Systemic Circulation And Cardiovascular Pressure

Question 0

Which blood vessels have the greatest total cross sectional area ?

Answer 0

Capillaries

Question 1

How is the circulatory system arranged ?

Answer 1

In series and in parallel

-important for resistance, flow and pressure

Question 2

Where is most of the blood in circulation?

Answer 2

Venous circulation - about 2/3 - in systemic veins

Known as capacitance vessels

Question 3

What is the relationship between velocity of flow and total cross sectional area ?

Answer 3

Essentially mirror images of one another
The larger the total cross sectional area the slower the flow of blood
- eg flow is slowest in capillaries

Question 4

What are the 3 distinctive layers of blood vessel walls ?

Answer 4

• tunica Adventitia- made of lots of collagen fibres - provides structural support
• tunica media- Lots of smooth muscle and elastin - elastin enables vessel to distend but muscle opposes this
• tunica intima-endothelium (squamous epithelium) - provides a smooth surface to reduce resistance

Question 5

Explain the structure of the elastic arteries ?

Answer 5

=aorta and its largest branches ( brachiocephalic trunk, left common carotid artery, left subclavian artery)

• large diameter 12.5mm= enabling low resistance
• lots of elastin - withstand pressure and smooth put pressure fluctuations
• known as pressure reservoirs
• they can stretch so during ejection they stretch the reduce the pressure rise

Question 6

Explain the structure of the muscular arteries ?

Answer 6

Deliver blood to specific organs
Smaller diameter to elastic - 0.3-10mm
Have less elastin and more smooth muscle - therefore less distension and more active in vasoconstriction
Important in redirecting blood to regions which need it more

Question 7

Explain the structure of the arterioles ?

Answer 7

Deliver blood to capillaries
Have smaller diameter than muscular arteries - 10-300 micrometers
Media is almost entirely smooth muscle
Regulates blood flow to capillaries - redirects blood flow

Question 8

Explain the structure of the continuous capillaries ?

Answer 8

Most common
Their endothelial cells have tight junctions between them
The intercellular clefts are just large enough to allow some solutes and fluid to pass through

Question 9

Explain the structure of fenestrated capillaries ?

Answer 9

Some of the endothelial cells have fenestrations which makes them more permeable to fluid and solutes
Mainly in places where active active absorption (GIT) or filtration (kidney) is occurring

Question 10

What are true capillaries ?

Answer 10

Actual exchange vessels - only 10-100 per capillary bed

Question 11

What are metarterioles ?

Answer 11

These are called vascular shunts which bypass the true capillaries
Enable control of blood flow through the capillary bed

Question 12

What is a precapillary sphincter ?

Answer 12

Ring of smooth muscle which wraps around the capillary at the arterioles end
- relaxed = they allow blood flow through the bed for exchange
- contracted= close off blood flow through the bed
Causes more blood flow through metarterieoles reducing exchange of solutes

Question 13

Explain the structure of venues ?

Answer 13

Diameter of 8-100 micrometers
Smaller venues have walls which consist of just an endothelium
Larger venules contain a sparse media and Adventitia

Question 14

What is the purpose of valves in veins ?

Answer 14

Prevent good flowing in the opposite direction

Due to the low pressure in the veins they are important for ensuring blood returns to the heart

Question 15

Where does the steepest drop in pressure occur in the systemic blood flow ?

Answer 15

Arterioles as they offer the greatest resistance due to their vasoconstrictive abilities

Question 16

Why is pressure in the aorta pulsatile ?

Answer 16

Due to the contraction and relaxation of the heart

Question 17

What does the arterial blood pressure reflect ?

Answer 17

The compliance of the elastic arteries near to the heart
The volume of blood forces into arteries at a particular point - as blood volume into arteries varies though th cycle this is a mother consequence of pulsatile flow

Question 18

What are the typical values of systolic and diastolic pressure in the arterial blood system ?

Answer 18

Systolic = 120mmHg 
Diastolic= 80mmHg

Question 19

What are the pressures at the arterial end of the capillaries and the venous end ?

Answer 19

Arterioles = 40mmHg 
Venous = 20mmHg

Question 20

Why is capillary pressure so important ?

Answer 20

Has to be low otherwise capillaries will rupture

Has to be closely controlled to regulate the extent of filtration into interstitial space

Question 21

What are the 2 factors which ensure blood is pumped back to he heart at the same rate as the heart is pumping blood into systemic arteries ?

Answer 21

RESPIRATORY PUMP
-inspiration increase abdominal pressure and compresses abdominal veins, this helps to force blood along the veins
- also it causes thoracic pressure to decrease so thoracic veins expand helping to move blood towards right atrium
- expiration the decrease in abdominal pressure helps blood return from the lower body and the increase in throes in pressure helps push blood into right atrium
SKELETAL PUMP
-skeletal muscles contract they compress deep veins and propel blood towards heart

Question 22

What is a sphygmomanometry used for ?

Answer 22

To indirectly measure systemic arterial blood pressure

Question 23

What are korotkoff sounds ?

Answer 23

Sounds produced when a distensible cuff is inflated to a pressure between systolic and diastolic and causes the interruption of smooth laminar flow through the occuled artery