Chapter 8 - Transport in Animals Flashcards
Why do animals need specialised transport systems?
- High metabolic demands
- Small SA:V ratio
- Long distances substances need to travel
What are the features of most animals’ circulatory system?
- Liquid transport medium that circulates around the system
- Vessels to carry transport medium
- Pumping mechanism to move medium around the body
What is an open circulatory system?
Where the transport medium is not enclosed within vessels, and is pumped from the heart straight into the body cavity of the animal (mostly insects)
What is haemolymph?
Insect blood; it transports food but not oxygen or carbon dioxide
What is haemocoel?
The open body cavity of insects, through which haemolymph (blood) circulates
What is a closed circulatory system?
The blood is enclosed in blood vessels and does not come into direction contact with the cells of the body. Substances leave and enter the blood through diffusion across the walls of the blood vessels
What is a single circulatory system?
Where the blood flows through the heart only once for every full circulation of the body
What is a double circulatory system?
Where the blood flows through the heart twice for every full circulation of the body
In single circulatory systems, how many sets of capillaries does the blood flow through per circulation?
Two- first it exchanges oxygen and carbon dioxide, and then it exchanges substances between the blood and the cells
In double circulatory systems, how many sets of capillaries does the blood flow through per circuit?
Only one before going back to the heart
What is the effect of passing through more sets of capillaries?
Lower blood pressure and slower rate of flow. Therefore double circulatory systems have a higher blood pressure and faster rate of flow than single circulatory systems
What do arteries carry?
Oxygenated blood away from the heart to the tissues of the body
What are the exceptional arteries?
The pulmonary artery, which carries deoxygenated blood from the heart to the lungs, and during pregnancy the umbilical artery, which carries deoxygenated blood from the fetus to the placenta
Where do arterioles do?
Arterioles link the arteries and the capillaries
What do elastic fibres do?
Provides vessel walls with flexibility
What does smooth muscle do?
Can contract or relax, controlling the size of the lumen
What does collagen do?
Provides structural support to maintain the shape and volume of the vessel
What is the order of blood vessels in the body?
Arteries - Arterioles - Capillaries - Venules - Veins
What are capillaries?
The microscopic blood vessels in which substance exchange takes place. Their lumen is so small that red blood cells must travel single file through them
How are capillaries adapted for their role?
- Large SA:V ratio to allow rapid diffusion in and out of the blood
- Blood must move slowly through the narrow capillaries, giving more time for exchange of substances to occur
- Single-cell thick walls give them small diffusion distance
How are arteries adapted for their role?
They have a high amount of elastic fibres, which allows them to withstand the high pressure of blood from the heart
How are arterioles adapted for their role?
They have less elastic fibres as blood pressure is lower, but a higher amount of smooth muscle, which is necessary to control the flow of blood into individual organs
What do veins do?
Carry deoxygenated blood away from the cells to the heart
What are the exceptional veins?
The pulmonary vein, which carries oxygenated blood from the lungs to the heart, and the umbilical vein which during pregnancy carries oxygenated blood from the placenta to the fetus
What do venules do?
They link the capillaries to the veins
What are the two main veins that carry deoxygenated blood back to the heart?
The inferior and superior vena cava
Where does the inferior vena cava carry deoxygenated blood from?
The lower parts of the body
Where does the superior vena cava carry deoxygenated blood from?
The head and the upper parts of the body
How are veins adapted for their role?
They have lots of collagen, a wide lumen and a smooth inner lining so blood flows easily- this is because they have a low pressure but still need to transport a lot of blood, so must have a high volume.
They do not have to withstand a high pressure, so have little elastic fibres.
What problem do veins face?
They must prevent blood from flowing backwards, which could occur due to the pull of gravity and the low pressure.
What 3 ways do veins prevent backflow?
- One way valves
- Muscle contraction squeezing veins up towards the heart
- Breathing movements of the chest act as a pump
What is blood plasma and what key components does it carry?
Yellow liquid solvent, which carries a wide of molecules, such as glucose and amino acids, as well as red and white blood cells, and platelets
Give 4 key functions of blood
- Gaseous exchange
- Thermoregulation
- Carries platelets to damaged areas
- Immune response
What is oncotic pressure?
