chapter 15

Anatomy ∙ Physiology IIChapter 15,

Section 1The Cardiovascular

System

FUNCTIONS OF THE HEART

It pumps 7000L (1800 gallons) of blood through our body every day.

The heart contracts 2.5 billion times in a lifetime.

The heart is composed of two pumps

The pulmonary circuit carries blood to the lungs

The systemic circuit carries blood to the body

The heart is located within the mediastinum

1/3 2/3

It is about the size of a fist (14cm x 9cm)

2/3 of the heart is left of the midline

The heart is posterior to the sternum

Baseattachment of major vessels2nd intercostal space

ApexPointed inferior margin5th intercostal space

The heart is surrounded by a pericardial membrane.

The fibrous pericardium forms a thick outer layer of connective tissue.

The parietal pericardium is a serous membrane attached directly to the fibrous layer.

A visceral pericardium is a serous membrane that forms the outer layer of the heart wall .

The pericardial cavity contains serous fluid.

The wall of the heart contains 3 layers

The epicardium is also called the visceral pericardium

The myocardium contains a thick layer of cardiac muscle, with blood vessels and nerves

The endocardium is a smooth layer of squamous epithelium that lines the heart chambers and valves

The heart contains 4 chambers

The left atrium receives blood from the lungs

The right atrium receives blood from the body

The left ventricle pumps blood towards the body

The right ventricle pumps blood towards the lungs

Interventricular septum

A pocket, called the auricleincreases the capacity of the atria .

blood enters the heart through the great veins

The superior vena cava returns blood from the upper body to the heart

The inferior vena cava returns blood from the lower body to the heart

The coronary sinus returns blood from the myocardium to the heart

Four pulmonary veins return blood from the lungs to the heart

Great arteries carry blood away from the heart

The aorta delivers oxygenated blood to the systemic circulation

The pulmonary trunk* delivers deoxygenated blood to the lungs

*The pulmonary trunk immediately divides into a left and right pulmonary artery.

AV valves prevent backflow into the atria .

The tricuspid valve guards the right AV orifice

The bicuspid (mitral) valve guards the left AV orifice

*AV = atrioventricular

Chordae tendineae anchored to the

cusps papillary muscles

Papillary muscles contract to pull the

valves tightly shut

AV valves are anchored to the ventricles by chordae tendineae

Mitral Valve Prolapse – cusp of the mitral valve protrudes into atrium .Symptoms include: chest pain, heart palpitations, and fatigue.

An aortic valve (not shown) is

located at the base of the aorta

Semilunar valves prevent backflow of blood into the ventricles

A pulmonary valve is located at the base of the pulmonary trunk

The semilunar valves close as the ventricles relax to prevent blood from entering the ventricles.

Each cusp of a semilunar valve is shaped like a crescent moon

path of blood through the right heart

1 .Blood enters right atrium through the SVC, IVC, and coronary sinus

2 .It passes through the tricuspid valve into the right ventricle

3 .Blood is pumped from the right ventricle, through the pulmonary valve, and into the pulmonary trunk.

4 .Blood passes into the pulmonary arteries towards the lungs

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path of blood through the left heart

5 .Oxygenated blood is returned to the heart through 4 pulmonary veins .

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9 .Blood enters systemic circulation to the tissues throughout the body .

6 .Blood enters the left atrium .

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7 .Blood passes through the bicuspid valve into the left ventricle .

8 .The left ventricle pumps blood through the aortic valve into the aorta.

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Section 2, Chapter 15

Cardiac Cycle & Cardiac Conduction

Systole – contraction

Diastole – relaxation

Ventricular Diastole• Ventricles are relaxed, filling with blood• Ventricles are 70% full before atria contract• Atrial systole pushes the remaining 30% of blood into ventricles• AV valves are opened while semilunar valves are closed

Ventricular Systole • Ventricles contract to expel blood• Atria are in diastole during ventricular systole, filling with blood• Semilunar valves are opened, while AV valves are closed

The left and right sides of the heart contract together in a coordinated fashion

The cardiac cycle

Heart SoundsThe heart valves produce a distinct sound as they close, which can be heard through a stethoscope.

