What is meant by a double circulatory system?

Blood passes through the heart twice for each complete circuit of the body, once on the pulmonary circuit and once on the systemic circuit.

Why is blood pressure in the pulmonary circulation much lower than in the systemic circulation?

High pressure would damage the very thin alveolar capillaries and force fluid into the alveoli, so the right ventricle generates only a fraction of the pressure produced by the left.

Give a typical value for systemic arterial blood pressure and for pulmonary arterial blood pressure in a healthy adult.

Systemic arterial pressure is about 120/80 mmHg and pulmonary arterial pressure is about 25/10 mmHg.

Apart from protecting the capillaries, give one advantage of the low pressure in the pulmonary circulation.

Blood moves more slowly through the lung capillaries, so there is more time for gas exchange to go to completion.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

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Transport Systems in Mammals

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Transport Systems in Mammals

The closed double circulatory system

3 things to know
Components 01, 02 and 03

Overview

Recall questions on closed and double circulatory systems, the pulmonary and systemic circuits, why pulmonary blood pressure is lower and its typical values, and why a double circulation supports the high metabolic rate of a mammal.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is meant by a closed circulation, what are typical systemic and pulmonary arterial pressures, and what is one advantage of the slow blood flow through the lungs?

Key term

What is meant by a closed circulatory system?

Key term

Name the two circuits of the mammalian circulation and state what each supplies.

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by a closed circulatory system?
Model answer
The blood is held within blood vessels at all times and does not flow freely through the body cavity.
2
What is meant by a double circulatory system?
Model answer
Blood passes through the heart twice for each complete circuit of the body, once on the pulmonary circuit and once on the systemic circuit.
3
Name the two circuits of the mammalian circulation and state what each supplies.
Model answer
The pulmonary circuit carries blood to and from the lungs, and the systemic circuit carries blood to and from the rest of the body.
4
Why is blood pressure in the pulmonary circulation much lower than in the systemic circulation?
Model answer
High pressure would damage the very thin alveolar capillaries and force fluid into the alveoli, so the right ventricle generates only a fraction of the pressure produced by the left.
5
Give a typical value for systemic arterial blood pressure and for pulmonary arterial blood pressure in a healthy adult.
Model answer
Systemic arterial pressure is about 120/80 mmHg and pulmonary arterial pressure is about 25/10 mmHg.
6
Apart from protecting the capillaries, give one advantage of the low pressure in the pulmonary circulation.
Model answer
Blood moves more slowly through the lung capillaries, so there is more time for gas exchange to go to completion.

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