Module: Adaptations for Transport in animals:
Q: What features does a transport system in animals need?
Suitable medium in which to carry materials
A pump, such as the heart, for moving the blood.
Valves to maintain the flow in one direction.
Q: What is an open circulatory system?
a circulatory system which contains no blood vessels, instead the blood bathes the
tissues directly while is held in a cavity called the haemocoel.
Q: What is a closed circulatory system?
The blood moves in blood vessels.
Two types; single and double.
Q: Compare circulatory system of fish, insects and an earthworm:
Earthworm – vascularisation, closed circulatory system and pumps, carriage of
respiratory gases in blood.
Insects – open circulatory system, dorsal-tube shaped heart, lack of respiratory gases
in blood.
Fish – single, closed circulatory system.
Q: Describe the structure and function of blood vessels:
Arteries, capillaries and veins.
Three layers:
1. Inner most layer, the endothelium, one cell thick and is smooth lined, reducing
friction with a minimum resistance to blood flow.
2. The middle layer, the tunica media, contains elastic fibres and smooth muscle.
Thicker in arteries than in veins. In arteries, the elastic fibres allow stretching to
accommodate changes in blood flow and pressure as blood is pumped from the
heart. Stretched elastic fibres recoil, pushing blood further on.
3. The outer layer, the tunica externa, contains collagen fibres which resist
overstretching.
Capillaries have thin walls, which are only one layer of endothelium on a basement
membrane. Pores between the cells make the capillary walls permeable to water
and solutes. They also have a small diameter.
Q: What type of muscle is present in the heart?
Cardiac muscle, which is myogenic.
, Q: Describe what the cardiac cycle is composed of:
1. Atrial systole = the atrium walls contract and the blood pressure in the artria
increases. This pushes blood through the tricuspid and bicuspid valves down into the
ventricles, which are relaxed.
2. Ventricular systole = the ventricle walls contract and increase the blood pressure in
the ventricles. This forces blood through the semi-lunar valves, out of the heart, into
the pulmonary artery and aorta. Atrioventricular valves are shut.
3. Diastole = ventricles relax. The volume of the ventricles increases and so pressure in
the ventricle falls. The semi-lunar valves shut. At the same time, the atria relax, so
blood from the vena cava and pulmonary veins enters the atria and the cycle starts
again.
Q: Describe the process of electrical excitation that makes the heartbeat:
A wave of electrical simulation arises at the SAN and spreads over both atria so they
contract together. The SAN is a cluster of specialised cardiac cells located on right
atrium.
The ventricles are insulated from the atria by a thin layer of connective tissue, except
at another specialised cluster of cardiac cells, the atrio-ventricular node (AVN). The
AVN introduces a delay between atrial systole and ventricular systole which allows
the ventricles to fill with blood.
The AVN passes the excitation down the nerves of the bundle of His, the left and
right branches and to the apex of the heart. The excitation is transmitted to Purkinje
fibres in the ventricle walls, which carry it upwards through the muscles of the
ventricle walls.
The impulses cause the cardiac muscle in each ventricle to contract, from the apex
upwards.
This pushes the blood up to the aorta and pulmonary artery and empties the
ventricles completely.
Q: What is an electrocardiogram?
Trace of the voltage changes produced by the heart, detected by electrodes on the
skin.
Q: Describe a basic trace of a healthy heart:
1. The P wave shows the depolarisation of the atria during atrial systole.
2. The QRS wave shows the spread of depolarisation through the ventricles resulting in
ventricular systole.
3. The T wave shows the repolarisation of the ventricles during ventricular diastole.
Q: Describe two ways in which Red blood cells are unusual:
1. Biconcave discs. Surface area is larger than a plane disc, so more oxygen diffuses
across the membrane.
2. No nucleus, more room for haemoglobin.
