Cardiovascular System

thye can expand more because they have thinner walls

relationship between volume and pressure

high capacitance

low capactitance

the systemic venous system

• blood pressure is the force exerted by circulating blood upon the walls of blood vessels 
• usually refers to the arterial pressure in the systemic circulation

mean arterial pressure

expressed in terms of the systolic(max) pressure over diastolic(min) pressure

• vessel diameter
• total cross-sectional area 
• vessel pressure 
• velocity of blood flow

it is abnormally high BP

it increases the risk of heart attack, heart failure, kidney disease,, stroke or dementia

120/80 mmHg or slightly lower is normal

over 140/90 mmHg is abnormal

can be treated with ACE inhibitors or Ca channel blockers

• it is abnormally low BP <90/60 mmHg
• no medication
• limit symptoms

released in response to decrease in blood volume

causes vasoconstriction evevating BP

renin released when renal BP falls

• starts an enzymatic cascade resulting in production of angiotensin II
• stimulates secretion of ADH, stimulates production of aldosterone, stimulate thirst, stimulates vasoconstriction

released by kidneys and causes vasoconstriction

aldosterone causes Na retention and K loss by the kidneys, increases water resorption and decreases urine output

• extensive vasodilation
• venous return increases -skeletal muscle contractions force blood along veins 
• cardiac output increases 
• with moderate exercise, blood-flow to non- essential tissues decreases
• skeletal muscle blood flow increases significantly 
• brain blood flow remains relatively constant
• skin blood flow increases to reduce body temperature

• initial increase in cardiac output and peripheral venoconstriction [short term rise in BP]
• venoconstriction in organs 
• mobilises venous reserve and increase venous return

reduces volume of blood in venous system and increases volume in arteries and capillaries

the amount of blood that can be shifted from veins to liver etc is called the venous reserve- 20% total blood volume

is the amount of blood returning to the heart through the veins

when part of coronary circulation is blocked and cardiac muscle cells die

infarct