blood vessels
TRANSCRIPT
Chapter 16
The Cardiovascular System: Blood Vessels and Circulation
Blood Vessels Arteries
Carries blood away from the heart to body tissues
2 large arteries aorta and pulmonary trunk
Arteries smaller and smaller arteries arterioles
Arterioles capillaries
Blood Vessels Veins
Convey blood from the tissues back to the heart
Veins smaller and smaller veins venules
Venules capillaries
Blood Vessels Capillaries
Microscopic vessels that connect arterioles to venules
“Exchange Vessels” permit exchange of nutrients and wastes between body’s cells and blood
Blood Vessel StructureArteries
Three layersInner layer: endothelium, a basement
membrane, internal elastic laminaMiddle layer: smooth muscle and elastic
tissueOuter layer: elastic and collagen fibers
Blood Vessel StructureVeins
Similar structure to arteriesThinner middle and inner layers, outer layer is the thickest
The lumen is wider than arterySome veins, inner layer folds inward valves to prevent backflow
Capillary Information• Capillaries – layer of endothelium surrounded by basement membrane
• Connected from arterioles venules in networks–Sometimes direct route from arteriole to venule
• Filling controlled by small arterioles & pre-capillary sphincters
Vessel FunctionsMuscular arteries & arterioles regulate flow
Sympathetic activity to smooth muscle vasoconstriction (narrowing)
Decreased sympathetic activity or NO causes relaxation or dilation
Vessel FunctionsArterioles adjust flow into capillariesSystemic veins & venules serve as blood reservoirs (~64% total blood volume)
Capillary ExchangeSlow flow through capillariesCapillary Exchange – movement of substances into and out of capillaries
Capillary Blood Pressure – pressure of blood against the walls of capillaries
Capillary Exchange• Osmosis (protein concentration)
–Reabsorption of fluid from outside to inside• Balance determines fluid in circulation–Excess fluid returned via lymphatic system–Local signals can adjust capillary flow
Venous ReturnVolume of blood flowing back to the heart through the systemic veins
Happens due to pressure generated in 3 ways:Contractions of the heartThe skeletal muscle pumpRespiratory pump
Venous ReturnContractions of the heart –
BP generated by ventricular systoleMeasured in mm of Hg (mercury)Small pressure difference between venules and right atrium is sufficient
Venous ReturnSkeletal muscle pump –
Standing at rest – venous valves in leg are open, blood flows up to heart
Contraction of leg muscles compresses vein pushes blood through valve closer to heart, called milking
Venous ReturnSkeletal muscle pump cont.
Same time as milking, valve farther from heart closes as some blood is pushed against it
After muscle relaxation, pressure drops in compression and open valve closes, and now farther valve opens since BP is higher in foot than leg, vein fills with blood from foot
Venous ReturnRespiratory pump –
During inhalationDiaphragm moves down, causes a drop in
pressure in the thoracic cavity and rise in abdominal(ab) cavity
Ab veins compressed, greater volume of blood from compressed ab veins decompressed thoracic veins rt atrium
During exhalation, pressures reverse
Blood Flow• From high pressure low pressure
–Greater gradient = greater flow• BP – pressure exerted by blood on the walls of a blood vessel
Blood PressureBP is highest in aorta and large systemic arteries
BP depends on total volume of bloodNormal volume of an adult ~5 L
Blood PressureBP rises to ~110 mmHg (systole) and drops to ~70 mmHg (diastole)
BP drops as blood enters veins and reaches 0 mmHg as blood returns right atrium
Blood Flow• Resistance – opposition to blood flow due to friction between blood and walls of vessels
• Increase in resistance = increase in BP
• Decrease in resistance = decrease in BP
• Resistance depends on 3 things
Resistance• Size of lumen
–Smaller lumen greater resistance• Blood viscosity
–Higher viscosity greater resistance• Total vessel length
–Longer length greater resistance
Regulation of Blood Pressure & Flow
CV Center (in the medulla oblongata)Regulate heart rate & stroke volumeControls neural & hormonal negative feedback systems that regulate BP and flow to tissues
Inputs (CV center)Higher centers:
Cerebral cortexLimbic systemHypothalamus
Inputs (CV center)Sensory receptor input:
Proprioceptors Monitor movements of joints and
musclesStart HR change as activity starts
Baroreceptors Monitor pressure changes
Inputs (CV center)Baroreceptors (cont.)
pressure parasympathetic stimulation of the heart sympathetic stimulation
ChemoreceptorsMonitor chemical changesLow O2, high H+, excess CO2 sympathetic stimulation vasoconstriction BP
Output (CV center)ANS to heart
Sympathetic HR & force of contraction
Sympathetic HR & force of contraction
Vasomotor to arterioles vasomotor tone (sets
resting level of vascular resistance)To veins move blood BP
Hormone RegulationRenin – Angiotensin – Aldosterone (RAA) systemAngiotensin II BP (vasocontriction) aldosterone Na+ & water by kidneys
Epinephrine and Norepinephrine CO ( HR & force of contraction)
Hormone RegulationADH = Vasopressin
Constriction BPANP
Vasodilation & loss of salt & water in urine BP and blood volume
PulsePulse strongest in arteries closest to heartRadial artery (at wrist), Carotid artery, Popliteal artery, Dorsal artery, Brachial artery
Tachycardia = rapid rest rate (>100 bpm)
Bradycardia= slow rest rate (<50 bpm)
Blood Pressure (measurement)Use sphygmomanometer
Usually on brachial artery in left armRaise pressure above systolic-
To stop blood flow
Blood Pressure (measurement)Lower pressure in cuff until flow just startsSystolic Pressure
Lower until sound suddenly gets faint (stops)Diastolic pressure
Normal values <120 mmHg for systolic & < 80 mmHg for diastolicEx. 115/75
Circulatory RoutesTwo parts: Systemic & PulmonarySystemic circulation- throughout body
Oxygenated blood deoxygenatedAll systemic arteries branch from aorta
Systemic CirculationAll systemic veins empty into Superior Vena Cava, Inferior Vena Cava or the Coronary SinusCarry deoxygenated blood to heart
Pulmonary CirculationRight ventricle pulmonary trunkR & L pulmonary arteries
Carry deoxygenated blood R & L lungs
Gas exchange occurs
Pulmonary Circulation R & L pulmonary veins
Carry oxygenated blood L atrium
Hepatic Portal CirculationPortal vein transports blood from one capillary bed to another
There are no valves Splenic & superior mesenteric veins
Fetal CirculationSpecialized for exchange of materials with maternal blood and bypass of lungs (placenta)
Umbilical artery: pathway for blood fetus mother
Fetal CirculationUmbilical vein brings O2 blood from placenta liver and Ductus Venosus Inferior Vena Cava R Atrium
Fetal CirculationForamen ovale - hole in atrial septum allows mixing of blood in heart (eventually becomes fossa ovalis)
At BirthUmbilical arteries medial umbilical ligaments
Umbilical vein ligamentum teresDuctus venosus ligamentum venosum
At Birth
Placenta is “afterbirth”Foramen ovalis closes fossa ovale
Ductus arteriosus ligamentum arteriosum
AgingStiffening of aortaLoss of cardiac muscle strength
Reduced CO & increased systolic pressure
Coronary artery disease (CAD)Congestive heart failureAtherosclerosis