Modo de aprendizaje: Anatomy and Physiology Ch. 20 The Heart

pulmonary circuit

carries blood to and from the gas exchange surfaces of the lungs

systemic circuit

transports blood to and from the rest of the body

arteries

efferent vessels that carry blood away from the heart

veins

afferent vessels that return blood to the heart.

capillaries

microscopic thin-walled vessels. AKA exchange vessels, because the thin walls permit exchange of nutrients, dissolved gases, and waste products.

Four muscle walls of heart

right atrium, right ventricle, left atrium, and left ventricle

right atrium

-Receives from superior and inferior vena cava and the coronary veins via the coronary sinus

-passes blood to right ventricle

-has an auricle

right ventricle

-receives blood from right atrium via atrioventricular valve or tricuspid valve.

-interior surface has muscular ridges called trabeculae carneae.

-has modurator band

-during contract, blood is moved through the pulmonary semilunar valve into the pulmonary trunk, which divides left and right pulmonary arteries.

-thinner walls than LV bc it has to do less work bc it is close to pulmonary circuit.

modurator band

in right ventricle only, a muscular band with conducting fibers that delivers the contraction signal to the papillary muscles so they contract before the ventricle contracts.

left atrium

-collects blood from right and left pulmonary veins and empties it into the left ventricle.

-has an auricle

-left atrioventricular valve/ bicuspid valve/ mitral valve separates left atrium from left ventricle

left ventricle

-receives blood from left atrium

-pumps blood through aortic semilunar valve into the ascending aorta, then into aortic arch to descending aorta.

-walls have trabecuale carnae but the muscle layer is much thicker than RV. This is necessary since the LV must create enough pressure to pump blood throughout the body.

muscle contractions during heart beat

first the atria contract, then ventricles contact at the same time and eject blood into pulmonary and systematic circuits.

The heart

a 4 chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body

vessels of the heart

arteries, arterioles, capillaries, venules, veins

lymphatic system

lymph vessels, lymph nodes and lymph glands

parietal pericardium

outer membrane that helps create the pericardial cavity.

fibrous layer

in parietal pericardium, is made of loose connective tissue and attached to dense connective tissue on the outside.

Serous layer

the inner layer of parietal pericardium, is composed of simple squamous epithelium. Secretes the pericardial fluid.

pericardial cavity

space between parietal and visceral pericardium that is filled with pericardial fluid

pericarditis

a condition in which the pericardium becomes inflamed.

pericardial fluid

lubricating fluid that reduces friction, normally 20-30 ml in the cavity.

base of heart

attached superior portion of the heart

apex

the inferior free pointed portion of the heart

atrium

seen as 2 auricles at base of heart. Function is to collect blood that is returning to the heart and convey it to the ventricles.

coronary sulcus

separates atrium and ventricles. anterior interventricular sulcus and posterior interventricular sulcus separate the left and right ventricles.

ligamentum arteriosum

attaches the pulmonary trunk and aortic arch. It is a remnant of and and important fetal blood vessel, the ductus arteriosis.

endocardium

inner layer of chamber walls, made of squamous epithelium and is continuous with the endothelium of vessels

myocardium

-forms the walls of the heart, made of cardiac tissue, blood vessels and nerves.

-atrial myocardium: figure 8 that passes through the interatrial septum.

-ventricular myocardium: two layers. Superficial muscles wrap around both ventricles. Deeper spiral around and between ventricles.

epicardium (visceral pericardium)

-serous membrane.

-Consists of loose connective tissue with an upper layer of exposed simple squamous epithelium, mesothelium

valves

structures that allow one way flow of blood

Right atrioventricular Valve / Tricuspid

-between RA and RV.

-has 3 cusps.

-has chordae tendinae that restrict cusp movement. Go from cusp to papillary muscle

Left atrioventricular Valve / Bicuspid / Mitral Valve

- between LA and LV

- only valve with 2 cusps

semilunar valves

-valves between heart and vessels that leave the heart.

-Has 3 cusps.

-prevent the backflow from the pulmonary trunk and aorta into the right and left ventricles

pulmonary semilunar valve

between pulmonary artery and RV

aortic semilunar valve

between LV and aorta

aortic sinuses

sac like dilations at base of ascending aorta that prevents individual cusps from sticking to the wall of the aorta when the valve opens.

Valvular heart disease, VHD

when serious valve problems occur and the heart cannot maintain adequate circulatory flow. Caused by congenital malformations, carditis, or rheumatic fever.

PULMONARY CIRCULATION

RV, pulmonary valve, pulmonary arteries, pulmonary capillaries, pulmonary veins, and LA.

