Anatomy Histology of the Circulatory System Blood Vessels

Anatomy (Histology) of the Circulatory System

Blood Vessels • 1. Histology • a. Terms: • (1) lumen – cavity • (2) tunica intima – simple squamous epithelium • (3) tunica media – elastic connective tissue and smooth muscle • (4) tunica externa (adventitia) – fibrous connective tissue

• (5) vasa vasorum – vessel of a vessel •

artery

b. Types of blood vessels • (1) Elastic Arteries • (a) contain much elastic connective tissue in walls • (b) act to smooth-out blood flow • (c) act to divert blood flow from inactive tissues to active tissues

Tunic means cloth or layers

• (2) Muscular Arteries • (a) contain much smooth muscle in walls • (b) innervated by autonomic motorneurons

• We have 60, 000 miles of blood vessels and we only have 5 -6 liters of blood

Muscular Artery

Microscopic Structure of Blood Vessels

• a. vein • b. large artery – elastic artery • c. arteriole (small artery) – contain more smooth muscles

Vein

Large Artery (Elastic Artery)

• (3) Capillary Bed – anastomose or interconnections of capillaries • (a) there about 60, 000 miles of capillaries in the body • (b) nutrients diffuse out of capillaries, while tissue waste products diffuse into capillaries • (c) metarteriole (capillary bed by-pass) – (thoroughfare channel) • (d) precapillary sphincters – muscular valves that regulate blood flow

• Vasoconstriction – when arteries constrict • Venoconstriction – when veins constrict

• (4) Venules – small veins

Capillary Bed picture

Venule Picture

Cross section of an artery and vein

Cross section of blood vessels

• • • (5) Veins (a) thinner-walled than arteries (b) no elastic connective tissue in walls - visceral smooth muscle (c) innervated by autonomic motorneurons (d) possess semi-lunar valves to prevent the back-flow of blood

Semi-lunar valves

• (6) venous sinuses – very thin wall; no tunica media • (a) veins with no elastic connective tissue or smooth muscle • (b) examples: cranial venous sinuses • coronary sinus • hepatic sinuses

Cranial venous sinuses

2. Pathologies & Disorders of Blood Vessels • a. Arteriosclerosis • b. Atherosclerosis • (1) plaque formation • (2) results in • (a) coronary artery disease (CAD) • (b) hypertension (increased BP)