biol 121 chp 20: the cardiovascular system - the heart

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Rob Swatski Associate Professor of Biology

HACC – York Campus

Chapter 20

Cardiovascular System: The Heart

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(a) Inferior view of transverse section of thoracic cavity showing heart in mediastinum

Sternum

Muscle

Left lung

Esophagus Sixth thoracic vertebra

LEFT PLEURAL CAVITY

Heart

PERICARDIAL CAVITY

Right lung

Aorta RIGHT PLEURAL CAVITY

POSTERIOR

ANTERIOR

View

Transverse plane

Pulmonary trunk (artery)

Heart LocaEon: MediasEnum

Arch of aorta

Anterior view of heart in thoracic cavity

Pulmonary trunk

Left lung

LEFT SURFACE

APEX OF HEART

Superior vena cava

RIGHT SURFACE

Right lung

Pleura (cut to reveal lung inside)

Diaphragm

INFERIOR SURFACE

Heart

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Heart OrientaEon

Apex: anteriorly, inferiorly, le6-‐side Base: posteriorly, superiorly, right-‐side Anterior surface: deep to sternum & ribs Inferior surface: on diaphragm Right border: faces right lung LeK (Pulmonary) border: faces le6 lung

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Heart Surface ProjecEon

Superior right point: sup border -‐ 3rd right costal carClage

Superior leK point: inf border -‐ 2nd le6 costal carClage, 3 cm le6 of midline

Inferior leK point: 5th intercostal space, 9 cm le6 of midline

Inferior right point: sup border -‐ 6th right costal carClage, 3 cm right of midline

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Pericardium

Fibrous pericardium (outer) -‐ dense irregular CT -‐ protects & anchors heart -‐ prevents overstretching

Serous pericardium (epicardium): -‐ thin, delicate membrane -‐ parietal & visceral layers -‐ pericardial cavity -‐ pericardial fluid

PericardiEs

Cardiac tamponade

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Layers of the Heart Wall Epicardium: 2 layers – 1) visceral layer of serous pericardium & 2)

adipose Cssue & fibroelasCc Cssue

Myocardium: cardiac muscle

Endocardium: endothelium & CT (lines chambers & valves)

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Muscle Bundles of the Myocardium

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MyocardiEs & EndocardiEs

endocardiEs myocardiEs

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Chambers & Sulci of the Heart

4 Chambers: -‐ 2 superior atria

-‐ 2 inferior ventricles

Sulci: grooves on heart surface -‐ contain coronary BVs & adipose

Coronary sulcus -‐ encircles heart b/w atria & ventricles

Anterior interventricular sulcus -‐ ant. boundary b/w ventricles

Posterior interventricular sulcus -‐ post. boundary b/w ventricles

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Right Atrium

Receives blood from 3 sources: superior vena cava, inferior vena cava, & coronary sinus

Interatrial septum

Fossa ovalis: remnant of fetal foramen ovale

Tricuspid valve -‐ blood flows through into right ventricle -‐ 3 cusps of dense CT -‐ “RAT on the Right” (Right Atrioventricular, Tricuspid)

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Right Ventricle

Forms most of ant. surface of heart

Interventricular septum

Trabeculae carneae

Papillary muscles

Chordae tendineae

Pulmonary semilunar valve -‐ allows blood into pulmonary trunk

Papillary Muscles & Chordae Tendineae

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LeK Atrium

Forms most of base of heart Receives blood from lungs through 4 pulmonary veins -‐ 2 right & 2 le6 Bicuspid valve: blood flows through into le6 ventricle -‐ 2 cusps -‐ “LAMB on the Le6”: Le6 Atrioventricular, Mitral, or Bicuspid

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LeK Ventricle

Forms apex of heart Chordae tendineae, papillary muscles, & trabeculae carneae

AorEc semilunar valve -‐ allows blood into ascending aorta -‐ openings to the coronary arteries directly above valve

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Myocardial Thickness & FuncEon Thickness varies based on each chamber’s funcCon:

-‐ Atria walls are thin; Ventricle walls are thick -‐ Right ventricle walls are thin; LeK ventricle walls are

thick

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Fibrous Skeleton of Heart

Dense CT rings surround heart valves -‐ fuse together & merge with interventricular septum

FuncEons of fibrous skeleton: -‐ valve support structure

-‐ Prevents overstretching of the valves -‐ inserCon point for cardiac muscle bundles -‐ electrical insulator b/w atria & ventricles

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AV Valves OPEN

Allow blood flow from atria into ventricles when ventricular pressure is lower than

atrial pressure Occurs during ventricular relaxaEon:

