Cardiovascular History: Heart and Blood vessels

Question 1

What are the 3 layers of blood vessels and what are their roles?

Answer 1

1. Tunica Adventitia - of connective tissue:
   Structural support, and carry nerve + blood supply to vessels (vasa vasorum in larger vessels)
2. Tunica Media - of smooth muscle:
   Support, contractility, and elasticity; Physically regulates blood flow.
3. Tunica Intima - of endothelium and collagen:
   Semi-permeable barrier to blood. Platelets and WBC’s can adhere to it. Layer makes mediators that control vessel tone and inflammation.

Question 2

What its the difference between these layers in arteries and veins?

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Answer 2

Arteries have a much thicker Tunica Media, are more rounded (veins more oval-shaped), and have a thicker wall.

Question 3

3 types of arteries:

1. Elastic (Conducting) arteries:
   Give some examples

What’s their distinctive feature?

What’s their role?

What is a dissecting aneurysm and what are the consequences?

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Answer 3

• Aorta, Pulmonary arteries, and their largest branches
• Have a VERY THICK Tunica Media, with lots of Elastin fibre sheets
• They absorb systolic blood flow by stretching, and they continue blood flow during diastole using it’s elastic recoil.
• Where there’s a partial tear of the arterial wall - bloods enters t.media. Can be fatal if t.adventitia also ruptures.

Question 4

2. Muscular (Distributing) arteries:
   What’s their role?

What are their features?

Answer 4

• Some elasticity as they still have to regulate blood flow and pressure.
• Prominent Internal elastic lamina (1 LAYER) between t.intima and t.media. Thick t.media with SOME elastic fibres. External elastic lamina (MANY LAYERS) in inner edge of t.adventitia. The t.adventitia is mainly composed of collagen.

Question 5

3. Arterioles:
   What’s their role?

What’s their main feature?

Answer 5

• Important in regulating blood flow and pressure.
• Smooth muscle in t.media is very well organised and runs in a CIRCULAR fashion around the vessel. Only have a couple layers of smooth muscle.

Question 6

Capillaries:
What’s their role?

What’s their structure?

What are the 2 types of capillaries?

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Answer 6

• Specialised for exchange.
• Made of 1-2 endothelial cells, therefore allowing for lots of exchange to occur, while being regulated by the layer of cytoplasm. Different organs require different capillary permeabilities.
• 1. Continuous capillaries - no holes in walls.
     
     2. Fenestrated capillaries - many tiny pores in their wall, so they’re more permeable. Sinusoids are capillaries with WIDER fenestrations, allowing for ↓Blood flow = ↑Exchange e.g. Liver, spleen

Question 7

Veins and Venules:
What are their roles?

What’s their structure?

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Answer 7

• Specialised to return low-pressure blood to heart.
• Thin, flexible walls with VALVES (often look collapsed due to low pressure). Valves help with flow against gravity. Prominent t.adventitia, THIN t.media. Some major veins have longitudinal smooth muscle in their walls to aid in the blood flow against gravity.

Question 8

What are the roles of the heart?

What are the 3 layers of the heart? What do they consist of?

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Answer 8

• Pump blood out and regulate BP (by ANP secretion from atria) - Over-filling lf stretches atria → ANP released → ↑Na and water excretion (Natriuresis) = ↓BP.
• 1. Epicardium (visceral pericardium) - has fatty loose connective tissue with nerves, blood vessels and a smooth epithelial covering (mesothelium).
     
     2. Myocardium - bundles of cardiac muscle that run in different directions and separated by dense layers of connective tissue. Layer contracts for heartbeat.
     3. Endocardium - thin layer of endothelium, collagen and some loose connective tissue. Rich in Purkinje fibres, which help in the impulse-conduction system.

Question 9

What is the normal structure of a heart valve?

How does it change when infected by bacteria?

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Answer 9

Top surface made of Elastic fibres.
Bottom layer made of a thick collagen tissue layer to support the valve.

• Bacterial Endocarditis
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