BY2: Transport In Animals

A transport system must:
-A suitable medium (i.e. blood) for carrying materials.
-A closed system of vessels that contain blood and distributions to all parts of the body.
-A pump (i.e. heart) for moving the blood.
-Valves to maintain flow.
-A respiratory pigment, to increase volume of oxygen transported.

Open Systems (i.e. Insects)
-Low pressure from one main tube-shaped heart.
-Blood is pumped into haemocoel where it bathes the tissues for exchanging materials.
-There is no respiratory pigment as they transport oxygen via the tracheae.
Closed Systems (i.e. Mammals)
-High pressure and rapid flow rate.
-Blood circulates in a continous system of tubes.
-Organs are not in direct contact with the blood.
-There is a respiratory pigment to aid oxygen transportation. 

Earthworms have a close circulation system, with dorsal and ventral vessels; connected by five 'pseudohearts'.

Single Circulations (i.e. Fish)
-Heart pumps deoxygenated blood to the gills, and oxygenated blood to the tissues.
-Blood goes through the heart once each circulation.

• Mammals have a double circulatory system, blood passes twice through the heart.
• When the blood reaches the lungs the pressure is reduced, requiring to be pumped again.
• It goes as follows:
  -The pulmonary circulation - the right side->deoxygenated to lungs->oxygenated to the heart.
  -Systemic circulation - the left side->oxygenated to tissues->deoxygenated to the heart.
  -In each circuit the blood passes the heart twice, once left and once right; meaning higher pressure.

• There are three type: arteries, veins, and capillaries.
• Arteries and veins have the same basic three-layered structure with different proportions.
  -The innermost layer is the endothelium, smooth lining to reduce friction.
  -The middle is made up of elastic fibres and smooth muscle, thicker in the arteries than in the veins to accomodate blood flow and pressure changes.
  -The outer is the tunica externa, made up of collogen fibres to stop overstretching.
• Capillaries have only a layer of endothelium.

• Arteries carry blood away from the heart, having thick muscular walls to withstand the high pressure of blood.
• Arteries contract to maintain blood flow, they also branch into smaller vessels call atrioles that further divide into capillaries.
   
• Veins have larger diameters and thinner walls than arteries due to lower pressure.
• Veins have semi-lunar valves along their length to ensure one-way flow.
  
  
• Capillaries are thin walled so they are permeable to water and dissolved substances.
• They have a small diameter and friction with the walls slows the blood flow.
• Their low velocity enhances ability to exchange materials. 

• A pump to circulate blood is an essential feature of a circulatory system.
• Consisting of:
  -A thin-walled collection chamber.
  -A thick-walled pumping chamber, split into two; allowing the complete seperation of deoxygenated/oxygenated blood. In summary there are two pumps, with two chambers an upper atrium and a lower ventricle.
  -It consists largely of cardiac muscle, capable of maintaining its own contractions and relaxations - being 'myogenic'.
  

• Three stages:
  -Atrial Systole - The right and left ventricles relax, the tricuspid and bicuspid valves open and the atria contract to let blood flow into the ventricles.
  -Ventricular Systole - The atria relax and ventricles contract, forcing blood out of the heart and into the pulmerary artery and the aorta as the semi-lunar valves open; the valves close by a rise in pressure.
  The pulmonary artery carries blood to the lungs, and the aorta carries oxygenated blood to the various parts of the body.
  -Diastole - Ventricles relax and pressure falls, blood under high pressure in the arteries causes the semi-lunar valves to close, forcing it one way.

Blood from the vena cavae and pulmonary veins enters the atria and it starts again.

• Highest pressure occurs in arteries that show rhythmic rise and fall.
• Friction with vessel walls causes progressive drop in pressure, artrioles have a large total surface area; pressure depends on dilation/contraction.
• Extensive capillary beds have large area, these beds create even greater resistance.
• Speed corresponds to pressure, and pressure drops further due to leakage from capillaries.
• The return flow is non-rhythmic and pressure in the veins are low.

