81 terms

Chapter 21

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Arterioles
are smallest branches of arteries
Capillaries
*Are the smallest blood vessels
*Location of exchange between blood and interstitial fluid
*have small diameter an thin walls
Venules
*Collect blood from capillaries
*Very small Veins
Pulmonary trunk
Carries blood from right ventricle to pulmonary circulation
Aorta
Carries blood from left ventricle to systemic circulation
3 Layers of Arteries and Veins
*tunica intima
*tunica media
*tunica externa
Tunica Intima
* Intermost Layer
-includes the endothelial lining
-connective tissue layer
Tunica Media
* middle layer
Exterman Elastic Membrane
* sperates Tunica Media layer from the tunica Externa layer
Tunica Externa
*Is outer layer
*Contains connective tissue sheath
*Anchors vessel to adjacent tissues
Tunica Externa in Arteries
*Contains collagen and elastic fibers
Tunica Externa in Veins
*Contains elastic fibers and smooth muscle cells
Vasa Vasorum
*small arteries and veins
*located in walls of large arteries and veins
*supply cells of tunica media and tunica externa
Arteries
*Carry Blood away from the heart
*have thinker walls and higher blood pressure.
*collapsed arteries have small round lumen.
*Arteries are more elastic
*lining does not contract
Veins
*Return Blood to Heart
*has a large flat lumen
*lining contracts
*Have valves
*Collect blood from capillaries in tissues and organs
*Returns blood to heart
*Carries Low BP
*Thinner walls than arteries
*Veins stretch more than arteries
Arteries and pressue: Elasticity
This is what allows arteries to absorb pressure waves that come with each heartbeat.
Contractility
*Arteries change diameter
*Controlled by sympathetic division of the ANS(autonomic nervous system)
Vasoconstriction
*The contraction of arterial smooth muscle of the ANS
*Controlled by adrenergic nerves (NE)
Vasodilation
*relaxation of arterial smooth muscle
*durning vasodilation the lumen enlarges
*Conrolled by cholinergic nerves (NO)
Vasoconstriction & Vasodilation
Affects
*Afterload on heart
*peripheral blood pressure
*capillary blood flow
Arteries change from heart to capillaries
From elastic arteries to muscular arteries to arterioles
Elastic Arteries
AKA Conducting Arteries
*Large Vessel EX: pulmonary trunk, Aorta...
*Tunica media has many elastic fibers and few muscle cells
*Elasticitty evens out pulse force
Muscular Arteries
AKA Distribution Arteries
*Are medium sized ( most arteries)
* Tunica Media has many muscle cells
Aerioles
*Small
Have little or no tunica externa
Aneurysm
*A bulge in an arterial wall
*caused by weak spot in elastic fibers
*Pressure may rupture vessel
Capillary Function
*Materials dffuse between blood and interstitial fluid
Capillary Structure
* Endothelial tube: inside thin basal lamina
*does not contain tunica media nor tunica externa
2 types of Capillaries
1-Continuous Capillaries
2-Fenestrated Capillaries
Continuous Capillaries
*has a complete endothelial lining
*is found in all tissue except epithelial cartilage
*permits diffusion of H2O, small solutes, lipid-soluble materials
*Blocks blood cells
Fenestrated Capillaries
*have pores in endothelial lining
*permit rapid exchange of H2O and large solutes between plasma and interstitial fluid
*Found in choroid plexus, endocrine organs, kidneys, and intestinal tract
Sinusoids
*Areas in liver, spleen, bone marrow,and endocrine organs
*has gaps between adjacent endothelial cells
*Permits free exchange of H2O and large plasma proteins between blood and interstitial fluid
*Phagocytic cells monitor blood at sinusoids
Capillary Network
Capillaries networks, capillary bed, or capillary plexus Connect 1 arteriole and 1 Venule
Thoroughfare Channels
*direct capillary connection between arterioles an venules
Metarterioles
are the where the Thoroughfare Channels are controlled by smooth muscle segments
Collaterals
*Are Multiple arteries that contribute to 1 capillary bed.
*Allow circulation if 1 artery is blocked
Arterial Anastomosis
* Fusion of 2 collateral arteries
Arteriovenous Anastomoses
*Direct connections between arterioles and venules
*Bypass the Capillary bed.
