ANUR 403Bood vessels.pdf

TONGA NATIONAL UNIVERSITY FACULTY OF NURSING AND HEALTH SCIENCE QUEEN SALOTE SCHOOL OF NURSING AND MIDWIFERY HUMAN BIO SCIENCE 1_2024 Session: Circulatory System---Blood Vessels Course Name: Human Bioscience 1 Course Code: ANUR 403 Dat...

TONGA NATIONAL UNIVERSITY FACULTY OF NURSING AND HEALTH SCIENCE QUEEN SALOTE SCHOOL OF NURSING AND MIDWIFERY HUMAN BIO SCIENCE 1_2024 Session: Circulatory System---Blood Vessels Course Name: Human Bioscience 1 Course Code: ANUR 403 Date: 26.06.2024 Time: 1030-1230 Week 16_session_2 Lile Tonga Taufa  Objectives At the end of the session, the students will be able to: Identify the five types of blood vessels and its structural characteristics  Cardiovascular System The circulatory system or the cardiovascular system consists of the heart, blood vessels, and the about five litters of blood, that the blood vessels are transport. Blood is responsible for transporting O2, nutrients, hormones, and cellular waste products throughout the body, the cardiovascular system is powered by the heart.  Blood Vessels Blood vessels allow blood to flow quickly and efficiently from the heart to every region of the body and back again. The size of blood vessels corresponds with the amount of blood that passes through the vessel. All blood vessels contain a hollow area called the lumen through which blood is able to flow. Around the lumen is the wall of the vessel, which may be thin in the case of capillaries or very thick in the case of arteries.  Types of blood vessels There are three major types of blood vessels: Image result for arteries veins and capillaries microscope Arteries, Veins, and capillaries. Blood vessels are often named after the region of the body through which they carry blood or for nearby structures. For example, the brachiocephalic artery carries blood into the brachial (arm) and cephalic (head) regions  Blood is carried through the body via blood vessels. An artery is a blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels. The smallest arteries, vessels called arterioles, further branch into tiny capillaries, where nutrients and wastes are exchanged. Capillaries come together to form venules, small blood vessels that carry blood to a vein, a larger blood vessel that returns blood to the heart. Shared Structures Arteries and arterioles have thicker walls than veins and venules because they are closer to the heart and receive blood that is surging at a far greater pressure. Arteries have smaller lumens than veins, a characteristic that helps to maintain the pressure of blood moving through the system. Together, their thicker walls and smaller diameters give arterial lumens a more rounded appearance in cross section than the lumens of veins. Structural differences among blood vessels  Structure of blood vessels Image result for arteries veins and capillaries microscope The tunica intima (also called the tunica interna) is composed of epithelial and connective tissue layers. Lining the tunica intima is the specialized simple squamous epithelium called the endothelium, the basement membrane, or basal lamina, that effectively binds the endothelium to the connective tissue. The tunica media is the substantial middle layer of the vessel wall. It is generally the thickest layer in arteries, and it is much thicker in arteries than it is in veins. The outer tunic, the tunica externa (also called the tunica adventitia), is a substantial sheath of connective tissue composed primarily of collagenous fibers. Some bands of elastic fibers are found here as well.  Arteries An artery is a blood vessel that conducts blood away from the heart. All arteries have relatively thick walls that can withstand the high pressure of blood ejected from the heart. However, those close to the heart have the thickest walls, containing a high percentage of elastic fibers in all three of their tunics. This type of artery is known as an elastic artery Con’t Arteries Vessels larger than 10 mm in diameter, such as the aorta, pulmonary trunk, common carotid, common iliac and subclavian arteries are typically elastic. Their abundant elastic fibers allow them to expand, as blood pumped from the ventricles passes through them, and then to recoil after the surge has passed.  Cont Arteries Farther from the heart, where the surge of blood has dampened, the percentage of elastic fibers in an artery tunica intima decreases and the amount of smooth muscle in its tunica media increases. The artery at this point is described as a muscular artery also called a distributing artery because the relatively thick tunica media allows precise control of blood vessel diameter to control blood flow to different areas or organs. Arterioles An arteriole is a very small artery that leads to a capillary. Larger arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. Capillaries Capillaries are the smallest and thinnest of the blood vessels in the body and also the most common. A capillary is a microscopic channel that supplies blood to the tissues themselves, a process called perfusion. Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). Cont Capillaries The wall of a capillary consists of the endothelial layer surrounded by a basement membrane with occasional smooth muscle fibers. For capillaries to function, their walls must be leaky, allowing substances to pass through. There are three major types of capillaries, which differ according to their degree of “leakiness:” continuous, fenestrated, and sinusoid capillaries The most common type of capillary, the continuous capillary, is found in almost all vascularized tissues.  