transport in animals

Why do multicellular animals need transport systems?

==*High metabolic rate*== - multicellular animals need lots of oxygen + food and produce lots of waste so diffusion over long distances is not enough to supply the quantities needed.

*Small SA:V ratio* - larger diffusion distances and small SA to absorb/remove substances.

closed circulatory system

==*Blood enclosed*== in blood vessels and doesnt have direct contact with all cells.

==*Heart pumps*== blood under pressure, blood *returns* to the heart.

substances enter/leave blood through blood vessel walls.

Blood flow of tissues adjusted by *widening/constricting* blood vessels.

*effective for multicellular mammals* - allows blood to travel rapidly under high pressure to wherever it's needed.

Single closed circulatory system

Blood passes through 2 sets of capillaries beforing returning to heart.

1st set of capillaries - O2 and CO2 exchanged.

2nd set of capillaries - substances exchanged between blood and cells in different organ systems.

Narrow capillaries so blood pressure drops before slowly returning to the heart. This limits efficiency of exchange processes so metabolic activity is relatively low.

fish open circulatory system

*counter-current exchange system*.

Water with *high* conc of O2 flow past blood with *low* conc of O2 at high pressure, in *opposite directions*.

ensures that there is always a *concentration gradient maintained*.

Efficient exchange process so metabolic activity is high.

Double closed circulatory system.

Blood completes two circuits.

Blood pumped from heart to lungs, to pick up O2 and unload CO2 and then returns to heart.

Blood flows through the heart and is pumped out to travel all around the body before returning to the heart again.

Open circulatory system in insect

Blood fills *haemocel* at a low pressure.

Blood *doesnt transport O2/CO2* but transports *food and nitrogenous waste products and immunological cells*.

O2/CO2 transported via spiracels and trachae.

*Haemolymph* bathes organs directly and moves slowly through the tissue, returning to heart via collecting ducts.

Function of blood

tranpsorts materials to and from cells

transports nutrients, carries O2, waste products, hormones to their target cells, regulates body temperature, protects against bacteria and viruses

transports platelets to damaged areas

Arteries

Carries ==oxygenated blood away== from heart except the pulmonary artery which carries deoxygenated blood away from the heart.

Carry blood from heart to rest of body at *high pressure* to meet cell's metabolic demands.

Thick muscle layer to maintain high pressure.

Thick *elastic tissue* layer to help *stretch and recoil* as the heart beats to maintain high pressure. This evens out the surges pumped from the heart to give a continous flow.

*Endothelium is folded* to allow the artery ot expand which helps maintain high pressure.

Arterioles

Branched off from artery, carries ==oxygenated== blood.

smaller than arteries.

Has a layer of smoth muscle but less elastic tissue than arteries.

Smooth muscle allows them to expand/contract, controlling blood flow to tissues.

Capillaries

Branched off from arterioles

smallest blood vessel

Venules

Brached off from capillaries

carries ==deoxygenated== blood from capillaries ==to veins==

thin walls.

contains some muscle cells.

Veins

Takes ==deoxygenated blood back== to heart under low pressure except in pulmonary veins where they carry oxygenated blood.

Very little elastic and muscle tissue.

*Wide lumen* relative to artery.

contains *valves* to stop blood backflow.

Formation of tissue fluid

1. ==*high hydrostatic pressure*== in arterial end of capillary bed. *higher than oncotic pressure* so fluid is pushed out into surrounding tissues, forming tissue fluid. Most of plasma is pushed out *except for RBC's and plasma proteins.*

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2. ==Diffusion takes place== between blood and cells via tissue fluid.

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3. ==*High oncotic pressure*== in venous end of capillary bed due to plasma proteins generating *low water potential* in the blood. Hydrostatic pressure is low. *95% tissue fluid moves back into capillary via osmosis.* remaining 10% move back into lymphatic tissue.

What happens to excess tissue fluid?

Excess tissue fluid passes into lymph vessels.

Once inside, it's called lymph.

*Valves* in the lymph vessels stop lymph backflow.

Lymph gradually moves up lymph vessels to *thorax* and is returned to the blood near the heart.

Why are red blood cells not found in tissue fluid and lymph?

Too big to fit through endothelium (capillary) walls.

Why are there very little white blood cells in tissue fluid?

Most white blood cells are in the lymph system.

They only enter tissue fluid during infection.

Why are there no platelets in tissue fluid or lymph?

Platelets are needed for clotting during a bleed.

No need for them as tissue fluid and lymph have no RBC's.

