Mass transport in mammals Flashcards
What do the transport systems of many organisms need in order to carry materials?
A suitable medium - normally a liquid based on water
Why should the medium of transport systems be based on water?
Water readily dissolves substances and can be moved around easily
Can also be a gas
How do transport systems ensure that the transport medium is moved around in bulk over large distances?
They have a form of mass transport
What kind of system do transport systems need?
A closed system of tubular vessels than contains the transport medium
What kind of network should the closed system of tubular vessels in transport systems be?
A branching network to distribute it to all parts of the organism
Why do we need pressure differences in different parts of the transport system?
As we need a mechanism for moving the transport medium within vessels
How do animals achieve the requirements of transport systems?
They use muscular contraction either of the body muscles or of a specialised pumping organ
What do plants rely on to achieve the requirements of the transport systems?
Natural, passive processes
What kind of mechanisms do we need in plants?
- A mechanism to maintain the mass flow of movement in one direction
- A mechanism for the mass flow of water or gases
Why do plants need a means of controlling the flow of the transport medium?
To suit the changing needs of different parts of the organism
What kind of circulatory system do mammals have?
A closed, double one
What is the flow of blood like in mammals?
Blood is confined to vessels and passes twice through the heart for each complete circuit
Why does the circulatory system of mammals need to be a double one?
When blood passes through the lungs, its pressure decreases and its pressure would be too low to pass immediately through the rest of the body as circulation would be too slow
So it returns to the heart to boost its pressure
Why do blood and its substances need to be delivered to the rest of the body quickly?
Mammals have a high body temperature and thus a high rate of metabolism
What kind of organ is the heart and where is it located?
It is a muscular organ that lies in the thoracic cavity behind the sternum
Is the heart one pump?
No - it is 2 separate pumps lying side by side
What are the 2 chambers of the heart?
Atrium and ventricle
What is the atrium?
It is thin-walled and elastic and stretches as it collects blood
What is the ventricle?
It has a much thicker muscle wall as it has to contract strongly to pump blood
Do the 2 pumps of the heart pump in time?
Yes - both atria and then ventricles pump together, pumping the same volumes of blood
What are there between each atrium and ventricle?
Valves - to prevent the back flow of blood
Which valve is found on the right side?
The right atrioventricular valve (tricuspid)
Which valve is found on the left side?
The left atrioventricular valve (bicuspid)
What are vessels connecting the heart to the lungs called?
Pulmonary vessels
What is the aorta?
Connected to the left ventricle and carries oxygenated blood to all parts of body except lungs
What is the vena cava?
Connected to right atrium and brings deoxygenated blood from tissues of the body
What is the pulmonary artery?
Connected to right ventricle and carries deoxygenated blood to lungs
What is the pulmonary vein?
Connected to left atrium and brings oxygenated blood back from lungs
How is the heart muscle supplied with oxygen?
By coronary arteries - branches off the aorta shortly after it leaves the heart
What happens if the coronary arteries are blocked?
Leads to myocardial infarction - a heart attack
What is the relaxation of the heart known as?
Diastole
What happens as the atria fill with blood?
The pressure in them rises
What happens when the pressure in the atria exceeds the pressure in the ventricles?
The atrioventricular valves open allowing the blood to pass into the ventricles (aided by gravity)
While blood passes from the atria to the ventricles, are the muscles of both chambers relaxed?
Yes
What does the relaxation of the ventricle wall cause?
It causes them to recoil and reduce the pressure within the ventricle
What happens as a result that the pressure in the ventricles is lower than the pressure in the aorta and pulmonary artery?
The semi-lunar valves close, accompanied by the ‘dub’ sound of the heart beat
What is the contraction of the atria known as?
Atrial systole
What happens after the blood has flown from the atria to the ventricles while the muscle of the chambers are still relaxed?
The atrial walls contract and this along with the recoil of the relaxed ventricle walls forces the remaining blood into the ventricle walls from the atria
Are the ventricle walls relaxed while the atrial walls contract?
Yes
What is contraction of the ventricles known as?
