3.1.2 Transport in animals

What is an exchange surface?

An area over which an organism can absorb certain substances and remove waste products of metabolism in exchange with its surroundings

Why do multicellular organisms need transport systems (3 reasons)?

They have higher metabolic rates, more cells and a small SA:V

What is a single circulatory system and give an example of an organism that has it

Single circulation is where blood passes through the heart once per complete circuit. This is seen in fish

Why is a single circulatory system effective for a fish?

They do not need to maintain their body temperature, and respire relatively less compared to mammals. However, it limits the rate of delivery of O2 and nutrients to cells

What is a double circulatory system and give an example of an organism that has it

Double circulation is where blood passes through the heart twice per complete circuit. Humans have a double circulatory system

Why is a double circulatory system effective for humans?

They have a higher level of activity and also need to maintain their body temp through respiration. A double circuit allows a faster delivery and removal of materials to and from cells

Give 2 similarities between the circulatory system of a fish and a mammal

They both are closed systems and both have a heart

Give 2 differences between the circulatory system of a fish and a mammal

The fish has a single circulation whereas mammals have a double circulation. Also, the blood pressure is lower in fish than in mammals

What is the structure of a fish's heart

They have one atrium and 1 ventricle so there is no septum.

What is the role of the pulmonary circuit?

It oxygenates blood and removes CO2

What is the role of the systemic circuit?

Oxygenated blood from the lungs is pumped rapidly at an increased pressure by the heart to the tissue.

What is an open circulatory system?

Blood is not contained in blood vessels. Instead it is pumped directly into body cavities. This is seen in arthropods and molluscs

What is a closed circulatory system?

Blood is pumped around the body and is always contained in a network of blood vessels. This is seen in all vertebrates and many invertebrates

What are the 5 blood vessels that carry blood around the body?

Arteries, arterioles, capillaries, venules and veins

Starting from the outside and working inwards, what are the layers of tissue in an artery/vein?

Tunica externa, tunica media, tunica interna and then the lumen

What is the function of arteries?

They transport blood away from the heart, usually at high pressure, to tissues

What is the function of arterioles?

They branch off arteries and transport blood into capillaries

What is the function of veins

They transport blood to the heart, usually at low pressure

What is the function of venules?

They transport blood from the capillaries to the veins

Describe the structure of arteries

1. A thick tunica media. This contains a layer of muscle cells, helping the artery to withstand high pressure. It also enables them to contract and narrow the lumen to reduce blood flow. Elastic tissue also maintains blood pressure by stretching and recoiling.

2. Narrow lumen helps to maintain a high blood pressure

Can you feel a pulse in arteries?

Yes

How are arterioles adapted to their function?

They have a muscular layer that allows them to contract and partially cut off blood flow to specific organs, for example during exercise

Describe the structure of veins

1. They have a thinner tunica media - there is no need to a thick muscular layer as the blood travels at a low pressure.

2. They have a very large lumen to ensure the blood returns to the heart at an adequate speed

3. They contain valves to prevent the backflow of blood

Why does is a large lumen important for veins?

It allows blood to return to the heart at an adequate speed. This is because it reduces the friction between the blood and endothelial layer of the vein

How does the rate of flow in veins compare to arteries?

The rate of blood flow is slower in veins, but the large lumen ensures the volume of blood delivered per unit of time is equal

Can you feel a pulse in veins?

No

How are venules adapted for their function?

They have few or no elastic fibres, and a large lumen.

What is the function of capillaries?

fenestrations in the capillary walls allow substances to leave the blood to reach the body's tissues. They can form networks called capillary beds which are important exchange surfaces

Describe the structure of capillaries?

1. A very small lumen so blood travels slowly, providing more opportunity for diffusion to occur

2. Their wall is 1 cell thick, reducing the diffusion distance for oxygen

3. Fenestrations in the cell wall allow blood plasma to leak out and form tissue fluid

What is systolic pressure?

pressure exerted on arterial walls during ventricular contraction (when the heart beates)

What is diastolic pressure?

pressure in the arteries during cardiac relaxation

What is plasma?

The liquid part of blood

What is tissue fluid?

The fluid that surrounds cells in tissues.

What is lymph?

a colorless fluid containing white blood cells, that bathes the tissues and drains through the lymphatic system into the bloodstream.

How is tissue fluid formed?

