Flashcards in Histology of the CVS Deck (134)
What are the best examples of an absolute end artery?
The central artery to the retina
The labyrinthine artery of the internal ear
What is bridging?
The compression of a segment of a coronary artery during systole, resulting in a narrowing that reverses during diastole
What are arterioles?
Arteries with a diameter of less than 0.1mm
What do arterioles have in their tunica media?
1 to 3 layers of smooth muscles
Do arterioles have a thin elastic lamina?
Only larger ones
What is the tunica media composed of in small arterioles?
A single smooth muscle cell that completely encircles the endothelial cells
Do arterioles have an external elastic lamina?
What is the tunica adventitia of arterioles made up of?
A few fibrous cells with a bit of connective tissue
What are metarterioles?
Arteries that supply blood to capillary beds
How do metarterioles differ from arterioles?
The smooth muscle layer is not continuous
What do individual muscle cells in metarterioles do?
They are spaced apart, and each encircle encircles the endothelium of a capillary arising from the metarteriole, called the precapillary sphincter
What is the function of the precapillary sphincter?
On contraction, it controls the blood flow into the capillary, reducing it
What does the precapillary sphincter allow?
Arterioles and metarterioles to serve as flow regulators for capillary beds
What happens when precapillary sphincters are open?
There is plentiful blood flow through the capillary bed
What happens when precapillary sphincters are closed?
Blood flow through the capillary bed is greatly reduced
How can the capillary bed be bypassed?
By a central channel, consisting of a metarteriole and a thoroughfare channel.
This happens when the sphincters are closed
What are most arterioles able to do?
Dilate to 60-100% of their resting diameter
Maintain up to 40% constriction for a long time
What does regulation by arterioles do?
Directs blood flow to where it may be most needed
What happens during strenuous physical exertion?
Blood flow to skeletal muscles is increased by dilation of arterioles, and blood flow to the intestine is decreased by constriction of arterioles
What do lymphatic capillaries do?
Drain away excess extracellular fluid
Where do lymphatic capillaries return extracellular fluid to the blood?
At the junctions of the internal jugular and subclavian veins
How much of the total blood volume do capillaries hold?
What do capillaries present?
The largest surface area for gas and nutrient exchange
How is the diffusion path to adjacent tissues minimised?
Passing red blood cells fill virtually the entire capillary lumen
How does blood velocity in capillaries differ from elsewhere?
It is lowest during passage through the capillaries
What does the low blood velocity through the capillaries allow?
Time for gas exchange and nutrient exchange with surrounding tissues
How big are capillaries?
30µm in diameter
Usually less than 1mm long
Essentially, what is the capillary?
A tube thats just large enough to allow passage of blood cells one at a time
What are capillaries made of?
A single layer of endothelium and its basement membrane