Copyright 2010 Pearson Education, Inc. Blood Vessel Structure

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1 Blood Vessel Structure

2 Structure of Blood Vessel Walls Arteries and veins Tunica intima, tunica media, and tunica externa Lumen Central blood-containing space Capillaries Endothelium with sparse basal lamina

3 Tunica intima Endothelium Subendothelial layer Internal elastic lamina Tunica media (smooth muscle and elastic fibers) External elastic lamina Tunica externa (collagen fibers) Valve Lumen Artery Capillary network Lumen Vein Basement membrane Endothelial cells (b) Capillary Figure 19.1b

4 Tunics Tunica intima Endothelium lines the lumen of all vessels In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present

5 Tunics Tunica media Smooth muscle and sheets of elastin Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels

6 Tunics Tunica externa (tunica adventitia) Collagen fibers protect and reinforce Larger vessels contain vasa vasorum to nourish the external layer

7 Table 19.1 (1 of 2)

8 Elastic (Conducting) Arteries Large thick-walled arteries with elastin in all three tunics Aorta and its major branches Large lumen offers low-resistance Act as pressure reservoirs expand and recoil as blood is ejected from the heart

9 Muscular (Distributing) Arteries and Arterioles Distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle Active in vasoconstriction

10 Arterioles Smallest arteries Lead to capillary beds Control flow into capillary beds via vasodilation and vasoconstriction

11 Vein Artery (a) Figure 19.1a

12 Venules Formed when capillary beds unite Very porous; allow fluids and WBCs into tissues Postcapillary venules consist of endothelium and a few pericytes Larger venules have one or two layers of smooth muscle cells

13 Veins Formed when venules converge Have thinner walls, larger lumens compared with corresponding arteries Blood pressure is lower than in arteries Thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks Called capacitance vessels (blood reservoirs); contain up to 65% of the blood supply

14 Capillaries structure and function

15 Capillaries Microscopic blood vessels Walls of thin tunica intima, one cell thick Pericytes help stabilize their walls and control permeability Size allows only a single RBC to pass at a time

16 Capillaries In all tissues except for cartilage, epithelia, cornea and lens of eye Functions: exchange of gases, nutrients, wastes, hormones, etc.

17 Pericyte Red blood cell in lumen Intercellular cleft Endothelial cell Basement membrane Tight junction Pinocytotic Endothelial vesicles nucleus (a) Continuous capillary. Least permeable, and most common (e.g., skin, muscle). Figure 19.3a

18 Pinocytotic vesicles Red blood cell in lumen Endothelial cell Endothelial cell nucleus Basement membrane Tight junction Intercellular cleft Fenestration (pore) Figure (1 of 2)

19 Lumen Intercellular cleft Caveolae Pinocytotic vesicles Endothelial fenestration (pore) 4 Transport via vesicles or caveolae (large substances) 1 Diffusion through membrane (lipid-soluble substances) Basement membrane 2 Movement through intercellular clefts (water-soluble substances) 3 Movement through fenestrations (water-soluble substances) Figure (2 of 2)

20 Fenestrated Capillaries Some endothelial cells contain pores (fenestrations) More permeable than continuous capillaries Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)

21 Endothelial nucleus Basement membrane Tight junction Pinocytotic vesicles Red blood cell in lumen Fenestrations (pores) Intercellular cleft Endothelial cell (b) Fenestrated capillary. Large fenestrations (pores) increase permeability. Occurs in special locations (e.g., kidney, small intestine). Figure 19.3b

22 Sinusoidal Capillaries Fewer tight junctions, larger intercellular clefts, large lumens Usually fenestrated Allow large molecules and blood cells to pass between the blood and surrounding tissues Found in the liver, bone marrow, spleen

23 Tight junction Incomplete basement membrane Endothelial cell Red blood cell in lumen Large intercellular cleft Nucleus of endothelial cell (c) Sinusoidal capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen). Figure 19.3c

24 Capillary Beds Interwoven networks of capillaries form the microcirculation between arterioles and venules

25 Blood Flow Through Capillary Beds Precapillary sphincters regulate blood flow into true capillaries Regulated by local chemical conditions and vasomotor nerves (sympathetic division of ANS).

26 Precapillary sphincters Metarteriole Vascular shunt Thoroughfare channel True capillaries Terminal arteriole Postcapillary venule (a) Sphincters open blood flows through true capillaries. Terminal arteriole Postcapillary venule (b) Sphincters closed blood flows through metarteriole thoroughfare channel and bypasses true capillaries. Figure 19.4

27 Blood Composition and Function

28 Blood Composition Blood: a fluid connective tissue composed of Plasma Formed elements Erythrocytes (red blood cells, or RBCs) Leukocytes (white blood cells, or WBCs) Platelets

29 Blood Composition Hematocrit Percent of blood volume that is RBCs 47% ± 5% for males 42% ± 5% for females

30 1 Withdraw blood and place in tube. 2 Centrifuge the blood sample. Formed elements Plasma 55% of whole blood Least dense component Buffy coat Leukocytes and platelets <1% of whole blood Erythrocytes 45% of whole blood Most dense component Figure 17.1

31 Physical Characteristics and Volume Sticky, opaque fluid Color scarlet to dark red ph C (100.4F) ~8% of body weight Average volume: 5 6 L for males, and 4 5 L for females

32 Functions of Blood 1. Distribution of O 2 and nutrients to body cells Metabolic wastes to the lungs and kidneys for elimination Hormones from endocrine organs to target organs

33 Functions of Blood 2. Regulation of Body temperature by absorbing and distributing heat Normal ph using buffers Adequate fluid volume in the circulatory system

34 Functions of Blood 3. Protection against Blood loss Plasma proteins and platelets initiate clot formation Infection Antibodies Complement proteins WBCs defend against foreign invaders

35 Blood Plasma 90% water Proteins are mostly produced by the liver 60% albumin 36% globulins 4% fibrinogen

36 Blood Plasma Nitrogenous by-products of metabolism lactic acid, urea, creatinine Nutrients glucose, carbohydrates, amino acids Electrolytes Na +, K +, Ca 2+, Cl, HCO 3 Respiratory gases O 2 and CO 2 Hormones

37 Formed elements Differential WBC count (All total ,800/l) Platelets Leukocytes Erythrocytes Granulocytes Neutrophils (50 70%) Eosinophils (2 4%) Basophils (0.5 1%) Agranulocytes Lymphocytes (25 45%) Monocytes (3 8%) Figure 17.9

38 Table 17.2 (1 of 2)

39 Table 17.2 (2 of 2)