Lecutre 12- Venous Blood Flow And The Heart Flashcards
Almost 2/3rds of blood in the body at any one time is found where?
Venous system
The great change in pressure between the veins and arteries is needed to…
Provide a floe
Veins vs arteries high vs low pressure
Veins:
- high volume
- low pressure
Arteries
- low volume
- high pressure
What is compliance
- the extent to which a vessel allows deformation in response to an applied force
Vein vs artery - compliance
Artery:
- rigid
- thick wall - thick tunica layer
Vein
- thin wall
- compliment T
Equation for compliance
^V/^P
- how much does it descend or expand when pressure increases
Venous vs arterial compliance
What does the graph look like if its a large change in pressure comnpared to a large change in volume
What happens when arterial puncture
- loss of arterial blood
- life-threatening fall in arterial pressure
Response to arterial puncter and loss of arterial blood
- venocontriction
- pushes blood into the atrial system from the distensible veins and lack of tunica media
- blood transfusion from venous to arterial system
- if blood in arteries isn’t restored - volume decreases and then so does mean arterial pressure
What high compliance in veins results in:
- venous volume is larger then arterial volume
- while supine (laying down), venous evaluate is uniform form head to toe
- in the upright position, venous volume below the heart increases; whereas venous volume above the heart decreases
- extream venous pooling the the legs and feet
How venous valine counteract venous pooling
How tone of surrounding tissue also counteracts venous pooling
- particularly in the case of skeletal muscle, because it can alter its tensile state
- resting muscle tone varies between individuals
- muscle tone acts to stiffen the veins - makes them less compliant and prone to pooling
- some preppie prone to fainting have low muscke tine and excessive venous pooling
How skeletal muscle contractions increase venous return to the heart
How skeletal muscle acts as a pump to affect venous return to the heart
Muscle contractions increase venous blood flow
Starlings law of the heart:
The more stretched muscle fibres are before contraction, the stronger the contraction will be
Cellular mechanism of cardiac control
• Ca2+ levels go up, and more Ca2+ is released from the sarcoplasmic reticulum (SR)
• Myosin binds to actin to form cross-bridges.
• Myosin pulls on actin to shorten the sarcomere and generate force
• Every myocyte activated during each heart beat……
Increasing venous return means…
Increased stroke volume
What are veins?
Thin-walled vessels that have high compliance compared to arteries
Blood can pool in veins, what mechanisms counter this?
- venous valves
- surrounding tissue tone
Starling Lae of the heart tells us that the _____ the __________ stretch prior to ________, the ________ a ______ and greater _____ ______ we will have
Starlings law of the heart tells us that the mire the walls of the heart stretch prior to contraction, the stronger a contraction and greater stroke volume we will have
Venous return directly effects
The stroke volume and performance of the heart