AL Bio notes Transport in Animal P.1 TRANSPORT IN ANIMALS

While D______remains as the most important means of short distance molecular movement in and out of cells, during the course of evolution, as animals became lar___ in size, more highly org____, and metabolically more a_____, an efficient circulatory system is required to carry r______gases, nu_____, and the products of met______for l_____ distance transport.

Different circulatory systems recognised (reference):

1 Intracellular transport In un______organisms e.g. protozoans and in cells of higher animals and plants cytoplasmic st r ______supplements d______as a means of moving substances around inside the cell.

2 Movement of external medium In small animals, notably sponges and coelenterates, the w____ in which they live serves as the transport medium and is moved about inside the body by cilia, flagella or muscular activity.

3 Circulation of Fluid in body cavity In some animals such as echinoderms, the fl___ in the body cavity (coelom) is a transport medium, it flows past all tissues and organs.

4 Movement of fluid in an open circulatory system In most arthropods and many molluscs the transporting fluid, is pumped by a muscular heart through vessels out into tissue spaces, bathing c___ directly. Blood flow in open circulatory system is generally sl___ and under l__ pressure.

5 Movement of fluid in a closed circulatory system In most annelids, octopus and squid, and vertebrates, the transporting fluid, blood, is circulated in a system of closed tubes, by one or more muscular hearts. The fluid that bathes the cells is the t______fluid, is derived from blood. In vertebrates the tissue fluid is returned to the blood vascular system through another system of vessels-- the lymphatic system.

I) MAMMALIAN BLOOD

A) COMPOSITION OF BLOOD

Blood consists of a suspension of b_____ c___ or corpuscles together with cell fragments, the plate____, in a yellowish, watery medium called p______.

There are two main types of blood cells; red cells or erythrocytes, and white cells or leucocytes.

An adult man has five to six l_____ of blood in his body; a woman has, on average, one litre less. AL Bio notes Transport in Animal P.2

a) Red blood cell (erythrocytes) Erythrocytes serve for the transport of the r______gases. They are minute, bi______d___ formed principally in the red m______of the sternum, ribs and vertebrae. During their formation they lose their n_____ (this does not happen in the other vertebrate classes). The cytoplasm of erythrocytes is packed with molecules of the red, i___-containing pigment, haemoglobin. This pigment greatly increases the oxygen-carrying c______of the blood. The biconcave shape of erythrocytes increases their s______area to volume ratio and greatly s_____ up gas exchange between the cells and the surrounding plasma.

There are between 4.5 to 6 million erythrocytes in each mm3 of human blood. This number varies according to factors like al_____ (people living at high altitude may have as many as 8 million Red blood cells per mm3) and the individual's state of health (people with severe a_____ tend to have a low red cell count).

Erythrocytes are produced and destroyed at a high and continuous rate. They live for about 4 months after which they are destroyed by phagocytic cells in the l____ and sp____. These organs retain the i____ for use in the manufacture of fresh haemoglobin. b) White Blood Cells (Leucocytes) They are concerned with fig_____ diseases. They are generally larger but l___ numerous than erythrocytes. There is approximately one leucocyte for every six hundred erythrocytes.

Two main types of leucocyte can be distinguished; ______cytes and a______. Granulocytes have an irregular shape, gr______cytoplasm and a l____ nucleus.

The most abundant of these, the neutrophils are ph______; they ingest bacteria and dead or damaged cells. Far less is known about the other two types.

Most agranulocytes are produced in the lymph nodes and spleen by the division of cells derived from bone marrow. They have a large, spherical or bean-shaped nucleus bordered by a rim of non- AL Bio notes Transport in Animal P.3 granular cytoplasm. Two main types are recognised, lymphocytes and monocytes. The former are involved in anti____ production while the latter are phagocytes. c) Blood platelets They play a vital role in blood c_____. They are cytoplasmic fragments of large blood cells produced in the bone marrow. There are between 250 000 and 500 000 platelets in each mm3 of blood. d) Plasma Plasma consists of w____ (approximately 90%) and a variety of d______substances. The most important constituents are:

Plasma proteins albumin, globulin and fibrinogen

Food glucose, other monosaccharides, amino acids and fats

Excretory material urea and other nitrogenous compounds

Ions e.g. NaCl, K+, Ca2+, phosphate , sulphate , bicarbonate.

Others hormones, small amounts of respiratory gases, vitamins and enzymes.

