Cardiovascular system - Blood Vessels Anatomy

Basic Anatomy of Circulatory routes Arteries Arterioles Capillaries Venules Veins Carry blood towards the heart Carry blood away from the heart Connect capillaries to veins Control blood flow into capillaries & help regulate BP Allow for “exchange” (filtration/reabsorption) of O2/CO2, nutrients/wastes

Structure of Blood Vessels

Arteries & Veins Both are comprised of 3 layers of tissue surrounding “lumen” through which blood will flow: tunica interna, tunica media & tunica externa Structural difference between arteries & veins primarily due to differences in pressure of blood flowing within

Arteries & Veins Tunica Interna – innermost endothelium of simple squamous epithelium + basement membrane Arteries – have an “internal elastic lamina” of elastic CT to allow for expansion under pressure Veins – may have “valves” (folds of endothelium + CT) to prevent backflow of blood due to low pressure

Arteries & Veins Tunica Media – middle layer containing smooth muscle (for contractility/vasoconstriction) & elastic CT (for elasticity) Arteries – have relatively thick tunica media allowing for significant vasoconstriction & elasticity Elastic/conducting arteries – relatively more elastic tissue than smooth muscle; ie. aorta, pulmonary trunk, etc. Muscular/distributing arteries - relatively more muscle tissue than elastic tissue; ie. brachial, femoral, etc. Veins – relatively thin tunica media therefore no significant constriction/elasticity

Arteries & Veins Tunica Externa (a.k.a. adventitia) – made of collagenous CT Arteries – thin layer Veins – thickest layer of vein, trying to support against gravity & low pressure

Arteries & Veins

Arterioles & Venules Very small, almost microscopic vessels with only 2 layers of tissue surrounding lumen Arterioles – endothelium (tunica interna) + very thin layer of smooth muscle cells (tunica media); regulate blood flow to tissues & affect arterial blood pressure Venules – endothelium (tunica interna) + thin layer of CT (tunica externa)

Capillaries Microscopic, very thin-walled vessels comprised of endothelium with basement membrane; allows for filtration and reabsorption Found in all tissues of the body except for those that are “avascular” Usually form branching networks (“capillary beds”) within tissues for increased surface area blood flow into capillaries may be regulated by “pre- capillary sphincters” may have a central or “thoroughfare” channel that provides direct connection between “metarteriole” (terminal end of arteriole) & venule Capillaries can be classified as continuous, fenestrated, or sinusoids

Circulatory Routes - overview

Circulatory Routes – Pulmonary Circuit

Circulatory Routes – Systemic circuit Ascending aorta (gives off coronary arteries) Aortic arch Brachiocephalic trunk Left common carotid artery Left subclavian artery Thoracic (descending) aorta Abdominal aorta Common iliac arteries Arterial blood from left ventricle into ascending aorta Venous return to right atrium through SVC, IVC & coronary sinus

Systemic circuit - Arteries

Systemic circuit - Veins

Cerebral circulation Cerebral arterial circle (“circle of Willis): Basilar artery (from union of vertebral arteries) + Internal carotid arteries

Hepatic portal circulation Venous blood flow from GIT & spleen to liver – ensures delivery of nutrients to liver first AORTA Hepatic artery Cystic vein Lt. gastric vein Splenic vein IVC LIVER Hepatic Veins (blood mixes in sinusioids) Hepatic Portal Vein Superior mesenteric vein Inferior mesenteric vein

Hepatic portal circulation Cystic vein, left gastric vein, splenic vein, inferior & superior mesenteric veins Hepatic portal vein Hepatic portal vein (deoxygenated/nutrient rich blood) + Hepatic artery (oxygenated blood) sinusoids of liver Sinusoids of liver  Hepatic veins  IVC

Fetal Circulation Placenta – O2/CO2 & nutrient/waste between mom & baby Umbilical cord – (2) umbilical arteries (baby  mom) & (1) umbilical vein (mom  baby) Umbilical vein (O2/nutrient rich blood)  hepatic portal vein & ductus venosus  IVC  Rt. atrium Rt. Atrium  some blood to rt. Ventricle, most shunts across foramen ovale in interatrial septum  lt. atrium  lt. ventricle

Fetal Circulation Blood from Rt. Ventricle  pulmonary trunk  across ductus arteriosus to aorta Aorta  systemic arteries internal iliac arteries  umbilical arteries  placenta

Fetal Circulation- Changes at Birth Umbilical vein  ligamentum teres (round ligament) Umbilical arteries  lateral umbilical ligaments Ductus venosus  ligamentum venosum Foramen ovale  fossa ovalis Ductus arteriosus  ligamentum arteriosum Placenta delivered (“afterbirth”)

Upper extremity arteries & veins

Coronary circulation