Ventricular systole
What happens after the ventricles fill with blood completely?
After a short delay, their walls contract simultaneously
What happens as a result of the contraction of the ventricular walls?
Blood pressure is increased, closing the atrioventricular valves to prevent back flow
What happens to the pressure as a result of atrioventricular valves closing?
It increases
What happens once the pressure in the ventricles exceeds that in the aorta and pulmonary artery?
Blood is forced from the ventricles into these vessels
Why do ventricles have thick muscular walls?
So they can contract forcefully - this creates high pressure necessary to pump blood
Why is the left ventricle wall thicker than the right?
The left has to pump blood to extremities while the right only has to pump blood to the lungs
When are valves designed to close?
When pressure differences are reversed and blood would tend to flow in the opposite direction
When do atrioventricular valves prevent back flow?
When ventricular pressure exceeds atrial pressure
Where are semi-lunar valves located?
Aorta and pulmonary artery
When do semi-lunar valves prevent back flow?
When pressure in aorta and pulmonary artery exceeds that in the ventricles
When is the pressure in the aorta and pulmonary artery greater than in the ventricles?
When the elastic walls of these vessels recoil, increasing the pressure within them, and when the ventricle walls relax, reducing the pressure
What are valves made up of?
A number of flaps of tough, but flexible fibrous tissue which are cusp shaped
When do valves move apart to let blood pass between the cusps?
When the pressure is greater on the convex side of the cusps than on the concave side
What happens when pressure is greater on the concave sides of cusps in a valve?
- Blood collects within the ‘bowl’ of the cusps
- This pushes them together to form a tight fit that prevents the passage of blood
What is cardiac output?
The volume of blood pumped by one ventricle of the heart in one minute
What is the stroke volume?
Volume of blood pumped out at each beat
What is the equation for cardiac output?
Heart rate x stroke volume
What do arteries do?
Carry blood away from the heart and into arterioles
What do arterioles do?
They are smaller arteries than control blood flow from arteries to capillaries
What do capillaries do?
Tiny vessels that link arteries to veins
What do veins do?
Carry blood from capillaries back to the heart
Do all of the blood vessels have the same basic layered structure?
Yes except the capillaries which only have a lining layer
What are the layers that make up the blood vessels?
Tough outer layer
Muscle layer
Elastic layer
Inner lining
Lumen
What is the tough outer layer of blood vessels like?
It is a tough fibrous outer layer that resists pressure changes from both within and outside
What is the muscle layer of blood vessels like?
It can contract and so control the flow of blood
What is the elastic layer of blood vessels like?
Helps maintain blood pressure by stretching and springing back (recoiling)
What is the inner lining like?
Known as endothelium and it is thin to allow diffusion and smooth to reduce friction
What is the lumen like?
Not an actual layer but the central cavity of the blood vessel through which blood flows
How do arterioles differ from arteries?
They are smaller in diameter
Have a relatively larger muscle layer and lumen
What is the function of arteries?
To transport blood rapidly under high pressure
What is the muscle layer of arteries like compared to veins ?
It is thicker
Why do arteries have a thick muscle layer?
So smaller arteries can be constricted and dilated in order to control the volume of blood passing though them
What is the elastic layer of arteries like compared to veins?
Relatively thick
Why is it important that arteries have a relatively thick elastic layer?
Blood pressure needs to be kept high to reach extremities
What happens at each beat of the heart in arteries?
The elastic wall is stretched out - systole
What happens to the elastic wall of the arteries when the heart relaxes?
It springs back (diastole)
movement of elastic wall mimics that of elastic band
What does the stretching and recoil action of the arteries help maintain?
High pressure and smooth pressure surges created by the beating of the heart
What is the overall thickness of the wall of the artery like?
It is great
What is the artery wall quite thick overall?
Resists the vessel bursting under pressure
What is the function of arterioles?
Carries blood from arteries to capillaries under lower pressure and controls the blood flow between the two
Why do arterioles have a thicker muscle layer than arteries?
- Contraction of this layer allows constriction of the arteriole lumen
- This restricts the flow of blood
- Controls its movement into capillaries
Why is the elastic layer of arterioles thinner than arteries?
