Body Fluids And Circulation

Step 1: Understanding the Fetal Circulatory Adaptations

- Statement I is incorrect: The correct name of the fetal heart opening is foramen ovale, not foramen Manro.
- Statement II is correct: The ligamentum arteriosum is a remnant of the ductus arteriosus, connecting the pulmonary and systemic circulation.

Step 1: Understanding the R-R Interval in ECG

- The R-R interval represents one complete cardiac cycle.
- It is used to determine heart rate.
Step 2: Calculating the Interval

- The normal resting heart rate is 60-100 beats per minute.
- The R-R interval is approximately 0.8 seconds for a heart rate of 75 bpm.
Step 3: Conclusion

Since the R-R interval is about 0.8 seconds, the correct answer is Option (3).

Step 1: Analyze Assertion (A):
The second heart sound, "Dub" (or Dup), is associated with the beginning of ventricular diastole (relaxation). As the ventricles relax, the intra-ventricular pressure falls. Thus, the assertion connects ventricular relaxation with the second sound, which is factually true.
Step 2: Analyze Reason (R):
The physical cause of the second heart sound is the sharp closure of the semilunar valves (aortic and pulmonary valves). This closure prevents the backflow of blood from the aorta and pulmonary artery into the relaxing ventricles. Thus, the reason is factually true.
Step 3: Establish the Link:
Why is the sound produced when ventricles relax? Because the relaxation causes a pressure drop, leading to the backward flow of blood, which snaps the semilunar valves shut, creating the sound. Therefore, (R) is the correct explanation for (A).

• Native insulin consists of two peptide chains: A chain = 21 amino acids; B chain = 30 amino acids.
• Therefore correct option is (3) A=21, B=30.

Sarcoma arises from connective tissues (bone, cartilage, muscle), not nervous tissue. Carcinoma → epithelial; Leukemia → bone marrow; Sporadic cancers → non-hereditary.

Soluble fibrin is formed initially; Factor XIII (fibrin stabilizing factor) cross-links the fibrin monomers to form insoluble fibrin fibers, stabilizing the clot. Both Assertion and Reason are correct.