The Histology of the Cardiovascular System

Question 1

What are the three layers of blood vessels?

Answer 1

Tunica intima – Inner layer, made of endothelium, basal lamina, and subendothelial connective tissue

Tunica media – Middle layer, composed of smooth muscle cells and elastic fibers

Tunica adventitia (externa) – Outer layer, made of collagen fibers, connective tissue, and vasa vasorum in large vessels

Question 2

What are the main cellular components of each blood vessel layer?

Answer 2

Tunica intima → Endothelial cells, connective tissue, sometimes an internal elastic lamina

Tunica media → Smooth muscle cells, elastic fibers, collagen

Tunica adventitia → Fibroblasts, collagen, vasa vasorum (in large vessels)

Question 3

How do the layers of blood vessels vary with size?

Answer 3

Large arteries (elastic arteries) → Thick tunica media with elastic fibers

Medium arteries (muscular arteries) → Prominent smooth muscle in tunica media

Arterioles → Thin walls, mostly smooth muscle

Capillaries → Only tunica intima (endothelium + basal lamina)

Veins → Thin tunica media, thicker tunica adventitia, contains valves

Question 4

What are the three types of capillaries, and how do they differ?

Answer 4

Continuous capillaries – No gaps, found in the brain, muscle, lungs

Fenestrated capillaries – Have pores, found in the kidneys, intestines, endocrine glands

Discontinuous (sinusoidal) capillaries – Large gaps, found in the liver, spleen, bone marrow

Question 5

How do lymphatic vessels differ from blood capillaries?

Answer 5

Lymphatic capillaries have thin walls and lack a basement membrane

They lack red blood cells but transport lymph

Have valves to prevent backflow

More permeable than blood capillaries, allowing large molecules to enter

Question 6

What are the histological differences between elastic and muscular arteries?

Answer 6

Elastic arteries (e.g., aorta) → Thick tunica media with many elastic fibers to stretch and recoil

Muscular arteries (e.g., brachial artery) → Thick tunica media with smooth muscle, well-defined internal and external elastic laminae

Question 7

What is an arteriovenous shunt, and what is its function?

Answer 7

A direct connection between an artery and a vein that:

• Bypasses capillaries
• Helps with thermoregulation (e.g., in the skin)
• Regulates blood flow in specialized areas

Question 8

How does blood vessel structure relate to function?

Answer 8

Elastic arteries → Stretch and recoil to maintain blood pressure

Muscular arteries → Distribute blood via vasoconstriction and vasodilation

Arterioles → Regulate resistance and control blood flow

Capillaries → Allow exchange of gases and nutrients

Veins → Have valves to prevent backflow and a thinner wall for blood storage