Cardiac cycle, Biology

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.

Posted Date: 10/30/2012 5:59:13 AM | Location : United States







Related Discussions:- Cardiac cycle, Assignment Help, Ask Question on Cardiac cycle, Get Answer, Expert's Help, Cardiac cycle Discussions

Write discussion on Cardiac cycle
Your posts are moderated
Related Questions
Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

CONCEPT OF NURSING UNIT: Concept in the design and facilities of nursing unit has been changed time to time based on the different categories of patients and peculiarities of

FOOD Food consists of H O, minerals, vitamins carbohydrate, lipid & protein. A person needs 1600 cal. per day. This is BMR (Basal metabolic rate). Needed 2500 cal. per

how is an increase in glucose concentration controlled in the human body?

Explain holding method of pasteurization In the holding method of pasteurization (62 o C for 30 minutes) or the high-temperature short-time (HTST), 71 o C for 15 minutes method

Explain Differential Staining Technique? It divides bacteria into separate groups based on staining properties, like Gram's stain, Acid-fast stain etc. Here 2 or more contrasti

Marine Ecosystems Marine ecosystems cover 70 per cent of the earth's surface and have an average depth of 3.750 m (the greatest known depth being 10,750 metres in the Mariana

Q. If a person eats raw or badly cooked meat infected by Taenia solium or Taenia saginata will this person develop taeniasis or cysticercosis? If a person eats badly cooked or

Q. Selection of foods for diabetic patients? Some handy guidelines for selection of foods for diabetic patients is presented next. You may be aware that some foods need to be

Entamoeba Histolytica Losch (1875), for the first time, described the disease symptoms of infection of Entamoeba histolytica. However, it was only in 1903 that Schaudin gave t