What exact events trigger the 'LUBB' and 'DUBB' heart sounds in an ECG sequence?

$LUBB$ ($S_1$) occurs immediately after the $QRS$ complex begins, caused by the closure of AV valves (tricuspid and bicuspid) during isometric ventricular contraction. $DUBB$ ($S_2$) occurs at the end of the $T$-wave, caused by the closure of semilunar valves at the onset of ventricular relaxation.

How does the SA node generate action potentials without external neural stimulation?

The Sinoatrial ($SA$) node consists of specialized auto-excitable cardiac tissue that undergoes slow spontaneous diastolic depolarisation through pacemaker channels, generating $70 - 75\text{ action potentials/min}$ independently.

Why is double circulation more efficient than single circulation in vertebrates?

Double circulation completely separates oxygenated and deoxygenated blood via systemic and pulmonary circuits, preventing arterial mixing and maintaining high systemic arterial pressure ($120/80\text{ mmHg}$) required for elevated metabolic demands.

Body Fluids and Circulation Notes, Formulas, Traps & PYQs | ExamiFly

Beta

Please wait while we prepare everything for you

Body Fluids and Circulation Notes, Formulas, Traps & PYQs | ExamiFly | Examifly

Solved High-Yield Sample Questions

Practice Mode

Question #1NEET 2023

If a person has a resting heart rate ( $HR$ ) of $75\text{ beats/min}$ and an End-Diastolic Volume ( $EDV$ ) of $110\text{ mL}$ with an End-Systolic Volume ( $ESV$ ) of $40\text{ mL}$ , calculate their Cardiac Output ( $CO$ ) in liters per minute.

Solution Locked

Step-by-Step Solution & Concept

Step 1

Calculate Stroke Volume ( $SV$ ) using $SV = EDV - ESV = 110\text{ mL} - 40\text{ mL} = 70\text{ mL}$ .

Step 2

Apply the Cardiac Output formula: $CO = SV \times HR = 70\text{ mL} \times 75\text{ beats/min} = 5250\text{ mL/min}$ .

Step 3

Convert $5250\text{ mL/min}$ to liters by dividing by $1000\text{ mL/L}$ , obtaining $CO = 5.25\text{ L/min}$ .

Select an option & click Check Answer to reveal solution

Question #2NEET 2022

During a single cardiac cycle lasting $0.8\text{ s}$ , if ventricular systole lasts for $0.3\text{ s}$ and atrial systole lasts for $0.1\text{ s}$ , for how long do the ventricles remain in a relaxed (diastolic) state during the entire cycle?

Solution Locked

Step-by-Step Solution & Concept

Step 1

Identify total cardiac cycle duration $T_{total} = 0.8\text{ s}$ and ventricular systole duration $T_{v-systole} = 0.3\text{ s}$ .

Step 2

Ventricular diastole duration is calculated using $T_{v-diastole} = T_{total} - T_{v-systole} = 0.8\text{ s} - 0.3\text{ s}$ .

Step 3

Calculating yields $T_{v-diastole} = 0.5\text{ s}$ (which includes $0.4\text{ s}$ of joint diastole plus $0.1\text{ s}$ of atrial systole while ventricles are relaxed).

Select an option & click Check Answer to reveal solution

If you want to explore more chapters of Biology then:

Click Here

Mastering Body Fluids and Circulation: Formulas, Traps & Exam Strategy | ExamiFly

Chapter Overview

Core Subtopics & Syllabus Breakdown

Key Formulas & High-Yield Equations

Cardiac Output (CO)

Stroke Volume (SV)

Duration of Single Cardiac Cycle (T_{cycle})

Mean Arterial Pressure (MAP)

Ejection Fraction (EF)

Common Mistakes & Traps to Avoid

Past Year Question (PYQ) Trends

Solved High-Yield Sample Questions

Frequently Asked Questions

Master Body Fluids and Circulation with 250+ Curated NEET Drills & AI Error-Correction