Blood Vessels, Ch. 19
Describe a capillary bed
A capillary bed is a concentration of capillaries which supply blood to a specific organ or area of the body. The density of the capillaries in a given bed can vary, depending on the requirements of the area it supports. These areas are an important part of the circulatory system, marking the point where the circulation reaches its terminus and loops back around to allow blood to pass through the heart and become reoxygenated so that it can return to circulation.
Explain the term lumen
A luminous term referring to the channel within a tube such as a blood vessel or to the cavity within a hollow organ such as the intestine. Lumen is a luminous term because it is Latin for light, including the light that comes through a window. When a hollow organ is cut across, you can see light through the space that has been opened. So the word "lumen" came to mean this space. For example, in arteriosclerosis, fat deposits narrow the lumen of the artery. For another example, cells called enetrocytes within the intestinal wall help transport water from the lumen of the intestine into the bloodstream.
Describe at which point in the circulatory system veins are found
A vein is an elastic blood vessel that transports blood from various regions of the body to the heart. Veins can be categorized into four main types: pulmonary, systemic, superficial, and deep veins. Pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart. Systemic veins return deoxygenated blood from the rest of the body to the right atrium of the heart. Superficial veins are located close to the surface of the skin and are not located near a corresponding artery. Deep veins are located deep within muscle tissue and are typically located near a corresponding artery with the same name (for example coronary arteries and veins). A vein can range in size from 1 millimeter to 1-1.5 centimeters in diameter. The smallest veins in the body are called venules. They receive blood from the arteries via the arterioles and capillaries. The venules branch into larger veins which eventually carry the blood to the largest veins in the body, the vena cava. The blood is then transported from the superior vena cava and inferior vena cava to the right atrium of the heart.
Describe elastic/conducting arteries
An elastic artery or conducting artery is an artery with a large number of collagen and elastin filaments in the tunica media. Arterial elasticity gives rise to the Windkessel effect, which helps to maintain a relatively constant pressure in the arteries despite the pulsating nature of the blood flow. The tunica media is made up of smooth muscle cells and elastic tissue. It lies between the tunica intima on the inside and the tunica externa on the outside. The middle coat (tunica media) is distinguished from the inner (tunica intima) by its color and by the transverse arrangement of its fibers. Elastic arteries include the largest arteries in the body, those closest to the heart. They give rise to medium-sized vessels known as distributing arteries (or muscular arteries). Elastic arterial wall layers include the tunica intima and the tunica media. Elastic arterial wall layers include the tunica intima and the tunica media.
Explain which have the thickest walls, veins or arteries and explain why
Arteries and arterioles have thicker walls than veins and venules, respectively. The increased amount of smooth muscle that is found in arteries gives them extra strength and elasticity to deal with the surges of blood from the heart The smallest arterioles cannot have thick walls. But they must also be able to deal with this pressure. So, even the smallest arterioles do have some supportive smooth muscle.
Briefly describe the functions of each of the three different types of blood vessels
Arteries carry oxygen-rich blood away from the heart to the organs and tissues of the body. The arterial system is under high pressure as it receives blood from the pumping heart. Therefore, the walls of arteries are thick. They contain elastic fibers and muscle cells, which help propel the blood through them. Commonly known arteries of the human body include the aorta, the pulmonary artery, the femoral arteries, the carotid arteries and the coronary arteries. Capillaries are tiny blood vessels that connect the arterial and venous sides of circulation. The walls of these vessels are only one-cell thick to allow for easy exchange of substances in the tissues. Oxygen is transported out of the capillaries into the tissues; carbon dioxide is flowing in the other direction, from the tissues into the capillaries. Similarly, nutrients and waste products cross back and forth as needed, across the capillary walls. Capillaries also have a role in regulating body temperature. When excess heat is present in the body, the capillaries release the heat into the tissues. You have surely noticed how your skin turns pink on a hot summer day or after you have taken a jog--that flush is the result of your capillaries working to rid your body of excess heat. The venous side of circulation carries deoxygenated blood that has picked up carbon dioxide back toward the heart and lungs. Venous circulation is under relatively low pressure compared to arterial circulation. Therefore, the walls of the veins are much thinner than those of the arteries. Veins have a feature not found in arteries--valves. Keeping in mind that there is not high pressure to force venous blood flow toward the heart, the valves are an aid to help prevent backflow and keep circulation a one-way system. Commonly known large veins of the body include the superior vena cava, the inferior vena cava, the pulmonary vein, the jugular veins and the great saphenous veins of the legs.
