Explain the cardiac cycle — Hinglish notes

4.2.5 · Biology › Circulatory System

Cardiac cycle KYA hota hai?

0.8 s KYUN? Kyunki duration = total time ÷ number of events. 60 seconds mein 75 beats hain, toh har beat ko $60/75 = 0.8$ s milta hai. Yeh ek derivation hai, fact nahi — heart rate badlo aur recompute karo.

0.8 s in mein split hota hai:

Phase	Duration	Kya ho raha hai
Atrial systole	~0.1 s	Atria contract karte hain, ventricles ko top up karte hain
Ventricular systole	~0.3 s	Ventricles contract karte hain, blood eject karte hain
Joint diastole	~0.4 s	Saare chambers relax karte hain, passive filling hoti hai

Check: $0.1 + 0.3 + 0.4 = 0.8$ s ✓

YEH KAISE kaam karta hai — step by step (pressure follow karo!)

Phase 1 — Atrial systole (0.1 s)

Atria contract karte hain → atrial pressure ventricular pressure se upar chala jaata hai.
AV valves (tricuspid + bicuspid/mitral) pehle se open hain → baaki ~20–30% blood ventricles mein push ho jaata hai.
Semilunar valves shut rehte hain (aorta/pulmonary pressure ventricle se zyada hota hai).

Phase 2 — Ventricular systole (0.3 s)

Isovolumetric contraction: ventricles squeeze karna shuru karte hain. Ventricular pressure atrial pressure se upar shoot kar jaata hai → AV valves slam shut ho jaate hain → yahi first heart sound "LUB" (S1) banata hai. Saare valves briefly shut ho jaate hain → volume constant rehta hai.
Ejection: ventricular pressure aortic/pulmonary pressure se zyada ho jaata hai → semilunar valves open ho jaate hain → blood aorta aur pulmonary artery mein eject hota hai.

Phase 3 — Ventricular diastole / Joint diastole (0.4 s)

Ventricles relax karte hain → ventricular pressure aortic pressure se neeche gir jaata hai → aortic blood wapas flow karne ki koshish karta hai → semilunar valves snap shut ho jaate hain → second heart sound "DUB" (S2).
Isovolumetric relaxation: saare valves thodi der ke liye shut rehte hain.
Jab ventricular pressure atrial pressure se neeche girta hai → AV valves open ho jaate hain → ventricles passively fill hote hain (~70–80% filling passive hoti hai, agli atrial systole se pehle).

Worked examples

Apni galtiyon ko steel-man karo

Flashcards

75 bpm par ek cardiac cycle kitni lambi hoti hai, aur yeh kaise nikaalte hain?

0.8 s,

T = 60/75

se.

First heart sound (S1, "LUB") kisse hoti hai?

Ventricular systole ke start par AV (tricuspid + bicuspid) valves ke close hone se.

Second heart sound (S2, "DUB") kisse hoti hai?

Ventricular diastole ke start par semilunar (aortic + pulmonary) valves ke close hone se.

Valve kab open hota hai, yeh golden rule batao.

Yeh tab open hota hai jab uske peeche ka pressure uske aage ke pressure se zyada ho (flow high→low).

Stroke volume define karo aur formula do.

Blood ejected per beat;

S V = E D V - E S V

(e.g.

120 - 50 = 70

mL).

Cardiac output formula aur ek resting value likho.

C O = S V \times H R = 70 \times 75 \approx 5

L/min.

Ventricular filling ka kitna fraction passive hota hai?

~70–80%, diastole ke dauran atrial contraction se pehle.

Isovolumetric contraction kya hai?

Brief phase jahan ventricles contract karte hain SAARE valves shut ke saath, toh pressure badhta hai lekin volume constant rehta hai.

Bahut high heart rate output kyun reduce kar deta hai?

Cycle length shrink ho jaati hai (

T = 60/ H R

), diastolic filling time cut ho jaati hai → lower EDV → lower SV.

Recall Feynman: 12 saal ke bachche ko samjhao

Heart ko do squishy paani ke balloon socho jo do bade walon ke upar rakhe hain, unke beech mein jhoolne wale chhote doors hain. Pehle upar wale balloon thoda squeeze karte hain paani neeche walon mein push karne ke liye. Phir bade neeche wale balloon zor se squeeze karte hain — upar aur neeche ke beech ke doors slam shut ho jaate hain ("LUB") taaki paani wapas na jaaye, aur bajaaye iske woh pipes mein se exit doors ke zariye shoot ho jaata hai. Phir sab kuch relax karta hai, exit doors slam shut ho jaate hain ("DUB"), aur paani upar se quietly refill hone lagta hai. Squeeze, shoot, relax, refill — baar baar, kareeban har 0.8 seconds mein ek baar. Paani hamesha tight squeeze wali jagah se loose jagah ki taraf flow karta hai, aur har door sirf ek hi taraf khulta hai.

Connections

Heart Structure and Chambers — woh anatomy jinpar yeh pressures act karti hain.
Cardiac Valves — AV vs semilunar mechanics.
Heart Sounds and Auscultation — S1/S2 clinical use.
Cardiac Output and Regulation — $C O = S V \times H R$ ko aage badhata hai.
Electrical Conduction of the Heart — SA/AV node signals jo har phase ko time karte hain.
Blood Pressure — systolic/diastolic pressures isi cycle se aati hain.