Maintaining a Balance Topic 10: Structure and Function of Arteries, Capillaries and Veins Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis

DOT POINT Compare the structure of arteries, capillaries and veins in relation to their function

Transport Vessels The transport or vascular system in mammals consists of the heart, blood vessels and lymph vessels, as well as the fluids transported in them - blood and lymph. These systems are interrelated and it is important to understand their interactive functioning. cikgurozaini.blogspot.com

Transport Vessels Transport vessels all have some structural features in common: They are long, hollow structures that consist of a lumen (cavity), surrounded by a wall. cikgurozaini.blogspot.com

Blood and Blood Vessels -Blood is transported by arteries away from the heart, towards the tissues of the body. -Blood is transported by veins from the tissues in the body back to the heart. cikgurozaini.blogspot.com

Blood and Blood Vessels Capillaries are tiny, thin-walled blood vessels in the tissues of the body that carry blood very close to the cells, linking the arteries and veins. Arteries branch to form arterioles (tiny arteries) that lead directly into capillary networks in the tissues. en.wikipedia.org

Blood and Blood Vessels Blood flows from the capillary networks of tissues into venules which join up to form veins so that blood can be returned to the heart. Fluids that seep out of capillaries into the surrounding tissues are returned to the bloodstream by the lymphatic system. medical-dictionary.thefreedictionary.com

Lymph and Lymphatic Vessels The lymphatic system is part of the circulatory system made up of a network of vessels. In the tissues of the body, water and dissolved substances diffuse out of the capillaries and bathe the tissues, as tissue fluid or interstitial fluid. This occurs partly as a result of blood pressure and partly due to the osmotic pressure of the tissues. en.wikipedia.org

Lymph and Lymphatic Vessels Some tissue fluid returns to the capillaries, but a large amount does not. Excess accumulation of fluid in the tissues is overcome by the presence of tiny lymphatic vessels which penetrate deep into the body. The fluid is absorbed into the lymphatic vessels and, together with the other substances there, and form the fluid called lymph. medical-dictionary.thefreedictionary.com

Lymph and Lymphatic Vessels Lymph is a milky white fluid which contains dissolved substances, a large number of white blood cells (called lymphocytes) and chylomicrons. Chylomicrons are the end product of lymph digestion which drain into the lymphatic vessels from the lacteals in the small intestines. en.wikipedia.org

Lymph and Lymphatic Vessels The lymph flows in one direction – from the tissues towards the heart. The flow is brought about partly by contractions if the muscles of the body through which the lymph vessels pass and partly by the pressure of the lymph accumulation in the tissues. lymphnotes.com

Lymph and Lymphatic Vessels The lymphatic vessels from all regions of the body eventually join up to form two main lymphatic channels and, in the regions of the shoulders, these drain into the venous system where the lymph fluid re-joins the blood. The lymphatic system therefore provides a link between the tissue fluids in the deeper cells of the body and the blood plasma. mayoclinic.com

Lymph and Lymphatic Vessels The lymphatic system also plays a role in the defence of the body. We all have lymph nodes which are small, oval bodies at intervals along the course of the vessels. They are the sites of lymphocyte production and they also filter out and destroy bacteria. Your tonsils are examples of lymph nodes. healthcaredir.com

Lymph and Lymphatic Vessels The interaction between the blood and lymphatic systems is important in the transport of nutrients to and wastes from the tissues of the body. remedialmassageforhealth.com

Arteries, Capillaries and Veins The function of arteries and veins is to carry blood over relatively long distances, from one organ to another. Capillaries form branching networks to carry blood over relatively short distances within organs. scientificpsychic.com

Arteries, Capillaries and Veins Arteries, Veins and Capillaries have similar basic structure, but they differ in terms of the layers of tissues that make up the wall of each and the size of the lumen, so that each vessel is structurally modified to best carry out its specific transport function. mysciencevirtualclass.blogspot.com

Arteries The function of arteries is to carry blood away from the heart to the various parts of the body. Since the blood is pumped out of the heart in regular bursts under high pressure, the walls if the arteries are thicker than those of veins, to withstand the force. hwcrc.org

Arteries Major arteries close to the heart have thick layers of smooth muscle in their walls to allow them to withstand the increase in blood pressure as blood is pumped from the heart. cikgurozaini.blogspot.com

Arteries The smooth muscle also functions to adjust the diameter of the lumen and therefore regulates blood flow in the arteries. When the smooth muscle contracts, the size of the lumen is decreased (vasoconstriction) and this slows down blood flow. When the smooth muscle relaxes (vasodilation) allows blood flow to increase. daniellefanfair.com

Arteries The walls of arteries also have a large proportion of elastic fibres in both the inner layer, surrounding the endothelium, and in the middle layer, surrounding the smooth muscle. This increased elasticity enables the arteries to expand (stretch) to accommodate the increased volume of blood pumped with each heartbeat. cikgurozaini.blogspot.com

Arteries When the heart relaxes, the elastic fibres allow the arteries to recoil, returning to their original diameter, squeezing the blood forward and propelling it along, ensuring a continuous flow in one direction. vetmed.vt.edu

Arteries In certain parts of the body where large arteries are near the surface of the skin, the expansion and recoil of the arteries can be felt by a pulse. You are feeling the arteries response to increased pressure with each heartbeat, followed by a decrease in pressure. The force that blood exerts against the walls of the blood vessels in which it is contained is called blood pressure. en.wikipedia.org

Veins Blood enters veins from the capillary networks of tissues, via venuels. Structurally, veins have walls that are thinner than those of arteries, since the blood that they receive flows in under lower pressure. Its not pumped in. beltina.org

Veins The walls have very few elastic fibres as no stretch and recoil is necessary and the smooth muscle layer is much thinner. The lumen also has a wider diameter, for easy flow of blood. leavingbio.net

Veins Since blood seeps into veins and is not pumped, two mechanisms prevent the backflow of blood. This is especially important in veins such as those in the legs, where blood flows against the force of gravity. muscleandstrength.com

Veins The first is many veins are situated between large groups of muscles (particularly in the legs and arms) and their relatively thin walls allow them to be easily compressed. When the muscles in the surrounding tissue contract, the veins are compressed and this propels the blood towards the heart. leavingbio.net

Veins And second, veins have valves – small pocket-like folds of the endothelium lining the lumen of veins. These valves occur at regular intervals along the inside walls and by their action they prevent blood from flowing backwards. merckmanuals.com

Veins Valves work like one-way swing doors – they open to allow blood to flow through in one direction (towards the heart), but the pressure of blood trying to flow backwards causes them to swing shut. veincenterofvirginia.com

Capillaries Capillaries are extremely tiny, microscopic vessels that bring the blood into close contact with the tissues, for the exchange of chemical substances between cells and the bloodstream. The walls of capillaries consist of only one layer of cells – the endothelium lining the lumen (cavity) of arteries and veins. biology.about.com

Capillaries Capillaries have no other layers in their walls. Diffusion is a fairly slow, passive process and so the structure of capillaries is suited to slowing down the flow of blood. To maximise exchange of substances between the blood and cells of the body, capillaries have: Thin walls A small lumen nature.com

Capillaries Thin walls allow for the efficient diffusion of substances, so that they do not have far to travel between the blood and body. A small lumen (only slightly larger than the diameter of red blood cells) to force the red blood cells to pass through in single file, slowing down their flow and increasing their exposed surface area for gaseous exchange. faculty.stcc.edu

Capillaries Capillaries form an expansive network to spread blood flow over a large surface are so that no cells are far from the blood supply. fineartamerica.com

Activity/Homework Students to complete: -10.1.2 Relating Structure to Function Activity