A&P Ch. 15: Cardiovascular System

Types of blood vessels:

arteries, arterioles, capillaries, venules, veins

types of heart chambers

atria, auricles, ventricles

ESV is affected by these factors:

preload, contractility, afterload

Colloid osmotic pressure

pressure due to plasma proteins

Superior and inferior venae cavae (structural function)

return oxygen-poor blood to heart

Pulmonary veins (4) (structural function)

return oxygen-rich blood from lungs to left atrium

4 chambers of the heart:

right atrium, right ventricle, left atrium, left ventricle

Interatrial septum (structural function)

separates left and right atria

Interventricular septum (structural function)

separates left and right ventricles

Aortic semilunar valve (structural function)

separates left ventricle from aorta

Tricuspid valve (structural function)

separates right atrium from right ventricle

Pulmonary semilunar valve (structural function)

separates right ventricle from pulmonary trunk

Tunica media:

smooth muscle and elastic tissue

Preload

can increase stroke volume: Higher the EDV, the greater the mechanical stretch of ventricular myocardial cells (preload), and greater the force of contraction that will follow (Frank-Starling Law of the Heart)

Types of capillaries:

continuous, fenestrated, sinusoidal

Blood from lower limb drains into

deep and superficial groups of veins:

Peripheral resistance (PR) in BP control

derived from changing arteriole diameter, also regulates blood pressure: • Vasoconstriction reduces arteriole diameter, increases PR, and increases blood pressure • Vasodilation increases arteriole diameter, decreases PR, and decreases blood pressure • Vasomotor center in medulla oblongata regulates diameter of arterioles, and therefore PR, by changing sympathetic stimulation of muscle in walls of arterioles

Types of capillary exchange

diffusion, filtration, osmosis, transcytosis

The heart wall has 3 distinct layers:

epicardium, myocardium, endocardium

Tunica interna (intima):

innermost layer, endothelium

QRS complex

(3 waves): Ventricular depolarization; occurs just prior to ventricular contraction • Record of atrial repolarization is "hidden" in the large QRS complex, since ventricular depolarization is a much larger event

Marfan syndrome

(a connective tissue defect): Involves an abnormal type of the protein fibrillin, which can weaken the wall of the aorta; can result in bursting of the aorta and sudden death.

Familial hypertrophic cardiomyopathy

(a myosin defect): Inherited overgrowth of myocardium, caused by abnormal myosin chain in cardiac muscle; can result in sudden death.

Diastole:

Relaxation of a heart chamber

Systemic circuit:

Transports oxygen-rich blood and nutrients to body cells, removes wastes from cells, flows back to heart

Central Venous Pressure

*Pressure in the right atrium* • All veins, except those returning to the heart from the lungs, drain into right atrium • Factors that influence it alter flow of blood into the right atrium • It affects pressure within the peripheral veins • A weakly beating heart increases central venous pressure • An increase in central venous pressure causes blood to back up into the peripheral veins • This can lead to peripheral edema • Increase in blood volume or venoconstriction increases blood flow to right atrium, which increases central venous pressure

Major Components of the Cardiac Conduction System:

- SA (sinoatrial) Node - Internodal Atrial Muscle - Junctional fibers - AV (Atrioventricular) Node - AV (Atrioventricular) Bundle (of HIS) - Left & Right bundle branches - Purkinje fibers

Heart Sounds

-A heartbeat through a stethoscope sounds like "lubb-dupp" -Sounds are due to closing of heart valves, and vibrations associated with a sudden slowing of blood flow during contraction/relaxation of chambers

Venous Blood Flow:

-Blood pressure decreases as the blood moves through the arterial system and into the capillary network, so very little pressure remains at the venous ends of the capillaries • Only partly a direct result of heart action • Also dependent on: skeletal muscle contraction, respiratory movements, vasoconstriction of veins (venoconstriction) -Veins act as blood reservoir, which can alter its capacity in response to changes in blood volume

Arch of the aorta

-Branches: Brachiocephalic trunk Left common carotid artery Left subclavian artery