Lubb-DuppLubb (S1) = sound of AV valves closing

occurs during ventricular systole

Dupp (S2) = sound of semilunar valve closing occurs during ventricular diastole

murmur = abnormal sound from the cusps not closing completely

Heart Sounds - Ausculation

Image from Grant’s Atlas of Anatomy. Each heart valve is indicated by a colored oval and the area of auscultation of the valve is indicated as a circle of the same color containing the first letter of the valve name.

aortic valve (A)heard at 2nd intercostal space, right of the sternum

pulmonary valve (P)heard at 2nd intercostal space, left of the sternum

tricuspid valve (T)heard at 5th intercostal space, either right or left of the sternum

mitral valve (M)heard at 5th intercostal space, below left nipple

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Cardiac Conduction of the Heart

The heart is autorhythmic:Specialized cardiac tissue initiate and distribute electrical impulses that generate heart contractions.

Syncytium – intercalated discs contain gap junctions that transmit action potentials from cell-to-cell. Cardiac muscles contract as a functional unit (syncytium)

Atrial Syncytium – left and right atria contract together

Ventricular Syncytium – left and right ventricles contract together


Pacemaker of heart

Initiates atrial syncytium

Fires 80 impulses per minute

Parasympathetic inhibition keeps heart rate at about 72 beats per minute

conduct impulses towards towards AV node

Figure 15.18 Illustrates the cardiac conduction system.

sinoatrial (SA) node

junctional fibers


Located within inferior wall of interatrial septum

Provides a junction between atrial and ventricular syncytia

Only known conduction pathway between atria and ventricles

divides into left and right bundle branches

Figure 15.18 Illustrates the cardiac conduction system.

atrioventricular (AV) node

AV Bundle (Bundle of His)


Conduction pathways along the interventricular septum

Gives rise to Purkinje Fibers

Transmits action potentials to ventricular myocardium and papillary muscles

Initiates ventricular syncytium at apex of heart

bundle branches (left and right)

purkinje fibers

Figure 15.19 Summarizes the cardiac conduction system

Figure 15.20 Muscle fibers of the ventricles are whorled shape, which increases the blood output during ventricular systole.

End of Section 2, Chapter 15

An electrocardiogram, or ECG (or EKG) is a recording of the electrical changes in the myocardium during the cardiac cycle.

Electrocardiogram

section 3, chapter 15

atrial depolarization that initiates atrial contraction

conduction of electrical impulse across atria from right to left and downward

Ventricular depolarization that initiates contraction of the ventricles

This massive wave hides the atria repolarization

Electrocardiogram

P Wave

QRS Complex

T Wave represents repolarization of ventricles

Electrocardiogram

Normal ECG pattern

ECG of a regular heart rhythm at 75 beats per minute

Atrial Flutter. Atria fire 250-350 times per minute. For every QRS complex there may be 4 or more P waves.

Heart Arrhythmias:

normal

Bradycardia – cardiac rhythm less than 60 beats per minute .

Tachycardia– cardiac rhythm greater than 100 beats per minute .

Examples of Heart Arrhythmias. Arrows indicate p Wave.

Atrial fibrillation. Instead of contracting, the atria become quivering chambers. The ventricles respond only to impulses that make it to the AV node .

Ventricular fibrillation = Life threatening arrhythmia. Ventricles quiver, and are unable to pump blood properly. Requires immediate defibrillation.

Examples of Heart Arrhythmias, fibrillation

The heart rate is controlled intrinsically by the SA node, but sympathetic and parasympathetic fibers alter the rate at which the pacemaker fires.

regulation of cardiac cycle

Cardiac Control Center

Located within Medulla Oblongata

Receives sensory impulses from throughout the cardiovascular system and relays motor impulses to heart in response.

The cardiac control centers include a Cardioinhibitor & cardioaccelerator reflex center

Cardioinhibitor reflex center

Parasympathetic fibers from vagus nerves innervate SA & AV nodes.

Vagus nerves release Acetylcholine (ACh) that decreases the firing rates of SA & AV nodes.

Heart rate decreases

Cardioaccelerator reflex center

Sympathetic fibers from accelerator nerves innervate SA & AV nodes.

Norepinephrine released from fibers increases the firing rates of SA & AV nodes.

