Blood Vessels Histology

What are the three main layers of all blood vessels?

Tunica intima, tunica media, tunica adventitia

What is the luminal lining cell of all blood vessels?

Simple squamous endothelial cell

What connective tissue lies immediately beneath endothelium?

Subendothelial connective tissue

Which vessel type has the thickest tunica media relative to lumen size?

Elastic artery

What is the hallmark structural feature of elastic arteries?

Numerous fenestrated elastic laminae in the tunica media

Name two examples of elastic (conducting) arteries.

Aorta, pulmonary artery

Why are elastic arteries called conducting arteries?

They conduct blood away from the heart and dampen pressure fluctuations

Which tunica is most prominent in elastic arteries?

Tunica media

What cells dominate the tunica media of elastic arteries?

Smooth muscle cells

What extracellular component is abundant in elastic artery media?

Elastic fibers arranged as fenestrated laminae

What is the function of fenestrated elastic laminae?

Allow stretch and recoil during systole and diastole

Where is the internal elastic lamina located?

Between tunica intima and tunica media

Is the internal elastic lamina distinct in elastic arteries?

No, it blends with multiple elastic laminae

What supplies blood to the wall of large elastic arteries?

Vasa vasorum

Which tunica contains vasa vasorum?

Tunica adventitia (and outer media in large vessels)

How does elastic artery lumen appear histologically?

Large and round

What stain best highlights elastic fibers in elastic arteries?

Elastic stains (e.g., Verhoeff–Van Gieson)

What is the key histological difference between elastic and muscular arteries?

Elastic arteries have many elastic laminae; muscular arteries have prominent smooth muscle

Which artery type is specialized for distribution of blood to organs?

Muscular (distributing) artery

What is the most prominent layer in muscular arteries?

Tunica media composed mainly of smooth muscle

How many elastic laminae are present in muscular arteries?

One internal elastic lamina (± external elastic lamina)

How does the internal elastic lamina appear in muscular arteries?

Thick, wavy, and prominent

Is the external elastic lamina present in muscular arteries?

May be present but less prominent

What is the major cell type in the tunica media of muscular arteries?

Smooth muscle cells

How does muscular artery media stain compared to elastic artery media?

More eosinophilic due to smooth muscle dominance

How does muscular artery lumen compare to elastic artery lumen?

Smaller and more circular

What is the main function of muscular arteries?

Regulation of blood distribution via vasoconstriction and vasodilation

Which vessel regulates peripheral resistance most strongly?

Arterioles

How many layers of smooth muscle are present in arterioles?

1–3 layers

What defines an arteriole histologically?

Small lumen with 1–3 concentric smooth muscle layers

Is an internal elastic lamina present in arterioles?

Usually absent or very thin

What is the functional role of arterioles?

Control blood flow into capillary beds

What structure regulates flow from arteriole to capillary?

Precapillary sphincter

Which vessel has the smallest diameter in the arterial system?

Arteriole

What fibers surround arterioles externally?

Reticular fibers

What is the diameter range of capillaries?

Approximately 7–9 micrometers

What cells form the wall of capillaries?

Endothelial cells only

Do capillaries have tunica media or adventitia?

No

What is the function of capillaries?

Exchange of gases, nutrients, and waste

What is the most common type of capillary?

Continuous capillary

Where are continuous capillaries found?

Muscle, skin, lung, CNS

What junctions are present between endothelial cells in continuous capillaries?

Tight, adherens, and gap junctions

What is transcytosis in capillaries?

Vesicular transport across endothelial cells

Which capillary type has fenestrae (pores)?

Fenestrated capillary

Where are fenestrated capillaries found?

Gut, kidney, endocrine glands

What is the function of fenestrated capillaries?

Rapid exchange of fluids and small molecules

Which capillary type has discontinuous basal lamina?

Sinusoidal capillary

Where are sinusoidal capillaries found?

Liver, spleen, bone marrow

What can pass through sinusoidal capillaries?

Large proteins and cells

Which capillary has the largest lumen?

Sinusoid

What supportive cell surrounds capillaries and venules?

Pericyte

What is the function of pericytes?

Contractile support and regulation of capillary blood flow

Which vessel collects blood from capillaries?

Venule

Which venule type is involved in inflammation?

Post-capillary venule

Why are post-capillary venules important in inflammation?

Site of leukocyte extravasation

How does venule wall structure compare to arteriole?

Thinner wall with fewer smooth muscle cells

Which vessel has less organized smooth muscle: arteriole or venule?

Venule

What is the defining feature of veins histologically?

Thin wall and thick adventitia

Which tunica is thickest in veins?

Tunica adventitia

How does vein media compare to artery media?

Thin and weak

Why do veins have valves?

Prevent backflow of blood

Which veins commonly have valves?

Medium and large veins of limbs

How does vein lumen appear compared to artery?

Large, irregular, and often collapsed

Is an internal elastic lamina present in veins?

Absent

Which vessel carries blood toward the heart?

Vein

What is the main structural component of vein adventitia?

Dense irregular connective tissue

How do smooth muscle cells appear in veins?

Widely spaced and poorly organized

What is a major histological difference between artery and vein walls?

Arteries have thick media; veins have thick adventitia

Which vessel is most prone to varicosities?

Veins

What disease involves lipid deposition in arterial walls?

Atherosclerosis

Which disease is associated with venous valves?

Deep venous thrombosis

What are lymphatics specialized for?

Return of interstitial fluid to circulation

How do lymphatics differ from veins histologically?

Very thin walls and no red blood cells in lumen

Which endothelial enzyme converts angiotensin I to angiotensin II?

Angiotensin-converting enzyme (ACE)

Where is ACE activity highest?

Lung endothelium

What endothelial product inhibits platelet aggregation?

Prostacyclin

What endothelial relaxing factor causes vasodilation?

Nitric oxide

What endothelial contracting factor causes vasoconstriction?

Endothelin-1

Which endothelial protein is involved in coagulation?

Von Willebrand factor

Which endothelial molecules mediate leukocyte adhesion?

Selectins