3.2 Exchange in animals Flashcards
What happens in a single circulatory system?
The blood passes through the heart once during one complete circuit of the body
What happens in a double circulatory system?
the blood passes through the heart twice during one complete circuit of the body
What is a closed circulatory system?
blood is pumped around the body and is always contained within a network of blood vessels
—> vertebrates and invertebrates
What is an open circulatory system?
blood is not contained within blood vessels but is pumped directly into body cavities
—> arthropods and molluscs
Explain the features of the circulatory system in insects
- The dorsal vessel is the main blood vessel
- The tubular heart in the abdomen pumps haemolymph into the dorsal vessel
- The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
What do arteries do?
transport blood away from the heart (usually at high pressure) to tissues
What do arterioles do?
arteries branch into narrower blood vessels called arterioles which transport blood into capillaries
What do veins do?
transport blood to the heart (usually at low pressure)
What do venules do?
these are narrower blood vessels transport blood from the capillaries to the veins
What is the structure of arteries?
Tunica externa: collagen shell to prevent the vessel bursting
Tunica media: Thick layer of smooth muscle and elastic fibres
Tunica intima: an endothelial layer, a layer of connective tissue and a layer of elastic fibres
—> smooth to reduce friction for smooth blood flow
What is the structure of arterioles?
Thin muscle layer which can contract, to direct blood to areas which need it
Connects arteries to capillaries
What is the structure of veins?
- Thinner tunica media as they don’t withstand high pressures
- Contains valves to prevent the backflow of blood
- Larger lumen helps to ensure that blood returns to the heart at an adequate speed
What is the structure of venules?
- Connect the capillaries to the veins
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
What is the function of capillaries?
allows 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
What is the structure of capillaries?
Very small diameter: Forces blood to travel slowly to allow more diffusion
Walls one cell thick: Reduces diffusion distance
Pores: allows blood plasma to leak out and form tissue fluid
What is hydrostatic pressure?
The pressure exerted by a fluid, e.g. blood
What is oncotic pressure?
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
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
This results in the formation of tissue fluid
What is the composition of tissue fluid?
Very similar to plasma - yet contains fewer proteins, as these are too large to fit through the gaps in the capillary walls
What happens at the arterial end?
- 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 fit out of pores in the capillary
- this creates a water potential gradient, between the capillary and tissue fluid
- the hydrostatic pressure is greater than the osmotic pressure so the net movement of water is out of the capillaries into the tissue fluid
What happens 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
- same WP gradient as at the arterial end
- the oncotic pressure is greater than the hydrostatic pressure and water begins to flow back into the capillary from the tissue fluid
—> 90% fluid lost is returned
—> 10% which remains is tissue fluid
What happens if blood pressure is high?
The pressure at the arterial end is even greater
This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema
How is lymph formed?
- Some tissue fluid enters lymph vessels
- These have larger pores and allow large molecules to pass through
- Plasma proteins return to the blood via lymph capillaries
What is the heart found inside of?
Pericardium - thin membrane attached to the diaphragm which keeps the heart in place
Which blood vessels bring deoxygenated blood to the heart?
Superior and inferior Vena Cava
Arrives at right atrium
Which blood vessels take deoxygenated blood from the heart to the lungs?
Pulmonary artery
Which blood vessel brings oxygenated blood from the lungs to the heart?
Pulmonary vein
Arrives at left atrium
Which blood vessel transports oxygenated blood from the heart to the body?
Aorta
Which valve is present between the atria and ventricles and what is its function?
Atrio-ventricular valves:
Prevent the backflow of blood from the ventricles when they contract
What are tendinous cords?
Attaches valves to the walls of ventricles to prevent valves turning inside out when ventricles contract
What is the wall down the centre of the heart?
The Septum: it prevents oxygenated and deoxygenated blood from mixing
What are the functions of the semilunar valves and where are they found?
At base of pulmonary artery and aorta
—> prevent blood flowing from arteries back into the ventricles when the ventricles relax
Which valve is found in the right atrium?
Tricuspid valve
Which valve is found in the left atrium?
Bicuspid valve
What is the function of the coronary arteries?
The provide oxygen to the tissues (cardiac muscle) of the heart, for respiration
Explain the changes in the cardiac cycle
- Atrial systole - the walls of the atria contract, forcing blood through the atrio-ventricular valves into the ventricles.
