Transport In Animals Flashcards
What are the main factors that influence the need for a transport system?
Size
Surface area to volume ratio
Level of metabolic activity
Why does ‘size’ affect the need for a transport system?
The cells inside a large organism are further from its surface therefore the diffusion pathway is increased and the diffusion rate is reduced meaning the diffusion is too slow to supply all the requirements
Outer cells will use up all the supplies so less reach the ones deep inside the body
What are the features of a good transport system?
A fluid to carry nutrients, oxygen and wastes around the body (blood)
A pump to create pressure that will push the fluid around the body (heart)
Exchange surfaces that enable substances to enter the blood and leave it where needed (capillaries)
Tubes or vessels to carry blood by mass flow to where the oxygen and nutrients are needed
Two circuits - one to pick up oxygen and another to deliver it to tissues
What is pulmonary and systemic circulation?
Pulmonary circulation carries blood to the lungs to pick up oxygen
Systemic circulation carries oxygen and nutrients around the body to the tissues
What route does blood take in the single circulatory system of a fish?
Heart
Gills
Body
Heart
What route does blood take in a double circulatory system?
Heart Body Heart Lungs Heart
How can blood be made to flow more quickly?
By increasing the blood pressure created by the heart
What are the advantages of a double circulatory system?
Heart can increase blood pressure after it has passed through the lungs so it flows faster
What does an open circulatory system mean?
blood not always held within blood vessels
instead circulates through body cavity
tissues and cells bathed directly in blood
How is blood pumped round the body in insects?
There is a long, muscular tube (heart) lying under the dorsal surface of the body
Blood from body enters heart/tube through ostia (pores)
Heart/tube pumps blood towards the head by peristalsis
At the end of the heart/tube nearest the head, blood pours into the body cavity
What are disadvantages of an open circulatory system?
Blood pressure is low so blood flow is slow
Circulation of blood may be affected by body movements or lack of body movements
What does a closed circulatory system mean?
The blood stays entirely inside vessels
a separate tissue fluid bathes the tissues and cells
What advantages does a closed circulatory system have over an open circulatory system?
Higher pressure so blood flows more quickly
More rapid delivery of oxygen and nutrients
More rapid removal of carbon dioxide and other waste products
Transport is independent of body movements
What do all types of blood vessel have?
A lining made of smooth endothelium to reduce friction with the flowing blood
What are the features of arteries?
Carries blood away from the heart
Blood is at high pressure so artery wall is thick to withstand it
Lumen is small to maintain high pressure
Inner wall is folded to allow lumen to expand as blood flow increases
What does the wall of an artery consist of?
Inner layer - thin layer of elastic tissue allowing the wall to stretch and recoil helping to maintain blood pressure
Middle layer - thick layer of smooth muscle
Outer layer - layer of collagen fibres and elastic tissue providing strength to withstand high pressure and recoil to maintain it
What are arterioles?
Small blood vessels that distribute the blood from an artery to the capillaries
What are the walls of arterioles like?
They contain a layer of smooth muscle that will constrict the diameter of the arteriole when contracted
This increases resistance to flow and reduces rate of blood flow
What can constriction of the arteriole walls be used for?
To divert the flow of blood to regions of the body that are demanding more oxygen
What are the features of a capillary?
Allow the exchange of materials between the blood and tissue fluid
Narrow lumen reduces diffusion pathway of oxygen to the tissues and increases resistance therefore reducing rate of flow
Walls that consist of a layer of flattened endothelial cells reducing diffusion distance for exchange
Leaky walls allowing blood plasma and substances to leave the blood
What are the features of a venule?
They collect the blood from the capillary bed and lead into the veins
Consists of thin layers of muscle and elastic tissue outside the endothelium, and a thin outer layer of collagen
How are veins adapted to carry blood back to the heart at low pressure?
Large lumen
Thinner layers of collagen, smooth muscle and elastic tissue than in artery walls as they don’t need to stretch and recoil
What is the main feature of veins?
They contain valves to help the blood flow back to the heart and to prevent it flowing in the opposite direction
How does surrounding skeletal muscle help the function of the valves?
It contracts which applies pressure to the blood, forcing the blood to move along a direction determined by the valves
What does blood plasma contain?
Dissolved substances
(oxygen, carbon dioxide, minerals, glucose, amino acids, hormones, plasma proteins)
Blood cells
(erythrocytes, leucocytes, platelets)
How is tissue fluid formed?
