Test: Human Circulatory System (NCERT) - NEET MCQ

As one ages, arteries lose their elasticity. Consequently the heart has to pump the blood more forcefully in order to fulfill the need of the body cells.

The heart beat originates from the SA node which acts a pacemaker. SA node lies in the wall of the right atrium near the opening of the superior vena cava.

A thin, muscular wall called as the inter-atrial septum separates the right and the left atria, whereas a thick-walled, inter-ventricular septum separates the left and the right ventricles.

On an average, capillaries are about 1 mm long and 8 mm in diameter. Although each capillary is very narrow, there are so many of them that the capillaries have the greatest total cross sectional area of any other type of vessel. Consequently, the blood decreases in velocity as it passes through the capillary beds, allowing more time for it to exchange materials with the surrounding extracellular fluid. Blood also loses most of its pressure in passing through the vast capillary networks and so is under very low pressure when it enters the veins.

SAN (sino-atrial node) is located in the right upper y corner of right atrium. AV bundle continues from AVN (Atrio-ventricular node). Purkinje fibres are modified cardiac muscle fibres that originate from AV node and spread into two ventricles. The nodal musculature has the ability to generate action potential without any external stimuli i.e. it is autoexcitable. AVN is located in the lower left corner of the right atrium close to the atrio-ventricular septum.

In the given diagram 'D' represent the vena cava. Vena cava is either of two large veins that carry deoxygenated blood into the right atrium.

A' is SA node that is the site for generation of action potential in human heart.

Sino-atrial node, also called pacemaker is situated in the right upper corner of the right atrium.

The opening between the left atrium and left ventricle is guarded by a bisuspid valve, also known as mitral valve.

Veins brings blood from different body parts to the heart. The flow of blood in veins is not so fast because the blood in veins is under low pressure. Veins posses valves which present backward flow of blood.

The cardiac impulse originates from SA node. This impulse is of highest rhythmicity. By determining the rate of discharge of the cardiac impulse the SA node determines the rate of heart beat.

Chordae tendineae are the special fibrous cords attached to the flaps of tricuspid valve on one end and on the other end with the special muscles of the ventricular wall, the papillary muscles.

Left ventricle has the thickest muscular wall as it has to pump the oxygenated blood with great force to all visceral organs and parts of body through aorta.

All veins carry deoxygenated blood from different parts of the body to heart, Pulmonary veins is the only vein that carries oxtgenated blood from the lungs to the left atrium of the heart.

The carotid arteries are major blood vessels in the neck that supply blood to the brain, neck, and face. There are two carotid arteries, one on the right and one on the left. In the neck, each carotid artery branches into two divisions:
(i) The internal carotid artery supplies blood to the brain.
(ii) The external carotid artery supplies blood to the face and neck.
So, the correct answer is 'Oxygenated blood to brain'