Lesson 2 Chapter 22 – Blood Vessels

Lesson 2 Chapter 22 – Blood Vessels 1 Unit 8 Study Guide Blood Vessels Vessel Walls Both arteries and veins have three layers, but differ in thickness from one another. • Tunica interna – Composed of simple squamous epithelium (endothelium) & thin layer of connective tissue • Tunica media – Thickest layer – Composed of elastic fibers & smooth muscle tissue which cause vasoconstriction and vasodilation. • Tunica externa – Composed of connective tissue – Attaches vessel to surrounding connective tissue Lesson 2 Chapter 22 – Blood Vessels 2 Lesson 2 Chapter 22 – Blood Vessels  Arteries Arteries are elastic vessels that transport blood away from the heart.  Veins Veins are elastic vessels that transport blood to the heart.  Capillaries Capillaries are extremely small vessels located within the tissues of the body that transport blood from the arteries to the veins.  Sinusoids Sinusoids are extremely small vessels located within the liver, spleen and bone marrow.  Types of vessels  Arteries  Arterioles  Capillary beds  Capillaries  Venules  Veins 3 Arteries Walls of arteries are thicker and stronger than the walls of veins and capillaries. Artery walls contain large amounts of muscle and elastic tissue. Muscle and elastic tissue allows an artery to change its diameter. [Thicker media] – Elastic tissue allows the artery to expand when the heart pumps blood into it. – The blood exerts pressure against the vessel walls as it moves through the vessel, this is referred to as blood pressure. – When an artery widens, more blood can flow through it, blood pressure decreases. – When an artery contracts, less blood can flow through it, blood pressure increases. – By changing diameter, an artery helps regulate blood flow and pressure. – Have NO valves Arterioles – – – – – Tiny branches off of the arteries. Cannot be seen with unaided eye - microscopic Thinner, less muscular walls (compared to arteries) Feed blood into the capillaries. Narrower than arteries, but wider than capillaries. Lesson 2 Chapter 22 – Blood Vessels Capillary Beds: Collection of capillaries forming and interweaving network. Flow of blood from arteriole, through capillary bed to a venule is called microcirculation. Capillary beds consist off two types of vessels: 1. A vascular shunt: a short vessel that connects an arteriole and a venule at opposite ends of a capillary bed. Also called Metarteriole – thoroughfare channel. 2. True capillary: exchange vessels. A metarteriole: A vessel intermediate between an arteriole and a capillary. A thoroughfare channel: A channel continuous between a capillary and a venule. Precapillary sphincter: A small cuff of smooth muscle surrounding the beginning of each true capillary. It regulates the flow of blood into the capillary. Capillaries – Flow and pressure of blood is controlled by sphincters that are outside of the capillaries. – Microscopic vessels ~ 8 µm in diameter. – Erythrocytes (rbc’s) pass through in single file. – Walls are only one cell thick (to facilitate diffusion of materials/exchange). – No capillaries in epithelia, cornea, and lens of eye, cartilage. – Three types of capillaries: o Continuous Capillaries – found in skin and muscles, endothelial cell is continuous. o Fenestrated Capillaries – found in small intestine, kidneys and endocrine glands, their endothelial cell has pores and openings to allow greater permeability. o Sinusoidal Capillaries – found in liver, bone marrow, lymphoid tissue, they are leaky, highly permeable capillaries. Venules – Venules are the smallest veins – Carry blood from capillaries to larger veins – Tend to lack media (so no smooth muscle tissue) except in the largest venules 4 Lesson 2 Chapter 22 – Blood Vessels Veins – – – – – Larger inside diameter compared to arteries Take blood towards the heart Thinner, less muscular walls than arteries, but still 3 layers No stretching or contracting of walls except by external muscles. Contain valves to help return the blood to the heart (compensate for lower venous pressure, less muscle in walls, and large diameter). – Media is thin, thickest layer is adventitia. – Has venous valves. 