Cardiovascular and Muscle Physiology: ECG, Cardiac Cycle, Blood Flow, and Muscle Types

Skeletal muscle characteristics

Multinucleated, voluntary muscle.

Cardiac muscle characteristics

Single nucleus, involuntary muscle with a long refractory period.

Where are pacemaker cells found

Autorhythmic SA/AV node cells.

Sarcomere contraction

Z-Z disk move closer, I band and H zone shorten, A band stays the same.

Excitation-contraction coupling (E-C) in cardiac muscle

AP (depolarization) → Ca2+ influx → Ca2+-induced Ca2+ release (RyR) → binds troponin → actin-myosin interaction → contraction.

ECG components

P wave = atrial depolarization; QRS = ventricular depolarization; T = ventricular repolarization.

ECG Pathologies

Arrythmias- irregular rhythm

Heart block- conduction failure

Fibrillation- chaotic electrical activity

Action potentials in cardiac contractile cells

Na+ depolarization, Ca2+ plateau, short refractory → tetanus possible.

Action potentials in pacemaker cells

gradual depolarization (Na⁺ in via If), threshold triggers Ca²⁺ influx, K⁺ efflux repolarizes .

what is the preload phase

Stretch of the ventricles before contraction.

what is the afterload phase

resistance the heart must work against to eject blood (arterial pressure)

If channels

'Funny' Na+ channels responsible for pacemaker potential

when do IF channels open

when membrane potential is more negative (hyperpolarized) closing near threshold

Blood flow calculation formula

Flow (Q) = ΔP / R (Poiseuille's law).

Factors affecting blood flow and velocity

Flow depends on pressure gradient and resistance.

velocity = flow/cross sectional area

what is the relationship between area and velocity

increased area = decreased velocity

sympathetic regulation of cardiovascular system

Sympathetic increases heart rate and contractility. (Beta1 receptors, NE)

parasympathetic regulation of cardiovascular system

decreased heartrate (ACh via muscarinic receptors)

when does Passive filling occur

During late diastole both chambers relax and fill 80% with blood.

What does the wiggers diagram show

ECG, pressure, and volume changes during the cardiac cycle.

what are the steps in the pressure volume curve

Atrial systole → isovolumic contraction → ejection → isovolumic relaxation → filling .

Cardiac output calculation

CO = HR × SV; typical ≈ 5 L/min.

Starling's law

Increased end-diastolic volume (EDV) = increased stretch, contractile force, and stroke volume

Mean arterial pressure (MAP) calculation

MAP ≈ Diastolic + ⅓(Systolic − Diastolic).

Factors affecting venous return

Skeletal/respiratory pumps, venous tone.

what does increased venous return cause

increased preload and stroke volume

Korotkoff sounds

Sounds heard when measuring blood pressure.

Systemic vs local control of blood flow

Systemic: ANS, hormones (NE, E);

Local: tissue metabolic needs.

Factors affecting blood pressure and its regulation

Cardiac output, resistance, volume, elasticity

what is blood pressure regulated by

baroreflex; increased BP = baroreceptors fire, decreased HR and vasodilation

Baroreflex

Sensors in carotid & aortic sinuses detect pressure changes; HR and vasodilation

Pulmonary and alveolar ventilation calculation

Vₑ = tidal volume × rate;

Vₐ = (tidal volume - dead space) × rate.

how does pressure change during breathing

Intra-alveolar pressure: ↓ inspiration, ↑ expiration.

Intrapleural pressure: always negative, more negative on inspiration

Transpulmonary pressure: ↑ inspiration, keeps lings open (Pₐ − Pᵢₚ)

Which of the following ECG interpretations is correct?

​​​​​​​The T wave corresponds to ventricular repolarization

Choose the correct statement about the pacemaker cells in the electrical conducting system of the heart.

The firing rates of SA node > AV node

Choose the correct statement of the afterload

When diastolic pressure increases, afterload increases.

In the Wiggers diagram, 

atrial contraction happens immediately after the P wave.

Bill's systolic pressure = 121mmHg, and pulse pressure = 30mmHg. Choose the correct answer.

His diastolic pressure is 91mmHg.

Choose the correct statement about the body’s response about the blood pressure change after a person drank 1L of water.

Both CVCC and kidneys as the integration centers are activated.

Select the correct statement regarding transpulmonary pressure (TPP).

The TPP of inspiration changes from 3 to 6 mmHg.

flow of blood through CV system

Superior/ inferior vena cava,

right atrium,

tricuspid valve,

right ventricle,

semilunar valve,

left pulmonary arteries,

left pulmonary veins,

left atrium,

bicuspid valve,

left ventricle,

aorta