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

What are the three main types of passive transport, What are the three main...

What are the three main types of passive transport? The three main kinds of passive transport are a)  simple diffusion, b)  osmosis and c)  Facilitated diffusion. C

Difference between unconditioned & conditioned reflex action, Difference be...

Difference between unconditioned and conditioned reflex action- S.NO .   1. UNCONDITIONED   It is inborn CONDITIONED

Explain genetic relatedness of the aid-giver, Aid-giving behaviour between ...

Aid-giving behaviour between genetically related individuals in animal groups is often observed in nature. This aid-giving behaviour can evolve when the advantages of helping relat

Protozoa., brief account on classification and general characters of protoz...

brief account on classification and general characters of protozoa

Discuss haematoxylin and its subtypes in detail, Question 1 Discuss how yo...

Question 1 Discuss how you would perform mounting of stained sections. List commonly used mounting media in histopathology laboratory. Add a note on advantages and disadvantages o

What is dextrin, Dextrin  Polymers of D-glucose, formed due to partial ...

Dextrin  Polymers of D-glucose, formed due to partial  hydrolysis of starch by enzymes.

Pulse oximetry readings, Outline three client considerations when taking an...

Outline three client considerations when taking an accurate pulse oximetry reading.

Source of nutrients and energy of microorganisms, Q. Source of nutrients an...

Q. Source of nutrients and energy of Microorganisms? Microorganisms use foods as a source of nutrients and energy. Each kind of microorganism has a definite range of food requi

List various liver function tests, Question 1 List various liver function ...

Question 1 List various liver function tests. Discuss the importance of each test. Add a note on standardization of various liver function tests Question 2 Discuss the follow

Explain about the reduction tests - carbohydrates, Explain about the Reduct...

Explain about the Reduction Tests - Carbohydrates? These are a group of tests answered by reducing sugars. Since we have already discussed  reducing sugars, you will be able to

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