5 Lesson 2 Chapter 22 – Blood Vessels 6 Edema Definition of Edema: Excessive fluid accumulation in interstitial tissues. An abnormal increase in interstitial fluid if filtration (fluid leaving the capillaries) exceeds reabsorption (fluid moving into capillaries) • • When edema results from excess filtration it is often due to: • increased blood pressure (hypertension) - in hydrostatic pressure at arteriolar end of capillary bed • increased permeability of capillaries When edema results from inadequate reabsorption, it is often due to: • decreased concentration of plasma proteins (lowers blood colloid osmotic pressure) –    inadequate synthesis or loss of plasma proteins (especially albumin) from liver disease, burns, malnutrition or kidney disease Exchange between blood and tissue depends on: o Characteristics of the transported molecule (size, shape, lipid solubility) o Characteristics of the capillary membrane (continuous, sinusoidal, fenestrated) o Capillary surface area o Opposing forces The direction of fluid movement depends on the difference between two opposing forces. These opposing forces are: o Hydrostatic pressure: is the force exerted by a fluid against the capillary wall. (pushing force) The hydrostatic pressure at the arterial and venous ends of a capillary bed are equal to the blood pressure at those locations. In the arterial end it is 30 mmHg while at the venous end it is 20mmHg. The hydrostatic pressure in the interstitial space is 0mHg. o Colloid Osmotic Pressure (Oncotic Pressure): is the pressure created by the presence of large molecules that can’t diffuse and are prevented from moving through the capillary membrane. These large molecules are plasma proteins such as albumin. They encourage osmosis and they draw water toward them. Because capillary blood has a high content of plasma proteins, the capillary has a high oncotic pressure of 25mmHg. Lesson 2 Chapter 22 – Blood Vessels 7 Fluid will leave the capillary if hydrostatic > oncotic pressure Fluid will enter the capillary if hydrostatic < oncotic pressure Map of the Circulatory System 1. Pulmonary circuit: 1. As blood leaves the right ventricle, it exits via the pulmonary trunk which branches into the left and right pulmonary arteries (carrying deoxygenated blood toward the lungs) 2. Oxygenated blood returning from the lungs to the heart does so via pulmonary veins which empty into the left atrium. NOTE: the pulmonary circuit is the only time arteries carry deoxygenated blood while veins carry oxygenated blood Lesson 2 Chapter 22 – Blood Vessels 2. Systemic circuit 1. As oxygenated blood leaves the left ventricle, it does so via the ascending aorta. The left and right coronary arteries branch off the ascending aorta. 2. The ascending aorta curves into the aortic arch, from which the brachiocephalic trunk (on the right), left common carotid, and left subclavian arteries arise. The brachiocephlic trunk divides into the right common carotid and the right subclavian artery. 3. The descending aorta gives rise to the thoracic aorta and the abdominal aorta. 4. The abdominal aorta eventually branches into the left and right iliac arteries. Clinical Application for Nurses Pulse taking sites [Check Canadian Jensen’s page 550-554 + know jugular veins ext. and int] 1. Carotid Either of two major arteries, one on each side of the neck, that carry blood to the head. 2. Brachial Upper arm artery. 3. Radial Radius of the arm or to the radial (lateral) aspect of the arm 4. Femoral The femur or to the thigh. 5. Popliteal Area behind the knee 6. Dorsalis pedis Dorsal of foot 7. Posterior tibialis Tibia Study application of venipuncture. Veins vs arteries. Commonly accepted locations. Venous valves-what they look like, what they do, and considerations for IV starts. 8 Lesson 2 Chapter 22 – Blood Vessels 9 Blood vessels in summary: I. Arteries contain three layers, or tunics: the interna, media, and externa. A. The tunica interna consists of a layer of endothelium, which is separated from the tunica media by a band of elastin fibers. B. The tunica media consists of smooth muscle. C. The tunica externa is the outermost layer. D. Large arteries, containing many layers of elastin can expand and recoil with rising and falling blood pressure. Medium and small arteries and arterioles are less distensible, and thus provide greater resistance to blood flow. II. Capillaries are the narrowest but the most numerous of the blood vessels. A. Capillary walls consist of just one layer of endothelial cells. They provide for the exchange of molecules between the blood and the surrounding tissues. B. The flow of blood from arterioles to capillaries is regulated by precapillary sphincter muscles. C. The capillary wall may be continuous, fenestrated, or discontinuous. III. Veins have the same three tunics as arteries, but they generally have a thinner muscular layer than comparably sized arteries. A. Veins are more distensible than arteries and can expand to hold a larger quantity of blood. B. Many veins have venous valves that ensure a one-way flow of blood to the heart. C. The flow of blood back to the heart is aided by contraction of the skeletal muscles that surround veins. The effects of this action is called the skeletal muscle pump.