A&P 2 Exam 2 - Cardiovascular System | Heart

Pulmonary and Systemic Circuits

Both circuits are connected to the heart by pumps on both the right and left side; right side receives oxygen-poor blood from tissues, left side receives oxygenated blood from lungs; right side pumps blood to lungs to get rid of CO2, pick up O2, via pulmonary circuit, left side pumps blood to body tissues via systemic circuit.

General Structure

Chambers: Right atrium, left atrium, right ventricle, left ventricle (atriums are receiving, ventricles are pumping), pericardium, superficial fibrous pericardium, parietal layer (deep two layered pericardium), visceral layer (epicardium/deep two layered pericardium), epicardium, myocardium, cardiac skeleton, endocardium, 4 chambers including 2 superior aorta, 2 inferior ventricles, interatrial septum, fossa ovalis, interventricular septum, foramen ovale, papillary muscles, atrioventricular valves, semilunar valves, chordae tendinae, biscupid valve, tricuspid valve, pulmonary semilunar valve, aortic semilunar valve.

Right Atrium

Receives blood returning from systemic circuit.

Left Atrium

Receives blood returning from pulmonary circuit.

Right Ventricle

Pumps blood through pulmonary circuit.

Left Ventricle

Pumps blood through systemic circuit.

Pericardium

Double-walled sac that surrounds heart; made up of two layers parietal and visceral layers.

Superficial Fibrous Pericardium

Functions to protect, anchor heart to surrounding structures, and prevent overfilling.

Epicardium

Visceral layer of serous pericardium.

Myocardium

Circular or spiral bundles of contractile cardiac muscle cells.

Cardiac Skeleton

Interlacing layer of connective tissue; anchors cardiac muscle fibers; limits spread of action potentials to specific paths.

Endocardium

Innermost layer; is continuous with endothelial lining of blood vessels; lines heart chambers and covers cardiac skeleton of valves.

Interatrial Septum

Separates atria.

Fossa Ovalis

Remnant of foramen ovale of fetal heart.

Intraventricular Septum

Separates ventricles.

Atria

The receiving chambers.

Auricles

Appendages that increase atrial volume.

Right Atrium

Receives deoxyginated blood from body.

Superior Vena Cava

Returns blood from body regions above the diaphragm.

Inferior Vena Cava

Returns blood from body regions below the diaphragm.

Coronary Sinus

Returns blood from coronary circulation.

Ventricles

The discharging chambers; makes up most of the volume of the heart; thicker walls than atria; right ventricle: pumps blood into pulmonary trunk; left ventricle: pumps blood into aorta (largest artery in body).

Papillary Muscles

Project into ventricular cavity.

Heart Valves

Ensure unidirectional blood flow through heart; atrioventricular valves located between atria and ventricles; semilunar valves located between ventricles and major ateries.

Atrioventricular (AV) Valves

Tricuspid valve (right AV valve) is made up of three cusps and lies between right atria and ventricle; Bicuspid (also, mitral) valve (left AV valve) is made up of two cusps, and life between left atria and ventricle.

Chordae Tendinae

Anchor cusps of AV valves to papillary muscles that function to hold value flaps in closed position and prevent flaps from everting back into atria.

Semilunar (SL) Valves

Open and close in response to pressure changes; pulmonary semilunar valve is located between right ventricle and pulmonary trunk; aortic semilunar valve is located between the left ventricle and aorta.

Pathway of Blood

Superior vena cava, right atrium, tricuspid valve, pulmonary trunk, pulmonary arteries, lungs (pulmonary circulation), left atrium, bicuspid valve, left ventricle, aortic semilunar valve, aorta (systemic circulation).

Pulmonary Circuit

Short, low-pressure circulation.

Systemic Circuit

Long, high-friction circulation.

Cardiac Muscle Fibers

Striated, short, branched, fat, interconnected; one central nucleus; contain numerous large mitochondria (25-35% of cell volume) that afford resistance to fatigue; rest of volume composed of sarcomeres.

Intercalculated Discs

Connecting junctions between cardiac cells that contain…

Desmosomes

Hold cells together; prevent cells from separating during contraction.

Gap Junctions

Allows ions to pass from cell to cell; electronically couple adjacent cells.

Electrical Events of the Heart

Presence of gap junctions; Network of noncontractile (autorhythmic) cells; intrinsic cardiac conduction system; initiate and distribute impulses to coordinate depolarization and contraction of heart.

Sequence of Excitation

Cardiac pacemaker cells pass impulses, in following order, across heart in ~0.22 seconds.

Sinoatrial (SA) Node

Pacemaker of heart in right atrial wall; depolarizes faster than rest of myocardium; generates impulses about 75x/minute (sinus rhythm); impulse spreads across atria, and to AV node.

Atrioventricular (AV) Node

Inferior interatrial septum; allows atrial contraction prior to ventricular contraction.

Atrioventricular (AV) Bundle

In superior interventricular septum; only electrical connection between atria and ventricles; atria and ventricles not connected via gap junctions.

Right and Left Bundle Branches

Two pathways in interventricular septum; carry impulses toward apex of heart.

Subendocardial Conducting Network

Complete pathway through interventricular septum into apex and ventricular walls; more elaborate on left side of heart; ventricular contraction immediately follows from apex toward atria; process from initiation at SA node to complete contraction takes ~0.22 seconds.

Electrocardiogram

A graphic recording of electrical activity; composite of all action potentials at given time; not a tracing of a single AP; electrodes are placed at various points on body to measure voltage differences.

Main Features of Electrocardiogram

P wave, QRS complex, T wave, P-R interval, S-T segment, Q-T interval.

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.

Mechanical Events

Systole: period of heart contraction; Diastole: period of heart relaxation.

Cardiac Cycle

Blood flow through heart during one complete heartbeat, atrial systole and diastole are followed by ventricular systole and diastole; cycle represents series of pressure and blood volume changes; mechanical events follow electrical events seen on ECG; ventricular filling, ventricular systole, isovolumetric relaxation: early diastole.

Ventricular Filling

Pressure is low; 80% of blood passively flows from atria through open AV valves into ventricles from atria (SL valves closed); atria finish contracting and return to diastole while ventricles begin systole.

Ventricular Systole

Atria relax: ventricles begin to contract; rising ventricular pressure causes closing of AV valves; ventricular pressure exceeds pressure in large arteries, forcing SL valves open.

Isovolumetric Relaxation: Early Diastole

Following ventricular repolarization (T wave), ventricles are relaxed; atria are relaxed and filling; backflow of blood in aorta and pulmonary trunk closes SL valves.

Regulation of Heart Rate

Regulated by autonomic nervous system; sympathetic nervous system activated by emotional or physical stressors; norepinephrine released causes: pacemaker to fire more rapidly, increasing HR; increased contractility; parasympathetic nervous system opposes sympathetic effects; acetylcholine hyperpolarizes pacemaker cells by opening K+ channels which slows HR → little to not effect contractility.

Chemical Regulation

Hormones, Ions.