8 - Transport In Animals 🫀 Flashcards
Why are specialised transport systems needed?
- metabolic demands
- SA:V
- transporting molecules (hormones/enzymes/food)
- waste products need to be removed
Most circulatory systems have what features in common?
- a liquid transport medium that circulates around the body
- have vessels that carry the medium
- a pumping mechanism to move fluid around the system
What processes take place over the membrane?
- diffusion
- osmosis
- active transport
- endocytosis
- exocytosis
Give an example of animals with open circulatory systems
Molluscs 🦑
Arthropods
Give an example of animals with closed circulatory systems
Vertebrates
What is a mass transport system?
When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body
Where is blood pumped in an open circulatory system?
Straight from the heart into the body cavity of the animal (called the haemocoel)
In the haemocoel, what is the pressure of tbe transport medium?
The transport medium is under low pressure, and comes under direct contact with tissue and cells
How do the transport medium return to the heart in an open circulatory system?
Through an open-ended vessel
What is an ostium in insects?
pl = Ostia
A small opening
What is haemolymph?
A circulating fluid in the bodies of some invertebrates that is the equivalent of blood
What is haemocoel?
The system of cavities between the organs through which blood circulates in an open system
What is carried by haemolymph?
Food and nitrogenous waste
What is not carried by haemolymph?
Oxygen and carbon dioxide as insects have a tracheal system for that
What is the problem with haemolymph in an open system?
- steep diffusion gradients can’t be maintained
- amount of haemolymph flowing can’t be varied to meet demands
What happens when the heart relaxes in an open circulatory system in insects?
The haemolymph blood is sucked back in via ostia
What happens in closed circulatory systems?
Blood is enclosed in blood vessels and doesn’t come directly into contact with the cells of the body
How do substances leave and enter blood in a closed system?
By diffusion
How can the amount of blood flowing to a tissue be adjusted in a closed system?
By widening or narrowing blood vessels
Fish
What is the structure of the single closed circulatory systems in fish?
- heart has 2 chambers
- blood passes through 2 sets of capillaries: 1 gill capillaries and systemic capillaries
Fish
Why is low pressure needed?
As blood goes through 2 sets of narrow vessels, so pressure must be low to avoid damage
Fish
How come fish can cope with high metabolic demand with a single circulatory system?
- SHC of water is hard to change = fish don’t need to worry about temperature
- counter-current mechanism = efficient
- water supports body weight
What happens in a single circulatory system?
The blood travels through the heart and is pumped around the body once
In a single closed system, what does the blood exchange in the first set of capillaries it passes through?
Oxygen and carbon dioxide
In a single closed system, what does the blood exchange in the second set of capillaries it passes through?
Substances are exchanged between blood and cells
As a result of passing through two sets of narrow capillaries, what happens in a single closed system?
- blood pressure drops
- blood returns slowly to heart
- limits efficiency of exchange process
What is the most efficient system for transporting substances around the body?
Double closed circulatory system
What are the 2 separate circulations in a double system?
- blood is pumped from the heart to the lungs
- blood flows through the heart and is pumped around the body
Why is there higher pressure and fast flow of blood in a double system?
Each circuit only passes through one capillary network, so no need to slow down as much as in a single
Why do birds and mammals need need a double closed circulatory system?
They need to maintain their own body temperature, so require high metabolic demand
Advantages to a single circulatory system
- less complex
- doesn’t require complex organs
Advantages to a double circulation
- separates blood
- higher pressure
- fast flow of blood
- blood pumped further around body
Disadvantages of single circulation
- low blood pressure
- slow movement of blood
- activity level of the mammal tend to be lower
Disadvantages of double circulation
- highly complex in development
What are the 5 types of blood vessels?
- arterioles
- arteries
- capillaries
- venules
- veins
What do elastic fibres do in vessels?
- stretch and recoil
- providing flexibility to ease blood flow
What does smooth muscle do in vessels?
- contract and relax
- changes size of lumen
What does collagen do in vessels?
- provides structural support
- maintains shape and volume of vessel
What do arteries carry?
carry oxygenated blood away from the heart to tissues
When do arteries carry deoxygenated blood?
in the pulmonary artery on the way to the lungs, and during pregnancy in the umbilical artery, carrying blood from fetus to placenta
How does blood flow out of the heart?
expelled from the heart upon ventricular contraction, and flows through the arteries in repeated surges called pulses
What assists in maintaining the pressure in the artery?
smooth muscle and elastic fibres
How does the structure of a narrow lumen help an artery’s function?
- creates less volume = increases pressure
- maintains high blood pressure
How does a thick wall containing an outer layer of collagen help an artery’s function?
