Histology TA Review Circulatory

Tunics of Vessels - Generically Speaking: 1.Tunica Intima - Innermost Endothelium, Internal Elastic Membrane, subendothelial connective tissue 2.Tunica Media - Middle Smooth muscle and elastic lamellae/fibers 3.Tunica Adventitia - Outermost CT, principally collagen, may contain neural networks, capillaries.

Endothelium: Cellular layer of Tunica Intima Influences blood flow, regulates diffusion through wall Secretes: Factor VIII ( coagulation factor) Plasminogen activator (clot dissolving) Nitric Oxide (NO) (a vasodilator) Endothelin (a vasoconstrictor) Angiotensin Converting Enzyme (vasoconstriction) Capable of proliferation in Angiogenesis

Vascular Smooth Muscle Only cell type found in tunica media Circular arrangement Sympathetic innervation Target tissue of Angiotensin II Regulates diameter and tone (vasodilation vs. vasoconstriction) Varicosities release neurotransmitters of ANS nerve endings

Classification of Vessels: 1.Conducting Or Elastic Aa. Aorta and Major Branches 2.Distributing or muscular aa Most named arteries 3.Resistance vessels or arterioles Smallest High Pressure Vessel 4.Exchange or capillary vessels Smallest vessel in body 5.Capacitance vessels or veins Return blood to heart

Muscular Arteries Tunica Media is primarily smooth muscle Thickest tunic is Tunica Media Generally have a very round appearance. Prominent internal elastic membrane Thickness of media, luminal diameter are similar

Arterioles: 1-3 layers of Smooth Muscle Greatest effect on blood pressure Endo Cells have Weibel-Palade bodies Nuclei bulge into lumen Round appearance of vessel No internal elastic membrane Metarteriole is terminal vessel, has precapillary sphincter. Can regulate flow to capillary bed

Capillary Types: 1.Continuous - common, no openings in vessel wall. Brain, muscle, CT, nn, ex glands 2.Fenestrated - Fenestrae (openings) in cells. Membranous diaphragm found in the fenestrae. Endocrine organs, intestine. 3.Fenestrated without diaphragm – kidney 4.Sinusoidal – a.k.a discontinuous, found in association with filtration processes of spleen, liver, and in bone marrow.

Pericytes: Found near capillary and venule endothelial cells. Have own basal lamina. Contain actin,myosin, tropomyosin. Proliferate after injury. May be replacement stem cell source.

Venules: Called ‘postcapillary venules’ Very ‘leaky’ vessels No smooth muscle Leukocyte diapedesis possible here 5mmHG pressure in vessel.

Veins: Large, wide lumen, thin walls Valves present Thin tunica media Tunica adventitia usually thickest tunic Lg veins may have vasa vasorum May be collapsed in histo sections

ID the vessels

Slide x ? ? ? ?

1000x Demo Slide ?

100x ?

Demo 1000x ? ?

? ? ? ?

100x Demo Slide ? ?