Term
| How are vessels arranged? |
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Definition
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Term
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Definition
| an end to end connection; there is only one path via which blood can flow |
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Term
| Define a parallel circuit |
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Definition
there are many paths via which blood can flow as there are many branches from the main circuit.
they are important |
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Term
| What is an exceptino to the rule that 'all organs are in parallel with each other'? |
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Definition
the liver and the small intestine (they are in series with each other)
the superior mesenteric vein drains blood away from the small intestine and becomes the hepatic portal vein |
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Term
| What does an artery carry? |
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Definition
blood away from the heart
most carry oxygenated blood |
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Term
| Which arteries do not carry oxygenated blood? |
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Definition
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Term
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Definition
blood towards the heart
most veins carry deoxygenated blood |
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Term
| Which veins do not carry deoxygenated blood? |
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Definition
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Term
| Simply describe blood flow pathway |
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Definition
| aorta -> arteries -> arterioles -> capillaries -> venules -> veins |
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Term
| Which vessel has the largest total cross-sectional area? why is this strange? |
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Definition
capillaries
even though they have the smallest vessel, simply because they are so abundant |
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Term
| Where is most of the blood located? |
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Definition
| in the venous system (67%) because of their structure |
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Term
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Definition
| If all the blood vessels contained within a human body were attached end to end, they would span the circumference of the Earth TWICE. |
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Term
| What does the microcirculation consist of? |
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Definition
arterioles, capillaries and venules
they can only be seen using a microscope |
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Term
| What is the relationship between the velocity of blood flow and the total cross-sectional area? why is this important? |
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Definition
they are essentially mirror images
capillaries have the lowest velocity to allow for exchange of solutes |
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Term
| Where is flow fastest and slowest? |
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Definition
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Term
| What are the 3 distinct layers of a blood vessel wall? |
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Definition
1. tunica adventitia (tunica externa)
2. tunica media
3. tunica intima |
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Term
| Describe the structure and function of tunica adventitia |
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Definition
- external layer
- made up of connective tissue (mainly collagen fibres)
- provides support for the blood vessel |
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Term
| What other function does the connective tissue have? |
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Definition
| it tethers the vessel to nearby organs and structures to hold them in place |
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Term
| Describe the structure and function of tunica media |
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Definition
- middle layer
- consists of smooth muscle which allows the vessels to contract and relax to adjust the size of the lumen
- consists of elastin which provides the vessel with its elasticity, allow it to stretch and recoil
the ratio changes depending on the vessel in question |
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Term
| Describe the structure and function of tunica intima |
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Definition
- innermost layer
- flattened squamous epithelial cells
- provides the first barrier to plasma leaving capillaries |
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Term
| What is the arterial system made up of? |
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Definition
1. elastic arteries
2. muscular arteries
3. arterioles |
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Term
| Describe the structure of elastic arteries |
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Definition
- largest arteries (mainly aorta and its major branches)
- large diameter (12.5mm) therefore low resistance which makes sense as the aorta is the first vessel the blood is pumped into |
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Term
| Why are they called the elastic arteries? |
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Definition
| tunica media contains large amounts of elastin relative to smooth muscle, this allows arteries to stretch and recoil, helping to withstand and smooth out large pressure fluctuations |
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Term
| Give two examples of muscular arteries |
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Definition
| these are the ones people are usually most common with eg the common carotid artery and the renal artery |
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Term
| What is the function of muscular arteries? |
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Definition
| deliver blood from the main blood supply (aorta) to specific organs, the reason why the names are recognisable as often they are named after the organs to which they are supplying blood |
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Term
| Describe the structure of muscular arteries |
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Definition
- diameter in range 10mm-0.3mm
- thickest tunica media of all arteries |
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Term
| Describe the smooth muscle to elastin ratio and what this means |
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Definition
- increased SM at the expense of elastin
- less distensible and are more active in vasoconstriction/vasodilation
- SM allows the muscular arteries to adjust the size of the lumen and have greater control of blood flow (aka distributing arteries) |
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Term
| What is the role of arterioles? |
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Definition
| deliver blood to capillaries |
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Term
| Describe the structure of arterioles |
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Definition
- diameters range 10-300micrometers
- tunica media is almost entirely smooth muscle |
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Term
| How dose the structure of arterioles change as they get smaller? |
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Definition
| larger ones may have all 3 layers however smaller one's tunica media may entirely be smooth muscle. Very small ones may not have any tunica adventitia |
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Term
| What does arteriole diameter regulate? why is this important? |
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Definition
blood flow to capillaries
it is important that blood is slowed before it reaches the capillaries because they do not have as many protective measure to prevent rupturing under high pressures. |
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Term
| Describe the structure of capillaries |
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Definition
- smallest blood vessel, diameter ranging from 6-10micrometers
- lumen is large enough for the passage of a single RBC |
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Term
| What do capillaries lack? |
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Definition
| Both the tunica adventitia and tunica media. They are simply tunica intima (squamous epithelium) surrounded (externally) by a basement membrane |
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Term
| Name the two main types of capillaries |
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Definition
| Continuous and fenestrated |
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Term
| Is there a third type of capillary? |
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Definition
Yes, a sinusoidal capillary.
