cardiovascular system

Question 1

3 circulations, where are the two portal veins ?

Answer 1

systemic, pulmonary, coronary.

Hepatic and renal portal veins

Question 2

what are the two kind of junctions present in cardiomyocytes ?

Answer 2

desmosomes (mechanical) and gap junction (electrical)

Question 3

which kind of muscle cell has the most mitochondria ?

Answer 3

cardiomyocytes

Question 4

how long is the actionp potential in cardiac vs skeletal muscle ? why ?

Answer 4

Cardiac : 200 ms
Skeletal : 1-5 ms

Cardiac muscle needs a contraction / relaxation cycle to empty the heart before refilling it. The long AP allows for this refractory period.
Skeletal can add up APs

Question 5

2 ways a cardiac muscle fiber can vary the amount of generated force

Answer 5

1) by concentration of Ca2+ : proportional to nb of active crossbridges between Ca2+ and troponin

2) by sarcomere length at beginning of contraction

Question 6

resting potential of cardiomyoctes ? Why is there a plateau in their AP ?

Answer 6

-90 mV.

K+ goes out but Ca2+ comes in

Question 7

pacemaker cells : do they have a resting potential ?

Answer 7

No, they are never really at rest. The potential becomes gradually less negative (Na+ in) until threshold -> Ca2+ in

Question 8

In which direction does the heart need to pump ?

Answer 8

From bottom to top, because the output vessels are at the top

Question 9

ECG : leads and direction, when does it deflect upward or downward ?

Answer 9

Negative to positive ;
I : right arm to left arm
II : right arm to left leg
III : left arm to left leg

Upward = current toward positive electrode
Downward : current toward negative electrode

Question 10

ECG : waves and segments, real timing ?

Answer 10

P wave : atrial depolarization
P-R segment : conduction through AV node and AV bundle
QRS complex : ventricular depolarization
T wave : ventricular repolarization

Actual contraction happens a few milliseconds after the electrical activity

Question 11

How are the ventricles filled ? When do we hear the 2 heart sounds ?

Answer 11

Filled by gravity, only 20% filles by atria contraction.

S1 = end of atrial systole (shutting of mitral and tricuspid valves)
S2 = end of ventricular systole

Question 12

How do we measure the effectiveness of the heart pump ?

Answer 12

stroke volume = EDV - ESV