Ascending aorta

-Branches: Right and left coronary arteries -Supplies: Heart

Control of Blood Pressure

-Cardiac output is limited by venous return (volume of blood returning to ventricles) -Stroke volume can be increased by sympathetic stimulation -Cardiac output, peripheral resistance, and therefore blood pressure are also regulated by baroreceptor reflexes (cardioaccelerator and cardioinhibitory reflexes)

Pressure and Volume Changes of a Cardiac Cycle

-During a cardiac cycle, the pressure in the heart chambers rises and falls -Pressure changes open and close the valves

Aortic valve

-Entrance to aorta -Prevents blood from moving from the aorta into the left ventricle during ventricular relaxation

Pulmonary valve

-Entrance to pulmonary trunk -Prevents blood from moving from the pulmonary trunk into the right ventricle during ventricular relaxation

Regulation of the Cardiac Cycle

-Heart rate and volume of blood pumped change to meet requirements -Cardiac center in medulla oblongata performs neural regulation of heart -SA node (pacemaker) normally controls the heart rate, and heart rate changes occur due to factors that influence the SA node -Sympathetic and parasympathetic fibers modify the heart rate in response to changing conditions, such as: • Physical exercise • Body temperature • Fight-or-flight response • Concentration of various ions, such as K+ and Ca+2

Capillary Arrangement

-Higher the metabolic rate in a tissue, the denser its capillary networks • Rich capillary supply in muscle and nerve tissue, since they use a large amount of O2 and nutrients • Tissues with lower metabolic rate, such as cartilage, have fewer capillaries -Capillary patterns differ; some directly connect arterioles to venules, others branch out into complex networks

Mitral valve

-Left atrioventricular orifice -Prevents blood from moving from the left ventricle into the left atrium during ventricular contraction

Capillary Permeability

-Openings in walls of capillaries are thin slits found where endothelial cells overlap -Sizes of openings vary among tissues; permeability varies with size of slits

Formula for blood pressure

-Product of cardiac output (CO) and peripheral resistance (PR) BP = CO × PR -Maintenance of blood pressure requires regulation of these 2 factors

Tricuspid valve

-Right atrioventricular orifice -Prevents blood from moving from the right ventricle into the right atrium during ventricular contraction

Cardiac output (CO):

-Volume of blood discharged from a ventricle each minute; blood pressure varies with cardiac output. • Increase in SV or HR causes increase in CO, which increases the blood pressure (BP) • Cardiac output = Stroke volume × Heart rate

Blood flow distribution to capillaries

-can change with situation: • During exercise, muscle capillaries receive more blood flow, and digestive system capillaries receive less • After a meal, digestive system capillaries receive more blood flow, and muscles receive less

Cardiac veins

-drain blood from myocardium • Paths of veins lie nearly parallel to those of coronary arteries • Coronary sinus: Enlarged vein into which other cardiac veins drain; drains into right atrium

Left and right coronary arteries

-supply blood to tissues of the heart • The coronary arteries are first 2 branches of the aorta • Branches of right coronary artery: -Posterior interventricular artery: Supplies posterior ventricles -Right marginal branch: Supplies right atrium and ventricle • Branches of left coronary artery: -Circumflex branch: Supplies left atrium and ventricle -Anterior interventricular (left anterior descending) artery: Supplies walls of ventricles

Aneurysm:

A bulge in the wall of an artery, formed when blood pressure dilates a weakened area of the vessel; can burst wall of artery

functional syncytium,

mass of merging cells that function as a unit: 2 such masses exist in the heart: • In the atrial walls; called the atrial syncytium • In the ventricular walls; called the ventricular syncytium

Familial hypercholesterolemia:

Abnormal LDL (low-density lipoprotein) receptors on liver cells do not take up cholesterol from blood; results in high cholesterol, coronary artery disease.

