Histology for PathologyCirculatory System

Theresa Kristopaitis, MDAssociate Professor

Director of Mechanisms of Human Disease

Kelli A. Hutchens, MD, FCAPAssistant Professor

Assistant Director of Mechanisms of Human Disease

Loyola Stritch School of Medicine

OBJECTIVES1. Given a histologic section of a large or medium sized artery, identify the

a) tunica intimab) tunica mediac) tunica adventitia

2. Identify the following structures in a histologic section of an arterya) Endotheliumb) Internal elastic laminac) External elastic laminad) Vasovasorum

3. Distinguish the characteristics which separate large, medium and small arteries and arterioles.4. In a tissue section, distinguish a medium sized artery from a medium sized vein5. In a tissue section identify capillaries, describe their structure and function6. Compare and contrast general structural features of the arterial vs venous system7. Describe the structure and function of a lymphatic vessel

Vessel Types• Arteries

– Large artery– Medium artery – Small artery– Arteriole

• Veins– Large Vein– Medium Vein– Small Vein– Venule

• Capillaries– Continuous– Fenestrated– Discontinuous

• Three layers (tunica)– Tunica intima(inner most layer)

• Endothelium• Subendothelium• Internal elastic lamina (IEL) in arteries

– Tunica media • Smooth muscle layer• External elastic lamina (EEL) in arteries

– Tunica adventitia (outer most layer)• Connective tissue and fibroblasts• Longitudinal smooth muscle in veins • Vasovasorum in large vessels

Overall Structure of Vessels

Structure of Vessels

a = tunica intima - endothelial lining plus thin layer of underlying connective tissue called the subendothelium. b = tunica media - alternating layers of elastic membranes (elastic lamina) and smooth muscle. c = tunica adventitia - fairly dense connective tissue carrying small blood vessels, the vasa vasorum

Large Artery

a

b

c

Endothelium

Subendothelium

Elastic fibers

Vasa vasorum

High Power of AortaTunica Media

Endothelium

Endothelium: Composed of single layer of squamous cells, provides a permeable barrier, angiogenesis, release of single molecules.

Medium Artery

Also called muscular artery because the wall is dominated by smooth muscle.Similar to large artery but internal and external elastic lamina are well defined and lack prominent vasovasorum.

Small Artery & Arterioles

Small Arteries: Generally have same structure as medium artery but have a smaller diameter and no external elastic lamina. The tunica media also has fewer layers of smooth muscle cells.

Arterioles: The smallest arteries, lead blood flow into capillary beds. Only two layers of smooth muscle cells. Internal elastic lamina, external elastic lamina, and subendothelial layers usually absent.

Arteriole

Large Arteries Medium Arteries

Small arteries Arterioles

Tunica Media Smooth muscle cells + Large quantity of elastic fibers

Dominated by multiple layers of smooth muscle cells(6-40)

2-6 layers of smooth muscle

1-2 layers of smooth muscle cells

Function Conduct blood from heart.Walls recoil.Accommodate pressure changes.Maintain continuous blood flow during diastole.

Distributing arteries

Help control and modulate blood pressure

Control blood flow to capillaries.Important role in regulating blood pressure.

Examples Aorta and its large branches – subclavian, carotid, iliac

Coronary, Renal Within substance of tissues and organs

Within substance of tissues and organs

Capillary

• Smallest vessels• Connect arterioles and

venules• One layer of endothelial

cells with a basal laminaA capillary lying in the endomysium between skeletal muscle fibers. This one shows very dark endothelial nuclei and has 3 pink red blood cells* lined up in a row inside

*

Venules and Small VeinsSimilar except

• Small veins may have slightly larger lumen and more visible smooth muscle layer

• Venules have small lumens, thin walls, and only single layer of endothelum. Have surrounding connective tissue

Vein

Medium-sized vein with a much less compact muscle layer than in arteries. a - tunica media b – tunica adventitia, which is at least as wide as the media, and often even wider.

LUMEN(filled withRBCs)

Medium VeinTunica intima

Smooth muscle bundles

Quite similar to a large vein but smaller lumen, tunica adventitia contains fewer bundles of longitudinal smooth muscle and vasa vasorum is not prominent.

Tunica media

Tunica adventitia

Valves

• Folds in the intima seen in medium and larger veins

• Number of valves increase with size of vessel

• Prevent backflow of blood

• Also present in the lymphatic vessels

Large VeinsVasa vasorum

Smooth muscle bundles

ca

b

a. Tunica intimab. Tunica media with a circular smooth muscle

layerc. Tunica adventitia: thickest layer with many

longitudinal smooth muscle bundles and vasa vasorum.

Artery vs Vein

Arterial system Venous system

Lumen Smaller, rounder.Prominent internal elastic lamina

Larger, flatter

Tunica media Thicker than tunica adventitia

Tunica adventitia Thicker than tunica mediaLongitudinal smooth muscle bundles present

Valves No Yes

ArteryVein

Lymphatic system

• Composed of lymphatic capillaries, vessels, and ducts

• Collect and drain interstitial fluid from tissue in the large veins

• Have large lumens and relatively thin walls• Single layer of endothelium • Connective tissue outer layer with few smooth

muscle cells• Also have valves

Lymphatics

Thinned walled vessels with large lumens and valves. There are some fat cells and lymphocytes in the surrounding connective tissue.

Valve