The eye is a complex sensory organ that allows us to see the world around us. The eye works by gathering light from the environment and converting it into electrical signals that can be interpreted by the brain. The basic structure of the eye includes the cornea, iris, pupil, lens, retina, and optic nerve. The cornea is the transparent outer layer of the eye that helps to focus incoming light. The iris is the colored part of the eye that regulates the amount of light that enters the eye through the pupil, which is the black circular opening in the center of the iris. The lens is a clear, flexible structure located behind the iris that helps to focus light onto the retina. The retina is a thin layer of tissue that lines the back of the eye and contains photoreceptor cells called rods and cones. These cells convert light into electrical signals that are sent to the brain via the optic nerve. The rods are responsible for the low light vision and detecting motion, while the cones are resp
The Cardiac event that occurs from the beginning of one heartbeat to the beginning of the next is called the cardiac cycle. The action potential travels rapidly through both atria and then through the AV bundle into the wall of ventricles. Because of the special arrangement of the conducting system from the atria to the ventricles, there is a delay of more than 1/10th a second between the passage of the cardiac impulse from the atria into the ventricles. this allows the atria to contract ahead of the ventricles, thereby pumping blood into the ventricles before the strong ventricular contraction begins.
Thus the atria are the primer pumps for the ventricles, and ventricles then provide the major source of power for moving blood through the vascular system.
The process of heartbeat begins from the time of embryonal development. Once the heartbeat starts, it continues thought out life (inherent capacity). In the resting stage of man in 1 minute, the heartbeat around 72 times and during this 1 minute, 5 litres of blood is a pump to a different part of the body through heart through the left ventricle.
The serial wise or sequential changes which take place in the heart are called the cardiac cycle. The contraction of the atria is termed as atrial-systole, and their relaxation is called atrial-diastole. the same way the contraction and relaxation of ventricles are termed as ventricular systole and ventricular diastole. The time the cardiac cycle is the reverse ratio of heartbeat per minutes. If heart beat per minute is 72, then the time of cardiac cycle is 60/72 = 0.8 seconds.
Joint Diastole: 0.8 - 0.4 = 0.4 sec. (Period during which entire heart is in Diastole)
Following events are related to the Cardiac cycle:
(1) "Ventricular-systole" - It is an important process because during it the blood is pumped out of the heart into the arteries. It has main parts:-
(a) "Isometric-contraction" - Walls of the ventricles start contracting, due to which pressure is more in the ventricles. Due to the increase of this pressure the "Cuspid valves" close producing "LUBB" sound.
(b) "Period of Ejection" - During this cycle when pressure increases in the ventricles, then the semi-lunar valves of the arches open and blood rapidly enters into the arches pushing the valves on one side.
Oxygenated blood from the left-ventricle enters into the carotico-systemic arch or aorta, and deoxygenated blood from the right-ventricle enter into the pulmonary-arch. During ventricular systole, the auricles receive blood from the veins.
(2) "Ventricular Diastole" -Ventricles start relaxing now due to which pressure inside them falls further. As a result of this, closure of semilunar valves occurs due to which "DUP" sound is heard at the onset of ventricular diastole.
Ventricular diastole have sub stages;-
(a) "Isometric Relaxation" - When due to blood ejection, the pressure inside the ventricles decreases as compared to the pressure inside the arches. The blood stops moving out and the ventricles prepare for relaxation.
(b) "Rapid in-flow"- After the systole in the ventricles the systolic pressure reduces very much. This pressure becomes very less than the atrial-pressure. Moreover due to relaxation in ventricles the pressure inside them falls further. So, now the cuspid valves open up and blood flows rapidly from the atria to the ventricles. S3 heart sound is produced.
(c) "Diastasis"- After rapid in flow, the atria transfer the blood to the ventricles at the same rate at which they receive blood from the veins, so the inflow of blood reduces considerably. At this moment pressure inside all four chambers is equal and entire heart is in diastole. Also at this moment of this time, the AV valves are open but semilunar valves are closed.
(3) "Atrial Systole"- Due to contraction in the atria the remaining blood comes into the ventricles so the atrial pressure now becomes zero. S4 heart sound is produced.
(4) "Atrial Diastole"- Atria start relaxing now. Due to the presence of almost zero pressure in the atria, during diastole the auricles start receiving further blood from the veins.
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