Varicose Veins:

Abnormal and irregular dilations in superficial veins; most common in legs

Murmur:

Abnormal heart sound derived from incomplete closure of cusps of a valve

Tachycardia:

Abnormally fast heartbeat, >100 beats/min at rest

Bradycardia:

Abnormally slow heartbeat, <60 beats/min at rest

Arrhythmias:

Altered heart rhythms; several types: fibrillation, tachycardia, bradycardia, flutter, premature beat, ectopic pacemaker; use of artificial pacemaker

P wave:

Atrial depolarization; occurs just prior to atrial contraction

Mean arterial pressure (MAP):

Average pressure in arterial system; represents average force driving blood to the tissues DP + 1/3PP

Precapillary Sphincter:

Band of smooth muscle that wraps around beginning of capillary, to regulate blood flow

Aortic bodies:

Baroreceptors in aortic arch that monitor blood pressure

Premature Beat:

Beat that occurs before expected in normal cardiac cycle; often originates from ectopic regions of heart (other than SA node)

Factors That Influence Arterial Blood Pressure

Blood pressure increases as these increase: -blood volume -heart rate -stroke volume -blood viscosity -peripheral resistance

Abdominal aorta (from descending aorta

Branches: Celiac trunk Phrenic artery Superior mesenteric artery Suprarenal artery Renal artery Gonadal artery Inferior mesenteric artery Lumbar artery Middle sacral artery Common iliac artery

thoracic aorta (from descending aorta)

Branches: Bronchial artery Pericardial artery Esophageal artery Mediastinal artery Posterior intercostal artery

Formula for cardiac output

CO = SV x HR

Stem Cell Technology:

Cardiac muscle tissue can now be cultured from altered somatic cells or from stem cells; may allow "stem cell heart patches" in the future

Pulmonary circuit:

Carries oxygen-poor blood from heart to lungs, drops off carbon dioxide, picks up oxygen, flows back to heart

Arteries:

Carry blood away from the ventricles of the heart

Branches of left coronary artery:

Circumflex branch and anterior interventricular (left anterior descending) artery

Junctional Fibers:

Conduct impulses from SA node to AV node

Internodal Atrial Muscle:

Conducts impulses from SA node to atria

AV (Atrioventricular) Bundle (of His):

Conducts impulses rapidly between SA node and bundle branches

AV (Atrioventricular) Node:

Conducts impulses to AV Bundle; delays impulse, so that atria finish contracting before ventricles contract

Cardiovascular System:

Consists of the heart and blood vessels:

Systole:

Contraction of a heart chamber

Ectopic Pacemaker:

Damage to SA node may lead to AV node taking over, and act as secondary pacemaker; 40 to 60/min, instead of 70 to 80

2 systems of veins drain the upper limb and shoulder:

Deep and superficial sets

Parietal pericardium:

Deep to fibrous pericardium; outer layer of serous membrane

Atherosclerosis:

Deposits of cholesterol plaque form in inner lining of walls of arteries

Artificial Pacemaker:

Device used to treat disorders of cardiac conduction system; implantable and battery-powered

Pulse pressure (PP):

Difference between systolic and diastolic blood pressures (SP − DP).

Deep set of veins:

Digital veins → radial and ulnar veins → brachial veins

Respiratory movements in venous blood flow

During inspiration, as thoracic cavity enlarges, pressure falls below abdominal pressure; this helps blood flow upward toward heart

Coronary sinus:

Enlarged vein into which other cardiac veins drain; drains into right atrium

Auricles:

Flap-like projections from atria, which allow atrial expansion

Afterload:

Force that ventricles must provide to open semilunar valves to eject blood

2/3rds of total blood in body

Found within veins and venules at any time (approximately)

Inherited deficiency of a mitochondrial enzyme that breaks down fatty acids:

Heart failure results from inability to break down long-chain fatty acids, and use them for energy. (Cardiac muscle uses them as primary energy source)

Phlebitis:

Inflammation of a vein; common disorder

Visceral pericardium:

Inner layer of serous membrane; attached to surface of heart; also called the epicardium

Purkinje Fibers:

Large fibers that conduct impulses to ventricular myocardium; conduct impulses to apex first; whorled pattern of muscle in ventricles contract with twisting motion

Left Ventricular Assist Device (LVAD):

Mechanical half- heart, used in some cases temporarily, until donor heart is available

SA (Sinoatrial) Node:

Pacemaker; initiates rhythmic contractions of the heart

Branches of right coronary artery:

Posterior interventricular artery and right marginal branch

Two closed circuits (pathways)

Pulmonary and systemic circuit

Flutter:

Rapid, regular contraction of a heart chamber, 250 to 350 beats/min.