Only present in tissue fluid when capillary is damaged.

Lymph has only what kind of protein?

antibodies.

why are there few proteins in tissue fluid?

Msot plasma proteins are too big to pass through capillary walls.

Which has a higher water potential? blood, tissue fluid or lymph?

Tissue fluid and lymph has a higher water potential than blood.

Why are solutes found in tissue fluid and lymph as well as blood?

Solutes are small enough to pass through the capillaries.

How do valves work?

Valves prevent blood backflow.

Only open one way.

*high pressure behind of valve* - valve forced *open*.

*High pressure in front of valve* - valve forced *shut*.

Cardiac cycle - atria contract, ventricles relax.

Atria *contract* - decrease in atrial volume in and *increase in atrial pressure*.

Causes blood to be *pushed into ventricles* via *atrioventricular valves*.

Slight increase in ventricular volume and pressure as ventricles recieve ejected blood from contracting atria.

ATRIAL SYSTOLE

Cardiac cycle - ventricles contract, atria relax.

Ventricles *contract* - decreases ventricular volume and *increases ventricular pressure*.

*atrioventricular valves shut* to prevent backflow due to higher pressure in ventricles and atria.

High pressure in ventricles *opens semi lunar valves* - blood forced into *pulmonary artery* and *aorta*.
VENTRICULAR SYSTOLE

Cardiac cycle - both ventricles and atria are relaxed.

Ventricles and atria both relax.

*Higher pressure* in pulmonary artery and aorta causes semi lunar valves to *close*.

Blood flows *down it's pressure gradient* from the *vena cava* and *pulomonary vein* *into the atria.*

Ventricular pressure falls below atrial pressure - atrioventricular valves open and blood flows *passively* (not through atrial contraction) into ventricles from atria.

Atria contract (cardiac cycle begins again) and *rest of blood* is pushed into ventricles through atrial contraction.
SYSTOLE

What is the 'lub dub' sound caused by?

'Lub' - atriventricular valves closing.

'dub' - semilunr valves closing.

Why is the pressure always lower in the right ventricle than the left during ventricular contraction?

Left ventricle of the heart needs to contract more powerfully to transport blood all around the body.

The right ventricle doesnt need to contract as hard as it is only pumping blood into the lungs.

Therefore the pressure has to be higher in left ventricles so it can contract with more force. Left ventricles are thicker and muscular to withstand the higher pressure.

Normal ECG

*P wave* - *contraction* (depolarisation) of *atria*.

*QRS Complex* - *contration* (depolarisation) of ventricles.

*T wave* - *Relaxation* - repolarisation of ventricles.

taller P and Q peak means stronger contraction.

Tachycardia

Heart beating too fast.

Normal in excercise, fever, when angry or scared.

Abnormal if caused by problems in electrical control of the ehart and may need medication/surgery.

Bradycardia

heart rate too slow.

Exercise training can cause bradycardia as heart beats more slowly and efficiently.

Severe bradycardia is serious and may need artificial pacemaker to keep heart beating steadily.

Ectopic heartbeat

Extra heartbeats that are out of the normal rhythm.

Normal to have 1 per day.

Linked to serious conditions when they're frequent.

Atrial Fibrillation

Example of *arrhythmia* (abnormal rhythm of heart.

*Rapid contraction of atria*. However they dont contract properly and only some of the impulses are sent to ventricles. Therefore ventricles contract less often.

Heart doesnt pump blood very efficiently.

Sino-atrial node

Specialsed cardiac muscle cells that generate action potentials which sets the pace at which the heart contracts. (acts as a *pacemaker*)

Once impulse is generated through SA node, it *spreads through both atria* and causes them to *contract simultaneously*.

Atrio-ventricular node

Found between atria and ventricles.

When it recieves action potential from the SA node it delays the action potential for a short time to wait for atria to finish contracting.

AV node then depolarises and sends electrical signals via *Bundle of His*.

Bundle of His

Splits into left and right bundles - runs along intraventricular septum (wall between right and left ventricle).

Conducts wave of excitation to apex (bottom) of the heart.

Purkinje Fibres

Found at the apex and spread out through both ventricular walls.

Spread of excitation causes ventricular contraction, starting at the apex.

Starting at the apex allows more efficient emptying of the ventricles.

Why is cardiac muscle considered myogenic?

It can generate it's own action potential to initiate contraction without nervous input.

Reversible binding of oxygen to haemoglobin

Oxygen loads onto haemoglobin to form oxyhaemoglobin where there's a *high pO2*.

