BY2 - Adaptations for transport in animals

All transport systems have: 

a suitable medium to carry materials

a pump for moving blood

valves to maintain the flow in oen direction

Some transport systems have:

a respiratory pigment to increase volume of O2 that can be transported

a system of vessels with a branching network, distribute transport medium to all body parts

The blood does not move aorund the body in blood vessels, it bathes the tissue directly whilst held in a cavity, haemocoel

e.g. insects - have a long, dorsal tube-shaped heart running the length of the body. It pumps blood out into haemocoel, where materials are exchanged between blood and body cells. Blood returns slowly to heart and open circulation repeats.

The blood moves in blood vessels

In a single circulation system, the blood moves through the heart once in its passage around the body.

e.g. in earthworm, blood moves forward in dorsal vessel, and back in ventral vessel. Five pairs of pseudohearts, thickened, musclar blood vessels, pump blood from dorsal to ventral vessel, keeping it moving

The blood passes through the heart twice in its circuit around the body. 

e.g. mammals

It serves the lungs. The right side of the heart pumps deoxygenated blood to the lungs, oxygenated blood returns from the lungs to the left side of the heart.

It serves the body tissues. The left side of the heart pumps the oxygenated blood to the tissues. Deoxygenated blood from the body returns to the right side of the heart. 

Arteries, veins and capillaries

Arteries and veins have the same basic three-layered structure, however the proportions vary.

Endothelium - the innermost layer, one cell thick and is surrounded by tunica intima. It is a smooth lining, reducing friction with a minimum reistance to blood flow

Tunica media - the middle layer which contains elastic fibres and smooth muscle. It's thicker in arteries than in veins. In arteries the elastic fibres allow stretching to accommodate changes in blood flow and pressure. Stretched elastic fibres recoil to push blood through artery.

Tunica externa - the outer layer, contains collagen fibres which resist overstretching.

They carry blood away from the heart. Their thick, musclar walls withstand bloods high pressure. Branch into smaller vessels, arterioles, further subdivide into capillaries.

They form a vast network, that penetrates all the tissues and organs of the body. Blood from capillaries collects into venules, which take blood into veins, which return it to the heart.

They have a large diameter lumen, and thinner walls with less muscle than arteries. The blood pressure and flow rate are lower. 

They have thin walls, one layer of endothelium on a basement membrane. Pores between cells make them pemeable to water and solutes. They have a small diameter and rate of blood flow slows down. So many capillaries in a capilly bed so reduces the rate of exchange of materials with the surrounding tissue fluids.

A pump to circulate blood, can be thought of as two separate pumps one dealing with oxygenated and one dealing with deoxygenated

Two relatively thin-walled collection chambers, the atria, which are above two thicker-walled pumping chambers, the ventricles, allowing separation of oxygenated and deoxygenated blood

Heart consists of cardiac muscle, myogenic contraction

It contracts and relaxes rhythmically, but never tires

Atrial systole, ventricular systole and diastole

The atrium walls contract, blood pressure in atria increases. Pushes blood through tricuspid and bicuspid valves, down into ventricles where are relaxed

The ventricle walls contract, increase the blood pressure in the ventricles. Forces blood up through semi-lunar valves, out of heart, into pulmonary artery and aorta.

Blood cannot flow back from ventricles to atria as tricuspid and bicuspid valves are closed.

Pulmonary artery carries deoxygenated blood to the lungs, aorta carries oxygenated blood to the rest of the body.

Ventricles relax, volume of them increases so pressure falls

Risks the blood in the pulmonary artery and aorta flowing backwards into ventricles, tendency to flow backwards causes the semi-lunar valves at their bases to shut to prevent blood re-entering

Atria relax so blood from vena cavae and pulmonary veins enters the atria, cycle restarts

Left atrium relaxes, recieves oxygenated blood from pulmonary vein

When full, pressure forces bicuspic valve open between atrium and ventricle

Relaxation of left ventricle draws blood from left atrium

Left atrium contracts, pushes blood into left ventricle, through the valve

With left atrium relaxed and biscupid valve closed, left ventricle contracts, exerts high pressure.

Pressure pushes blood up out of the heart, through semi-lunar valves into aorta, closes bicuspid valve, prevents backflow of blood into left atrium

Wave of electrical stimulation arises at sino-atrial node, spreads over both atria, they contract

Electrical stimulation only spreads to ventricles. The atrio-ventricular node introduces a delay in the transmission of electrical impulse. Ventricle muscles don't contract until atria muscles finish

Atrio-ventricular node passes excitation down nerves of bundle of His, the left and right bundle branches to the apex of the heart. Excitation is transmitted to Purkinje fibres in venricle walls, carry it upwards through muscles of ventricle walls

Impulse causes cardiac muscle in each ventricle to contract, from apex upwards

Pushes blood up to aorta and pulmonary artery, empties ventricles completely 

P wave shows voltage change generated by sino-atrial node, contraction of atria (small waves)

