Vessels Flashcards
What are the three types of vessels in the cardiovascular system
Arteries, Veins and capillaries.
How do you define an artery? Vein? What’s a capillary?
An artery takes blood away from the heart. Veins bring blood back towards the heart. Capillaries are the smallest vessels. They are simple squamous epithelium and are only big enough to allow one red blood cell through at a time. This is where nutrients, wastes and gases (oxygen and carbon dioxide) are exchanged between the blood and the tissues/cells of the body.
What’s the role of the lymphatic system?
In a capillary bed, fluids from the blood are forced into the intersticial space at the entry side (the artery side) and much of this fluid is picked back up and reenters the veins on the vein side. However, as much as 3 liters of fluid would be left behind per day, which is more than half the blood plasma. Lymphatic capillaries pick up this fluid and return it to the heart.
Describe the following structures in a blood vessel:
Lumen, tunica intima, endothelium, subendothelial layer, inner and outer elastic membranes, tunica media, tunica externa. Starting from the inside, the space inside a vessel (and any organ) is called the lumen. The very first layer of tissue that articulates with the lumen is the tunica intima. The tunica intimas first layer is simple squamous epithelium (the endothelium). Behind that is a very thin layer of areolar connective tissue that forms a basement membrane. In arteries, this layer has a inner elastic membrane (made out of elastic tissue). Capillaries only have the endothelium and the very thin basement membrane in the tunica intima. Outside of the tunica intima is the tunica media. This is a layer of smooth muscle (innervated by the autonomic nervous system, the ANS). In arteries there is an external elastic membrane behind this. Outside of the tunica media there is one more layer called the tunica externa or adventicia. This is made up of collagen fibers and there is a blood supply to this layer called the vaso vasorum.
Compare and contrast elastic and muscular arteries.
Said simply, elastic arteries have a lot more elastic tissue in the inner and outer elastic membranes and a lot less smooth muscle as compared to muscular arteries. Muscular arteries have much less elastic tissue and a thicker layer of smooth muscle. Also, elastic arteries are closer to the heart and lead into muscular arteries. The aorta is an elastic artery. Elastic arteries have a larger diameter than muscular arteries. The function of an elastic artery is to expand when a pulse of blood comes through (when the heart contracts) and then be able to recoil after the pulse of blood moves through. The function of a muscular artery is to use the muscular layer to constrict or relax and therefore control the supply of blood to certain parts of the body. For example, during stress, more blood moves to the brain and muscle. During relaxation, more blood moves to the digestive tract.
How does an elastic artery maintain a blood pressure gradient and protect arteries downstream from high blood pressure?
When blood is pumped from the heart into the aorta (an elastic artery), the aorta expands to accomodate this increase in volume of blood that is entering. The pressure that the blood is exerting on the walls of the aorta increases, but because the walls of the aorta expand, allowing the vessel to hold more volume, the pressure doesn’t get too high. If the walls didn’t expand, then the pressure would become very high every time blood entered from the heart. This increase in pressure could cause damage to the artery. Then, between heart beats the blood moves downstream (on to the next part of the vessel). As blood leaves, the vessel has the ability to retract or recoil. If it didn’t do this, the diameter of the vessel remained high, then the pressure that the blood could exert on the walls would fall dramatically. There wouldn’t be any force that was forcing blood to move downstream to the next artery - as blood moves from an area of high pressure to an area of low pressure. Vessels would go from very high pressure every time blood came through to very low pressure and a trickle of blood moving through. Instead the walls expand and recoil, so blood pressure is continually exerted on the walls of the vessel. In this way, blood can continue to move from an area of high pressure to an area of low pressure, and therefore be delivered to the entire body along this gradient.
Describe the structure of an arteriole.
Larger arterioles have all three tunics, but smaller arterioles that lead to capillary beds are just the tunica intima with a small layer of tunica media (smooth muscle) surrounding it.
Describe the main function of an arteriole and how its structure is suited to carry out this function.
The function is to control how much blood any particular tissue/organ in the body is receiving at any given time. By constricting the smooth muscle layer in the arterioles near capillary beds, blood supply can be reduced to a tissue. If the smooth muscle relaxes, the diameter of the arteriole increases and more blood is delivered to a tissue.
What is the function of capillaries?
To exchange oxygen, carbon dioxide, nutrients and wastes between the blood and cells.
How is a capillaries structure ideally suited for its function?
They are only one cell thick, so it is easy for diffusion of these things to take place.
What is a pericyte and what is its function?
A pericyte is a cell attached to the outside of a capillary. It’s job is to generate new vessels, scar tissues, and help control the permeability of the capillary.
What is meant by the term ‘microcirculation’?
This is the flow of blood from the arteriole end of a capillary bed to the venule end of the capillary bed.
What’s a capillary bed? What two types of vessels does it connect?
Capillaries don’t exist by themselves, they form capillary beds which are networks of capillaries interwoven together. They connect arterioles to venules.
Describe how blood is cut off from certain places in the body at certain times. Give an example of when this might happen.
The smooth muscle surrounding arterioles contracts, decreasing blood flow to the adjacent capillary bed. One example is that during stress, blood flow decreases to the digestive tract and increases to the brain and muscle tissues.
What is bulk flow and describe how fluid moves into and out of capillaries in the capillary bed. What role does the lymphatic system have in this?
Bulk flow is the movement of water and solutes across a membrane based on the pressure gradients between the two spaces (on either side of the membrane). If there is high pressure inside the capillary bed, then fluids are forced out. If there is high pressure outside the capillary bed, then fluids and the solutes they contain are forced into the capillary bed. When fluids enter a capillary bed from the arteriole, there is high pressure in the capillaries. The diameter of the arteriole is much bigger then the combined diameter of the capillaries in the capillary bed, creating high pressure. Because of this bulk flow occurs and fluids and solutes move out of the capillary and into the interstitial space around the capillary. At the venule side of the capillary bed the pressures reverse and fluids move back into the capillary. Some fluid, however, is left behind. The lymphatic system picks these fluids up and returns them to the heart.
Describe the structure of a venule.
This is the smallest kind of vein. Smaller venules are like small arterioles - they are the tunica intima with a thin layer of tunica media (smooth muscle). Larger venules have thin layers of all three tunics.
What are some main differences between veins and arteries?
Arteries are defined as vessels that are moving away from the heart. Veins are vessels moving towards the heart. All arteries except for the pulmonary artery are oxygenated (carrying oxygenated blood to the tissues of the body). All veins except for the pulmonary vein are deoxygenated (carrying deoxygenated blood from the tissues back to the heart).
What parts of the body would you find valves in the veins? Why?
In the extremities because there is a very low pressure gradient there, so blood is moving slowly. Also, blood is fighting gravity to be delivered back to the heart. Valves prevent backflow of blood on its way back to the heart.
Define the term ‘blood flow’.
The volume of blood flowing through a vessel or organ.
Define the term ‘blood pressure’.
The pressure exerted by the blood on the vessel wall surrounding it. The hydrostatic pressure gradient is the pressure difference throughout the vascular system.
Define the term ‘resistance’.
Resistance is the opposition to blood flow. The amount of friction blood encounters as it passes through the system.
What is a hydrostatic pressure gradient?
same as blood pressure, the pressure difference throughout the vascular system