- to withstand high pressure to prevent the artery from rupturing
How does an inner layer of muscle and elastic fibres help an artery’s function?
- maintains pulse flow smoothly
- controls diameter of lumen
- does not pump blood
What does elastic do in artery walls?
- allows stretch and recoil
- evens out surges of blood pumped from hart to create a continuous flow
Why is the lining of an artery smooth?
so blood flows over it easily
What links arteries and capillaries?
arterioles
How are arterioles different to arteries?
have more smooth muscle and less elastin in their walls, as they have little pulse surge, but can constrict or dilate to control the flow of blood
What happens when smooth muscle in the arteriole contracts?
it constricts the vessel and prevents blood flowing into a capillary bed = vasoconstriction
What is vasodilation?
when the smooth muscle in the wall of an arteriole relaxes, blood flows through into the capillary bed
How does a very narrow diameter help a capillary’s function?
reduces blood flow to allow time for exchange between blood and surrounding cells to take place more efficiently
How does having thin walls only 1 cell thick help a capillary’s function?
ensures maximum rate of transfer between blood and surrounding tissue fluid (short diffusion pathway) as they don’t need to withstand high pressure
How does having walls have gaps (leaky walls) help a capillary’s function?
allows plasma and dissolved substances to leave the blood ()high permeability
What shows just how tiny capillaries are?
Red blood cells have to travel single file through them
Why do capillaries have such large gaps in their walls?
where many substances pass out of the capillaries into the fluid surrounding the cells
the exception of these gaps is in the CNS, which have very tight junctions between cells
What does it mean if the capillary wall is continous?
the capillary wall may be continuous with endothelial cells held together by tight junctions to limit permeability of large molecules
What does it mean if the capillary wall is fenestrated?
occurs in tissues specialised for absorption, the capillary contains pores
What does it mean if the capillary wall is sinusoid?
they have open spaces between cells and be permeable to large molecules and cells to allow large molecules to exchange
How does a very wide lumen (relative to wall thickness) help a vein’s structure?
maximises blood flow for more effective return
How does a thin wall containing less muscle/elastin but more collagen help a vein’s structure?
carries blood at low pressure (5-10mmHg) so doesn’t need to withstand high pressure
How does a vein having valves help its function?
prevents backflow and pooling
Why do veins not have a pulse?
the surges from hearts are lost at capillaries
Why do veins not have a pulse?
the surges from hearts are lost at capillaries
What do several venules rejoin to form?
one vein
What do venules contain?
no elastin fibres or smooth muscle, only collagen for structural support
What % of your blood volume is in your veins at any 1 time?
60%
What are the 3 adaptations of veins to move blood against gravity?
- 1-way valves that close if blood starts to flow back
- bigger veins run between big, active muscles in body so when the muscle contracts, the veins are squeezes
- the breathing movements of the chest act as a pump as the pressyre changes and squeezing actions move blood
What are varicose veins?
- a vein wall becomes weakened, valves may no longer close properly
- this allows backflow of blood causing vein to become enlarged and bumpy
- usually happens to surface veins
What does blood consist of?
Plasma
What does plasma contain?
- dissolved glucose
- amino acids
- mineral ions
- hormones
- plasma proteins
- albumin
- fibrinogen
- globulins
What does albumin do in the blood?
Important for maintaining the osmotic potential of the blood
What does fibrinogen do in the blood?
Important in blood clotting
What does globulin do in the blood?
Involved in transport and the immune system
How are platelets carried?
By plasma in the blood
What are platelets?
Fragments of large cells called megakaryocytes found in the red bone marrow
What does blood transport?
- oxygen and CO2
- digested food
- nitrogenous waste
- chemical messages (hormones)
- food molecules from storage
- platelets to damaged areas
- cells and antibodies
What roles does the blood do?
- defence
- thermoregulation
- maintaining pH of body fkuids
What % of the blood is plasma?
55%
What % of the blood is red blood cells?
45%
What % of the blood is buffy coat and what does it contain?
<1%
Contains white blood cells and platelets
Why would you examine a buffy coat?
To look for abnormal white blood cells such as a mast cell
What is the buffy coat?
The fraction of anticoagulated blood that contains most of the white blood cells and platelets following density gradient centrifugation
What are the main electrolytes in blood?
Sodium, chloride, potassium, magnesium, calcium
Why should capillary walls be impermeable?
As solutes lower w.p., so should be impermeable as to not lower w.p. of cells, reducing w.p. gradient for diffusion
What does albumin do in the blood?
give the blood a relatively high solute potential, so low w.p. compared with surrounding fluid
What does a low w.p. in blood in capillaries cause to happen?