By blood plasma leaking from the capillaries:
At the arterial end of a capillary, the blood is at high hydrostatic pressure which pushes the blood fluid out of the capillaries through the capillary wall
This fluid consists of plasma with dissolved nutrients and oxygen as the rest of the cells are too large to be pushed out through the gaps in the capillary wall
The tissue fluid surrounds the body cells so that exchange can occur by diffusion, facilitated diffusion and active transport across the plasma membranes
What is the function of tissue fluid in regards to the body cells?
It exchanges gases and nutrients with them across the plasma membranes
Oxygen and nutrients enter the cells; carbon dioxide and other wastes leave
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How does tissue fluid return to the blood?
The blood pressure at the venous end of the capillary is much lower allowing some of the tissue fluid to return to the blood in the capillary carrying carbon dioxide and other wastes
Where does the tissue fluid that doesn’t return to the blood go?
Directed into the lymphatic system which drains the excess tissue fluid out of the tissues and returns it to the blood system in the subclavian vein
What is the fluid in the lymphatic system like?
It is called lymph and is similar in composition to the tissue fluid but contains more lymphocytes as these are produced in the lymph nodes
What are lymph nodes?
Swellings found at intervals along the lymphatic system which play an important part in the immune system
What is hydrostatic pressure and oncotic pressure?
Hydrostatic pressure is the pressure that a fluid exerts when pushing against the sides of a vessel
Oncotic pressure is the pressure created by the osmotic effects of the solutes
What effect do the hydrostatic and oncotic pressures of the blood and tissue fluid have on fluid and water?
Hydrostatic pressure of the blood pushes fluid out into the tissues
Hydrostatic pressure of the tissue fluid pushes fluid into the capillaries
Oncotic pressure of the blood tends to pull water back into the blood
Oncotic pressure of the tissue fluid pulls water into the tissue fluid
What is the net result of the forces from the hydrostatic and oncotic pressure?
A pressure to push blood out of the capillary at the arterial end and into the capillary at the venule end
What are the similarities and differences between the right and left side of the heart?
The right side pumps deoxygenated blood to the lungs to be oxygenated (pulmonary circuit)
The left side pumps oxygenated blood to the rest of the body (systemic circuit)
On both sides the heart squeezes the blood, putting it under pressure forcing it along the arteries and circulatory system
Where does the heart lie in humans?
Just off-centre towards the left of the chest cavity
What are the external features of the heart?
Cardiac muscle, ventricles (pumping chambers), atria (thin-walled chambers), coronary arteries and a number of tubular blood vessels
What do coronary arteries do?
Supply oxygenated blood to the heart muscle
What can happen if the coronary arteries become restricted?
Restricted blood flow reduces the delivery of oxygen and nutrients to the heart muscle potentially causing angina or a heart attack
What are the internal features of the heart?
Atria Vena cava Pulmonary vein Atrio-ventricular valves Ventricles Tendinitis cords Septum Pulmonary artery Aorta Semilunar valves
How are atria involved in the structure of the heart?
Two atria receive blood from the major veins - deoxygenated blood flows through the vena cava into the right atrium and oxygenated blood from the lungs flows through the pulmonary vein into the left atrium
From the atria, blood flows down through the atrio-ventricular valves into the ventricles
What are tendinous cords?
Cords attached to the atrio-ventricular valves which prevent them from turning inside out when the ventricle walls contract
What is the septum?
A wall of muscle that separates the ventricles from each other ensuring that oxygenated blood in the left side of the heart and the deoxygenated blood in the right side are kept separate
Describe how blood leaves the ventricles
Deoxygenated blood leaving the right ventricle flows into the pulmonary artery leading to the lungs where it is oxygenated
Oxygenated blood leaving the left ventricle flows into the aorta carrying blood to several arteries that supply all parts of the body
The semi-lunar valves prevent blood returning to the heart as the ventricles relax
How does blood pressure affect the structure of the atria?
The muscle of the atrial walls is thin because the chambers don’t need to create much pressure as their function is to receive blood from the veins and push it into the ventricles
Why are the walls of the right ventricle thicker than the walls of the atria?
It enables the right ventricles to pump blood out of the heart and to the lungs
Why doesn’t the blood being pumped out of the right ventricle need to be at very high pressure?
