The Heartbeat

Cardiac cycle = contractions and relaxations of heart muscles in a complete heartbeat

Takes ~0.8 s

4 Valves

Atrioventricular (AV) valves -are tricuspid valve made of 3 flaps and bicuspid (mitral) valve made of 2 flaps

- Prevents backflow into atria when ventricles contract “lub”

Semilunar valves (both pulmonary and aortic valves; half-moon shape)prevent backflow into ventricles while they relax “dub”

•flaps of connective tissue•prevent backflow

Blood flow through valves: https://www.youtube.com/watch?v=rguztY8aqpk

Heart sound: “Lub-dub, lub-dub”

Heart murmur:defective valves causing hissing sound when blood squirts backward through valves

•Heart sounds are caused by the closing of valves

“Lub” “Dub”recoil of blood against closed AV valves

recoil of blood against closed semilunar valves

Lub-dub with Bill Nye: https://www.youtube.com/watch?v=riDPxasIz_I

How the heart contracts

How the heart contracts:

Sinoatrial (SA) node: • Pacemaker, in the wall of right

atrium• Sends out electrical signal

causing two atria to contract simultaneously

Atrioventricular (AV) node• transmits signal through

specialized fibres called bundle of His and Purkinje fibres

•Purkinje fibres initiate almost simultaneous contraction of all cells of the right and left ventricles

https://www.youtube.com/watch?v=bwBM2Pa1LA8 with Bill Nye. Watch all

Electrocardiograph: records electrical impulses by a beating heart

• P wave = atrial contractions• QRS wave = ventricular contractions• T wave = ventricle recovers

“lub” “dub”

The “LUB” “DUB” of Our Hearts!

LUB1 2 3

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DUB4 5

the ventricles relax and the semilunar valves close to produce the second heart sound (“DUB”).

The relaxation of the ventricles is followed by the next firing of the SA node for the next heartbeat.

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10Heartbeat in real time https://www.youtube.com/watch?v=G4dFVeP9Vdo

MRI- imaging tool for the heart

Blood Pressure• Blood pressure= force exerted on vessels’

walls as blood flows through them• Pulses = evidence of artery under pressure due

to heart’s contraction

https://www.youtube.com/watch?v=u6saTO8_o2g

A digital sphymomanometermeasuring blood pressure

1. Inflate the cuff to close off flow to brachial artery2. Listening to pulse, slowly release air until pulse is heard

and read the pressure – Systolic (i.e. pressure when the ventricles contract)

3. Slowly release air until no pulse is heard and then read the pressure – Diastolic (i.e. The pressure when the ventricles relax; heart is at rest)

4. Healthy = 120/80 (units = mmHg)

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Factors affecting Blood pressure• Diameter of blood vessels• Volume of blood• Physical activity• Temperature• Body position• Age (blood pressure usually increases with age) • Stress level• Diet• Drinking too much alcohol• Medication etc.

Too much Na+ in diet causes H2O to enter blood by osmosis increases blood volume increases blood pressure

High blood pressure reading: above 140/90 mmHg

Stiffer arteries make heart work harder

Arteries may rupture leading to stroke, heart attack, kidney damage etc.

Hypertension (high blood pressure)

14Bypass surgery: https://www.youtube.com/watch?v=7PpidBmoA4c (@6min)

Resource link: https://www.hypertension.ca/en/

Diagnosis https://www.youtube.com/watch?v=IGyeNtZZnrk

Atherosclerosis = Hardening of the arteriesPlaque (fat, cholesterol, Ca etc) built up in the artery

leading to stroke, heart attack, death

Balloon angioplasty

https://www.youtube.com/watch?v=RwWDOZ9oTP8

Heart Bypass surgery