B) FUNCTIONS OF MAMMALIAN BLOOD a) Transport

The blood transports a variety of substances around the body.

1 Products of digestion are carried from the capillaries in the i______to the liver where the sugar content is regulated, after which the soluble foods, as well as vitamins and minerals derived from the food, are carried to the cells.

2 Excretory materials such as urea and uric acid are carried from the tissues or organs where they are formed (l______) to the organs where they are removed (k______, sk__).

3 Hormones are carried from the e______organs where they are made to the target organs.

4 Respiratory gases are transported between the l_____ and respiring c___. b) Oxygen Transport i) Respiratory pigment Most oxygen is carried in the blood as o______. Haemoglobin readily associates with oxygen in regions of high oxygen tension (concentration) such as occurring at the respiratory surface (the lungs). Equally important, oxyhaemoglobin readily diss______, giving up its o______in the regions of low oxygen tension that prevail in the tissues.

high O2 tension Hb + O2 HbO2 haemoglobin low O2 tension oxyhaemoglobin

Haemoglobin is made up of a pigment, h____, combined with a protein, globin. Haem consists of a porphyrin ring linked to an atom of ferrous iron. Oxygen combines loosely with the ferrous iron without ox______it to the ferric state (such a reaction would not be readily reversible). AL Bio notes Transport in Animal P.4 ii) Oxygen Dissociation / Equilibrium Curve

The aff____ of haemoglobin for oxygen can be determined by exposing a solution of deoxygenated haemoglobin to a gradually increasing oxygen t______and then measuring the proportion of haemoglobin which is in the ox______state (HbO2) at each tension.

The relationship between oxygen tension and the percentage of HbO2 produces a characteristically ___-shaped graph .known as the oxygen dissociation curve.

It shows that oxygen is taken up r______at low oxygen tensions, but at higher tensions the rate of absorption s____ down and approaches the 100% saturation level very slowly.

Ideally, the oxygen tension of blood at the respiratory surface should be fully saturated with oxygen. In practice, the maximum operating capacity of the pigment is unlikely to be more than 95% of the saturation level. The tension at which the pigment can become 95% saturated is accordingly called the l______tension.

Analysing in the reverse direction, the curve shows how the pigment re_____ oxygen in area of low O2 tension. (dissociates). Below the loading tension a small drop in oxygen tension results in the release of a l______amount of oxygen from the pigment.

The tension at which only 50% of the pigment is oxygenated is known as the un______t______, AL Bio notes Transport in Animal P.5 because at this tension the pigment will give up nearly h___ its oxygen load. The unloading tension corresponds with oxygen levels encountered in the t______.

Reference reading: Why is the curve S-shaped?

The explanation lies in the way that haem group binds to oxygen. When an oxygen molecule combines with the ferrous iron atom of a single haem unit it distorts its shape slightly. Further structural alterations occur when oxygen molecules attach to the second and third haem groups, each one facilitating much faster uptake of oxygen than the preceding one. When the last haem monomer is ready to pick up oxygen it does so several hundred times faster than the first.

iii) Adaptive feature of Oxygen dissociation curves

1) Habitats and activity

The adaptive nature of respiratory pigments is revealed in the oxygen equilibrium curves of the haemoglobin of different animals living in different h______. AL Bio notes Transport in Animal P.6

The haemoglobin of Arenicola, the lugworm, has a very h____ affinity for oxygen, it is ninety five per cent saturated at a very low oxygen tension (about 13 mm Hg). This ensures that the lugworm's blood can become saturated in the conditions of l___ oxygen availability that prevail in its environment. Lugworms live in b______in the sand where, at low tide, the oxygen tension falls to about 13 mm Hg.

The curve for human haemoglobin is to the ______of that for Arenicola showing that it has a ______affinity for oxygen. This is to be expected in a creature that lives in an environment where oxygen is plentiful.

The curve for pigeon haemoglobin is to the ______of human haemoglobin, showing that it has an even lower affinity for oxygen. Flight is an e_____-demanding activity, a lower affinity means a more rapid u______of oxygen to flight muscle during vigorous activity.

Q. Do you think the lower affinity of pigeon haemoglobin significantly affects the loading of oxygen at the respiratory surface? AL Bio notes Transport in Animal P.7

2) Myoglobin and Haemoglobin

Muscles of vertebrate contain a pigment called muscle haemoglobin or myoglobin. The curve for this pigment lies to the ______of the curve for 'blood' haemoglobin so that oxygen is easily t______from haemoglobin to the m______.