The tendency of water to move into blood in capillaries. Its value is around -3.3kPa
What causes oncotic pressure?
The large plasma proteins in blood, especially albumin, which give blood a low water potential, meaning water often travels into the blood down the pressure gradient
What causes hydrostatic pressure to be high at the arterial end?
The pressure from the contractions of the heart result in a hydrostatic pressure higher than the oncotic pressure
What is the result of this higher hydrostatic pressure at the arterial end?
There is a net movement of water out of the blood in the capillaries, which becomes tissue fluid
What is tissue fluid?
The fluid that leaves the blood in the capillaries, filling the spaces between cells. It has the same composition as blood plasma minus the red blood cells and plasma proteins
What happens at the venous end of the capillaries?
The hydrostatic pressure of the blood in the capillaries is lower than the oncotic pressure, resulting in net movement of fluid back into the capillaries
What is the hydrostatic pressure value at the arterial end?
4.6kPa
What is the hydrostatic pressure value at the venule end?
2.3kPa
What is the oncotic pressure value?
-3.3kPa
What happens to tissue fluid that does not return to the capillaries?
It drains into a system of tubes called lymph capillaries
What is the difference in composition between plasma and lymph?
Lymph has less oxygen and fewer nutrients, and contains fatty acids
Where do fatty acids in the lymph come from?
They have been absorbed into the lymph from the villi
Where are lymph nodes and what are their roles?
Lymph nodes are found along lymph vessels. Lymphocytes build up in the lymph nodes when necessary and produce antibodies.
Lymph nodes also intercept bacteria and other debris from the lymph
What are enlarged lymph nodes a sign of?
The body fighting off an invading pathogen
What is the process of tissue fluid to lymph known as?
Drainage
What is the shape of erythrocytes?
Biconcave shape
What is the advantage of red blood cells having a biconcave shape?
The shape has a larger surface area, increasing the area available for the diffusion of gases.
It also helps them pass through narrow capillaries
In adults, where are erythrocytes formed?
Red bone marrow
What has happened by the time red blood cells enter circulation and what is the effect?
By the time mature erythrocytes have entered circulation, they have lost their nuclei, which maximises the amount of haemoglobin they can fit.
It also limits their lifetime- they only last for about 120 days
What is haemoglobin?
A large globular conjugated protein made up of four peptide chains, each with an iron-containing haem prosthetic group
How many haemoglobin are in each red blood cell?
Around 300 million
What is the reaction between oxygen and haemoglobin?
Oxygen binds to haemoglobin forming oxyhaemoglobin. Hb + 4O2 -> Hb(O2)4
What is positive cooperativity in haemoglobin?
As soon as one oxygen molecule binds to a haem group, the molecule changes shape, making it easier for the next oxygen molecules to bind
How is a steep diffusion gradient maintained until all haemoglobin is saturated with oxygen?
Because the oxygen binds to the haemoglobin, the free oxygen concentration in the erythrocyte remains low
What happens when blood reaches body tissues?
The concentration of oxygen in the cytoplasm of cells in lower than in the erythrocytes. As a result, oxygen moves out of the erythrocytes
What happens once the first oxygen molecule is released by haemoglobin?
The molecule changes shape again, making it easier to remove the remaining oxygen
What percentage of oxygen is released into body cells from erythrocytes when you are not very active and why?
Only around 25%. The rest acts as a reservoir for when the demands of the body increases suddenly
What is the Bohr effect?
At higher partial pressures of carbon dioxide, haemoglobin’s affinity for oxygen is lower, meaning it gives up oxygen more easily
What is the significance of the Bohr effect?
- In active tissues, which will have a higher partial pressure of CO2, haemoglobin gives up its oxygen more readily, allowing for more rapid transfer of oxygen
- In the lungs, where the partial pressure of CO2 is relatively low, haemoglobin will have a higher affinity for oxygen, allowing for quicker and easier binding
What is the impact of the Bohr effect on oxygen dissociation curves?
The curve will move to the right at higher CO2 partial pressures
What is affinity between haemoglobin and oxygen?
The attraction of haemoglobin to oxygen
What is the difference between adult and fetal haemoglobin?
The affinity for oxygen of fetal haemoglobin is higher than adult haemoglobin
Why must fetal haemoglobin have a higher affinity for oxygen than adult?
As the blood of the fetus must take oxygen from the blood of the mother as they pass each other. If they had the same affinity, then little or no oxygen would be passed from the mother to the fetus
How is most carbon dioxide transported from the tissues to the lungs?
75-85% of CO2 is converted into hydrogen carbonate ions (HCO3) in the cytoplasm of red blood cells
What other ways is carbon dioxide transported around the body?
- Some is carried dissolved in plasma
- Some is combined with the amino groups of haemoglobin to form carbaminohaemoglobin
How is CO2 transformed into HCO3?
CO2 reacts with H2O to form H2CO3.
This then dissociates to form H+ ions and HCO3- ions
Why does the transformation of CO2 to HCO3- occur more quickly in the cytoplasm of red blood cells than in blood plasma?
Because in the cytoplasm, they are high levels of the enzyme carbonic anhydrase, which catalyses the reaction between CO2 and H2O
What is chloride shift?
When HCO3- move out of erythrocytes into the plasma, Cl- move into the erythrocytes, which maintains the electrical balance of it.
What is the effect of removing carbon dioxide and converting it to HCO3- in the erythrocytes?
The erythrocytes maintain a steep concentration gradient for carbon dioxide to diffuse in from other respiring tissues
In the transport of CO2, what happens when the blood reaches the lung tissue?
HCO3- ions diffuse back into the erythrocyte and Cl- back out, and the HCO3- ions react with H+ ions to form Carbonic acid again.
Carbonic anhydrase catalyses the reverse reaction, breaking down the carbonic acid into CO2 + H2O, releasing free CO2 which diffuses out of the blood into the lungs.
In the transport of CO2, what happens when the blood reaches the lung tissue?
HCO3- ions diffuse back into the erythrocyte and Cl- back out, and the HCO3- ions react with H+ ions to form Carbonic acid again.
Carbonic anhydrase catalyses the reverse reaction, breaking down the carbonic acid into CO2 + H2O, releasing free CO2 which diffuses out of the blood into the lungs.
What is the role of haemoglobin as a buffer in the transport of CO2?
It prevents changes in the pH of blood by accepting free H+ ions in the reversible reaction to form haemoglobinic acid
Where does deoxygenated blood enter the lungs?
Into the right atrium, and is then pumped to the lungs out of the right ventricle
Where does oxygenated blood enter the heart?
Into the left atrium, and is then pumped to the rest of the body out of the left ventricle
What muscle is the heart made up of, and how is it different from skeletal muscle?
Cardiac muscle. It does not get fatigued and need to rest
How does cardiac muscle not got fatigued?
The coronary arteries supply the cardiac muscle with the oxygenated blood it needs to contract and relax constantly
What is the heart surrounded by and what does this prevent?
It is surrounded by inelastic pericardial membranes, which help prevent the heart from over-stretching with blood
What is tachycardia?
When the heartbeat is very rapid (over 100 BPM).
This is common when you exercise, or are scared or angry.
What is bradycardia?
When the heart slows down below 60 bpm. This is common in fit athletes, who’s hearts are more efficient. However people with severe bradycardia may need an artificial pacemaker.
What is an ectopic heartbeat?
Where there is an extra beat, followed by a longer than normal gap. Most people have at least one a day, however they can be linked to serious conditions when they are very frequent
What is atrial fibrillation?
Rapid electrical impulses generated in the atria cause abnormal rapid rhythm from atria, and ventricles lose regular rhythm. The atria do not contract properly, and the ventricles contract much less often. The result is the heart not pumping blood effectively
What is the blood pressure in the arteries during diastole?
At a minimum
What happens during diastole?
The heart relaxes.
The artia and ventricles fill with blood.
Volume and pressure if the blood in the heart increases as the heart fills
What happens during systole?
The atria contract, closely followed by the ventricles contracting.