Water moves into the blood from the surrounding fluid by osmosis
Define oncotic pressure
The tendency of water to move into the blood by osmosis at -3.3kPa
What is tissue fluid and how is it formed?
Extracellular fluid that comes from substances that leak out of blood capillaries via fenestrations
What is the hydrostatic pressure as the blood arrives at the arteriole end of capillaries?
- Hydrostatic pressure forces fluid out of the capillaries (4.6kPa)
- This is higher than oncotic pressure attracting water in by osmosis
- so fluid is squeezed out if capillaries
- new flow out
What is the hydrostatic pressure as the blood reaches the venous of the capillary?
- Hydrostatic pressure falls to 2.3kPa in the vessels as fluid moves out and pulse is lost
- the oncotic pressure is now stronger than hydrostatic
- so water moves back into capillaries by osmosis
- net flow in
By the time blood returns to the veins, what % of tissue fluid is back in blood vessels
90% - the other 10% is used to bathe cells
Does oncotic pressure ever change?
No remains at -3.3kPa
Tissue fluid has what composition?
Same as plasma except cells and plasma proteins
What happen to the 10% of tissue fluid that leaves the blood vessels?
It drains ins or a system of blind-ended tubes called lymph capillaries, where it is known as lymph
What is lymph’s composition?
Similar to plasma/tissue fluid but has fewer oxygen and nutrients
Lymph also contains fatty acids
How does lymph end up with fatty acids in it?
They have been absorbed him to the lymph from the villi of the small intestine
Name some major lymphatic organs
Spleen, tonsils, thymus and adenoids
What is the lymphatic systems role?
- immune function
- absorbing fats from gut
- lipid transport
- maintaining viable blood pressure
What are the characteristics of lymph capillaries?
- separate from circulatory system
- closed ends and large pores
- valves prevent back flow
How does lymph return to the blood eventually?
Flowing into the right and left subclavian veins (under the collar bone)
How is lymph transported in lymph capillaries?
By the squeezing of body muscles
What would happen in plasma proteins weren’t removed from tissue fluid?
They would lower w.p. of the tissue fluid and prevent the reabsorption of water into the blood from capillaries
After digestion, where are lipids transported?
From the intestines to the blood stream by the lymph system
What do lymph nodes do?
- allow lymphocyte to gather
- intercept bacteria and other debris from lymph which are ingested by phagocytes
- defence mechanism
Where are lymph nodes found?
Along lymph vessels
What actually IS lymph?
A clear fluid that contains white blood cells
What do enlarged lymph nodes mean?
That the body is fighting off an invading pathogen
Why would the loss of the lymphatic system be fatal within a day?
It wouldn’t drain excess fluid, so our tissue would swell, blood volume would be lost and pressure would increase
The Heart
What is the pericardium?
An inelastic double-walled sac containing the heart and the roots of the great vessels
The Heart
What is the pericardium’s role?
- creates a closed chamber with sub atmospheric pressure that aids atrial filling and prevents it from distending
- shields heart by reducing external friction
- acts as a barrier against infection
The Heart
What is the left side of the heart thicker?
- must pump blood at higher pressure over a further distance to whole body
- has to overcome resistance of aorta and arterial systems of body
The Heart
What is the structure of the heart?
Inferior / superior vena cava
Right atrium
Tricuspid AV valve
Right ventricle
SL valve
Pulmonary artery
Lungs
Pulmonary vein
Left atrium
Bicuspid AV valve
Left ventricle
SL valve
Aorta
The Heart
What does it mean if cardiac muscle is myogenic?
It has its own beat - they contract involuntarily
The Heart
Why does cardiac muscle have more mitochondria?
Cardiac muscle is more reliant on aerobic respiration than skeletal muscle
The Heart
Why are cardiac muscle cells branched?
- faster signal propagation
- contraction in 3 dimensions
The Heart
How is cardiac muscle connected?
By gap junctions at intercalated discs
The Heart
Does heart tissue ever get fatigued?
No
The Heart
What are the vessels that supply the heart called
Coronary artery
The Heart
What stops the valves from inverting?
Tendons
The Heart
How long does each stage of the cardiac cycle take?
Atrial systole = 0.1 sec
Ventricular systole = 0.3 secs
Diastole = 0.4 secs
The Heart
What is meant by systole and diastole?
Systole = contraction
Diastole = relaxtion
The Heart
What happens in atrial systole?
- muscle contracts, increasing pressure in ventricles
- blood flows from atrium to ventricles
- AV valves open as blood is forced through
- SL valves shut
The Heart
What happens in ventricular systole?
