Blood vessels

Anatomy and Physiology of blood vessels, from the unit cardiovascular system. It can be used by nursing students to understand the blood vessels.

1. Cardiovascular System: The Blood vessels Livson Thomas M.Sc. (N) College of Nursing Christian Hospital, Bissamcuttack Rayagada, Odisha 765019

2. 5 main types of blood vessels

3. Structure of a Blood Vessel The wall of a blood vessel consists of three layers or tunics Tunica Interna Tunica Media Tunica Externa

4. Tunica Interna / intima Forms the inner lining of a blood vessel Direct contact with blood Made up of endothelium cells (innermost) & basement membrane Theses smooth endothelial cells help in - Efficient flow of blood - Chemical mediators - Influence contraction of blood vessels

5. The basement membrane lies above the endothelium and- - provides physical support base for the endothelial layer - provides tensile strength due to network of collagen fibers - Stretching and recoiling - guiding cell movement during tissue repair of blood vessel walls - Facilitate diffusion of materials through interna and media

6. Tunica Media It is the middle muscular and connective tissue layer It varies according to different blood vessels It consist mainly of smooth muscle cells and elastic fibers The smooth muscles encircles the lumen (like a ring on finger) - to regulate the diameter of the lumen - Increase in diameter of lumen : Vasodilation - Decrease in diameter of lumen : Vasoconstriction (Sympathetic stimulation) Hence regulating the Blood pressure. Limits blood loss when a small arteriole or artery is damaged by vascular spasm

7. The outer covering of the blood vessel. It is made up of elastic and collagen fibers Consist of numerous nerves Tiny blood vessels that supply blood to tissue of vessels are called vasa vasorum also present in this layer The tunica externa also helps in anchoring the blood vessels to surrounding tissues Tunica Externa

8. Arteries The wall of the arteries have three layers The muscular and elastic tunica media is very thick to comply to the high pressure blood flow. Types: - Elastic arteries : Largest arteries in the body with large diameters. Consist more of elastic lamellae (e.g. Aorta, Pulmonary trunk, branches of aorta) - Muscular arteries: Tunica media contains more smooth muscles and fewer elastic fibres (3/4 th ). - Capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow. (e.g. femoral arteries, axillary arteries)

9. Means small arteries Microscopic vessels that regulate the flow of blood into capillary networks of the body’s tissues. Approximately 400 million arterioles Diameter : 15 μ m to 300 μ m Arterioles have thin tunica interna, porous internal elastic lamina Tunica media consist of 1 or 2 layers of smooth muscles Tunica Externa is made up of areolar CT and unmyelinated sympathetic nerves Arterioles play a major role in regulating blood flow from arteries into capillaries by regulating resistance (Resistance vessels). Arterioles

10. This is the smallest of blood vessels Diameter: 5 – 10 μ m The part that connects arterial flow to venous return. Numbers: 20 Billion Branched into interconnecting vessels which make contact the body’s cells. 3 types - Continuous (Intercellular clefts- CNS, lungs, muscle tissue and skin) - Fenestrated ( Small pores- kidney, villi of small intestine, eye, endocrine glands - Sinusoids (Very large pores- Red bone marrow, liver, spleen) Capillaries

11. Capillary Exchange Diffusion Transcytosis Bulk flow: Filtration & Reabsorption

12. These blood vessels have thin walls. They don’t maintain shape. Venules receive blood from capillaries are called postcapillary venules . - 10 to 50 μ m - very porous - Site for exchange of nutrients, waste and WBC Continuing it forms the muscular venules - 50 to 200 μ m - most distensible element of vascular system - Reservoir for accumulating large volumes of blood Venules

13. Veins in general have thin walls Size: 0.5 mm to 3 cm diameter Has all three layers Tunica interna and tunica media are very thin, and the tunica externa is the thickest layer. Veins lack the internal or external elastic laminae found in arteries, but the lumen is larger than artery. The average BP in veins is lower than arteries. Most of the veins contains valves, which are thin fold of Tunica interna that form flap like cusps. These valves prevent back flow of blood. Veins

14. Assignment List down the distinguishing features of the different blood vessels Elastic arteries Muscular arteries Arterioles Cappilaries Post capillary venules Muscular veins Veins

15. Blood distribution in the CVS at rest