Chemical regulation of the heart in animals Cations Na+ and K+ ions favour diastole, whereas Ca++ ion favours systole. Sudden infusion of the Ca++ ions into the heart causes calcium rigor or systolic arrest. Catecholamines Epinephrine and norepinephrine are the neurotransmitters of sympathetic division, acts on β1 receptors and exerts positive chronotropic (atria and ventricles) and inotropic effects on heart. β1 receptors are found […]

Nervous Regulation of Heart rate in animals Sympathetic and parasympathetic divisions of ANS play a key role in the regulation of heart rate. The nerves regulate to a larger extent the rate rather than the force of contraction either directly or indirectly. The two atria are especially well supplied with large number of both sympathetic and

Extrinsic Regulation of Heart in animals Heart regulates its cardiac output based on the functional blood requirement of different parts of the body by adjusting its rate. Heart rate is directly proportional to metabolic activity, but inversely proportional to the size of the animal. Large animals have a slower heart rate than smaller ones. Athletic

Intrinsic Regulation of heart in animals Frank’s Starling Mechanism/Heterometric Regulation Regulation of the cardiac function is independent of the nervous or humoral control. This was proved by the Starling’s experiment using Starling’s heart lung preparation i.e., isolating the heart from the body so as to remove humoral and neural influences. The heart is perfused through

Regulation of cardiac output in animals Heart functions (cardiac output, heart rate) can be regulated by- Intrinsic mechanisms, operating within the myocardium itself and Extrinsic mechanisms (by factors outside the heart). this both will be discussed in later part. Factors influencing cardiac output Muscular exercise (4-6 times increase), pregnancy, hypoxia, active digestion, stress and increased

Cardiac output or minute volume in animals Cardiac output or minute volume in animals is the volume of blood ejected by either the left or the right ventricles into the greater vessels, the aorta or pulmonary artery in a minute. Cardiac Output (L/min) → Stroke Volume × Pulse Rate In most animals, the cardiac output

Stroke volume The definite volume of blood pumped into the aorta / pulmonary trunk by each ventricular contraction (left / right) is referred to as stroke or pulse volume or the systolic discharge. If the stroke volume is expressed based on body weight it is known as stroke index. A portion of the blood is

Cardiac sounds Cardiac sounds are the distinct sounds produced during systole (S1) and diastole (S2) of the cardiac cycle, which can be recorded by the phonocardiogram. The first heart sound “lub”, is systolic sound indicates the firm closure of AV valves, occur during ventricular systole. It is associated with the vibration of the valves (valvular

Pressure and volume changes in atrium and ventricle Pressure changes in the atria The intraatrial pressure records three major positive waves- ‘a’ wave: Results from atrial systole. Atrial systole causes an increase in the atrial pressure resulting in the opening of the AV valves and blood flows into the ventricles. ‘c’ wave: It results due to bulging

Cardiac cycle Cardiac cycle is defined as sequence of events such as pressure and volume changes, cardiac sounds and changes in the electrical potential occurring during the period between two successive ventricular contractions. It is characterised by one complete contraction (systole) and relaxation (diastole) and indicates a complete heart beat. These periods are not equal in duration, when heart