- atrium is relaxed
- ventricle contracts
- pressure exceeds atrial pressure
- both AV valves shut, increasing pressure
- SL valves open to decrease pressure
The Heart
What happens in diastole?
(It’s passive)
- pressure in ventricles decreases
- as ventricular pressure drops below arterial pressure, SL valves shut
- all heart muscles relax
- AV valves open
- blood pressure increases as blood flows into atria
The Heart
What makes the first ‘lubb’ sound of the heart?
Closure of AV valves at start of ventricular systole
The Heart
What makes the second ‘dupp’ sound?
Closure of SL valves at start of ventricular diastole
The Heart
What is the septum?
The inner dividing wall of the heart preventing the mix of oxygenated and deoxygenated blood
The Heart
Pressure changes
When does aortic pressure rise?
When ventricles contract as blood is forced into aorta, but it gradually falls again as it moves the blood
The recoil of the elastin produces a temporary rise in pressure at the start of the relaxation phase
Never dropped below 12kPa
The Heart
Pressure changes
When does atrial pressure change?
It is always relatively low, because the thin walls of the atrium can’t create much force
Highest when atria are contracting but drops when AV valves close and it’s walls relax
Filling of blood increases pressuree
The Heart
Pressure changes
When does ventricular pressure change?
Low at first but gradually increases as atria contracts
Left AV valves close and pressure rises dramatically due to thick muscle walls
When ventricular pressure is above pressure of aorta, blood is forced past SL valves to aorta
The Heart
Pressure changes
How does ventricular volume change?
Rises as the atria contract and ventricles fill with blood, but suddenly drops as blood moves into aorta
The Heart
What is the bpm of pacemaker cells?
60bpm - anything higher has input from the brain
The Heart
What do pacemaker cells do?
Ensure heart beats in Union
The Heart
What does the sino-atrial node do?
Sends out a wave of electrical activity (depolarisation) which are propagated throughout the entire atria via gap junctions in the intercalated discs
The Heart
What does cardiac muscle do in response to the SAN depolarisation?
Cardiac muscle within atrial walls contract almost simultaneously = atrial systole
Forces blood through AV valves
The Heart
What does the AVN do?
Picks up the wave from SAN but imposes a slight delay before sending its own wave of depolarisation down the Bundle of His into the Purkyne fibres
The Heart
Why does the AVN impose a delay on the SAN signal?
Delay allows time for ventricles to fill before AV valves close, increasing efficiency
The Heart
What happens once the depolarisation has travelled to Purkyne fibres?
The ventricular walls contract, starting at the apex and forcing blood up and out of heart to lungs/body
The Heart
Why is the refractory period?
After every contraction, there’s a period of insensitivity to stimulation to allow the heart to refill passively and prevent fatigure
The Heart
What is the recording of electrical activity of the heart called?
Electrocardiogram (ECG)
The Heart
What does an ECG actually measure?
Tiny electrical differences in your skin, which result from electrical activity in the heart
The Heart
ECG
What is the P wave?
Depolarisation if the atria in response to SAN
The Heart
ECG
What is the QRS complex?
Depolarisation of the ventricles triggered by the AVN
The Heart
ECG
What happens at the PR interval?
A delay to allow filling of ventricles
The Heart
ECG
What is the ST segment?
Blood flows
The Heart
ECG
What is the T wave?
Repolarisation of the ventricles and the completion of a standard heart beat
The Heart
Formula for cardiac output and units
Stroke volume x heart rate
cm3/min
The Heart
Heart conditions
What is Tachycardia?
Elevated rested heart rate (>120bpm)
The Heart
Heart conditions
What is Bradycardia?
Depressed resting heart rate (<40bpm)
The Heart
Heart conditions
What is Arrhythmias?
Irregular heart beats
The Heart
Heart conditions
What are fibrillations?
Unsynchronised contractions of either atria or ventricles leading to dangerous spasmodic heart activity
The Heart
Heart conditions
What is an ectopic heart beat?
Altered rhythm - an extra beat then a gap
How are erythrocytes adapted for their function to carry oxygen?
- biconcave shape = large SA
- small = fit through capillaries
- no nuclei = more space for haemoglobin
What is haemoglobin?
Large, globular, conjugated protein with 4 peptide chains, each with an iron-containing haem prosthetic group
What is the reversible reaction to form oxyhaemoglobin?
Hb + 4O2 = Hb(O2)4
What is positive cooperativity?
The binding of oxygen to haemoglobin alters the shape of haemoglobin, making it easier for the next oxygen to hind
How many oxygen can bind to haemoglobin?
