A&P 2- Blood Vessels and Circulation

Describe hydrostatic pressure and colloid osmotic pressure

hydrostatic pressure: drives fluid out of capillary -high on arterial end of capillary, low on venous end -physical force exerted against a surface by a liquid (blood pressure) colloid osmotic pressure: draws fluid into capillary -results from plasma proteins (albumin)-more in blood

Describe how autoregulation controls blood flow to tissues

the ability of tissues to regulate their own blood supply -metabolic theory of autoregulation: if tissue is inadequately perfused, wastes accumulate, stimulating vasodilation which increases perfusion -bloodstream delivers oxygen and removes metabolites -when wastes are removed, vessels constrict

Describe the role of arterioles in regulating tissue blood flow and systemic arterial blood pressure

-Arterioles are most significant point of control over peripheral resistance and flow -On proximal side of capillary beds and best positioned to regulate flow into the capillaries -Outnumber any other type of artery, providing the most numerous control points -More muscular in proportion to their diameter -highly capable of vasomotion -produce half of the total PR

Explain how net filtration pressure across the capillary wall determines movement of fluid across that wall

-At the arteriolar end, hydrostatic pressure is higher so fluid is lost to the interstitial fluid; some of it enters the lymphatic capillary 35mmHg HP (driving water out) - 22mmHg COP (drawing water in) = 13mmHg NFP (outward) -At the venular end, osmotic pressure is higher so fluid lost to the interstitial fluid is drawn back into blood 15mmHg HP (driving water out) - 22mmHg COP (drawing water in) = -7mmHg NFP (inward) Overall NFP= 13mmHg (driving water out) - 7mmHg (drawing water in) = 6 mmHg overall NFP outward

Define blood flow, blood pressure, and peripheral resistance

-Blood flow: volume of blood flowing through a vessel, organ, or entire circulation in a given period; for entire vascular system= cardiac output (5-6 L/min) -blood flow(F)= blood pressure gradient (delta P)/resistance (delta R) -pressure gradient= cardiac output (CO) x peripheral resistance (PR) -cardiac output= stroke volume x heart rate -Blood pressure: force per unit area exerted by blood on a vessel wall (mmHg); typically refers to arterial blood pressure in aorta and its branches -outward pressure blood exerts on a blood vessel wall -Peripheral resistance: resistance of the arteries to blood flow -blood flow (F) proportional to the fourth power of radius (r) -A 3-fold increase in the radius of a vessel results in an 81-fold increase in flow -vessel radius, arterioles, blood viscosity, and blood vessel length determine resistance

Explain how blood pressure varies in different parts of the systemic and pulmonary circuits

-From aorta to capillaries (systemic): blood pressure is higher due to greater distance (more friction), smaller vessel diameter (more resistance) -From capillaries to vena cave (systemic): blood pressure lower due to veins being larger than capillaries (decreased resistance), large amount of blood forced into smaller channels -Arterioles are more muscular in proportion to their diameter and are the most significant point of control over peripheral resistance and flow (produce half of total PR) -Pulmonary circuit has lower resistance and therefore lower blood pressure since blood vessel length is shorter, so less resistance

Describe how blood pressure changes in the arteries, capillaries, and veins

-From aorta to elastic arteries to muscular arteries= blood pressure around 95mmHg and very slightly decreases -In arterioles, blood pressure drops rapidly to around 35mmHg -From capillaries, venules, veins, and venae cavae, it slows decreases until at venae cavae, it is almost at 0mmHg

Explain the relationship between vessel diameter, cross-sectional area, blood pressure, and blood velocity

-Smaller vessel diameter(more resistance) and higher cross-sectional area= slower blood velocity, higher blood pressure

Describe the different types of capillaries, and explain how their structure relates to their function

