ANATOMY & PHYSIOLOGYTHE HEART+

CIRCULATORY SYSTEM

I. StructureA. General – hollow cone-shaped muscle; 4 chambers• Approx. 9 cm X 14 cm• 2/3 of mass is found on the left side of the body• Rt. Ventricle- mostly on anterior side• Lft. Ventricle- mostly on posterior side

B. Walls of the Heart Pericardium – heart sac, fibrous and parietal layer (outer sac),

pericardial gap; contains serous fluid to reduce friction, visceral layer (epicardium)

Epicardium – thin outer covering; protection and lubrication

Myocardium – thick middle layer of cardiac muscle which makes up most of the heart

Endocardium – thin, elastic inner lining made of endothelium

C. Chambers & Valves 4 chambers:• Right Atrium – pump CO2 rich blood to the right ventricle• Right Ventricle – bigger; pumps blood to the lungs• Left Atrium – smaller; pumps blood from lungs to left ventricle• Left ventricle – more muscle mass, pumps O2 rich blood to the

rest of the body

Valves:• Tricuspid valve – allows blood right atrium to the right ventricle,

usually 3 flaps• Bicuspid (mitral) valve – allows blood from the left atrium to the

left ventricle, usually 2 flaps• Pulmonary (semi-lunar) valve – allows blood to the lungs,

prevents backflow to the right ventricle• Aortic valve – allows blood from the left ventricle to the aorta,

prevents backflow

Pathway of Blood to and from the Heart1) Circulated blood from the body (CO2) returns to the heart via the

superior and inferior vena cava right atrium2) Right atrium contracts and pumps through the tricuspid valve to

the right ventricle

3) Right ventricle pumps blood through the pulmonary valve to the lungs

4) In the lungs, CO2 and O2 diffuse through the capillaries and alveoli

5) Oxygenated blood returns from the lungs via the pulmonary vein

6) The left atrium pumps oxygenated blood through the bicuspid valve to the left ventricle

7) The left side of the heart pumps the hardest to send blood out to the rest of the body via the aortic valve• Through the carotid artery into the brain• Through the auxiliary arteries into the arms• Through the aorta into the torso and legs

8) Blood moves away from the heart via arteries and capillaries then returns to the heart through veins

Cardiac Muscle Tissue• Striated; consists of sarcomeres just like skeletal muscle• Cells contain numerous mitochondria (up to 40% of cell volume) • Intercalated disc: double membrane with two cardiac muscle

cells close together• Desmosomes: hold the cells tightly together

Gap Junctions• Gap junctions: channels that directly connect cytoplasm of the

two cells allows ions and molecules to move easily between cells.

• low electrical resistance, impulses pass from one cardiac muscle cell to another

• An action potential originating anywhere in a myocardium will always be transmitted to all cells of the myocardium

• No gap junctions between atria and ventricles, these cells are separated by a layer of dense connective tissue that does not conduct impulses

Electrically nonconductive fibrous tissue

Cells of the myocardium• Contractile cells: require outside stimulus• Automatic cells: pace-maker cells, contract without stimulus

Areas of Automatic Cells (Intrinsic Conduction System)1). Sinoatrial (SA) node 2). Atrioventricular (AV) node 3). Atrioventricular (AV) bundle 4). R and L Bundle branches5). Purkinje fibers

Cardiac Excitation• Begins at the SA node & quickly spreads through both atria • Also travels through the heart's 'conducting system' (AV node > AV

bundle > bundle branches > Purkinje fibers) through the ventricles • For efficient pumping:

- The atria should contract (& finish contracting) before the ventricles contract.- The atria should contract as a unit, & the ventricles should contract as a unit.