Myoglobin thus acts as a re______of oxygen in muscle, it releases its oxygen to muscle only when O2 supply from blood becoming li______.

In human, myoglobin is abundant only in c_____ muscle. However, in di____ mammals, the myoglobin content of muscles is particularly high; the relative concentrations of myoglobin in muscles correlate roughly to the dur_____ of their dives.

Q. Can you account for the different coloured flight muscles in flying (eg. pigeon) and non-flying birds (eg. hen).

3) Human adult and foetal haemoglobin

Foetal haemoglobin is to the ______of the curve for adult haemoglobin showing that it has a ______affinity for oxygen. This situation ensures that oxygen can be transferred easily from m______blood to f_____ blood at the placenta. AL Bio notes Transport in Animal P.8

4) Effect of temperature and CO2

The affinity of a pigment for oxygen varies with temperature, carbon dioxide tension and other factors.

I______temperature and increasing carbon dioxide tension both ______the pigment's affinity for oxygen and so shift the curve to the ______.

The effect of increased carbon dioxide concentration is known as the B____ effect.

The significance of the Bohr effect is that in regions of h____ carbon dioxide tension oxygen is r______to the tissues more readily.

Q. An investigation on oxygen saturation of blood was carried out. Blood samples were exposed to two different mixtures of oxygen and carbon dioxide.

In one mixture, the carbon dioxide was at a partial pressure of 1.0 kN m-2 and in the other it was at 1.5 kN m-2. The oxygen equilibrium / dissociation curves were then plotted on a graph. Notice how these oxygen equilibrium curves differ.

Time Blood (p.p. O2) Tissue (p.p. CO2)

X A = 9 C = 3 A = 1 B = 1 Y A = 9 C = 3 A = 1.5 B = 1.5 Z A = 9 C = 3 A = 1 B = 1.5

1. Describe the effect that carbon dioxide has on the oxygen-haemoglobin equilibrium curves.

2 a) For the time X, the state of the blood and tissues is shown in the above diagram. Calculate the decrease in haemoglobin saturation when blood travels from A to C (use the graph as dissociation curves).

b) For time Y, calculate the decrease in haemoglobin saturation between A and C. AL Bio notes Transport in Animal P.9

c) For time Z, calculate the decrease in haemoglobin saturation when blood travels from A to C.

3. What information does your answers to 2 (a) and (b) give you about the shape of the equilibrium curves in the graph above?

4. What is the effect of an increase in the partial pressure of carbon dioxide in blood as it enters a capillary network?

5. Sketch on the graph shown above and indicate, using a dotted line, the approximate dissociation curve for blood flowing through the capillaries at time Z.

6. What tissues of the body would you expect to have higher carbon dioxide partial pressures than blood?

7. How does decreasing the partial pressure of carbon dioxide in lungs contribute to the efficiency of haemoglobin as an oxygen carrier?

This shift in the oxygen-haemoglobin equilibrium due to changes in carbon dioxide concentration is called the Bohr effect (after the scientist who first recorded it). It has been found that carbon dioxide has no direct effect on haemoglobin but that carbon dioxide dissolving in the plasma changes pH that causes the shift.

8. Does an increase in dissolved carbon dioxide cause an increase or decrease in (a) acidity, (b) pH? A shift to the right of the equilibrium curve is also caused by an increase in temperature.

9. From your knowledge of protein structure, how might pH and temperature affect the functioning of haemoglobin?

10. Explain how actively respiring tissues, e.g. contracting muscle, can acquire greater amounts of oxygen due to the shift in the equilibrium curve.

11. Arenicola, a lugworm that live in environment that contains little oxygen. Increased partial pressure of carbon dioxide does not affect its dissociation curve. Explain the advantage to lugworm of possessing this ‘unresponsive’ haemoglobin.

c) Carbon Dioxide Transport

i) Means of CO2 Transport in Blood in Plasma in physical solution (~7%)

in Red Blood Cells combine with the amino groups of amino acids and proteins, including haemoglobin, forming carbamino compounds (~23%)

in Plasma (mostly) as bicarbonate ions (~70%) AL Bio notes Transport in Animal P.10

Carbonic acid dissociates into bicarbonate and hydrogen ions.

