The Systemic Circulation Flashcards
Vessels cane arranged in either S______ or in P________
Series
Parallel
which blood vessel has the greatest total cross sectional area? State this area given units
Capillaries
1357cm^2
In which blood vessel is the majority of blood found? State the percentage of blood found in that vessel
Veins
67% of all blood is found in the venous circulation
In which blood vessel is flow rate slowest?
The capillaries
In which blood vessel is flow rate fastest?
Aorta
What is the relationship between velocity of blood flow and the Toal cross sectional area?
They are mirror images of each other
Approximately how many arteries are there?
10^6
1,000,000
Approximately how many arterioles are there?
10^7
10,000,000
Approximately how many capillaries are there?
10^10
10,000,000,000
Approximately how many veins are there?
10^12
1,000,000,000,000
What are the 3 district layers (Walls) in blood cells?
Tunica adventitia (outermost) Tunica media Tunica intima (innermost)
Describe the tunica adventitia
Outermost layer made up of connective tissue (collagen fibre)
Describe the tunica media
Middle layer made up of smooth muscle and elastin
Describe the tunica intima
Innermost layer made up of endothelium (specifically squamous epithelium)
Name the two variations in arteries
Elastic arteries
Muscular arteries
What are the main elastic arteries?
Aorta and major branches
State the characteristics of elastic arteries
Large diameter
Low resistance pathway
Large amounts of tunica media to be able to withstand and smooth out large pressure fluctuations
What do muscular arteries do?
Deliver blood to specific organs
What is the diameter range for muscular arteries?
0.3-10mm
State the characteristics of muscular arteries
Less elastin and more smooth muscle in the tunica media
Less distensible
more active in vasoconstriction
What do arterioles do?
Deliver blood to the capillary beds
What is the diameter range for arterioles?
10 micrometres - 0.3mm
State some characteristics of arterioles
Their tunica media is made of entirely smooth muscle
The arterioles diameter regulates blood flow to capillary beds in response to neural stimuli and local chemical influences
What are the two different types of capillaries?
Continuous
Fenestrated
Describe some of the general features of capillaries
They are the smallest blood vessel
Diameter range: 8-10micrometres
They are just large enough for red blood cells to pass through them
Which of the two types of capillaries is the most common type?
The continuous capillaries
Describe some features of continuous capillaries
Endothelial cells have tight junctions between them
Have intercellular clefts which limit passage of fluid and small solutes
Where are fenestrated capillaries found?
Areas where active absorption of filtrate formation occurs
E.g. Small intestine, kidneys
Describe some features of fenestrated capillaries
Some of the endothelial cells have oval pore (fenestrations)
This makes them more permeable to fluids and small solutes
What are capillary beds?
Interweaving networks of capillaries
What is microcirculation?
Blood flow through the capillary beds
Interweaving networks of capillaries is called
Capillary beds
Blood flowing through the capillary beds is termed…?
Microcirculation
What are true capillaries and how many are their per capillary bed?
Actual exchange vessels
Around 10-100 per bed
What is capillary flow regulated by?
A ring of smooth muscle fibres called the precapillary sphincter
What, in most beds, by passes the true capillaries?
A vascular shunt called a metarteriole
What is a metarteriole?
A vascular shunt that bypasses the true capillaries
How do venules form and what is their diameter range?
They form when capillaries unite
Their diameter range: 8-100 micrometers
Describe the differenced between small and large venules
Small venules consists of only endothelium
Larger venules posses a sparse tunica media and tunica adventitia
Give some characteristics of veins
They have 3 distinct tunicae Walls are thinning Lumen is larger Capacitance vessels They have valves to ensure blood flows to the heart even at lore pressures
Where in the systemic circulatory system is pressure greatest?
In the left ventricles and then the aorta
Basically closer to the pump=greater pressure
Where in the systemic circulatory system is pressure smallest?
Right atrium
Where does the steepest drop in pressure occur?
In the arterioles as they offer the greatest resistance to flow
When does pressure occur?
When flow is opposed by resistance
What 2 things does arterial blood pressure reflect?
- The compliance (distensibility) of the elastic arteries near the heart
- The volume of blood being forced into these arteries at a particular point in time
Why does arterial blood pressure vary during the cardiac cycle?
As the volume of blood being forced into the arteries at a particular point in time varies during the cardiac cycle
When is arterial pressure at its highest?
During the systolic phase of the cardiac cycles
Typically 120mmHg
When is arterial pressure at its lowest?
During the diastolic phase of the cardiac cycles
Typically 80mmHg
How do you calculate pulse pressure (PP)?
Systolic pressure-Diastolic pressure
SP-DP= PP
E.g. 120-80=40mmHg
How do you calculate mean arterial pressure (MAP)?
Diastolic pressure + (Pulse pressure/3)
DP+(PP/3)= MAP
E.g. 80+(40/3)=93.3
What is the blood pressure at the arterial end of the capillary bed?
Around 40mmHg
What is the blood pressure at the venous end of the capillary bed?
Around 20mmHg
Why is capillary pressure important?
It must be low or the capillary walls may rupture
It must be closely controlled so that the filtration of solutes in the interstitial space is regulated
What is the pressure gradient over the whole venous system?
About 20mmHg
What is the pressure gradient over the whole arterial system?
About 60mmHg
Since the venous pressure is quite low what problems does this create?
It means the blood is returning to the heart at a slower rate than which the heart is pumping the blood out into the systemic arterial system
This imbalance is unsustainable
What special adaptations does the body have to counter act the imbalance in blood into and out of the heart caused by low venous blood pressure?
Respiratory pump
The skeletal muscle pump
How does the respiratory pump influence venous return?
Inspiration increases abdominal pressure and compresses the abdominal veins
Venous valves prevent the back flow of blood forcing blood to the heart
Inspiration also decreases thoracic pressure. So thoracic veins expand further aiding the movement of blood towards the right atrium
How does the skeletal muscle pump influence venous return?
When skeletal muscle contract they compress deep veins and propel blood towards the heart
Valved prevent the backflow of blood