These are fenestrated capillaries with larger opening in the endothelium and are much rarer. Mainly found in bone marrow. |
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Term
| Which is the most common capillary? |
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Definition
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Term
| Describe the structure of continuous capillaries |
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Definition
the endothelial cells provide an uninterrupted lining and only allow small molecules, like water and ions to diffuse through the tiny intracellular gaps of the tunica intima.
They are therefore able to staunchly regulate solute exchange |
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Term
| Describe the structure of fenestrated capillaries |
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Definition
- they have pores (fenestrations) in the endothelial cells (60-80nm in diameter) to allow small molecules and limited amounts of protein to diffuse across
- more permeable to fluid and small solutes |
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Term
| Where are fenestrated capillaries found? |
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Definition
| where active absorption or filtrate formation occurs, such as in the kidney and small intestine |
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Term
| What is a capillary bed comprised of? |
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Definition
1. true capillaries
2. metarteriole
3. pre-capillary sphincter |
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Term
| What are true capillaries? |
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Definition
| these are the actual exchange vessels. There are 10-100 true capillaries per capillary bed |
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Term
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Definition
| a 'vascular shunt' connecting the terminal arteriole with the postcapillary venule, which blood flows through to 'bypass' the true capillaries |
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Term
| How is capillary flow regulated? |
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Definition
| by a ring of smooth muscle fibres that wrap around the capillaries at the arteriole end called a pre-capillary sphincter |
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Term
| Describe how the metareriole regulates the flow of blood through the capillary bed? |
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Definition
| - prevents a sudden rush of uncontrolled blood flow going throughout the entire capillary bed and in doing so prevents the capillaries themselves from rupturing |
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Term
| Describe how the pre-capillaryy sphincter regulates the flow of blood through the capillary bed? |
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Definition
| If the sphincter contracts, the vessel will be constricted, narrowing the lumen. If the sphincter relaxes, the vessel with be released, widening the lumen. |
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Term
| What are the 3 types of veins? |
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Definition
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Term
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Definition
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Term
| Describe the structure of a venule |
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Definition
- diameter 8-100micrometers
- walls of small venules consist solely of endothelium
- larger venules possess a sparse tunica media and tunica adventitia |
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Term
| Describe the structure of a vein |
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Definition
| - usually have 3 distinct tunica layers |
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Term
| What are the two main differences between veins and arteries? |
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Definition
| walls are thinner so lumens are larger than corresponding arteries |
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Term
| Why are veins called 'capacitance vessels'? |
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Definition
| they accommodate a large blood volume (65% of total) so have thin walls so they can stretch to do this |
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Term
| Why are valves present in veins? |
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Definition
| so they can work against gravity - they stop the blood from pooling in the feet - in circulating the blood back to the heart for reoxygenation |
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Term
| What is systemic blood pressure? |
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Definition
| the blood pressure throughout the arteries, veins and capillaries |
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Term
| What drives blood through vessels? |
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Definition
pressure
blood flows down a pressure gradient, from an area of higher pressure, to an area of lower pressure |
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Term
| Where is the greatest pressure? |
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Definition
| the closer to the exiting pump (LV of heart) |
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Term
| On a systemic blood pressure graph, why are two numbers given? |
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Definition
| the pressure in the aorta is pulsatile, it changes from systole to diastole |
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Term
| What is the role of the elastic arteries in this sense? |
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Definition
| to smooth the blood flow so that by the time it has reached the arterioles, it is no longer pulsatile, it is constant |