1. Continuous -occur in most tissues (abundant in skin and muscle) -no breaks between endothelial cells -small gaps between tight junctions= intercellular cleft (through which fluids and solutes pass) -pinocytotic vesicles shuttle fluids across capillaries Endothelial cell joined by tight junctions, least leaky and permit a narrow range of substances to cross capillary walls 2. Fenestrated -some endothelial cells have fenestra (pores) covered by membrane -much more permeable to fluids and solutes than continuous -Found where capillaries need to absorb materials released by organs (endocrine system) -found where filtrate formation occurs (kidneys) Contain fenestrations in the endothelial cells, moderately leaky to allow large volumes of fluid and larger molecules to cross capillary walls 3. Sinusoidal -large lumen and fenestrations -fewer tight junctions, larger intercellular clefts than other types -large molecules allowed to pass between blood and surrounding tissue -found in liver, bone marrow, lymphoid tissues, and endocrine organs -often have specialized macrophages (Kupffer cells) associated with them, kupffer cells destroy bacteria -blood flow is slow Discontinuous sheet of endothelium, irregular basal lamina, very large pores, leakiest to allow large substances such as cells to cross the capillary walls

Describe the mechanisms that assist in the return of venous blood to the heart

1. Pressure gradient -blood pressure is the most important force in venous return -7-13mmHg venous pressure toward heart -venules (12-18mmHg) to central venous pressure: point where the venae cavae enter the heart (~5mmHg) 2. Gravity -drains blood from head and neck 3. Skeletal muscle pump -in the limbs -contracting muscle squeezed out of the compressed part of the vein 4. Thoracic (respiratory) pump -inhalation: thoracic cavity expands and thoracic pressure decreases, abdominal pressure increases forcing blood upward -central venous pressure fluctuates -2mmHg: inhalation, 6mmHg: exhalation -blood flows faster with inhalation 5. Cardiac suction -of expanding atrial space -slight suction that draws blood into atria from vena cava

Compare and contrast the structures of arteries and veins, and of arterioles and venules

Arteries and veins: -both have tunica intima (interna), tunica media, and tunic externa (adventitia) -tunica media in arteries is thicker -walls thinner and lumens larger in veins -veins have one way valves -arteries are circular even when not filled with blood, veins are collapsed Arterioles and venules: -arterioles have smallest diameter of all arteries, tunica media mostly smooth muscle and few elastin fibers -thin walls with three tunics -small venules have only a tunica intima, larger venules have all three -highly porous -larger venules have smooth muscle layers (tunica media) and thin tunica externa

Describe the structure and function of the types of arteries and veins

Arteries: 1. Elastic arteries: -thick walled, near heart (aorta and branches) -conduct blood under high pressure to organs -lumen has largest diameter of all arteries -high in elastin content, present in all 3 tunics -elastin allows expansion and retraction in response to blood from heart 2. Muscular arteries: -deliver blood to organs; most of the arteries -control blood flow to organs, regulate blood pressure -thickest tunica media of all vessels, intermediate lumen diameter -more smooth muscle, less elastin in tunica media than elastic arteries -better at vasoconstriction (moving blood) 3. Arterioles: -delivers blood to capillary beds within tissues -control blood flow to tissues, feed capillary beds -lumen has smallest diameter of all arteries -tunica media mostly smooth muscle, few elastin fibers Veins 1. Venules: -result from convergence of capillaries -drain capillary beds -endothelium plus some surrounding connective tissue -highly porous (fluid and white blood cells freely move across walls) -larger venules have smooth muscle layers (tunica media) and thin tunica externa 2. Veins -result from convergence of venules -return blood to the heart -3 tunics -walls thinner and lumens larger than arteries -very little smooth muscle in tunica media -thick tunica externa with thick collagen fibers and elastic fibers -blood pressure lower in veins but poses problems of getting blood back to heart (large lumens provide little resistance to blood flow) -venous valves: of the tunica intima, similar to semilunar valves of the heart

Explain how the respiratory and cardiovascular systems maintain blood flow to tissues via the chemoreceptor complex

Chemoreceptors perform chemoreflex, an automatic response to changes in blood chemistry, especially pH and concentrations of O2 and CO2 Primary role: adjust respiration to changes in blood chemistry Secondary role: vasomotion -Hypoxemia, hypercapnia, and acidosis stimulate chemoreceptors, acting through vasomotor center to cause widespread vasoconstriction, increasing BP, increasing lung perfusion, and gas exchange

Explain the roles of diffusion, filtration, and osmosis in capillary exchange

Diffusion (most important): glucose and oxygen being more concentrated in blood diffuse out of blood -CO2 and other waste being more concentrated in tissue fluid diffuse into blood Filtration and osmosis: fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end -delivers materials to the cells and removes metabolic wastes

