3.2 Tranport In Animals Flashcards
What’s the need for transport systems in animals
They need to take oxygen and nutrients in, waste products generated need to be released
Where does exchange occurs
Exchange site, eg, lungs (gases) roots in plants(water and minerals)
Why do small organisms not require a specialised transport system
Their large S:V ratio,
the diffusion or transport distance in the organisms are very small so essential nutrients can reach necessary parts of the cell efficiently,
smaller organisms tend to have lower levels of activity and so smaller metabolic demands
Why do larger organisms require specialised mass transport systems
Increasing transport distances, SA:V ratio, increasing levels of activity
Increasing transport distances
In large organisms exchange sites tend to be far away this transport distance makes simple diffusion a non-viable method as diffusion wouldn’t be fast enough to meet the metabolic requirements of cells
Surface area: volume ratios
As the SA and V increases the ratio decreases because volume increases much more rapidly than surface area as size increases
Single-celled organisms
Have high SA:V ratio which allows for exchange of substances to occur via simple diffusion
What does a high SA:V ratio lead to
Large SA allows for maximum absorption of nutrients and gases and secretion of waste products.
The small volume means the diffusion distance to all the organelles is short
What does lower SA:V ratio lead to?
There is less surface for absorption of nutrients, gases and secretion of waste products,
The greater volume results in longer diffusion distance to the cells and tissues of the organism
What does increasing levels of activity lead to
Larger organisms are more physically active and contain more cells, this results in a higher level of metabolic activity
The demand for oxygen and nutrients is greater and more waste is produced
What is the need for a circulatory system
Cells of all living organisms need a constant supply of reactants for metabolism
Types of circulatory system
Single and double
Single circulatory system
The blood passes through the heart once during one complete circuit of the body
Double circulatory system
The blood passes through the heart twice during one complete circuit of the body
What has a single circulatory system
Fish
What has a double circulatory system
Mammals
Pathway in single circulatory system in fish 1.
Deoxygenated blood is pumped to the gills from the heart
Pathway in single circulatory system in fish 2.
The gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood
Pathway in single circulatory system in fish 3.
The oxygenated blood flows from the gills to the rest of the body
It travels through the capillaries in organs, delivering oxygen and nutrients
Pathway in single circulatory system in fish 4.
The blood returns to the heart, the heart only has one atrium and one ventricle
Double circulatory system in mammals
Blood passes through heart twice as a results the Malian heart has a left and right side with a wall (septum) dividing the two
What does left side of heart contain
Oxygenated blood
What does right side of heart contain
Deoxygenated blood
Cycle of the heart
Vena cava, right atrium, av valve, right ventricle, semi-lunar valve, pulmonary artery, lungs, pulmonary vein, left atrium, av vale, left ventricle, semi-lunar valve, aorta, to body
Vena cava
From body to heart deoxygenated blood
Aorta
To body from left ventricle oxygenated blood
Pulmonary artery
To lungs
Pulmonary vein
To heart form lungs
Septum
Divide left and right side [preventing mixing of blood)
Left ventricle structure
Thicker muscular wall than right side
Much larger distance for blood to travel, has to overcome resistance of aorta, and arterial systems of whole body, has to move blood under pressure to all extremities of the body
Atrial systole
Atria walls contract, pressure increases in atria above pressure in ventricles, atria volume decrease, blood pushed into ventricles through the av valves
Ventricular systole
Ventricles contract, pressure in ventricles increases above pressure in the atria and aorta, ventricular volume decreases, Av valve close to prevent back flow, blood ejected from heart through semi-lunar valves
Aortic systole
Aorta contracts, pressure in aorta increases
What causes av valve to close
Pressure in the ventricle rises above pressure in atria, causing av valve to snap shut preventing back flow into atria (end of atrial systole)
What causes semi-lunar valve to shut
Pressure in ventricle drops below pressure in aorta and pulmonary artery, semi-lunar valve shuts, preventing back flow into ventricle (during ventricular systole)
What causes semi-lunar valve to open
The pressure in the ventricles rises above that in the aorta and pulmonary artery
What causes av valve to open
Pressure in ventricles decrease below the atrial pressure (during aortic systole)
Function of heart
A hollow, muscular organ located in the chest cavity which pumps blood, cardiac muscle is specialised for repeated involuntary contraction without rest
Function of arteries
Blood vessels, which carry blood away from the heart. The walls of the arteries contain lots of muscle and elastic tissue and a narrow lumen, to maintain high blood pressure, range from 0.4-2.5cm in diameter
Structure of arterioles
Small arteries which branch from larger arteries and connect to capillaries, around 30 um in diameter (micrometers)
Function of capillaries
Tiny blood vessels (5-10 um(micrometers) in diameter) which connect arterioles and venules. Their size means they pass directly past cells and tissues and perform gas exchange and exchange of substances such as glucose.
