Heart and Blood Vessels

Jugular veinCarotid artery

Superiorvena cava

Inferior vena cavaRenal vein

Commoniliac veinCommoniliac artery

Subclavian veinSubclavian artery

Aorta

Renal artery

Femoral veinFemoral artery

Great saphenous vein

Figure 8.9

Three Types of Blood Vessels Transport Blood

• Arteries– Carry blood away from heart– Blood under high pressure

• Capillaries– Metabolic exchange with tissues

• Veins– Return blood to heart– Very low pressure

Arteries

• Structure– Thick-walled, three layers • Innermost: endothelium• Middle smooth muscle• Outer: connective tissue

• Branch into arterioles– Small arteries

Arterioles and Precapillary Sphincters– Blood flow• Heart → Arteries → Arterioles → Capillaries

– Precapillary sphincters: control flow into capillaries• Vasodilation: increases blood flow to capillaries• Vasoconstriction: decreases blood flow to capillaries

Capillaries• Structure– Smallest blood vessels– Thin-walled: one cell-layer thick– Porous

• Function: exchange of substances with interstitial fluid

Veins

• Structure– Three layers, thin-walled– Larger lumen than arteries

• Functions– Serve as blood reservoirs– Blood flow• Capillaries → Venules → Veins

→ Heart

Venous Return to the Heart

• Mechanisms in blood return– Contraction of skeletal

muscles– One-way valves– Pressure changes associated

with breathing

The Heart - Layers• Surrounded by fibrous sac – pericardium• Layers of the heart– Epicardium: thin covering– Myocardium: cardiac muscle– Endocardium: thin lining

Heart Chambers• Four chambers– Right atrium– Left atrium– Right ventricle– Left ventricle

Heart Vessels• Superior and inferior vena cava– Carry low-oxygen blood into RA

from body• Pulmonary trunk and arteries– Carry low-oxygen blood from RV to

lungs• Pulmonary veins– Carry high-oxygen blood from lungs

to LA• Aorta– Carries high-oxygen blood from LV

to body

Aorta

Pulmonary trunk

Superiorvena cava

Inferiorvena cava

L. Pulmonary Artery

R. Pulmonary Artery

Heart Valves• Prevent backflow– Two atrioventricular valves• Tricuspid valve

– Between RA and RV

• Mitral (bicuspid) valve– Between LA and LV

– Two semilunar valves• Pulmonary valve

– Between RV and pulmonary trunk

• Aortic valve– Between LV and aorta

Two Circuits of Circulation• Pulmonary circuit– RV Pulmonary trunk/arteries

lungs (oxygen) pulmonary veins LA

• Systemic circuit– LV aorta arteries of body

capillaries veins SVC and IVC RA

Cardiac Cycle• Atrial systole – Both atria contract– AV valves open, semilunar valves closed– Ventricles fill

• Ventricular systole– Both ventricles contract– AV valves close, semilunar valves open– Blood flows into arteries

• Diastole– Both atria and ventricles relax– Semilunar valves close

Heart Sounds and Heart Valves

• Lub-dub heart sound– Lub: closing of AV valves during ventricular systole– Dub: closing of semilunar valves during ventricular

diastole

• Heart murmurs– Caused when blood flow is disturbed– May be a sign of a defective valve

Cardiac Conduction System• SA node – Cardiac pacemaker– Initiates heartbeat– Pace can be modified by nervous system

• AV node – Relays impulse

• AV bundle and Purkinje fibers – Carry impulse to ventricles

Electrocardiogram (EKG/ECG)• Tracks electrical activity of heart• Characteristic pattern– P wave: impulse across atria– QRS complex: spread of impulse thru septum and ventricles– T wave: end of electrical activity in ventricles

• EKGs can detect– Arrhythmias– Ventricular fibrillation

Blood Pressure• Force blood exerts on walls of blood vessels– Systolic pressure – highest pressure, during ventricular systole– Diastolic pressure – lowest pressure, during ventricular diastole

• Measurement– Use sphygmomanometer– “Normal” readings

• Systolic pressure <120 mmHg• Diastolic pressure <80 mmHg

Blood Pressure

• Hypertension: high blood pressure– The silent killer– At risk for stroke, heart attack, bleeding, kidney disease

• Hypotension: blood pressure too low– Inadequate blood supply to organs– Clinical signs – dizziness, fainting– Causes – orthostatic, severe burns, blood loss

Regulation of Blood Pressure• Baroreceptors: pressure receptors in arteries• Steps in mechanism:

1. Blood pressure rises, vessels stretched2. Signals sent to cardiovascular center in medulla

oblongata3. Heart signaled to lower rate and force of contraction4. Arterioles vasodilate, reducing resistance to blood flow5. Combined effect lowers blood pressure

Regulation by Nervous and Endocrine Systems

• Medulla oblongata signals– Sympathetic nerves – constrict blood vessels, raise blood

pressure– Parasympathetic nerves – dilate blood vessels, lower

blood pressure

• Hormones: epinephrine (adrenaline) triggers sympathetic response

• Local requirements dictate local blood flow• Exercise – increased blood flow and cardiac output

Cardiovascular Disorders• Angina pectoris: chest pain– narrowed coronary arteries impair blood flow

• Myocardial infarction/heart attack: permanent cardiac damage due to blockage in a coronary artery

• Congestive heart failure: decrease in pumping efficiency

• Embolism: blockage of blood vessels• Aneurysm: ballooning of artery– due to hypertension, hardening of arteries

(atherosclerosis)• Stroke: impaired blood flow to the brain

Heart Attack• Also known as myocardial infarction– Permanent damage to myocardium

• Symptoms– Intense chest pain, nausea, heaviness in the chest,

difficulty breathing, pain radiating to left arm, jaw, back, upper abdomen

• Diagnosis– EKG– Blood test for cardiac enzymes

• Prevention/Treatment– Clot-busting medications– CABG (bypass)

Aorta

Vein grafts

Plaqueblockingblood flow

Figure 8.19

Reducing Risk of Cardiovascular Disease

• Smoking – don’t • Blood lipids – monitor cholesterol levels• Exercise – regular and moderate• Blood pressure – treat hypertension• Weight – being overweight increases risk of heart

attack and stroke• Control of diabetes mellitus – early diagnosis and

treatment delays onset of related problems• Stress – avoid chronic stress