Heart rate and force of contraction increases

Cardioinhibitor & cardioaccelerator reflex centers alter the heart rate in response to sensory impulses from receptors

Baroreceptors – monitor blood pressure•Located within aortic arch and carotid sinuses

•Rising blood pressure stimulates cardioinhibitor center

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Figure 15.24b Illustration of the baroreflex arc



Blood Vessels

Arteries•Convey blood away from the

heart

Arterioles•Thinner vessels that convey

blood towards capillaries

Capillaries•Site of exchange between blood and

body tissues

Venules•Receives blood from capillaries

Veins•Returns blood towards the

heart

Endothelium •A layer of smooth simple squamous

epithelium

•Secretes biochemicals with a wide variety of functions.

Basement membrane•Bed of connective tissue with elastic &

collagenous fibers

Tunica Interna (inner)

Walls of the blood vessels consists of 3 Layers

Tunica Media (middle)

Smooth Muscles •Vasoconstriction – muscles contract, decreasing

diameter of vessel

•Vasodilation – muscles relax, allowing vessel diameter to increase

Elastic Connective tissue• Recoil of elastic fibers helps propel

blood through vessels

3 Layers of the blood vessel wall

Tunica Externa (outer)

Fibrous Connective TissueElastic and collagenous fibers

Attaches blood vessel to organs

Vasa Vasorum “vessels of the vessels”Provide blood supply to walls of thicker arteries

3 Layers of the blood vessel wall

Figure 15.27An arteriovenous shunt

provided by a metarteriole.

Arterioles are smaller divisions of arteries .

metarterioles – small arterioles that join capillaries

Arteriovenous shunt – connects an arteriole directly to a venuleShunt allows blood to bypass a capillary bed.

Arterioles

Figure 15.28 Substances are exchanged through openings (slits) separating endothelial cells.

Capillaries smallest diameter blood vessels that

consists of a single layer of endothelial cells

Site of gas, nutrient, and waste exchange

Capillaries

Slits Spaces between endothelia that

facilitate diffusion across vessel wall

Figure 15.26 A precapillary sphincter at the base of a capillary.

Capillaries

Precapillary sphincters Smooth muscles that regulate the flow of blood

through a capillary

Closes a capillary bed when oxygen demand to an organ is low

Artificially colored electron micrograph depicts sinusoids throughout the liver.

Capillaries

large cavities within discontinuous capillaries

Sinusoids allow a rapid exchange of nutrients, debris, proteins, and even cells.

located throughout the liver and spleen.

Sinusoids

VenulesContinue from capillaries and merge to form veins

VeinsConvey blood from body back to the atria of heart

Veins follow a pathway roughly parallel to arteries

Vessel wall of veins has 3 layers (tunics) similar to arteries

Figure 15.31. Venous valves (a) open as blood moves towards the heart, but (b) close to prevent blood from moving backward away from the

heart.

Veins have poorly developed tunica mediaThinner walls, and a larger lumen than arteries

Tunica Interna of veins contain valvesValves prevent blood from flowing backwards towards capillaries.

Veins act as blood reservoirsMost blood (60-70%) is in the veins and venules.

Differences between veins and arteries

Figure 15.25 Blood vessels (a) the wall of an artery. (b) The wall of a vein. (c) cross section

of an arteriole (bottom) and a venule (top).

Differences between veins and arteries

Blood Pressure


Blood PressureBlood pressure is the force the blood exerts against the inner walls of the blood vessels

Usually refers to pressure in systemic arteries

Arterial blood pressure:Rises with ventricular contractions and falls as ventricles relax

Systolic pressure is the maximum pressure during ventricular contraction

Diastolic pressure is the minimum pressure when the ventricles relax

.1Cardiac Output- volume of blood ejected from one ventricle per minute

Volume of blood expelled from ventricle with each contractionAverage = 70 milliliters per beat (mL/beat) for adult male

Average = 72 beats per minute

Stroke Volume

70 mL/beat X

Heart Rate

70 beats/minute =

Cardiac Output

5040mL/minuteexample:

Factors that influence blood pressure

cardiac output = stroke volume (mL) X heart rate (beats/minute)

Stroke Volume

Heart Rate

Cardiac output (and blood pressure) increases with an increase in stroke volume or heart rate.


blood pressure increases

heart rate increases stroke volume increasesor

Blood VolumeAverage blood volume in adults = 5 Liters (1.3 gallons)As blood volume increases, blood pressure initially increases

Peripheral ResistancePeripheral resistance = friction between blood and blood vesselsVasoconstriction increases resistance and increases blood pressureVasodilation decreases blood pressure

Viscosity of bloodViscosity = resistance of a fluid to flow (thickness of a fluid).Blood cells and some plasma proteins increase the viscosity of blood.

