Cardiovascular system (Blood vessels) Flashcards
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