CO2 is formed from carbonic acid and unload from haemoglobin. CO2 diffuses out of the blood, into the interstitial fluid, and into

1 CO2 produced by body tissues diffuses into intersititial fluid and

H+ released from haemoglobin, combines with bicarbonate ions to form carbonic acid

Haemoglobin binds with most of the H+ from carbonic acid, preventing them from acidifying the blood---the Bohr shift. The reversible conversion of carbonic acid and bicarbonate ion also helps buffer the blood, releasing or removing H+ depending on pH

into the plasma. Less than 10% remains in the plasma as dissolved CO2

Most of the bicarbonate ions diffuse out into the plasma

Most of the CO2 reacts with H20 in the RBC to form carbonic acid. This reaction normally proceed very slowly but RBCs contain an enzyme, carbonic anhydrase, which catalyses this reaction..

Over 90% of the CO2 diffuses into the RBCs

Some is picked up and transported by the haemoglobin

13 The aveolar space, from which it is expelled during exhalation.

The processes that occur in the tissue capillaries are reversed in the lungs. The bicarbonate ions diffuse from the plasma into the RBCs

They are carried in the bloodstream to the lungs AL Bio notes Transport in Animal P.11 d) Distribution of heat Heat is generated largely as a result of cellular re______. It follows then, that most heat is generated in the most metabolically active tissues, notably the l_____ and m_____. Blood carries this heat to all parts of the body. e) Body Defence The blood is involved in 3 defence mechanisms –cl_____, phago______and the i______response.

A clot is a plug of protein fi____ and blood c___ that forms to close damaged blood vessels thereby reducing blood l___ and excluding potentially harmful m______. The essential feature of clot formation is the conversion of the s______plasma p______fibrinogen, into the insoluble fibrous protein f_____. A meshwork of fibrin fibres forms across the wound, in which blood cells become entangled. If the clot is external it dries and hardens to form a scab.

At least twelve f______are known to play a part in the conversion of fibrinogen to fibrin. When a vessel is damaged, p______stick to areas of vessel wall denuded of endothelium. They also release phospholipid which, together with a tissue factor released by the damaged vessel, initiates the clotting sequence.

f) Maintenance of a stable internal environment

The protective mechanisms are one of the many ways in maintaining the con______of the internal environment.

The transporting role of the blood pro____ all the cells with the substances they need to maintain themselves. It also re_____ substances the cells do not require.

The plasma proteins contribute to the colloid os_____ pressure of the blood which helps to control blood vo____ and water balance in the body. They also act as b______helping to minimise changes in the pH of the blood.

II) THE MAMMALIAN HEART

The mammalian heart lies in the thorax enclosed in a membranous sac, the peri______.

It is a f___-chambered, muscular, pumping organ with two thin-walled atria and two thick-walled ventricles.

The muscle is a special type of st______muscle called c_____ muscle. It differs from normal striated muscle in that it can contract continuously without fa_____, and it is m______, that is, contractions are initiated within the m____ itself not by nerves. AL Bio notes Transport in Animal P.12

A) THE PUMPING ACTION OF THE HEART AND THE CARDIAC CYCLE Recordings of Blood pressure changes in the aorta, the left atrium (auricle) and the left ventricle in the cardiac cycle of a mammal .

N.B. ‘atrio-ventricular valves’ here refers to the bicuspid valve

‘aortic valves’ are the semilunar valves at the base of the aorta

The right sides of the heart has a very similar cycle but with a smaller amplitude

1 a. Ventricular pressure exceeds aortic pressure and so pushes open the aortic valves. This allows blood to flow into the aorta which increases aortic pressure b. Shortly after ventricular systole, ventricular pressure exceeds atrial pressure, 2 causing atrio-ventricular valves to close. (the 1st heart sound) c. Pressure in relaxing ventricle falls below aortic pressure causing aortic valves to 3 close (the 2nd heart sound) d. Start of atrial systole lasts ~0.1s. Rising atrial pressure leads to blood filling into 3.1 ventricles e. Aortic pressure increases as distended artery wall recoils to regain its shape--in so 3.1→4 doing pushing blood along the artery away from the heart. f. Short-lived increase in atrial pressure caused by ventricular contraction which bulges 4 the atrio-ventricular valves into the atrium. g. Atrial pressure starts to rise as it fills with blood from the veins 5 h. Ventricular pressure goes on increasing steeply as contraction continues 6 i. Start of atrial diastole causes drop in atrial pressure 7 j. Start of ventricular systole. 8 k. Pressure in relaxing ventricles fall below atrial pressure causing atrio-ventricular 9 valves to open. This allows the rapid filling of the ventricles with blood from the atria l. Atrio-ventricular valves open 3.1→9 m. Atrio-ventricular valves close. 9→3.1 4→7 n. Aortic valves close

