Physiology Exam 3

What does the cardiovascular system do?

Transport of material: gases, nutrients, waste, communication, degense against pathogens, temperature homeostasis

• The heart is a pump in the cardiovascular system,how?

The atria receives blood returning to the heart, the ventricles pump the blood out, the septum divides left and right halves

What are the blood vessels in cardiovascular system?

-veins, arteries, capillaries

-pulmonary and systemic circulation

-portal system joins two capillary beds in series

Where is the heart within the thoracic cavity?

Ventral side; sandwiched between the lungs

What allows for ventricular contraction to squeeze blood upward from the apex of the heart?

The spiral arrangement of ventricular muscle

What is the pericardium

It encases a heat with a membranous fluid filled sac

-inner and outer layer to the heart

The internal structure of the heart is

Mostly myocardium, has two heart valves for 1 way flow

Atrioventricular valves: between atria and ventricles, tricuspid valve on right, mitral valve on left

Semilunar valves: between ventricles and arteries, aortic valve, pulmonary valve

Ventricular contraction

Left ventricle contracted, pushing from the wall

The mitral valve on the left will close

Aortic valve will open

Means the papillary muscles and the chordal tendineae tenses up

The atrioventricular valve remains closed to prevent blood backward into atria

Ventricular relaxation

The left ventricle is dilated

The aortic valve is closed

The mitral valve is open

Chordae tendineae and papillary muscles are relaxed

Semilunar valves prevent blood that entered the arteries from flowing back into ventricles

What does cardiac muscle have?

contractile cells and autorhythmic cells/pacemakers

Contractile-pumps blood

Autorhytmic/pacemakers- signal and how nerves react

What does cardiac muscle not have?

organized sarcomeres

Myocardial characteristics

Branched, uninucleate, cells attached to each other by specialized junctions called intercalated disks

Function of desmosomes

transfer force from cell to cell; in intercalated disks

Function of gap junctions

Provide electrical connection to pass rapidly from cell to cell, without this electrical signal it can cause arrhythmia

How much volume do mitochondria occupy in cardiac muscle?

one-third, helps generate energy for pump

Which type of muscle is the slowest to contract and to relax?

Smooth muscle

Where does an action potential in the heart start?

SA node, starts with heart pacemaker cells

Pacemaker potential?

Is the unstable membrane potential in autorhymthic cells

The depolarization is due to Ca channels opening

What does the pacemaker potential look like on a graph?

It depolarizes from -60 to -40 at a constant rate

Gradually becomes less negative until reaches the threshold, thus new triggers action potential

What is important to remember about the pacemaker potential?

It is caused by leakage of potassium out and sodium in (net sodium in); comparable to an hourglass/timer

What happens after the threshold is reached in myocardial autorhythmic cells?

Calcium channels open and let calcium in the cell, further depolarizing the membrane, then calcium channels close at the peak, and potassium channels open and let potassium out, repolarizing the membrane back to -60 and the process starts over once the If channel opens

What effect do parasympathetic nerves have on the heart?

Decreases heart rate through acetylcholine on muscarinic receptors

What effect do sympathetic nerves have on the heart?

Increases heart rate through norepinephrine on beta1-adrenergic receptors

How does parasympathetic stimulation slow the heart rate?

Hyperpolarizing the membrane potential/ rate depolarization decreases, and decreasing permeability, causes K+ increase efflux and Ca decrease influx increasing the time it takes for the potential to reach threshold, slowing heart rate

How does sympathetic stimulation speed up the heart rate?

Depolarizing the membrane potential increases the rate and increasing permeability, sodium increases and calcium influx decreasing the time it takes for the potential to reach threshold, speeding up heart rate

The autonomic control of heart rate

Parasympathetic stimulates hyperpolarizing the membrane potential, slowing depolarization, slowing heart rate

Sympathetic stimulation and epinephrine depolarizes autorhytmic cells, speeding up pacemaker potential and increasing heart rate

What are the phases of the action potential of a cardiac contractile cell?

0. sodium channels open

1. sodium channels close at the peak

2. calcium channels open; fast potassium channels close

3.calcium channels close; slow potassium channels open

4. resting potential

What is the importance of the longer myocardial action potential?

