cardio

The cardiovascular system consists of:
- Heart: pumps blood.
- Blood Vessels: conduits through which blood flows.
- Blood: the fluid that transports nutrients, gases, and wastes.
The system transports materials throughout the body, including:
1. Nutrients: absorbed from the gastrointestinal tract.
2. Oxygen: supplied by the lungs.
3. Waste products: removed from tissues and delivered to excretion organs.
The idea of a closed cardiovascular system evolved over time, with significant contributions from historical figures. For example:
- William Harvey demonstrated the circulatory nature of blood flow.

Pressure in Fluid:
- Hydrostatic pressure relates to the height of a fluid column, with pressure exerted equally in all directions in a static state.
- In a flowing system, pressure decreases over distance due to friction.
Fluid moves from areas of higher pressure to lower pressure, which is described by a pressure gradient ( $<br>abla P$ ).
Poiseuille’s Law describes that resistance ( $R$ ) depends on:
- The radius ( $r$ ) of the vessel, which has a significant impact on flow.
  $R = rac{8Lh}{ ext{π}r^4}$
Factors affecting resistance include:
1. Length of the vessel ( $L$ )
2. Viscosity of the fluid ( $h$ )
3. Diameter of the vessel ( $r$ )
Flow Rate ( $Q$ ) is directly proportional to the pressure gradient and inversely proportional to resistance:
$Q ext{ is proportional to } <br>abla P / R$

The heart has four chambers:
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
Cardiac Muscle Cells: They are striated, branched, and connected by intercalated disks.
Conduction System: The sequence of electrical signal conduction is:
1. SA Node: initiates the heartbeat.
2. AV Node: delays the signal slightly to ensure atrial contraction completes.
3. AV Bundle and Purkinje Fibers: transmit impulses rapidly throughout the ventricles.
Electrocardiogram (ECG) reflects electrical activity of the heart with waves corresponding to different phases of cardiac muscle contraction:
- P wave: Atrial depolarization.
- QRS complex: Ventricular depolarization.
- T wave: Ventricular repolarization.

Cardiac Cycle:
- Includes phases of both contraction (systole) and relaxation (diastole).
- Phases:
1. Late diastole: Both chambers relaxed, ventricles fill with blood.
2. Atrial systole: Atria contract, forcing additional blood into ventricles.
3. Ventricular systole: Ventricles contract, ejecting blood into arteries. Closing AV valves causes sound S1.
4. Isovolumic relaxation: Ventricles relax without volume change, closing semilunar valves causes sound S2.
- End-Diastolic Volume (EDV): Volume of blood in ventricles before contraction.
- End-Systolic Volume (ESV): Volume of blood remaining in ventricles after contraction.

Heart Rate: ~70 bpm at rest.
Cardiac Output (CO): volume of blood pumped per ventricle per minute.
$CO = ext{Heart Rate} imes ext{Stroke Volume}$
CO can increase to 30-35 L/min during intense activity.
Stroke Volume (SV): Amount of blood pumped with each contraction, usually around 70 mL at rest.
Frank-Starling Law: The strength of ventricular contraction is related to the initial length of cardiac muscle fibers (preload). More blood in the ventricles leads to stronger contractions.

Parasympathetic Nervous System: Slows heart rate using acetylcholine.
Sympathetic Nervous System: Increases heart rate using norepinephrine, enhancing contractility.
Both systems modulate heart rate, with parasympathetic being dominant at rest.

The cardiovascular system’s efficiency as a transport and communication system is essential for maintaining homeostasis and responding to physiological needs. Its intricate balance of pressure, flow, and resistance ensures that all tissues receive adequate blood supply while removing waste products.
Understanding the functions and regulatory mechanisms of the cardiovascular system is crucial in the context of various diseases, particularly those affecting heart function, such as myocardial infarction (MI) and heart failure.