7→4 o Aortic valves open AL Bio notes Transport in Animal P.13

The two at____ contract sim______as do the ventricles. Contraction of heart muscle is called S______, while relaxation of heart muscle is called d______. Atria and ventricles contract in turn so that while the atria are in systole the ventricles are in diastole, and vice versa.

Heart rate is in______related to body size. This is to be expected as small mammals have higher me______rates than large mammals. The elephant has a resting heart rate of about 25 beats per minute while the tiny shrew's resting rate is about 600 beats per minute.

During atrial systole the entrances to the veins are c_____ by the contraction of the muscle that surrounds them. The increasing pressure in the atria eventually forces blood through the a______valves (the bicuspid and tricuspid valves) into the ventricles which are relaxing.

During ventricular systole the increasing pressure in the ventricles c_____ the atrioventricular valves. They cannot be pushed through into the atria because they are held in position by the taut tendinous c___ (heartstrings). Eventually blood is pushed out of the ventricles through the s______valves that guard the entrances to the arteries. These valves are closed when the ventricles are relaxing, which prevents b______of blood into the heart from the arteries.

While the ventricles are contracting the atria are relaxing. The vein entrances open and blood is drawn into the heart by the reduced p______in the atria.

During this cycle the sound of the a______v_____ closing (‘dub’), followed slightly later by the sound of the s______valves closing (‘lub’), together make up the heart beat sound.

B) INITIATION OF HEART BEAT

The heart receives two nerves, the sympathetic nerve, and a parasympathetic nerve. If these two nerves are cut the heart will continue to beat rhythmically for some time, demonstrating that nerve impulses do not i______contraction.

In fact, contraction of the heart is initiated within the heart m_____ itself. A region of fine muscle fibres in the wall of the atrium called the s____-a_____ node (SAN) or p______sends out waves of electrical ex______that pass through the heart muscle causing it to contract.

The electrical excitation passes through the atria to another node, the a____-v______node (AVN), and then spreads rapidly along the Purkinje tissue.

These tracts of fine muscle fibres pass down through the interventricular septum and fan out into the v______walls.

Once the wave of excitation has passed, the cardiac muscle re_____.

It is now possible to correct abnormalities of heart rhythm by the implantation of a battery-operated a______pacemaker.

Q. The SAN acts as a pacemaker from which originate successive waves of excitation that determine the rhythm of heart AL Bio notes Transport in Animal P.14 beat. The excitation wave is delayed for a fraction of a second at a second patch of cells, the atrioventricular node (AVN), before being conducted along the special conducting muscle fibres (Purkinje fibres) to the ventricles.

1. What is the importance of the time delay at the AVN?

2. Look at the timing of conduction by the Purkinje fibres. Describe the way in which the ventricles will contract.

C) Nervous and Hormonal regulation of Heart Beat Rate

The nerves that pass to the heart do, of course, serve a purpose. They mo____ the activity of the p______. Impulses passing to the heart along the parasympathetic nerve s____ the heart rate while impulses arriving via the sympathetic nerve s_____ up heart rate. The advantages of this double innervation and anta______control of heart rate are apparent. A 'brake' and an 'accelerator' make possible a much q_____, and much more del_____ adjustment of rate than either could alone.

Higher c_____ in the brain can also have an effect on the circulatory system. During periods of ex______or sh____, the cerebral cortex passes nerve impulses to the adrenal glands which respond by secreting the hormone ad______into the blood-stream. Adrenaline increases cardiac fre______and con______of the peripheral arterioles, has the same effect on heart rate as sympathetic stimulation.

Although the nervous and hormonal systems produce identical effects, there is an important difference. The nervous system (cardiovascular centre) adjusts the body to changes that are taking place. The hormonal system (cerebral cortex / adrenaline) adjusts the body to changes that have yet to occur. The hormonal system of control p______the body for action in emergencies.