- Functions to remove carbon dioxide from the blood and add oxygen

SYSTEMIC CIRCULATION

LV, Aorta, arteries, capillaries, veins, superior and inferior vena cava, and RA

- Functions to supply the tissues with oxygen and remove carbon dioxide

coronary circulation

two coronary arteries branch at the base of the aorta

left coronary

gives rise to the anterior interventricular branch for the ventricles and the circumflex to the LV and LA

right coronary

gives rise to the right marginal branch for the RV and LV and the posterior interventricular branch for the RV and LV

anastomoses

when two arteries are connected. There are interconnections between the posterior and anterior branches of the interventricular arteries. It allows free circulation between arteries insuring equal flow.

anterior interventricular vein/ Great Cardiac Vein

returns blood from the anterior aspect of the heart served by the anterior interventricular artery.

Posterior Cardiac Vein

drains the areas served by the circumflex artery

Middle Cardiac Vein

drains the area supplied by the posterior interventricular artery

Small Cardiac Vein and Anterior Cardiac Vein

drain the regions supplied by the right coronary artery

coronary sinus

veins converge to form a vein that returns blood to the heart through an opening near the base of the inferior vena cava into the right atrium.

heart conducting system

specialized strands of cardiac tissue or cells responsible for initiating and distributing the stimulus to contract.

Automaticity

heart muscles contract on their own. System needed to coordinate contraction. Atria at 60 bpm and ventricles at 20 bpm.

Sinoatrial Node (SA)

-the "pacemaker", at the posterior wall of the RA near the superior vena cava.

-composed of nodal cells

-spontaneous depolarization is fastest at SA node, so it reaches threshold first and so controls heart rate.

-conducting fibers pass through the atria to the AV via internodal pathway. Fibers stimulate atria to contract along the way.

Atrioventricular Node (AV)

-sits on the floor of the RA.

-slight delay in signal, 100 msec, due to smaller diameter fibers that are less efficient. Delay allows blood to flow from the atria to ventricles.

- max limit of about 230 bpm

-composed of nodal cells

Atrioventricular Bundle/ Bundle of His

-only electrical connection between atria and ventricles

-Goes from Bundle of His to Bundle Branches

-left and right Bundle Branches go to RV and LV

- moves to apex of the heart and then to Purkinje fibers

-have a branch to the papillary muscles before they reach the apex

conduction myofibrils/Purkinje Fibers

-fibers that conduct impulses to ventricles

-bundle branches go directly to papillary muscles, they contract first

-Purkinje fibers then cause ventricles to contract

Electrocardiogram, EEG

a recording of the electrical activities of the heart

P wave

small wave that accompanies the depolarization of the atria

QRS complex

appears as the ventricles depolarize. The ventricles begin to contract shortly after the peak of the R wave. Atria repolarization occurs at this time but the electrical activity of the ventricles is so large repolarization of the atria are masked.

T wave

ventricular repolarization

Cardiac Cycle

the period between the start of one heartbeat and the beginning of the next. Divided in 2 cycles: systole and diastole.

systole

contraction, when blood is forced out of the chamber.

diastole

relaxation, when blood flows into the chamber.

Blood flow

can occur because of pressure differences. It occurs from an area of higher pressure to an area of lower pressure. Meaning atrial systole cannot occur during ventricular systole and atrial diastole cannot occur during ventricular diastole.

foramen ovale

opening in fetal heart that connects the two atria. It permits blood flow from the right atrium to the left atrium while lungs are developing. At birth, the foramen ovale closes and becomes the fossa ovalis.

Papillary muscles

cone shaped muscles, 3 in RV and 2 in LV to constrict to tighten cords and prevent valves from everting.

When ventricles are RELAXED, what are the valves like?

the AV valves are OPEN and SL valves are CLOSED. Chordae tendineae are loose and papillary muscles are relaxed

When ventricles are CONTRACTING, what are the valves like?

the AV valves are CLOSED and SL valves are OPEN

cardiac skeleton

consists of 4 dense bands of tough elastic tissue that encircle the heart valves and bases of the pulmonary trunk and aorta. Stabilize the positions of the heart valves and ventricular muscle cells.

coronary ischemia

reduced circulatory supply that results from partial or complete blockage of the coronary arteries. Usual cause is from atherosclerosis

Conducting System pathway

SA node --> internodal pathways (conducting cells) --> AV node --> AV bundle --> bundle branches --> purkinje fibers

purkinje fibers

distribute the stimulus to the ventricular myocardium, specifically the contractile cells in the walls of the atrium and ventricles.

Q-T interval

time required for the ventricles to undergo a single cycle of depolarization and repolarization. Longer interval indicates a problem in heart.

P-R interval

extends from start of atrial depolarization to start of QRS complex. Longer interval indicates conducting pathway or AV node problems.

(Rapid) Depolarization

-at threshold, voltage-gated Na channels open and Na goes in and depolarizes the sarcolemma. AKA fast sodium channels.

