A&P3 - Week 6 - Blood Vessels Part. 1

9. What are the structure and function of a capillary? Define microcirculation. What is a capillary bed?

*3 Types of Capillaries:* *Continuous* ● Endothelial cell plasma membranes form a continuous tube *Fenestrated* ● Have many fenestrations or small pores *Sinusoids* ● Endothelial cells have unusually large fenestrations *Microcirculation* is the flow of blood from metartarteriole through capillaries and into postcapillary venule. *Capillary bed*, a network of 10-100 capillaries that arises from a single metarteriole.

1. Name the 5 main types of blood vessels. What are their functions?

*Arteries* - carry blood away from the heart to tissues and organs *Arterioles* - are smaller arteries that connect to capillaries. *Capillaries* - are the site of substance exchange between the blood and the body tissues. *Venules* - connect capillaries to larger veins. *Veins* - convey blood from the tissues back to the heart.

8. What are the functions of the *arteriole*? Why are they called *resistance vessels*? Define *metarteriole*. What is the function of *precapillary sphincter*?

*Artrioles* are abundant microscopic vessels that regulate blood flow to capillaries. The arterioles are called *resistance vessels* because they regulate blood flow from arteries into capillaries by regulating resistance. *Metarteriole* - is the terminal region of the arteriole Metarteriole has *precapillary sphincter* at the metarteriole - capillary junction which monitors blood flow into the capillary

21. Define blood flow. What is the relation of blood flow to the cross-sectional area of blood vessels?

*Blood flow* is the volume of blood flow that flows through a tissue in a given period of time. • The *velocity of blood flow* is inversely related to the *cross-sectional area of blood vessels*; blood flows most slowly where cross-sectional area is greatest. • Blood flow decreases from the aorta which has a cross-sectional area of 3-5 cm2 to arteries to capillaries which have a cross-sectional area of 4500-6000 cm2 and increases as it returns to the heart. • Slow rate in capillaries allows for exchange.

17. Define bulk flow. What are different outward and inward pressures controlling the bulk flow?

*Bulk Flow* ● Bulk flow is a passive process in which large numbers of ions, molecules, or particles in a fluid move together in the same direction *Ultrafiltration* occurs when pressure inside the capillary exceeds pressure outside and fluid is pushed out through the pores. *Reabsorption* occurs when inward-driving pressures exceed outward pressures and net movement of fluid back into the capillaries occurs.

16. What are the three mechanisms of *capillary exchange*? What are the substances exchange by each process?

*Diffusion* ● Substances such as *oxygen, carbon dioxide, glucose, amino acids*, and *some hormones* cross capillary walls via simple diffusion. *Transcytosis* ● Large, lipid-insoluble molecules (like insulin) cross capillary walls in vesicles via transcytosis *Bulk Flow* ● Bulk flow is a passive process in which large numbers of ions, molecules, or particles in a fluid move together in the same direction ○ Bulk flow occurs from an area of higher pressure to an area of lower pressure, and it continues as long as a pressure difference exists ● Bulk flow is more important for regulation of the relative volumes of blood and interstitial fluid

5. What are the structural characteristics of *elastic arteries*? What are their functions?

*Elastic Arteries* ● These are the largest arteries of the body. ● Largest diameter but walls are relatively thin ● Tunica media is dominated by elastic fibers. ● Includes aorta, pulmonary trunk, brachiocephalic, common carotid, subclavian arteries, and common iliac arteries ● Functions as pressure reservoir ● Help propel blood forward while ventricles relaxing ○ As blood is ejected from the heart during ventricular contraction, their walls stretch, easily accommodating the surge of blood. As they stretch, elastic fibers momentarily store mechanical energy,functioning as a pressure reservoir ○ During ventricular relaxation, the elastic fibers recoil so that the blood continues to flow ● Also known as conducting arteries- conduct blood from the heart to medium sized arteries.

6. What are the structural characteristics of *muscular arteries*? What are their functions?

*Muscular arteries* ● These are medium sized arteries, such as axillary and Femoral arteries ● Tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries ● Walls relatively are thick due to large amount of smooth muscle ● Capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow. ● Also called distributing arteries because they ultimately distribute to various organs ● Do not have the ability to recoil because of reduced amount of elastic tissue.

