- tunica intima

- tunica media

- tunica adventitia

endothelial cells

basement membrane

thin layer of CT under it

internal elastic lamina - separates intima from media

stains with silver stain - black squiggle

Mostly smooth muscle

            Thickness varies with type of vessel

            Some collagen +/- elastic fibers (elastin)

            +/- external elastic lamina

Connective tissue (collagen)

§  Collagen is blue on trichrome stain

            Blends with and anchors to surrounding tissue

            +/- Vasa vasorum = small vessels that supply large vessels

            +/- Nervi vasorum = nerve supply to blood vessels    

elastic arteries

muscular arteries

arterioles

Aorta and largest branches

            Tunic media contains elastic fibers (elastin) in addition to collagen and smooth muscle

Medium-sized arteries/Distributing arteries

            Tunica media is muscular

            Very common type of artery

<5 layers of smooth muscle cells

            Innervated by sympathetic nervous system

            Regulate blood flow into capillaries

§  via pre-capillary sphincter

Where oxygen, nutrients, and carbon dioxide diffuse

            Almost every cell in the body has a capillary nearby

            Erythrocytes often single file in lumen

            Most numerous type of vessel

3 types: continuous, fenestrated, discontinuous

Complete basement membrane (BM)

            Complete endothelial cells (EC) joined by tight junctions

            Thin endothelial cells allow gas transport                

            Other substances transported by transcytosis

            Muscle, brain, lung (most tissues)

Complete basement membrane

            Holes in endothelial cells (pores, fenestrae)

§  not visible by light microscopy

            Substantial transport of fluid, ions, hormones, and nutrients

            Intestine, glomeruli, endocrine glands

 (sinuses and sinusoids)

            Incomplete basement membrane and endothelial cells

            Large molecules and cells can pass through gaps

            Liver, spleen, lymph nodes, bone marrow, placenta

Venules

Medium-sized veins

Large veins

Thin muscular tunica media

            Valves for one-way flow

Thin muscular tunica media with collagen and elastin

            Tunica adventitia may contain smooth muscle

            Valves (exceptions...)

Simple squamous

            Same as endothelium

            Subendocardial collagen

§  increases with animal size

Thin connective tissue core

§  may contain collagen, elastin, muscle

            Covered with endothelial/endocardial cells

Modified cardiac muscle fibers

                        Conduct impulses from pacemaker to myocardium

                        Larger diameter than cardiomyocytes

                        Pale eosinophilic cytoplasm (contains glycogen)

                        Prominence/visibility varies with species

Four fibrous rings (one for each valve)

Fibrous triangle (trigona fibrosa) and septum (all continuous)

            May be cartilaginous (esp. cats) or osseous (esp. cattle = os cordis)

(visceral pericardium)

Adipose tissue

            Coronary arteries

            Mesothelium

(parietal pericardium)

Thin collagen layer with mesothelium

can contain adipose tissue