biology module 3 transport in animals

why do living organisms have the need to exchange substances with their surrounding environment

They need to take oxygen and nutrients in

Waste products generated need to be released

what is mass flow

the bulk movement of materials

what do mass transport systems help do

Bring substances quickly from one exchange site to another

Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings

Ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range

difference between single and double circulatory systems

In a single circulatory system, the blood passes through the heart once during one complete circuit of the body

In a double circulatory system, the blood passes through the heart twice during one complete circuit of the body

single circulatory system in fish

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

Double circulatory system in mammals

In mammals the blood passes throught the heart twice during a single circuit of the body

As a result the mammalian heart has a left side and right side with a wall (septum) dividing the two

The left side contains oxygenated blood and the right side contains deoxygenated blood

Blood in the right side of the heart leaves and travels to the lungs

The blood returns to the left side of the heart before being pumped around the rest of the body

Once the blood has passed through all the other organs and tissues it returns to the right side of the heart

In general, any blood that has just passed through an organ goes straight back to the heart, not to another organ

The hepatic portal vein is the exception to this rule, it allows blood from the gut to flow to the liver

the heart

a hollow, muscular organ located in the chest cavity which pumps blood. cardiac muscle tissue is specialised for repeated involuntary contraction without rest

arteries

blood vessels which carry blood away from the heart. the walls of the arteries contain lots of muscle and elastic tissue and a narrow lumen, to maintain high blood pressure. arteries range from 0.4 to 2.5 cm in diameter

arterioles

small arteries which branch from larger arteries and connect to capillaries.

capillaries

tiny blood vessels which connect arterioles and venules. their size means they pass directly past cells and tissues and perform gas exchange and exchange of substances such as glucose

venules

small veins which join capillaries to larger veins

veins

blood vessels which carry blood back towards the heart. thin walls in comparison to arteries, having less muscle and elastic tissue but a wider lumen. valves help maintain blood flow back towards the heart

advantages of double circulation

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

closed vs open circulatory systems

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

circulatory systems in humans

Humans have a closed double circulatory system

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

what is plasma

a straw-coloured liquid that constitutes around 55 % of the blood

Plasma is largely composed of water (95 %) and because water is a good solvent many substances can dissolve in it, allowing them to be transported around the body

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

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

what happens 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

what happens 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

what happens if the blood pressure is high

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

formation of lymph

Some tissue fluid reenters the capillaries while some enters the lymph vessels

The lymph vessels are separate from the circulatory system

They have closed ends and large pores that allow large molecules to pass through

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

when do valves in the heart open and close

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

why are valves important

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

what are the right atrium and right ventricle separated by

the atrioventricular valve, which is otherwise known as the tricuspid valve

what are the right ventricle and pulmonary artery separated by

the pulmonary valve

what are the left atrium and the left ventricle separated by

the aortic valve

coronary arteries

The heart is a muscle and so requires its own blood supply for aerobic respiration

The heart receives blood through arteries on its surface, called coronary arteries

It’s important that these arteries remain clear of plaques, as this could lead to angina or a heart attack (myocardial infarction)

what is the cardiac cycle

the series of events that take place in one heart beat, including muscle contraction and relaxation

what is systole

contraction of the heart

what is diastole

relaxation of the heart

how do volume changes in the heart occur

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

how are volume changes linked to pressure changes

When volume decreases, pressure increases

When volume increases, pressure decreases

events of the cardiac cycle - 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

events of the cardiac cycle - ventricular 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

events of the cardiac cycle - 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

Valve movements during the cardiac cycle

Stage in cardiac cycle Atrioventricular valves Semilunar valves

Atrial systole Open Closed

Ventricular systole Closed Open

Diastole Open Closed

what does it mean when they say the control of the basic heartbeat is myogenic

the heart will beat without any external stimulus

stages of cardiac cycle

1. sinoatrial node sends out a wave of extinction

2. atria contract

3. atrioventricular node sends out a wave of excitation

4. purkyne tissue conducts the wave of extinction

5. ventricles contract

explain the letters in this diagram

• The P wave

  • Caused by the depolarisation of the atria, which results in atrial contraction (systole)

• The QRS complex

  • Caused by the depolarisation of the ventricles, which results in ventricular contraction (systole)

  • This is the largest wave because the ventricles have the largest muscle mass

• The T wave

  • Caused by the repolarisation of the ventricles, which results in ventricular relaxation (diastole)

• The U wave

  • Scientists are still uncertain of the cause of the U wave, some think it is caused by the repolarisation of the Purkyne fibres

tachychardia

• When the heart beats too fast it is tachycardic

• An individual with a resting heart rate of over 100 bpm is said to have tachycardia

Bradycardia

• When the heart beats too slow it is bradycardic

• An individual with a resting heart rate below 60 bpm is said to have bradycardia

• A lot of fit individuals or athletes tend to have lower heart rates and it is usually not dangerous

Ectopic heartbeat

This condition is caused by an early heartbeat followed by a pause

It is common in the population and usually requires no treatment unless very severe

fibrillation

An irregular heartbeat will disrupt the rhythm of the heart

Severe cases of fibrillation can be very dangerous, even fatal

the role of haemoglobin - transport of oxygen

• The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells

  • Red blood cells are also known as erythrocytes

• Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen

  • This means that each molecule of haemoglobin can carry four oxygen molecules, or eight oxygen atoms in total

role of haemoglobin - carbon dioxide transport

Waste carbon dioxide produced during respiration diffuses from the tissues into the blood

There are three main ways in which carbon dioxide is transported around the body

A very small percentage of carbon dioxide dissolves directly in the blood plasma and is transported in solution

Carbon dioxide can bind to haemoglobin, forming carbaminohaemoglobin

A much larger percentage of carbon dioxide is transported in the form of hydrogen carbonate ions (HCO3-)

formation of hydrogen carbonate ions

• Carbon dioxide diffuses from the plasma into red blood cells

• Inside red blood cells carbon dioxide combines with water to form H₂CO₃

CO₂ + H₂O  ⇌  H₂CO₃

• Red blood cells contain the enzyme carbonic anhydrase which catalyses the reaction between carbon dioxide and water

  • Without carbonic anhydrase this reaction proceeds very slowly

  • The plasma contains very little carbonic anhydrase hence H₂CO₃ forms more slowly in plasma than in the cytoplasm of red blood cells

• Carbonic acid dissociates readily into H⁺ and HCO₃^- ions 

H₂CO₃  ⇌  HCO₃^– + H⁺

• Hydrogen ions can combine with haemoglobin, forming haemoglobinic acid and preventing the H⁺ ions from lowering the pH of the red blood cell

  • Haemoglobin is said to act as a buffer in this situation

• The hydrogen carbonate ions diffuse out of the red blood cell into the blood plasma where they are transported in solution

the chloride shift

• The chloride shift is the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed

• Hydrogen carbonate ions are formed by the following process

  • Carbon dioxide diffuses into red blood cells 

  • The enzyme carbonic anhydrase catalyses the combining of carbon dioxide and water to form carbonic acid (H₂CO₃)

CO₂ + H₂O ⇌ H₂CO₃ 

• Carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions

H₂CO₃ ⇌ HCO₃^- + H⁺

 

• 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

  • If this did not occur then red blood cells would become positively charged as a result of a buildup of hydrogen ions formed from the dissociation of carbonic acid