Chapter 20: The Heart

3 major components of the cardiovasular system

heart, blood vessels, and blood

function of heart

pumps blood

blood vessels

transport blood throughout the body

blood

carries oxygen, nutrients, and waste products

amount of blood pumped by the heart per minute

5 liters per minute

total volume of blood in the body

5-6 liters

two main circulatory circuits of the cardiovascular system

pulmonary circulation and systemic circulation

pulmonary circulation function

right heart pumps deoxygenated blood to lungs for gas exchange

systemic circulation function

left heart pumps oxygenated blood to the rest of the body

why is the pulmonary circuit a low-pressure system?

it only pumps blood to the lungs, a short distance, so less force is needed

why is the systemic circuit a high-pressure system?

it pumps blood to the whole body, a long distance, so it needs more pressure

shape of the heart

cone-shaped

size of the heart

about the size of a fist

location of the heart

located in the mediastinum between the lungs, 2/3 to the left of midline, with apex pointing left and resting on diaphragm

where is the apex located and what forms it

pointed inferior (bottom) tip formed by the left ventricle

where is the base located and what forms it

broad posterior (top) surface formed by the atria

3 layers of the heart wall

epicardium (visceral pericardium), myocardium, endocardium

epicardium (visceral pericardium) function

outer protective layer, reduces friction

myocardium function

middle muscular layer responsible for contraction

endocardium function

inner layer lining chamber and valves; smooth surface for blood flow

2 layers of pericardium

fibrous pericardium, serous pericardium

fibrous pericardium function

tough outer layer anchoring the heart, prevents overstretching

serous pericardium

double-layered membrane (parietal and visceral) with pericardial fluid to reduce friction

what happens if pericardial fluid decreases excessively?

friction between heart and pericardium

what happens if pericardial fluid increases excessively?

compression of the heart, reduced filling, reduced cardiac output

4 chambers of the heart

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

function of right atrium

receives systems venous blood

function of right ventricle

pumps blood to lungs

functions of left atrium

receives oxygenated blood from lungs

function of left ventricle

pumps oxygenated blood to body

what are auricles?

small pouch-like extensions of atria (plural of atrium)

what do auricles do?

they increase the volume capacity of atria (plural of atrium)

which ventricle has the thickest wall and why?

the left ventricle- it must pump blood throughout the entire systemic circuit at high pressure

what is the interventricular septum?

a muscular partition separating the right and left ventricles, crucial for preventing mixing of oxygenated and deoxygenated blood

what is a sulcus (plural sulci)

a groove on the external surface of the heart that marks the division between its chambers and provides a pathway for major coronary arteries and veins

3 sulci of the heart

coronary sulcus, anterior interventricular sulcus, and posterior interventricular sulcus

what does the coronary sulcus mark?

separates atria and ventricles

what does the anterior interventricular sulcus mark?

separates ventricles anteriorly

what does the posterior interventricular sulcus mark?

continuation of the anterior sulcus on posterior surface

what are the atrioventricular valves?

tricuspid valve & bicuspid (mitral) valve

where is the tricuspid valve?

between the RA (right atrium) and RV (right ventricle)

where is the bicuspid (mitral) valve?

between the LA (left atrium) and LV (left ventricle)

what are the semilunar valves?

pulmonary valve & aortic valve

where is the pulmonary valve?

between right ventricle and pulmonary trunk

where is the aortic valve?

between left ventricle and pulmonary trunk

what structures prevent aortic valves from prolapsing during contraction?

chordae tendineae attached to papillary muscles

stenosis

narrowing of valve opening

insufficiency

valve fails to close fully, causing regurgitation

flow of blood through the right side of the heart

SVC/IVC/coronary sinus, RA, tricuspid valve, RV, pulmonary valve, pulmonary trunk lungs

flow of blood through the left side of the heart

Pulmonary veins, LA, mitral valve, LV, aortic valve, aorta, systemic circulation

purpose of coronary circulation

to supply oxygen and nutrients to the myocardium, which is too thick to receive oxygen directly from blood in the chambers

what happens during coronary artery blockage?

Decreased oxygen supply, ischemia, angina pectoris, possible myocardial infarction if prolonged

intercalated discs

junctions between cardiac cells

junctions that hold cells together

desmosomes: hold cells together gap junctions: allow action potential spread between cells

autorhythmic cells

cells that spontaneously depolarize to generate action potentials, forming the conduction system

conduction pathway in order

SA node, AV node, AV bundle, bundle branches, Purkinje fibers.

why does the AV node slow down conduction?

to allow atrial contraction to finish before ventricular contraction begins

sympathetic nervous system

increases heart rate and contractility

parasympathetic nervous system

decreases heart rate

3 phase of cardiac muscle action potential

depolarization, plateau, repolarization

depolarization

Na⁺ influx

plateau

Ca²⁺ influx maintains depolarization

repolarization

K⁺ efflux

refractory period

time during which another AP cannot be generated

why is the refractory period important?

prevents tetanus in cardiac muscle, ensuring rhythmic contractions

ECG component

P wave, QRS complex, T wave

P wave

atrial depolarization

QRS complex

ventricular depolarization (and hidden atrial repolarization)

T wave

ventricular repolarization

P-Q interval

atrial to ventricular conduction

Q-T interval

entire ventricular depolarization-repolarization

what are the phases of the cardiac cycle

atrial systole, ventricular systole, atrial diastole, ventricular diastole

how does atrial systole contribute to ventricular filling?

adds ~25 mL of blood to the ventricles; ensures full preload before ventricular contraction

EDV

End-Diastolic Volume- volume in ventricles at end of filling, ~130

ESV

End-Systolic Volume- volume remaining after contraction, ~60 mL

stroke volume

EDV-ESV. Normal ~70 mL/beat

isovolumetric contraction

both valves closed; ventricles contract; pressure builds to open semilunar valves

what happens to the relaxation period as HR increases?

it shortens, decreasing coronary perfusion time

what causes the first heart sound (“lubb”)?

closure of the AV valves at the start of ventricular systole

what causes the second heart sound (“dupp”)?

closure of semilunar valves at the start of ventricular diastole

what is a heart murmur and what can cause it?

abnormal heart sound caused by valve stenosis or insufficiency

positive inotropic agents

increase contractility (e.g., sympathetic stimulation, epinephrine, calcium)

negative inotropic agents

decrease contractility (e.g., acidosis, high K⁺, calcium channel blockers)

cardiac reserve

the difference between resting and maximal stroke volume

3 major factors affecting stroke volume

preload, contractility, and afterload

what factors influence heart rate through autonomic control

baroreceptors, chemoreceptors, limbic system, proprioceptors, sympathetic/parasympathetic stimulation

how do hormones affect heart rate?

epinephrine, norepinephrine, and thyroid hormones increase HR; hyperthyroidism can cause tachycardia

tachycardia

heart rate is greater than 100 bpm

bradycardia

heart rate is less than 60 bpm

myocardinal ischemia

reduced blood flow → hypoxia → reversible

infarction

complete blockage → tissue death → irreversible

left heart failure

fluid backs up into lungs → pulmonary edema

right heart failure

fluid backs up into systemic veins → peripheral edema