Page 423 - Atlas of Histology with Functional Correlations

Found in the thicker walls of large arteries and veins that do not allow

diffusion from lumina
Small adjacent arterial blood vessels supply tunica media and tunica
adventitia
More extensive in the walls of veins than arteries because of poor oxygen
content of veins

TYPES OF CAPILLARIES

Average diameter is about the size of a RBC (about 8 μm)
Consist of thin endothelium, basal lamina, and pericytes
Continuous capillaries are most common; endothelium forms solid lining
Continuous capillaries found in most organs

Fenestrated capillaries contain pores or fenestrations in endothelium
Fenestrated capillaries found in endocrine glands, small intestine, and kidney
glomeruli
Sinusoidal capillaries exhibit wide diameters with wide gaps between

endothelial cells
Basement membrane incomplete or absent in sinusoidal capillaries
Sinusoidal capillaries found in the liver, spleen, and bone marrow

LYMPHATIC VASCULAR SYSTEM

Associated with the circulatory system and drains extracellular fluid lymph

from tissues
Lymphatic capillaries start as blind dilations and form the lymph drainage
system
Lymph eventually returned to the circulatory system after filtering lymph in

lymph nodes
Vessels are very thin and show greater permeability than capillaries
Lymph vessels contain valves, and lymph movement is slow
Lymph movement is assisted by muscular contractions, arterial pulsations,

and intrinsic muscular contraction in vessel walls
Lymph flows through lymph nodes and is exposed to macrophages
Lymph contains lymphocytes, fatty acids, and immunoglobulins (antibodies)
Integral component of immune system of the body

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