Basics of blood and heart - class-VII

The correction in statements (2) and (4) are:

• In vertebrates, the mitral valves are present
  between the left atrium and the left ventricle.
• The T wave of ECG represents repolarization
  of the ventricles, not depolarization.

The heart of the higher organism is well equipped with the vascular system. the arteries carry the oxygenated blood while the veins carry the deoxygenated blood. This prevents the mixing of oxygenated and deoxygenated blood.

A normal heart has two upper and two lower chambers. The upper chambers, the right, and left atria, receive incoming blood. The lower chambers, the more muscular right, and left ventricles pump blood out of your heart.

When the muscles of the heart relax, the right atrium receives deoxygenated blood from all parts of the body through superior, inferior vena cava and coronary sinus. The left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins. Thus option C is the correct answer. 

During ventricular systole, the deoxygenated blood from the right ventricle enters the pulmonary trunk, which carries blood to lungs for oxygenation. Thus option A is the correct answer. 

The pulmonary artery arises from the right ventricle and carries deoxygenated blood to lungs for oxygenation. Lungs oxygenate the deoxygenated blood. This oxygenated blood is pumped to all parts of the body. Thus option C is the correct answer. 

The upper chambers are called the left and right atria, and the lower chambers are called the left and right ventricles. A wall of muscle called the septum separates the left and right atria and the left and right ventricles. The left ventricle is the largest and strongest chamber in your heart.

During ventricular systole, the deoxygenated blood from the right ventricle enters the pulmonary trunk, which carries blood to lungs for oxygenation. Thus option B is the correct answer. 

The left ventricle is the thickest of the heart's chambers and is responsible for pumping oxygenated blood to tissues all over the body. By contrast, the right ventricle solely pumps blood to the lungs.

The left atrium or left auricle receives oxygenated blood from the lungs through four openings of pulmonary veins. Thus option C is the correct answer. 

The serosal pericardium is a closed sac within the fibrous pericardium. It consists of two layers. The visceral layer, called the epicardium, covers the heart and great vessels and is reflected back onto the parietal layer, which lines the interior of the fibrous pericardium.

Aquatic mammals, such as whales and dolphins, often have larger hearts relative to their body size to support efficient circulation and oxygen delivery during long periods of diving.

Papillary muscles are located in the ventricles of the heart; they attach to the chordae tendineae and help prevent the inversion of the atrioventricular valves during ventricular contraction.

Trabeculae carneae are the irregular muscular ridges and columns found on the inner walls of the ventricles of the heart.

Chordae tendineae, or 'heart strings', are fibrous cords that connect the papillary muscles to the tricuspid and mitral valves within the ventricles of the heart.

Blood flows from the right ventricle into the pulmonary arteries to reach the lungs for oxygenation. After gas exchange, it returns via the pulmonary veins to the left atrium before entering the left ventricle.

Ventricular diastole is the relaxation phase of the heart muscle. Since the heart is composed of cardiac muscle tissue, the activity of this tissue governs the relaxation process.

In a healthy individual, there are two normal heart sounds called lub and dub. Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole. The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.

Human blood passes from the inferior vena cava into the diastolic right atrium of the heart because of a pressure differential between the atrium and the vena cava. This negative pressure gradient is created by atrial diastole and pulls blood to the atrium which is then pumped to the ventricles by contraction.

Due to one complete cardiac cycle, the two atria contract during the first 0.1 seconds, followed by ventricular systole for 0.3 seconds and finally joint diastole for 0.4 seconds.