8
What happens when the blood reaches body tissues with the concentration of oxygen?
Conc of oxygen in cytoplasm of the body cells is lower than in the erythrocytes, so oxygen moves out of the erythrocytes down a gradient
Why is oxygen loaded in the lungs?
Haemoglobin has a higher affinity for O2 in oxygen rich areas = lungs
This promotes oxygen loading = rapid loading
Why is oxygen unloaded in tissues?
Haemoglobin will have a lower affinity for O2 in oxygen-starved areas, promoting rapid oxygen unloading
What is plotted on an oxygen dissociation curve?
The % saturation of oxygen (y-axis)
Oxygen partial pressure (x-axis)
This shows the affinity of Hb for O2
What shape is the oxygen dissociation curve for adults?
Sigmoidal (S-shaped) due to cooperative binding
Why does the dissociation curve level out at higher partial pressures of oxygen?
All the haem groups are bound to oxygen and so the haemoglobin is saturated and can’t take up any more
Why does a very small change in the partial pressure of oxygen make a significant difference to saturation of Hb?
Due to positive cooperativity
How much oxygen is released by erythrocytes when you’re not very active?
Only about 25% of oxygen is released as the rest acts as a reservoir for when demands increase
Different globins
How does foetal haemoglobin differ from adult haemoglobin?
- foetal has a higher affinity for O2
- because maternal haemoglobin must unload the oxygen at a given partial pressure
- so the foetal haemoglobin can load it over a diffusion gradient
Different globins
What would happen if foetal and adult haemoglobin had the same affinity for O2?
Then little to no oxygen would be transferred to the blood of the foetus as there would be no affinity difference
Different globins
What is myoglobin?
Oxygen-binding molecule in muscles made of a single polypeptide with 1 haem group (so can’t cooperatively bind)
Different globins
How does the affinity of myoglobin differ to adult and foetal?
Has a higher affinity so curve is to the left
Different globins
Why is it important myoglobin has a higher affinity?
So it holds oxygen longer, so aerobic respiration occurs, not anaerobic in muscles
Different globins
When does myoglobin release oxygen?
When oxygen partial pressure falls to reduce the chance of anaerobic respiration
What is the Bohr Effect?
At lower pH values, Hb gives up oxygen more easily
The Bohr Effect
What happens at active tissues?
- higher partial pressure of CO2 and lower pH
- oxygen given up more readily
The Bohr Effect
What happens at the lungs?
- lower partial pressure of CO2
- oxygen binds more easily
The Bohr Effect
Why does the Bohr Effect move the dissociation curve to the right?
A decrease in pH shifts the oxygen dissociation curve to the right
The Bohr Effect
Why is pH lower at respiring tissues?
As partial pressure of CO2 rises, pH decreases due to protons making it more acidic
How is CO2 transported in the lungs?
- 5% is carried dissolved in plasma
- 10-20% is bound to a.a. in haemoglobin to form carbaminohaemoglobin
- 75-85% is converted into hydrogen carbonate ions in erythrocytes
What does CO2 form when it reacts with water?
Carbonic acid
What does newly formed carbonic acid do?
Dissociates to form hydrogen ions and hydrogen carbonate ions
What enzyme is in high levels in erythrocytes, catalysing the formation of carbonic acid?
Carbonic anhydrase
What happens to the negatively charged hydrogen carbonate ions once they’re produced?
Move out of the erythrocytes into the plasma by diffusion down grad and negatively charged chloride ions move into erythrocytes = chloride shift
Why does the chloride shift occur?
To maintain the electrical balance of the erythrocytes
Why do erythrocytes remove CO2 and convert it into hydrogen carbonate ions?
To maintain a steep conc grad for CO2 to diffuse from the respiring tissues
What does HCO3- (hydrogen carbonate ions) do once it has diffused out of erythrocyte in plasma?
Combines with sodium to form sodium bicarbonate which travels to the lungs
What is the effect of hydrogen ions in an erythrocyte?
- make environment more acidic
- causes haemoglobin to release O2
- haemoglobin absorbs H+ ions
- haemoglobin acts as a buffer
What happens when blood reaches the lung tissue with a low conc of CO2?
Carbonic anhydrase catalyses the reversible reaction, breaking down carbonic acid into CO2 and water
What happens to chloride ions when CO2 diffuses out of erythrocytes?
Chloride ions diffuse back into the plasma down an electrochemical gradient
How does haemoglobin act as a buffer?
Prevents change in pH by accepting free H+ ions in a reversible reaction to form haemoglobinic acid