-‐ papillary muscles are relaxed -‐ chordae tendineae are slack

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AV Valves CLOSED

Prevents backflow (regurgita/on) of blood into atria

Occurs during ventricular contracEon: -‐ papillary muscles contract -‐ chordae tendineae pulled taut -‐ valve cusps pushed closed

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SL valves OPEN during ventricular contracCon -‐ allow blood flow into pulmonary trunk & aorta

SL valves CLOSE during ventricular relaxaCon -‐ blood fills cusps & valves close

-‐ prevents blood from flowing backwards into ventricles

Semilunar Valves

Superior view with atria removed: pulmonary and aortic valves closed, bicuspid and

tricuspid valves open

PULMONARY VALVE (closed)

Left coronary artery

BICUSPID VALVE (open)

TRICUSPID VALVE (open)

AORTIC VALVE (closed)

Right coronary artery

POSTERIOR

ANTERIOR

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Heart Valve Disorders Stenosis: narrowing of valve that restricts blood flow

-‐ Surgically repaired or replaced with mechanical valves or valves from human donors or pigs

Insufficiency or incompetence: valve cannot close completely

Balloon valvuloplasty

Mitral Valve Stenosis 35

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Systemic CirculaEon

LEFT side of heart pumps oxygenated blood to body

LeK atrium à LeK ventricle à Aorta à Systemic arteries à Arterioles à Systemic capillaries à Organsà Systemic venules à Systemic veins à Superior/Inferior vena

cava/Coronary sinus à Right atrium

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Pulmonary CirculaEon

RIGHT side of heart pumps deoxygenated blood to lungs

Right atrium à Right ventricle à Pulmonary trunk à Pulmonary arteries à Pulmonary capillaries à Lungs à Pulmonary Veins

Oxygen-rich blood

Path of blood flow through heart

Oxygen-poor blood

10. 8.

5.

7.

2.

1.

3.

5.

6.

10.

4. Pulmonary capillaries of right lung

Key:

4. Pulmonary capillaries of left lung

9. Systemic capillaries of head and upper limbs

9. Systemic capillaries of trunk and lower limbs

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Coronary CirculaEon

Blood flow into the myocardium

Supplies the cardiac muscle Cssue of the heart wall

Many anastomoses

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Coronary Arteries

Right coronary artery

Marginal branch Posterior interventricular branch

LeK coronary artery

Anterior interventricular branch

or Le6 anterior descending (LAD)

Circumflex branch

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Coronary Veins

Collect wastes from myocardium

Great cardiac vein, Middle cardiac vein, Small cardiac vein, Anterior cardiac vein

Drain into coronary sinus

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Cardiac Muscle Tissue

Striated, branching,

shorter fibers of heart

Intercalated discs with gap juncEons

One central nucleus per fiber

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Cardiac Muscle Histology

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Cardiac Muscle Tissue

Same acCn & myosin

arrangement as skeletal muscle

Autorhythmic

Longer contracCons (longer Ca+2 delivery)

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Cardiac Myofibril

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ConducEon System

Autorhythmic fibers à

spontaneous APs

Propagate APs through

myocardium

Sinoatrial (SA) node =

pacemaker

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SA node

AV node

AV bundle (of His)

Right & leK bundle branches

Purkinje fibers

ConducEon System

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RegulaEon of the ConducEon System

Autonomic Nervous System

(ANS)

Hormones (epinephrine)

Modify heart rate & strength of contracCon

They do NOT establish the fundamental

rhythm

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AcEon PotenEal

DepolarizaEon

Plateau

RepolarizaEon

Refractory period

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Physiology of ContracEon

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Electro-‐cardiogram (ECG or EKG)

Visual record of all APs during each cardiac cycle (heartbeat)

Detected at body’s surface

DiagnosCc value

Detects abnormal conducCon,

enlargement, muscle damage, & reasons for

chest pain

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ECG

P wave

QRS complex

T wave

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DiagnosEc Value of the ECG

P-‐Q interval

S-‐T segment

Q-‐T interval

Ventricular diastole (relaxation)

6 Repolarization of ventricular contractile fibers produces T wave

5 Ventricular systole (contraction)

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Depolarization of ventricular contractile fibers produces QRS complex

3 Atrial systole (contraction)

2 Depolarization of atrial contractile fibers produces P wave

1

Action potential in SA node

P P P

P P P

R

Q S

T

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Cardiac Cycle

Systole = ContracCon Diastole = RelaxaCon

At 75 beats/min, 1 cycle = 0.8 sec

Pressure & volume changes during

cycle

Blood pumped from high to low pressure areas

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Atrial systole (contrac'on)

Atrial diastole (relaxa'on)

Ventricular systole

Ventricular diastole

Cardiac Cycle

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Blood Volumes

End Diastolic Volume (EDV)

= 130 ml

End Systolic Volume (ESV)

= 60 ml

Stroke Volume (SV)

= 70 ml

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SV = EDV -‐ ESV

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Phases of the Cardiac Cycle

Isovolumetric RelaxaEon

(all valves close)

Ventricular Filling

(AV valves open)

Isovolumetric ContracEon

(AV valves close)

Ventricular EjecEon

(SL valves open)

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Ventricular Pressures

AorCc BP = 120 mmHg

Pulmonary trunk BP = 30 mmHg

Why? How?