D) ADJUSTMENT OF HEART RATE TO BODY NEEDS

The volume of blood flowing from the heart over a given period of time is known as the cardiac o______and depends upon the volume of blood expelled at each beat (the st____ volume) and the heart r____:

CARDIAC OUTPUT = STROKE VOLUME X HEART RATE

The cardiac output is the important variable. One way of controlling cardiac output is by varying the heart r____ and the s______volume.

Within the walls of the aortic arch, the carotid sinuses and the vena cava are st_____ receptors which sent s______impulses to the cardiovascular centre in the me____.

The stretching of the vessel wall increases the number of impulses transmitted to the c______centre:

 Impulses received from the a____ and c______arteries decrease the heart rate,

 whilst those from the v___ c____ increases the heart rate. AL Bio notes Transport in Animal P.15

E.g., under intense activity body muscles contract strongly and this i______the rate at which venous blood re_____ to the heart. Consequently the vena cava is distended by large quantities of blood and the heart rate is i______.

At the same time the increased blood flow to the heart places the c______muscle of the heart under t_____. Cardiac muscle responds to this tension by contracting more st______during systole and pumping out an i______volume of blood (the stroke volume). This relationship between the volume of blood returned to the heart and cardiac output was known as Starling's law.

The increased stroke volume stretches the a____ and c______arteries which in turn, via stretch reflexes, signal the cardiovascular centre to s_____ the heart rate. Therefore there is an automatic fail-safe / feedback mechanism which serves to prevent the heart from working too f___, and to enable it to adjust its activity in order to cope effectively with the v______of blood passing through it at any given time.

III) BLOOD VESSELS AND THE MAINTENANCE OF BLOOD FLOW

Blood is pumped by the heart along a______to c______and then returned to the heart by v____.

Capillaries are microscopic vessels that receive blood from the smaller arteries (ar______) and deliver it into the smaller veins (ve______).

The ex______of substances between the blood and the tissues takes place through the capillary walls which offer little re______as they consist of a single layer of cells, the endo______.

Arteries convey blood from the heart under high p______, and their walls are very t_____ to withstand this pressure.

 They have an outer f______coat which confers strength and protection,

 a thick middle layer of involuntary m______& e_____ fibres,

 and a lining of e______

The lumen of arteries and arterioles can be altered – const_____ or dil____ by c______and r______of the muscle layer. AL Bio notes Transport in Animal P.16

Origin of Pulses:

The pumping action of the h______provides the main driving force responsible for blood flow, but it is assisted by several other mechanisms.

Art______are distended as blood is forced into them, following which, the elastic re____ of the artery walls p_____ blood into the next part of the artery, which becomes dis______in its turn.

The rhythmical distension and return to shape of the arteries keeps time with the heart beat, and can be felt as p_____ along the arteries.

Venous blood pressure is much l______than arterial pressure and the walls of veins, although comprising the same layers as artery walls, are much th_____. Veins have pocket v_____ at intervals in their walls which permit blood to flow only t_____ the heart.

In veins there is little pressure to force blood along. The reduction in pressure created in the thoracic cavity during in______, and the reduced pressure in the rel______atria , both help to draw blood along veins and back to the heart.

When muscles contract they squeeze the veins running through or alongside them, in so doing pushing blood towards the heart: pocket valves in the veins prevent blood being sq______back. Finally, blood return from regions above the heart is assisted by gr______. AL Bio notes Transport in Animal P.17

Q. Blood vessels

The table gives some of the characteristics of various types of blood vessels in the systemic circulation in man.

Diameter of Thickness Total cross-sectional area % of total blood volume lumen of wall for all vessels of each contained in all vessels of type, relative to aorta each type

Aorta 25 mm 2 mm 1 2 Artery 4 mm 1 mm 4.5 8 Arteriole 30 m 20 m 89 1 Capillary 6 m 1 m 1000 5 Venule 20 m 2 m 890 Vein 5 mm 500 m 9 50 Vena cava 30 mm 1.5 mm 4

1 Comment on any relationships you observe in this table, and explain them as far as you can.

2 Explain the percentage of blood volume contained in the arterial system compared with the venous system.

3 The same volume of blood which leaves the heart returns to it, but the velocity at which blood flows through the system varies. The average velocity is inversely proportional to the total cross-sectional area of the part of the system the blood is in. Arrange these in order of the velocity you would expect: aorta, venule, capillary, vein.