Anemia (deficiency of red blood cells) reduces viscosity & lowers blood pressure


Some of the factors that influence arterial blood pressure


blood volume increases heart rate increases stroke volume increases

blood viscosity increases peripheral resistance increases

blood pressure increases

blood pressure is maintained

Increased blood pressure

heart rate decreases stroke volume decreases

cardiac output decreases peripheral resistance decreases

cardiac output increases peripheral resistance increases

heart rate increases stroke volume increases

decreased blood pressure

Control of Blood Pressure

Factors that affect stroke volume

End-diastolic volume (EDV)Volume of blood in ventricles at the end of ventricular diastoleVentricles are filled with blood

End-systolic volume (ESV)Volume of blood in ventricles at the end of ventricular systoleOnly 60% of blood is expelled from heart during a normal contractionIncreasing the force of ventricular contractions decreases ESV

Stroke volume = EDV– ESVIncrease stroke volume by increasing EDV or decreasing ESV

stroke volume

Stroke Volume is directly related to the force of ventricular contraction.

Two events that occur in the ventricles coincide with stroke volume:

1 .End-diastolic volume (EDV)Volume of blood in ventricles at the end of ventricular diastole

As ventricles fill with blood, muscle fibers are mechanically stretched - preload

2 .End-systolic volume (ESV)Volume of blood in ventricles at the end of ventricular systole

A normal health heart expels 60% of blood present in ventricle .

stroke volume

Stroke Volume is the difference between end diastolic volume (EDV) and end systolic volume (ESV) : Stroke Volume = EDV - ESV

Frank-Starling Principle:

The ability of a heart muscle to generate force depends on the original stretch of a muscle prior to contraction (similar to stretching a rubber band)

The degree of stretch (preload) of the myocardial fibers before contraction determines the stroke volume

A greater end diastolic volume results in a greater force of contraction, leading to a greater stroke volume.

Figure 15HBlood pressure decreases as blood moves away from the heart.

Blood pressure rapidly decreases as the blood moves through the arterial system and into the capillary network.

Little pressure remains in the veins, therefore heart actions contribute very little to venous return.

Venous Return

Venous return depends on:

Skeletal muscle contractions – massaging actions push blood towards heart

Respiratory movements – generates pressure in abdominal and thoracic cavitiesChanges in pressure pushes blood along veins

Vasoconstriction – contraction of smooth muscles in tunica mediaSympathetic reflexes vasoconstrict the smooth muscles in veins, which can propel additional blood from venous reservoir towards the heart.

Venous Return

AortaMain trunk of the systemic circulation

Divisions of the aortaAortic root = attachment to heartAscending AortaAortic arch

Thoracic aorta Abdominal aorta

Arterial System

Aortic Valve

Aortic Sinus Swelling at aortic root

Right and left coronary arteries Supply blood to myocardium of the heart

Myocardial infarction = blocked coronary artery

Aortic BodiesChemoreceptors - monitor CO2 & O2 levels in blood

Components of the aortic root

Brachiocephalic Artery Brachiocephalic artery divides into:Right common carotid artery Supplies blood to right side of face and head

Right subclavian artery - Supplies blood to right arm

Left common carotid arterysupplies blood to left side of face and head

Left subclavian artery supplies blood to left arm

Branches of the aortic arch

Figure 15.42 The major branches of the aortic arch are highlighted in yellow.


•Aorta - Main trunk of the systemic circulation.

•Divisions of the aorta•Aortic root = attachment to heart

•Ascending Aorta

•Aortic arch

•Thoracic aorta

•Abdominal aorta

Arterial Divisions


Systemic arteries and veins

Aorta - Main trunk of the systemic circulation.