As the lungs are in the chest cavity next to the heart so the blood doesn’t need to travel very far
The alveoli in the lungs are also very delicate
Why can the walls of the left ventricle be much more thicker than the walls of the right ventricle?
The blood from the left ventricle is pumped out though the aorta and needs sufficient pressure to overcome the resistance of the systemic circulation
What do the cross-bridges produced by the cardiac muscle ensure?
That the stimulus is spread around the heart and that the muscle can produce a squeezing action rather than a simple reduction in length
How does the structure of cardiac muscle aid contraction?
The mitochondria between the muscle fibres supply energy for contraction
The muscle cells are separated by intercalated discs which facilitate synchronised contraction
What is the cardiac cycle?
The sequence of events in one full beat of the heart
What are the stages of the cardiac cycle?
ATRIAL SYSTOLE - Both atria contract, the muscle in the walls is thin so there is only a small increase in pressure which helps to push blood into the ventricles
VENTRICULAR SYSTOLE - Both ventricles pump together, contraction starts at the apex of the heart so that blood is pushed upwards towards the arteries
DIASTOLE - Walls of all chambers relax, elastic recoil causes the chambers to increase volume allowing blood to flow in from veins
What is the role of the valves?
To ensure that blood flows in the correct direction
How do valves open and close?
By changes in the blood pressure in the chambers of the heart
How do the atria-ventricular valves function?
After systole, the ventricular walls relax and recoil
Ventricular pressure drops below atrial pressure
Blood in the atria push the valves open
Blood entering the heart flows straight through the atria and into the ventricles
Atrial and ventricular pressure rises as they fill with blood
Valves remain open while atria contract and close when they relax
As systole begins ventricular blood pressure rises
When pressure rises above that in the atria, the blood moves upwards
This movement fills the valve pockets and keeps them closed preventing back flow
What is the closure of the atrio-ventricular valves caused by?
A swirling action in the blood around the valves when the ventricle is full
How do the semilunar valves function?
Before ventricular contraction the pressure in the major arteries in higher than the ventricles meaning the valves are closed
Ventricular systole raises the blood pressure in the ventricles and once it rises above that in the major arteries, the valves are pushed open
Blood is forced out under high pressure
Heart muscle starts to relax and elastic tissue in the walls recoils stretching out the muscle and returning the ventricle to original size
Pressure drops - once below that in the major arteries blood flows back towards ventricles
Valves are pushed closed by blood collecting in the pockets preventing blood returning to ventricles
What creates our pulse?
The pressure waves created when the left semilunar valve closes
How does the structure of the artery walls create an even flow?
Has a lot of elastic tissue close to the heart
When blood leaves the heart, the walls stretch
As blood leaves aorta, pressure in aorta drops
Elastic recoil helps to maintain blood pressure in aorta
The pressure drops further the further the blood flows along the arteries
Why is it important to maintain the pressure gradient between the aorta and arterioles?
It is what keeps the blood flowing towards the tissues
Why is the heart muscle described as myogenic?
Because it can initiate its own contraction and will contract and relax rhythmically even if it isn’t connected to the body
Why does the heart need a mechanism that can coordinate the contractions of all four chambers?
Because the atrial muscle contracts at a higher frequency than the ventricular muscle and so this property could cause fibrillation
What is fibrillation?
Uncoordinated contractions of the atria and ventricles
What is the sino-atrial node?
A patch of tissue at the top of the right atrium that generates electrical activity and initiates waves of excitation at regular intervals
How often do waves of excitation occur in humans?
55-80 times a minute
How does a wave of excitation cause an atrial systole?
Wave of excitation spreads over the walls of both atria
It travels along the membranes of the muscle tissue
As it passes, it causes cardiac muscles cells to contract
Why can’t waves of excitation spread directly down to the ventricle walls?
Because the tissue at the base of the atria is unable to conduct the wave of excitation
How is the wave of excitation conducted through to the ventricles?
It is conducted to the atrio-ventricular node where it is delayed allowing time for the atria to finish contracting and for the blood to flow down into the ventricles before they contract
How do the ventricles contract?
After the delay in the AVN, the wave of excitation is carried down the Purkyne tissue which runs down the septum
At the base of the septum, the wave spreads out over the ventricular walls then spreads upwards causes contraction
The ventricles contract from the apex pushing the blood towards the major arteries at the top of the heart
How can we monitor electrical activity of the heart?