Arterioles:

Receive blood from the arteries, and carry it to the capillaries

Venules:

Receive blood from the capillaries, and conduct it to veins

Veins:

Receive blood from venules, and carry it back to the atria of the heart

Left ventricle:

Receives blood from the left atrium; pumps blood to systemic circuit

Left atrium:

Receives blood from the pulmonary veins; pumps blood to left ventricle

Right ventricle:

Receives blood from the right atrium; pumps blood to lungs

Right atrium:

Receives blood returning from systemic circuit (from the superior and inferior vena cavae and coronary sinus); pumps blood to right ventricle

Heart Transplant:

Replacement of most of a failing heart with a donor heart

Capillaries:

Sites of exchange of substances between the blood and the body cells

Pericardial cavity:

Space between visceral and parietal layers of serous pericardium

Cardiac Conduction System:

Specialized group of cardiac muscle cells, which initiate and distribute cardiac action potentials through myocardium

Left and Right Bundle Branches:

Split off from AV bundle, conduct impulses to Purkinje fibers on both sides of heart

Contractility:

Strength of contraction at a specific preload (EDV)

Left subclavian artery:

Supplies left arm

Circumflex branch:

Supplies left atrium and ventricle

Left common carotid artery:

Supplies left side of head and neck

Posterior interventricular artery:

Supplies posterior ventricles

Right marginal branch:

Supplies right atrium and ventricle

Brachiocephalic trunk:

Supplies right side of head and upper limb; splits into right common carotid and right subclavian arteries

Anterior interventricular (left anterior descending) artery:

Supplies walls of ventricles

Arterial systolic pressure (SP):

The maximum pressure reached during ventricular contraction.

Arterial diastolic pressure (DP):

The minimum pressure remaining before next ventricular contraction.

Tunica externa (adventitia):

outer layer, connective tissue

Ventricles:

Thick-walled lower chambers; pump blood into arteries

Atria:

Thin-walled upper chambers; receive blood returning to heart

Implantable Replacement Heart:

Titanium and plastic artificial heart, used in people that cannot have heart transplant, and do not have long to live

Fibrous pericardium:

Tough outer layer, that surrounds double-layered serous membrane

Vasoconstriction of veins (venoconstriction) in venous blood flow

Under conditions of low blood pressure, sympathetic reflexes cause contraction of smooth muscle in walls of veins

Deep set of veins from lower limbs:

Veins in foot → anterior and posterior tibial veins → popliteal vein → femoral vein → external iliac vein

Superficial set of veins in lower limbs

Veins in foot → small and great saphenous veins -Great saphenous vein is the longest vein in the body

T wave:

Ventricular repolarization; occurs just prior to ventricular relaxation

End-diastolic Volume:

Volume of blood in each ventricle at end of ventricular diastole

End-systolic Volume:

Volume of blood remaining in each ventricle at end of ventricular systole

Stroke volume (SV):

Volume of blood that enters the arteries with each ventricular contraction (70 mL/beat) -Difference between end-diastolic volume (EDV) and end-systolic volume (ESV)

Skeletal muscle contraction in venous blood flow

When muscle contract, they squeeze veins, and help move blood back toward heart

Heart

a hollow, cone-shaped, muscular pump; generates force to transport respiratory gases, nutrients, and wastes through body

Epinephrine in BP control

a hormone from adrenal medulla, increases heart rate, cardiac output, blood pressure

Chordae tendineae (structural function)

are fibrous strings that attach cusps of tricuspid and mitral valves to papillary muscles in wall of heart

