Flashcards in Session 1 Deck (19)
What do arteries and veins do?
Extra point - Can you think of one exception in the body?
Arteries carry oxygenated blood away from the heart and veins carry deoxygenated blood back to the heart.
Extra point - the pulmonary veins/arteries are the only exception to this rule.
What has the highest velocity of blood flow and why?
The arteries as they have the smallest cross sectional area.
What has the slowest blood flow and why?
The capillaries because they have the largest cross sectional area. This is important as the nutrients have more time to diffuse.
What are the name of the 3 layers which make all veins and arteries?
Tunica intima (inner), tunica media and tunica adventitia (outer)
What is the main structural difference between the tunica media in an elastic artery and a muscular artery?
Elastic - many fenestrated elastic membranes with smooth muscle and collagen between the lamellae. There are many elastic lamellae.
Muscular - 40 layers of smooth muscle connected by gap junctions for coordinated contractions.
What is the diameter of arterioles?
A diameter less than 0.1mm
What are the layers of an arteriole?
Thin internal elastic lamina in larger arterioles only.
Tunica media has 1 --> 3 layers of smooth muscle.
Tunica adventitia is scarce and external elastic lamina is absent.
What are the layers of a metarteriole?
The smooth muscle layer is not continuous.
There are pre capillary sphincters.
What is a pre capillary sphincter?
Extra point - what is their function?
A smooth muscle cell that encircles the endothelium of a capillary arising from a metarteriole.
Extra point - they can control the blood flow to the capillary bed by contraction and relaxation.
What is the structure of capillary walls?
A single layer of endothelium and a basement membrane.
What are the 3 different types of capillaries?
Continuous, fenestrated and sinusoidal (discontinuous)
What are continuous capillaries?
They have a continuous endothelial layer and the cells are joined by tight/occluding junctions. They are common in nervous, muscle and connective tissue.
What are fenestrated capillaries?
Small gaps exist in the endothelium bridged by a thin diaphragm. They are found in the gut and exocrine glands.
*also in renal glomerulus, but they do not have a diaphragm covering the gaps in endothelium*
What are sinusoidal capillaries?
Larger in diameter and gaps in the wall to allow whole cells to move between the blood and the tissue. They are in the liver, spleen and bone marrow.
Fluid tends to drain into post capillary venules due to their lower pressure, in what situation does this not occur?
In an inflammatory response where fluid and leukocytes emigrate.
Do venules have valves?
Yes. They have thin intimal extensions which can restrict the transport of blood by pressing together.
*also have smooth muscle fibres and a tuck media begins to form*
What structural differences are there between arteries and veins?
Veins have less muscle and elastic fibres, but more connective tissue. *The veins in the leg have very defined muscular walls due to having to pump blood against gravity*
What are venae comitantes?
Extra point - how do they work?
They are deep paired veins which usually have a smaller artery in between them. They all wrap together in one sheath.
Extra point - The sheath means that the pulsing of the artery promotes the valves to allow venous return in the adjacent parallel paired veins.