Pressure and Flow in Veins Flashcards
What is pressure like in veins?
Low
Describe the pressure difference between the veins and venules and the right venule.
Small pressure change as veins and venules push blood into the right atria.
RECAP- describe the structure of veins and venules.
Distensible and collapsible so can store a lot of blood.
Thin walls.
What can the distensible structure of veins mean in terms of influences?
As veins are very thin, they are susceptible to external influences, like flow.
Does gravity affect where the blood goes in the body?
Yes
Does gravity affect the driving pressure of the blood in the body?
No
What happens to blood when you go from sitting to standing?
Blood will go down your body and pool at venules in your feet, causing the venules to increase in size due to the volume of blood.
What can happen when people, particular taller people, stand up after sitting.
They can go light headed or even faint
What is the term used to describe the light headed feeling experienced when going from sitting/lying to standing?
Orthostatic (postural) hypotension
Describe what happens regarding blood flow etc. when most of the blood is in the venules in the legs and the arteries have less blood to pump in the heart.
End diastolic value decreases
Preload decreases
Stroke volume decreases
Cardiac outflow decreases
Mean arterial pressure decreases.
What could happen if your mean arterial pressure fell too much?
Tissues and organs wouldn’t be adequately perfused leading to things like postural/orthostatic hypertension.
What would happen to the pressure in the column of blood as you moved closer to the head after lying?
Pressure would become increasingly negative.
What would happen to compensate for this lower pressure?
As pressure in the vessel is less than the pressure outside of the vessel, the vessel will collapse and there will be less volume so pressure will increase.
Is the point of collapse due to pressure often seen?
No as it usually occurs under the clavicle.
What would happen to the pressure in your head area if your central venous pressure increased?
The point of collapse would move further up your neck and may become visible as the jugular vein could be pushing out.
What can a raised jugular venous pressure be used to estimate?
Central venous pressure.
What else can affect pressure and flow in the veins, other than gravity?
Skeletal muscle pump.
What are the veins and venules in your legs surrounded by?
Skeletal muscle.
What happens when the skeletal muscle surrounding veins and venules contracts?
It becomes shorter and fatter
What happens to the veins when skeletal muscle contracts?
It squeezes the veins and venules and pushes blood in both directions- towards the heart and towards the feet.
What limits the back flow of blood in your veins and venules?
Valves
Give examples of rhythmic exercise.
Walking, cycling, running
What happens to the veins/ venules in your legs during rhythmic exercise?
Skeletal muscle contracts and squeezes the extra capacitance back to the heart, increasing venous return and end diastolic volume..
What happens to fill rate and end diastolic volume during exercise?
They both decrease
What offsets the reduced fill rate and end diastolic volume?
Activity of the skeletal muscle pump.
What may happen to patients lying in hospital beds for long periods of time or those going on a long haul flight?
They may develop deep vein thrombosis.
Why do people get deep vein thrombosis?
Increased venous pooling in the legs and static blood is more likely to clot.
How can you prevent deep vein thrombosis?
Wearing travel socks or specialised DVT socks
How do these DVT socks work?
Tight fitting so compress the vessels in the legs and push the blood back to the heart more quickly.
List the five things that can affect venous return to the heart.
Gravity
Skeletal muscle pump
Respiratory pump
Venomotor tone
Systemic filling pressure
What does respiratory pump do in terms of venous return?
Increases venous return
Increases diastolic volume
What happens to pressure upon inspiration?
Diaphragm moves down and causes a negative pressure within the thorax and a positive pressure below.
The positive pressure below gets transmitted down to the vessels and causes a larger pressure gradient, pushing blood back to the heart and increasing venous return.
What happens to blood return when you are breathing faster and deeper?
Increase of blood return to the heart.
How can respiratory pump help to offset the decreased filling time and diastolic volume experienced upon exercising?
Respiratory pump will direct more blood to the heart when increase in rate and depth of breathing.
What is meant by tone?
Ongoing activity
What type of muscle are veins and venules surrounded by?
Smooth muscle.
What is smooth muscle innervated by?
Sympathetic NS
Discuss how venomotor tone can help increase end diastolic volume.
The release of adrenaline and noradrenaline binds to adrenergic receptors on that smooth muscle, causes them to contract and squeeze that capacitance back to the heart increasing EDV.
What is systematic filling pressure?
Pressure created by ventricles and transmitted through vascular tree to the veins
What happens to systemic filling pressure upon exercise?
It increases