Brachiocephalic trunk

supplies Right upper limb, right side of head

Suprarenal artery

supplies adrenal glands

Bronchial artery

supplies bronchi

Phrenic artery

supplies diaphragm

Esophageal artery

supplies esophagus

Renal artery

supplies kidney

Left common carotid artery

supplies left side of head

Left subclavian artery

supplies left upper limb

Common iliac artery

supplies lower abdominal wall, pelvic organs, lower limb

Inferior mesenteric artery

supplies lower portions of large intestine

Mediastinal artery

supplies mediastinum

Gonadal artery

supplies ovaries/testes

Pericardial artery

supplies pericardium

Superior mesenteric artery

supplies portions of small and large intestines

Lumbar artery

supplies posterior abdominal wall

Middle sacral artery

supplies sacrum and coccyx

Celiac trunk

supplies stomach, spleen, liver

Posterior intercostal artery

supplies thoracic wall

aortic sinuses

swelling in aorta near valve cusps -Left and right coronary arteries begin at aortic sinuses

arteries

transport blood away from heart

Capillaries

transport blood between arteries and veins, and perform nutrient, gas, and waste exchange

Blood vessels

transport blood throughout the body: arteries, veins, capillaries

Veins

transport blood toward heart

Electrocardiogram (ECG, EKG):

• A recording of electrical changes that occur in the myocardium during the cardiac cycle • Used to assess ability of heart to conduct impulses • The deflections in the normal ECG, or waves, include: P wave, QRS complex, T wave

Superficial set of veins:

• Anastomoses in palm and wrist → basilic and cephalic veins • Basilic vein joins brachial vein, and cephalic vein joins axillary vein

Cardiac Cycle (the events that occur during a heartbeat):

• Atria contract (atrial systole) while ventricles relax (ventricular diastole) • Then ventricles contract (ventricular systole) while atria relax (atrial diastole) • Then both chambers relax briefly

During atrial systole and ventricular diastole:

• Atria contract and ventricles are relaxed • The AV valves open and the semilunar valves close • Atrial systole pushes remaining 30% of blood into the ventricles, causing ventricular pressure to increase

Example of baroreceptor reflex response:

• Baroreceptors in aortic arch and carotid artery sinuses detect blood pressure • Increased pressure stretches receptors • Parasympathetic cardioinhibitory reflex lowers heart rate and blood pressure -*baroreceptors decrease heart rate, stretch receptors increase*

Promoting angiogenesis:

• Body secretes VEGF in response to blocked coronary artery • If not sufficient, VEGF may be able to be delivered in time-release capsules, or gene therapy, which delivers genes encoding VEGF to area that lacks oxygen

Life-Span Changes

• Cholesterol deposition in the blood vessels • Narrowed coronary arteries • Heart may shrink slightly, or enlarge due to disease • Proportion of heart consisting of cardiac muscle declines • Increase in fibrous connective tissue of the heart • Increase in adipose tissue of the heart • Heart valves and left ventricular wall may thicken • Increase in systolic blood pressure • Decrease in resting heart rate • Lumens of large arteries narrow, as arterial walls thicken • Decrease in arterial elasticity

Pericardium (pericardial sac):

• Covering over heart and proximal ends of large blood vessels • Portions of the pericardium: fibrous pericardium, parietal pericardium, visceral pericardium, pericardial cavity

Viscosity:

• Difficulty with which molecules of fluid flow past each other • Greater the viscosity, the greater the resistance to blood flow • Blood cells and plasma proteins increase the viscosity of the blood • Greater the resistance to flow → greater the force necessary to transport the blood → greater the blood pressure becomes • Any factor that alters concentration of blood cells or plasma proteins also alters blood viscosity • Example: Anemia lowers concentration of blood cells → lowers blood viscosity → lowers the blood pressure

Coronary Artery Disease (CAD):

• Disease involving deposition of cholesterol plaque on inner walls of coronary arteries • Leads to obstruction of coronary arteries, O2 deficiency in cardiac muscle • Often accompanied by high serum cholesterol and hypertension • Often causes pain in the chest upon exertion, called angina pectoris • A major contributing factor to myocardial infarction (heart attack) • Treatments include: -Percutaneous transluminal coronary angioplasty (PTCA) -Coronary bypass surgery

Exercise and the Cardiovascular System

• Exercise is good for heart, but it has to be regular part of life.