PR interval is the time taken for excitation to spread from atria to ventricles through atrio-ventricular node

QRS complex shows depolarisation and contraction of ventricles (amplitude bigger than P wave)

T wave shows repolarisation of ventricle muscles. ST segment lasts from end of S wave, to beginning of T wave

The line between T wave and P wave of next cycle is baseline of trace, isoelectric line

Atrial fibrillation has a rapid heart rate - may lack a P wave

Heart attack - wide QRS complex

Enlarged ventricle walls - QRS complex showing greater voltage change

Insufficient blood being delivered to heart muscle - changes in height of ST segment and T wave

Cells 45% and plasma 55%

Erythrocytes, contain haemoglobin to transport oxygen from lungs to respiring tissues

Biconcave discs, surface area larrger so more oxydgen diffuses across membrane, reduces diffusion distance due to thin centre

No nucleus, more room for haemoglobin maximising oxygen that can be carried

A pale yellow liquid about 90% water

Contains solutes, hormones and plasma proteins

Distributes heat

Haemoglobin associates readily with oxygen where gas exchange takes place (alveoli), and readily dissociates from oxygen at respiring tissues (muscle)

It changes its affinity for oxygen, as it changes it shape (degree of attraction)

Each haemoglobin molecule has 4 haem groups, one oxygen molecule can bind to each iron ion, four molecules can bind

First oxygen molecule changes shape, making it easier for second. Second oxygen molecule changes shape again, makes it easier for third. Third doesn't change the shape, takes a large increase in oxygen partial pressure to bind fourth oxygen molecule

At very low oxygen partial pressure, difficult for haemoglobin to load oxygen

At high oxygen partial pressure, percentage saturation of oxygen is very high

In the lungs where oxygen partial pressure is high, haemoglobin becomes saturated with oxygen

Cells carry oxygen as oxyhaemoglobin to respiring tissues where partial pressure of oxygen is low as oxygen is being used up in respiration

Oxyhaemoglobin unloads its oxygen, dissociates

To the left of adult haemoglobin 

It absorbs oxygen from maternal haemoglobin at plactena, has a higher affinity for oxygen as same partial pressure for oxygen

Blood flows close in placenta, oxygen transfers to fetus's blood at any partial pressure of oxygen, % saturation of fetus's blood is higher than mothers

If CO2 concentration increases, haemoglobin releases oxygen more readily

At any oxygen partial pressure, haemoglobin is less saturated with oxygen, dissociation curve is lower

Curve moves to right, Bohr effect

Accounts for unloading of oxygen from oxyhaemoglobin in respiring tissues, where partial pressure of CO2 is high and O2 is needed

In solution in plasma

As hydrogen carbonate ion, HCO3-

Bound to haemoglobin as carbamino-haemoglobin

1) CO2 in blood diffuses into red blood cell

2) Carbonic anhydrase catalysed combination of CO2 with H2O, makes carbonic acid

3) Carbonic acid dissociates into H+ and HCO3- ions

4) HCO3- ions diffuse out of red blood cells into plasma

5) Balance outflow of - ions and maintain electrochemical neutrality, chloride ions diffuse into red blood cell from plasma - chloride shift

6) H+ ions cause oxyhaemoglobin to dissocate into oxygen and haemogloin. H+ ions combine with haemogloin to make haemoglobinic acid, HHb. Removes hydrogen ions so pH of red blood cells doesn't fall

7) Oxygen diffuses out of red blood cells into tissues

Have thin, permeable walls

Provide a large surface area for exchange of materials

Blood flows through them very slow, allows time for exchange

It is forced through capillary walls as tissue fluid and bathes the cells to supply them with solutes

Tissue fluid removes waste made by cells

Diffusion of solutes in and out of capillaries relates to bloods hydrostatic pressure and solute potential

Blood under pressure from heart and muscle contraction. High hydrostatic pressure pushes liquid outwards frm capillaries to spaces between cells

Plasma has a low solute potential and pulls water back into capillary, by osmosis

Hydrostatic pressure is greater than plasma's solute potential, water and solutes forced out through capillary walls into spaces between cells

Solutes are used during cell metabolism, concentration in/around cells is low, but in blood is higher. Favours diffusion from capillaries to tissue fluid

Bloods hydrostatic pressure is lower than at arterial end as fluid has been lost

Plasma proteins more concentrated in blood as much water has been lost, solute potential of plasma is more negative. Osmotic force pulls water in is greater than hydrostatic force pushing water out, water passes back into capillaries by osmosis

Tissue fluid surrounding cells picks up CO2 and other wastes, diffuses down a concentration gradient into capillaries

Not all fluid passes back into capillaries, 10% drains into blindy-ending lympth capillaries of lymphatic system. Fluid is lymph. Eventually returns to venous system through thoracic duct, empties into left subclavian vein above heart