THE CARDIOVASCULAR SYSTEM: BLOOD VESSELS AND CIRCULATION Arteries- from heart 1. Elastic => large 2. Muscular => distribution to organs 3. Arterioles => distribution to capillaries- mostly muscle Capillaries- thin walled for diffusion Veins- to heart 1. Venules => from capillaries 2. Veins from tissue to vena cavae to heart BLOOD VESSELS FIGURE 16.1AB FIGURE 16.1C Three layers • Tunica Intima (Interna)- Innermost, endothelial layer • Tunica Media- Middle, muscular layer • Tunica Externa- Outermost layer BLOOD VESSEL STRUCTURE Differences Arteries-> thicker tunica media Elastic tissue and/or muscle As they get smaller-> more muscle Arterioles-> very muscular- control Veins- bigger lumen and thinner walls Veins-> valves to prevent backflow Venules very thin, no valves BLOOD VESSEL STRUCTURE Differences • Muscular arteries & arterioles regulate flow • Sympathetic activity to smooth muscle vasoconstriction (narrowing) • Decreased sympathetic activity or NO causes relaxation or vasodilation • Arterioles adjust flow into capillaries • Systemic veins & venules serve as blood reservoirs (~64% total blood volume) VESSEL FUNCTIONS Capillaries only have endothelium Very thin cells & cell nuclei protrude into lumeneasy diffusion Connected from arterioles to venules in networks Sometimes direct route from arteriole to venule Filling controlled by small arterioles & precapillary sphincters CAPILLARY DETAILS FIGURE 16.2A FIGURE 16.2B Slow flow through capillaries Allows time for exchange through wall Blood pressure filtration of fluid out of capillary Mostly in first ½ of vessel length Osmosis (protein concentration) Reabsorption of fluid from outside to inside Mostly in last ½ of vessel length Balance determines fluid in circulation Excess fluid returned via lymphatic system Local signals can adjust capillary flow CAPILLARY EXCHANGE FIGURE 16.3 • Blood enters veins at very low pressure. • Needs more pumping to get back to heart • = action of heart; muscle pumps; respiratory pump • Some pressure from heart action • Not enough to overcome gravity VENOUS RETURN • Contracting skeletal muscles squeeze veins emptying them Venous valves flow is toward heart • Respiratory pump has similar action • Inhalation decreased thoracic pressure & increased abdominal pressure Blood flows toward heart • Exhalation allows refilling of abdominal veins MUSCLE & RESPIRATORY PUMPS FIGURE 16.4 From high pressure area to lower pressure area, i.e. down pressure gradient Greater gradient greater flow Ventricular contraction blood pressure (BP) Highest in aorta and declines as flows through vessels 110-70 mmHg in aorta ~16 mmHg at venules 0 at R. Atrium Resistance= opposition to flow BLOOD FLOW Depends on: Vessel lumen diameter Smaller lumen greater resistance Blood viscosity (thickness) Higher viscosity greater resistance Viscosity of blood depends on Hct Total vessel length Longer the length of flow the more friction with wall Total body resistance increases with growth and addition of tissue RESISTANCE FIGURE 16.5 Fast responses: e.g. standing up Slower responses: e.g. blood volume Distribution: e.g. to working muscles Balance of CO (cardiac output) with flow to body • Interacts with many other control systems • Cardiovascular (CV) Center major regulator • • • • REGULATION OF BLOOD PRESSURE & FLOW Higher centers: Cerebral cortex, Limbic system Hypothalamus Flow adjusted for body temperature Sensory receptor input: Proprioceptors Baroreceptors Chemoreceptors INPUTS Proprioceptors: Start HR change as activity starts Baroreceptors: in aorta & carotid pressure parasympathetic & sympathetic stimulation CO Chemoreceptors: in aorta & carotid Low O2, high H+, CO2 vasoconstriction BP INPUTS FIGURE 16.6 ANS to heart Sympathetic HR & force of contraction Parasympathetic HR Vasomotor To arterioles vasomotor tone (vasoconstriction) To veins move blood to heart BP OUTPUT Renin-Angiotensin system Angiotensin II vasoconstriction+ thirst aldosterone Na+ & water loss in urine on Epinephrine & Norepinephrine CO ADH = Vasopressin constriction BP Thirst & water retention in kidney BP ANP- from cells in atria Vasodilation & loss of salt & water in urine BP HORMONE REGULATION FIGURE 16.7 Pulse in arteries = HR (Heart Rate) Use radial artery at wrist carotid artery- neck brachial artery- arm Tachycardia = rapid rest rate (>100 bpm) Bradycardia= slow rest rate (<50 bpm) CHECKING CIRCULATIONPULSE Arterial Blood Pressure Systolic pressure Peak arterial pressure during ventricular systole Diastolic pressure Minimum arterial pressure during diastole BLOOD PRESSURE Use sphygmomanometer Usually on brachial artery Raise pressure above systolicstop flow Lower pressure in cuff until flow just starts first sound Systolic Pressure Lower until sound suddenly gets faint Diastolic pressure BLOOD PRESSURE Normal = 120/80 Hypertension Abnormally high blood pressure Greater than 140/90 Hypotension Abnormally low blood pressure Less than 90/60 BLOOD PRESSURE Stiffening of aortae Loss of cardiac muscle strength Reduced CO & increased systolic pressure Coronary artery disease Congestive heart failure Atherosclerosis AGING From Heart Arteries Arterioles Capillaries Venules Veins To Heart BLOOD FLOW THROUGH VESSELS FIGURE 16.1AB FIGURE 16.1C Three layers • Tunica Intima (Interna)- Innermost, endothelial layer • Tunica Media- Middle, muscular layer • Tunica Externa- Outermost layer BLOOD VESSEL STRUCTURE Differences Arteries-> thicker tunica media Veins- bigger lumen and thinner walls, valves to prevent backflow Capillaries only have endothelium BLOOD VESSEL STRUCTURE Two parts: Systemic & Pulmonary Systemic circulation- throughout body Oxygenated blood deoxygenated as it goes All systemic arteries branch from aorta All systemic veins empty into Superior Vena Cava, Inferior Vena Cava or the Coronary Sinus Carry deoxygenated blood to heart CIRCULATORY ROUTES Pulmonary Circulation From right ventricle pulmonary trunk R. & L. pulmonary arteries Carry deoxygenated blood R. & L. lungs Gas exchange occurs 2 R. & 2 L. pulmonary veins Carry oxygenated blood L. atrium PULMONARY CIRCULATION Brain Upper limbs Pulmonary circuit (veins) Lungs LA Left ventricle Systemic circuit (arteries) Kidneys Spleen Liver Digestive organs Gonads Lower limbs © 2012 Pearson Education, Inc. Brain Upper limbs Pulmonary circuit (arteries) Lungs RA Systemic circuit (veins) Right ventricle Kidneys Liver Digestive organs Gonads Lower limbs © 2012 Pearson Education, Inc.