Question

Blood returns from the body into the heart where it then moves through the structures of the heart and finally out into the systemic circulation. Place the following structures in the order that the blood would pass through them.

1.right ventricle

2.left atrium

3.right atrium

4.pulmonary artery

5.left ventricle

6.pulmonary vein

part b.

The importance of the plateau phase of the action potential of myocardial cells is in?

a.preventing overstretching of the cells.

b.enhancing the efficiency of oxygen use by the cells.

c.preventing summation and tetanus.

d.preventing fibrillation.

e.regulating Ca²⁺ availability to the cells.

part c.

The only blood vessels whose walls permit exchange between the blood and the surrounding interstitial fluids are the?

a. arteries.

b.arterioles.

c.veins.

d.venules.

e.capillaries.

Answer 1

1.a.Heart has 4 chambers_rt atrium and rt ventricle(deoxygenated blood) ,lt atrium and lt ventricle(oxygenated blood).

Atriums open into ventricles via atrioventricular passage mediated by bicuspid and tricuspid valves.

Ventricles open into great vessels.Rt ventricle into pulmonary trunk(arteries)guarded by semilunar valve.Lt ventricle into aorta (systemic circulation)guarded by semilunar valves.

Thus the series of blood flow is_All the blood from body coming via superior and inferior venacava also coronary sinus and some independent veins open into Right atrium--Right ventricle--pulmonary arteries(rt and lt)which goes to lungs and blood is oxygenated--oxygenated blood comes via pulmonary veins(4 in no)--received by left atrium-- left ventricle --and finally into aorta(systemic circulation).

2.plateau phase is seen transmembrane potential of nonautomatic myocardial fibres.here calcium channels come into action,occours after action potential achived.Here the membrane potential is maintained at relatively same level for a considerable period during which ca2+ ions flow in and bring about contraction.Option e is correct.

3. Only vessel whose walls permit exchange between the blood and surrounding interstitial fluid are the capillaries also called exchange vessels.

These form link between arterioles and venules.Their walls have an endothelial cell lining but no media ,although variable no of pericytes which resemble smooth muscle cells,typically lie just deep to the endothelium.

Capillaries have a huge crosssectional area,and also have relative low flow rate.(ideally suitable for exchange of diffusable substances)

Tissues with high metabolic rates such as myocardium and brain,have highest density of capillaries.