Peripheral Resistance (PR):

• Force of friction between blood and walls of blood vessels • Blood pressure must overcome PR in order to flow • Factors that change PR also change blood pressure • Vasoconstriction of arterioles increases PR, which increases the blood pressure • When blood is pumped out of ventricles, arteries swell; rapid elastic recoil sends the blood through the arteries, against PR in arterioles and capillaries

Angiogenesis:

• Formation of new blood vessels • Mainly controlled by Vascular Endothelial Growth Factor (VEGF) • Regulated in the body, since excess, deficient, or inappropriate blood vessel formation can cause common diseases

cardiac muscle cells:

• Have 1 central nucleus, and form branching networks • Intercalated discs between cells contain desmosomes for structural support, and gap junctions to spread action potentials through a network of cells • Form a functional syncytium, mass of merging cells that function as a unit: 2 such masses exist in the heart: -In the atrial walls; called the atrial syncytium -In the ventricular walls; called the ventricular syncytium

Fenestrated capillaries:

• Have large openings in cell membranes and between endothelial cells • Found in endocrine glands, kidneys, small intestine

Sinusoidal capillaries:

• Have largest openings; spaces between cells are small cavities • Discontinuous • Found in liver, spleen, and red bone marrow

Continuous capillaries:

• Have small openings • Found in muscle, connective and nervous tissues, and skin

For exercise to benefit cardiovascular system:

• Heart rate must increase to 70 to 85% of maximum (220 − your age) • Must last 30 to 60 minutes • At least 3 to 4 times/week

Filtration:

• Hydrostatic pressure forces molecules through membrane • Pressure is derived from ventricular contraction

Other factors that affect heart rate:

• Impulses from hypothalamus and cerebrum • Body temperature • Levels of K+ and Ca+2

Stretch Receptors in venae cavae:

• Increase in blood pressure stretches receptors • Sympathetic cardioaccelerator reflex increase heart rate and force of contraction, to lower venous pressure

Cardiovascular system adaptations to aerobic exercise:

• Increased pumping efficiency, blood volume, hemoglobin concentration, number of mitochondria • Heart may enlarge 40% or more • Stroke volume increases • Heart rate and blood pressure decrease

Endocardium:

• Inner layer, thin • Forms inner lining of all heart chambers

Baroreceptor reflexes:

• Involve cardiac control center in medulla oblongata • Balance inhibitory and excitatory effects of parasympathetic and sympathetic fibers • Contains a *cardioinhibitor reflex center* and a *cardioaccelerator reflex center*

Transcytosis:

• Large substances (antibodies and lipoproteins) use this method • Substances enter endothelial cell by endocytosis, and leave other side of cell by exocytosis

Aorta:

• Largest diameter artery in body • Portion attached to heart is aortic root • Main portions include ascending aorta, aortic arch, descending aorta (which contains the thoracic aorta and the abdominal aorta) • Aortic semilunar valve lies at root • Swellings near valve cusps are aortic sinuses • Left and right coronary arteries begin at aortic sinuses • Aortic bodies: Baroreceptors in aortic arch that monitor blood pressure • Major branches of aortic arch: brachiocephalic trunk, left common carotid artery, left subclavian artery • Aorta eventually branches into the 2 Common iliac arteries • Cerebral arterial circle (Circle of Willis): -System which supplies blood to the brain -Formed by merging of the internal carotid arteries and basilar artery (formed by 2 vertebral arteries uniting inside cranial cavity)

Hypertension (high blood pressure):

• Long-lasting elevated arterial blood pressure • Causes: unknown cause, increased Na+ intake, psychological stress that activates the sympathetic nervous system, obesity (by increasing the peripheral resistance), kidney disease (via renin-angiotensin response) • "Silent killer," because it may not cause any direct symptoms • Contributes to formation of atherosclerosis • May lead to coronary thrombosis or embolism • May lead to cerebral thrombosis, embolism, or hemorrhage, perhaps resulting in a transient ischemic attack (TIA, ministroke) or a cerebral vascular accident (CVA, stroke) • Prevention: healthy diet and weight, regular exercise, limiting Na+ intake • Treatments: diuretics, sympathetic inhibitors

Structure of venules

• Microscopic vessels that transport blood from the capillaries to veins. • Thinner walls and less smooth muscle than arterioles.

