Which structure is called the pacemaker of the human heart?
- A.Atrio-ventricular node
- B.Sino-atrial node
- C.Bundle of His
- D.Purkinje fibres
Correct answer
Explanation
The correct answer is B, the sino-atrial node. The sino-atrial node is a small patch of specialised muscle tissue in the wall of the right atrium near the opening of the superior vena cava, and it generates the impulse that sets the rate of each heartbeat without any outside stimulus, which is why it is called the pacemaker. Option A is wrong because the atrio-ventricular node only receives that impulse from the sino-atrial node and passes it on after a slight delay; it can act as a pacemaker only if the sino-atrial node fails. Option C is wrong because the bundle of His conducts the impulse from the atrio-ventricular node into the ventricles. Option D is wrong because the Purkinje fibres spread the impulse through the ventricular walls so that they contract together.
Read the full article: Human Body Important Facts for Competitive Exams
Practice Questions
View allWhich is the smallest bone in the human body?
- A.Stapes
- B.Malleus
- C.Incus
- D.Hyoid
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The stapes, shaped like a stirrup, is the innermost of the three ossicles of the middle ear and is the smallest bone in the human body, measuring only a few millimetres; the smallest muscle of the body, the stapedius, is attached to it.
Read the full explanation →How many bones are there in the body of an adult human being?
- A.186
- B.206
- C.256
- D.300
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The adult human skeleton has 206 bones, of which 80 belong to the axial skeleton, that is the skull, vertebral column and chest, and 126 to the appendicular skeleton of the limbs and girdles.
Read the full explanation →Which is the largest gland in the human body?
- A.Thyroid
- B.Pancreas
- C.Liver
- D.Pituitary
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The liver weighs about one and a half kilograms and is both the largest gland and the largest internal organ of the body; it secretes bile, stores glycogen, iron and vitamin A, converts ammonia into urea and detoxifies drugs and poisons.
Read the full explanation →What is the average life span of a red blood cell in the human body?
- A.About 10 days
- B.About 60 days
- C.About 120 days
- D.About 365 days
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Red blood cells are produced in the red bone marrow, lose their nucleus on maturing and survive roughly four months, after which they are broken down in the spleen, which is accordingly called the graveyard of red blood cells; the iron released from their haemoglobin is used again.
Read the full explanation →Human blood groups were discovered by:
- A.William Harvey
- B.Karl Landsteiner
- C.Robert Koch
- D.Edward Jenner
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The Austrian scientist Karl Landsteiner discovered the A, B and O blood groups in 1901 and received the Nobel Prize for Physiology or Medicine in 1930 for the work; he was also associated with the discovery of the Rh factor, named after the rhesus monkey.
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