2. What are the 3 layers of blood vessel wall? Name important components of each layer.

*Tunica interna (intima*) ● Inner lining in direct contact with blood ● Component layers are endothelium, basement membrane, and internal elastic lamia ● It's inner most layer in called endothelium ○ Endothelium is continuous with the endocardial lining of the heart ○ Secrete chemical mediators that influence the contractile state of vessels overlying smooth muscle. *Tunica media* ● Made up of smooth muscle cells and elastic fibers ● Greatest variation among vessel types ● Smooth muscle diameter of lumen ○ Smooth muscle contraction causes vasoconstriction ○ Smooth muscle relaxation causes vasodilation ● Elastic fibers allows the vessels to stretch and recoil *Tunica externa* ● Consists of elastic and collagen fibers ● Contains numerous nerves and Vasa Vasorum ○ Vasa Vasorum are small blood vessels that supply blood to tissue of the vessel wall. ● Helps anchor vessel to surrounding tissue

14. Define Venous sinuses. Where are they located?

*Vascular (venous) sinuses* are veins with a thin endothelial wall with not smooth muscle to alter their diameters. Examples are the brain's dural venous sagittal sinus and the coronary sinus of the heart.

19. Define *vascular resistance*?What are the factors on which vascular resistance depends? Know the relation of each factor with vascular resistance. What is the total peripheral resistance?

*Vascular resistance* refers to the opposition to the blood flow as a result of friction between blood and the walls of the blood vessels which fact. Resistance depends on the size of the: ● blood vessel lumen ● blood viscosity ● total blood vessel length *Systemic vascular resistance* (also known as *total peripheral resistance*) refers to all of the vascular resistance is offered by systemic blood vessels; most resistance is in arterioles, capillaries, and venules due to their small diameters.

13. What is the characteristic of vein wall? Define valve of a vein. What is its function?

*Vein walls* in general, are very thin walls in relation to total diameter and not as distinct as arteries. *Valves of a vein* are folds on tunica interna forming flaplike cusps that aid in venous return (the volume of blood flowing back to the heart through the systemic veins) by preventing backflow.

20. Define venous return. What are the mechanisms which assist venous return? How they do that?

*Venous return* refers to the volume of blood flowing back to the heart through the systemic veins, occurs due to the pressure generated by contractions of the heart's left ventricle. Venus return is assisted by: — *Valves* — *Respiratory pump* — *Skeletal pump* *Valves* While you are standing at rest, both the venous valve closer to the heart (proximal valve) and the one farther from the heart (distal valve) in this part of the leg are open, and blood flows upward toward the heart. *Respiratory pump* Decreased thoracic pressure and increased abdominal pressure during inhalation , moves blood into thoracic veins and the right atrium. *Skeletal pump* Contraction of leg muscles compresses the vein and pushes blood through the proximal valve. At the same time, the distal valve in the uncompressed segment closes as some blood is pushed against it, Relaxation of the leg muscles cause proximal valve to close and distal valve to open. (Absent in immobilized patients)

4. Define *Vasa Vasorum*. Where is it located?

*vasa vasorum* (vas - vessel), or vessels to the vessels. They are easily seen on large vessels such as the aorta.

15. What is the percentage of blood distribution in the circulatory system at rest?Which blood vessels are blood reservoirs?

64% At rest, the largest portion of the blood is in *systemic veins* and *venules* (blood reservoirs)

11. Define a portal vein. What are the 2 portal veins present in the body?

Blood passes from one capillary network into another through a vein called *portal vein*. ● Hepatic portal vein. ● Hypophyseal portal system

3. What is the *endothelium*? What are its functions?

The *endothelium* is a thin layer of flattened cells that lines the inner surface of the entire cardiovascular system (heart and blood vessels). Endothelial cells are active participants in a variety of vessel-related activities, including physically influencing blood flow, secreting locally acting chemical mediators that influence the contractile state of the vessel's overlying smooth muscle, and assisting with capillary permeability.

7. Define *collateral circulation* . What's it's function? *Define end arteries*.

The alternative route of blood flow to a body part through an anastomosis is known as *collateral circulation*. Anastomoses may also occur between veins and between arterioles and venules. ● Blockage of only one pathway does not stop the circulation to the organ Arteries that do not anastomose are known as *end arteries*. ● Occlusion of an end artery interrupts the blood supply to a whole segment of an organ, producing necrosis of that segment.

12. What are the functions of *venules*?

● Thinner walls than arterial counterparts. ● Postcapillary venules are the smallest venules receiving blood from capillaries. ○ Form part of microcirculatory exchange unit with capillaries. ● Function as site exchange of nutrition and recent immigration of white blood cells. ● Muscular venules have thicker walls with 1 to 2 layers of smooth muscles.