Arteries

Elastic Arteries | Conducting

1. Tunica Intima

Endothelial layer | contains Weibel-Palade bodies

Subendothelial Connective Tissue | narrow

Internal Elastic Lamina | thin/incomplete

2. Tunica Media

Layers of elastic fibres | 40-70

Layers of Circular Smooth Muscle Cells | longer than normal

External Lamina | thin

Vasa Vasorum | may be present

 3. Tunica Adventitia

Loose Connective Tissue | thin

Fibroblasts, type I collagen, and elastic fibres

Vasa Vasorum, nervi vasorum, lymphatic vessels

Muscular Arteries | Distributing

1. Tunica Intima

Endothelial layer

Subendothelial Connective Tissue | thinner than elastic arteries

Internal Elastic Lamina | distinct, may be bifid

2. Tunica Media

Layers of Elastic Fibres | 4 (small arteries) – 40 (larger arteries)

Layers of circular smooth muscle cells, elastic fibres, and type III collagen

External Lamina | present

Vasa Vasorum | may be present

3. Tunica Adventitia

Fibroblasts, type I collagen, and elastic fibres

Vasa vasorum, nervi vasorum

Artery & Vein

Blood Vessels, Trachea & Esophagus

Arterioles

1. Tunica Intima

Endothelial Layer | thin

Subendothelial Connective Tissue | type III collagen and elastic fibres

Internal Elastic Lamina | thin and fenestrated (larger arterioles), absent (small arterioles)

2. Tunica Media

Layers of Elastic Fibres | 1 (small arterioles) – 3 (larger arterioles)

Layers of circular smooth muscle cells, elastic fibres, and type III collagen

External Lamina | absent

3. Tunica Adventitia

Fibroblastic Connective Tissue | few fibroblasts

Veins

Large Veins

Lumen

Usually collapsed due to thin walls and less elastic fibres in comparison to arteries

1. Tunica Intima

Endothelial Layer

Subendothelial Connective Tissue | thick, contains reticular fibres, elastic fibres, and fibroblasts

Internal Elastic Lamina | present

2. Tunica Media

Usually absent

3. Tunica Adventitia

Loose Connective Tissue | Type I collagen, and elastic fibres

Muscle Layer | longitudinal smooth muscle cells (inferior vena cava), cardiac muscle (pulmonary veins and Vena Cava)

Vasa Vasorum

Medium Veins

1. Tunica Intima

Endothelial Layer

Subendothelial Connective Tissue | contains reticular fibres, elastic fibres, and fibroblasts

Internal Elastic Lamina | absent

2. Tunica Media

Muscle Layer | smooth muscle cells interwoven with collagen and fibroblasts

 3. Tunica Adventitia

Muscle Layer | longitudinal collagen and elastic fibres, with few smooth muscle cells

Venules & Small Veins  

1. Tunica Intima

Endothelial Layer | thin

Subendothelial Connective Tissue | reticular fibres and pericytes

Capillaries

Epithelium | single layer of endothelial cells surrounded by pericytes