The Cardiovascular System: Blood Vessels and Circulation Chapter 16

Blood Vessels Arteries- from heart Elastic => large Muscular => distribution to organs Arterioles => distribution to capillaries- mostly muscle Capillaries- thin walled for diffusion Veins- to heart Venules => from capillaries Veins from tissue to vena cavae to heart

Figure 16.1ab

Figure 16.1c

Blood Vessel Structure Three layers 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

Vessel Functions Muscular arteries & arterioles regulate flow Sympathetic activity to smooth muscle vasoconstriction (narrowing) Decreased sympathetic activity or NO causes relaxation or dilation Arterioles adjust flow into capillaries Systemic veins & venules serve as blood reservoirs (~64% total blood volume)

Capillary Details Capillaries only have endothelium Very thin cells & cell nuclei protrude into lumen- easy diffusion Connected from arterioles to venules in networks Sometimes direct route from arteriole to venule Filling controlled by small arterioles & precapillary sphincters

Figure 16.2a

Figure 16.2b

Capillary Exchange 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

Figure 16.3

Venous Return 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

Muscle & Respiratory Pumps Contracting skeletal muscles squeeze veins emptying them Because of 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

Figure 16.4

Blood Flow Resistance= opposition to flow 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 depends on lumen diameter & length & blood viscosity Smaller lumen  greater resistance Higher viscosity greater resistance viscosity of blood depends on Hct

Resistance Depends on vessel lumen diameter And blood viscosity Smaller lumen  greater resistance And blood viscosity Higher viscosity greater resistance viscosity of blood depends on Hct And total vessel length Longer the length of flow the more friction with wall Total body resistance increases with growth and addition of tissue

Anatomical Design Length and pressure Design and local flow control- central pressure

Pressure Gradients Adult anatomy gives constant length If central blood pressure is controlled it is constant Only variable is radius of the arterioles Each tissue can do it separately Review design in picture below All tissues have the same pressure gradient

Pressure Gradients (Cont.) Note pulse in aorta & large arteries MAP pressure fall related to resistance Note role of arterioles Note low venous pressures can’t get back to the heart!

Figure 16.5

Regulation of Blood Pressure & Flow Fast responses: e.g. standing up Slower responses: e.g. blood volume Distribution: e.g. to working muscles Balance of CO with flow to body Interacts with many other control systems Cardiovascular (CV) Center major regulator

Inputs Higher centers: Sensory receptor input: cerebral cortex, limbic system, hypothalamus HR increases before race; flow adjusted for body temperature Sensory receptor input: proprioceptors, baroreceptors chemoreceptors

Inputs (Cont.) Proprioceptors: Baroreceptors: in aorta & carotid 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

Figure 16.6

Output ANS to heart Vasomotor  Sympathetic  HR &  force of contraction  Parasympathetic  HR Vasomotor to arterioles  vasomotor tone To veins move blood to heart  BP

Hormone regulation 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

Figure 16.7

Checking Circulation- Pulse Pulse in arteries = HR Use radial artery at wrist, carotid artery, brachial artery Tachycardia = rapid rest rate (>100 bpm) Bradycardia= slow rest rate (<50 bpm)

Blood Pressure Use sphygmomanometer Raise pressure above systolic- Usually on brachial artery Raise pressure above systolic- stop flow Lower pressure in cuff until flow just starts first sound  Systolic Pressure Lower until sound suddenly gets faint Diastolic pressure Normal values <120 mmHg for systolic & < 80 mmHg for diastolic

Circulatory Routes 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

Figure 16.8

Figure 16.9

Figure 16.10a

Figure 16.10b

Figure 16.10c

Figure 16.11

Figure 16.12

Figure 16.13

Figure 16.14a

Figure 16.14b

Figure 16.14c

Figure 16.15

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

Hepatic Petal Circulation Portal vein transports blood from one capillary bed to another GI organs  Splenic & superior mesenteric veins  hepatic portal vein sinusoids in liver Mixes with oxygenated blood  hepatic vein inferior Vena Cava

Figure 16.16a

Figure 16.16b

Fetal Circulation Specialized for exchange of materials with maternal blood and bypass of lungs Exchange in placenta umbilical vein  liver ductus venosus  inferior vena cava  R. atrium Mixes with deoxygenated blood from lower body  foramen ovale L. Atrium Or  R. Ventricle Pulmonary trunk  ductus arteriosus  aorta  internal iliacs  umbilical arteries Placenta

Figure 16.17

At Birth Umbilical arteries medial umbilical ligaments Umbilical vein  ligamentum teres Ductus venosus  ligamentum venosum Placenta expelled Foramen ovalis closes fossa ovale Ductus arteriosus  ligamentum arteriosum

Aging Stiffening of aortae Loss of cardiac muscle strength Reduced CO & increased systolic pressure Coronary artery disease Congestive heart failure atherosclerosis