BSC2086CChapter 20

Cardiovascular System Introduction1) Divided into 2 circuits

a. Pulmonary circuit

b. Systemic circuit

2) Three types of blood vesselsa. Arteries

b. Veins

c. Capillaries

3) Heart: the topic of this chapter

Anatomy of the Heart (Much of this section is covered in lab and in homework, meaning the lecture on this section may be abbreviated or left for independent study depending upon time.)

1) Locationa. Size of closed fistb. In mediastinum

c. 2/3 of mass to left of midlined. Apex

e. Base

f. Surrounded by a pericardial sac

2) Cardiac muscle tissue (how are they different from skeletal muscle cells?)a. Cardiac muscle cells

i. Branching cells connected by intercalated discs

1. Contain desmosomes and gap junctionsa. Functional significance?

ii. Smalliii. Single nucleus

3) Chambers of the hearta. Two atria

i. Auricle

ii. Interatrial septum

iii. Coronary sulcus

iv. Foramen Ovale

1. Fossa ovalis

b. Two ventricles

i. Anterior interventricular sulcus

ii. Posterior interventricular sulcus

iii. Interventricular septum

4) Structural differences between left and right ventricles (and atria!)a. Thin layer of myocardium in atria

i. Why?

b. Thicker myocardium in ventriclesi. Why?

ii. Left ventricle has more myocardium then the right ventricle1. Why?

5) Heart Valvesa. 2 atrioventricular valves

i. Location & purpose:

ii. Leaf-shaped cusps 1. Attached to ventricles through chordae tendineae and papillary muscles

iii. Right atrioventricular valve

iv. Left atrioventricular valve (mitral valve)

b. 2 semilunar valves

i. Location and purpose:

ii. 3 moon-shaped cusps (little hammocks)

iii. Aortic valve

iv. Pulmonary valve

c. How do these valves operate?i. Valves open and close in response to pressure changes as heart relaxes and contracts

1. Importance of valves?

ii. Atrioventricular valves1. Ventricles relaxed

a. AV valves openb. Points of cusps point into ventriclec. Papillary muscles relaxed, slack chordae tendinaea. Movement of blood?

2. Ventricles contracta. Pressure of blood presses cusps upwardb. Cusps meet and close off openingc. Papillary muscles contract and tighten chordae tendinaeb. Importance?

iii. Semilunar valves3. Ventricles contract

a. Pressure of blood higher in ventricle then in arteriesb. Valves openc. Movement of blood?

4. Ventricles relaxa. Pressure of blood higher in arteries then in ventriclesb. Blood flows down towards ventricles, due to pressure (gravity) c. Blood fills valve cusps so valves close tightlya. Importance?

d. Heart valve disordersi. Stenosis

ii. Mitral valve prolapse

iii. Rheumatic fever

6) Flow of blood through the heart as if you are a drop of deoxygenated blood coming from the body a. Superior vena cava, inferior vena cava, coronary sinus

b. Right atriumc. Right atrioventricular valved. Right ventriclee. Pulmonary valvef. Pulmonary trunkg. R and L Pulmonary arteriesh. Pulmonary capillaries in lungsi. 4 Pulmonary veinsj. Left atriumk. Left atrioventricular valvel. Left ventriclem. Aortic valven. Ascending aorta

The Conducting System of the Heart and The Electrocardiogram

1) Cardiac Physiologya. Two types of cells involved in a normal heart beat

i. Cells of conducting system

ii. Contractile cells

b. Cardiac cyclei. Sinoatrial node produces an action potential that begins each heartbeat

ii. Action potential stimulates contraction of contractile cells

2) The Conduction Systema. Specialized cardiac muscle fibers called autorhythmic fibers

i. Self-excitable, repeatedly generate action potentials that trigger heart contractions

ii. Act as pacemaker

iii. Form conduction system1. Network of specialized cardiac muscle fibers that provide a path for each cycle of

cardiac excitation to progress through the heart2. Significance?

b. Componentsi. Sinoatrial node

1. Possesses a prepotential (pacemaker potential)

2. 80-100 per min

ii. Atrioventricular node1. Possesses a prepotential (pacemaker potential)

2. 40-60 per min

iii. Conducting cells

1. Internodal pathway

2. Atrioventricular bundle

3. Bundle branches

4. Purkinje fibers

c. Action potential propagationi. Sinoatrial (SA) node…atria contract…atrioventricular (AV) node…AV bundle…bundle

branches in interventricular septum…Purkinje fibers…ventricles contract

ii. Ventricles contract from apex to base so blood is pushed toward semilunar valves

d. Heart beat is intrinsic to the heart

i. **Heart rate can be modified but heart beat- fundamental rhythm- is caused by the cardiac muscle itself

e. Problems associated with pacemaker functioni. Tachycardia

ii. Bradycardia

iii. Ectopic pace maker

3) The Electrocardiograma. ECG, EKG

b. Record of action potentials produced by all the heart muscle fibers during each heartbeati. Uses

c. Electrocardiograph

d. 3 Major components of ECGi. P wave

1. Atrial depolarization

ii. QRS complex1. Rapid ventricular depolarization

iii. T wave1. Ventricular repolarization

4) Contractile cellsa. Action potential begins at SA node and excites contractile fibers

b. Similarities to skeletal muscle contraction (Ch 10)i. AP increases Ca2+ around myofibrils

ii. Ca2+ -troponin binding permits contraction to occur

c. Action potential in cardiac muscle cellsi. Rapid depolarization

1. Resting membrane potential is –90mV in ventricular cardiac muscle fibers (skeletal muscle fibers is –85mV, neuron is -70mV))

2. At threshold (-75mV), voltage-gated fast Na+ channels open3. Rapid inflow of Na+ causes rapid depolarization= +30mV4. Channels close and inflow decreases

ii. Plateau1. Period of maintained depolarization: 0mV, lasts 0.175 sec (neuron or skeletal

muscle= 1 msec)a. Active contraction continues until plateau ends

2. Due to opening of voltage-gated slow Ca2+ channels

3. Ca2+ influx balances Na+ active transport outward (and some K+ outflow: small # of voltage-gated K+ channels open)

a. Significance?

4. Ca2+ influx causes more Ca2+ to be released from sarcoplasmic reticuluma. Significance?

iii. Repolarization1. Voltage-gated Ca2+ channels close2. Voltage-gated K+ channels open and K+ outflow restores –90mV

5) Energy for cardiac contractionsa. Almost exclusively aerobic respiration

i. Where does the oxygen come from?

b. Primary energy sources: fatty acids and glucose

Events of the Cardiac Cycle (The information below has been pulled from the reading on pages 682-693 BUT the specific items may not follow the order presented in the text.)

1) Cardiac cycle= all events associated with one heartbeata. Alternate contraction and relaxation of chambers force blood from areas of high pressure to areas

of low pressure

i. Occurs on both sides of heart at the same time

ii. Contraction causes high pressure

b. Systole: contraction of a chamber

c. Diastole: relaxation of a chamber

2) Phases of the cardiac cyclea. Atrial and ventricular diastole (Ventricular diastole- Late)

i. AV valves openii. SL valves closed

iii. Ventricles fill passively (70%, ~105ml))

b. Atrial systole (ventricles in diastole)i. Atria contract

ii. Forces last bit of blood into ventricles (~25ml)iii. At the end of atrial systole/ventricular diastole, ventricles contain the end-diastolic

volume (EDV)

c. Ventricular systole i. Ventricles are contracting due to depolarization while atria are relaxing and filling with

blood ii. First phase

1. Increase in blood pressure in ventricle closes AV valves2. Semilunar valves still closed3. Isovolumetric contraction occurs

iii. Second phase1. Ventricular ejection occurs

2. Pressure in ventricle rises above blood vessels and SL valves open

3. Stroke volume

a. Ejection fraction

4. End-systolic volume (40%, ~50ml)

d. Ventricular diastole (Relaxation Period)i. Ventricles and atria both are in diastole

ii. Early1. Pressure in ventricles drops below that in the blood vessels2. Blood flows towards ventricles and closes SL valves3. AV valves still closed (ventricle pressure still greater then atrial pressure)

a. Causes isovolumetric relaxation

4. Blood still flows into atriaiii. Late

1. Ventricular pressure drops below atrial pressure2. AV valves open3. Ventricular filling begins

3) Heart Soundsa. Auscultation

b. 4 heart sounds occur but 1 and 2 are the only one loud enough to be heard by a stethoscopei. S1: lubb: AV valves closing

ii. S2: dupp: SL valves closingiii. S3: blood movement iv. S4: blood movement

c. Abnormal soundsi. Heart murmurs

Cardiodynamics: Factors That Affect Cardiac Output1) Cardiac output= the amount of blood ejected from the left ventricle into the aorta each minute

a. Affected by stroke volume and heart ratei. CO= SV x HR

ii. Close to total blood volume

iii. If SV or HR increase, cardiac input will increase

2) Factor affecting heart ratea. Autonomic innervation

i. Nervous control from cardiovascular center in medulla oblongata1. Input from:

a. Proprioceptors

b. Chemoreceptors

c. Baroreceptors

2. Sympathetic innervation: cardioaccelatory center

a. Effect:

3. Parasympathetic innervation: cardioinhibitory centera. Effect:

ii. Autonomic tone1. Resting: parasympathetic effects dominate

a. Acetylcholineb. Effect:

c. Slows heart rate

2. During exercise: sympathetic effects dominatea. Norepinephrineb. Effect:

c. Increases heart rate

iii. Atrial Reflex1. Increase in venous return= increase R atrial stretch= increase sympathetic

activity= increase heart rate

iv. Venous Return (in addition to atrial reflex)1. SA nodes stretching = more rapid depolarization

b. Chemical regulation of heart ratei. Hormones

1. Epinephrine, Norepinephrine, thyroid hormone increase heart rate and contractility

a. Tachycardia

ii. Cations1. Potassium

2. Calcium

3. Sodium

c. Other factors in heart rate regulationi. Age

ii. Gender

iii. Physical fitness

1. Bradycardia

iv. Body temperature

1. Hypothermia

3) Factors affecting stroke volume

a. A healthy heart will pump out the blood that entered its chambers during the previous diastoleIf more blood returns during diastole, more is ejected during the next systole

b. Factor 1: Preload (degree of stretch on a ventricle)i. Proportional to end-diastolic volume

ii. Frank-Starling law of the heart1. “The more in, the more out”

2. What does this mean???

iii. Factors that determine EDV1. Duration of ventricular diastole

2. Venous return

iv. Frank-Starling Law equalizes output of the R & L ventricles and keeps the same volume of blood flowing in systemic and pulmonary circulations

c. Factor 2: Contractilityi. Strength of contraction at any given preload

ii. Positive inotropic agents

iii. Negative inotropic agents

d. Factor 3: Afterloadi. Amount of tension the contracting ventricle must produce to force open the semilunar

vales and eject blood (20mmHg in pulmonary trunk, 80mmHg in aorta)

ii. An increase in afterload, decreases stroke volume