AQA GCSE Rate of blood flow (Biology)

Rate of blood flow

You need to calculate rate of blood flow. This formula will help:

Example Question

Blood flows through a vessel at a rate of 80 cm³ in 20 seconds. Calculate the rate of blood flow.

There is another formula, which could also be used:

Cardiac output is a measure of the rate of blood flow

Example question.

A person’s heart rate is 75 beats per minute, and their stroke volume is 70 cm³ per beat.
Calculate the cardiac output (rate of blood flow from the heart).

Cardiac output = Heart rate × Stroke volume

Cardiac output = 75 × 70 = 5250 cm³/min

Pacemaker of the heart.

The wall of the right atrium of the heart contains specialised cells which act as a pacemaker for the heart.

This region of cells sends out a wave of electrical excitation, causing the heart to contract.

During exercise when heart rate needs to increase, this pacemaker will automatically increase the heart rate, which will increase the rate of blood flow.

During sleep the pacemaker will decrease the heart rate, which decreases the rate of blood flow.

Problems with this natural pacemaker

However, sometimes this natural pacemaker can go wrong, the heart rate of a person could be too slow, or too fast.

This natural pacemaker needs to be replaced with an artificial pacemaker to correct this irregular heart rate. The artifical pacemaker is placed under the skin, but it has wires, which connect to the heart. An electrical impulse sent along these wires will cause the heart to contract.

Practice Questions

1.Blood flows through a vessel at a rate of 120 cm³ in 30 seconds. Calculate the rate of blood flow.

2.A person’s heart rate is 95 beats per minute, and their stroke volume is 60 cm³ per beat.
Calculate the cardiac output (rate of blood flow from the heart).

3. Use the following table to answer the next question.