Lecture 9 - Cardiac muscle and pump function

Question 1

what does fluid around the heart in an alveolar bats wing like shape indicate?

Answer 1

pulmonary oedema

Question 2

what happens during systole

Answer 2

Phase 1 . sodium entry into the cell - depolarises the cell
Phase 2 then entry of calcium into cell - causes contraction
Phase 3 - potassium exit - repolarisation and back to normal

Question 3

When does the aortic pressure wave peak

Answer 3

during ventricular ejection of systole. reaches 120 mm/hg from 80 mmhg. returns to normal after

Question 4

When does the left pressure wave peak

Answer 4

During isolvolumetric contraction - when the ventricles contract
drops during isovolumetric relaxation

Question 5

What happens to the atrial pressure wave

Answer 5

it remains quite low and peaks a little during atrial contraction when the mitral valve opens (2 cusps)

Question 6

what is a skeletal muscle composed of?

Answer 6

Each muscle fibre is composed of myofibrils, which contain adjacent rows of sarcomeres

Question 7

What causes contraction of a myofibril

Answer 7

The overlap of the thin actin and thick myosin filaments shorten the row of sarcomeres resulting in contraction of the muscle.

Question 8

What are the cardiac muscles like?

Answer 8

are branched and are connected by gap junctions which allow electrical activity and allow action potentials to travel through the heart.

Question 9

Why is calcium important for contraction?

Answer 9

at rest there’s blocking of the myosin binding sights by troponin as they form a complex which block the binding sites on the actin thin filament.
when calcium comes it binds to the troponin and complex and moves it which allow it expose myosin binding sites - contraction starts

Question 10

Why is troponin important

Answer 10

blocks binding sites

Question 11

Cardiac energetics - what do they use?

Answer 11

myocardial cells use AT6 - 6kg per day.

Question 12

what does ATP store?

Answer 12

Chemical energy which is converted to mechanical energy

Question 13

what does the energy transfer result in

Answer 13

force generation

myofilament shortening

Question 14

what transformations occur

Answer 14

basic mechanical energy to hydraulic function for the whole organ

Question 15

what occurs in hydraulic function?

Answer 15

forced generation causes some ejection.
shortening of longitudinal filaments and horizontal thickening
reduces LV chamber diameter and causes further ejection

Question 16

What is the wall of the left ventricle like

Answer 16

thick and muscular

Question 17

what is cardiac adaptability??

Answer 17

The heart needs to pump at rest
Coping with higher demands
Exercise, intercurrent illness,fluid overload and pregnancy

Question 18

What is cardiac reserve

Answer 18

is the capacity of the heart to increase its performance on demand (maximum capacity)

Question 19

Equation for cardiac output

Answer 19

heart rate x stroke volume

Question 20

Cardiac reserve equation

Answer 20

Maximum cardiac output - cardiac output at rest

Question 21

What is cardiac reserve critically dependent on?

Answer 21

Sympathetic system

Question 22

What does sympathetic innervation do?

Answer 22

speeds up heart rate through speeding up sa node depolarisation, more frequent action potentials which increase conduction through AV node

Question 23

How does adrenaline increase sympathetic activity?

Answer 23

Through b1 agonism

Question 24

how else can we augment cardiac output

Answer 24

increasing stroke volume
prolongued opening of calcium channels - enhances calcium action in excitation/contraction coupling mechanisms
ionitropic - force of contraction

Question 25

What does stroke volume also depend on

Answer 25

preload is the end diastolic volume (stretchin of cardiac muscle prior to contraction)

Question 26

what happens to sarcomeres with change in length

Answer 26

as they increase the tension increases to a certain point and then declines as the stretch becomes more extreme

Question 27

What factors affect cardiac output

Answer 27

cardiac rate and stroke volume

Question 28

what is franklin-starling law

Answer 28

the length of the muscle fibers is proportionate to the end diastolic volume.

Question 29

what does small changes in cardiac sarcomere length result in

Answer 29

large variations in tension

Question 30

what will stretching the LV do?

Answer 30

it will aid contraction.

Question 31

What does end LV diastolic volume determine

Answer 31

how stretched the LV wall is

Question 32

what will increasing preload do

Answer 32

increase cardiac output upto certain point.

Question 33

how does this contraction happen when muscle stretches?

Answer 33

as muscle stretches, the diameter of the myofibrils is reduced, acting and myosin filaments are closer together, leading to more contraction.

Question 34

what is starlings law?

Answer 34

energy of contraction is a function of the length of the muscle fibre. like elastic band

Question 35

What does the franklin-starling curve indicate?

Answer 35

relationship between end diastolic volume and stroke volume

Question 36

What does cardiac output correlate with?

Answer 36

venous return, | left cardiac output =rv preload

Question 37

What does exercise and other demands do?

Answer 37

increases venous return | allows augmentation of stroke volume

Question 38

What would cause a left shift in the frank-starling curve

Answer 38

exercise, pharmacological stimulation

Question 39

What would cause a right shift in the frank-starling curve

Answer 39

pharmacological depression, myocardial loss

Question 40

Describe effects of a left shift

Answer 40

during pharmacological stimulation there will be a decrease in the end diastolic volume as heart rate increases and the diastolic period will be shorter, this will increase the stroke volume as there is an increase in pressure. this will be followed by parasympathetic stimulation which will cause a decrease in the afterload.

Question 41

Describe effects of a right shift

Answer 41

an increase in the end diastolic volume caused by pharmacological depression will allow ventricles to fill for longer and hence decrease stroke volume due to a decrease in contractility. This will be followed by an increase in the afterload due to sympathetic stimulation.

Question 42

what happens to the curve on sympathetic stimulation

Answer 42

noradrenaline and adrenaline stimulate cAMP. more calcium enters the cell, cross-linking in sarcomeres curve shifts to the left as edv decreases and stroke volume increases.

Question 43

When is cardiac output augmented

Answer 43

at all levels of ventricular preload

Question 44

ejection fraction

Answer 44

stroke volume/end diastolic volume | physiological ef - 50 to 75%

Question 45

what happens to EF in a failing heart

Answer 45

reduces

Question 46

what happens to EF on exercise

Answer 46

can reach 90%

Question 47

What happens during heart failure

Answer 47

``` myocardium is diseased - contracts less ischaemia - scarred myocardium viral infection/alcohol - wall thinning there is a right shift increase in afterload - due to sympathetic overactivation due to a decreased stroke volume RAA system kicks in ```

Question 48

during physiological ventricular stretch

Answer 48

ventricular sarcomere length is on the ascending limb

Question 49

during heart failure where does the sarcomere tension fall on the curve

Answer 49

on the descending limb

Question 50

during heart failure, what happens to the preload

Answer 50

preload rises this works for a while but the heart stretches but lv stretches exceeds physiological levels eventually

Question 51

what does a failing left ventricle cause

Answer 51

pulmonary oedema

Question 52

what can you do to help with pulmonary oedema

Answer 52

alveolar ventilation high-flow oxygen relaxing pulmonary vessels would reduce preload and take strain off left V morphine - help breathing and pain furosemide - takesome fluid off lungs (treats oedema)

Question 53

what does furosemide do

Answer 53

treats oedema - fluid retention