Structure of venules
Small veins which join capillaries to larger veins. They have a diameter of 7um(micrometres)-1mm
Veins
Blood vessels which carry blood back towards the heart. The walls of veins are thin compared to arteries, having less muscle and elastic tissue but a wider lumen. Valves help maintain blood flow back towards the heart
Advantages of double circulation
Blood only passes through 1 capillary network (single system passes through 2) meaning the double circulation maintains higher blood pressure and average speed of flow, helps maintain a steeper concentration gradient which allows for the efficient exchange of nutrients and waste with surrounding tissues
Closed circulatory system
Blood is pumped around the body and is always contained within a network of blood vessels
Opened circulatory system
Blood is contained within blood vessels but is pumped directly into body cavities eg. Arthropods and molluscs
Circulatory system in insects 1.
One main blood vessel- dorsal vessel
The tubular heart in abdomen pumps haemolymph (insect blood) into the dorsal vessel
Circulatory system in insects 2.
The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
Circulatory system in insects 3
Haemolymph surrounds the organs and eventually reenters the heart via one-way valves called ostia
Difference between mammals and insect circulatory system
the haemolymph is not specifically directed towards any organs in an insect
Why do insects and mammals have different circulatory systems
Insects are able to survive with this less efficient circulatory system because oxygen is delivered directly to their tissues via tracheae (a system of tubes) that connect directly to the outside
What circulatory system do insects have
Open
Function of arterioles
Transport blood in capillaries
Function of venules
transport blood from the capillaries to the veins
Structure of arteries
Three layers: tunica externa, tunica media, tunica intima
Tunica intima (inner layer) arteries
Made up of an endothelial layer, a layer of connective tissue and a layer of elastic fibres.
The endothelium is one cell thick and lines the lumen of all blood vessels. It is very smooth and reduces friction for free blood flow
Tunica media (middle layer) arteries
Made up of smooth muscle cells and a thick layer of elastic tissue
Arteries have a thick tunica media
Smooth muscle cells in tunica media (arteries)
The layer of muscle cells strengthen the arteries so they can withstand high pressure. It also enables them to contract and narrow the lumen for reduced blood flow
Thick layer of elastic tissue in tunica media(arteries)
The elastic tissue helps to maintain blood pressure in the arteries. It stretches and recoils to even out any fluctuations in pressure
Tunica externa (outer layer) arteries
covers the exterior of the artery and is mostly made up of collagen
Collagen is a strong protein protects blood vessels from damage by over-stretching
Lumen in arteries
Arteries have a narrow lumen which helps to maintain a high blood pressure
Structure of arterioles
Arterioles possess a muscular layer that means they can contract and partially cut off blood flow to specific organs
Eg. During exercise blood flow to the stomach and intestine is reduced which allows for more blood to reach the muscles
Difference between arteries and arterioles
Unlike arteries, arterioles have a lower proportion of elastic fibres and a large number of muscle cells
The presence of muscle cells allows them to contract and close their lumen to stop and regulate blood flow
Tunica media in veins
The tunica media is much thinner in veins
There is no need for a thick muscular layer as veins don’t have to withstand high pressure
Lumen in veins
The lumen of the vein is much larger than that of an artery
A larger lumen helps to ensure that blood returns to the heart at an adequate speed
A large lumen reduces friction between the blood and the endothelial layer of the vein
The rate of blood flow is slower in veins but a larger lumen means the volume of blood delivered per unit of time is equal
Valves in veins
Prevent back flow of blood
Pulse in arteries compared to veins
No pulse in veins, pulse in arteries
Structure of venules
They have few or no elastic fibres and a large lumen
As the blood is at low pressure after passing through the capillaries there is no need for a muscular layer
Structure of Capillaries
They have thin walls which are “leaky”, allowing substances to leave the blood to reach the body’s tissues
They can form networks called capillary beds which are very important exchange surfaces within the circulatory system
Small diameter in capillaries (lumen)
This forces the blood to travel slowly which provides more opportunity for diffusion to occur
What does a large number of capillaries branch between cells mean
Substances can diffuse between the blood and cells quickly as there is a short diffusion distance
Wall of capillaries is made solely from a single layer of endothelial cells
The wall is only one cell thick – this reduces the diffusion distance for oxygen and carbon dioxide between the blood and the tissues of the body
