Details of blood transport (under high / low pressure systems), capillary action and exchange, blood distribution, classification of vessels ( e.g. vasa vasorum etc), capillary beds, portal circulation and fetal circulation properties
The Cardiovascular system
Monday, 20 September 2021 4:58 PM
Blood transport
- Arteries and Veins
o Arteries Have branches
§ They diverge
o Veins join / merge
§ Tributaries
o Surrounding the vessels is connective tissue
o Veins have thinner walls relative to arteries and often look collapsed
o Layers
§ Tunica interna – intima
• Inner lining of blood vessel
• In direct contact with blood
• Endothelial cells are active in influencing blood
• Endothelial cells / basement membrane / internal elastic
lamina
§ Tunica media
• Greatest variations amount different vessel types
• Regulates the diameter of the lumen – vasomotion
o Regulate blood flow / pressure and limits blood loss
• Smooth muscle and elastic fibres
§ Tunica externa – adventitia
• Outer covering of a blood vessel
• Contain vasa vasorum
o Small blood vessels that supply the larger arteries and
veins
o Inners layers are nourished by diffusion
• Connective tissue
o Histological organization and tissue composition reflect physiological
conditions under which they operate
- High pressure system
o Arterial system
§ Tissue composition developed to resist high blood pressure
• Each beat of heart creates high pressure of blood ejected into
arteries
• Due to elastic fibers they stretch easily without tearing and
return/recoil to their original shape
o Contain a lot of elastin in their walls
• Retain round shape even when empty due to wider tunica
media with elastic fibers and smooth muscles
o Not only the heart that moves the blood but also the elastic properties of
the arteries
, • Due to elastic fibers they stretch easily without tearing and
return/recoil to their original shape
o Contain a lot of elastin in their walls
• Retain round shape even when empty due to wider tunica
media with elastic fibers and smooth muscles
o Not only the heart that moves the blood but also the elastic properties of
the arteries
o Elastic arteries
§ Nearest to the heart
• Aorta / pulmonary arteries
§ Have large amount of elastic tissue in tunica media
o Muscular artery
§ Medium sized vessels
§ They have a lot of smooth muscles in their walls
§ Have tunica interna
• Endothelial cells / very thin
• Basement membrane
• Internal elastic lamina
§ Tunica media
• Very thick
• Smooth muscle cells
• External elastic lamina
o Elastic fibers
§ Tunica externa
• Holds the blood vessel in the surrounding tissue
- Lower pressure system
o Venous system
o Don’t need to regulate the walls of the blood vessels
o Don’t need elastic / muscular layer
o Have tunica interna
§ Forms valves that prevent blood flowing backwards – unilateral flow
§ Endothelium sitting on basement membrane
o Tunica media
§ Thin layer of smooth muscle and elastic tissue
• Just for regulation
o Tunica externa
§ Thin as well
o Walls could be thinner without danger bursting
§ Expand easily to accommodate an increased volume of blood
- Valves
o Pocket valves like semilunar valves of heart
o 2 cusps
Exchange of substances
- Capillary exchange
o Allow movement of substances between blood and interstitial fluid
o Thin wall
§ Endothelial cell sitting on basement membrane
- Continuous capillaries
o Endothelial cells provide an uninterrupted lining
o Least permeable and most common
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