Circulatory System Flashcards
How does the vasculature of the CVS change as it goes from the heart to the body?
from the heart, large arteries branch into progressively smaller arteries that deliver blood to various parts of the body
What do arteries branch into when reaching an organ?
when a small artery reaches an organ, it branches into smaller arterioles , which branch into capillaries
What do capillary networks do and what do they rejoin to form?
capillary networks exchange
substances between the blood and cells, then rejoin to form small venules
What do small rejoin to form?
small veins progressively join to form larger veins that eventually become the veins that enter the heart
What is the general structure of arteries? Why do they need this structure?
arteries have relatively large diameters to deal with higher blood pressures
What are the three major layers of arteries?
(Describe what type of cells are in each layer)
artery walls consist of three major tissue layers
-an outer layer of connective tissue containing collagen and elastin fibers, which gives the vessel recoil ability
-a relatively thick middle layer of vascular smooth muscle cells, also mixed with elastin fibers
-a thin inner layer of flattened cells ( endothelium )
What is the structure of capillaries? Why does it have this structure?
capillary walls consist of a single layer of endothelial cells through which gases, nutrients, and wastes are exchanged with the interstitial fluid
How is blood flow through capillaries regulated?
blood flow through the capillary networks is controlled by contraction of smooth muscle in the arterioles
a small ring of smooth muscle (precapillary sphincter) at the junction between an arteriole and a capillary adjusts the rate of flow through the capillary network
a small ring of smooth muscle (____ ____) at the junction between an arteriole and a capillary adjusts the rate of flow through the capillary networks
precapillary sphincter
How is the flow of blood through and organ regulated?
the volume of blood flowing through an organ is adjusted by regulating the internal diameter of the arterioles of the organ
How small is a capillary?
the diameter of capillaries is so small that red blood cells must squeeze through in single file
What can pass through during vasoendothelial exchange?
narrow spaces between capillary endothelial cells allow water, ions, and small molecules such as glucose to pass freely between the blood and interstitial fluid
resistance to blood flow in capillaries is ____?
High
resistance to blood flow in capillaries is high. What does this cause and why is this necessary?
resistance to blood flow in capillaries is high, so blood slows down – rate of flow increases when blood returns to veins
slow movement of blood through capillaries maximizes the time for exchange of substances between blood and tissues
What can pass through during vasoendothelial exchange and by what means does this occur?
narrow spaces between capillary endothelial cells allow water, ions, and small molecules such as glucose to pass freely between the blood and interstitial fluid
leukocytes are able to squeeze actively between the cells and pass from the blood to the interstitial fluid
What drives exchange between capillaries and interstitial fluid?
two major mechanisms drive exchange of molecules and ions between capillaries and interstitial fluid: (1) diffusion along concentration gradients, and (2) bulk flow
What is unable to pass through in vasoendothelial exchange?
erythrocytes, platelets, and plasma proteins are too large to pass between cells, and are retained inside the capillaries – except for molecules transported by specific carriers
How does glucose, O2, and CO2 pass through endothelial cells plasma membrane?
O2 and CO2 diffuse directly through the lipid bilayer of endothelial cell plasma membranes – glucose passes by facilitated diffusion through transport proteins
What does bulk flow do?
bulk flow carries water, ions, and molecules out of the capillaries through spaces between capillary endothelial cells
Where is total diffusion in capillaries the greatest and why?
total diffusion is greatest near the arterioles, where the concentration differences between blood plasma and interstitial fluid are highest
What is bulk flow driven by?
bulk flow is driven by blood pressure, which is higher than the pressure of the interstitial fluid
Where is bulk flow the greatest?
like diffusion, bulk flow is greatest near the arterioles, where the pressure difference is highest
What is the structure of veins?
What can they act as?
the walls of venules and veins are thinner than those of arteries and contain little elastin
many veins have interior flaps of connective tissue that form one-way valves that keep blood flowing toward the heart
the thin walls expand and contract over a relatively wide range, allowing venules and veins to act as blood reservoirs
What is deep vein thrombosis?
lack of skeletal muscle activity can lead to blood clots ( deep vein thrombosis ) and cause serious medical problems
[Blood clot in deep veins of legs]
