Blood Vessels, Ch18 Flashcards
The distribution circuit of the vasculature. Those in the pulmonary circuit carry deoxygenated blood, while those in the systemic carry oxygenated. As they travel away from the heart, they branch into vessels that become progressively smaller.
Arteries
The exchange system of the vasculature. Very-small-diameter vessels that form branching networks called what?
Capillaries. Capillary beds.
The collection system of the vasculature, draining blood from capillary beds and returning it to the heart. Small ones merge with others to become progressively larger as they progress toward the heart. In the pulmonary circuit, they carry oxygenated blood, and deoxygenated in the systemic.
Veins
This is the innermost tunic of blood vessels. What is it composed of?
Tunica intima, composed of endothelium which consists of a sheet of squamous epithelium and its basal lamina. Deep to the endothelium is a layer of subendothelial connective tissue and a layer of elastic fibers called internal elastic lamina, which provide the vessel with distensibility and elasticity.
What is the middle tunic of blood vessels? What is it composed of?
Tunica media, composed of a layer of smooth muscle cells arranged circularly around the lumen, and a layer of elastic fibers called the external elastic lamina. The smooth muscle cells control diameter and thus blood flow.
These nerves stimulate the smooth muscle cells of the tunica media in what two ways?
Vasomotor nerves. When they stimulate contraction and narrowing of the vessel, it’s known as vasoconstriction. When sympathetic stimulation of the cells decreases, they relax and the vessel’s diameter increases, which is vasodilation.
What is the outermost tunic of blood vessels? What is it composed of?
Tunica externa/adventitia. It’s composed of dense irregular collagens connective tissue that supports the blood vessel to prevent overstretching.
This is the ability to stretch when subjected to increased pressure. This is the ability to recoil back to original size when the stretching force is removed.
Distensibility. Elasticity.
“Vessels to the vessels.” What do they do?
Vasa vasora. They supply oxygen and nutrients to the tunica media and externa, whose cells are too far away from the lumen to receive oxygen and nutrients by diffusion alone.
How do arteries differ from veins in structure?
Most arteries have much thicker tunicae mediae than do veins, which reflects their role in controlling blood pressure and flow to the organs. The internal and external elastic laminae are much more extensive in arteries than in veins, reflecting the fact that the arteries are under much higher pressure than are veins.
This type of artery has the largest diameter. They are nearest to the heart and therefore under the highest pressure of any vessels in the cardiovascular system.
Elastic/conducting arteries. The tunica media contains 40-70 sheets of elastic fibers arranged between thin layers of smooth muscle cells. The relatively small amount of smooth muscle tissue mean that their diameter does not change much with each stimulation from vasomotor nerves.
This type of artery is generally intermediate in diameter. They contain a well-developed tunica media composed primarily of smooth muscle cells. Most likely to become blocked.
Muscular/distributing arteries. Due to all the smooth muscle cells, their diameter does change a lot with vasoconstriction and dilation. This allows the nervous and endocrine systems to adjust local blood flow to different organs by changing the vessel diameter. Also controls blood pressure.
The smallest kind of artery, ranging from 0.3mm to 70-120um. Tunica media contains only 1-3 layers of smooth muscle cells. Diameter is affected by both vasomotor nerves and hormones the blood.
Arterioles. The smallest arterioles, called metarterioles, directly feed capillary beds in most tissues. The smooth muscle cells of met arterioles are confined mostly to a circular precapillary sphincter that encircles the metarteriole-capillary junction.
These pressure receptor arteries are found in the aorta, as well as in the common carotid artery in the neck. What is their overall purpose? Also in the aorta and carotid are these that detect blood oxygen, carbon dioxide, and hydrogen ion concentrations.
Baroreceptors, whose purpose is to protect the body from sudden increases or decreases in BP from moment to moment. Chemoreceptors.
How do veins differ from arteries?
Veins typically outnumber arteries and their lumens have a larger average diameter. 70% of the total blood in the body is located in the veins at any given moment, which allows them to function as blood reservoirs. Have much thinner walls, fewer elastic fibers, less smooth muscle.
These are the smallest veins, which drain blood from the capillary beds. The tiny ones consist of little more than endothelium and some surrounding connective structure, which enables them to exchange material with the surrounding interstitial fluid.
Venules. Postcapillary venules. Small ones have only a tunica intima, larger ones have all three tunics. The three tunics become more distinct as the venules merge to become larger venules and then veins.
Most veins contain these, which are extensions of the tunica intimate that overlap and prevent blood from flowing backward in the venous circuit.
Venous valves. Especially numerous in the veins of the legs, where blood flow to the heart is strongly opposed by gravity.
Locations where vessels connect via pathways called collateral vessels. What is the most common type?
Anastomoses. Venous anastomosis is the most common, in which neighboring veins are connected by small collaterals.
This type of anastomoses exists in many organs such as the heart and brain, as well as around joints. Tissues deprived of oxygen secrete chemicals that trigger a process called what, or the formation of new blood vessels?
Arterial anastomosis. Angiogenesis.
This type of anastomosis is when an artery empties directly into a vein without passing through a capillary bed.
Arteriovenous anastomosis. Found in the skin and fetal circulation.
This is the leading cause of death in the developed world, an arterial disease that affects large and medium size muscular arteries. Characterized by the formation of plaques, which are buildups of lipids, cholesterol, calcium salts, and cellular debris within the tunica intima. How does it occur?
Atherosclerosis. Plaques are generated in response to injury to the endothelium, which causes the vessel wall to become inflamed, which attracts phagocytes. The damaged area turns into a plaque, causing changes in the tunica media.
This is the outward force that the blood exerts on the walls of the blood vessels. It is highest in the large systemic arteries and lowest in the large systemic veins. How is it measured?
Blood pressure. Expressed in units millimeters of mercury, or mm Hg. This is the force exerted by a column of mercury one millimeter in height.
The volume of blood that flows per minute, which generally matches CO, averaging about 5-6 L/min. Its velocity is largely determined by the cross-sectional area of blood vessel. What is it affected by?
Blood flow. It’s directly proportional to the pressure gradient, meaning blood flow increases when the pressure gradient does and vice versa. Resistance also determines it, which is any impedance to blood flow. Resistance is inversely proportional to blood flow.
Most of the resistance in vessels is encountered away from the heart, which gives rise to what term? How is it related to blood pressure?
Peripheral resistance. They are directly related. As peripheral resistance increases, blood pressure increases.
What are the three main variables that determine peripheral resistance? Which is the fastest to change and which is the slowest?
Blood vessel radius, blood viscosity, and blood vessel length. Vessel radius is the quickest, whereas vessel length is the slowest.
How is resistance related to blood vessel radius?
Resistance varies inversely with the vessel’s radius. As a radius increases, and the vessel dilates, the resistance to blood flow decreases and vice versa.