Blood Circuits Pulmonary circuit• Carries deoxygenated blood from the right side of the

heart to the lungs• Brings oxygenated blood back from the lungs to the left

side of the heart

Blood Circuits Systemic circuit• Carries oxygenated blood from the left side of the heart to the rest of the body

• Brings deoxygenated blood back from the body to the right side of the heart

D) Heartbeat & Blood Pressure Stroke Volume (SV) = EDV - ESV

• SV – amount of blood pumped out of each ventricle at each beat, avg. 70mL/beat

• EDV (end diastolic volume) – amount of blood left in ventricles at rest, avg. 120mL/beat (filling up heart with blood)

• ESV (end systolic volume) – amount of blood left after contraction, avg. 50mL/beat (after blood is pumped out how much is left in heart)

Cardiac output – heart rate x stroke volume• Amount of blood pumped out per minute, avg. heart rate = 70-

80 beats/minute Blood Pressure – pressure blood exerts on walls of vessels• Arteries – increase in pressure• Systolic – max amount of pressure exerted on the walls of

arteries during ventricle contraction (120)• Diastolic – minimum amount of pressure exerted on the walls of

the arteries during relaxation(80)

Three important factors affecting blood pressure are: – Stroke volume (SV)• amount of blood pumped out by ventricles with each

contraction – Diameter of the vessel. What happens with big diameter?

Low?• decrease diameter, increase pressure

– Viscosity of blood (thickness of blood). What happens?• Thinner blood = lower blood pressure• Thick blood= high blood pressure

Blood pressure is regulated by– Autonomic Nervous system- influences the heart rate and

stroke volume Blood pressure is maintained through activity of the – Baroreceptors: stretch receptors in aortic arch and carotid

sinuses• Increase in blood pressure causes the walls of the vessels to stretch thus

stimulating the nerves to regulate BP

– Chemoreceptors: measure O2, CO2 content of blood, pH of blood; located in the aortic arch and carotid sinuses• BP too low, increases CO2, sends signal in order to increases heart rate

and vice versa

Electrocardiography (ECG or EKG) – interpretation of the electrical activity of the heart

• Depolarization: Electrical activation of the myocardium.• Repolarization: Restoration of the electrical potential of the

myocardial cell. P wave: represents atrial depolarization; Atrial repolarization occurs

during ventricular depolarization and is obscured QRS complex: represents ventricular depolarization T wave: represents ventricular repolarization

Disorders detected by EKG (http://www.bem.fi/book/19/19.htm)

Myocardium decreased in size smaller than normal electric charge Myocardium increased in size larger than normal electric charge Longer P-R interval conduction problem with SA + AV nodes Tachycardia high heart rate (100b/m); overactive SA node Bradycardia slower heart rate (60b/m); AV node takes over for SA

Heart Block: damage to AV node; interferes with ventricles• 1st degree Heart Block abnormally long P-R wave; delay between atrium +

ventricle

• 2nd degree Heart Block not all impulses make it to ventricles; skips; 2 P waves then 2 QRS waves

• Total Heart Block no impulses to ventricles; uneven ratio of P and QRS waves

Fibrillation: different arrhythmias; uncoordinated muscle movement in the heart• Atrial Fibrillation no P waves; SA node no longer works; AV node takes

over

• Ventricular Fibrillation ventricles aren’t depolarizing, only P waves – cardiac arrest

Diseases CAD or CHD (coronary artery/heart disease)• Full or partial blockage (plaque), lack of oxygen• Symptoms – shortness of breath, chest pain (angina), coronary

ischemia (reduction of O2 because of reduced blood flow) • Can be controlled by behavior modifications• Nitroglycerin + surgery balloon angioplasty or coronary artery

bypass graph• Sew femoral + pectoral veins to bypass blockage

CABG: Coronary Artery Bypass Grafting• Most common type of open heart surgery in US

Myocardial infarction (Heart Attack!) A portion of the heart is starved of oxygen = cardiac ischemia If cardiac ischemia lasts too long, the starved heart tissue dies

otherwise known as a myocardial infarction -- literally, "death of heart muscle."

Symptoms• Chest pain or discomfort (angina pectoris). Most heart attacks involve

discomfort in the center or left side of the chest. The discomfort usually lasts more than a few minutes or goes away and comes back. It can feel like pressure, squeezing, fullness, or pain. It also can feel like heartburn or indigestion.

• Upper body discomfort. You may feel pain or discomfort in one or both arms, the back, shoulders, neck, jaw, or upper part of the stomach (above the belly button).

• Shortness of breath. This may be your only symptom, or it may occur before or along with chest pain or discomfort. It can occur when you are resting or doing a little bit of physical activity.

• Breaking out in a cold sweat• Feeling unusually tired for no reason, sometimes for days

(especially if you are a woman)• Nausea (feeling sick to the stomach) and vomiting• Light-headedness or sudden dizziness