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Heart Sounds

AuscultaEon

Produced when valves close

S1: “lubb” = AV valves close (louder, longer)

S2: “dupp” = SL valves close (quiet, shorter)

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Heart Sounds

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Heart Murmurs

Abnormal sounds before, b/w, or a6er normal sounds

May also mask normal sounds

Caused by valve disorders (stenosis,

incompetency)

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Cardiac Output Volume of blood ejected each

minute from either ventricle

CO = Stroke Volume (SV) x Heart Rate (HR)

70 ml SV x 75 beats/min = 5.25 L/min

Cardiac reserve

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RegulaEon of Stroke Volume

Preload

ContracElity

AKerload

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Preload The greater the stretch, the

greater the force of contracCon

The greater the blood volume, the greater the force of contracCon

Frank-‐Starling Law of the Heart

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ContracElity

PosiEve inotropic agents

SCmulaCon of he SympatheCc division of the Autonomic Nervous

System (ANS)

Hormones: epinephrine & norepinephrine

Higher intersCCal Ca+2

Drugs (digitalis)

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ContracElity

NegaEve inotropic agents

InhibiCon of the SympatheCc division of the Autonomic Nervous

System (ANS)

Anoxia, acidosis, some anestheCcs

Higher intersCCal K+

Drugs (Calcium channel blockers)

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AKerload

The back pressure in the arteries that

the ventricles must overcome…

…in order to open the semilunar

valves

The greater the BP = the greater the a6erload

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CongesEve Heart Failure

If a6erload is high, more blood remains in the ventricles…

…which increases the preload

Le? ventricular failure = pulmonary

edema

Right ventricular failure = peripheral

edema

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Neural RegulaEon of Heart Rate

Cardiovascular center in medulla

oblongata

SympatheEc impulses increase HR & force of contracCon

ParasympatheEc impulses

decrease HR

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Nervous System

Receptors

Proprioceptors: monitor

movements

Chemoreceptors: monitor blood chemistry

Baroreceptors: monitor BP

Cardiovascular (CV) center

Key: Sensory (afferent) neurons Motor (efferent) neurons

Medulla oblongata

Glossopharyngeal nerves (cranial nerve IX)

Vagus nerves (cranial nerve X, parasympathetic)

SA node

Sympathetic trunk ganglion

Cardiac accelerator nerve (sympathetic)

Ventricular myocardium

AV node

Baroreceptors in arch of aorta

Baroreceptors in carotid sinus

Spinal cord

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Biochemical RegulaEon of Heart Rate

Oxygen level: hypoxia

pH: acidosis and alkalosis

Hormones: Epinephrine, norepinephrine, thyroid

hormones

CaEons: Na+, K+, Ca+2

Other factors: Age, gender, physical fitness, body temperature, stress

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High blood cholesterol High BP Smoking

Obesity Lack of regular exercise

Family history

Male gender Diabetes Le6

ventricular hypertrophy

Risk Factors for Heart Disease

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Plasma Lipids & Heart Disease High blood cholesterol:

promotes plaques

High-‐Density Lipoproteins

(HDLs)

Low-‐Density Lipoproteins

(LDLs)

Very Low-‐Density Lipoproteins

(VLDLs)

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Coronary Artery Disease (CAD)

Ischemia

Reduced blood flow through

coronary arteries

Causes hypoxia & weakens

cardiac muscle

Angina Pectoris

Narrowing of coronary arteries

Leads to reduced blood flow, chest pain, pressure, discomfort

Myocardial InfarcEon

Complete obstrucCon of coronary blood

flow causing heart amack

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Coronary Artery Disease ObstrucEons

Atherosclerosis

Coronary artery spasm

Coronary artery thrombosis

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Coronary Artery Bypass GraKing (CABG)

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Congenital Heart Defects

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Congenital Heart Defects, cont.

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Arrhythmia

Irregularity in heart rhythm due to

conducCon system defect

Bradycardia

Tachycardia

FibrillaEon

(d) Ventricular tachycardia

Ventricular fibrillation

(e) Ventricular fibrillation

Ventricular tachycardia

biol 121 chp 20: the cardiovascular system - the heart

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