A&P Cardiovascular System: The Heart

Size: closed fist weighing 250-350g or 8-10 oz

Location: mediastinum (medial cavity of thorax)

Orientation: base = posterior surface & apex = point of anterior surface

Pericardium and Pericardial cavity

Double walled sac that surrounds and protects the heart

Fibrous Pericardium: outer fibrous layer which protects heart, anchors to surrounding structures, and prevents the heart from overfilling with blood

Serous Pericardium: inner layer composed of two layers (parietal and visceral)

Contains fluid between the parietal and visceral layers of the serous pericardium which reduces friction between the two layers

Epicardium, myocardium, endocardium

Visceral layer of serous pericardium, thin transparent layer

Middle layer of cardiac muscle, skeleton of heart

Inner thin layer of endothelium (squamous epithelium)

Four chambers, three sulci, atria, ventricles

Atria: two superior receiving chambers divided by interartrial septum

Ventricles: two inferior discharging chmbers divided by interventricular septum

Thickness of myocardium of the four chambers varies according to the chamber's function

Coronary: between atria and ventrices

Anterior: between ventricles on anterior surface

Posterior: between ventricles on posterior surface

Small thin-walled chambers which return blood to heart

a. Auricles: external flaps on each atrium that increases their volume

b. Pectinate Muscles: internal ridges in each atrium composed of bundles of muscle tissue

c. Fossa Ovalis: shallow depression remnant of an opeing in fetal heart (foramen ovale)

Blood enters right atrium via superior vena cava, inferior vena cava and coronary sinus

Blood enters left atrium via four pulmonary veins

Large thick-walled chambers (left ventricle thickest wall) which pump blood away from heart

a. Trabeculae Carnea: internal irregular ridges of muscle in each ventricle

b. Papillary Muscles: cone-like muscles involved in valve function

Blood leaves right ventricle via pulmonary trunk

Blood leaves left ventricle via aorta

The heart is a double pump

Pulmonary Circuit: circulation of blood through the lungs, function of the right side of heart

Systematic Circuit: circulation of blood throughout the body except the air sacs in the lungs, function of the left side of the heart

Functional blood supply to heart

Arterial: left and right coronary arteries

Venous: cardiac veins and coronary sinus

Atrioventricular: tricuspid and bicuspid (mitral)

Chordae Tendinae: strands of collagen cords which anchor cusps of valve to the papillary muscles

Semilunar: pulmonary semilunar and aortic semilunar

a. striated

b. short, fat, branched

c.one or two large nuclei

d. interconnected by intercalated discs

e. large numerous mitochondria

f. sarcomeres with Z discs, A bands, and I bands

g. calcium delivering system least elaborate, no triads

a. 1% of cardiac cells are self-excitable and autorhythmic

b. all cardiac muscle cells are a single contractile unit which contracts as a unit or not at all

c. long absolute refractory period which prevents tetanic contractions

d. sequence of electrical events (ion movements) similar to that in skeletal muscle fibers

Aerobic Respiration: greater dependence on oxygen therefore more mitochondria than skeletal muscle

Not dependent on nervous system but autorhythmic cells

Intrinsic Conduction System: noncontractile cardiac cells specialized to initiate and distribute impulses throughout heart

a. Sinoatrial (SA) node: pacemaker

b. Atrioventricular (AV) node

c. Atrioventricular bundle: bundle of His

d. right and left bundle branches

e. perkinje fibers

Extrinsic innervation of heart

a. Cardioacceleratory center (sympathetic)

b. Cardioinhibitory center (parasympathetic)

Record of electrical changes during each cardiac cycle

a. P wave: atrial depolarization

b. QRS complex: onset of ventricular depolarization

c. T wave: ventricular repolarization

d. P-Q interval or P-R interval: conduction time from beginning of atrial excitation to beginning of ventricular excitation

e. S-T segment: time when ventricular contractile fibers are fully depolarized

f. Q-T interval: beginning of ventricular depolarization through ventricular repolarization

S1 = "lubb" - blood turbulence associated with closing AV valves

S2 = "dubb" - blood turbulence associated with closing semilunar valves

a. Ventricular filling (mid-to-late diastole): ventricular filling and atrial contraction

b. Ventricle systole (atria in diastole): isovolumetric contraction and ventricular ejection

c. Isovolumetric relaxation (early diastole)

The amount of blood ejected by the left ventricle into the aorta or right ventricle into the pulmonary trunk per minute

Product of heart rate (beats per minute) x stroke volume (ml per minute)

Stroke volume

a. amount of blood ejected by a ventricle during systole

b. end diastolic volume (EDV) - end systolic volume (ESV)

• c. Regulation of stroke volume
• i. preload = degree of stretch (Starling's Law)
• ii. contractility = contractile strength achieved as a given muscle length
• iii. afterload = pressure that must be overcome for the ventricles to eject blood

Cardiovascular center in medulla oblongata

a. sympathetic impulses increase heart rate and force contraction

b. parasympathetic impulses decrease heart rate, vagal tone

a. Hormones: epinephrine, norepinephrine, and thyroxine

b. Ions: Na⁺, K⁺, and Ca²⁺

• Body temperature
• Age
• Gender
• Emotions
• Exercise

Trachycardia: abnormally fast heart rate ( > 100 beats/min)

Brachycardia: heart rate slower than 60 beats/min