1 Topics to be addressed: Blood Anatomy of Blood Vessels Anatomy of the Heart The Conduction System The Cardiac Cycle Cardiodynamics Blood Flow and its Regulation Adaptation and Disorders of the Cardiovascular System Overview of the Cardiovascular System

2 Blood Vessels : Anatomy To understand the construction of a blood vessel, let’s first review the important tissue types involved. Endothelium Recall that epithelial cells occur in sheets, with junctions (tight junctions and desmosomes) tightly binding each cell to its neighbors. A simple squamous epithelium contains a single layer of flat cells; in blood vessels this simple squamous epithelium is commonly called the endothelium.

3 Blood Vessels : Anatomy Connective tissue Connective tissue is usually located between layers and on the outside of organs; nerves travel in the connective tissue layers of an organ.

4 Blood Vessels : Anatomy Smooth muscle Smooth muscle is so named because it does not have visible striations in its cytoplasm. It does contain actin and myosin, and contracts in the presence of calcium. When the smooth muscle layer contracts, the vessel diameter narrows (vasoconstriction). When the smooth muscle layer relaxes, the vessel diameter increases (vasodilation). Nature Neuroscience Uvahealth.cm

5 Blood Vessels : Anatomy Most blood vessels have a 3-layered wall (3 tunics) Tunica Intima : innermost lined by the endothelium supported by connective tissue (collagen) Tunica Media : middle layer smooth muscle with various amounts of elastic fibers Tunica Externa : outer layer connective tissue

6 Nerves innervate blood vessels, but are seldom seen in images as they are diffusely spread out within the muscle layer. These nerves are important for controlling blood vessel diameter.

7 Blood Vessels : Anatomy Most blood vessels have a 3-layered wall Arteries have stronger, thicker walls than the vein of the same size; arteries generally contain more smooth muscle and often more elastic fibers.

8 Vessels can be Categorized by Size Blood vessels closest to the heart have the largest diameter There is little smooth muscle in most veins

9 Vessels can be Categorized by Function Capacitance Vessels: Because veins have little muscle and few elastic fibers in their wall, they have little ability to resist stretch, and often hold much of the circulating blood Elastic Arteries: The largest arteries closest to the heart contain a lot of elastic fibers, and swell with blood each time the heart pumps Muscular Arteries: Smaller diameter arteries distributing to organs Resistance Vessels: Arterioles are small diameter with a few layers of smooth muscle; contraction or relaxation of that muscle creates great changes in diameter, and thus great changes in resistance to blood flow. Exchange vessels Capillaries are the only vessels where materials move through the vessel wall

10 Distribution of Blood 30–35% of blood volume contained in heart, arteries and capillaries 60–65% of blood in the venous system

11 Formed from foldings of tunica intima Skeletal muscle activity around deep veins compresses veins and pushes blood toward heart : the “muscular pump” Veins have valves to prevent blood from flowing backward

12 Venous Valve Failure Allows Blood to Pool in Veins and Creates Distension in the Vein Walls Varicose VeinsHemorrhoids are distensions of anal veins Valve failure may be due to genetic factors or to locally high venous pressure

13 Blood Vessels : Anatomy of Capillaries A capillary is little more than a tube of endothelial cells supported by a basal lamina. The thin wall allows exchange of materials (nutrients, wastes, oxygen and carbon dioxide) between the bloodstream and the tissues Capillaries are thus called the exchange vessels

14 How substances pass through a capillary wall Through the epithelial cell membrane diffusion (passive) pinocytosis (active) Though pores (fenestrations) in the epithelial cell membranes (size filter) Through spaces between epithelial cells (bulk flow)

15 There are 3 types of Capillaries based on the degree of “leakiness” 1. Continuous Capillaries Have complete endothelial lining – cells tightly bound to one another Are found in all tissues except epithelia and cartilage Permit diffusion of water, small solutes, and lipid-soluble materials Block RBC and plasma proteins Specialized continuous capillaries are found in the CNS and create the “blood-brain barrier”

16 There are 3 types of Capillaries based on the degree of “leakiness” 2. Fenestrated Capillaries Have small pores in endothelial lining Permit rapid exchange of water and larger solutes between plasma and interstitial fluid Found in areas requiring more exchange Choroid plexus Endocrine organs Kidneys Intestinal tract

17 There are 3 types of Capillaries based on the degree of “leakiness” 3. Sinusoidal Capillaries Have large gaps between adjacent endothelial cells Permit free exchange of water and large plasma proteins between blood and interstitial fluid Found in: Liver Spleen Bone marrow Endocrine organs Phagocytic cells monitor blood at sinusoids

18 Pre-capillary Sphincters Arterioles often have areas of extra muscle in their wall as they branch into a capillary network; these sphincters contract to decrease blood flow into a capillary bed

19 Arteries and veins generally parallel one another and share the same names.

20 The Systemic Arteries The single vessel leaving the left side of the heart is the Aorta Parts of the aorta include: The aortic arch The thoracic aorta (in the thoracic cavity) The abdominal aorta (below the diaphragm)

21 The Systemic Veins Blood returns to the right side of the heart through two large unpaired veins. Above the diaphragm, blood returns through the superior vena cava Below the diaphragm, blood returns through the inferior vena cava

22 Pulmonary and Systemic Circulation Patterns General Functional Patterns –Peripheral artery and vein distribution is the same on right and left (ie: is symmetrical), except near the heart –The same vessel may have different names in different locations –Tissues and organs usually have multiple arteries and veins; vessels may be interconnected with anastomoses

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