cardio blood vessels

• Cardiovascular system


  Contributes to homeostasis of other body systems by transporting and distributing blood throughout the body to deliver materials (such as oxygen, nutrients, and hormones) and carry away wastes
• Blood vessels


  • Form a closed system of tubes that carries blood away from the heart, transports it to the tissues of the body, and then returns it to the heart
  • The left side of the heart pumps blood through an estimated 100,000 km (60,000 mi) of blood vessels
  • The right side of the heart pumps blood through the lungs, enabling blood to pick up oxygen and unload carbon dioxide
• Chapters 19 and 20 described the composition and functions of blood and the structure and function of the heart. In this chapter, we focus on the structure and functions of the various types of blood vessels; on the forces involved in circulating blood throughout the body; and on the blood vessels that constitute the major circulatory routes.
• Blood vessels


  Contribute to homeostasis by providing the structures for the flow of blood to and from the heart and the exchange of nutrients and wastes in tissues<|>They also play an important role in adjusting the velocity and volume of blood flow
• Generalized blood vessel structure

  • Three structural layers from innermost to outermost: tunica interna (intima), tunica media, and tunica externa (adventitia)
  • Modifications of this basic design account for the five types of blood vessels and the structural and functional differences among the various vessel types
• Tunica interna (intima)


  Forms the inner lining of a blood vessel and is in direct contact with the blood as it flows through the lumen (interior opening) of the vessel<|>Its innermost layer is called endothelium, which is continuous with the endocardial lining of the heart<|>Endothelial cells are active participants in a variety of vessel-related activities, including physical influences on blood flow, secretion of locally acting chemical mediators that influence the contractile state of the vessel's overlying smooth muscle, and assistance with capillary permeability<|>The basement membrane deep to the endothelium provides physical support and regulates molecular movement<|>The internal elastic lamina forms the boundary between the tunica interna and tunica media and facilitates diffusion of materials through the tunica interna to the thicker tunica media
• Tunica media


  A muscular and connective tissue layer that displays the greatest variation among the different vessel types<|>Comprises mainly smooth muscle cells and substantial amounts of elastic fibers<|>The smooth muscle cells regulate the diameter of the lumen, causing vasoconstriction (narrowing) or vasodilation (widening) in response to various stimuli<|>The external elastic lamina separates the tunica media from the tunica externa
• Tunica externa


  The outer covering of a blood vessel, consisting of elastic and collagen fibers<|>Contains nerves and tiny blood vessels (vasa vasorum) that supply the tissue of the vessel wall<|>Helps anchor the vessels to surrounding tissues
• Types of blood vessels

  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
• Arteries


  Carry blood away from the heart to other organs<|>Large, elastic arteries leave the heart and divide into medium-sized, muscular arteries that branch out into the various regions of the body<|>Medium-sized arteries then divide into small arteries, which in turn divide into still smaller arteries called arterioles
• Arterioles


  Small arteries that regulate the flow of blood into the capillary networks of the body's tissues<|>Have a thin tunica interna with a thin, fenestrated internal elastic lamina, and a tunica media consisting of one to two layers of smooth muscle cells
• As the arterioles enter a tissue, they branch into numerous tiny vessels called blood capillaries or simply capillaries
• Capillaries


  The thin walls of capillaries allow the exchange of substances between the blood and body tissues
• Venules


  Small veins that form as groups of capillaries within a tissue reunite
• Veins


  The blood vessels that convey blood from the tissues back to the heart
• Elastic arteries


  The largest arteries in the body, ranging from the garden hose-sized aorta and pulmonary trunk to the finger-sized branches of the aorta<|>Characterized by well-defined internal and external elastic laminae, along with a thick tunica media dominated by elastic fibers<|>Help propel blood onward while the ventricles are relaxing by functioning as a pressure reservoir
• As blood is ejected from the heart into elastic arteries


  Their walls stretch, easily accommodating the surge of blood
• As the elastic fibers recoil


  They convert stored (potential) energy in the vessel into kinetic energy of the blood, allowing blood to continue moving through the arteries even while the ventricles are relaxed
• Pressure reservoir


  The function of elastic arteries in helping propel blood onward while the ventricles are relaxing
• Arterioles


  Microscopic vessels that regulate the flow of blood into the capillary networks of the body's tissues
• Arterioles


  • Diameter range from 15 μm to 300 μm
  • Wall thickness is one-half of the total vessel diameter
• Tunica interna of arterioles

  Thin, with a thin, fenestrated (with small pores) internal elastic lamina
• Tunica media of arterioles


  Consists of one to two layers of smooth muscle cells having a circular orientation in the vessel wall
• Metarteriole


  The terminal end of the arteriole, tapers toward the capillary junction
• Precapillary sphincter


  The distal-most muscle cell at the metarteriole–capillary junction, monitors the blood flow into the capillary
• Tunica externa of arterioles

  Areolar connective tissue containing abundant unmyelinated sympathetic nerves
• Resistance vessels

  Arterioles play a key role in regulating blood flow from arteries into capillaries by regulating resistance
• Vasoconstriction


  Contraction of the smooth muscle of an arteriole, increases resistance and decreases blood flow into capillaries
• Vasodilation

  Relaxation of the smooth muscle of an arteriole, decreases resistance and increases blood flow into capillaries
• Capillaries


  The smallest of blood vessels, have diameters of 5–10 μm, form the U-turns that connect the arterial outflow to the venous return
• Capillaries


  • Approximately 20 billion in number, form an extensive network of short, branched, interconnecting vessels
  • The primary function is the exchange of substances between the blood and interstitial fluid
• Microcirculation


  The flow of blood from a metarteriole through capillaries and into a postcapillary venule
• Continuous capillaries


  The plasma membranes of endothelial cells form a continuous tube interrupted only by intercellular clefts
• Fenestrated capillaries


  The plasma membranes of the endothelial cells have many fenestrations (small pores) ranging from 70 to 100 nm in diameter
• Sinusoids


  Wider and more winding than other capillaries, have unusually large fenestrations and an incomplete or absent basement membrane
• Venules


  Drain the capillary blood and begin the return flow of blood back toward the heart
• Postcapillary venules


  The smallest venules, initially receive blood from capillaries
• Venules


  • Thin walls that do not readily maintain their shape
  • Drain capillary blood and begin the return flow of blood back toward the heart
• Postcapillary venules


  Smallest venules that initially receive blood from capillaries
• How materials move through capillary walls

  1. Diffusion

  2. Transcytosis

  3. Bulk flow