Blood Vessels Part I Anatomy 4 PDF

The Cardiovascular System: Anatomy of Blood Vessels Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Video: Why This Matters Understanding how the body controls blood pressure helps to measure a patient’s blood pressure accurately Copyright...

The Cardiovascular System: Anatomy of Blood Vessels Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Video: Why This Matters Understanding how the body controls blood pressure helps to measure a patient’s blood pressure accurately Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Angiogram of the Brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Blood Vessel Structure and Function Blood vessels: delivery system of dynamic structures that begins and ends at heart Arteries: carry blood away from heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus Capillaries: direct contact with tissue cells; directly serve cellular needs Veins: carry blood toward heart; deoxygenated except for pulmonary circulation and umbilical vessels of fetus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall All vessels consist of a lumen, central blood-containing space, surrounded by a wall Walls of all vessels, except capillaries, have three layers, or tunics(coverings): 1. Tunica intima 2. Tunica media 3. Tunica externa Capillaries – Endothelium with sparse basal lamina Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall 1. Tunica intima  Innermost layer that is in “intimate” contact with blood  Endothelium: simple squamous epithelium that lines lumen of all vessels – Continuous with endocardium – Slick surface reduces friction  Subendothelial layer: connective tissue basement membrane – Found only in vessels larger than 1 mm Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall 2. Tunica media  Middle layer composed mostly of smooth muscle and sheets of elastin  Sympathetic vasomotor nerve fibers innervate this layer, controlling: – Vasoconstriction: decreased lumen diameter – Vasodilation: increased lumen diameter  Bulkiest layer responsible for maintaining blood flow and blood pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall 3. Tunica externa  Outermost layer of wall  Also called tunica adventitia (coming from outside)  Composed mostly of loose collagen fibers that protect and reinforce wall and anchor it to surrounding structures  Infiltrated with nerve fibers, lymphatic vessels – Large veins also contain elastic fibers in this layer  Vasa vasorum (vessels of the vessels): system of tiny blood vessels found in larger vessels – Function to nourish outermost external layer Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Arteries Arteries divided into three groups, based on size and function – Elastic arteries – Muscular arteries – Arterioles Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Elastic Arteries Elastic arteries: thick-walled with large, low-resistance lumen – Aorta and its major branches: also called conducting arteries because they conduct blood from heart to medium sized vessels Elastin found in all three tunics, mostly tunica media Contain substantial smooth muscle, but inactive in vasoconstriction Act as pressure reservoirs that expand and recoil as blood is ejected from heart – Allows for continuous blood flow downstream even between heartbeats Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Muscular Arteries Elastic arteries give rise to muscular arteries Also called distributing arteries because they deliver blood to body organs – Diameters range from pinky-finger size to pencil-lead size Account for most of named arteries Have thickest tunica media with more smooth muscle, but less elastic tissue – Tunica media sandwiched between elastic membranes Active in vasoconstriction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Arterioles Arterioles: smallest of all arteries – Larger arterioles contain all three tunics – Smaller arterioles are mostly single layer of smooth muscle surrounding endothelial cells Control flow into capillary beds via vasodilation and vasoconstriction of smooth muscle Also called resistance arteries because changing diameters change resistance to blood flow Lead to capillary beds Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillaries Microscopic vessels; diameters so small only single RBC can pass through at a time Walls just thin tunica intima; in smallest vessels, one cell forms entire circumference Pericytes: spider-shaped stem cells help stabilize capillary walls, control permeability, and play a role in vessel repair Supply almost every cell, except for cartilage, epithelia, cornea, and lens of eye Functions: exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Types of Capillaries All capillary endothelial cells are joined by tight junctions with gaps called intercellular clefts – Allow passage of fluids and small solutes Three types of capillaries 1. Continuous capillaries  Abundant in skin, muscles, lungs, and CNS – Continuous capillaries of brain are unique Form blood brain barrier, totally enclosed with tight junctions and no intercellular clefts Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Types of Capillaries 2. Fenestrated capillary  Found in areas involved in active filtration (kidneys), absorption (intestines), or endocrine hormone secretion  Endothelial cells contain Swiss cheese–like pores called fenestrations (windows) – Allow for increased permeability – Fenestrations usually covered with thin glycoprotein diaphragm Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Types of Capillaries 3. Sinusoidal capillaries  Fewer tight junctions; usually fenestrated with larger intercellular clefts; incomplete basement membranes – Usually have larger lumens  Found only in the liver, bone marrow, spleen, and adrenal medulla  Blood flow is sluggish—allows time for modification of large molecules and blood cells that pass between blood and tissue  Contain macrophages in lining to capture and destroy foreign invaders Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Capillary Beds Capillary bed: interwoven network of capillaries between arterioles and venules Microcirculation: flow of blood through bed from arteriole to venule Terminal arteriole: branch off arteriole that further branches into 10 to 20 capillaries (exchange vessels) that form capillary bed – Exchange of gases, nutrients and wastes from surrounding tissue takes place in capillaries Capillaries then drain into postcapillary venule Flow through bed controlled by diameter of terminal arteriole and upstream arterioles – Arteriole and terminal arteriole dilated when blood needed; constricted to shunt blood away from bed when not needed Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Anatomy of a Typical Capillary Bed Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Capillary Beds Capillaries found in serous membranes of intestinal mesenteries have two additional features that form a special arrangement of capillaries: 1. Vascular shunt: channel that directly connects arteriole with venule (bypasses true capillaries) - consists of metarteriole and thoroughfare channel 2. Precapillary sphincter: cuff of smooth muscle surrounding each true capillary that branches off metarteriole; acts as valve regulating blood flow into capillary bed Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Anatomy of a Special (Mesenteric) Capillary Bed Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Veins Veins: carry blood toward the heart Formation begins when capillary beds unite in postcapillary venules and merge into larger and larger veins Venules Have all tunics, but thinner walls with large lumens compared with corresponding arteries Large lumen and thin walls make veins good storage vessels – Called capacitance vessels (blood reservoirs) because they contain up to 65% of blood supply Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Veins Blood pressure lower than in arteries, so adaptations ensure return of blood to heart – Large-diameter lumens offer little resistance Other adaptations – Venous valves  Prevent backflow of blood  Most abundant in veins of limbs – Venous sinuses  Flattened veins with extremely thin walls  Composed only of endothelium  Examples: coronary sinus of the heart and dural sinuses of the brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Generalized Structure of Arteries, Veins, and Capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Relative Proportion of Blood Volume Throughout the Cardiovascular System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Anastomoses (union of parts) Vascular anastomoses: interconnections of blood vessels Arterial anastomoses: provide alternate pathways (collateral channels) to ensure continuous flow, even if one artery is blocked – Common in joints, abdominal organs, brain, and heart; none in retina, kidneys, spleen Arteriovenous anastomoses: shunts in capillaries; example: metarteriole–thoroughfare channel Venous anastomoses: so abundant that occluded veins rarely block blood flow Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Circulatory Routes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved