Integrative physiology (The Cardiovascular System: The Heart)

pulmonary and systemic circulation

Pulmonary circulation - for oxygenation of the blood. Right ventricle to pulmonary artery to lungs to pulmonary vein to left atrium.

Systemic circulation - to supply cells with oxygenated blood and remove waste. Left ventricle to aorta to body to vena cave to right atrium.

heart

hollow organ about the size of a fist

located in thoracic cavity

lies mostly to the left

pericardium

protects and anchors the heart

heart chambers

right atrium, right ventricle, left atrium, left ventricle

can be divided into right and left:

2 atria

2 ventricles

right side of the heart function:

serves pulmonary circuit

left side of the heart function:

serves systemic circuit

top two chambers of the heart

atria

bottom 2 chambers of the heart

ventricles

atria

great vessels leading blood to the atria

right atria contains...

superior vena cava

inferior vena cave

left atria contains...

pulmonary veins

ventricles

great vessels leading blood away from ventricles

right ventricle

pulmonary trunk

left ventricle

aorta

heart valves

ensure one way blood flow

righ heart valve

tricuspid atrioventricular valve (AV)

pulmonary semilunar valve

left heart valve

bicuspid valve antroventricular valve (AV)

aortic semilunar valve

valves have a fibrous skeleton that prevents

them from stretching

Blood flow though the heart

1. right atrium (deoxygenated blood)

2. rigth ventricle

3. pulmonary trunk and pulmonary arteries

4. in pulmonary capillaries, blood loses CO2 and gains O2

5. pulmonary veins (oxygenated blood)

6. left atrium

7. left ventricle

8. aorta and systemic arteries

9. in systemic capillaries, blood loses O2 and gains CO2

cardiac muscle tissue structure

interconnected cells act as a functional syncytium:

1. all cells depolarize and contract at the same time

2. connected via intercalated disks

conduction system functions:

- ensures coordinated contraction

- collection of modified muscle cells (pacemaker)

- initiate action potentials

- conduct action potentials to other heart cells via gap channels

- do not contribute significantly to contractile forces

conduction system process

starts at the superior wall of the rigth atrium

continues through the apex of the heart and myocardium of the ventricles

see slide 51 for visual

conduction system structures

1. sinoatrial (SA) node

2. atrioventricular (AV) node

3. antroventricular (AV) bundle: bundle of HIS

4. rigtht and left bundle branches

5. purkinje fibers

pacemaker potentials- nodal cells

during first half of pacemaker potential, voltage- gated K+ channels close and F-type Na+ channels are open; during second half of pacemaker potential, T-type voltage-gated Ca2+ channels open

1. depolarizing phase

2. repolarizing phase

nodal cells

responsible for establishing the rate of cardiac contraction

contractile cells

- produce force

- do not spontaneously depolarize

- contract in a similar fashion to skeletal muscle

- produce action potentials only in response to signals from the nodal cells

contractile cell action potential

- Rapid depolarization phase

- Initial repolarization phase

- Plateau phase

- Repolarization phase

excitation-contraction coupling

events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract

electrocardiogram

records electrical signals of the heart

consists of waves, intervals and segments that

can be read to provide clues for abnormalities

P wave

represents the depolarization of the atria

P-R interval

represents the AV node delay

QRS complex

represents ventricular depolarization

S-T segment

depolarized state of the ventricular muscle

T wave

represents ventricular repolarization

ECG and heart action potentials

1. depolarization of atrial contractile fibers produces P wave

2. atrial systole (contraction)

3. depolarization of ventricular contractile fibers produces QRS complex

4. ventricular systole (contraction)

5. repolarization of ventricular contractile fibers produces T wave

6. ventricular diastole (relaxation)

cardiac cycle

1. passive ventricular filling

2. atrial contraction

3. isovolumetric ventricular contraction

4. ventricular ejection

5. isovolumetric ventricular relaxation

heart sounds

first sound: S1

second sound: S2

S1

- sound of Lubb

- louder and a bit longer

- caused by vibrations associated with closure of the AV valves

S2

- sound of Dubb

- shorter and not as loud

- caused by vibrations associated with closure of the SL valves

cardiac output

the amount of blood ejected per minute

cardiac output= stroke volume (left ventricle contracting and ejecting blood) X heart rate (SA node generating an action potential)

stroke volume

Amount of blood pumped by one ventricle during a contraction

stroke volume= EDV-ESV

EDV

end diastolic volume

ESV

end systolic volume

stroke volume increases as _______ increases

EDV

EDV is affected by __________ return

venous

venous return is affected by...

- Skeletal muscle pump

- Respiratory pump

- Sympathetic innervation

force of contraction is affected by ...

- Stroke volume

- Length of muscle fiber and contractility of heart

stroke volume regulated by:

preload

contractility

afterload

contractility

inotropic agents (ex. sympathetic nervous system)

change intracellular Ca2+ concentrations

inotropic agents- effects on contractility

increase the stroke volume and EDV (increase contraction) --> positive inotropic effect

decrease the stroke volume and EDV (decrease contraction) --> negative inotropic effect

inotropic agents (positive)

increases stroke volume by increasing cardiac contraction

makes your heart muscle contractions stronger, raising your cardiac output to a normal level and increasing the amount of blood your heart can pump out. This helps your organs get the blood and oxygen they need to keep working.

agents: Dopamine, epinephrine, norepinephrine

inotropic agents (negative)

decreases stroke volume by decreasing cardiac contraction

keeps your heart muscles from working too hard by beating with less force. This is helpful when you have high blood pressure, chest pain, an abnormal heart rhythm or a disease like hypertrophic cardiomyopathy.

agents: flecainide, verapamil

autonomic regulation

Cardiovascular Control Center in brain, releases epinephrine which circulates throughout system & binds B1 receptors, increasing heart rate and contractility

sympathetic regulation

faster rate of spontaneous depolarization

1. norepinephrine attaches to receptor

2. This activates the Gs protein

3. this activates ATP from Adenylyl cyclase into cAMP

4. the cAMP binds to the F-type Na+ channel which causes the channel to stay open longer, increasing Na+ flow

5. increased rate of spontaneous depolarization of SA node cell

parasympathetic stimulation

slower rate of spontaneous depolarization

1. ACh attaches to Muscarinic receptor

2. The Gi protein is activated

3. The activation of the Gi protein opens the K+ channel, which increases the K+ flow, which hyperpolarizes the cell membrane

4. cAMP production decreases which accelerates closure of F-type Na+ channel, reducing Na+ flow

5. both the reducion in Na+ and the hyperpolarization of the cell membrane due to the increases K+ flow decreases the rate of spontaneous depolarization of SA node cell

exercise and the heart

cardio fitness can be improved at any age

aerobics

- any exercise that works a large muscle group for 20 mins or more

- after several weeks of training, maximal cardiac output increases

- training will lead to hypertrophy of the heart

- well trained individuals can have resting bradycardia

40-60 bpm