4 Blood pressure varies with age and sex, but on average one can say that the pressure in the aorta rises to about 120 mmHg during systole (the contraction phase of the heart), and falls to about 70 mmHg during diastole (heart relaxed). Because systole is shorter than diastole the mean pressure is about 80 mmHg. How would you expect pressure to change in the vessels from aorta to vena cava?

5 The figure gives diagrammatic curves for total cross- sectional area, mean velocity of blood flow, and mean pressure, drawn to different scales. Say which curve is which. AL Bio notes Transport in Animal P.18

IV) THE FORMATION OF TISSUE FLUID

Blood entering the art______end of a capillary network has a high ‘hydrostatic’ p______(approximately 40 mm Hg), which tends to force w____ and small s_____ out of the vessel.

This is opposed by the colloid o______force of the blood, which tends to draw water and small solutes i____ the vessel.

As the hydrostatic pressure exceeds the osmotic pressure/force, water, ions and molecules are f_____ out through the c______w___.

The capillary wall is per______to all components of the blood except the ery______and plasma p______.

The fluid that leaves the capillaries bathes the tissues and is called t fluid. It resembles plasma in its composition but has a lower plasma protein content.

The tissue fluid is the m______of ex______between the blood and the cells:

Oxygen and nutrients d______from the blood to the cells via the tissue fluid, while waste materials and secretary products d______in the opposite direction:

The blood cannot afford to lose so much fluid and much of it is returned. This occurs in two ways:

 At the venous end of the capillary network the h______pressure has fallen to about 15 mm Hg and no longer exceeds the osmotic pressure, so there is a net movement of water and small solutes b____ to the capillaries.

 The rest of the tissue fluid drains into blindly ending ly______capillaries, and once inside these the fluid is termed l______.

The lymphatic capillaries join to form larger lymphatic vessels. The lymph is moved through the vessels by contraction of the m______surrounding them, and backflow is prevented by v____ present in the major vessels which act in a similar fashion to those found in veins. The large lymphatic vessels eventually drains lymph back into the big v____.

Situated at intervals along the lymphatic system are lymph glands or n____. L______, in the course of circulation through the blood and lymph, 'rest' and accumulate in the lymph nodes. They produce anti_____ and are an important part of the body's immune system. The nodes also f_____ out bacteria and foreign particles from the lymph, which are ultimately ingested by ph______. AL Bio notes Transport in Animal P.19

arteriole carrying blood tissue cell tissue fluid lumph capillary carries oaway of high blood pressure bathing cells some of the tissue fluid as lymph

filtration of plasma lymph vessel under high hydrostatic pressure at arteriole end of the capillary

valve prevent backflow reabsorption of tissue fluid into capillary at the venous end of the capilary due to osmosis blind end lymph capillary lymph node Venule

A diagrammatic representation of the relationship between tissue cells, tissue fluid and lymph

Q. The figure below shows diagrammatically the opposing forces acting in a capillary bed. The hydrostatic pressure (HP) of the blood, which differs at the two ends of the capillary, is opposed by the HP of the tissue fluid. The osmotic pressure (OP) of the blood plasma protein is opposed by the OP of the tissue fluid. The number are in mmHg.

HP=32 OP=25 Capillary HP=12

HP=8 OP=10 Tissue Fluid HP=8

Arteriole Venule

1. What is the effective or net hydrostatic pressure of the blood in the capillary a) at the arteriole end

b) at the venous end ?

2. What is the effective osmotic pressure of the blood plasma ?

3. What, therefore, is the filtration pressure at a) the arteriole end of the capillary

b) the venous end of the capillary ?

4. Which way, therefore, will fluid move at each end of the capillary ?

5. Kwashiorkor is a condition common to people living on a diet which is adequate in calorie but grossly deficient in protein. One of its characteristics is oedema : accumulation of tissue fluid in abnormally large amount causing swelling. Suggest a reason for the odematous condition in kwashiorkor. AL Bio notes Transport in Animal P.20

Reference Reading : Adjustments during exercise

We will see how the circulatory and other systems enable the body to adjust during a sprint. A number of processes occur before, during and after the sprint. Here they are, in roughly the order in which they occur.

1 Before and during the early stages of the sprint the sympathetic nervous system is alerted and adrenaline is secreted into the bloodstream. Triggered by impulses received from the brain in anticipation of the race, there is an increase in the cardiac output and general constriction of arterioles except for those serving vital organs, so that blood under high pressure is diverted to the active muscles. Anticipation of the race also brings about an increase in the ventilation rate.