Capillary Sphincter
*Guards entrance to each capillary
*Opens and Closes causing capillary blood flow in pulses
Vasomotion
*Contraction and relaxation of capillary sphincters
*Causes blood flow in capillary beds to constantly change routes
3 Vein Catergories
1-Venules
2-Medium-Sized Veins
3-Large Veins
Medium-Sized Veins
*Thin tunica media and few smooth muscle
*Tunica externa with longitudinal bundles of elastic fibers
Large Veins
*Have all 3 tunica layers
*thick tunica externa
*thin tunica media
Blood Distribution
Heart, arteries, and capillaries 30-35% of blood volume
Venous system 60-65%
1/3 of venous blood in large venous networks of the liver, bone marrow, and skin
Capacitance
*Ability to Stretch
* veins response to blood loss
Cardiac Output
Determined by pressure and resistance in the cardiovascular system
Pressure Gradient
The difference between pressure at the heart & pressure at peripheral capillary beds :ΔP
Blood Pressure (BP)
Arterial Pressure (mmHg)
Capillary Hydrostatic Pressure (CHP)
Pressure within the capillary beds
Venous Pressure
Pressure in venous system
Resistance
*resistance increases exponentially as diameter increases
*Depends on vessel length and vessel diameter
Hypertension
Abnormally high BP Greater than 140/90
Hypotension
Abnormally Low BP
Elastic Rebound
Arterial walls stretch during systole, rebound during diastole, keep blood moving during diastole.
Venous Return
*Amount of blood arriving at right atrium each minute.
* is assisted by muscular compression of peripheral veins
Compression of skeletal muscles
Push blood toward heart ( 1-way valve)
Diffusion
*Movement of ions or molecules from high to low concentration along concentration gradient
5 Routes
1-H2O,ions, & small molecules diffuse between adjacent endothelial cells or fenestrated capillaries
2-some ions (Na+,K+,Ca2+,Cl-) diffuse through channels in cell membranes
3-Large H2O soluble compounds pass through fenestrated capillaries
4-Lipid and Lipid Soluble materials such as O2 and Co2 diffuse through endothelial cell membranes
5-Plasma Proteins
Capillary Exchange
At arterial end of capillary fluid moves out of capillary into interstitial fluid and at venous end of capillary fluid moves into capillary out of the interstitial fluid
Hemorrhagining
Reduces CHP NFP increases reabsorption of interstitial fluid (recall of fluids)
3 short term responses :
increase cardiac output vasoconstriction improves venous return and hormonal effects
Dehydration
*increases BCOP
*Accelerates reabsorption
Increase in ChP or BCOP
*fluid moves out of blood and build up in peripheral tissue (edema)
If BP is too high
Vessel walls stiffen and capillary beds may rupture (aneurism)
If BP is too low
Vessels collapse,Blood stops, and tissue dies
Tissue perfusion
Blood flow through the tissues carries O2 and nutrients to tissue/organs carries CO2 an wastes away
*is affected by cardiac output peripheral resistance and BP
3 Regulatory Mechanisms that control cardiac output and BP
1-Autoregulation
2-Nueral Mechanisms
3-Endocrine Mechanism
Autoregulation
causes immediate localized homeostatic adjustments...
Neural mechanism
Responds quickly to changes at specific sites
Endocrine mechanism
direct long term changes
Vasoldilators
dilate pre capillary sphincters
Local Vasoconstrictors
accelerate blood flow at tissue level. constricts precapillary sphincters
* affect a single capillary bed
Cardioacceleratory Center
increases cardiac output
Cardioinhibitory Center
Reduces cardiac output
Baroreceptor Reflexes
respond to changes in BP
*stretches receptors in wall of carotid sinuses, aortic sinuses, right atrium
Chemoreceptor Reflexes
Respond to changes in chemical composition partially Ph and dissolved gases
When BP rises CV centers
Decrease cardiac output and cause peripheral vasodilation
When PB falls CV centers
increases cardiac output causes peripheral vasoconstriction
ADH ( antidiuretic hormone)
*Elevates BP
*Reduces H2O loss at kidneys
-Responds to low blood volume
-high plasma osmotic concentration
-Circulating angiotensin 2
Angiotensin 2
Responds to the fall in renal BP
Stimulates: aldosterone production,ADH, production,thirst,cardiac output, and peripheral vasoconstriction
Erythroproietin (EPO)
Released at kidneys
Responds to low BP and Low O2 content
Stimulates red blood cell production
Atrial Natriuretic Peptide (ANP)
Produced by cells in right atrium
Brain Natriuretic Peptide (BNP)
Produced by ventricular muscle cells
3 Effects of Light Exercise
1-Extensive vasodilation increased circulation
2-Venous return increases with muscle contractions
3-cardiac output rises due to rise in venous return