Circulatory System

Cardiovascular System

It pumps and directs blood cells and substances carried in blood to all tissues of the body.

Cardiovascular System

It includes both the blood and lymphatic vascular systems.

Heart

It propels blood through the system.

Arteries

These are a series of vessels efferent from the heart that become smaller as they branch into the various organs and carry blood to the tissues.

Capillaries

These are the smallest vessels that are the sites of oxygen, carbon dioxide, nutrient and waste product exchange between blood and tissues.

Microvasculature

A complex network of thin, anastomosing tubules.

Veins

These result from the convergence of venules into a system of larger channels which continue enlarging as they approach the heart, toward which continue enlarging as they approach the heart, toward which they carry the blood to be pumped again.

Systemic Circulation

The process in where the blood brings nutrients and removes waste in tissues throughout the body.

Pulmonary Circulation

The process where is blood is oxygenated in the lungs.

Lymphatic Capillaries

These are thin-walled, closed-ended tubules carrying lymph which merge to form vessels of steadily increasing size.

Endothelium

The internal surface of all components of the blood and lymphatic systems that is lined by a simple squamous epithelium.

Ventricles

These propel blood to the pulmonary and systemic circulations, respectively.

Atria

These receive blood from the body and the pulmonary veins, respectively.

Endocardium

This consists of the lining endothelium.

Myocardium

This consists mainly of typical contractile cardiac muscle fibers arranged spirally around each heart chamber.

Epicardium

This is a simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves.

Cardiac Skeleton

This separates the musculature of the atria from that of the ventricles.

Cardiac Skeleton

This forms part of the interventricular and interatrial septa.

Impulse Conducting System

This is specialized to generate and conduct waves of depolarization which stimulate rhythmic contractions in adjacent myocardial fibers.

Impulse Conducting System

This is made up of both the subendocardial layer and the adjacent myocardium or the modified cardiac muscle cells.

Sinoatrial Node

It is located in the right atrial wall near the superior vena cava. This is a region of less well-stained cardia muscle cells with smaller size, fewer myofibrils, and fewer typical intercalated discs than the neighboring contractile fibers.

Atrioventricular Node

This where the atrioventricular bundle (bundle of His) emerges.

Atrioventricular Node

It is located at the floor of the the right atrium near the AV valve that stimulate depolarization myocytes there.

Purkinje Fibers

These bundles subdivide further into a subendocardial and conducting network of cardiac muscle fibers that is found at the apex of the heart.

Endothelium

This is a specialized epithelium that acts as a semipermeable barrier between two major internal compartments: the blood and the interstitial tissue fluid.

Smooth Muscle

These occurs in the walls of all vessels larger than capillaries and are arranged helically in layers.

Smooth Muscle

In arterioles and small arteries, these muscle cells are connected by many more gap junctions and permit vasoconstriction and vasodilation that are of key importance in regulating the overall blood pressure.

Connective Tissue

Its components are present in vascular walls in variable amounts and proportions based on local functional requirements.

Collagen Fibers

These are found in the subendothelial layer, between the smooth muscle layers, and in the outer covering.

Elastic Fibers

They provide the resiliency required for the vascular wall to expand under pressure.

Elastin

The major component in large arteries where it forms parallel lamellae, regularly distributed between the muscle layers.

Tunica Intima

The innermost layer that consists of the endothelium and a thin subendothelial layer of loose connective tissue sometimes containing smooth muscle fibers.

Tunica Media

The middle layer that consists chiefly of concentric layers of helically arranged smooth muscle cells.

Tunica Externa / Adventitia

This is a connective tissue consisting principally of type I collagen and elastic fibers.

Tunica Externa / Adventitia

This is continuous with and bound to the stroma of the organ through which the blood vessel runs.

Internal Elastic Lamina

This is a thin layer found in the intima of arteries that is composed of of elastin, with holes allowing better diffusion of substances from blood deeper into the wall.

External Elastic Lamina

The layer found in the media that separates the arteries from the outermost tunic.

Vasa Vasorum

This is required to provide metabolites to cells in those tunics in larger vessels because the wall is too thick to be nourished solely by diffusion from the blood in the lumen.

Vasa Vasorum

This is referred to as “vessels of the vessel.”

Elastic Arteries

It is composed of the aorta, the pulmonary artery, and their largest branches.

Elastic Arteries

These large vessels are also called conducting arteries because their major role is to carry blood to smaller arteries.

Ventricular Contraction / Systole

During this process the blood is moved through the arteries forcefully and the elastin is stretched, distending the wall within the limit set by the wall’s collagen.

Ventricular Relaxation / Diastole

During this process the ventricular pressure drops to a low level, but the elastin rebounds passively, helping to maintain arterial pressure.

Aortic and Pulmonary Valves

These prevent backflow of blood into the heart, so the rebound continues the blood flow away from the heart.

Carotid Sinuses

These are slight dilations of the bilateral internal carotid arteries where they branch from the (elastic) common carotid arteries.

Carotid Sinuses

They act as important baroreceptors monitoring arterial blood pressure.

Muscular Arteries

These are also called distributing arteries because they distribute blood to the organs and help regulate blood pressure by contracting or relaxing the smooth muscle in the media.

Arterioles

These are known as the smallest arteries which have only one or two smooth muscle layers.

Microvasculature

This is where exchanges between blood and tissue fluid occur.

Capillaries

These permit and regulate metabolic exchange between blood and surrounding tissues.

Capillary Beds

This is referred to as “networks” of the smallest blood vessels.

Continuous Capillaries

These have many tight, well-developed occluding junctions between slightly overlapping endothelial cells, which provide for continuity along the endothelium and well-regulated metabolic exchange across the cells.

Continuous Capillaries

This is the most common type of capillary and is found in muscle, connective tissue, lungs, exocrine glands, and nervous tissue.

Fenestrated Capillaries

These have a sieve-like structure that allows more extensive molecular exchange across the endothelium.

Fenestrated Capillaries

The endothelial cells are penetrated by numerous small circular openings or fenestrations (L. fenestra, perforation), approximately 80 nm in diameter.

Fenestrated Capillaries

These are found in organs with rapid interchange of substances between tissues and the blood, such as the kidneys, intestine, choroid plexus, and endocrine glands.

Discontinuous Capillaries

These are also commonly called sinusoids, permit maximal exchange of macromolecules as well as allow easier movement of cells between tissues and blood.

Postcapillary Venules

These are similar to capillaries with pericytes but larger, ranging in diameter from 15 to 20 μm.

Postcapillary Venules

These are the primary site at which white blood cells adhere to endothelium and leave the circulation at sites of infection or tissue damage.

Collecting Venules

These are the convergence of postcapillary venules that have more distinct contractile cells.

Muscular Venules

This is referred to venules which have increased in size and become surrounded by a recognizable tunica media with two or three smooth muscle layers.

Veins

These carry blood back to the heart from microvasculature all over the body.

Large Veins

These are referred to as the big venous trunks, paired with elastic arteries close to the heart.

Valves

These are an important feature of large and medium veins which consist of thin, paired folds of the tunica intima projecting across the lumen, rich in elastic fibers and covered on both sides by endothelium.

Valves

These are especially numerous in veins of the legs, help keep the flow of venous blood directed toward the heart.

Thoracic Duct and Right Lymphatic Duct

These are the largest lymphatic vessels that both has walls having tunics like those of veins, return lymph to the circulatory system by joining veins near the heart.

Lymphatic Capillaries

This is a system of very thin-walled channels.

Lymph

It is referred to as the tissue spaces which collect excess interstitial fluid and return it to the blood.