HSEB Notes on Origin and Conduction of Heart Beat | Class 12 Zoology

Biology | Zoology
HSEB Notes on Origin and conduction of Heart Beat
Class : 12

In the wall of right atrium, there is a special node called Sino Atrial node(SA node). It is self excitatory. It is the point of origin of heart beat. It is also called Pace maker. It is natural Pace maker. The heart cant work without it. If it is injured or damaged artificial pace maker is implanted. 

Near inter atrial septum, there is Atrioventricular node (AV node). It receives the impulses in the form of wave and passes it to Purkinje’s system. This system consists of Bundle of His, purkinje fibres. With the help of this system impulses are carried to the wall of ventricle. Then both ventricles contract pumping out blood. 

In the normal adult man, heart beats 70 to 80 times per minute. The average is 72 beats per minute. It is called heart rate. 

Heart sounds

The first heart sound is lubb. It is produced due the sharp closing of atrioventricular valves like the bicuspid and tricuspid valves. At the beginning of ventricular systole, these valves are closed. 

The second heart sound is dup. It is produced due the closing of semilunar valves at the end of the aortic arch and pulmonary aorta. It occurs at the end of ventricular systole. 

Blood pressure

It is a force exerted by blood against the wall of arteries, veins and capillaries. It is called BP in short. It is of two types. Systolic blood pressure is maximum pressure during contraction. Diastolic blood pressure is minimum pressure during the relaxation. The systolic and diastolic blood pressure of a normal adult is 120/80 mm of Hg. The range of systolic blood pressure is 100 to 140. 100 is lower limit and 140 is upper limit. The range of diastolic blood pressure is 55 to 80.

Problems related to BP

Hypertension or high BP

It is the condition when the systolic and diastolic blood pressure is 150/90 or above persistently.  Causes 

• Unbalanced diet, cholesterol rich food 
• Smoking 
• Alcohol consumption
• Stress, anxieties 
• Loss of elasticity of arteries, arterosclerosis
• Vasoconstriction 

Hypotension or low BP

It is the condition when the systolic and diastolic blood pressure is below the lower limit persistently. Causes 

• Unbalanced diet, less nutrient food.
• Loss of blood or less volume of blood
• Vasodilation

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