CH 20 - THE HEART

The heart

heart serves as primary pump for human body, pumps blood through a closed system of blood vessles

Coverings Around the Heart

Pericardium and Pericarditis

Heart Coverings: Pericardium

1st layer: Fibrous Pericardium - dense connective tissue, a bag that encloses and anchors the heart

2nd layer: Serous Pericardium -

• Parietal Layer: lines the internal surface of the fibrous

• Visceral layer: layer attaches to the heart muscle (myocardium)

• Pericardial cavity: space between the parietal and visceral layers. Cavity is filled w serous fluid which prevents friction between the layers as the heart movies

• Cardiac Tamponade: condition in which excess fluid accumulates in pericardial cavity. Puts pressure on the heart limits the heart from fully contracting

Heart Coverings: Pericarditis

Inflammation of the pericardium. Cause by bacteria, viruses. Serious fluid production is reduced, layers of pericardium stick together. This restricts heart movement

Heart Wall Layers

Epicardium, Myocardium, Endocardium

Epicardium

Visceral layer of the serous pericardium. Thin, outer, protective layer around the heart

Myocardium

Middle layer, composed of cardiac muscle tissue. Layer forms the bulk of the heart wall

Endocardium

Lines the inside of the heart (and chambers). Cover the heart valves. Layer is composed of epithelial and connective tissue. Internally, this layer is covered by an epithelial membrane known as endothelium.

4 Heart Chambers

• 2 superiors atria (separated by interatrial septum)

• 2 inferior ventricles (separated by interventricular septum)

The Atria (atrium)

Small, thin-walled upper chambers. Their primary function is to receive incoming blood from the body. Blood is then pumped into the ventricles.

Atria Structure

• Auricles - small warlike extensions of the atria that increase the surface area of these chambers

• Atria is separated by interatrial septum

• Inner wall covered by Pectinate Muscle

• The Fossa Ovale allows blood to bypass the pulmonary circulation

• Coronary Suculus- external groove on the heart that separates the atria from the ventricles

Ventricles

Lower heart chambers, make up mass of heart. Right snd left ventricles. They are the lower chambers

Ventricles Structure

• Separated by the interventricular septum

• Ventricles pump blood to the body, mulch more muscular than atria

• Trabeculae carnae- ridges on internal surface of each ventricle. Present walls for, sticking together.

• Anterior and Postier Interventricular Suci- separate ventricles on external surface of heart

• Ducrus Arteorisus- bypass the pulmonary artery and aorta. The also allows blood to bypass the pumlmosry circulation

4 Heart Valves

Ensure blood flows in one direction through the heart (atria-ventricles-out of artistries that attach to the heart). Valves open and close in response to differences in blood pressure on their 2 sides. Once blood passes a valve, the pressure associated w the blood pushes the valve closed

Valves

2 atrioventricular valves, 2 semilunary valves

2 AV Valves

• Triscupid Valve: consists of 3 flaps or cusps and is located between right atrium and right ventricle

• Biscupid Valve: consists of 2 flaps and it is located between the left atrium and left ventricle. Also known as Mitral Valve

2 Semilunary Valves

Located between the ventricles and the major arteries attached to the heart. Prevent blood from flowing into ventricles.

Valve Related Diseases

• Incompetent Valve: valve does not open and close

• Valvular Stenoisis: valve flap becomes stiff and constricts the opening

• Mitrial Valve Prolapse: 1% of population, most common in young women

Blood Circulation in Heart:

1. Pulmonary circulation: carried right side of the heart. Blood is pumped into lungs and back to left side of the heart

2. Systemic circulation: carried out by left side of heart. Blood is pumped from the body

3. Coronary Circulation: blood flows to and from the heart muscles

• Left coronary artery

• Right coronary artery

Heart Blood Circularion Events

1. Blood enters right atrium via superior and inferior vena cava. This is deoxygenated blood

2. The right atrium contracts, pushing blood past the tricuspid to the ventricle. Blood fills the right ventricle, and the tricuspid valve closes to prevent back-flow of blood.

3. Right ventricle contracts to push blood past the pulmonary semilunar valve through the pulmonary trunk (artery) into the lungs

4. Oxygenated blood returns to the left atrium via the pulmonary veins (This ends Pulmonary Circulation)

5. Left atrium contacts to to force blood past the mitral (bicuspid) valve into the left ventricle. Once filled w blood, mitral valve closes to prevent back-flow of blood.

6. Left ventricle contracts to force blood past aortic semilunar valve into aorta and rest of body (Systemic Circulation)

7. Coronary Arteries carry oxygenated blood to the myocardium. Left anterior descending artery brances into anterior interventricular artery and circumflex artery. Supports external portisns of left atrium and left ventricule w oxygen. Left anterior descending artery is often referred to as the “Widow Maker”. (Coronary Circulation)

Heart Blood Flow Disorders

1. Angina petoris - inadequate blood supply to the myocardium. Leads to pain and tightness in chest or arms. Treated w nitrates.

2. Ischemia- reduced oxygen supply to the heart

3. Myocardial infarction- heart attach or coronary

• Infarction- death of tissue due to interrupted blood supply

• Often caused by a blockage in one of coronary arteries. Can be caused by blood clot, fat, etc.

• Can be treated w streptokinase (thru a catheter) which dissolves the blood clot

• Surgery may also be an option

Cardiac Muscle Fibers

• Striated and involuntary. Contracts thru sliding filament mechanism

• Intercalated discs- only in cardiac muscle fibers. provide support and strength to contracting muscle fibers

• Cardiac fibers exhibit audtorhythmicity, fibers contract in a coordinated fashion

• Cardiac muscle fibers contain numerous mitochondria which are involved in ATP production (Aerobic Cellular Respiration)

• Cardiac Muscle has a limited ability for repair and regeneration

Heart Physiology: Cardiac Conduction System

1. Normal heartbeat: 2 atria contract (2 ventricles relax) then 2 ventricles contract (while 2 atria relax)

2. Auto-rhythmic Cells make up cardiac conduction system. Specialized neurons, cells make up the following structures:

• Sinoatrial node (SA Node), Atrioventricular node (AV node), Atrioventricular Bundle (Bundle of His), R/L Bundle Branches, Purkinje Fibers

3. Nerve impulses travel over heart in order of systems above

4. Events in Cardiac Conduction System:

• Impulses produce contractions of heart muscle (heartbeat)

• SA node is the pace maker. It producers impulses that begin heart muscle contraction. Generates abt 75 impluses per minute. Impulses produced here spread to both atria. SA Node sets rhythm.

• Impulses (and contractions) pass to AV Node. Located in the lower portion of the interatrail septum. AV Node impluses are briefly delayed so the atria can complete its contraction b4 ventricles contract.

• AV node impluses spread to Atrioventricular Bundle. AV Bundle is only connection between h