The Vascular System Blood consists of blood cells and platelets floating in plasma, 8% of body weight: Plasma makes up 55% of blood volume Red blood cells contain iron-rich protein called haemoglobin, which combines with oxygen and transports it in blood. White blood cells protect the body by fighting infection and disease. Platelets are responsible for clotting the blood.

KEY FUNCTIONS OF BLOOD TRANSPORTATION of:  oxygen  carbon dioxide  waste products of respiration  food fuels, vitamins, minerals  plasma  hormones

Blood vessels Arteries, arterioles, venules and veins all have a similar structure.

VesselsStructure and Function Arteries Arterioles

VesselsStructure and Function Arteries Arterioles Carry blood away from heart, further from heart they get smaller (Arterioles) Carry blood at high pressure Aorta is main artery Walls made up of elastic fibres that enable them to stretch Generate wave of pressure (pulse) They can Vasoconstrict, reducing diameter to reduce amount of blood flow to inactive organs Can also relax the elastic fibres to Vasodilate, increasing diameter for more O2 to reach muscles This mechanism of blood redistrubution is called Vascular Shunt Arteries have No Valves

VesselsStructure and Function Veins Venules Blood from capillaries is transported back towards the heart via veins and venules Carry deoxygenated blood back to heart at low pressure Less elastic, but involuntary muscle help return blood Pocket valves exist in veins which aid return of blood to heart, ensuring there is no backflow

VesselsStructure and Function Capillaries Blood from arterioles enter a network of capillaries that surround the tissues Walls are just one cell in thickness so diffusion distance is short for oxygen and other nutrients Narrow diameter, blood flow is slow, maximising diffusion Vast number of capillaries, huge surface area

VENOUS RETURN Venous Return Gravity Skeletal muscle pump Pocket Valves Smooth muscle in veins Respiratory pump

Venous Return Mechanism VENOUS RETURN is affected by : SKELETAL MUSCLE PUMP Walls of veins are thin and contraction of muscles squeeze and pump blood back to heart contraction of skeletal muscle exerts pressure on veins forcing blood to flow towards the heart backflow is prevented by pocket valves

POCKET VALVES These exist in veins which snap shut, ensuring no backflow SMOOTH MUSCLE WITHIN VEINS Located in the walls is smooth muscle to squeeze the blood back to the heart Pre-capillary sphincters regulate blood flow into capillaries by narrowing or opening RESPIRATORY PUMP Increase rate and depth of breathing create pressure in abdomen which compresses veins and squeeze blood in veins blood moves up from compressed high pressure (in abdomen) to low pressure (in thorax) during expiration, pocket valves prevent backflow of blood into abdomen GRAVITY In the upper body, gravity assists the flow Venous Return Mechanism

During exercise Venous return mechanism is particularly important at the start of exercise in order to increase stroke volume and cardiac output.

Blood Pressure & Blood Flow Blood pressure is the force exerted by the blood against the blood vessel wall. Ejection of blood by the ventricles contracting creates a high pressure pulse of blood, which is systolic pressure. The lower pressure as the ventricles relax is known as the diastolic pressure.

During exercise, changes in blood pressure occur, but these depend on the type and intensity of the exercise being performed. Systolic pressure increases during aerobic exercise due to an increase in cardiac output, whilst diastolic pressure remains constant

Blood Velocity The velocity of blood flow changes as it passes from one type of blood vessel to another (affected by the diameter of the blood vessels). The velocity is related to the force with which the blood is pumped and the cross-sectional area of the vessels the blood is passing through. The smaller the cross-sectional area, the faster the blood flows (water hose effect). Blood viscosity describes the thickness of the blood. If high then blood does not flow quickly

Vascular Shunt mechanism -Redistribution of blood during exercise The vascular shunt mechanism is regulated by the process of vasomotor control (located in medulla oblongata) As we exercise, the destination of blood flow changes dramatically. Blood flow can be diverted away from non-essential tissues and organs and directed to working muscles During exercise muscles gain 85-90% of total blood flow DestinationRestMaximal exercise Muscle20%88% Brain15%3% Heart5%4% Skin10%3% Liver & Intestines30%1% Kidneys20%1%

Redirection is important to: Increase blood supply to the working muscles Provides muscles with fuels (glucose and fatty acids) Removes CO2 & lactic acid Maintains body temperature Copy Fig The redistribution of blood flow during exercise

Vasomotor control Chemical changes in the blood are detected by Chemoreceptors which inform the vasomotor centre to stimulate the sympathetic nerves Sympathetic nerves will cause vasoconstriction of arterioles and pre-capillary sphincters supplying non-essential muscles and organs At same time vasodilation will supply more blood to the active working muscles

Putting it all together Draw a flow diagram using Fig of what happens to the cardiovascular system when we exercise, page 74 Training effects upon the vascular system Page 79. Draw a revision diagram outlining the long term effects of exercise on the vascular system

CARDIAC HYPERTROPHY REGULAR AEROBIC TRAINING results in hypertrophy of the cardiac muscle, meaning that the muscle becomes larger and stronger this means that the heart pumps a larger volume of blood out per beat, hence the stroke volume is larger this is termed bradycardia and has the consequence of producing a resting HR below 60 bpm at rest, a bigger stronger heart pumps more blood out per beat hence resting heart rate decreases, with the net effect of an unchanged cardiac output highly trained sportspeople tend to have resting heart rates of well below 60 bpm during maximum exercise, an increase in heart rate, coupled with an increase in stroke volume, results in an increase in cardiac output

EFFECTS OF EXERCISE ON THE CARDIOVASCULAR SYSTEM

Complete questions at the back of the Heart stapled booklet. Make sure you have a complete glossary of terms for the Heart Revision of Chapters 1-4 work covered so far – use the revision handout for the level of understanding