NEET Biology Body Fluids and Circulation MCQs Set 21

Answer: (c) Pulmonary aorta

Explanation:
1. The right ventricle sends deoxygenated blood through the pulmonary trunk (pulmonary artery) to the lungs.

Teacher's Note:
1. The pulmonary artery is the only artery that carries deoxygenated blood in adults.

Answer: (a) Oxygen

Explanation:
1. In the lungs, blood takes up oxygen and gives out carbon dioxide.

Teacher's Note:
1. The pulmonary vein therefore carries the most oxygenated blood.

Answer: (d) Heart

Explanation:
1. Purkinje fibres are modified cardiac muscle fibres in the ventricular walls that spread the impulse.

Teacher's Note:
1. They form the last part of the conducting system.

Answer: (d) Heart

Explanation:
1. The coronary arteries arise from the base of the aorta and nourish the heart muscle itself.

Teacher's Note:
1. Blockage of a coronary artery causes a heart attack.

Answer: (a) More than that of adults

Explanation:
1. Children have a faster heart rate, about 90 to 100 beats a minute against 72 in adults, because of their higher metabolic rate.

Teacher's Note:
1. Heart rate generally falls with age and with physical fitness.

Answer: (b) Middle layer, myocardium

Explanation:
1. The myocardium is the thick middle layer of cardiac muscle that does the pumping work.

Teacher's Note:
1. The three layers from inside out: endocardium, myocardium, epicardium.

Answer: (b) Right ventricle

Explanation:
1. The pulmonary trunk springs from the right ventricle, and the systemic aorta from the left ventricle.

Teacher's Note:
1. Both vessels have semilunar valves at their bases.

Answer: (b) Lungs

Explanation:
1. The right ventricle drives deoxygenated blood to the lungs through the pulmonary artery.

Teacher's Note:
1. Pulmonary veins bring blood back to the heart and never receive it from a ventricle.

Answer: (b) Auriculo-ventricular node

Explanation:
1. The AV node passes the impulse to the bundle of His, which runs in the inter-ventricular septum.

Teacher's Note:
1. The sequence is SAN, AVN, bundle of His, Purkinje fibres.

Answer: (b) Fossa ovalis

Explanation:
1. The fossa ovalis is the remnant of the foetal foramen ovale, which closes after birth.

Teacher's Note:
1. Foramen ovale lets blood pass from right to left atrium in the foetus.

Answer: (c) Ventricles

Explanation:
1. They carry the impulse quickly through both ventricles so that they contract almost together.

Teacher's Note:
1. Contraction therefore starts at the apex and moves upward.

Answer: (c) Closing and opening of the valves of the heart

Explanation:
1. These muscles pull on the chordae tendineae, which keep the flaps of the AV valves closed during systole.

Teacher's Note:
1. Their function is to prevent backflow into the atria.

Answer: (d) Both sinus venosus and conus arteriosus

Explanation:
1. Both sinus venosus and conus arteriosus are present in lower vertebrates but are absent as separate parts in the human heart.

Teacher's Note:
1. Right auricle is certainly present in humans.

Answer: (b) Elephant

Explanation:
1. Among these, the elephant has the heaviest heart, about 20 kg, ahead of the giraffe.

Teacher's Note:
1. Heart size is related to body mass.

Answer: (d) Pericardium

Explanation:
1. The double-layered pericardium secretes the fluid that fills the cavity around the heart and reduces friction.

Teacher's Note:
1. The pericardial cavity lies between the two pericardial layers.

Answer: (c) SA node

Explanation:
1. The SA node is the pacemaker and starts every normal beat.

Teacher's Note:
1. If the SA node fails, the AV node can take over at a slower rate.

Answer: (d) All of the above

Explanation:
1. The heart wall has three layers: the inner endocardium, middle myocardium and outer epicardium.

Teacher's Note:
1. The epicardium is also the visceral layer of the pericardium.

Answer: (c) a-t, b-r, c-p, d-q

Explanation:
1. The SVC drains the upper body (t) and the IVC the lower body (r). The pulmonary artery takes blood to the lungs (p) and the pulmonary vein brings it back oxygenated (q).

Teacher's Note:
1. Remember: only the pulmonary vessels differ from the usual artery/vein oxygen rule.

Answer: (c) Pulmonary vein

Explanation:
1. Four pulmonary veins return oxygenated blood from the lungs to the left atrium.

Teacher's Note:
1. Venae cavae empty into the right atrium.

Answer: (c) Purkinje fibres

Explanation:
1. Purkinje fibres spread the impulse through the ventricular muscle and trigger ventricular systole.

Teacher's Note:
1. The AV node only delays and passes on the signal.

Answer: (b) Muscle fibres found only in the inter-ventricular septum

Explanation:
1. The bundle of His is a bundle of modified cardiac muscle fibres that runs through the inter-ventricular septum and divides into two branches.

Teacher's Note:
1. Its branches end in the Purkinje fibres.

Answer: (b) Sinuatrial node

Explanation:
1. An artificial pacemaker takes the place of the failed SA node, so it is placed near the SA node in the right atrial wall.

Teacher's Note:
1. It sends electrical impulses at a set rate.

Answer: (d) Left ventricle

Explanation:
1. The left ventricle pumps blood to the whole body against high pressure, so its wall is the thickest.

Teacher's Note:
1. Atria have thin walls as they only push blood into ventricles.

Answer: (b) AV node

Explanation:
1. The AV node delays the impulse by about 0.1 second so that the ventricles fill before they contract.

Teacher's Note:
1. This delay allows complete atrial emptying.

Answer: (a) Left atrium and left ventricle

Explanation:
1. The valve has two flaps and stops backflow from the left ventricle to the left atrium.

Teacher's Note:
1. The right side valve has three flaps, the tricuspid.