B5 - The Circulatory System and The Cardiac Cycle Flashcards
Describe the ‘circulatory system’ of single called organisms
- Small organisms such as amoebae do not need a circulatory system.
- They have a large surface area compared with their volume.
- They are surrounded by the water they live in.
- Dissolved oxygen diffuses from this water into the cell through the cell membrane. Waste material can diffuse out of the cell.
- There is no need for a special transport system.
Describe the circulatory system of insects. What does their blood contain?
- open circulatory system = no arteries or veins -> their blood flows freely through their body cavity -> makes direct contact with the organs and tissues.
- Blood travels in the aorta from the heart up to the head. It bathes the organs and muscles of the head and then trickles back through the body cavity. It passes over the gut and gets back into the heart through small holes.
- Insect blood does not carry oxygen, because the insect’s breathing tubes deliver oxygen directly to the tissues. Their watery, greenish yellow blood carries amino acids, sugars, and ions. There are some white cells to ingest pathogens.
Describe the circulatory system of vertebrates.
closed circulatory system = blood is contained in blood vessels – arteries, veins, and capillaries.
Describe the circulatory system of a fish.
The blood circulates once around the body, from the heart to
• the gills, where it collects oxygen and unloads carbon dioxide
• the body organs and tissues.
The fish heart is a single pump consisting of two chambers
Describe the circulatory system of humans.
Humans and other mammals have a double circulatory system. There are two circuits from the heart.
Blood passes
• from the heart to the body organs and tissues
• back to the heart
• to the lungs to remove carbon dioxide and collect oxygen
• back to the heart before being pumped out to the body again.
Because the blood makes two circuits from the heart, the heart needs four chambers. It is a double pump. Blood in a double circulatory system is under high pressure and so it transports materials more quickly around the body.
What did Galen do? ( and Da Vinci?)
In the second century AD, Galen, dissected monkeys and pigs. He noticed that blood in veins was darker than blood in arteries. He mistakenly thought that the liver made blood and pumped it in the veins to the organs, which consumed it.
In the sixteenth century, Leonardo da Vinci studied anatomy and made drawings showing how blood passed through the heart chambers, and how the heart valves worked.
What did William Harvey do?
- In the seventeenth century, William Harvey published a book showing how blood circulates in the body, from the heart and back again, and to and from the lungs.
- He realised that the pulse in arteries was linked to the contraction of the left ventricle of the heart.
- He discovered that veins have valves to prevent backflow. He postulated that there were capillaries, but did not see them as he did not have a microscope.
Explain how the heart works? Describe the changing pressures in the blood vessels.
Heart muscles contract rhythmically to squeeze blood out of the atria, into the ventricles and then out into the arteries and around the body. .
The strong contractions of the heart mean that blood leaving the heart in the arteries is at high pressure. As it passes along the circulatory system through increasingly branching arterioles to the capillaries, the blood pressure falls. In the wide tubes of the veins the blood pressure is very low; valves are needed to keep the blood flowing in one direction.
What does the heart need and why ?
The powerful heart muscle needs a continuous supply of glucose, fatty acids, and oxygen so that the muscle cells can respire aerobically and release energy for contraction
Explain why the two sides of the heart have different thicknesses.
The left ventricle wall is thick muscle that produces enough pressure to push blood in the arteries all over the body. The right ventricle wall is thinner and the muscle is less powerful – it only has to send blood as far as the lungs. The lungs are delicate and too much pressure in the blood entering them could damage them.
What are pacemakers?
The rate at which the heart contracts is controlled by a group of cells called the pacemakers. These produce a small electrical current that stimulates the cardiac muscle to contract.
What is pulse?
As the ventricles contract and send blood into the arteries, the thick, muscular, and elastic walls of the arteries expand and recoil as a spurt of blood enters. This is the pulse that is transmitted all along the length of the arteries in the body. You can detect it where an artery passes over a bone or is near to your skin. Pulse rate is a measure of heart rate.
Explain how the nodes aid contraction in the heart .
• The sinoatrial node (SAN) produces electrical impulses.
• These spread quickly across the two atria, which contract.
• This forces open the atrioventricular (AV) valves and pushes blood into the ventricles.
• A patch of muscle fibres called the atrioventricular node (AVN) conducts the impulses to special conducting muscle fibres, called Purkyne fibres, which carry the impulses to the tip of the ventricles.
• The two ventricles contract. This closes the AV valves and pushes blood out of the ventricles, through the open semilunar valves, into the arteries.
• The atria relax and fill with blood.
Then the cycle starts again. Each cycle is one heartbeat.
How when and why does heart rate speed up?
When you exercise, your muscles respire more oxygen and glucose and make more carbon dioxide, which enters the blood. Part of the brain detects the extra carbon dioxide in the blood. It sends impulses to the heart’s pacemaker to speed up the heart rate.
You also make more adrenaline when you exercise, and when you are frightened or excited. Adrenaline travels in your blood and affects many target tissues, including the heart’s pacemaker, which speeds up the heart rate.
An increased heart rate also delivers more oxygen and glucose to the heart muscle itself, via the coronary arteries. The heart muscle needs to respire more if it is beating more times each minute.
How can the heart be monitored?
They get a trace called an ECG (electrocardiogram) and this tells them whether your heart is normal or not, by measuring the electrical activity of your heart. A patient with an irregular heart rate or one that is too fast or too slow may need an artificial pacemaker fitted.
An echocardiogram uses ultrasound to make a scan and show any heart defects.