Myocardium:

• Middle layer; thickest layer • Composed of cardiac muscle tissue

Diffusion:

• Most important method of transfer • Lipid-soluble substances diffuse through cell membrane; water-soluble substances diffuse through membrane channels and slits

Epicardium:

• Outer layer, thin • Also called visceral pericardium • Reduces friction

Blood Flow Through the Heart, Lungs, and Tissues

• Oxygen-poor blood from venae cavae and coronary sinus enter right atrium • Blood flows from right atrium, through tricuspid valve, into right ventricle • Right atrium contracts, sending remaining blood into right ventricle • Right ventricle contracts • Tricuspid valve closes right atrioventricular orifice • As pressure rises in right ventricle, pulmonary semilunar valve opens • Blood flows into pulmonary trunk • Blood flows to lungs, drops off carbon dioxide, picks up oxygen • Blood returns to left atrium via pulmonary veins • Blood flows from left atrium, though mitral valve, into left ventricle • Left atrium contracts, sending remaining blood into left ventricle • Left ventricle contracts • Mitral valve closes left atrioventricular orifice • As pressure rises in left ventricle, aortic semilunar valve opens • Blood flows into aorta, transporting oxygen-rich blood to body cells

Systemic circuit path

• Oxygen-rich blood moves from left atrium to left ventricle • Contraction of left ventricle sends blood into systemic circuit • Left ventricle → aorta → all arteries and arterioles leading to body tissues → systemic capillaries → systemic venules and veins → right atrium

Osmosis:

• Presence of impermeant solute, such as plasma proteins, inside capillaries creates osmotic pressure • Osmotic pressure draws water into capillaries, opposing filtration • Colloid osmotic pressure refers to pressure due to plasma proteins • At arteriolar end of capillary H2O and other substances leave capillary by filtration, because hydrostatic pressure > colloid osmotic pressure • At venular end of capillary, H2O is reabsorbed into capillary, because colloid osmotic pressure > hydrostatic pressure • More fluid leaves capillaries at arteriolar end than returns at venous end • Lymphatic vessels return excess fluid through the lymphatic system to the venous blood

Sympathetic impulses that innervate heart:

• Reach heart on accelerator nerves • Increase heart rate, due to influence on SA and AV nodes, atrial and ventricular myocardium

Parasympathetic impulses that innervate heart:

• Reach heart via vagus nerves • Lower SA node rate of 100 beats/min to 60 to 80 beats/min • Decrease heart rate, due to influence on SA and AV nodes

Organization of the heart:

• Right side pumps to pulmonary circuit, blood returns to left side • Left side pumps to systemic circuit, blood returns to right side

Pulmonary circuit path

• Right ventricle → pulmonary trunk → right and left pulmonary arteries → lobar branches, repeated divisions → pulmonary arterioles → alveolar capillaries → pulmonary venules and veins → left atrium • Blood in pulmonary arteries and arterioles is low in O2 and high in CO2 • Gas exchange occurs in pulmonary (alveolar) capillaries • Blood in pulmonary venules and veins is rich in O2 and low in CO2

Skeleton of the Heart

• Rings of dense connective tissue surround origins of pulmonary trunk and aorta, and orifices between atria and ventricles. • Provide attachments for heart valves and muscle fibers • Prevent excess dilation of heart chambers during contraction -Structure includes these rings along with other fibrous masses in the interventricular septum

Arterial blood pressure:

• Rises when the ventricles contract • Falls when the ventricles relax -Blood pressure is stated as a fraction: systolic/diastolic 120/80 -Blood pressure is stated in units of mm Hg, and is typically measured with a sphygmomanometer (blood pressure cuff).

