Cardiac cycle

Cardiac Cycle

Cardiac cycle is the complete sequence of events in one heartbeat. Three main stages : Diastole ,  Atrial systole and ventricular systole. 

1. Late diastole ( Relax ):  - Both atria and ventricles relax .

                                              - Atrioventricular (AV) valve open .

                                              - Semilunar valves close. 

                                              - Now , ventricles are filling with blood . ( 75-85% volume of chambers )

2. Atrial systole ( contraction ) : - The contraction exerts pressure on the blood within the atrial chambers which forces open the                                                                            bicuspid & tricuspid valves ( AV valves ) .

                                                         - Blood flows into the ventricles through the open AV valves .

                                                         - Ventricles expand .

                                                         - Ventricles now contains an average volume of about 130 ml of blood at the end of ventricular                                                                            diastole .(end- diastolic volume ) 

     

  

  

Opening and Closing of stomata base on potassium ion accumulation hypothesis .

                   


                                

Gaseous exchange in plants occurs through pores in the stomata      ( plural) ( singular : stoma ) . They are found on the epidermis of leaves . In dicotyledonous leaves , more stomata on the lower epidermis than on the upper epidermis . This is because to reduce the water loss by transpiration .In monocotyledonous leaves stomata are found on the two epidermal layers . Besides , lenticels found in bark of stem and root hairs with thin walls and large surface area also allow gaseous exchange to take place. A stoma consists of a pair of guard cells and a stomatal pore .
( Biology lesson )

Haemoglobin Structure ( 2 alpha chains & 2 beta chains )

Haemoglobin ( Hb ) combines with oxygen( O2 ) to form oxyhaemoglobin ( HbO2 ) .Each haemoglobin will bind with four oxygen molocules . Each oxygen binds to a haem group of one polypeptide chain ( alpha / beta polypeptide chain ) in haemoglobin . Binding the first oxygen is difficult . After binding the first oxygen to a haemoglobin , haemoglobin undergoes conformational change . Binding the second and third oxygen is easier .Binding the fourth oxygen is more difficult due to distorted shape of the molecule .