- Atrial diastole - the atria relax as blood is in the ventricles
- Ventricular systole - forces AV to close, forces SL valves open and blood flows into arteries.
What does myogenic mean?
The heart will beat without any external stimulus
What is the function of the SAN?
It initiates a wave of depolarisation that causes the atria to contract
What are the steps in the initiation and co-ordination of heart action?
- SAN initiates a wave of depolarisation that causes the atria to contract
- Annulus fibrosus (non-conducting tissue) - prevents depolarisation spreading
–> depolarisation is carried to the AVN - After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
4.
What is the bundle of His and where is it located?
Conducting tissue in the septum
- The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
Purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart
This makes the ventricles contract
What is an ECG?
Electrocardiogram:
monitors and investigates the electrical activity of the heart
What causes the P wave?
depolarisation of the atria, which results in atrial contraction
What causes the QRS complex?
Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)
—> largest wave because the ventricles have the largest muscle mass
What causes the T wave?
repolarisation of the ventricles, which results in ventricular relaxation (diastole)
What causes the U wave?
repolarisation of the Purkyne fibres
What is tachycardia?
Heart beats too fast
over 100 bpm
What is bradycardia?
Heart beat too slow
below 60 bpm
What is an ectopic heartbeat?
an early heartbeat followed by a pause
What is fibrillation?
An irregular heartbeat will disrupt the rhythm of the heart
How is oxygen transported in the blood?
Oxygen binds to haemoglobin
What is the equation for oxygen binding to haemoglobin?
4O2 + Hb <–> Hb 4O2
Oxygen + Hb –> Oxyhaemoglobin
What is meant by co-operative binding?
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;
How are hydrogen carbonate ions formed?
- Carbon dioxide diffuses from the plasma into red blood cells
- Inside red blood cells carbon dioxide combines with water to form H2CO3
–> this is catalysed by the enzyme carbonic anhydrase - Carbonic acid (H2CO3) dissociates readily into H+ and HCO3 - ions
What happens to the H+ ions after the dissociation of Carbonic acid?
H+ ions combine with haemoglobin, forming Haemaglobonic acid, and this prevents the H+ from lowering the pH of the blood stream
—> Hb acts as a buffer
What happens to the Hydrogencarbonate ions?
They diffuse out of the red blood cell into the blood plasma where they are transported in solution
Explain the stages of the Chloride shift
- Negatively charged hydrogen carbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane
- To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein
What does the oxygen dissociation curve show?
the rate at which oxygen associates, and also dissociates, with haemoglobin at different partial pressures of oxygen (pO2)
When is haemoglobin saturated?
when all of its oxygen binding sites are taken up with oxygen
What does oxygen affinity mean?
The ease with which haemoglobin binds and dissociates with oxygen
If haemoglobin has a high oxygen affinity it…
binds easily and dissociates slowly
What does the oxygen dissociation curve show in terms of oxygen affinity?
haemoglobin’s affinity for oxygen changes at different partial pressures of oxygen
Explain the shape of the oxygen dissociation curve
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
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 and explains the steeper part of the curve in the middle of the graph
The shape change of haemoglobin leading to easier oxygen binding is known as cooperative binding
As the haemoglobin molecule approaches saturation it takes longer for the fourth oxygen molecule to bind due to the shortage of remaining binding sites, explaining the levelling off of the curve in the top right corner of the graph
What happens at low pO2?
oxygen binds slowly to haemoglobin; this means that haemoglobin cannot pick up oxygen and become saturated as blood passes through the body’s oxygen-depleted tissues
What is haemoglobins oxygen affinity like at low pO2?
Haemoglobin has a low affinity for oxygen at low pO2, so saturation percentage is low
What happens at medium pO2?
oxygen dissociates readily from haemoglobin, as shown by the steep region of the curve; this region corresponds with the partial pressures of oxygen present in the respiring tissues
What happens at low pO2?
Dissociation slows again
What is the difference between foetal and adult haemoglobin?
haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin
Why is foetal haemoglobin important?
it allows a foetus to obtain oxygen from its mother’s blood at the placenta
Foetal haemoglobin can bind to oxygen at low pO2
Why is the foetal haemoglobin curve shifted to the left of the adult curve?
at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin
