TOPIC NAME: ����BLOOD VESSLE AND ITS TYPES

Contents

• Arteries
• Veins
• Capillary
• Venioles
• Structure
• Function
• Blood distribution
• Capillary Exchange

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• Diffusion
• Blood Flow
• Starling Law

Structure and function of blood vessels

• 5 main types
• Arteries – carry blood AWAY from the heart
• Arterioles-- artries divide to form arteriole
• Capillaries – site of exchange
• Venule -- veins divide to form venule
• Veins – carry blood TO the heart

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Basic structure

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• 3 layers or tunics
1. Tunica interna (intima)
2. Tunica media
3. Tunica externa
• Modifications account for 5 types of blood vessels and their structural/ functional differences

Structure

• Tunica interna (intima)
• Inner lining in direct contact with blood
• Endothelium continuous with endocardial lining of heart
• Active role in vessel-related activities
• Tunica media
• Muscular and connective tissue layer
• Greatest variation among vessel types
• Smooth muscle regulates diameter of lumen
• Tunica externa
• Elastic and collagen fibers
• Vasa vasorum
• Helps anchor vessel to surrounding tissue

Arteries

• All arteries carry oxygenated blood except pulmonary artery.
• There is no valve is present in them.
• Aorta-a largest artery have diameter range from 10 to 25mm.
• 3 layers of typical blood vessel
• Thick muscular-to-elastic tunica media
• High compliance – walls stretch and expand in response to pressure without tearing
• Vasoconstriction – decrease in lumen diameter
• Vasodilation – increase in lumen diameter

Elastic Arteries

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• Largest arteries
• Largest diameter but walls relatively thin
• Function as pressure reservoir
• Help propel blood forward while ventricles relaxing
• Also known as conducting arteries – conduct blood to medium-sized arteries

Arteries

• Muscular arteries
• Tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries
• Walls relatively thick
• Capable of great vasoconstriction/ vasodilatation to adjust rate of blood flow
• Also called distributing arteries
• Anastomoses
• Union of the branches of 2 or more arteries supplying the same body region
• Provide alternate routes – collateral circulation

Arterioles

• Abundant microscopic vessels
• Metarteriole has precapillary sphincter which monitors blood flow into capillary
• Sympathetic innervation and local chemical mediators can alter diameter and thus blood flow and resistance
• Resistance vessels – resistance is opposition to blood flow
• Vasoconstriction can raise blood pressure

Capillaries

• Diameter range between 8 to 10 micrometer
• Smallest blood vessels connect arterial outflow and venous return
• Microcirculation – flow from metarteriole through capillaries and into postcapillary venule
• Exchange vessels – primary function is exchange between blood and interstitial fluid
• Lack tunica media and tunica externa
• Substances pass through just one layer of endothelial cells and basement membrane
• Capillary beds – arise from single metarteriole
• Vasomotion – intermittent contraction and relaxation
• Throughfare channel – bypasses capillary bed

Arteries, Capillaries, and Venule

Types of Capillaries

• 3 types
• Continuous
• Endothelial cell membranes from continuous tube
• Fenestrated
• Have fenestrations or pores
• Sinusoids
• Wider and more winding
• Unusually large fenestrations

Cont….

• Portal vein – blood passes through second capillary bed
• Hepatic or hypophyseal
• Venules
• Thinner walls than arterial counterparts
• Postcapillary venule – smallest venule
• Form part of microcirculatory exchange unit with capillaries
• Muscular venules have thicker walls with 1 or 2 layers of smooth muscle

Veins

• All veins carry deoxygenated blood except pulmonare vein.
• normal portal vein diameter is 7 to 15mm.
• Structural changes not as distinct as in arteries
• In general, very thin walls in relation to total diameter
• Same 3 layers
• Tunica interna thinner than arteries
• Tunica interna thinner with little smooth muscle
• Tunica externa thickest layer
• Not designed to withstand high pressure
• Valves – folds on tunica interna forming cusps
• Aid in venous return by preventing backflow

Venous Valves

Blood Distribution

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• Largest portion of blood at rest is in systemic veins and venules
• Blood reservoir
• Venoconstriction reduces volume of blood in reservoirs and allows greater blood volume to flow where needed

Capillary exchange

• Movement of substances between blood and interstitial fluid
• 3 basic methods
1. Diffusion
2. Transcytosis
3. Bulk flow

Diffusion

• Most important method
• Substances move down their concentration gradient
• O₂ and nutrients from blood to interstitial fluid to body cells
• CO₂ and wastes move from body cells to interstitial fluid to blood
• Can cross capillary wall through intracellular clefts, fenestrations or through endothelial cells
• Most plasma proteins cannot cross
• Except in sinusoids – proteins and even blood cells leave
• Blood-brain barrier – tight junctions limit diffusion

Transcytosis

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• Small quantity of material
• Substances in blood plasma become enclosed within pinocytotic vessicles that enter endothelial cells by endocytosis and leave by exocytosis
• Important mainly for large, lipid-insoluble molecules that cannot cross capillary walls any other way

Bulk Flow

• Passive process in which large numbers of ions, molecules, or particles in a fluid move together in the same direction
• Based on pressure gradient
• Diffusion is more important for solute exchange
• Bulk flow more important for regulation of relative volumes of blood and interstitial fluid
• Filtration – from capillaries into interstitial fluid
• Reabsorption – from interstitial fluid into capillaries

STARLINGS LAW:��

Starling’s law of the cappilaries state’s that the movement of the movement of fluid between cappiolaries and intestinal fluid is due to net effect of all four of the pressures described. An equation can be used to calculate the NFP and determine the direction of fluid movement.

NFP=(BHP+IFCOP)-(BCOP+IFHP)

BHP and IFCOP promote the movement of fluid out of the cappilaries or reabsorption.If the pressure that promote filtration are greater than the pressure that promote reabsorption the NFP will have a

CONTINUE...

positive value.If the pressure that promote reabsorption are greater the NFP will have a negative value.Under normal conditions in most tissues the rate of filtration and reabsorption is due to BHP.

BHP=35mmHg

IFHP=0mmHg

BCOP=26mmHg

IFCOP=1mmHg

NFP=(35mmHg+1mmHg)-(26mmHg+0mmHg)

CONTINUE.....

NFP=+10mmHg

Because the value of NFP is positive, filtration occours at the atrial end of the cappilaries. Moving along the cappilary the BHP becomes lower as blood moves along the pressure gradient of the vascular system but other three pressure will not fluctate.At midpoint of cappilary the filtration pressure are equal to reabsorption pressure. Moving away from the midpoint toward the venous end of the cappilary the BHP dips down below the BCOP. Near the junction of the cappilaries with venules the BHP is about 16mmHg.

NFP=(16mmHg+1mmHg)-(26mmHg+0mmHg)

NFP=-9mmHg

Dynamics of Capillary Exchange

D/W

Prepared by : Rasheeqa Shafqat