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