Anatomy and Physiology
Anatomy and Physiology BIOH 113 - 01
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BIOH 112 - 01
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This 6 page Class Notes was uploaded by Meaghan Raw on Monday March 21, 2016. The Class Notes belongs to BIOH 113 - 01 at University of Montana taught by Heather Dawn Labbe (P) in Spring 2016. Since its upload, it has received 56 views. For similar materials see Human Form and Function II in Biological Sciences at University of Montana.
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Date Created: 03/21/16
BIOH 113 Chapter 20 Blood Vessels: - Blood is carried in a closed system of vessels that begins and ends at the heart - There are 3 major types o Arteries- carry blood away o Capillaries- directly serve the cells o Veins- carry blood back to the heart Structure: - Arteries and veins are composed of 3 tunics (layers) o Tunica interna o Tunica media o Tunica externa Tunica interna: Thin inner lining Has direct contact with the blood as it flows through the lumen (an interior opening) Has an endothelial layer that lines the lumen to allow smooth passage Tunica media: Relatively thick layer Smooth muscle and elastic fiber are found in this layer Regulated by the sympathetic nervous system Controls vasoconstriction/vasodilation Tunica externa: Outer covering which consists of elastic and collagen fibers Protects and reinforces the vessels Larger vessels contain vaso vasorum Arteries: Elastic: o Thick walled arteries near the heart (aorta and its major branches) o Have a large lumen which allows low resistance conduction of the blood o Contains elastin in all three tunics o Can withstand and control large fluctuations in blood pressure (BP) o Allows blood to flow fairly continuously through the body Muscular: o Distal to the elastic arteries o Deliver blood to body organs o Have a thick tunica media with more smooth muscle and less elastic tissue o Are active in vasoconstriction o Are called distributing arteries Arterioles: o Smallest arteries o Lead to capillaries o Control the flow of blood into capillary beds using vasodilation/constriction o Have a thin tunica interna with a thin fenestrated (holey) internal elastic lamina o Have a 2-layer tunica media o The tunica externa contains sympathetic nerves Capillaries: - Smallest blood vessels - Approximately 20 billion of them in the body - Walls are a thin tunica interna that is one cell thick - Only a single RBC can pass through at a time - There are 3 types: continuous, fenestrated, and sinusoids Continuous Capillaries: o Abundant in the skin and muscles o Have endothelial cells that provide an uninterrupted lining o Adjacent cells that are held together with tight junctions o Intercellular clefts of un-joined membranes allow the passage of fluids o Tight junctions are completely around the endothelium which contributes to the blood brain barrier Fenestrated Capillaries: o Found wherever active capillary absorption or filtrate formation occurs o Have an endothelium filled with pores o Have a greater permeability to solutes than other capillaries o Found in great quantity in the kidneys Sinusoid Capillaries: o Highly modified leaky, fenestrated o Have large lumens o Allow for large molecules to pass between the blood and surrounding tissues o Blood flows sluggishly Capillary Beds: o A microcirculation of interwoven networks of capillaries consisting of: Vascular shunts- met-arteriole, thoroughfare channel connecting an arteriole directly with a post capillary venule True capillaries- 10-100 per capillary bed; capillaries branch off the met- arteriole and return to the thoroughfare channel at the distal end of the bed o Blood Flow: Precapillary sphincter Cuff of smooth muscle that surrounds each true capillary Regulates blood flow into the capillary Blood flow is regulated by the vasometer nerves and local chemical conditions so that it can either bypass or flood the capillary bed Venous Systems: Venules: o Formed when capillary beds unite o Allow for fluids and WBC’s to pass from the blood stream to the tissues o Post capillary venules=smallest venules composed of endothelium and some connective tissue o Large venules have one or two layers of smooth muscle (tunica media) Veins: o Formed when the venules converge o Composed of 3 tunics, with a thin tunica media and a thick tunica externa consisting of collagen fibers and elastic networks o Blood reservoirs that contain 65% of the blood supply o Have a much lower blood pressure and thinner walls than the arteries o To return blood to the heart, veins have special adaptations Large diameter lumens which offer little resistance to flow Valves which prevent backflow of blood o Venous sinuses- specialized, flattened veins with extremely thin walls Vascular Anastomoses: o Merging blood vessels, more common in veins than arteries o Arterial anastomoses provide alternative pathways for the blood to reach a given body region If one branch is blocked the collateral channels can supply the area with adequate blood supply o Thoroughfare channels are examples of arteriovenous anastomoses Blood Flow: Poiseuille’s Law: o Actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given period: Flow = delta P divided by R Measured in mL per minute Relatively constant at rest Varies widely through individual organs according to immediate needs Resistance: o Opposition to flow o Three important sources Viscosity- thickness of the blood; remains relatively constant Length of the vessel- the longer the vessel the greater the resistance; remains relatively constant th Diameter of the vessel- resistance varies inversely with the 4 power of the vessel radius; changes are frequent and significantly alter peripheral resistance; small diameter arterioles are the major determinants of peripheral resistance Blood Pressure: - Pumping action of the heart generates blood flow through the vessels along a pressure gradient, always moving from higher to lower pressure areas - Pressure results when flow is opposed to resistance Systemic: o Highest in the aorta o Declines throughout the length of the pathway o Is 0 mm Hg as the vena cava enter the right atrium o Steepest change in BP occurs in the arterioles Arterial: o Reflects two factors of the arteries close to the heart: Elasticity Amount of blood o BP in elastic arteries is the pulsatile (pulses) o Systolic pressure- pressure exerted during ventricular contraction o Diastolic pressure- pressure at the lowest level during ventricular cycle o Pulse pressure- difference in systolic and diastolic pressures o Mean arterial pressure- pressure that propels blood to the tissues Capillary: o Ranges from 20-40 mm Hg o Low capillary pressure is desirable because high BP would rupture the fragile, thin walled capillaries o Low BP is sufficient to force filtrate out into the interstitial space and distribute nutrients, gases, and hormones from the blood to tissues Venous: o Steady and changes little during the cardiac cycle o 20 mm Hg Maintenance: o Requires cooperation of the heart, blood vessels, kidneys, and brain supervision o Main factors are: Cardiac output- determined by venous return and neural and hormonal controls Peripheral resistance Blood volume Blood pressure Controls of Blood Pressure: o Neural Baroreceptor reflexes Carotid sinus reflex Aortic reflex Chemoreceptor reflexes Carotid bodies Aortic bodies Both monitor changes in blood levels of oxygen, carbon dioxide, and hydrogen ions o Hormonal RAA Epi-and norepinephrine ADH ANP Chemicals: o Increase BP: Adrenal medulla hormones ADH Angiotensin II o Decrease BP: ANP Nitric Oxide Inflammatory responses Alcohol Tissue Perfusion: - Blood flow to the tissues o Delivers oxygen and nutrients o Removes wastes from the cells o Allows for gas exchange in the lungs Blood Flow Viscosity: - Changes as it travels through the systemic circuit - Inversely proportional to the cross sectional area Capillary Dynamics: - Substances can enter and leave by 3 main mechanisms o Diffusion: plasma solutes travel down the concentration gradient by passing through intracellular clefts or fenestrations o Transcytosis: Substances become enclosed in the endothelial cells and the exocytosed out the other side o Bulk Flow: Large numbers of solutes move together in the same direction based on a pressure gradient Circulatory Pathways: - The vascular system has two distinct circulations o Pulmonary: Short loop that runs from the heart to the lungs and back to the heart o Systemic: Routes the blood through a long loop from the heart through the body and back to the heart