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Term
| Where is the steepest drop in pressure in the systemic circulation? |
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Definition
the arterioles
this is because they provide the greatest resistance to blood flow, reducing the pressure. |
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Term
| What two things does arterial blood pressure reflect? |
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Definition
1. the distensibility of the elastic arteries near the heart
2. the volume of blood being forced into these arteries |
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Term
| What cause pulsatile flow? |
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Definition
| the volume of blood being forced into the arteries varies during the cardiac cycle, therefore so does the arterial blood pressure |
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Term
| What is systolic pressure due to? |
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Definition
the volume of blood ejected during systole (stretching of the aorta)
120mmHg
BPs |
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Term
| What is diastolic pressure due to? |
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Definition
the volume of blood ejected during diastole (recoiling of the aorta)
80mmHg
BPd |
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Term
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Definition
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Term
| Why must capillary pressure be low? |
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Definition
| otherwise the fragile capillary walls will rupture because the capillaries don't have the tunica adventitia and tunica media |
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Term
| What does capillary pressure regulate? |
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Definition
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Term
| Give the arteriole and venule end capillary blood pressure values |
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Definition
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Term
| What is the main difference between venous and arterial pressure? |
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Definition
- venous pressure is steady and does not change significantly during the cardiac cycle.
- pressure gradient over the whole venous system is about 20mmHg (as compared to 60mmHg for arterial) |
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Term
| What is the main issue with venous pressure? |
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Definition
| too low to ensure blood is returned to the heart at the same rate as the heart is attempting to pump blood into arterial systemic system. |
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Term
| What are the factors influencing venous return? |
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Definition
1. the respiratory pump
2. the skeletal muscle pump |
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Term
| How does the skeletal muscle pump work? |
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Definition
- when skeletal muscles contract, they compress the deep veins and propel blood towards the heart
- valves distal to the point of compression prevent back flow of blood |
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Term
| Why is the skeletal pump so necessary? |
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Definition
| the veins have to work against gravity and at low pressure (the pressure in the right atrium when blood reaches the heart is almost zero) not a good mix when you need blood to go back to the heart for reoxygenation |
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Term
| What pressure does inspiration increase? |
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Definition
| inspiration increases abdominal pressure and compresses the abdominal veins - this forces blood towards the heart as valves prevent backflow |
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Term
| What pressure does inspiration decrease? |
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Definition
| inspiration decreases thoracic pressure therefore thoracic veins expand, further aiding movement of blood towards right atrium |
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Term
| How does inspiration affect the pressure gradient? |
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Definition
| pressure gradient between thoracic and abdominal cavity increases, driving blood flow to the heart |
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Term
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Definition
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Term
| What is sphygmomanometry? |
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Definition
| used to indirectly measure systemic arterial blood pressure |
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Term
| How does sphygmomanometry measure blood pressure? |
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Definition
1. surround the arm with a distensible cuff to compress the arm
2. pressure in the cuff exceeds pressure in the artery is squeezed shut
3. when pressure drops, turbulent flow in compressed artery makes audible vibrations (Korotkoff sounds) |
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Term
| How is capillary blood flow essentially non-pulsatile? |
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Definition
| pulsatile pressure is progressively damped by the elasticity of the arterial walls and the frictional resistance of the small arteries and arterioles. |
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Term
| What does the % of blood pumped to any of the vascular beds depend on? |
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Definition
| the state of the individual (eg. rest/exercise) |
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