Circulatory system IV Flashcards
what is the function of arteries
they are stout walled vessels which carry oxygenated blood away from the heart
- with the exception of the PA as it carries deoxygenate blood from the RV to the lungs
what are the smallest arteries?
arterioles
what is the function of a vein?
veins transport deoxygenated blood back to the heart
- with the exception of pulmonary veins as they carry oxygenated blood
what is the relationship between veins and venules?
after blood passes through the capillaries it enters the smallest veins called venules, it flows into progressively larger and larger veins until it reaches the heart
describe the structure of veins
veins have thinner walls than arteries, they have the same 3 layers present but less smooth muscle and CT
why are vein walls thinner than artery walls?
they withstand less pressure, they’re less rigid and can hold more blood
- 70% of total blood volume is in veins
what are capillaries?
capillaries are the smallest and most numerous BV
- they form the connection between arteries and veins
what is the primary function of capillaries?
the exchange of materials between the blood and tissue cells
what do arterioles break up into?
capillaries
describe the structure of a capillary wall?
consists of a single layer of curved endothelial cells which water and other small molecules can pass through into the blood
- CO2 is released out capillaries and into veins
- blood and plasma cells don’t pass through
what is the diameter of a capillary?
7 microns, same as erythrocyte
What are the 3 layers of blood vessels
- tunica intima
- tunica media
- tunica adventia
What is the tunica intima?
Inner layer of squamous epithelium surrounded by a connective tissue basement membrane with elastic fibres
What is the tunica media?
Middle layer of smooth and elastic tissue, usually the thickest but allows changes in diameter
What is the tunica adventia?
Outer layer of fibrous connective tissue (elastic and collagen fibres)
What nervous system controls blood vessel diameter?
Autonomic nervous system, arises from the vasomotor centre of the medulla oblongata
What controls the smooth muscle in the tunica media?
Sympathetic nervous system
What does decreased nerve stimulation cause?
Smooth muscle relaxation -> Vasodilation
What does increased nerve stimulation cause?
Smooth muscle contraction -> vasoconstriction