Capillaries and its types Continuous capillaries are characterised by a complete endothelial lining with tight junctions between endothelial cells.  Capillaries and its types Fenestrated capillary is one that has pores (or fenestrations), in addition to tight junctions in the endothelial lining. These make the capillary permeable to larger molecules. The number of fenestrations and their degree of permeability vary, however, according to their location. Fenestrated capillaries are common in the small intestine, which is the primary site of nutrient absorption, as well as in the kidneys, which filter the blood. They are also found in the choroid plexus of the brain.  Capillaries and its types Sinusoid capillary (or sinusoid) is the least common type of capillary. Sinusoid capillaries are flattened, and they have extensive intercellular gaps and incomplete basement membranes, in addition to intercellular clefts and fenestrations. Types (3) of Capillaries  Venules A venule is an extremely small vein, generally 8–100 micrometers in diameter. Postcapillary venules join multiple capillaries exiting from a capillary bed. Multiple venules join to form veins. The walls of venules consist of endothelium, a thin middle layer with a few muscle cells and elastic fibers, plus an outer layer of connective tissue fibers that constitute a very thin tunica externa Veins A vein is a blood vessel that conducts blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens. Because they are low-pressure vessels, larger veins are commonly equipped with valves that promote the unidirectional flow of blood toward the heart and prevent backflow toward the capillaries caused by the inherent low blood pressure in veins as well as the pull of gravity.  Structural differences among blood vessels Image result for differences between arteries veins and capillaries  Comparison of Arteries and Veins Characteristics Arteries Veins Direction of blood flow Conducts blood away from the heart Conducts blood toward the heart General appearance Rounded Irregular, often collapsed Pressure High Low Wall thickness Thick Thin Relative oxygen Higher in systemic arteries Lower in systemic veins concentration Lower in pulmonary arteries Higher in pulmonary veins Valves Not present Present most commonly in limbs and in veins inferior to the heart  Re-Capped Blood pumped by the heart flows through a series of vessels known as arteries, arterioles, capillaries, venules, and veins before returning to the heart. Arteries transport blood away from the heart and branch into smaller vessels, forming arterioles. Arterioles distribute blood to capillary beds, the sites of exchange with the body tissues. Capillaries lead back to small vessels known as venules that flow into the larger veins and eventually back to the heart.  Re-Capped The arterial system is a relatively high-pressure system, so arteries have thick walls that appear round in cross section. The venous system is a lower-pressure system, containing veins that have larger lumens and thinner walls. They often appear flattened. Arteries, arterioles, venules, and veins are composed of three tunics known as the tunica intima, tunica media, and tunica externa.  Re-Capped Capillaries have only a tunica intima layer. The tunica intima is a thin layer composed of a simple squamous epithelium known as endothelium and a small amount of connective tissue. The tunica media is a thicker area composed of variable amounts of smooth muscle and connective tissue. It is the thickest layer in all but the largest arteries. The tunica externa is primarily a layer of connective tissue, although in veins, it also contains some smooth muscle. Blood flow through vessels can be dramatically influenced by vasoconstriction and vasodilation in their walls. Activity---Direct Question and Answer 1. Blood vessel that drain blood AWAY from the heart. 2. Blood vessel that drains blood TOWARDS/BACK to the heart 3. The hollow space within a blood vessel 4. Process by which contraction of the smooth muscles within blood vessels increases and a causes a decrease in blood flow to the extremities/skin Activity---Direct Question and Answer 5. Process by which contraction of the smooth muscles within the blood vessels relaxes and allows an increase in blood flow to the extremities/skin 6. Microscopic artery, serves as a transition between arteries and capillaries 7. Blood vessels that are only one-cell layer think and allow for the rapid exchange of oxygen and nutrients for carbon dioxide and waste products Activity---Direct Question and Answer 8. Tiny veins that connect veins and capillaries and help to drain blood back to the heart 9. A structure within a vein that prevents the backflow of blood on its return to the heart 10. What type of vessel is capable of allowing the passage of gasses and nutrients though its walls to nourish surrounding tissue? Activity---Direct Question and Answer 11. True/False Arteries always carry oxygenated blood away from the heart  Reference Tortora, G., Derrickson, B. (2012). Principles of Anatomy and Physiology (13th ed). USA: John Wiley & Sons, Inc