Blood pressure is lower
Why do veins have a thinner muscle layer compared to arteries?
They carry blood away from tissues so their constriction and dilation cannot control the flow of blood to the tissues
Why do veins have a thinner elastic layer than arteries?
Veins will not burst as they have low pressure and pressure is too low to create a recoil action
Why is the overall thickness of the vein small?
No need for thick one as pressure too low to create any risk of bursting
Also allows them to be flattened easily, aiding flow of blood
Why are there valves in the veins?
To prevent back flow of blood which might otherwise happen as pressure is so low
What aids the flow of blood in veins?
Contraction of body muscles - veins are compressed, pressurising the blood within them
How do valves interact with the contraction of body muscles in terms of flow of blood on veins?
Ensure that the pressure created by the contraction directs the blood towards the heart
What do the capillaries wall mostly consist of and why is this important?
The lining layer, making them extremely thin - short diffusion distance - rapid diffusion of materials
How do capillaries have a large surface area for exchange?
Numerous and highly branched
What is caused by capillaries having a narrow diameter?
Can permeate tissues, so no cell is far from a capillary - short diffusion distance
What is caused by capillary lumen being narrow?
Red blood cells are squeezed flat against the side of the capillary which brings them even closer to cells
What is there between the lining(endothelial) cells?
Spaces that allow white blood cells to escape in order to deal with infections within tissues
What is tissue fluid?
Watery liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen
What does tissue fluid do with all the substances it contains?
Supplies it to the tissues
What does tissue fluid receive from tissues?
CO2 and other waste materials
Why does tissue fluid bathe all the cells in the body?
It is the means by which materials are exchanged between blood and cells
What is tissue fluid in terms to cells?
The immediate environment of cells and it is where they live
What is tissue fluid formed from?
- Blood plasma
- Composition of blood plasma controlled by various homeostatic systems
- So, provides a mostly constant environment for cells
What does pumping by the heart create in terms of tissue fluid?
A pressure, called hydrostatic pressure, at the arterial end of the capillaries
Why does blood have a lower water potential?
Due to plasma proteins
What are the 2 pressures acting alongside the movement of tissue fluid in and out of the capillaries?
Hydrostatic pressure and osmotic pressure
What does the combined effect of hydrostatic pressure and osmotic pressure only allow the movement of and what is this known as?
This pressure is only enough to force small molecules out of the capillaries, leaving all cells and proteins in blood, as these are too large - known as ultrafiltration
How does most tissue fluid return directly to the blood plasma?
Via the capillaries
How does tissue fluid leave the capillaries initially at the arterial end?
The hydrostatic pressure within them is greater than outside so tissue fluid moves out of the capillaries - osmotic pressure within them also greater
What happens when tissue fluid leaves the capillaries?
Reduces the hydrostatic pressure within them
What happens as a result that the hydrostatic pressure inside the capillaries is lower when they reach the venous end?
As the hydrostatic pressure of the blood is usually lower than that of the tissue fluid outside of it, tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them
What also aids the movement of tissue fluid back into the capillaries at the venous end?
The plasma has lost water and still contains proteins - so has a lower water potential than tissue fluid - water leaves tissue by osmosis down a water potential gradient
Given that not all the tissue fluid can return to the capillaries, how is the remainder returned?
Via the lymphatic system
What is the lymphatic system?
- System of vessels that begin in tissues
- Vessels have dead ends
- Gradually merge into larger vessels that form a network throughout the body
How do the larger vessels of the lymphatic system return the tissue fluid to the blood plasma?
They drain their contents back into the bloodstream via 2 ducts that join veins close to the heart
How are the contents of the lymphatic system moved by?
Hydrostatic pressure
Contraction of body muscles
How does hydrostatic pressure move the contents of the lymphatic system?
It is the hydrostatic pressure of the tissue fluid that has left the capillaries
How do contraction of body muscles move the contents of the lymphatic system?
They squeeze the lymph vessels - valve in the vessels ensure that fluid moves away from tissues and in direction of the heart