The cells of the wall have gaps called pores which allow blood plasma to leak out and form tissue fluid
White blood cells can combat infection in affected tissues by squeezing through the intercellular junctions in the capillary walls
Plasma
Plasma is a straw-coloured liquid that constitutes around 55 % of the blood
Plasma is largely composed of water (95 %) and because water is a good solvent many substances can dissolve in it, allowing them to be transported around the body
How is tissue fluid formed
As blood passes through capillaries some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
Difference is composition of plasma and tissue fluid
very similar, although tissue fluid contains far fewer proteins
Proteins are too large to fit through gaps in the capillary walls and so remain in the blood
Tissue fluid
Where exchange of substances between cells and the blood occurs
Example of tissue fluid in action
For example, carbon dioxide produced in aerobic respiration will leave a cell, dissolve into the tissue fluid surrounding it, and then move into the capillary
Hydro static pressure
This is the pressure exerted by a fluid, e.g. blood
The hydrostatic pressure in this example is the blood pressure, generated by the contraction of the heart muscle
Oncotic pressure
This is the osmotic pressure exerted by plasma proteins within a blood vessel
Plasma proteins lower the water potential within the blood vessel, causing water to move into the blood vessel by osmosis
At the arterial end
When blood is at the arterial end of a capillary the hydrostatic pressure is great enough to force fluid out of the capillary
Proteins remain in the blood as they are too large to pass through the pores in the capillary wall
The increased protein content creates a water potential gradient (osmotic pressure) between the capillary and the tissue fluid
At the arterial end the hydrostatic pressure is greater than the osmotic pressure so the net movement of water is out of the capillaries into the tissue fluid
At the venous end
the hydrostatic pressure within the capillary is reduced due to increased distance from the heart and the slowing of blood flow as it passes through the capillaries
Water potential gradient at the venous end compared to arterial end
The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end
Pressure at then venous end
osmotic pressure is greater than the hydrostatic pressure and water begins to flow back into the capillary from the tissue fluid
Roughly 90 % of the fluid lost at the arterial end of the capillary is reabsorbed at the venous end
The other 10 % remains as tissue fluid and is eventually collected by lymph vessels and returned to the circulatory system
What happens if blood pressure is high (hypertension )
The pressure at the arterial is even greater
This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema
Formation of lymph
Some tissue fluid reenters the capillaries while some enters the lymph vessels
Lymph vessels
The lymph vessels are separate from the circulatory system
They have closed ends and large pores that allow large molecules to pass through
What happens to larger molecules (lymphatic system)
Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph
Small valves in the vessel walls are the entry point to the lymphatic system
What does lymph do with the larger molecules
The liquid moves along the larger vessels of the lymphatic system by compression caused by body movement. Any backflow is prevented by valves
The lymph eventually reenters the bloodstream through veins located close to the heart
Transportation of lipids with lymph
After digestion lipids are transported from the intestines to the bloodstream by the lymph system
Transportation of plasma proteins with lymph
Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries
What would happened if plasma proteins were not removed from tissue fluid
If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water into the blood in the capillaries
When do valves open and close in the heart
Open when the pressure of blood behind them is greater than the pressure in front of them
Close when the pressure of blood in front of them is greater than the pressure behind them
What 2 vessels bring blood to the heart
Vena cava and pulmonary vein
What two blood vessels take blood away from the heart
Pulmonary artery and aorta
Coronary arteries
Supply’s the heart with blood as it is a muscle and so requires its own blood supply for aerobic respiration
Why is it important coronary arteries remain clear of plaques
could lead to angina or a heart attack (myocardial infarction)
Ethical concerns surrounding dissection
People worry about how the animals for dissections are raised and killed
It goes against the religious beliefs of some individuals
Apparatus and its use for heart dissection
Scissors can be used for cutting large sections of tissue (cuts do not need to be precise)
Scalpel enables finer, more precise cutting and needs to be sharp to ensure this
Use pins to move the other sections of the specimen aside to leave the desired structure exposed
Systole
Contraction of the heart
Diastole
Relaxation of the heart