It helps prevent the sustained contraction called tetanus due to calcium, entry, creating the plateau

Why is it important that cardiac muscle don't achieve tetanus?

Cardiac muscles must relax between contractions so the ventricles can fill with blood

How long is the refractory period in cardiac muscle?

Almost as long as the entire muscle twitch; prevents tetanus

EC coupling in cardiac muscle

1. action potential enters from adjacent cell

2. voltage-gated calcium channels open and calcium enters the cell

3. calcium induces calcium release through ryanodine receptor-channels (RyR)

4. local release causes calcium spark

5. summed calcium sparks create a calcium signal

6. calcium ions bind to troponin to initiate contraction

7. relaxation occurs when calcium unbinds from troponin

8. calcium is pumped back into the sarcoplasmic reticulum for storage

9. calcium is exchanged with sodium by the NCX antiporter

10. sodium gradient is maintained by the Na K ATPase

What percentage does the ECF contribute to calcium stores in cardiac muscle?

10 percent

Action potential, excitation-contraction coupling in cardiac muscle

Starts with the heart pacemaker cells

Voltage gated L type ca channels in cardiac muscle cell membrane opens (extra cellular calcium contributes 10%)

Ryanodine receptors open in the SF in excitation contraction coupling in cardiac muscle

Calcium ion is released, calcium binds to troponin to start muscle contractions

The cords bridge cycle as in skeletal muscle

Relaxation in excitation contraction coupling In cardiac muscle

Calcium unbinds troponin

Calcium removed from cytoplasm

Back into the SR with ca ATPase

Out of cell through Na+ Ca2+ exchanger

What is the force generated in cardiac muscle proportional to?

To the number of active crossbridges; determined by how much calcium is bound to troponin, sacromere length affects force of contraction

Where does the right atrium receive blood from?

Superior and inferior vena cava; from the body

Where does the right ventricle pump blood to?

Lungs through pulmonary arteries

Where does the left atrium receive blood from?

Lungs through pulmonary veins

Where does the left ventricle pump blood to?

To the body through the Aorta

What happens if the right side of the heart slows down?

Backup/pressure buildup that causes edema in the body

What happens if the left side of the heart slows down?

Backup/pressure buildup that causes edema in the lungs

Where is the tricuspid valve located?

between right atrium and right ventricle

Where is the bicuspid valve located?

between left atrium and left ventricle

What is important to remember about valves within the cardiovascular system?

To prevent backflow

Sinoatrial SA node for cardiac electrical conduction

Sets the pace of heartbeat at 70 bpm, AV node is 50 bpm and purkinje fibers (24-40 bpm) can act as pacemakers under som,e conditions

Intermodal pathway from SA to atrioventricular AV node

Routes the direction of electrical signals so heart contracts from apex to base

AV node delay is accomplished by slower conduction signals through nodal cells

Purkinje fibers

Transmits electrical signals down the atrioventricular bundle to left and right bundle branches

What are the steps involved in the conducting system of the heart?

1. SA node depolarizes

2. electrical activity goes rapidly to AV node via internodal pathways

3. depolarization spreads more slowly across atria. conduction slows through AV node

4. depolarization moves rapidly through ventricular conducting system to the apex of the heart

5. depolarization wave spreads upward from the apex

What is the P wave associated with?

Atrial depolarization

What is the QRS complex associated with?

Ventricular depolarization

R wave

Atrial repolarization

What is the T wave associated with?

ventricular repolarization

P-R segment? Or P-Q segment?

Conduction through AV nodes and AV bundle

How is heart rate determined?

time between two P waves or two Q waves

The electrical events of the cardiac cycle

-p wave: atrial depolarization

P-Q; conduction through AV node and AV bundle, atria contract

Q wave

R wave: atria, repolarization

QRS; ventricular depolarization

S wave

S-T: ventricles contract

T waves: ventricles repolarization

Normal ECG and abnormal

Diastole

cardiac muscle relaxes

Systole

cardiac muscle contracts

What are the steps of mechanical events of the cardiac cycle?

