Cardiovascular system (Blood vessels) Flashcards
(28 cards)
Types of blood vessels
3 major groups;
-Arteries
-Veins
-Capillaries
The blood vessels transport blood throughout the body as a result of being pumped out by the heart
Walls of the blood vessels
Have 3 layers called tunics;
-Tunica intima; the inner layer consisting of a simple squamous endothelium, endothelium overlying a basement membrane and a sparse layer of fibrous tissue
-Tunica media; the middle layer (usually the thickest. Consists of smooth muscle cells, collagen and elastic fibres
-Tunica externa; the outermost layer. Consists of loose connective tissue with vasa vasorum and nervi vasorum.
Arteries
-Strong, elastic vessels adapted for carrying blood away from the heart at relatively high pumping pressure
-Divide into progressively thinner tubes and eventually become arterioles
-Arteries have to be flexible, they pulsate with the spurts of blood flow
Conducting arteries (elastic type)
-Includes the largest arteries like the aorta and carotids
-Their recoil helps to move blood forward towards tissues
-Arising directly from the heart and their main branches, whose walls have a high degree of elasticity
Distributing arteries (muscular type)
-Control the blood flow by vasoconstriction and vasodilation
-Transport blood to specific organ systems, with a high muscular component in their walls
-Contain a large proportion of smooth muscle in their tunica media
Large elastic arteries
-They are the conducting arteries and include the aorta and its main branches; the brachiocephalic trunk, the left common carotid artery, the left subclavian artery and the terminal common iliac arteries
-These carry blood from the heart to the smaller conducting arteries
-Pressure in these arteries is at the highest level of the entire circulatory system
Arterioles
-The smallest division of the arteries
Histological layers;
-Tunica intima
-Tunica media (with 2-3 muscle layers)
-Tunica adventitia
Capillaries
-Have a diameter of about 10um
-Built up of a single layer of endothelium allowing the exchange of substances and gases across their walls between the blood and tissue fluid
-After blood delivers oxygen to the tissues and picks up CO2, it returns to the heart through a system of veins
Features of capillaries
-1-3 endothelial cells
-Basement membrane
-Pericyte
Transport of substances;
-Transmembrane; active and passive
-Vesicular; pinocytosis
-Receptor-mediated endocytosis
-Intracellular; by zonula occludentes
Classification of capillaries
Can be classified according to the arrangement of the endothelium along the vessel walls;
-Continuous
-Discontinuous/sinusoidal capillaries
-Fenestrated
Continuous capillaries
-Diameter; 6-10um
-The endothelial cells in these vessels are traditionally arranged; the cells are in close proximity with each other and fitted with gap junctions
-Designed to isolate luminal content from the interstitial space
Where are continuous capillaries found
-Skin
-Muscle tissue
-Connective tissue
-Nervous tissue
-Respiratory tract
Discontinuous/sinusoidal capillaries
-Diameter; 30-40um
-They have incompletely formed (or completely absent) basement membranes underlying widely spaced endothelial cells.
-Usually, no gap junctions between these cells and the vessels allow for direct transportation from the vascular lumen to the surrounding cells
Where are discontinuous capillaries found?
In the bone marrow, liver and spleen
Fenestrated capillaries
-Diameter; 6-10um
-The capillary beds are perforated along the endothelial cells
-This facilitates rapid molecular exchange between the luminal space of the capillary and the surrounding tissues
Location of fenestrated capillaries
-In the glomerulus of the kidneys
-In the endocrine tissue and parts of the small intestine
Veins
-Carry blood at low pressures and velocities
-Venous valves assist in flowing the slow-moving blood back to the heart.
-They prevent blood from staying in the legs, arms and abdomen
-Most veins run parallel to arteries
-The structure of the veins’ walls is somewhat similar to that of arteries but the intermediate layer contains fewer elastic fibres
Histological layers of veins
3 basic layers;
-Tunica intima; a thin endothelial lining (in some veins valves are present)
-Tunica media; contains 2-3 layers of muscle cells
-Tunica adventitia; the broadest layer. It contains longitudinal collagen fibres and vasa vasorum
Large veins
-Diameter> 1cm
-Vena cava inferior
-Carries deoxygenated blood from the lower half of the body
-Tunica intima, media and adventitia
-Longitudinal, thick muscle bundles
Muscular veins
-No internal/external elastic membranes surrounding the muscle layer
-Medium veins (d<1cm)
-Small veins (1mm)
-Tunica intima (thin subendothelium)
-Tunica media and adventitia (thick collagenous layer)
Vein valves
-Medium and large veins have venous valves, that help keep the blood flowing toward the heart
-Important in the arms and legs where they prevent the backflow of blood in response to the pull of gravity
Histological features of vein valves
Duplication of the intima; double endothelial layer and fibrous core
Venules
Connect capillaries to larger veins
Histological layers of venules
-Tunica intima; without any elastic fibres
-Tunica media; with one or two layers of muscle fibres (in some venules muscle cells are absent)
-Tunica adventitia; fuses with surrounding tissue