Size and location of heart:

• Size of fist, varies with body size, averages 14 cm long, 9 cm wide • Located in inside thoracic cavity, in mediastinum, behind sternum, above diaphragm, near lungs • Broad base lies beneath the 2nd rib • Pointed apex lies at the 5th intercostal space • Hollow, cone-shaped organ, containing double pump • Divided into left and right halves

Structure of arterioles

• Smaller and thinner-walled than arteries (same 3 layers or tunics) • Walls of middle and outer layers become thinner as arterioles become smaller -Both arteries and arterioles can undergo vasoconstriction and vasodilation

Structure of capillaries

• Smallest-diameter blood vessels • Connect the smallest arterioles and the smallest venules • Extensions of the inner lining of arterioles • Walls consist of endothelium (simple squamous epithelium) only • Semipermeable; exchange substances between blood and tissue fluid • Capillary blood flow regulated mainly by precapillary sphincters: smooth muscle surrounding capillary when it branches off arteriole or metarteriole

Blood Volume:

• Sum of volumes of plasma and formed elements • Varies with age, body size, gender • Usually about 5 L for adults (about 4 to 5 liters in a female and 5 to 6 liters in a male) • 8% of body weight • Blood pressure (BP) is directly proportional to blood volume • Any factor that changes blood volume can change BP • Example: Decreased blood volume, due to hemorrhage, decreases BP

Cerebral arterial circle (Circle of Willis):

• System which supplies blood to the brain • Formed by merging of the internal carotid arteries and basilar artery (formed by 2 vertebral arteries uniting inside cranial cavity)

Characteristics of Venous Pathways

• Systemic venous circulation returns blood to heart after exchange of gases, nutrients, and wastes between blood and cells • Vessels of the venous system originate from the merging of capillaries into venules, venules into small veins, and small veins into larger ones • Unlike arterial pathways, those of the venous system are difficult to follow, due to irregular networks and unnamed tributaries • Pathways of larger veins usually parallel arteries of the same name • All systemic veins converge into the superior and inferior venae cavae, and return to the heart through the right atrium

"Lubb":

• The first heart sound (S1) • Occurs during ventricular systole • Associated with closing of the AV valves

Blood pressure:

• The force the blood exerts against the inner walls of the blood vessels • Circulates the blood • "Blood pressure" usually refers to pressure in systemic arteries • Exists throughout the vascular system • Blood moves from higher to lower pressure throughout the system

"Dupp":

• The second heart sound (S2) • Occurs during ventricular diastole • Associated with closing of the pulmonary and aortic semilunar valves

Structure of arteries

• Thick, strong wall, thicker than walls of veins • 3 layers or tunics: turnica interna (intima), tunica media, tunica externa (adventitia) • Transport blood under high blood pressure • Give rise to smaller arterioles

Structure of veins

• Thinner walls than arteries, but still have 3 layers (tunics) • Tunica media less developed than in arteries • Carry blood under relatively low pressure • Function as blood reservoirs • Many have one-way valves to help with blood flow

Veins that drain the abdominal and thoracic walls:

• Tributaries of the brachiocephalic and azygos veins • The azygos vein drains directly into the superior vena cava

Preventing angiogenesis:

• Tumors secrete VEGF to nourish themselves • Antiangiogenesis drugs are used to treat cancer and age-related macular degeneration

Fibrillation:

• Uncoordinated, chaotic contraction of small areas of myocardium • Atrial fibrillation not life-threatening; ventricular fibrillation is often fatal

Hepatic portal system:

• Unique venous pathway that drains abdominal viscera • Blood from capillaries in the stomach, intestines, pancreas, and spleen drain into the hepatic portal vein, which transports it to the liver for processing, before it is delivered to inferior vena cava • Liver adjusts nutrient concentrations before blood enters general circulation • After passing through the hepatic portal system, blood drains out of liver though hepatic veins, and enters inferior vena cava -Other veins drain directly into inferior vena cava

Portal veins:

• Unusual, in that they do not transport blood directly to the heart • Filter blood through 2 sets of capillaries, instead of the usual 1 set • One set of capillaries performs a unique function in the body • Examples: Hepatic Portal System and the Renal Portal System

Early in ventricular diastole:

• Ventricular pressure is lower than atrial pressure • Atria and ventricles are relaxed • AV valves open, and semilunar valves are closed • About 70% of blood flows passively from atria into ventricles

During ventricular systole and atrial diastole:

• When ventricular pressure rises about atrial pressure, AV valves close • Chordae tendineae prevent the cusps of the valves from bulging too far backward into the atria • Atria relax • Blood flows into atria from venae cavae and pulmonary veins • Ventricular pressure continues to increase, and opens the semilunar valves • Blood flows into the pulmonary trunk and aorta