Circulatory system and the cardiac cycle

Question 1

What do animals need?

Answer 1

Many animals need a blood circulatory system to ensure all their cells receive enough food and oxygen and to remove waste products, such as carbon dioxide

Question 2

What happens to the arteries, veins and capillaries?

Answer 2

As blood flows through arteries, veins, and capillaries, the blood pressure decreases. Veins have valves to ensure there is no backward blood flow. High blood pressure would damage the fragile walls of the capillaries.

Question 3

A single circulatory system…

Answer 3

(such as in fish) has a single blood circuit of the heart, gills and body.

Question 4

A double circulatory system…

Answer 4

• (such as in mammels) has two circuits:
  
  • the heart and lungs form one (to obtain oxygen),
  • the heart and rest of the body form the other (to deliver oxygen to the body cells).

Question 5

What does a double circulatory system requires?

Answer 5

• A double circulatory system requires a four-chambered heart:
  
  • two atria to receive blood (from the lungs and body)
  • two ventricles to distribute blood (to lungs and body).
• It ensures high blood pressure for efficient and fast circulation of food and oxygen.

Question 6

What does a single circulatory system need?

Answer 6

A single circulatory system needs only two chambers in the heart, one to receive and one to distribute blood.

Question 7

Historical understanding of the Heart

Answer 7

• In the 2nd century, Galen knew that the heart acted as a pump and the importance of the pulse. However, he thought that the liver made blood flow backwards and forwards.
• In the 17th century, William Harvey knew that blood circulated around the body, that the heart has four chambers and about the tiny vessels that today we know as capillaries.

Question 8

What is the cardiac cycle?

Answer 8

The cardiac cycle is the sequence of events as blood enters and leaves the heart.

Question 9

What happens in the cardiac cycle.

Answer 9

• The muscles of the two atria contract together as the two ventricles relax to receive the blood through the atrio-ventricular valves, which prevent backward flow into the atria.
• Muscles of the two ventricles then contract together to force blood to the lungs or around the body.
• Semi-lunar valves prevent backward flow into the ventricles.

Question 10

What increases the heart rate?

Answer 10

• More muscular activity causes a greater demand for oxygen and food. Heart rate therefore increases with increasing muscular activity.
• Heart rate is increased by the presesence of the hormone adrenaline to prepare for ‘fight or flight’.

Question 11

What forms pacemakers?

Answer 11

Groups of cells in the heart formed pacemakers, which control the rate of heart beat by producing a small electric current to stimulate muscle contractions. An artificial pacemaker can be placed near the heart to send an electrical signal to the heart muscles.

Question 12

What is an ECG used for?

Answer 12

An electrocardiogram (which shows changes in electrical impulses in heart muscle) and an echocardiogram (which displays a video of the heart in action) can be used to investigate irregular heart actions.

Question 13

Natural pacemakers

Answer 13

• Two pacemakers, the sino-atrial node (SAN) and the atrio-ventricular node (AVN) generate electrical impulses a to co-ordinate heart muscle contractions.
• Impulses from the SAN cause the atria to contract and simulate the AVN.
• Impulses from the AVN cause the ventricles to contract