Blood Vessels Flashcards
What is blood pressure equal to?
Cardiac output x peripheral resistance
Why do capillaries have a very low pressure?
There is a very high total cross-sectional area.
What are elastic arteries?
The largest arteries, which have a relatively thin wall relative to lumen, and function on the distribution of blood.
The internal and external elastic laminae are well defined, because the arteries are pulsator you and maintain blood pressure by elastic recoil.
More elastic fibres than muscle in tunica media.
Poor distribution throughout wall so vasa vasorum are present.
What are muscular arteries?
Arteries where the tunica I media contains more smooth muscle and less connective tissue.
Blood pressure is maintained more by active contraction of smooth muscle than by passive elastic recoil.
The tunica media is almost absent in capillaries, apart from occasional cells called…
Pericytes
Why are arterioles good for controlling blood pressure?
They have a relatively thick wall in relation to the lumen (even though the tunica media has a smooth muscle layer only 1-2 cells thick), and so a small change in tension produces a big change in blood flow.
What are the three types of capillary?
Continuous - the plasma membrane of the endothelium forms a continuous tube and gas exchange is across the flattened out cytoplasm
Fenestrated - there are small regular pores (fenestrations) in the plasma membranes of the epithelial cells, so the rate of diffusion of small molecules is increased e.g in glomerulus in kidney, villi in small intestine, endocrine glands
Discontinuous - there are irregular fenestrations AND gaps between endothelial cells, so cells as well as molecules can be exchanged, and there is a sub-endothelial space e.g in spleen, sinusoids in liver
What is a portal vessel?
One that links successive capillary beds.
Portal system can be arterial (e.g afferent and efferent arterioles in kidney) or venous (e.g hepatic portal vein).
Name some features of venules and veins.
Low pressure
Thin walls relative to lumen
No internal elastic lamina in tunica intima
May contain semi lunar valves
Venous return from limbs involves muscle pump
Name 3 features of lymphatic vessels.
Lined by endothelium
May contain valves
Lymph filtered by lymph nodes
Not continuous circulation, blind ending lymphatics drain fluid from tissues and intimately drain into superior vena cava via thoracic duct
What is orthostatic hypotension?
A sudden drop in upper body blood pressure when standing up from supine position.
What is the vasomotor centre in the medulla oblongata?
Controls blood vessel diameter, so can cause vasodilation or vasoconstriction.
In the baroreceptor reflex, what happens if blood pressure increases?
The baroreceptors in the atria and carotid sinuses (in internal carotid artery) are stimulated, this means the cardioaccelerator centres are inhibited, the cardioinhibitory centres are stimulated (Ach released by vagus nerve), the vasomotor centre is inhibited. This means heart rate and contractility is decreased, vasodilation occurs.
Blood pressure is reduced.
In the baroreceptor reflex, what happens if blood pressure decreases?
The baroreceptors are inhibited, the cardioaccelerator centre is stimulated (sympathetic nerves), and the cardioinhibitory centres are inhibited, and the vasomotor centre is stimulated. This means there is increased contractility and heart rate as adrenaline is released from adrenal medulla, and there is vasoconstriction if muscular arteries. Blood pressure is increased.
What type of blood pressure is fast so can combat orthostatic hypotension, and which type is slow?
Fast = baroreceptor reflex Slow = renin-angiotensin-aldosterone system
