Chapter 18

Heart

A transport system consisting of 2 side-by side pumps

Right side pump

* receives oxygen-poor blood from tissues
* pumps blood to lungs to get rid of CO2, pick up O2 via pulmonary circuit

Left side pump

* receives oxygenated blood from lungs
* pumps blood to body tissues via systemic circuit

How does blood move?

from areas of high pressure to areas of low pressure

Mediatsinum

Between second rib and fifth intercostal space

Epicardium

Visceral layer of serous pericardium

Myocardium

Circular or spiral bundles of contractile cardiac muscle cells

Cardiac skeleton

* crisscrossing, interlacing layer of connective tissue
* anchors cardial muscle fibers
* supports great vessels/valves
* limits spread of action potential to specific paths

Coronary Sulcus

Encircles junction of atria and ventricles

Anterior interventricular sulcus

anterior potions of interventricular septum

Posterior interventricular sulcus

landmark on posteroinferior surface

Heart has a double blood supply

* pumped blood
* blood feeds the heart O2 and nutrients

Desmosomes

hold cells together’ prevent cells from separating during contraction

Gap Junctions

allow ions to pass from cell to cell; electrically couple adjacent cells

Which has a slower contraction? heart muscles or skeletal muscles

heart muscles

What does a slow contraction prevent?

Tetanus

Contractile cells

responsible for contraction

Pacemaker cells

noncontractile cells that spontaneously depolarize

Angina pectoris

* thoracic pain caused by fleeting deficiency in blood delivery to myocardium
* cells are weakened

Myocardial infarction (heart attack)

* prolonged coronary blockage
* areas of cell death are repaired with noncontractile scar tissue

Hystemia

low blood flow

Cardiac muscle cells

striated, short, branched, fat, interconnected

Intercalated discs

connecting junctions between cardiac cells that contain desmosomes and gap junctions

Functional syncytium

single coordinated unit

Intrinsic conduction system

* network of noncontractile cells
* initiate and distribute impulses to coordinate depolarization and contraction of the heart

Where does parasympathetic division occur?

Vagus Nerve

Where does sympathetic division occur?

Cardiac accelerator nerve

Cardiac cycle

* Blood flow through heart during one complete heartbeat
* takes 0.8 seconds

Electrocardiograph

Can detect electrical currents generated by heart

Electrocardiogram

A graphic recording of electrical activity

Systole

period of heart contraction

Diastole

period of heart relaxation

End diastolic volume

* volume of blood in each ventricle at the end of the ventricular diastole
* average is 130mL

End systolic volume

* blood volume remaining in each ventricle after contraction
* average is 60mL
* 70mL is ejected from EDV

How to find Stroke volume

subtract EDV from ESV

Heart murmur

abnormal heart sounds heard when blood hits obstructions

Cardiac output

* amount of blood pumped out by each ventricle in 1 minute
* HR times SV

Cardiac reserve

Difference between resting and maximal CO

Stroke Volume

volume of blood pumped out by one ventricle with each beat

Three factors that affect SV

* preload
* contractility
* afterload

Preload

* Stretch of a chamber
* increased SV

Contractility

* increase contractile strength with Na+. Ca2+, T3/T4, etc..
* decrease contractile strength with K+ etc.
* increase or decrease SV

Afterload

* decrease SV
* back pressure exerted by arterial blood

Hypocalcemia

* depresses heart
* decrease Ca2+

Hypercalcemia

* increase HR and contractility
* increase Ca2+

Hyperkalemia

* alters electrical activity which can lead to heart block and cardiac arrest
* increase K+

Hypokalemia

* results in feeble heartbeats; arrhythmias
* decrease K+

Factors that influence HR

* age
* gender
* exercise
* body temperature

Tachycardia

abnormally fast HR

Bradycardia

slower HR than normal

P wave

Depolarization of SA node and atria

QRS complex

Ventricular depolarization and atrial repolarization

T wave

Ventricular repolarization

P-R interval

Beginning of atrial excitation to beginning of ventricular excitation

S-T segment

entire ventricular myocardium depolarized

Q-T interval

beginning of ventricular depolarization through ventricular repolarization

Arrhythmias

Irregular heart rhythms

Fibrillation

rapid, irregular contractions

Sinoatrial node (SA)

* pacemaker of the heart in right atrial wall
* depolarizes faster than rest of myocardium
* impulses spread across atria to AV node

Atrioventricular node (AV)

* in inferior interatrial septum
* delays impulses approximately 100ms

Atrioventricular bundle

* in superior interventricular septum
* only electrical connection between atria and ventricles

Right and left bundle branches

* two pathways in interventricular septum
* carry impulses toward apex of heart

Sequence of excitation

* sinoatrial node
* atrioventricular node
* atrioventricular bundle
* right and left bundle branches
* subendocardial conducting network (purkinje fibers)

Coronary sinus

empties into right atrium formed by merging cardiac veins

Cardiac veins

Collect blood from capillary beds

Left coronary artery

supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle.

Two branches of the left coronary artery

* anterior interventricular artery
* circumflex artery

Right coronary artery

Supplies right atrium and most of right ventricle

Two branches of the right coronary artery

* right marginal artery
* posterior interventricular artery

Semilunar valves

* prevent backflow from major arteries back into ventricles
* open and close in response to pressure change
* each valve consists of three cusps

Pulmonary semilunar valve

located between right ventricle and pulmonary trunk

Aortic semilunar valve

located between left ventricle and aorta

Tricuspid valve

* in the right AV valve
* made up of three cusps and lies between right atria and ventricle

Mitral valve

* in the left AV valve
* made up of two cusps and lies between left atria and ventricle

Chordae tendineae

anchor cusps of AV valves to papillary muscles

Right ventricle

most of the anterior surface

Left ventricle

posteroinferior surface

Papillary muscles

* project into ventricular cavity
* anchor chordae tendeneae that are attached to heart valves

Atria

* the receiving chambers
* small thin walled chambers; contribute little to propulsion of blood

Auricles

appendages that increase atrial volume

Right atrium

Receive deoxygenated blood from the body

Superior vena cava

returns blood from body regions above the diaphragm

Inferior vena cava

Returns blood from body regions below the diaphragm

Left atrium

Receives oxygenated blood from lungs

Pericardium

double walled sac that surrounds heart

Where is the base of the heart loacted

leans towards right shoulder

Where is the apex of the heart located

points toward left hip