Cardiac cycle, Biology

Assignment Help:

Cardiac Cycle

Cardiac cycle has two phases-systole and diastole. Ventricular systole and diastole occur as a result of depolarization and chamber volume and pressure. The diastolic phase of both ventricles normally occurs simultaneously. 

This phase of ventricular myocardial relaxation permits emptying of atrial contents through the open atrio-ventricular valves (tricuspid and bicuspid or mitral). Rapid ventricular filling, a passive gravity flow of blood form atria to ventricles of starts when atrial pressure exceeds ventricular pressure and AV valves open. Increasing blood volume causes ventricular pressure to rise, which slows further filling. Atrial musculature contracts propelling additional blood into the ventricle before ventricular contraction (atrial systole ).

There is increase in myocardial tension and intra-ventricular pressure without change in blood volume. AV. Valves dose. For one short period, all the valves are closed until, with ventricular depolarization, the pressure in the ventricles exceeds that of pulmonary artery and aorta. (Isovolumetric ventricular contraction).

The systolic phase is the active contraction of the ventricular myocardium causing ejection of blood into the pulmonary artery and aorta. The right and left ventricle contract simultaneously. Systole begins when the semi- lunar valves open and end when they close. The higher pressure in the aorta and pulmonary artery than that in ventricles causes the closure of the semi-lunar valves. With each contraction, a volume of blood is ejected, called the stroke volume. Normal stroke volume (SV) is approximately 70 ml.

Cardiac output = SV x Heart rate /minute.

Three important factors affecting stroke volume and in turn cardiac output, are preload, contractility and after load. Preload is related to the volume of blood distending the ventricles at the end of diastole. Contractility refers to a change in the inotropic state of the muscle without a change in myocardial fiber length or preload. After load is the amount of tension the ventricle must develop during contraction to eject blood from the left ventricle into the aorta.

The 'lub-dub' sounds heard on auscultation corresponds with the closure of heart valves. The 'lub' sound corresponds with closure of AV valves at the beginning of ventricular systole and 'dub' sound corresponds with the closure of semilunar valves at the end of ventricular systole.


Related Discussions:- Cardiac cycle

Chlorophyll, Chlorophyll is the pigment in the green plants which absorbs ...

Chlorophyll is the pigment in the green plants which absorbs solar energy.   chlorophyll a -  It is a green photosynthetic pigment common to all the photosynthetic organisms.

What is phosphorylation, Q. What is phosphorylation? What are various biolo...

Q. What is phosphorylation? What are various biological processes in which phosphorylation plays a critical role? Phosphorylation is the name given to procedure of the addition

Scientific methord, how adoctor dicide a sickness of a patiant

how adoctor dicide a sickness of a patiant

Can obesity causes the cardiovascular disease, Q. Can Obesity causes the ca...

Q. Can Obesity causes the cardiovascular disease? As you know obesity or excessive weight is the primary cause of cardiovascular disease. It is an independent risk factor for h

What are properties that make water special for life, Q. What are the major...

Q. What are the major water properties that make water special for life? The water properties that make water biologically important are molecular polarity, thermal stability (

Explain enfuvirtide, Explain Enfuvirtide Enfuvirtide is the first fusio...

Explain Enfuvirtide Enfuvirtide is the first fusion inhibitor approved by the FDA for treatment of HIV infection and is indicated for treatment-experienced patients with ongoin

Explain the fermentability or degradability, Explain the Fermentability or ...

Explain the Fermentability or Degradability? As you are aware that colon contains over 400 known species of bacteria that exist in a symbiotic relationship with the host. All f

Which types of mammal are included in the primate group, Which types of mam...

Which types of mammal are included in the Primate group?  The Primate group contains a) Lemurs, b) Monkeys, c) Apes and humans.

Explain the physiologic mechanism of osseointegration, Q. Explain the Physi...

Q. Explain the Physiologic mechanism of osseointegration It has been suggested that the physiologic mechanism for maintaining osseous integration is a sustained evolution in re

Internal factor - factor controlling metamorphosis in insect, Internal Fact...

Internal Factor - Factors Controlling Metamorphosis in Insects Likewise to the amphibian metamorphosis, moulting and metamorphosis in insects has been found to be initiated in

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd