Test: Circulatory System - 1 - NEET MCQ

• In the given diagram of the cross section of the heart, the indicated valve is the bicuspid valve.
• It is also known as the mitral valve.
• The bicuspid valve is the opening between the left auricle and left ventricle.

• In the given diagram of the cross-section of the heart, the indicated structure is the superior vena cava.
• The superior vena cava delivers deoxygenated blood from the upper parts of the body to the heart.

• In the joint diastole state, all four chambers of the heart are relaxed.
• The tricuspid and bicuspid valves are open while the semilunar valves are closed.
• Blood from pulmonary vein flows into the left ventricle.

The heart sound ‘’DUP’’ is produced when a semilunar valve at the base of aorta classes.
Two distinct sounds can be heard during a heart beat with the help of a stethoscope. These are 'lubb' and 'dup'.Lubb is the first sound which has a low pitch and produced by the closure of tricuspid and bicuspid valves (collectively called atrioventricular valves) at the beginning of ventricular systole.
Dup is the second sound which is sharp and has a high pitch. It is produced by closure of semilunar valves by the end of ventricular systole.

• During the atrial systole, both the atria contract simultaneously while the ventricles remain relaxed.
• It occurs due to the action potential generated by the SAN.
• The tricuspid and bicuspid valves open.

Sino-atrial node is the natural pacemaker of the heart. These are a group of small, flattened and ellipsoid strip cardiac muscle fiber situated in the upper lateral wall of the right atrium near the Eustachian valve (valve of the inferior vena cava).
So, the correct answer is option B.

• SAN or the sinoatrial node is auto excitable and is responsible for generating the action potential.
• This action potential is transmitted to the ventricles via the AVN, the AV bundle and the Bundle of His.

• The relaxation of the atria or the atrial diastole coincides with the contraction of the ventricles or the ventricular systole.
• The right and left semilunar valves open up due to the increase in pressure in the ventricles.

The blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta. The deoxygenated blood pumped into the pulmonary artery is passed onto the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium. This pathway constitutes the pulmonary circulation. The oxygenated blood entering the aorta is carried by a network of arteries, arterioles, and capillaries to the tissues from where the deoxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is the systemic circulation. The systemic circulation provides nutrients, O2 and other essential substances to the tissues and takes CO2 and other harmful substances away for elimination.
So, the correct answer is option A.

Veins carry the deoxygenated blood from the body to the heart.
Any arteries or veins that originate from the heart are known as pulmonary veins and arteries.
Pulmonary veins are the only veins in the entire body that carries the pure blood from the lungs through the heart after the purification.
The oxygenation of the blood takes place in the lungs and this oxygenated blood is done carried by the pulmonary veins.

A node is a specialized type of tissue that behaves as both muscle and nervous tissue. There are 2 nodes present in the human heart. SA node and AV node. 
The sinoatrial node, also referred to as the pacemaker of the heart, coordinates heart contractions. Located in the upper wall of the right atrium, it generates nerve impulses that travel throughout the heart wall causing both atria to contract.
The atrioventricular node lies on the right side of the partition that divides the atria, near the bottom of the right atrium. When the impulses generated by the SA node reach the AV node, they are delayed for about a tenth of a second. This delay allows the atria to contract, thereby emptying blood into the ventricles. The AV node then sends the impulses down the atrioventricular bundle. This bundle of fibers branches off into two bundles and the impulses are carried down the center of the heart to the left and right ventricles. 
Hence, the correct answer is option B.

Cardiac muscle is characterized by striped muscle fibers, connected together by intercalated disks, where the membranes are specialized to allow electrical signals to pass easily. Like smooth muscles, cardiac muscles can remain in contraction for a sustained period. Like skeletal muscles, cardiac muscles also contract quickly. The formation of contractile proteins in cardiac muscle cells also allows for stronger contractions when the fibers are stretched, which makes the heart pump more efficiently.

The hepatic portal vein leads from the small intestine to the liver. The hepatic vein carries blood away from the liver to the vena cava which transports it back to the heart. The hepatic vein has the highest concentration of urea. This is because urea is a by-product of amino acid catabolism, that occurs in the liver. Hence liver is the primary site for urea production

So, the correct answer is 'Hepatic Vein'.

During cardiac cycle in humans, the blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta. The deoxygenated blood pumped into the pulmonary artery is passed onto the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium. This pathway constitutes the pulmonary circulation.

Lymph is a colorless fluid, containing specialized lymphocytes, which are responsible for the immune responses of the body. 

Lymph is also an important carrier for nutrients, hormones, etc. Fats are absorbed through lymph in the lacteals present in the intestinal villi. 

Lymph lacks RBCs and platelets. Lymph contains white blood cells. So option D is correct.

An instrument for measuring blood pressure, typically consisting of an inflatable rubber cuff which is applied to the arm and connected to a column of mercury next to a graduated scale, enabling the determination of systolic and diastolic blood pressure by increasing and gradually releasing the pressure in the cuff.

The chordae tendineae known as the heartstrings are tendon resembling fibrous cords of collective tissue that connects the papillary muscles to the tricuspid valve and the tricuspid valve in the heart.
So the correct option is "Ventricles of heart".

• During ventricular systole or the contraction of the ventricles, the tricuspid and bicuspid valves close and the semilunar valves open.
• The atrial diastole occurs at the same time as the ventricular systole.

The SA node is the heart's natural pacemaker. 
The SA node is a muscular tissue where electrical impulses are generated for the rhythmic contractions of the heart.
Hence, option D is correct.

Diastole This should really be called “ventricular diastole”, but don't worry about this for GCSE. During diastole the thick muscular walls of the ventricles relax. Again, this happens to both sides of the heart. The pressure of the blood in the ventricles falls low enough for the bicuspid valve to open.

The valve of the inferior vena cava also called as a Eustachian valve lies at the junction of the inferior vena cava and right atrium. It prevents the backflow of the deoxygenated blood from the lower part of the body to the right atrium.

The human heart is an example of myogenic heart, it possesses cardiac muscle helping the heart to automatically contract spontaneously; which do not need any stimuli as in neurogenic heart. A myogenic heart is capable of generating a cardiac contraction independent of nervous input. In a myogenic heart, contraction is initiated by the cells called myocyte  (Pacemakers)itself instead of an outside occurrence or stimulus such as nerve innervation.

In the human heart, the opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, the tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle.
So, the correct answer is option C.