Transport in animals (The heart) Flashcards Preview

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How does size affect the need for a transport system?

Larger multicellular organisms are usually multilayered as well, meaning that not all cells of the organism are exposed to the external medium. This means that exchange by diffusion can only take place with surface cells, not cells below. Cells below would therefore receive enough nutrients. A transport system carries the nutrients to every cell in the organism.


How does surface area-to-volume ratio affect the need for a transport system?

Larger, multicellular organisms have a relatively small surface area-to-volume ratio compared to unicellular organisms. This means that the diffusion surface is not large enough to supply all of the cells in the organism with enough nutrients and oxygen at the rate required. Exchange surfaces and transport systems are needed to supply all the cells in the organism with enough oxygen and nutrients at the rate required.


How does level of activity affect the need for a transport system?

Higher levels of activity have higher energy requirements. This means that cells need to have a constant supply of oxygen and nutrients in order to generate that energy. A good transport system is required to ensures that every cell receives enough oxygen and nutrients.


What are the typical features of a good transport system?

- A medium to carry the nutrients and oxygen around the body (blood).
- A pump to ensure that the blood is constantly moving and cells have a fresh supply of nutrients and oxygen.
- Exchange surfaces to allow for nutrients and oxygen to leave and enter the blood when required.
- Specialised vessels to carry the blood to ensure that all the blood is saturated with nutrients and oxygen, as well as all the cells are getting enough nutrients and oxygen.
- An efficient way of picking up and depositing nutrients and oxygen.


What is a single circulatory system?

- A circulatory system where the blood is oxidised and then pumped around the body in the same circuit.
- Fish have a single circulatory system:
Heart -> Gills -> Tissues -> Heart


What is a double circulatory system?

- A circulatory system where the blood is oxidised in one circuit and is pumped around the body in a separate circuit.
- Mammals have a double circulatory system:
Heart -> Lungs -> Heart -> Tissues -> Heart


What are the two parts of a double circulatory system?

- Systemic circulation carries oxidised blood and nutrients from the heart to the body tissues and back to the heart.
- Pulmonary circulation carries blood from the heart to the lungs where it's oxidised and back to the heart.


What are the disadvantages of a single circulatory system?

1. Blood pressure is reduced as it passes through the arrow capillaries of the gaseous exchange organ (e.g. gills).
2. Blood flows around the body slower due to reduced pressure so oxygen and nutrients are not delivered to respiring tissue at a fast rate.


What are the advantages of a double circulatory system?

1. Pressure is reduced when blood is oxygenated at the lungs, but pressure is increased again as blood passes though the heart, before being on its way around the body.
2. Lower pressure can be maintained in pulmonary circulation so capillaries are not damaged, but kept high in systemic circulation.
3. Blood is pumped around the body at a quick rate and high pressure without the lungs being damaged.


Why do mammals need a double circulatory system?

Mammals are very active and has to maintain a constant body temperature, so tissues have high energy requirements.


What are the valves in the heart and what are they for?

- The tricuspid valve lies between the right atrium and the right ventricle and prevents blood from flowing back into the left atrium when the left ventricle is in systole.
- The bicuspid (mitral) valve lies between the left atrium and the left ventricle and prevents blood from flowing back into the left atrium when the left ventricle is in systole.
- The semilunar valves are located at the start of the aorta and pulmonary artery. They prevent blood from flowing back into the ventricles when they're in diastole.


Why are the walls of the left ventricle thicker than that of the right?

- Right ventricle only needs to pump blood from heart to lungs and back, so not much pressure is needed. High pressure would also damage capillaries in lungs.
- Left ventricle needs to pump blood around the whole body, so much higher pressures need to be generated.


What is the cardiac cycle?

1. Diastole: Heart is in diastole and there are no contractions. Blood fills the atria and then the ventricles from the vena cava and pulmonary vein.
2. Atrial systole: Atrial walls contract and blood in the atria is forced into the ventricles. Atrioventricular valves remain open since atrial pressure is greater than ventricular pressure. Sphincters in the vena cava and pulmonary vein prevent back flow of atrial blood.
3. Ventricular systole: Ventricular walls contract. Pressure in ventricles are greater than the atria, so atrioventricular valves shut to prevent back flow of blood into atria. Pressure in ventricles become greater than that of the aorta and pulmonary artery. This means that semilunar valves open.
4. Diastole: Atria and ventricles relax. Pressure in aorta and pulmonary artery becomes greater than ventricles, so semilunar valves close. Atrial pressure becomes greater than ventricular pressure, so atrioventricular valves open.


Why are the cardiac muscles described as myogenic?

Because they are able to contract at a regular rhythm even when disconnected from the rest of the body (mainly the brain). The contraction signal is generated by the pacemaker region of the heart called the Sinoatrial Node (SAN).


What are the stages involved in controlling heartbeat?

1. The SAN sends a wave of excitation or depolarisation across the 2 atria that travels along the membranes of atrial tissue. This causes muscles in the atrial walls to contract and cause atrial systole.
2. Blood is pushed through the atrioventricular valves into the ventricles.
3. The excitation cannot spread to the ventricular tissue due to a band of non-conducting tissue across the atria and ventricles.
4. Excitation activates the Atrioventricular Node (AVN) which lies in the septum.
5. After a delay of 0.02 seconds, the AVN depolarises.
6. This generates a wave of excitation down the bundle of His in the septum containing fast-conducting Perkyne fibres.
7. The wave of excitation reaches the tip of the heart and spreads upwards along the ventricles, causing ventricular systole.
8. Ventricles contract from bottom to top, pushing blood upwards into the aorta/pulmonary artery.


Why are there 2 signals generated to cause a heartbeat and not 1?

- To introduce a delay, allowing time for blood to move from atria to ventricles.
- To ensure that the ventricles travel from bottom upwards, pushing the blood upwards.