Test: Body Fluids & Circulation - 1 - NEET MCQ

• The nodal musculature has the ability to generate action potentials without any external stimuli.
• The number of action potentials that could be generated in a minute varies at different parts of the nodal system.
• The SAN can generate the maximum number of action potentials and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
• Therefore, it is called the pacemaker.

Line in NCERT: "The SAN can generate the maximum number of action potentials, i.e., 70-75 min⁻¹, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker."

The hepatic portal vein carries blood from the intestine to the liver before it is delivered to the systemic circulation.

Line in NCERT: "A unique vascular connection exists between the digestive tract and liver called hepatic portal system. The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation."

A special case of Rh incompatibility (mismatching) has been observed between the Rh^-ve blood of a pregnant mother with Rh^+ve blood of the foetus.

Line in NCERT: "Rh incompatibility (mismatching) has been observed between the Rh-ve blood of a pregnant mother with Rh+ve blood of the foetus."

• The arteries carry blood from the heart to all over body parts. Hence, statement (i) is correct.
• The vessels which carry blood from the heart to the lungs is the pulmonary artery but it carries deoxygenated blood. Hence, statement (ii) is correct.

Line in NCERT: "The deoxygenated blood pumped into the pulmonary artery is passed on to the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium."

A- Pulmonary vein
B- Dorsal aorta
C- Vena cava
D- Pulmonary artery

Line in NCERT: "Pulmonary artery" "Pulmonary Vein" "Dorsal aorta" "Vena cava"

An open circulatory system is commonly found in arthropods and molluscs. In this system, the blood pumped by the heart flows through large vessels into open spaces or body cavities called sinuses. This system contrasts with closed circulatory systems found in annelids and chordates, where blood is circulated through a closed network of blood vessels. The open circulatory system allows for the flow of fluid to be less precisely regulated compared to closed systems.

Line in NCERT: "Open circulatory system is present in arthropods and molluscs in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses."

Amphibians and reptiles, except crocodiles, possess a 3-chambered heart with two atria and a single ventricle. This heart structure allows for a degree of separation between oxygenated and deoxygenated blood, although there is some mixing in the single ventricle before circulation. This setup contrasts with the more efficient 4-chambered heart found in crocodiles, birds, and mammals.

Line in NCERT: "Amphibians and the reptiles (except crocodiles) have a 3-chambered heart with two atria and a single ventricle."

The human heart is situated in the thoracic cavity, between the two lungs, slightly tilted towards the left. It occupies a position in the chest that is protected by the pericardium, a double-walled membranous bag. This positioning is crucial for its function in pumping blood throughout the body.

Line in NCERT: "Heart, the mesodermally derived organ, is situated in the thoracic cavity, in between the two lungs, slightly tilted to the left."

The right and left atria of the heart are separated by a thin, muscular wall called the interatrial septum. This partition ensures that blood from the systemic and pulmonary circulations does not mix within the heart, allowing for efficient oxygenation and circulation of blood throughout the body.

Line in NCERT: "A thin, muscular wall called the inter-atrial septum separates the right and the left atria."

The atrioventricular bundle (AV bundle) is a bundle of nodal fibers that continues from the atrioventricular node (AVN) and passes through the atrioventricular septa. It emerges on the top of the interventricular septum, where it immediately divides into a right and left bundle. These branches further propagate into minute fibers throughout the ventricular musculature of the respective sides, playing a crucial role in coordinating the electrical impulses that regulate the contraction of the ventricles.

Line in NCERT: "A bundle of nodal fibres, atrio-ventricular bundle (AV bundle) continues from the AVN which passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum and immediately divides into a right and left bundle."

2. Double circulation system

Birds and mammals have a double circulation system, meaning their heart has two separate circuits: the pulmonary circuit (for oxygenating blood) and the systemic circuit (for distributing oxygenated blood to the rest of the body). This system ensures that oxygenated and deoxygenated blood do not mix, providing more efficient oxygen delivery to tissues.

In contrast:

• Fishes have a single circulation system with a two-chambered heart, where blood passes through the heart only once before going to the gills and then to the rest of the body.
• Amphibians typically have a three-chambered heart (two atria and one ventricle), leading to some mixing of oxygenated and deoxygenated blood, and also have a single circulation system.

Line in NCERT: "In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides. The ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation."

Thrombin plays a crucial role in the coagulation process by converting fibrinogen, an inactive plasma protein, into fibrin, which forms the meshwork that constitutes a blood clot. This conversion is essential for the formation of a stable clot that traps blood cells and prevents further bleeding. An interesting fact about thrombin is that it not only aids in clot formation but also has roles in wound healing and inflammation, showcasing its importance beyond just coagulation.

Line in NCERT: "Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin."

• Assertion Analysis: The assertion is true as coronary artery disease (CAD) is indeed caused by the buildup of substances such as calcium, fat, and cholesterol in the arterial walls.
• Reason Analysis: The reason is also true because the described accumulation does lead to the narrowing of the arteries, which is a key characteristic of CAD.
• Explanation Relation: The reason directly explains the assertion as it describes the process through which CAD occurs. Thus, both the assertion and reason are true, and the reason accurately explains the assertion.

Line in NCERT: "Coronary Artery Disease, often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle. It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower."