Histology and Physiology of the Heart

Flashcards on Histology and Physiology of the Heart

Heart

The motor of the circulatory system with a muscular wall that pumps blood rhythmically.

Location of the Heart

Thoracic cavity behind and left to the sternum.

Shape of the Heart

Conical, with the basis upside and apex downside.

Auricles

Dilated parts of the atria found on both sides of the basis.

Heart Chambers

4 chambers: 2 ventricles, 2 atria.

Left Ventricle Function

Supplies blood to the body.

Right Ventricle Function

Supplies blood to the lungs.

Septum

Separates the two sides of the heart.

Atria Position

Located up in both sides of the heart.

Ventricles Position

Located down in both sides of the heart.

Valves

Located between the atrium and ventricle.

Right Atria

Receives blood from the superior vena cava, inferior vena cava, and sinus coronarius.

Blood in Right Atria

Venous blood.

Right Ventricle

Pulmonal trunk starts from here.

Blood in Right Ventricle

Venous blood.

Left Atria

Receives blood from 4 pulmonal veins (O2 rich blood from lungs).

Blood in Left Atria

Arterial blood.

Left Ventricle

Has the thickest wall and the aorta starts from here.

Blood in Left Ventricle

Arterial blood.

Heart Wall Layers

Myocardium, Endocardium, Epicardium, Pericardium.

Endocardium

Innermost layer of the heart.

Endocardium Composition

Simple squamous epithelium (endothelium), Connective Tissue.

Subendocardium

In contact with cardiac muscle and contains small vessels, nerves, and Purkinje Fibers.

Endocarditis

Inflammation of the endocardium.

Purkinje Fibers

Impulse conducting fibers in the heart.

Purkinje Fibers Characteristics

Large modified muscle cells, cluster in groups, 1-2 nuclei, stain pale due to fewer myofibrils.

Purkinje Fibers Location

Terminal branches of the AV bundle branches located in the subendocardial connective tissue.

Myocardium

Thickest layer of the heart.

Myocardium Thickness

Thickest in left ventricle because must pump hard to overcome high pressure of systemic circulation.

Myocardium Composition

Cardiac muscle cells (myocytes).

Intercalated Disks

Junctional complexes that contain fascia adherens, desmosomes, and gap junctions to provide connection and communication.

Epicardium

Outermost layer of the heart.

Epicardium Composition

Connective tissue with nerves, vessels, adipocytes and an outer layer of mesothelium.

Mesothelium

Secretes pericardial fluid.

Cardiac Valves

4 valves in the heart.

AV Valves

Mitral and tricuspid valves, located in the chambers.

Semilunar Valves

Aortic/pulmonary valves.

Cardiac Valve Layers

Spongiosa, Fibrosa, Ventricularis.

Annulus Fibrosus

Surrounds all valves and separates atria and ventricles.

Annulus Fibrosus Composition

Fibrous connective tissue.

Arteries of the Heart

Start from the aorta.

Right Coronary Artery

Supplies right side of the heart and posterior 1/3 of septum.

Left Coronary Artery

Supplies left side of the heart and anterior 2/3 of septum.

v.cordis magna

Largest vein which enters to the right atria through sinus coronarius.

Myocardium Cells

Small cells (100×20 µm), Y-shape, with one nucleus and rich in mitochondria.

Intercalated Disc

Found between myocardial cells, where cells connected with desmosomes and gap junctions (through connexins).

Myocardial Pacemaker Cells

Initiate and propagate the action potential (1% of cells).

Myocardial Contractile Cells

Conduct impulses and responsible for contraction (99% of cells).

Autorhythmic Cells

Smaller than contractile cells, don’t contain many myofibrils, and have no organized sarcomere structure.

Pacemaker Cells

Have unstable membrane potential, bottoms out at -60mV and drifts upward to -40mV, forming a pacemaker potential (Myogenic).

Chronotropic Effects

Refers to factors affecting heart rate.

Dromotropic Effects

Refers to factors affecting conduction of action potentials.

Inotropic Effects

Refers to factors affecting contractility.

Intercalated Discs

Highly convoluted and interdigitated junctions that joint adjacent cells with desmosomes and fascia adherens as also with gap junctions.

Graded Contractions

Myocardial contractions are graded.

Tetanus

Plateau phase prevents summation due to the elongated refractory period, so there is No summation capacity and no tetanus.

CICR

Refers to Calcium induced Calcium release, used during action potential spreading along sarcolemma.

T-tubules

Contain voltage gated L-type Ca2+ channels which open upon depolarization, used during action potential spreading along sarcolemma.

stroke Volume during one systole

70-80ml

End-systolic volume

After systole 40-80 ml blood remain in ventricule.

Fast ventricular ejection

Early ejection of ventricule is fast, later slower

Sinoatrial (SA) Node

Generates impulses about 75 times/minute and Initiates action potentials.

Cardiac Cycle

Electrical Conduction Pathway. Initiated by Sino-Atrial node (SA node) which is myogenic at 70-80 action potentials/minute.

Systole

The contraction phase of the ventricle chambers.

Diastole

The relaxation phase.

Complete Heartbeat

Cardiac Cycle = “events of one complete heart beat”.

Ventricular Systole

Blood pressure builds before ventricles contract pushing blood out.

Early Isovolumic ventricular relaxation

Blood flows back into cusps of semilunar valves and snaps them closed.

Ventricular Ejection

as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected.

P Wave

Contraction of atria.

R Wave

Contraction of left ventricle.

T Wave

Ventricles relaxing.

Ejection fraction

EF, the percentage of the blood that leaves ventricule at the end of diastole – 0.5- 0.75

SA Node

Depolarizes first in the cardiac cycle.

Cardiac Cycle Synchronization

Intrinsic Electrical Conduction System.

stroke volume

The stroke volume (SV) is the volume of blood ejected from the left (or right) ventricle every beat.

Cardiac output.

the SV x heart rate (HR).

Preload

amount ventricles are stretched by contained blood .

Contractility

cardiac cell contractile force due to factors other than EDV .

Afterload

back pressure exerted by blood in the large arteries leaving the heart .

Starling’s Law of the heart

The more the heart muscle is stretched (filled) before contraction (preload), the more forcefully the heart will contract.

At rest cardiac output

it is about 5l/ min

During exercise cardiac output

it can increased up to 25 l/min.