The Cardiovascular System: Blood Vessels and Circulation

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 Blood Vessels

Figure 16.1ab

Figure 16.1c

Blood Vessel Structure Three layers Tunica Intima (Interna)- Innermost, endothelial layer Tunica Media- Middle, muscular layer Tunica Externa- Outermost layer Blood Vessel Structure

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

Vessel Functions 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

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 Capillary Details

Figure 16.2a

Figure 16.2b

Capillary Exchange Slow flow through capillaries Blood pressure  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

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 Venous Return

Muscle & Respiratory Pumps 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 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

Resistance 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

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 (cardiac output) with flow to body Interacts with many other control systems Cardiovascular (CV) Center major regulator Regulation of Blood Pressure & Flow

Inputs Higher centers: Sensory receptor input: Cerebral cortex, Limbic system Hypothalamus Flow adjusted for body temperature Sensory receptor input: Proprioceptors Baroreceptors Chemoreceptors Inputs

Inputs 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 Inputs

Figure 16.6

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

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 Hormone regulation

Figure 16.7

Checking Circulation- Pulse 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 Circulation- Pulse

Blood Pressure Arterial Blood Pressure Systolic pressure Peak arterial pressure during ventricular systole Diastolic pressure Minimum arterial pressure during diastole Blood Pressure

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 Blood Pressure

Blood Pressure Normal = 120/80 Hypertension Hypotension Abnormally high blood pressure Greater than 140/90 Hypotension Abnormally low blood pressure Less than 90/60 Blood Pressure

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

Anatomy of Blood Vessels

Blood flow through Vessels From Heart Arteries Arterioles Capillaries Venules Veins To Heart Blood flow through Vessels

Figure 16.1ab

Figure 16.1c

Blood Vessel Structure Three layers Tunica Intima (Interna)- Innermost, endothelial layer Tunica Media- Middle, muscular layer Tunica Externa- Outermost layer Blood Vessel Structure

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

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 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

Pulmonary circuit (veins) Systemic circuit (arteries) Brain Upper limbs Pulmonary circuit (veins) Lungs LA Systemic circuit (arteries) Left ventricle Kidneys Spleen Digestive organs Liver Gonads Lower limbs 40

Pulmonary circuit (arteries) Systemic circuit (veins) Brain Upper limbs Pulmonary circuit (arteries) Lungs RA Right ventricle Systemic circuit (veins) Kidneys Digestive organs Liver Gonads Lower limbs 41