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.

• Platelets, also called thrombocytes, are cell fragments produced from megakaryocytes.
• Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood.

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

Prehypertension is defined as a systolic pressure from 120–139 millimeters of mercury (mm Hg) or a diastolic pressure from 80–89 mm Hg.

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.

• In ECG, P-Wave represents depolarization of atria.
• The QRS complex represents the depolarization of ventricles.
• T-wave represents repolarization of ventricles i.e., returns from excited to the normal state.
• Reduction in the size of T-wave i.e., if the T-Wave represents the insufficient supply of Oxygen i.e. coronary ischemia.
• Hence,
  (a) – (iv)
  (b) – (i)
  (c) – (ii)
  (d) – (iii)

• 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.

- Statement (i): The instrument used for recording the heart's electrical events is indeed named an electrocardiograph.

- Statement (ii): In any ECG, the part of the baseline between any two deflections is actually called a segment, not an interval. Therefore, this statement is incorrect.

- Statement (iii): Abnormalities in the working of the heart can indeed change the wave pattern of an ECG. This is because different heart conditions can affect the electrical activity of the heart, leading to changes in the ECG wave pattern.

Therefore, the correct option is C

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.

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.

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.

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.

The sinoatrial node (SAN) is a specialized cardiac muscle tissue located in the right upper corner of the right atrium. It has the remarkable ability to generate action potentials without any external stimuli. The SAN is often referred to as the pacemaker of the heart because it initiates and maintains the rhythmic contractile activity of the heart by producing the highest number of action potentials, typically around 70-75 per minute. This crucial function regulates the heart's beating rhythm, making the SAN a vital component of the heart's electrical conduction system.

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.

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.