C2 - Transport in animals, open and closed circulatory systems, single and double closed circulatory systems, the cardiac cycle, the flow of blood through the heart, arteries, veins, capillaries

What are 3 key features all transport systems in animals have?

a suitable medium to carry materials, a pump for moving blood, valves to maintain flow in one direction

What do some animal transport systems have? (2)

a respiratory pigment that increases the volume of oxygen that can be transported, a system of vessels with a branching network to distribute the transport medium to all parts of the body

What is an open circulatory system? (2)

blood does not move around the body in blood vessels, blood bathes the tissues directly while held in the cavity called the haemocoel

Which animals have an open circulatory system?

insects

What are 2 key features of an insects open circulatory system?

dorsal tube-shaped heart, haemocoel

What is a dorsal tube-shaped heart? (2)

runs the length of the body, pumps blood out at a low pressure into the haemocoel

What is a haemocoel?

a cavity where materials are exchanged between blood and body cells

What happens once materials are exchanged between blood and body cells in the haemocoel?

blood slowly returns to the heart and the open circulation starts again

How come insects blood does not transport oxygen and has no respiratory pigment?

oxygen diffuses directly from the tissues to the tracheoles

What is a closed circulatory system?

blood moves in blood vessels, either in a single or double circulatory system

What is single circulation? (2)

Where blood moves through the heart once on its circuit around the body, e.g. in fish

Explain the process of single circulation through a fish (5)

ventricle pumps deoxygenated blood to the gills, at the gills a well-developed capillary network reduces its pressure, oxygenated blood is carried to tissues, from the tissues deoxygenated blood returns to the atrium, oxygenated blood moves to the ventricle and circulation starts again

Explain the process of single circulation through an earthworm (2)

blood moves forward in the dorsal vessel, blood moves back in the ventral vessel

What are the 5 pairs of ‘pseudohearts’ that are found in an earthworm? (3)

thickened and muscular blood vessels, that pump blood from the dorsal to the ventral vessel, and keep it moving

What is double circulation? (2)

where blood passes through the heart twice in its circuit around the body, e.g. in mammals

What gives blood a rapid flow rate through blood vessels in double circulation?

blood is pumped by a muscular heart at a high pressure

In a double circulation system, why are organs not in direct contact with the blood? (2)

they are bathed by tissue fluid, that seeps out of the capillaries

What is the blood pigment found in a double circulation system? (2)

haemoglobin, that carries oxygen

What happens initially in a double circulation system? (2)

blood pressure is reduced in the capillaries of the lungs, this pressure would be too low to make circulation efficient in the rest of the body

What happens to blood when blood pressure is reduced in the capillaries of the lungs? (4)

blood is returned to the heart, which raises its pressure again, to pump it to the rest of the body, materials are then delivered quickly to the body cells

Why is it significant that mammals have a high body temperature and a high metabolic rate?

the greater the metabolic rate, the greater the need for rapid delivery of oxygen and glucose and removal of waste such as carbon dioxide

What is pulmonary circulation? (3)

serves the lungs, right side of heart pumps deoxygenated blood to the lungs, left side of heart receives oxygenated blood from the lungs

What is systemic circulation? (3)

serves the body tissues, left side of heart pumps oxygenated blood to tissues, right side of heart receives deoxygenated blood from body

How does blood pass through the heart twice in pulmonary and systemic circulation?

once through the right side and once through the left side

Why is the double circulation of a mammal more efficient than the single circulation of a fish?

oxygenated blood can be pumped around the body at a higher pressure

What is myogenic contraction? (2)

the heartbeat is initiated within the muscle cells themselves, and is not dependent on nervous or hormonal stimulation

What is the cardiac cycle? (2)

the sequence of events of one heartbeat, in an adult its about 0.8 seconds

What is systole? (2)

a stage in the cardiac cycle, in which heart muscle contracts

What is diastole? (2)

a stage in the cardiac cycle, in which heart muscle relaxes

What are the 3 stages of the cardiac cycle?

atrial systole, ventricular systole, diastole

Explain the process of atrial systole (3)

atrium walls contract, causing blood pressure to increase in the atria, this pushes blood through the bicuspid and tricuspid valves down into the relaxed ventricles

Explain the process of ventricular systole (3)

ventricle walls contract increasing blood pressure in ventricles, this forces blood up through the semi-lunar valves and out of the heart, into the pulmonary artery and aorta

Why can’t blood flow back from the ventricles into the atria?

tricuspid and bicuspid valves are closed by the rise in ventricular pressure

Where does the pulmonary artery carry blood?

deoxygenated blood to the lungs

Where does the aorta carry blood?

oxygenated blood to the rest of the body

Explain the process of diastole (4)

ventricles relax, volume of ventricles increases so pressure in ventricles falls, the tendency of blood to flow backwards causes semi-lunar valves at their bases to shut, preventing blood re-entering the ventricles

What is the risk in diastole when ventricles relax?

the blood in the pulmonary artery and aorta risk flowing backwards into the ventricles

What happens to the atria in diastole? (2)

atria relax, so blood from vena cavae and pulmonary veins enters the atria and the cycle starts again

Explain the flow of blood through the left side of the heart (part 1) (3)

left atrium relaxes and receives oxygenated blood from pulmonary vein, when left atrium is full pressure forces open bicuspid valve between left atrium and left ventricle, relaxation of left ventricle draws blood from left atrium

Explain the flow of blood through the left side of the heart (part 2) (3)

left atrium contracts which pushes remaining blood into left ventricle through the valve, left atrium relaxes and left ventricle contracts, its strong muscular wall exerts high pressure

Explain the flow of blood through the left side of the heart (part 3) (3)

pressure pushes blood up and out of heart through semi-lunar valves into aorta, pressure also closes the bicuspid valve, which prevents backflow of blood into left atrium

Explain the flow of blood through the right side of the heart (part 1) (3)

right atrium relaxes and receives deoxygenated blood from vena cava, when right atrium full pressure forces open tricuspid valve between the right atrium and right ventricle, right ventricle relaxes drawing blood from right atrium

Explain the flow of blood through the right side of the heart (part 2) (2)

right atrium contracts pushing the remaining blood into right ventricle through the valve, right atrium relaxes and right ventricle contracts

Explain the flow of blood through the right side of the heart (part 3) (3)

right ventricle strong muscular wall exerts a high pressure, pulmonary semi-lunar valve is forced open, blood passes through out to the lungs

Explain the flow of blood through the right side of the heart (part 4) (3)

pulmonary semi-lunar valve closes, pressure also closes tricuspid valve, preventing backflow of blood into right atrium

What are 2 key features of the cardiac cycle? (3)

2 sides of the heart work together, atria contract at the same time, followed by the ventricles contracting together

What is a heartbeat?

a complete contraction and relaxation of the whole heart

What happens when a chamber of the heart contracts and relaxes? (2)

when it contracts it is emptied of blood, when it relaxes it fills with blood

Why do atria walls contain little muscle?

the blood only has to go to the ventricles

Why do ventricle walls contain more muscle and generate more pressure? (2)

they have to send blood further, either to the lungs or to the rest of the body

Why does the left ventricle have a thicker muscular wall than the right ventricle? (2)

left ventricle has to pump blood all around the body, whereas the right ventricle only has to pump blood a short distance to the lungs

What is the role of valves?

valves prevent backflow of blood

How do atrio-ventricular (bicuspid and tricuspid) valves, semi-lunar valves at the base of the aorta and pulmonary artery, and valves in veins operate? (2)

by closing under high blood pressure, preventing blood flowing backwards

Order blood vessels from smallest to largest (3)

capillary, vein, artery

What is the diameter of an artery?

10 mm

What is the diameter of a vein?

6 mm

What is the diameter of a capillary?

0.02 mm

What structures are present in both arteries and veins? (3)

tunica intima, tunica media, tunica externa

What is the tunica intima? (4)

innermost layer, a singe layer of endothelium, a smooth lining that reduces friction, producing minimal resistance to blood flow

What do some arteries tunica intima contain?

elastin-rich collagen

What is the tunica media? (2)

middle layer, contains elastic fibres and smooth muscle

Is the tunica media thicker in veins or in arteries?

tunica media is thicker in arteries than in veins

How does tunica media function in an artery? (3)

elastic fibres in tunica media allow stretching to accommodate changes in blood flow and pressure, as blood is pumped from the heart, at a certain point stretched elastic fibres recoil which pushes blood on through the artery

How is the elastic fibres recoiling in tunica media felt? (2)

as the pulse, and this mechanism maintains blood pressure

How does contraction of smooth muscle in tunica media help?

regulates blood flow and maintains blood pressure as blood is transported further from the heart

What is tunica externa? (3)

outer layer, contains collagen fibres, which resist overstretching

What is the function of arteries?

arteries carry blood away from the heart

Describe the structural features of arteries (3)

thick muscular walls withstand blood’s high pressure derived from the heart, arteries branch into smaller arterioles, that further sub-divide into capillaries

What is the function of capillaries?

form a vast network that penetrates all the tissues and organs of the body

Explain what happens to the blood from capillaries (3)

blood from capillaries collects into venules, which take blood into veins, which return it to the heart

Explain structural features of veins (2)

have a larger diameter lumen and thinner walls with less muscle than arteries, so blood pressure and flow rate are lower

Explain how blood returns to the heart for veins above the heart

blood returns to the heart by gravity

Explain how blood returns to the heart for veins not above the heart

it moves through other veins by the pressure of surrounding muscles

What structural feature do veins have that ensure flow in one direction and prevent backflow?

semi-lunar valves along the length of the veins

How are arteries different from veins? (2)

semi-lunar valves are only present at the base of the aorta and pulmonary artery, semi-lunar valves are not found across the length of arteries

What can faulty functioning of valves in veins contribute to? (3)

varicose veins, heart failure

Describe thin walls as a structural feature of capillaries

only one layer of endothelium on a basement membrane

Describe pores between cells as a structural feature of capillaries (2)

make capillary walls permeable to water and solutes like glucose, so exchange of materials between blood and tissues takes place

Describe small diameter as a structural feature of capillaries (3)

rate of blood flow slows down, there are many capillaries in a capillary bed which reduces rate of blood flow, so there is plenty of time for the exchange of materials within the surrounding tissue fluid