As blood passes through capillaries some plasma leaks out and surrounds the cells of the body, forming tissue fluid

Why do proteins not leak out of capillaries?

They are too large to fit through the fenestrations

Where does exchange of substances between cells and blood occur?

Via the tissue fluid - e.g carbon dioxide produced in aerobic respiration will leave a cell, dissolve into tissue fluid and then move into a capillary

What is hydrostatic pressure?

The pressure exerted by a fluid e.g blood

What is oncotic pressure?

The pressure exerted by plasma proteins within a blood vessel

What happens at the arterial end of a capillary to form tissue fluid?

When blood is at the arterial end of a capillary the hydrostatic pressure is high enough to force fluid out of the capillary. Proteins remain in the blood, creating a water potential between the capillary and the tissue fluid. However, the hydrostatic pressure is greater than the osmotic pressure so the net movement of water is out of the capillaries

What is the net movement of water at the arterial end of a capillary?

It moves out as the hydrostatic pressure is greater than the oncotic pressure.

What happens at the venous end of a capillary to form tissue fluid?

The hydrostatic pressure within the capillary is reduced due to increased distance from the heart. The water potential gradient between the capillary and tissue fluid remains the same at the arterial end. The oncotic pressure is greater than the hydrostatic pressure, so water flows back into the capillary from the tissue fluid.

What is the net movement of water at the venule end of a capillary?

Water moves in as oncotic pressure is greater than hydrostatic pressure

Does oncotic pressure change across a capillary?

No it remains the same. Hydrostatic pressure changes though.

What is osmotic pressure also known as?

Oncotic

How would hypertension affect tissue fluid formation?

The pressure at the arterial end is even greater so more fluid is pushed out of the capillary. It then begins to accumulate around tissues - this is oedema.

How is lymph formed?

Larger molecules that are not able to pass through the capillary wall enter the lymphatic system through small valves in the vessel walls as lymph

How does liquid move along the lymphatic system?

Compression caused by body movement. Any backflow is prevented by valves so the flow is in one direction

How does lymph re-enter the bloodstream

Through veins located close to the heart

Why do lymph nodes swell?

Excess tissue fluid has drained to lymph vessels, allowing the pathogens in the tissue fluid to enter the nodes. The activity of phagocytes then causes swelling of the lymph nodes

How are plasma proteins that have escaped from the blood returned to the blood, and why is this important?

Via the lymph capillaries. This is important as if they were not removed from the tissue fluid they would lower the water potential and prevent reabsorption of water into the capillaries

What is the pericardium and what is its function?

The fibrous sac that surrounds the heart. It keeps it in a stable location and separates it from the lungs

Briefly outline the key structure of the heart (not the vessels)

The heart has four chambers, and is separated in two halves by the septum

What are the top two chambers of the heart called?

Atria

What are the bottom two chambers of the heart called?

Ventricles

Why is the septum important in the heart?

It ensures the blood doesn't mix between the left and right sides of the heart

Why is there a difference in the thickness of the ventricle walls in the heart?

The left ventricle pumps blood to the body whereas the right only pumps to the lungs. Therefore a greater force is required and so blood is pumped at a higher pressure. Also, less force to the lungs helps prevent damage to the capillaries

Describe the flow of deoxygenated blood

Superior and inferior vena cava release deoxygenated blood from the body into the right atrium. Blood flows through the right tricuspid valve to the right ventricle. Blood then travels through the pulmonary valve to the pulmonary artery, which then splits left and right and carries blood to the lungs

What is the tricuspid valve also known as?

right atrioventricular valve

What is the pulmonary valve also known as?

semilunar valve

Describe the flow of oxygenated blood?

The pulmonary vein releases oxygenated blood from the lungs into the left atrium. Blood then flows through the left bicuspid valve into the left ventricle. Blood then flows through the aortic valve to the aorta, and the blood then flows to the body.

What vessel brings deoxygenated blood to the heart?

Vena cava

What vessel takes deoxygenated blood away from the heart

Pulmonary artery

What vessel takes oxygenated blood to the heart?

Pulmonary vein

What vessel takes oxygenated blood away from the heart?

Aorta

Why are valves important in the heart?

They ensure blood flows in one direction and prevent backflow. They also maintain the correct pressure in the chambers of the heart

How does the heart receive its own blood supply?

