12th Zoology

Cardiac cycle

Cardiac cycle

The sequential events occuring from the initiation of one heartbeat to
the commencement of the next is called as one cardiac cycle. In this cycle,
the contraction phase is called systole. The relaxation phase is the diastole.

A single heart beat comprises a systole and diastole in both atria and
ventricles.

Atrial systole

There is a continuous flow of blood into the right atrium
through superior and inferior vena cava and coronary sinus. Simultaneously
the left atrium receives blood from 4 plulmonary veins. There is a passive
movement of nearly 70% of the blood. The remaining 30% is pumped into
the ventricles by atrial contraction.

Ventricular filling

When the valves in between atria and ventricles open
nearly two-third of the ventricle is filled. Remaining space gets filled up by
atrial contraction. (Cardiac Cycle)

Ventricular systole

As the atrial systole ends, the action potential
generated by the SA node reaches the AV node and rest of the fibrous
system. It causes contraction of the ventricular wall. Thus ventricular
pressure results. The very strong ventricular pressure pumps the blood into
respective arteries by causing the semilunar valves to open.

Ventricular diastole

Soon after the blood leaves the ventricles there is a
fall in the ventricular pressure. The semilunar valves close and the atrial
valves open to begin the next cycle. (Cardiac Cycle)

Heart sound

The heart sound felt by a stethescope is caused due to the
closure and opening of the valves. The generation of sound is rhythmic. The
first sound is louder (lubb) and of longer duration (0.16-0.90sec). It is due
to closure of the atrioventricular valves at the beginning of the ventricular
systole. The second sound is of shorter duration (dubb) (0.10sec). It is caused
at the end of the ventricular systole by the closure of semilunar valve. The
heart beats at the rate of about 72-80 times per minute in adults. The ventricular
systole causes a wave of distension due to blood flow. It is called as arterial
pulse. It can be felt on the wrist. The pulse rate corresponds to rate of
heartbeat. (Cardiac Cycle)

Related Topics in Zoology:

Bio Zoology All Important Topics


  1. Human Physiology Introduction

  2. Nutrition

  3. Carbohydrates Poly hydroxyaldehydes (or) ketones

  4. Proteins (Polypeptides)

  5. Lipids

  6. Vitamins – Functions Of Vitamins

  7. Deficiency of Vitamin

  8. Minerals – Water – Role of water

  9. Balanced diet

  10. Obesity

  11. Digestive System

  12. Dental Caries (Tooth decay)

  13. Root Canal Treatment

  14. Peptic ulcer

  15. Hernia and Types

  16. Appendicitis (Appendix)

  17. Gall Stones

  18. Hepatitis

  19. Fractures – Types of fractures

  20. Mechanism of fracture

  21. Dislocation of joints

  22. Arthiritis

  23. Rickets and Osteomalacia – Orthopedics

  24. Muscles

  25. Mechanism of muscle contraction

  26. Types of muscle contraction

  27. Myasthenia Gravis

  28. Respiration – Process of pulmonary respiration

  29. Mechanism of Breathing

  30. Regulation of Respiration

  31. Pneumonia Tuberculosis Symptoms Treatment

  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes

  33. Circulatory System – Functioning of Human heart

  34. Cardiac Cycle

  35. Coronary blood vessel and its significance

  36. Myocardial infarction

  37. Angina pectoris

  38. Angiogram – Angioplasty

  39. Atherosclerosis

  40. Heart block Echo cardiography Heart Valves

  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)

  42. Blood Pressure

  43. Heart transplantation

  44. Pulse rate

  45. Cardio Pulmonary Resuscitation (CPR)

  46. Blood – Composition of plasma – Blood cells

  47. Clotting of Blood or Haemostasis

  48. Thrombosis

  49. Nervous system Co-ordination systems

  50. The Brain – Fore Brain, Midbrain, Hindbrain

  51. Memory

  52. Sleep – Types of sleep

  53. Stroke – Brain haemorrhage

  54. Alzheimer – Meningitis (Brain fever)

  55. Conditioned reflex

  56. Electroencephalography EEG

  57. Right and Left brain concept

  58. Spinal cord functioning

  59. Chemical co-ordination – Functions of Endocrine glands

  60. Hypothalamus

  61. Pituitary gland – hormone

  62. Hormones of Neurohypophysis – vasopressin

  63. Thyroid gland

  64. Parathyroid Gland

  65. Pancreas

  66. Adrenal gland

  67. Gonads

  68. Receptor Organs – Eye

  69. Photochemistry of Retinal visual Pigments

  70. Errors of refraction

  71. Optometry – Retinopathy

  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia

  73. Eye Infections and Eye Care

  74. Ear

  75. Mechanism of hearing

  76. Defects of the ear

  77. Hearing Aid – Noise pollution

  78. Skin and functions of skin

  79. Melanin functions

  80. Effects of solar radiation / UV radiation – Skin grafting

  81. Dermatitis

  82. Tongue – Mechanism of Stimulation

  83. Excretion Ureotelism Nephron

  84. Mechanism of urine formation

  85. Renal Failure, Dialysis, Kidney Machines

  86. Kidney stone – Kidney transplantation

  87. Diabetes mellitus

  88. Functioning of male reproductive system

  89. Functioning of female reproductive system

  90. Ovulation and fate of the ovum – Menstrual cycle

  91. Fertilization

  92. Birth control

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