Oxyhaemoglobin unloads its oxygen when theres a *low pO2*.

100% saturation of haemoglobin with oxygen

Every haemoglobin molecule is carrying the maximum of 4 molecules.

0% saturation of haemoglobin with oxygen

None of the haemoglobin molecules are carrying any oxygen.

Explain the part of the oxygen dissociation curve where there is a *low saturation of haemoglobin with oxygen*

Where pO2 is *low*, e.g in *respiring tissues*, haemoglobin has a *low affinity* for oxygen.

It releases oxygen rather than combining with it.

Explain the part of the oxygen dissociation curve where there is a *high saturation of haemoglobin with oxygen*

Where pO2 is *high*, e.g in the *lungs*, it has a high affinity for oxygen.

It will readily combine with oxygen.

Why is the oxygen dissociation curve 'S' shaped?

When haemoglobin combines with the 1st O2 molecule, it's shape alters ina way that makes it easier for other molecules to join too.

But has Hb becomes more saturated, it becomes harder for more oxygen molecules to join.

As a result, the curve has a steep bit in the middle where it's really easy for oxygen molecules to join but shallow bits at the end where its harder. When the curve is steep, a small change in the amount in pO2 causess a big change in the amoung of oxygen carried by the Hb.

Why does fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin at the same pO2?

By the time the mother's blood reaches the fetus, it's oxygen saturation has decreased (some has been used up by mother's body)

Fetal Hb has to have a higher affinity for oxygen to get enough oxygen to survive.

If it's Hb had the same afinity for oxygen as adult haemoglobin, it's blood would be saturated enough.
It also have gamma chains which increase the affinity for oxygen unlike maternal blood

Transport of CO2 in blood. (5 steps)

CO2 from respiring tissues diffuse in RBC's - reacts w/H20 to form *carbonic acid* - catalysed by *carbonic anhydrase*.

Carbonic acid *dissociates* into *HCO3-* and *H+* ions. Increase in H* causes oxyhaemoglobin to unload it's oxygen so that Hb can bind to H+ ions-forms haemoglobinic acid. (also stops H+ ions increasing blood acidity.)

HCO3- ions diffuse out RBC's and transported in plasma. To compensate for *change in pH* caused by *loss of HCO3- ions*, Cl- ions diffuse into RBC's. (*chloride shift*)

When blood reaches lungs, low pCO2 causes some of HCO3- and H+ ions to *recombine into CO2* and H20.

CO2 then *diffuses into alveoli* and is breathed out.

Bohr effect carbon dioxide

Dissociation curve shifts to the right when pCO2 increases, showing that *more oxygen is released from the blood*.

Advantages and disadvantages of single circulatory systems

+ve-less complex
-ve-low BP, slow movement of blood, lower activity levels

Advantages and disadvantages of double circulatory systems

+ve- higher BP, faster flow of blood

What do elastic fibres do?

Can stretch and recoil which makes the vessel walls flexible

What does smooth muscle do?

Contracts and relaxes to change the size of the lumen

What does collagen do?

Provides structural support to maintain the shape and volume of the vessel

Why is it important that the pressure changes from the aorta to the capillaries?

The capillaries are only one cell thick so a high pressure would burst the capillary wall
Reduce the change of a build up of tissue fluid

formula of cardiac output

stroke volume x heart rate in cm³/min

Low pH

Low oxygen affinity so graph shifts to the right

low temperature

High oxygen affinity so graph shifts to the left

What does haemoglobin act as in the transportation of carbon dioxide?

A buffer to prevent changes in pH

Why is oxygen not released until the blood reaches the capillaries?

-artery walls too thick for diffusion to take place
-arteries have a thick wall
-capillary wall is only 1 cell thick
-short diffusion distance for capillary

How does llama haemoglobin differ from camel haemoglobin?

-difference in primary structure
-different amino acid sequence\=possible change in secondary structure e.g beta pleated sheets, hydrogen bonding etc
-amino acid changes could cause changes in tertiary structure
-no change in quaternary structure

Difference between tissue fluid and lymph

Lymph has less oxygen, fewer nutrients and contains fatty acids

How does the arteries withstand and maintain a high hydrostatic pressure

Withstand\=
-thick wall
-thick layer of collagen to provide strength
Endothelium is folded
Maintain
-narrow lumen
-thick layer of elastic tissue
-to allow it to recoil/return to original size
-thick layer of smooth muscle