Chapter 21- Heart
In which chamber can the pectinate muscles and fossa ovalis be found?
-right atrium
Describe the movement of electrical impulses thru. the conducting system:
1. TIME=O: • The SA node depolarizes and atrial activations begin. 2. ELAPSED TIME= 50 MSEC: • Depolarization spreads across the atrial surfaces and reaches the AV node. 3. ELAPSED TIME= 150 MSEC: • Atrial contractions begin. The AV node delays the spread of electrical activity to the AV bundle by 100msecs. 4. ELAPSED TIME= 175 MSEC: • Impulses travel along the AV bundle within the interventricular septum to the apex of the heart. Impulses also spread to the papillary muscles of the right ventricle by the moderator band. 5. ELAPSED TIME= 225 MSEC: • The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed and ventricular contraction begins.
What causes valves to open? What keeps valves closed?
AV VALVES: • Papillary muscles relax. • Due to the pressure in the atria, the AV valves open. • When ventricles contract, blood forces the AV valves closed. • When ventricles contract, AV valves are held closed by the papillary muscles pulling on the chordae tendinae. SEMILUNAR VALVES: • When the ventricles contract, pressure causes the semilunar valves to open. • Also upon contraction, the blood forces the AV valves closed, thus resulting in blood going through the semilunar valves.
Describe how a signal travels from the Cardiac Pacemaker to the myocardium:
CARDIAC CYCLE: 1. Impulse travels from the SA node to the AV node: • Atrial contraction occurs. 2. Impulse travels from the AV node to the AV bundle: • The AV bundle travels along the interventricular septum and then divides to form the right and left bundle branches. 3. The bundle branches send impulses to the Purkinje fibers: • Ventricle contraction occurs.
Which chamber has the thickest walls? What is the significance of the thick wall?
Left ventricle has the thicker wall: • Powerful contraction. • 6-7 times more powerful than the right ventricle b/c it needs to pump blood to the rest of the body (not just to the lungs).
In which chamber can the moderator band be found? What is its function?
MODERATOR BAND: found only in the right ventricle: • Muscular band that extends from the interventricular septum to the ventricular wall. • Prevents overexpansion of the thin-walled right ventricle. • Passes electrical impulses from interventricular septum to muscles in the right ventricle.
Define Nodal cells and conducting fibers:
NODAL CELLS: • Sinoatrial nodes (SA) and atrioventricular nodes (AV). • Establish the rate of contractions. • Cell membranes automatically depolarize. • Sinoatrial node (SA node): o Sits within the floor of the right atrium. o Located in the posterior wall of the right atrium. o Also called the cardiac pacemaker. o Generates 80-100 action potentials per minute. • Atrioventricular node (AV node): o Sits within the floor of the right atrium. CONDUCTING FIBERS: • Distribute the contractile stimulus to the myocardium.
How are Norepinephrine and Acetylcholine related to heart rate?
Norepinephrine from the ANS causes: • An increase in the heart rate. • An increase in the force of contractions. Acetylcholine from the ANS causes: • A decrease in the heart rate. • A decrease in the force of contractions.
What is the pericardium? How many layers does it have? Where is each layer located?
PERICARDIUM: • Thick, membranous, fluid-filled sac. • Encloses, protects and nourishes the heart. 1. FIBROUS PERICARDIUM: outer layer of pericardium: • Comprised of dense CT: protects the heart, anchors it to the surrounding walls, and prevents it from overfilling. 2. SEROUS PERICARDIUM: inner layer of the pericardium: • Further divided into two layers: parietal pericardium & visceral pericardium. • Functions to lubricate the heart with pericardial fluid: stored in the space between the parietal and visceral layers.
Define Systole and Diastole:
SYSTOLE: contraction: • Blood is ejected into the ventricles. • Blood is ejected into the pulmonary trunk and the ascending aorta. DIASTOLE: relaxation: • Chambers are filling with blood.
Anatomically, how is the heart positioned in the body?
The heart lies slightly to the left of midline: • Located in the mediastinum. • Base= superior portion • Apex= inferior portion • Heart sits at an oblique angle. • Right border formed by right atrium. • Inferior border formed by right ventricle. The heart is rotated slightly toward the left: • Basically, the heart appears to be twisted just a bit. • Sternocostal surface is formed by the right atrium and right ventricle. • Posterior surface is formed by the left atrium.
How many circuits does the heart pump blood into and what are they called?
The heart pumps blood into 2 circuits: • Pulmonary circuit: carries deoxygenated blood away from the heart, to the lungs, and returns oxygenated (oxygen-rich) blood back to the heart. • Systemic circuit: carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. Each circuit involves arteries, veins, and capillaries: ARTERIES: • Transport blood away from the heart. VEINS: • Transport blood toward the heart. CAPILLARIES: • Vessels that interconnect arteries and veins.
How do the papillary muscles and chordae tendineae prevent valve inversion when the ventricles contract?
The right AV (tricuspid) valve is connected to papillary muscles via chordae tendineae: • Since there are three cusps to the valve, the chordae tendineae are connected to three papillary muscles. • Papillary muscles and chordae tendineae prevent valve inversion when the ventricles contract. • When the ventricles contract, AV valves are held closed by the papillary muscles pulling on the chordae tendineae.
What valve is found between the left atrium and left ventricle? How many cusps does it have? What is another name for the valve?
a. Blood passes through the bicuspid (mitral) valve: • Left atrioventricular valve. • Evolves from 2 cusps: anterior and posterior.
How many layers does the heart have and what are they called? Which layer is considered the cardiac muscle layer?
a. EPICARDIUM: • External surface b. MYOCARDIUM: "cardiac muscle layer:" • Consists of cardiac muscle cells c. ENDOCARDIUM: • Internal surface.
What type of cells coordinates cardiac contractions? How many types are there?
• CONDUCTING CELLS: nodal cells and conducting fibers.
What brings deoxygenated blood to the heart? Where is it brought to?
• Deoxygenated blood enters the right atrium through 3 major veins: a) Superior vena cava: Returns all of the blood to the heart from tissues superior to the heart in the head, neck, arms and upper thorax. b) Inferior vena cava: Returns blood to the heart from tissues inferior to the heart, including the legs, abdomen and lower thorax. c) Coronary sinus: Collects blood from the exterior of the heart itself to be returned to the interior of the heart.
Where is the coronary sinus and which heart chamber does it empty into?
• Drains directly into the posterior aspect of the right atrium. • Coronary sinuses are in select coronary veins. • Coronary veins drain cardiac venous blood ultimately into the right atrium.
What are 3 major veins that return deoxygenated blood from the heart?
• Great cardiac vein, small cardiac vein, middle cardiac vein (merge as a large coronary sinus).
What are 2 major arteries that supply oxygenated blood to the heart?
• Select coronary arteries: originate at the base of ascending aorta & supply the cardiac muscle tissue. Right coronary artery (RCA): • Right marginal branch. • Posterior interventricular branch. Left coronary artery (LCA): • Circumflex branch. • Left marginal branch. • Anterior interventricular branch.
List the 4 chambers of the heart:
• Two atria: right atrium, left atrium. • Two ventricles: right ventricle, left ventricle.
What valve leads to the aorta?
• aortic (semilunar) valve
Which vessels return oxygenated blood to the left atrium?
• left & right pulmonary veins.
What valve leads to the pulmonary trunk?
• pulmonary (semilunar) valve