How volume affects pressure in the heart
When volume decreases, pressure increases
When volume increases, pressure decreases
How does volume change in the heart
Contraction of the heart muscle causes a decrease in volume in the corresponding chamber of the heart, which then increases again when the muscle relaxes
Diastole
Ventricles and atria relaxed
Ventricular diastole
The pressure in the ventricles drops below that in the aorta and pulmonary artery, forcing the SL valves to close
Atria diastole
The atria continue to fill with blood
Pressure in the atria rises above that in the ventricles, forcing the AV valves open
Blood flows passively into the ventricles without need of atrial systole
Valves during atrial systole
Av- open
Sv- closed
Valves during ventricular systole
Av- closed
Sl- opened
Valves during diastole
Av- opened
Sl- closed
Cardiac output
describe the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time
An average adult has a cardiac output of roughly 4.7 litres of blood per minute when at rest
Who has higher cardiac output
Individuals who are fitter often have higher cardiac outputs due to having thicker and stronger ventricular muscles in their hearts
Why does cardiac output increase when an individual is exercising
This is so that the blood supply can match the increased metabolic demands of the cells
Heart rate
Number of beats per minute
Stroke volume
volume of blood pumped out of the left ventricle during one cardiac cycle
Cardiac output formula
Cardiac output= heart rate x stroke volume
How does the heart beat
Hart is myogenic so heart will beat without external stimulus
How heart beat is initiated and coordinated 1
The sinoatrial node (SAN) is a group of cells in the wall of the right atrium. The SAN initiates a wave of depolarisation that causes the atria to contract
How heart beat is initiated and coordinated 2
Layer of non-conducting tissue prevents the excitation passing directly to the ventricles
How heart beat is initiated and coordinated 3
Atria-ventricular node picks up electrical activity from sino-atrial node
How heart beat is initiated and coordinated 4
atria-ventricular node imposes a slight delay before stimulating the bundle of his, the delay means that the ventricles contract after the atria
Bundle of his
A bundle of conducting tissue made up of purkyne fibres
How heart beat is initiated and coordinated 5
Bundle of his splits into two branches and conducts the wave of excitation to the apex of the heart
How heart beat is initiated and coordinated 6
At the apex the purkyne fibres spread out through the walls of the ventricles on both sides
How the heart beat is initiated and coordinated 7
The spread of excitation triggers the contraction of the ventricles starting at the apex. Contraction at the apex allows more efficient emptying of the ventricles
Stages of cardiac cycle
- Sinoatrial node sends out a wave of excitation
- Atria contact
- Atrioventricular node sends out a wave of excitation
- Purkyne tissue conducts to the wave of excitation
- Ventricles contract
electrocardiographs (ECGs)
Electrocardiography can be used to monitor and investigate the electrical activity of the heart
Electrodes that are capable of detecting electric signals are placed on the skin
These electrodes produce an electrocardiogram (ECG)
P wave (first part) ecg
Caused by the depolarisation of the atria, which results in atrial contraction (systole)
QRS complex (second part) ecg
Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)
This is the largest wave because the ventricles have the largest muscle mass
T wave (third part) ecg
Caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole)
U wave (last part) ecg
Repolarisation of the purkyne fibres
Tachycardia
When the heart beats too fast it is tachycardic
An individual with a resting heart rate of over 100 bpm is said to have tachycardia
Bradycardia
When the heart beats too slow it is bradycardic
An individual with a resting heart rate below 60 bpm is said to have bradycardia
A lot of fit individuals or athletes tend to have lower heart rates and it is usually not dangerous
Ecotopic heartbeat
This condition is caused by an early heartbeat followed by a pause
It is common in the population and usually requires no treatment unless very severe
Fibrillation
An irregular heartbeat will disrupt the rhythm of the heart
Severe cases of fibrillation can be very dangerous, even fatal
Haemoglobin
The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells
Red blood cells are also known as erythrocytes
Structure of haemoglobin
Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen
This means that each molecule of haemoglobin can carry four oxygen molecules, or eight oxygen atoms in total, quaternary structure- 4 globin subunits
What forms when oxygen binds to haemoglobin
Oxyhaemoglobin
How is oxygen dissociated from oxyhaemoglobin
The binding of the first oxygen molecule 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
The reverse of this process happens when oxygen dissociates in the tissues
Partial pressure
Relative pressure gas contributes to a number of gases
Carbon dioxide transport
Transported in 3 different ways:
