Module 3: Transport in animals Flashcards
What is the circulatory system?
Organ system that permits blood to circulate.
What is blood?
A tissue that transports many vital components around the body like oxygen and CO2.
How does a single celled organism gain the oxygen and glucose needed for aerobic respiration?
Through the cell membrane. Molecules can diffuse to all parts of the cell quickly due to short diffusion distances.
Oxygen diffuses through cell membrane from high to low conc. This process is passive and doesn’t require energy.
Glucose passes through by facilitated diffusion or active transport.
Why do multicellular organisms require a transport system?
As organisms get larger, diffusion alone cannot supply the body with enough O2 and nutrients. CO2 also cannot be removed quick enough.
Open vs closed circulatory system.
Open - blood flows freely through body cavities.
Closed - blood flows inside the body through vessels such as arteries and veins (humans).
What are the cons of having an open circulatory system?
As blood is not confined to blood vessels, blood pressure is much lower in open so slower circulation and less effective delivery of oxygen and nutrients to tissues.
Also makes it difficult to regulate blood flow to specific tissues or organs according to their needs.
What are the limitations of a single closed circulatory system?
Low blood pressure in systemic circulation - blood passes through the heart only once before being pumped to the body. Once it passes through the gills, the blood loses pressure. Therefore the flow of blood to various tissues can be slower and less efficient
What are the advantages to a double circulatory system?
Blood passes through the heart twice which allows high blood pressure in the systemic circulation, so O2 and nutrients are delivered more effectively.
Double circulatory system keeps oxygenated blood separate from deoxygenated blood - oxygen rich blood.
When blood enters a capillary network the pressure and speed drops significantly
In a single circulatory system, the blood has to pass through two capillary networks before returning to the heart
In a double circulatory system, the blood only passes through one capillary network before returning to the heart
As a result, the double circulation maintains higher blood pressure and average speed of flow
This increased pressure and speed helps to maintain a steeper concentration gradient which allows for the efficient exchange of nutrients and waste with the surrounding tissues
Difference between single and double circulatory system?
Single - blood passes through heart once in one complete circuit in the body.
Double - blood passes through heart twice in one complete circuit:
How does the single circulatory system in fish work?
Deoxygenated blood is pumped to the gills from the heart
The gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood
The oxygenated blood flows from the gills to the rest of the body
It travels through the capillaries in organs, delivering oxygen and nutrients
The blood returns to the heart
The heart only has one atrium and one ventricle
Difference between open and closed circulatory system?
In a closed circulatory system, blood is pumped around the body and is always contained within a network of blood vessels
All vertebrates and many invertebrates have closed circulatory systems
In an open circulatory system, blood is not contained within blood vessels but is pumped directly into body cavities
Organisms such as arthropods and molluscs have open circulatory systems.
Humans have a closed double circulatory system: in one complete circuit of the body blood passes through the heart (the pump) twice
The right side of the heart pumps blood deoxygenated blood to the lungs for gas exchange; this is the pulmonary circulatory system
Blood then returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (at high pressure) around the body; this is the systemic circulatory system
circulatory system in insects?
Insects have one main blood vessel - the dorsal vessel
The tubular heart in the abdomen pumps haemolymph (this is what blood in insects is called) into the dorsal vessel
The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
Haemolymph surrounds the organs and eventually reenters the heart via one-way valves called ostia
Unlike the blood in a mammals circulatory system, the haemolymph is not specifically directed towards any organs in an insect
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
Arteries
Transports blood away from the heart (usually at high pressure) to tissues.
Artery walls consist of three layers: tunica externa, tunica media and tunica intima.
The tunica intima is 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
The tunica media is made up of smooth muscle cells and a thick layer of elastic tissue
Arteries have a thick tunica media
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
The elastic tissue helps to maintain blood pressure in the arteries. It stretches and recoils to even out any fluctuations in pressure
The tunica adventitia 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
Arteries have a narrow lumen which helps to maintain a high blood pressure
A pulse is present in arteries
Arterioles
arteries branch into narrower blood vessels called arterioles which transport blood into capillaries
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
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
Veins
Transport blood to the heart (usually at low pressure)
Veins return blood to the heart
They receive blood that has passed through capillary networks (blood pressure is very low and it must be returned to the heart)
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
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
Veins contain valves
These prevent the backflow of blood, helping return blood to the heart
A pulse is absent in veins
Venules
these narrower blood vessels transport blood from the capillaries to the veins
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
Capillaries
Capillaries are a type of blood vessel present in the circulatory system
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
Structure and function of capillaries
Capillaries have a very small diameter (lumen)
This forces the blood to travel slowly which provides more opportunity for diffusion to occur
A large number of capillaries branch between cells
Substances can diffuse between the blood and cells quickly as there is a short diffusion distance
The wall of the capillary is made solely from a single layer of endothelial cells (this layer also lines the lumen in arteries and veins)
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
What is tissue fluid?
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
The composition of plasma and tissue fluid are 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 bathes almost all the cells of the body that are outside the circulatory system
Exchange of substances between cells and the blood occurs via the tissue fluid
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
How is tissue fluid formed?