Arteries on the surface of the heart called coronary arteries deliver blood to the heart

What is the contraction of the heart called?

Systole

What is the relaxation of the heart called?

Diastole

What happens during atrial systole?

atria are contracted, forcing more blood to the ventricles. The AV valves are open and semilunar valves are closed

What are the semilunar valves?

pulmonary and aortic

What are the AV valves?

tricuspid and bicuspid

What happens during ventricular diastole?

Both ventricles fill with blood. The AV open and semilunar close.

When analysing the cardiac cycle, what do the curves on the graph represent?

The pressure of the left atria, aorta and left ventricle

When the curves cross on a cardiac cycle diagram, what is occuring?

The valves are opening or closing

Describe the pressure changes in a heart on the left side

Both the left atrium and left ventricle start relaxed. Atrial systole then occurs - the left atria contracts and blood moves into the left ventricle. Ventricular systole then occurs - the AV valve shuts as left ventricular pressure increases. The pressure in the left ventricle then exceeds that in the aorta, so the aortic valve opens and blood flows in. Diastole then occurs as the left ventricle has been emptied of blood. The aortic valve closes and the AV valve opens.

Is there a gap between heart cycles?

No - the blood constantly flows

Where does the maximum pressure occur in the heart and why?

It occurs in the ventricles as there is more muscle in the walls so they can exert more force when they contract.

What does myogenic mean?

It causes its own contractions and relaxations

What is the equation for cardiac output?

heart rate x stroke volume

Explain how the heart action is initiated and coordinated

The SAN initiates a wave of depolarisation that causes the atria to contract. A region of non-conducting tissue prevents the depolarisation spreading straight to the ventricles, and is instead carried to the AVN. After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His. Purkyne fibres spread around the ventricles and initiate the depolarisation of the ventricles from the bottom up.

Why is there a slight delay between the stimulation of the SAN and the AVN?

This allows the atria to fully contract before the ventricles

Why is it important that depolarisation in the ventricles starts from the bottom of the heart?

This makes the ventricles contract from the bottom, pushing blood into the aorta and pulmonary artery.

Where is the SAN located?

In the wall of the right atrium

Where is the AVN located?

between atria and ventricles towards the centre of the heart

What is a myocyte?

cardiac muscle cell

What is the P wave in an ECG?

Depolarisation of the atria in response to the SAN triggering. Atrial systole.

What is the PR interval in an ECG?

The delay of the AVN to allow filling of the ventricles

What is the QRS complex in an ECG?

Ventricular depolarisation, triggering main pumping contractions. Ventricular systole.

What is the ST segment of an ECG

Time between ventricle depolarization and repolarization. Should be flat.

What is the T wave of an ECG?

Ventricular repolarisation causes ventricular diastole

What is fibrillation and what would you see on an ECG trace?

Fibrillation is an irregular heartbeat. It occurs when either the atria or ventricles lose their rhythm and stop contracting properly

What is a longer T wave and what would you see in an ECG trace?

The electrical signals are slowed down. This can be due to taking a toxin such as Digitalis

What is an ectopic heartbeat and what would you see on an ECG trace?

It is an extra systole with a compensatory pause.

Why does oxygen need to be carried in the blood?

It isn't very soluble as it isn't polar

What is partial pressure?

the pressure exerted by a particular gas in a mixture of gases. It is a measure of concentration.

What is the reversible equation for oxygen binding to haemoglobin

4O2 + Hb <-> Hb4O2

What happens when the first oxygen molecule binds to haemoglobin, and what is this called?

It results in a conformational change in the structure of the haemoglobin molecule, making it easier for each successive oxygen molecule to bind. This is cooperative binding.

Explain the shape of the oxygen dissociation curve for adult haemoglobin

Due to the shape of the haemoglobin molecule, it is different for the first oxygen to bind so there is a shallow curve at the start. Cooperative binding means that the following oxygen molecules are easier to bind, so the curve becomes steeper. As the haemoglobin molecule approaches saturation it takes longer for the 4th oxygen to bind, causing the curve to level off.

Why is the oxygen dissociation curve useful for tissues? (upwards)

When there is a low partial pressure of oxygen e.g at respiring cells, the saturation of haemoglobin is low. As deoxygenated blood approaches the lungs, the steep part of the curve means that a small increase in partial pressure of oxygen causes a large increase in saturation. There is then a high partial pressure at the lungs.