By using an electrocardiogram involving attaching a number of sensors to the skin
Some of the electrical activity spreads through the tissues and outwards to the skin, the sensors then pick it up and convert it to a trace
What do the series of waves on the trace produced by an ECG represent?
P wave shows the excitation of the atria
QRS complex shows ventricular stimulation
T shows diastole
Name and explain some heart abnormalities
Bradycardia - slow heart rhythm
Tachycardia - fast heart rhythm
Atrial fibrillation - atria beating more frequently than ventricles, no clear P waves seen
Ectopic heartbeat - an extra beat or an early beat of the ventricles
What is haemoglobin?
The red pigment used to transport oxygen in the blood
What is produced when oxygen combines with haemoglobin?
Oxyhaemoglobin
What is the structure and function of haemoglobin?
Four subunits, each consisting of a polypeptide chain and a haem group containing a single iron ion which can attract and hold an oxygen molecule, having a high affinity for it
Each molecule can carry four oxygen molecules
How is oxygen transported from the lungs around the body?
Absorbed into the blood as it passes the alveoli
Diffuses into the blood plasma, enter erythrocytes and become associated with haemoglobin
This takes it out of solution maintaining a concentration gradient allowing more to enter the blood and diffuse into the cells
It is carried to the heart and then around the body to supply tissues for aerobic respiration
What does association and dissociation mean?
Association means that the oxygen binds reversibly to the haemoglobin
Dissociation means that oxyhaemoglobin is able to release the oxygen
What does haemoglobin’s ability to associate with and dissociate from oxygen depend on?
The concentration of oxygen in the surrounding tissues
What is the partial pressure of oxygen/oxygen tension?
The measure of the concentration of oxygen
Measured by the relative pressure oxygen contributes to a mixture of gases
Measured in kPa
Why does haemoglobin dissociation produce an S-shaped curve?
Due to haemoglobin not readily associating with oxygen at low partial pressures (low saturation level of haemoglobin at low partial pressures of oxygen)
As the partial pressure rises, the diffusion gradient into the haemoglobin increases and eventually one oxygen enters associating with one of the haem groups - causes a slight change in the shape of the haemoglobin allowing oxygen to enter and associate easily
As haemoglobin approaches 100% saturation the curve levels off
What is a conformational change?
The slight change in the shape of the haemoglobin molecule caused by an oxygen molecule associating with a haem group
Why is the partial pressure of oxygen low in respiring body tissues?
To cause oxygen to dissociate readily from the oxyhaemoglobin
Why is fetal haemoglobin different from adult haemoglobin?
It has a higher affinity for oxygen
Why does fetal haemoglobin produce a curve to the left of the curve for adult haemoglobin?
It has a higher affinity for oxygen because it must be able to associate with oxygen in an environment where the partial pressure of oxygen is low enough to make adult haemoglobin release oxygen
What 3 ways can carbon dioxide be transported to the lungs for excretion?
Dissolved directly in the plasma
Combined directly with haemoglobin to form carbaminohaemoglobin
Transported in the form of hydrogencarbonate ions
How is carbonic acid produced?
When carbon dioxide in the blood plasma diffuses into the erythrocytes and combines with water catalysed by carbonic anhydrase
What is chloride shift?
The movement of chloride ions from the blood into the erythrocyte which maintains the charge inside the red blood cell in the absence of hydrogencarbonate ions
What prevents the contents of erythrocytes becoming acidic due to the build up of hydrogen ions?
The haemoglobin acting as a buffer
The hydrogen ions are taken out of the solution by associating with haemoglobin to produce haemoglobinic acid
What is the Bohr effect?
The effect that extra carbon dioxide has on the haemoglobin, explaining the release of more oxygen
How does the Bohr effect describe the effect an increase of carbon dioxide has on haemoglobin?
Carbon dioxide enters the erythrocytes forming carbonic acid which dissociates to release hydrogen ions
These reduce the pH of the cytoplasm
This reduces haemoglobin’s affinity for oxygen and it is unable to hold as much
Oxygen is released from the oxyhaemoglobin to the tissues
What happens where tissues are respiring more?
There will be more carbon dioxide so more hydrogen ions will be produced making oxyhaemoglobin release more oxygen
What is the Bohr shift?
Dissociation curve changing in the presence of carbon dioxide
A dissociation curve reflecting haemoglobin becoming less saturated with oxygen when more carbon dioxide is present - it shifts downwards and to the right