• Cardiac muscle is myogenic.
• Within the wall is the SAN, that acts as a pacemaker.
• A wave of stimulation arises and spreads over the two atria causing them to contract.
• This stimulation is prevented from spreading to the ventricles by insulating tissue; which is important so that they don't contract at the same time.
• The stimulation reaches the AVN, which lies between atria and passes to ventricles.
• The AVN passes the exitation down bundle of His, the bundle branches into Purkinje fibres which carry the exitation upwards; causing the emptying completely of ventricles. 

• Made up of 45% cells, and 55% fluid plasma.
  
  
• Red Blood Cells
  -Carry haemoglobin to carry O2 from lungs to respiring tissue.
  -They are biconcave in shape, to increase surface area; enabling quick O2 diffusion.
  -They have no nucleus, for extra room for haemoglobin. 
  
  
• White Blood Cells 
  -These are larger, possess and nucleus and are spherical/irregular in shape.
  -There are two kinds: granulocytes and agranulocytes; the first are phagocytic, have granular cytoplasm and engulf bacteria; the second produce antibodies and have clear cytoplasm.
  
  
• Plasma
  -Made up of around 90% water, with soluble food, waste products, hormones, mineral ions, and vitamins dissolved in it.
  -It transports CO2, digested food products, hormones and antibodies.
  -It also distributes heat. 

• Haemoglobin can change its affinity for O2 in presence of CO2, by changing shape.
• When exposed to increasing partial pressures of O2 it does this:
  
• At low concentrations it's difficult to absorb oxygen but once loaded, associates readily.
• At high PP, the percentage saturation is very high; the cells carry the oxygen as oxyhaemoglobin to respiring tissues where PP is low as O2 is used up.

• The more the dissociation curve is to the left, the more readily it picks up O2, the less readily is releases it.
• The more right, the less it picks up O2, the more readily it releases it.
• At higher partial pressures of CO2, the more the graph shifts to the right - Bohr Shift.

-When CO2 PP is high, haemoglobin associates with O2 less, and releases more.

• Foetal Haemoglobin
  -The blood of the foetus and mother never mix, but flow closely; to enable the foetus to absorb oxygen the foetus has haemoglobin that shifts the dissociation curve to the far left.
• Transport in other animals
  -Lugworms have low metabolic rate and lives in the sand, with limited oxygen.
  -High altitudes have lower PP of O2, so llama's have specialised haemoglobin.
  -Both of these enable more readily association with O2, shifting the graph to the far left.
  

• Furthermore myoglobin is a much more stable molecule which will not release O2 until very low PP of oxygen, with a far left dissociation curve.
• To summarise:

• CO2 is transported: in plasma(5%), hydrogen carbonate(85%), haemoglobin(10%).
• The following describes the Chloride Shift:
  -CO2 diffuses into RBC and combines with water to form carbonic acid; catalysed by carbonic anhydrase.
  -Carbonic acid dissociates into H+ and HCO3- ions, the second diffuse out of the RBC to combine with Na+ to form sodium hydrogen carbonate.
  -H+ provide the conditions for oxyhaemoglobin to dissociate into O2 and haemoglobin.
  -H+ combine with haemoglobin to form haemoglobinic acid.
  -The oxygen diffuses out of the RBC into tissues, and to balance outward movement of negative ions, Cl- diffuses in; so electrochemical neutrality of the RBC is maintained.

• Capillaries are the site of exchange in the body, they:
  -Have thin, permeable walls.
  -They provide a large surface area for exchange.
  -Blood flows slowly, allowing time for exchange.

-Tissue fluid bathes the cells and supplies: glucose, amino acids, salts and oxygen.
-The factors responsible for movements of water/solutes are blood pressure and diffusion.
-When blood reaches atrial end it is under pressure because of the pumping action of the heart, the hydrostatic pressure forces the blood into spaces between cells.
-The outward flow is opposed by the reduced water potential of blood, created by proteins.
-The hydrostatic pressure of blood is greater than osmotic forces, so there is a net flow of water and solutes out of the blood.
-At the atrial end, diffusion favours movement into tissue fluid due to cell metabollism.

-At the venous end, the blood pressure is lower and water passes into the capillaries by osmosis; the reduced water potential of blood causes a net flow of water into the blood.
-The tissue picks up CO2 and other extretory substances, some passes back into capillaries but most drains into the lymphatic system which eventually reaches the venous system which empties into a vein near the heart.