The volume of liquid that leaves the plasma to form tissue fluid depends on two opposing forces
Hydrostatic 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?
At the venous end of the capillary 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
The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end
At the venous end the 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
If blood pressure is high (hypertension) then 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
What is the lymph?
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
The liquid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves
This is why people who have been sedentary on planes can experience swollen lower limbs
The lymph eventually reenters the bloodstream through veins located close to the heart
Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries
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
After digestion lipids are transported from the intestines to the bloodstream by the lymph system
What is the heart!
The heart is a hollow, muscular organ located in the chest cavity
It is protected in the chest cavity by the pericardium, a tough and fibrous sac.
The portion of the septum which separates the left and right atria is called the interatrial septum, while the portion of the septum which separates the left and right ventricles is called the interventricular septum
The role of valves 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
Valves are important for keeping blood flowing forward in the right direction and stopping it flowing backwards. They are also important for maintaining the correct pressure in the chambers of the heart
The right atrium and right ventricle are separated by the atrioventricular valve, which is otherwise known as the tricuspid valve
The right ventricle and the pulmonary artery are separated by the pulmonary valve
The left atrium and left ventricle are separated by the mitral valve, which is otherwise known as the bicuspid valve
The left ventricle and aorta are separated by the aortic valve
There are two blood vessels bringing blood to the heart; the vena cava and pulmonary vein
Coronary arteries?
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
Valves are important for keeping blood flowing forward in the right direction and stopping it flowing backwards. They are also important for maintaining the correct pressure in the chambers of the heart
The right atrium and right ventricle are separated by the atrioventricular valve, which is otherwise known as the tricuspid valve
The right ventricle and the pulmonary artery are separated by the pulmonary valve
The left atrium and left ventricle are separated by the mitral valve, which is otherwise known as the bicuspid valve
The left ventricle and aorta are separated by the aortic valve
There are two blood vessels bringing blood to the heart; the vena cava and pulmonary vein
Cardiac cycle
The cardiac cycle is the series of events that take place in one heart beat, including muscle contraction and relaxation
The contraction of the heart is called systole, while the relaxation of the heart is called diastole
One cardiac cycle is followed by another in a continuous process
There is no gap between cycles where blood stops flowing
Volume and pressure changes
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
Volume changes lead to corresponding pressure changes
When volume decreases, pressure increases
When volume increases, pressure decreases
Throughout the cardiac cycle, heart valves open and close as a result of pressure changes in different regions of the heart
Valves open when the pressure of blood behind them is greater than the pressure in front of them
They close when the pressure of blood in front of them is greater than the pressure behind them
Valves are an important mechanism to stop blood flowing backwards
Atrial systole
The walls of the atria contract
Atrial volume decreases
Atrial pressure increases
The pressure in the atria rises above that in the ventricles, forcing the atrioventricular (AV) valves open
Blood is forced into the ventricles
There is a slight increase in ventricular pressure and chamber volume as the ventricles receive the blood from the atria
The ventricles are relaxed at this point; ventricular diastole coincides with atrial systole
The walls of the ventricles contract
Ventricular volume decreases
Ventricular pressure increases
The pressure in the ventricles rises above that in the atria
This forces the AV valves to close, preventing back flow of blood
The pressure in the ventricles rises above that in the aorta and pulmonary artery
This forces the semilunar (SL) valves open so blood is forced into the arteries and out of the heart
During this period, the atria are relaxing; atrial diastole coincides with ventricular systole
The blood flow to the heart continues, so the relaxed atria begin to fill with blood again
Ventricular systole
Diastole
The ventricles and atria are both relaxed
The pressure in the ventricles drops below that in the aorta and pulmonary artery, forcing the SL valves to close
The atria continue to fill with blood
Blood returns to the heart via the vena cava and pulmonary vein
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
The cycle then begins again with atrial systole.
Heart action
Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus
This intrinsic rhythm means the heart beats at around 60 times per minute
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
The Annulus fibrosus is a region of non-conducting tissue which prevents the depolarisation spreading straight to the ventricles
Instead, the depolarisation is carried to the atrioventricular node (AVN)
This is a region of conducting tissue between atria and ventricles
After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
This delay means that the ventricles contract after the atria
The bundle of His is a collection of conducting tissue in the septum (middle) of the heart. The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
The 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 and blood is forced out of the pulmonary artery and aorta
Explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne fibres in a heartbeat.
The Sinoatrial node sends out a wave of excitation and this spreads across both atria, causing atrial systole. Non-conducting tissue called the Annulus fibrosus prevents the excitation from spreading to the ventricles and so this ensures that atria and ventricles don’t contract at the same time. The Atrioventricular node then sends the wave of excitation to the ventricles after a short delay of around 0.1 - 0.2 seconds, ensuring that the atria have time to empty their blood into the ventricles. The Purkyne fibres conduct the excitation down the septum of the heart and to the apex, before the excitation is carried upwards in the walls of the ventricles. This means that during ventricular systole, the blood contracts from its base and blood is pushed upwards and outwards.