About 5% carried dissolved in plasma
10-20% is combined with the amino groups in the polypeptide chains of haemoglobin to form a compound called carbaminohaemoglobin
75-85% is converted into hydrogen carbonate ions in the cytoplasm of the red blood cells
Formation of hydrogen carbonate ions 1
Carbon dioxide diffuses from the plasma into red blood cells
Inside red blood cells carbon dioxide combines with water to form H2CO3
CO2 + H2O ⇌ H2CO3 (carbonic acid)
Carbonic anhydrase
Red blood cells contain the enzyme carbonic anhydrase which catalyses the reaction between carbon dioxide and water
Without carbonic anhydrase this reaction proceeds very slowly
The plasma contains very little carbonic anhydrase hence H2CO3 forms more slowly in plasma than in the cytoplasm of red blood cells
Formation of hydrogen carbonate ions 2
Carbonic acid dissociates readily into H+ and HCO3- ions
H2CO3 ⇌ HCO3– + H+
Hydrogen ions can combine with haemoglobin, forming haemoglobinic acid and preventing the H+ ions from lowering the pH of the red blood cell
Haemoglobin is said to act as a buffer in this situation
The hydrogen carbonate ions diffuse out of the red blood cell into the blood plasma where they are transported in solution
Chloride shift
the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed
Why do we need the chloride shift
To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein
If this did not occur then red blood cells would become positively charged as a result of a buildup of hydrogen ions formed from the dissociation of carbonic acid
Oxygen dissociation curve
the rate at which oxygen associates, and also dissociates, with haemoglobin at different partial pressures of oxygen (pO2)
When is haemoglobin referred to as saturated
Haemoglobin is referred to as being saturated when all of its oxygen binding sites are taken up with oxygen; so when it contains four oxygen molecules
Partial pressure of oxygen
Partial pressure of oxygen refers to the pressure exerted by oxygen within a mixture of gases; it is a measure of oxygen concentration
Affinity for oxygen
The ease with which haemoglobin binds and dissociates with oxygen
What happens when haemoglobin has a high affinity
It binds easily and dissociates slowly
What happens when haemoglobin has a low affinity
When haemoglobin has a low affinity for oxygen it binds slowly and dissociates easily
What can be said about the relationship between haemoglobin as affinity and partial pressures of oxygen
haemoglobin’s affinity for oxygen changes at different partial pressures of oxygen
Shape of oxygen dissociation curve (initial slow rise)
Due to the shape of the haemoglobin molecule it is difficult for the first oxygen molecule to bind to haemoglobin; this means that binding of the first oxygen occurs slowly, explaining the relatively shallow curve at the bottom left corner of the graph
Shape of dissociation curve (steeper part)
After the first oxygen molecule binds to haemoglobin, the haemoglobin protein changes shape, or conformation, making it easier for the next oxygen molecules to bind; this speeds up binding of the remaining oxygen molecules (cooperative binding)
Oxygen dissociation curve levelling of at the top
As the haemoglobin molecule approaches saturation it takes longer for the fourth oxygen molecule to bind due to the shortage of remaining binding sites
Interpreting dissociation curve low p02
Haemoglobin has a low affinity for oxygen at low pO2, so saturation percentage is low as oxygen binds slowly
Interpreting dissociation curve middle p02
oxygen binds more easily to haemoglobin and saturation increases quickly; at this point on the graph a small increase in pO2 causes a large increase in haemoglobin saturation
Interpreting dissociation curve high p02
Haemoglobin has a high affinity for oxygen at high pO2, so saturation percentage is high
Note that at this point on the graph increasing the pO2 by a large amount only has a small effect on the percentage saturation of haemoglobin; this is because most oxygen binding sites on haemoglobin are already occupied
Foetal haemoglobin
The haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin
Why does a developing foetus have a higher affinity for oxygen than adult haemoglobin
This is vital as it allows a foetus to obtain oxygen from its mother’s blood at the placenta
Fetal haemoglobin can bind to oxygen at low pO2
At this low pO2 the mother’s haemoglobin is dissociating with oxygen
Foetal haemoglobin on dissociation curve
the curve for foetal heamoglobin shifts to the left of that for adult haemoglobin
This means that at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin (start and end at same point)
What happens to foetal haemoglobin after birth
a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin
This is important for the easy release of oxygen in the respiring tissues of a more metabolically active individual
Effects of altitude
The partial pressure of oxygen is lower at higher altitudes
Species living at high altitudes have haemoglobin that is adapted to these conditions
Bohr effect
As partial pressure of co2 rises haemoglobin gives up oxygen more easily