2 During the sprint the metabolic rate increases. This is caused by shortage of ATP. We only have enough ATP in our muscles at any one time to provide for several seconds maximal exertion. It is therefore manufactured on the go. A decrease in the amount of ATP relative to ADP activates the enzyme (reduce in ‘end-product inhibition) which initiates the further breakdown of glucose or muscle glycogen.

3 The increased metabolic rate results in carbon dioxide building up in the skeletal muscle tissues. This causes local dilatation of the arterioles, leading to an increased blood flow through the muscles. It has been found that the increase in body temperature (which may be up to 2_ C after a game of squash and up to 4_ C in a marathon) renders the tissues more sensitive to carbon dioxide, thereby accentuating this mechanism.

4 Rapid movement of the limbs stimulates stretch receptors in the skeletal muscles and tendons. These transmit impulses to the cardiovascular centre leading to a further increase in the cardiac output.

5 Any fluctuations in the level of carbon dioxide in the bloodstream are monitored by the chemoreceptors in the carotid and aortic bodies and medullary centre, leading to appropriate adjustments in the ventilation rate.

6 During the race the metabolic rate of the active muscles increases greatly and the demand for oxygen rises accordingly. Despite the mechanisms described above, insufficient oxygen is delivered to the muscles to keep pace with their demands. As a result the muscles start respiring anaerobically with the formation of lactic acid. This accumulates during the race, but afterwards it is oxidised via the Krebs cycle or circulated to the liver where it is converted back to glycogen. For this to happen oxygen is required. Constituting the so-called oxygen debt, it accounts for the heavy panting that ensures after the race.

7 The lactic acid which accumulates during the sprint has the same effect on the arterioles as carbon dioxide, i.e. it causes local vasodilatation. It also stimulates the aortic and carotid bodies, thereby accentuating the ventilation responses initiated by the carbon dioxide.

8 Carbon dioxide itself will continue to increase, partly because of the oxidation of lactic acid in the Krebs cycle, but also because of the way lactic acid is buffered in the bloodstream. In this process lactic acid dissociates into lactate and hydrogen ions:

lactic acid lactate + H+

The hydrogen ions then combine with hydrogencarbonate ions to form carbonic acid, which splits into carbon dioxide and water:

+ - H + HCO3 H2CO3

9 While all this has been happening, the greatly increased metabolic rate results in a rise in body temperature. This is offset by the body's cooling processes.

The same kind of adjustments occur in longer races. One difference, however, is that the oxygen debt may be paid on the run, an equilibrium being established between oxygen supply and oxygen usage. When this point is reached second wind is said to be acquired.

For the short period involved in a sprint, the muscles can function perfectly efficiently under anaerobic conditions, provided of course that the oxygen debt is paid immediately afterwards. This enables an athlete to hold his or her breath during a sprint, the hundred metres for example. Under these circumstances circulatory and metabolic adjustments occur as described above, but changes in breathing are temporarily suspended until after the race.

Many complex physiological changes occur during muscular activity. What this brief and simplified account shows is that several different systems cooperate in bringing about appropriate adjustments, which together maintain the continued efficiency of the body. AL Bio notes Transport in Animal P.21

Common Misconceptions The rate of production and reabsorption of tissue fluid at the capillary is relatively stable 1 regardless of blood pressure and volume changes.

2 The formation and absorption of tissue fluid in the capillary network is essential to the exchange of nutrients and wastes between blood and body cells. AL Bio notes Transport in Animal P.22

3 In the mammalian circulatory system, blood flow rate is lowest at the capillaries because the very narrow capillaries offer great resistance to blood flow.

A summary of the adaptive features of the capillary and their significance: Adaptive features Effect Significance 1. Large total cross-sectional area 2. Thin capillary wall

3. Numerous narrow branches AL Bio notes Transport in Animal P.23

4 The following question (2002 CE Biology 1 Q4(b) assesses understanding of blood flow in the vein:

In the vein of the leg, the blood pressure is very low while the velocity Describe how a high velocity of blood flow in the vein is maintained. AL Bio notes Transport in Animal P.24

5 The muscular wall of the artery helps to pump blood along the blood vessel.

Structural features Adaptive function 1. Thick, elastic wall

2. Elastic wall (presence of elastic fibres)

3. Muscular wall (in arterioles)

6 The larger lumen of a vein allows blood to flow through it faster despite the low blood pressure in a vein.

End