The pressure inside the heart increases rapidly as volume decreases.
Blood is forced out of the left and right ventricles.
At the end of systole, volume and pressure of blood in the heart is low
What is the pressure of the blood in the arteries at the end of systole?
Blood pressure is at a maximum
What causes the ‘lub-dub’ heart sounds?
The first sound happens from the closing of the atrioventricular valves.
The second sounds happens from the closing of the semilunar valves
Where is the tricuspid valve found?
Between the right atrium and right ventricle
What is the first step in the journey of blood through the heart?
Blood flows into the atria until the atrio-ventricular valves open to let blood also flow into ventricles
When do the atria contract?
Once both the atria and ventricles are filled with blood, the atria contract, forcing all the blood into the ventricles
What happens once all the blood is forced into the ventricles?
The atrio-ventricular valves close preventing any back flow into the atria, and the ventricle contracts, forcing blood past the semi-luna valves and out of the heart
What is the role of tendinous cords in the heart?
The tendinous cords ensure the atrio-ventricular valves are not turned inside out by the contraction of the ventricle
Through what blood vessel does oxygenated blood enter the left atrium?
The pulmonary vein
Through what blood vessel does oxygenated blood leave the left ventricle?
The aorta
Where is the bicuspid valve found?
Between the left atrium and left ventricle
What side of the heart is more muscular and why?
The left side of the heart has much thicker muscle than the right; this is because the right side only has to pump the relatively short distance to the lungs and only has to overcome the resistance of the pulmonary circulation.
In contrast, the left side has to produce sufficient force to pump blood to all extremities of the body, and to overcome the resistance of the aorta and arterial systems of the whole body
What is the septum?
The inner dividing wall of the heart which prevents the mixing of oxygenated and deoxygenated blood
When does aortic pressure rise?
When the left ventricle contracts, making the blood pressure in the ventricles higher than that of the aorta, forcing blood into the aorta
What is the trend of ventricular pressure?
It starts low, gradually rising as it fills with blood.
Then once the atrioventricular valves close and the ventricles contract, the ventricular pressure increases rapidly, forcing blood out of the ventricles into the aorta. Pressure then falls as the ventricles empty and relax
Why is atrial pressure always relatively low?
Because the thin walls of atria cannot create much force
What is the trend of atrial pressure?
It remains constantly relatively low.
It is highest when the atria contract.
It drops when the atrio-ventricular valve closes after contraction, and when the atrio-ventricular opens and some blood moves into the ventricle
How is the heart myogenic?
The cardiac muscle has its own intrinsic rhythm of bpm. The basic rhythm of the heart is maintained by a wave of electrical excitement, rather than a nerve impulse
What is the role of the sino-atrial node?
The SAN initiates the heartbeat by sending a wave of electrical excitation, which causes the atria to contract
Why doesn’t the electrical excitement wave from the SAN directly cause the ventricles to contract?
Because a layer of non-conducting tissue prevents the excitation from reaching the ventricles
What is the role of the atrio-ventricular node?
The AVN picks up the excitation from the SAN, and imposes a slight delay before stimulating the bundle of His, which will in turn stimulate the contraction of the ventricles
Why does the AVN impose a slight delay?
To ensure the atria have stopped contracting before the ventricles start
What is the bundle of His?
A bundle of conducting tissue made up of fibres, which penetrate through the septum and around the ventricles
What are Purkyne fibres?
Purkyne fibres are the fibres that make up the bundle of His
How is the excitation moved from the AVN to the ventricles?
The bundle of His splits into two branches and conducts the wave of excitation to the apex (bottom) of the heart.
At the apex, the Purkyne fibres spread out through the walls of the ventricles.
The excitation is passed through the Purkyne fibres to the ventricles, causing contraction
Where does contraction of the ventricles start, and why?
Contraction starts at the apex (bottom) of the heart; this allows for more efficient emptying of the ventricles
How do electrocardiograms work?
They measure tiny electrical differences in your skin, which allows us to see the electrical activity of the heart
What are electrocardiograms used for?
They are used to help diagnose heart problems e.g. heart attack