1. late diastole - both sets of chambers are relaxed and ventricles fill passively, atria are filling with blood from the vein. if the AV valves are open, ventricles are filling

2. atrial systole - atrial contraction forces a small amount of additional blood into ventricles

3. Isovolumic ventricular contraction - first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves. this means all valves are shut, but atria relax and blood flows in atria

4. ventricular ejection - as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected.

5. Isovolumic ventricular relaxation - as ventricles relax, pressure in ventricles falls, but still higher than atrial pressure. Blood flows back into cusps of semilunar valves and snaps them closed

the AV valve will open again once the ventricular pressure drops below atrial pressure

Where is the first heart sound heard?

following closure of the AV valves; Lub

Where is the second heart sound heard?

following closure of semilunar valve; Dub

Auscultation

Listening to the heart through the chest wall through a stethoscope

What is the pathway of electrical signals of the heart?

SA node, through internodal pathways to the AV node, through the AV bundle, bundle branches, and finally Purkinje fibers

What is the normal max fill volume of a ventricle?

135 mL

What is the normal volume of blood that stays behind in the ventricles?

65 mL

End-systolic volume (ESV)

volume of blood remaining in each ventricle after systole; blood that stays behind after contraction; normally around 65 mL

End-diastolic volume (EDV)

volume of blood in each ventricle at the end of diastole; total blood volume; normally about 135 mL

Stroke volume

Amount of blood pumped by one ventricle during a contraction

How do you calculate stroke volume?

EDV-ESV=SV

volume of blood before contraction- volume of blood after contraction= SV

What is the average stroke volume?

70 mL

Cardiac output (CO)

heart rate x stroke volume

What is the average cardiac output?

5 L/min

How does the sympathetic nervous system control cardiac contraction?

catecholamines bind to beta1 receptors to affect voltage-gated calcium channels, where open time increases and theres an increase of calcium entry from ECF ——and phospholamban to create more forceful and faster contractions

phospholamban

are regulatory protein that increases the Calcium ATPase on SR

How are more forceful contractions produced in cardiac muscle?

calcium stores are increased in the SR, allowing more calcium to be released, producing a more forceful contraction

How are faster contractions produced in cardiac muscle?

calcium is removed from cytosol faster, shortening calcium-troponin binding time, producing a faster contraction

Inotropic agent

Any chemical that affects contractility

What kind of effects do epinephrine, norepinephrine, and digitalis have on contractility?

positive inotropic effects

What do negative inotropic effects do?

Decrease contractility

What is the force of contraction affected by?

length of muscle fiber and contractility of the heart

What happens when the ventricular wall stretch increases?

Stroke volume increases

Preload

The degree of myocardial stretch before contraction

afterload

force or resistance the heart must overcome to eject blood during systole, like the pressure in the aorta against left ventricle contracts

Frank-Starling Law

stroke volume increases as end-diastolic volume (EDV) increases

What is EDV determined by?

venous return

What is venous return affected by?

skeletal muscle pump, respiratory pump, and sympathetic innervation of veins

What is cardiac output a function of?

Heart rate and stroke volume

What is driving pressure created by?

Ventricles

Where is pressure created and then thereafter transferred to?

Created by contracting muscles and transferred to the blood

What happens to blood pressure if blood vessels dilate?

Blood pressure decreases

What happens to blood pressure if blood vessels constrict?

Blood pressure increases

What does the pressure gradient in blood vessels look like?

High in the Aorta and arteries, medium in capillaries, and low in the veins and Vena cavae

What is the relationship between flow and pressure gradient?

Directly proportional, as pressure increases, so does flow and vice versa

What determines whether or not a fluid flows through a tube?

Whether or not there is a positive pressure gradient; fluid moves from high pressure to low pressure

What is important to remember about flow and pressure gradient?

Flow depends on pressure gradient (delta pressure), not on the absolute pressure

How is flow related to resistance?

flow is inversely proportional to resistance; if resistance increases, flow decreases and vice versa

velocity relation to narrowness

the narrower the vessel, the faster the velocity of flow

How is resistance related to length of the tube? (blood vessel)

directly proportional; resistance increases as length increases

How is resistance related to viscosity? (blood)

directly proportional; resistance increases as viscosity increases