Explain how changes in hydrostatic and colloid osmotic pressure may cause edema

Edema- the accumulation of excess fluid in a tissue -occurs when fluid filters into a tissue faster than it is absorbed -results from increased capillary filtration, elevated hydrostatic pressure

Describe the local, hormonal, and neural factors that affect and regulate blood pressure

Local Control 1. Autoregulation: the ability of tissues to regulate their own blood supply -metabolic theory of autoregulation: if tissue is inadequately perfused, wastes accumulate, stimulating vasodilation which increases perfusion -bloodstream delivers oxygen and removes metabolites -when wastes are removed, vessels constrict 2. Vasoactive chemicals: substances secreted by platelets, endothelial cells, and perivascular tissue to stimulate vasomotion -During trauma, inflammation, and exercise: (all stimulate casodilation) *histamine *bradykinin *prostaglandins -During sheer stress (blood rubbing against vessels), endothelial cells secrete: (vasodilators) *prostacyclin and nitric oxide 3. Angiogenesis: growth of new blood vessels, typically in tissues with long term hypoxia -occurs in regrowth of uterine lining, around coronary artery obstructions, in exercised muscle, and malignant tumor -controlled by growth factors Neural Control -vessels under remote control by the central and autonomic nervous systems 1. Vasomotor center (cluster of neurons in medulla) of medulla oblongata exerts sympathetic control over blood vessels throughout the body -stimulates most vessels to constrict, but dilates vessels in skeletal and cardiac muscle to meet demands of exercise -Vasomotor center regulates blood vessel diameter -increased sympathetic activity->vasoconstriction->increased BP -decreased sympathetic activity->vasodilation->decreased BP -1. baroreceptors: stretch in response to increased arterial pressure -2. chemoreceptors: respond to changes in blood levels of O2, CO2, H+ -increase blood return to lungs when deficient in O2 or when increased CO2 sensed -Medullary ischemic reflex: automatic response to a drop in perfusion of the brain -3. Higher brain centers: hypothalamus, cerebral cortex relay info to medulla (e.g. fight or flight response) Hormonal Control 1. Angiotensin II: potent vasoconstrictor -promotes Na+ and water retention by kidneys -raises blood pressure and volume 2. Aldosterone: salt-retaining hormone -promotes Na+ and water retention by kidneys -raises blood pressure and volume 3. Atrial natriuretic peptide: increases urinary sodium excretion -promotes vasodilation -lowers blood pressure and volume 4. Antidiuretic hormone (ADH): vasoconstrictor at high concentrations -promotes water retention -raise blood pressure 5. Epinephrine and 6. Norepinephrine -Most blood vessels bind to alpha-adrenergic receptors= vasoconstriction (raise BP) -Skeletal and cardiac muscle blood vessels bind to beta-adrenergic receptors= vasodilation (raise BP and flow)

Explain how mean arterial pressure is calculated

MAP= diastolic pressure + ((systolic-diastolic)/3) MAP= diastolic pressure + (Pulse Pressure/3)

Explain the main effects and importance of the baroreceptor reflex

Response to rising blood pressure: 1. Increased blood pressure 2. Baroreceptors stretch 3. Send impulses to vasomotor center 4. Inhibits sympathetic outflow 5. Decrease cardiac output and decrease resistance 6. Decrease blood pressure Response to decreasing blood pressure: 1. Decreased blood pressure 2. Baroreceptors de-stretch 3. Send impulses to vasomotor center 4. Increases sympathetic outflow 5. Increase cardiac output and increase resistance 6. Increase blood pressure

Define vascular anastomosis, and explain the significance of anastomoses

Vascular anastomosis: the point where two blood vessels merge 1. Arteriovenous anastomosis (shunt) -artery flows directly to vein, bypassing capillaries -fingers, toes- reduce heat loss (but frostbite) 2. Venous anastomosis -most common -one vein empties directly into another -reason vein blockage is less serious than arterial blockage 3. Arterial anastomosis -two arteries merge -provides collateral (alternative) routes of blood supply to a tissue -coronary circulation and around joints