                               Contraction and relaxion of muscles during exercise squeeze the veins and pump blood back to the heart, this emphasises the importance of a cool down, preventing DOMS by removing lactic acid form the blood and stopping blood pooling by the use of an active cool down.
• Pocket valves                                                                                                         valves within the veins snap shut ensuring that there is no backflow of blood, thus the blood is directed back to the heart. 
• The repiratory pump                                                                                                   The increased rate and depth of breathing during exercise creates pressure changes in the thorax and abdomen. The increased pressure in the abdomen compresses the veins and squeezes blood into the veins that supply the heart.

Smooth muscle in walls -  helps squeeze blood back towards the heart 

Gravity - helps blood return to the heart from the upper body

Heart - suction pump action in the heart

3% Oxygen is soluble in plasma                                                                                               97% is attached to haemaglobin (Hb)

When oxygen is attached to haemaglobin it forms oxyhaemaglobin (HbO2)

Hb + O2 < = = > HbO2

The amount of O2 attached to haemaglobin s dependant on the partial pressure of O2

Partial pressure is the portion  of total blood gas pressure exerted by oxygen.

Myoglobin is situated in muscles  and so has a higher affinity for oxygen than haemaglobin, this causes the oxygen to tranfer from Hb to Myoglobin as the red blood cells pass through the capillaries. myoglobin is the supply of oxygen for the muscle cell.

The partial pressure (PO2) of oxygen determines how much oxygen combnes with haemaglobin. when the partial pressure is high haemaglobin is almost fully saturated with oxygen - 96%. When partial pressure is low, haemaglobin saturation is also low as it realeases the rest to tissues - 20%.

This represented by the oxyhaemaglobin dissosiation curve.

In the lungs there is almost full saturation of Haemaglobin but at the tissues the PO2 is lower, Haemaglobin gives up 23% O2 to the muscles and is therefore is no loner saturated. At rest this is fine when the O2 demand is low in the muscles.during exercise this needs to increase and occur faster, so a bigger percentage of O2  is released from haemaglobin to the muscles.

During exercise, the s-shaped curve shifts to the right because the muscles need more O2, the dissociation of  O2 from haemaglobin in the capillaries to muscle tissue occurs more rapidly, this shift to the tght is called the BOHR shift. Exercise = more rapid dissociation of oxygen from haemaglobin                                                                                                                     BOHR effect - Oxy- haemaglobin dissocation curve shifts to the right, freeing up  more oxygen for the muscles to use.

• Reasons:                                                                                                             Increased blood temperature -  O2 readily dissociating from haemaglobin.
• PO2 of CO2 increases - as the level of bood CO2 rises  during exrcise the BOHR shift occurs
• PH- increased CO2 means lower PH in the blood, this drop causes the shift
• increase in lactic acid - as a result of muscle contractions

The redistribution of blood flow is different at rest than it is during exercise. the skeletal muscles requiere more oxygen so more blood needs to be directed at them to meet the Oxygen demand, this is known as vascular shunting. 

Performers should not eat at least 1 hour before activity as a full gut will result in more blood being directed at the stomach instead of the working muscles, having a detrimental effect on performance.

02 to the brain must stay constant to ensure brain function is mantained. More blood must go to the heart due to it beating faster and so needing more energy to cotract and relax through the cardiac cycle.

More blood goes to the skin as energy is needed to cool the body down and reduce skin temperature. Blood pressure and blood flow are controlled via the vasomotor centre located at the medulla oblongata in the brain.Chemoreceptors  detect changes in CO2 and lactic acid levels, stimulating the vasomotor centre, thus redistributing blood flow through vasodilation, vasocontriction. 

Vasodilation

Blood vessels widens to increase blood flow into the capillaries.

Vasocontriction

Blood vessels narrow to decrese blood flow into the capillaries

Redirection of blood flow also occurs through the stimulation of the sympathetic nervous system  via sympathetic nerves in the walls of blood vesse, when this stimulation increases vasocontriction occurs and blood flow reduces to be redistributed to other parts of the body such as the muscles during exercise. When stimulation by the sympathetic nerves decreases vasodilation occurs, increasing blood flow to that part.

Pre-capillary sphincters also aid blood redistribution, they are tiny rings of muscle located at capillary openings. when they contract blood flow is restricted when they relax blod flow flow increases. During exercise, the capillary networks supplying skeletal muscles will relax pre-capillary sphincters to increase blood flow and thus saturate the tissues with oxygen .

• Increases oxygen supply to working muscles 
• Removes waste products from muscles e.g. lactic acid 
• Increases supply to skin to regulate temperature
• Direct more blood to the heart as it requires more oxygen to contract

The rate of Gaseous Exchange is dependant on the partial pressure gradient. when exercising the percentage of oxygen partial pressure in the muscle is low, so oxygen from the blood is rapidly exchanged. 

The A-VO2 diff is the difference between the Oxygen content of arterial blood arriving at the muscles and the venous blood leaving the muscles, at rest the A-VO2 diff is low as not as much oxygen is required by the muscles. During exercise much more oxygen is needed from the blood for the muscle so the A-VO2 diff is high.

Thius increase affects gaseous exchange  at the alveoli so more o2 is taken by the myoglobin and more co2 is removed by the red blood cells, training increases this A-VO2 diff.