List the three different layers found in the walls of arteries and veins and describe their relative positions
Basic structure - Capillaries consist of an endothelium which is only one cell thick - Walls of arteries and veins consist of 3 layers - The inner layer consists of a thin layer of endothelial cells - The middle layer is made up of smooth muscle with some elastic fibres. This layer controls the diameter of the vessel and hence the amount of blood and its rate of flow - The outer layer is composed of connective tissue, this holds the blood vessels in place in the body Detailed Structure Arteries - The walls of arteries are much thicker as it carries blood away from the heart at high pressure - Major arteries close to the heart also have thick layers of smooth muscle in their walls to withstand the increases in pressure as the heart pumps - The walls also have a large proportion of elastic fibres in both the inner and middle layers - this allows for the arteries to stretch according to the increases in volume of blood. As the heart relaxes the artery walls return to their original position, hence pushing the blood along - maintaining a constant flow in one direction. - Arteries near the surface of the skin, the changes in the arteries diameter can be felt as a pulse. Veins - The walls of veins are thinner than the walls of arteries, as the blood they receive from the capillaries is at a much lower pressure. - The walls have fewer elastic fibres and the lumen is wider (to allow for easier blood flow) - Veins have two mechanisms for keeping the blood flow constant and in one direction. Firstly many veins are close to muscles, hence when the muscles contract they compress the walls of the vein - pumping blood forwards. Veins also have valves (small pocket like folds of the endothelium lining the lumen of veins), they are spaced along regular intervals in veins. They work much like one-way swinging doors - as the blood is forced through the valve opens, however once the pressure drops and the blood flow decreases, the valve shuts - preventing backflow of blood. Capillaries - They are extremely tiny microscopic vessels that bring blood into close contact with the tissues, for the exchange of chemical substances between cells and the bloodstream. - The one cell thick endothelial layer is a continuation of the lumen arteries and veins - Diffusion is a relatively slow process and hence the structure of capillaries is suited to slowing down the flow of blood - In order to maximize the exchange of substances between the blood and cells capillaries have, thin walls (more efficient diffusion) a small lumen (forces blood cells to pass through in single file, slowing down the rate of flow and maximizing their exposed surface area) - They form an expansive blood flow network, such that no cells are far from blood supply
Explain what vein adaptions ensure blood returns to the heart
Blood pressure within the veins is low and some special adaptations that help return blood to the heart must be made. The large diameter lumens are one structural adaptation. Another is the presence of valves that prevent blood from flowing backward. Valves are most abundant in the veins of the limbs. They are absent in veins of the ventral body cavity.
What are the three different types of capillaries
Capillaries are the smallest and most fragile of the body's blood vessels. They are responsible for what is known as microcirculation, meaning that they create a circulatory network within the organs of the body. There are three different types found in the human body: continuous, fenestrated, and sinusoidal.
Describe capillaries and give their function
Capillaries are the smallest of all blood vessels and form the connection between veins and arteries. As arteries branch and divide into arterioles and continue to reduce in size as they reach the muscle they become capillaries. Here the capillaries form a capillary bed, which is a vast expanse of very small vessels forming a network throughout the muscle. However, unlike veins and arteries, their main function is not transporting blood. They are specially designed to allow the movement of substances, mainly gases Oxygen and Carbon Dioxide into and out of the capillary.
Describe continuous capillaries and give their function
Continuous capillaries get their name from the fact that the cells forming them provide a continuous lining with no interruptions. There are very tight junctions inside of these small blood vessels, which only allows the smallest of molecules, such as water molecules, to penetrate through the lining. This type is found in areas of the body such as the central nervous system, skeletal muscles, and skin.
Explain what tissue makes up the tunica intima
Endothelium and Internal elastic membrane make up this layer
Describe fenestrated capillaries and give their function
Fenestrated capillaries contain very small pores or openings called fenestra. These vessels allow small molecules as well, as limited amounts of nutrients, to pass through their walls. They are most commonly found in the endocrine system of the body, which helps to regulate growth and reproduction and includes such glands as the pituitary and thyroid. This type of blood vessel is also found in lesser degrees in other organs, including the kidneys, pancreas, and the intestines
Describe arterioles and explain their relationship with capillaries
In general, arteries get smaller as they get further away from the heart. When they have decreased in size to a certain point, they are then referred to as arterioles.Structure:Arterioles share many of the properties of arteries they are strong, have a relatively thick wall for their size, and contain a high percentage of smooth muscle.Function:Just like arteries, arterioles carry blood away from the heart and out to the tissues of the body. In addition to this "supply train" function, arterioles are very important in blood pressure regulation.Special Properties:Arterioles are very important because, as a group, they are the most highly regulated blood vessels in the body, and contribute the most to overall blood pressure. Arterioles respond to a wide variety of chemical and electrical messages and are constantly changing size to speed up or slow down blood flow. Smaller arteries called arterioles diverge into capillary beds, which contain 10-100 capillaries that branch among the cells and tissues of the body.
Describe the tissue tunica media
Its the middle tissue layer that contains concentric layers of smooth muscle
Describe a vascular anastomses
Locations where vascular channels untie, branches joining together
Describe the role of vasa visorum
Small arteries that are distributed to the outer and middle coats of the larger blood vessels and to their corresponding veins.
Describe the composition of the tunica externa
The outermost layer, and has loosley woven collagen fibers
Describe sinusoidal capillaries and give their function
The shape of these vessels is a bit irregular, not having the typical cylindrical shape of the other types. These vessels can also be fenestrated, although due to their irregular shape, they are categorized separately. They are found in organs such as the liver and spleen, as well as in the bone marrow and portions of the endocrine system.
