General Histology Lecture 15: Circulatory System 1 PDF

General Histology Lecture 15 Circulatory System 1 Ahmed Abdul-Aziz Muhammad. PhD Cardiovascular System Lecture Outline Introduction Blood vessels Basic structure Types of blood vessels Heart Gross structure Three layers of the heart Em...

General Histology Lecture 15 Circulatory System 1 Ahmed Abdul-Aziz Muhammad. PhD Cardiovascular System Lecture Outline Introduction Blood vessels Basic structure Types of blood vessels Heart Gross structure Three layers of the heart Embryological development of the heart Function of the Cardiovascular System The main job of the Cardiovascular system is to transport (and exchange) nutrients, oxygen, body fluids, waste material, heat, and blood cells around the body. Components of the Cardiovascular System The cardiovascular system is basically a closed system of plumbing: blood circulates through pipes (blood vessels) and is propelled by an in-line pump (the heart). Blood flows through the system from: heart  elastic artery  muscular artery  arteriole  capillaries  venules  vein  heart Vessels of the Cardiovascular System  The Three Layers (Tunics) of Blood Vessels Artery Vein Intima Endothelium Subendothelium Media Externa Vasa vasorum  Capillaries Smallest diameter of all blood vessels (7-9 μm). Allow exchange of metabolites and waste between blood and surrounding tissue. Composed of a single layer of endothelial cells resting on a basal lamina. Three types: Continuous capillaries (least permeable) Fenestrated capillaries Sinusoidal capillaries (most permeable)  Continuous (Tight) Capillaries Intact endothelium and basement membrane. May contain tiny pinocytotic vesicles that transport certain substances across the endothelium. Least permeable of all three capillary types. Found in muscle, connective tissue, glands and nerve tissue. Continuous Capillary  Fenestrated Capillaries Endothelial cells are perforated with small fenestrations (holes). Basement membrane is intact. Permeability somewhere between that of continuous and sinusoidal capillaries. Found in places where substances need to move quickly between tissues and blood (e.g. kidney, intestine, and endocrine organs). Fenestrated Capillary Sinusoidal Capillaries (Sinusoids) Endothelial cells have big fenestrations and gaps (clefts) between cells. Basal lamina is discontinuous. Most permeable of all three capillary types. Located in liver, bone marrow, and spleen. Sinusoid  Venules and Arterioles Relatively thin wall and big Relatively thick wall and lumen. small lumen. Media has just a few Media has 1-3 layers of smooth muscle cells here smooth muscle cells. and there. Arterioles and venules  Arteries Muscular arteries Elastic arteries Thick media composed of Thick media composed of smooth muscle cells. sheets of elastic fibers Prominent internal and interspersed with layers of external elastic lamina. smooth muscle cells. “Named” arteries (e.g. Vasa vasorum in the externa. femoral artery) are usually The aorta and its large muscular arteries. branches are elastic arteries. Small muscular artery Elastic artery  Veins Medium-sized vein Large vein Thin intima, may have valves. Thin intima, may have valves. Thin media composed of a few Thin media, like medium-sized elastic fibers and smooth veins. muscle cells. Relatively thick externa Relatively thick externa composed of longitudinal composed of longitudinal collagen fibers, elastic fibers, collagen and elastic fibers. and smooth muscle cells. Also has Vasa vasorum. “Named” veins (e.g., portal vein) are usually large veins.