Divisions of the aortaAortic root = attachment to heart

Ascending Aorta

Aortic arch

Thoracic aorta

Abdominal aorta

Arterial Divisions

Aortic Valve

Aortic Sinus - Swelling at aortic root

Aortic BodiesChemoreceptors - monitor CO2 & O2 levels in blood

4 .Right and left coronary arteries

Structures at the aortic root

Right Coronary Artery branchesPosterior interventricular artery :

supplies walls of both ventricles

Marginal artery:supplies right atrium and right ventricle

Coronary Arteries

Left Coronary Artery branchesAnterior interventricular artery:

supplies walls of both ventricles

Circumflex Artery: supplies left atrium and left ventricle

Blocked coronary artery = myocardial infarction

Brachiocephalic artery Right common carotid artery: supplies right

neck and head

Right subclavian artery: supplies right arm

2 .Left common carotid artery supplies left neck and head

3 .Left subclavian artery Supplies left arm

Branches of Aortic Arch

Branches of Thoracic Aorta

Grant’s Anatomy. Branches of the thoracic aorta

Bronchial Arteries – supplies bronchi

Pericardial artery – supplies pericardium

Esophageal arteries – supplies esophagus

Branches of Abdominal Aorta

Phrenic arteries supply diaphragm

Celiac Trunk Gastric a. - supply stomachSplenic a. – supply spleen & pancreasHepatic a. – supplies liver with O2 blood

Superior Mesenteric a .Supplies small intestine

Suprarenal a.Supplies adrenal glands

Branches of Abdominal Aorta

Gonadal arteries .Male = testicular arteriesFemale = Ovarian arteries

Renal arteriesSupplies kidneys

Lumbar arteriesSupplies skin and muscles of lower back

Inferior mesenteric arterySupplies most of large intestine

Divisions of Common Carotid Arteries

External Carotid ArteriesSupplies blood to face, neck, and scalp

Internal Carotid ArteriesSupplies blood to brain

Provides 75% of blood to brain

Carotid Sinus - point of bifurcationCarotid bodies – chemoreceptorsCarotid baroreceptorsCommon site of stenosis (narrowing)

Arteries to the Brain, Head, and Neck

Branches of Internal Carotid Artery

1 .Ophthalmic arterysupplies eyes

2 .Anterior cerebral artery supplies medial surface of brain

3 .Middle cerebral artery Supplies lateral surface of brain

Internal carotid arteries


Vertebral Arteries Provides 25% of blood supply to

brain

Branch from subclavian arteries

Pass through transverse foramen of cervical vertebrae

Enter skull through foramen magnum


Basilar Artery Both vertebral arteries merge to form a basilar

artery at the base of the brain .

Supplies blood to brainstem

Branch: Posterior cerebral arterySupplies occipital and temporal lobes


Cerebral Arterial Circle (Circle of Willis) Joins the internal carotid arteries with basilar artery at base of brain

Provides anastomoses (alternate routes) for blood flow


Arteries to the Shoulder and Upper Limb

Axillary Artery Arises from subclavian artery

Brachial Artery Continuation of axillary arteryUsed for measuring blood pressure

Ulnar ArteryContinues along medial arm to wrist

Radial Artery Continues along lateral arm to wrist

Convenient vessel for taking your pulse

Veins that drain the head and neck

Dural Venous SinusesLocated between 2 layers of dura materMajor CSF draining pathway from brain

Internal Jugular VeinsDrains blood from brain and

deep faceArise from dural sinuses

External Jugular VeinsDrains blood from face, scalp, and neck

Veins that drain the arm

Ulnar & Radial Veins drain forearm and handsMerge for form brachial veins

Basilic VeinLocated on medial aspect of armJoins the brachial vein near the axilla

Cephalic VeinCourses upward on the lateral armJoins axillary vein to form subclavian vein

Axillary VeinFormed from the merging of basilic and brachial veins

Median Cubital VeinJoins basilic and cephalic veins at elbowOften the site of venipuncture

Hepatic Portal System

Portal System – drains blood from one capillary bed into a second capillary bed.

Hepatic Portal Vein (HPV)•Carries nutrient rich blood

from abdominal viscera to the liver for processing

Hepatic Portal SystemTributaries of Hepatic Portal Vein

•Gastric vein – blood from stomach

•Splenic vein – blood from spleen & pancreas

•Superior mesenteric vein – blood from small intestine

•Inferior mesenteric vein – blood from large intestine

Pathway of Hepatic Portal System

End of Chapter 15

heart aorta abdominal viscera HPV liver hepatic vein IVC heart

chapter 15

Education

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