List the three different types of blood vessels
Three types of blood vessels comprise the circulatory system: arteries, veins and capillaries.
Describe the difference between a capillary bed that is a vascular shunt and a capillary bed that is referred to as a true capillary bed.
Two kinds of vessels make up the capillary bed, namely, true capillaries and vascular shunt. The true capillary provides exchange between the cells and blood while vascular shunt is the vessel that connects the arteriole and the venule from both sides of the capillary beds. Capillary transport is basically done by bidirectional diffusion on the capillary beds.
Explain why veins are referred to as capacitance vessels
Veins are also called "capacitance vessels" because most of the blood volume of the body (60%) is contained within veins.
Explain which contains the greater volume of blood, arteries or veins
Veins are larger and more compliant (stretchable) than arteries, thus they can hold more blood. In fact, the veins act somewhat like a blood reservoir, containing 60% of the total blood volume at rest. As physical activity increases, the veins undergo vasoconstriction, driving more blood back to the heart and increasing circulation. Also, the return of venous blood to the heart is aided by one-way valves that insure unidirectional flow of blood.
Describe the valves in the veins and explain how they work
Veins receive blood from the capillaries after the exchange of oxygen and carbon dioxide has taken place. Therefore, the veins transport waste-rich blood back to the lungs and heart. It is important that the waste-rich blood keeps moving in the proper direction and not be allowed to flow backward. This is accomplished by valves that are located inside the veins. The valves are like gates that only allow traffic to move in one direction. The vein valves are necessary to keep blood flowing toward the heart, but they are also necessary to allow blood to flow against the force of gravity. For example, blood that is returning to the heart from the foot has to be able to flow up the leg. Generally, the force of gravity would discourage that from happening. The vein valves, however, provide footholds for the blood as it climbs its way up. Veins appear because of light refracting off the skin. Blood that flows up to the brain faces the same problem. If the blood is having a hard time climbing up, you will feel light-headed and possibly even faint. Fainting is your brain's natural request for more oxygen-rich blood. When you faint, your head comes down to the same level as your heart, making it easy for the blood to quickly reach the brain. Because it lacks oxygen, the waste-rich blood that flows through the veins has a deep red color, almost like maroon. Because the walls of the veins are rather thin, the waste-rich blood is visible through the skin on some parts of the body. Look at your wrist, or hands, or ankles. You can probably see your veins carrying your blood back to your heart. Your skin refracts light, though, so that deep red color actually appears a little blue from outside the skin.
Explain at what point in the circulatory system are venules found and what is their structural relationship with capillaries.
Venules are small blood vessels in the microcirculation that connect the capillary beds to the veins. Many venules unite to form a vein. Venule walls have three layers: An inner endothelium composed of squamous endothelial cells that act as a membrane, a middle layer of muscle and elastic tissue, and an outer layer of fibrous connective tissue. In contrast to regular venules, the high endothelial venules are specialized post-capillary venous swellings characterized by plump endothelial cells as opposed to the usual thinner endothelial cells found in regular venules.
Describe where vascular anastomoses are usually formed
Where vessels unite or interconnect, they form vascular anastomoses (= coming together). Most organs receive blood from more than one arterial branch, and nearby arteries often communicate with one another to form arterial anastomoses.The anastomoses between the various arteries of the body are of great importance in medicine as well as surgery. Venous anastomoses are much more freely than arteries, therefore, venous anastomoses are more commonly found throughout the body. Because of the abundance of venous anastomoses, occlusion of a vein rarely blocks blood flow or leads to tissue death.
Tell who is given credit for, in the 1620's, developing the theory that blood circulates through the body
William Harvey
Describe muscular/distributing arteries
a medium-sized artery that draw blood from an elastic artery and branch into "resistance vessels" including small arteries and arterioles. In contrast to the mechanism elastic arteries use to store energy generated by the heart's contraction, distributing arteries contain layers of smooth muscle. Under the microscope distributing arteries can be identified by their clearly defined internal elastic lamina. In constricted vessels the elastic lamina of distributing arteries appears thick and kinky. The elastic lamina is best visualized using Verhoeff's stain, but can be easily detected in specimens stained using other techniques as a well-defined negative staining region. Examples of distributing arteries include the radial artery and the splenic artery.
Explain the term vasoconstriction and vasodilation and describe the role of the tunica media in vasoconstriction and vasodilation
the term vasoconstriction is used to describe the narrowing of the blood vessel due to contraction of the muscular wall. When an artery constricts, the flow of blood decreases and the pressure within the vessel rises. Vasoconstriction is a mechanism your body uses to regulate important functions in the body, such as body temperature and blood pressure. Vasodilation is the opposite of vasoconstriction and is the term used to describe the widening of the blood vessel due to relaxation of the muscular wall. When a blood vessel dilates, blood is able to flow through the vessel with less resistance. Therefore, vasodilation has the opposite effect of vasoconstriction on such function as body temperature and blood pressure. The tunica media of arteries contains more smooth muscle than the tunica media of the counterpart, the veins, and this allows the arteries to constrict and dilate to adjust the volume of blood needed by the tissues that they feed.
