Cardiovascular: Anatomy - Blood vessels

Question 1

What are the three layers of blood vessels, from innermost to outer?

Answer 1

1. Tunica intima
2. Tunica media
3. Tunica adventitia

Question 2

Compare and contrast the composition of the various layers of blood vessels

Answer 2

1. Tunica intima: single layer of extremely flatted epithelial cells (endothelium) supported by delicate connective tissue
   - Capillaries consist of only this layer, with blood capillaries also having a supporting basement membrane
2. Tunica media: middle layer consisting primarily of smooth muscle
   - Most variable coat: different vessels are distinguished by the thickness of this layer relative to the lumen size, its organisation, and its composition (arteries have variable amounts of elastic fibres)
3. Tunica adventitia: outer connective tissue layer or sheath

Question 3

What is the general difference in blood vessel composition between arteries, veins, and capillaries?

Answer 3

Arteries: elastic and muscle fibres within their walls, allowing them to propel blood throughout the CV system
Veins: thinner walls than arteries with relatively wider lumens, distinguished by valves which prevent backflow of blood
Capillaries: smallest blood vessels, simple endothelial tubes linking arterioles and venules

Question 4

What are the three types of arteries? Give an example of each

Answer 4

1. Large elastic or conducting arteries (e.g. aorta, brachiocephalic trunk, subclavian and carotids, pulmonary trunk and arteries)
2. Medium muscular or distributing arteries (most of the named arteries are medium muscular arteries)
3. Small arteries and arterioles (not named)

Question 5

What is the role of the conducting arteries and how is this achieved?

Answer 5

Many elastic layers
Initially receive cardiac output: expand when receiving CO, minimising pressure change, and return to normal size between ventricular contractions, pushing the blood into medium arteries downstream
This maintains the blood pressure in the arterial system even as ventricular pressure falls to zero between cardiac contraction

Question 6

What is the roles of the distributing arteries and how is this achieved?

Answer 6

Walls consist chiefly of circularly disposed smooth muscle fibres
Vasoconstriction regulates blood flow to different parts of body
Pulsatile contractions of their muscular walls temporarily and rhythmically constrict their lumina in progressive sequence, to propel and distribute blood (like peristalsis!)

Question 7

What is the role of small arteries and arterioles, and how is this achieved?

Answer 7

Relatively narrow lumina and thick muscular walls
Degree of filling of capillary beds and level of arterial pressure within the vascular system are regulated mainly by the degree of tonus (firmness) in the smooth muscle of arteriolar walls
If tonus is above normal, hypertension occurs

Question 8

What is the difference between true and functional terminal arteries? Where are they found?

Answer 8

True terminal arteries (end arteries) do not anastamose with adjacent arteries, and occlusion interrupts blood supply to the downstream structure or segment (e.g. in the retina)
Functional terminal arteries (arteries with ineffectual anastamoses) supply segments of the brain, liver, kidneys, spleen, and intestines, and may also exist in the heart

Question 9

What proportion of the blood volume is found in the venous vs arterial circulation?

Answer 9

Typically only 20% of the blood occupies arteries, and 80% is in the veins

Question 10

What are the three types of veins?

Answer 10

1. Large veins
2. Medium veines
3. Venules

Question 11

What is the composition of large veins? Give an example of a large vein

Answer 11

Wide longitudinal smooth muscle and well-developed adventitia
E.g. SVC

Question 12

What is the role of medium veins? How is this achieved? Give an example of a medium vein

Answer 12

Drain venous plexuses and accompany medium arteries
Have valves in locations where flow of blood is opposed by pull of gravity (e.g. limbs)
Accompanying veins surround deep arteries in an irregular branching network and also serve as a countercurrent heat exchanger: the warm arterial blood warms the cooler venous blood as it returns to the heart from a cool limb
Includes named superficial veins (e.g. cephalic and basilic, great and small saphenous) and accompanying veins named according to the artery they accompany

Question 13

Describe the structure of venous valves

Answer 13

Venous valves are cusps of endothelium with cup-like valvular sinuses that fill from above

Question 14

Define arteriovenous pump

Answer 14

Accompanying arteries and veins are contained within a relatively unyielding vascular sheath - the veins are stretched and flattened as the artery expands with cardiac contraction, aiding in driving venous blood back towards the heart

Question 15

Define musculovenous pump

Answer 15

Muscular contractions in the limbs function with the venous valves to move blood towards the heart - the outward expansion of contracting muscle bellies is limited by deep fascia and becomes a compressive force, propelling the blood against gravity

Question 16

Explain the Starling hypothesis

Answer 16

Hydrostatic pressure in arterioles forces blood through the capillary bed, and forces fluid containing oxygen, nutrients, and other cellular materials out of the blood at the arterial end into the extracellular spaces, allowing exchange with cells of the surrounding tissue
However, capillary walls are relatively impermeable to plasma proteins
At the venous end, most of the ECF (now containing waste products and CO2) is reabsorbed into the blood as a result of oncotic pressure from the higher concentrations of proteins within the capillary

Question 17

Define Starling’s hypothesis

Answer 17

Starling’s hypothesis states that the fluid movement due to filtration across the wall of a capillary is dependent on the balance between the hydrostatic pressure gradient and the oncotic pressure gradient across the capillary

Net driving pressure = [(Pc-Pi) - (pc-pi)]
Where:
• hydrostatic pressure in the capillary (Pc)
• hydrostatic pressure in the interstitium (Pi)
• oncotic pressure in the capillary (pc)
oncotic pressure in the interstitium (pi

Question 18

What are arteriovenular anastamoses? Give an example of their function

Answer 18

Direct connections between arterioles and venules proximal to capillary beds
Allow blood to bypass capillary beds
Numerous in the skin, where they play an important role in conserving body heat

Question 19

What is a portal venous system? Give an example

Answer 19

Venous system linking two capillary beds
E.g. hepatic portal system (venous system by which nutrient-rich blood passes from capillary beds of alimentary tract to capillary beds - sinusoids - of liver)