The Plateau

-Na channels close and remain closed until transmembrane potential drops.

-Na is pumping out of the cell and Ca is coming into the cell to balance the charge and the transmembrane potential is 0mV = plateau

-major difference between cardiac muscle cells and skeletal muscle fibers, which has no plateau.

Repolarization

slow Ca channels close and slow K channels open to let K out of the cell to restore the resting potential.

refractory period

when a membrane will not respond normally to a second stimulus for some time after an action potential begins.

Role of Calcium Ions in Cardiac Contractions

The appearance of an action potential produces a contraction by causing an increase in the Ca concentration around the myofibrils in 2 steps

1. Ca ions crossing the plasma membrane during plateau phase provide 20% of Ca required for a contraction

2. Arrival of this extracellular Ca triggers release of more Ca from reserves in the sarcoplasmic reticulum.

Role of Calcium Ions in Cardiac Contractions

Cardiac muscle tissue is highly sensitive to changes in Ca concentration of the extracellular fluid. The action potential is prolonged for plateau in cardiac muscle cells, while in skeletal muscle it does not and twitches or tetany instead. The heart in tetany could not pump blood due to limitations of the conducting system.

Phases of cardiac cycle

Atrial systole begins --> Atrial systole ends and atrial diastole begins --> Ventricular systole 1st phase, AV valves close --> ventricular systole 2nd phase, SL valves open and blood ejects --> Ventricular diastole early, SL valves close --> Ventricular diastole late, chambers relax.

EDV, end diastolic volume

maximum amount of blood in VENTRICLES at end of atrial systole.

stroke volume

-ventricular blood ejection.

SV = EDV-ESV

-The amount of blood pumped out of each ventricle during a single beat.

-most important factor in an examination of a single cardiac cycle

ESV, end systolic volume

amount of blood remaining in ventricle when SL valve closes.

isovolumetric contraction

in ventricular systole when ventricles are contracting to generate pressure and tension, but valves are closed so blood does not flow out. Ventricular pressure rising.

isovolumetric relaxation

in ventricular diastole when all valves are now closed, ventricle walls relaxing and ventricular pressures are still higher than atrial pressures so blood cannot flow into ventricles. This is isovolumetric relaxation. Ventricular pressures drop rapidly over this period because elasticity of the CT of the heart and cardiac skeleton helps re-expand the ventricles toward their resting dimensions.

dicrotic notch

in ventricular systole. Marked when AV valves CLOSE. At end of ventricular systole, pressure falls and blood in aorta and pulmonary trunk flow back toward ventricles which closes SL valves. This causes pressure to rise and this small, temporary rise produces a valley in the pressure tracing, called dicrotic notch.

atrial systole

atria contract and complete filing of ventricles. Atrial pressure is higher than ventricular pressure.

ventricular systole

atria begin a period systole as blood passing begins to fill atria. Ventricular systole begins as blood is forced from ventricles into pulmonary and systemic circulation.

ejection fraction

percentage of the EDV represented by the SV

cardiac output

amount of blood pumped by the LV in one minute. It is an indication of blood flow through peripheral tissues.

CO = HR x SV

cardioacceleratory center

controls sympathetic neurons that increase the heart rate

cardioinhibitory center

controls the parasympathetic neurons that slow the heart rate.

parasympathetic nerves

VAGUS NERVE causes HR to decrease. More parasympathetic activity when resting to keep below 100bpm. AcH causes an increase in K ion channel activity so the cardiac cell membranes are held closer to the potassium equilibrium potential.

Sympathetic nerves

Increases HR. It releases NE from postganglionic fibers and causes adrenal medulla to secrete E and NE.

Lub (s1)

first heart sound, marks ventricular contraction. Sound caused by AV valves closing.

Dub (s2)

second heart sound, marks start of ventricular filling. Sound caused by SL valves closing.

s3 and s4

sounds are faint and rarely detected. s3 is when blood flow into ventricles. s4 is when atrial contracts.

starlings law of the heart

increasing the EDV results in a corresponding increase in the SV.

venous return

Amount of blood returning to heart through veins. It directly affects nodal cells. When venous return increases, atria receive more blood and walls are stretched. Stretching of cells of SA node leads to more rapid depolarization and an INCREASE HR

Hormones and HR

E, NE, and thyroid hormone INCREASE HR by their effect on the SA node. E also effects contractile cells. After sympathetic stimulation of the adrenal medullae, the myocardium may become so excitable that abnormal contractions occur.

atrial reflex

AKA Bainbridge reflex, involves adjustments in HR in response to increase in venous return. When right atrium walls are stretched, receptors trigger a reflexive INCREASE in HR by stimulating sympathetic activity.